Search

Neonicotinoid insecticides are nicotine-derived molecules which exert acute neurotoxic effects over the insect central nervous system by activating nicotinic acetylcholine receptors (nAChRs). However, these receptors are also present in the mammalian central and peripheral nervous system, where the effects of neonicotinoids are faintly known. In mammals, cholinergic synapses are crucial for the control of vascular tone, blood pressure and skeletal muscle contraction. We therefore hypothesized that neonicotinoids could affect cholinergic networks in mammals and sought to highlight functional consequences of acute intoxication in rats with sub-lethal concentrations of the highly used acetamiprid (ACE) and clothianidin (CLO). In this view, we characterized their electrophysiological effects on rat α3β4 nAChRs, knowing that it is predominantly expressed in ganglia of the vegetative nervous system and the adrenal medulla, which initiates catecholamine secretion. Both molecules exhibited a weak agonist effect on α3β4 receptors. Accordingly, their influence on epinephrine secretion from rat adrenal glands was also weak at 100 μM, but it was stronger at 500 μM. Challenging ACE or CLO together with nicotine (NIC) ended up with paradoxical effects on secretion. In addition, we measured the rat arterial blood pressure (ABP) in vivo by arterial catheterization. As expected, NIC induced a significant increase in ABP. ACE and CLO did not affect the ABP in the same conditions. However, simultaneous exposure of rats to both NIC and ACE/CLO promoted an increase of ABP and induced a biphasic response. Modeling the interaction of ACE or CLO on α3β4 nAChR is consistent with a binding site located in the agonist pocket of the receptor. We present a transversal experimental approach of mammal intoxication with neonicotinoids at different scales, including in vitro, ex vivo, in vivo and in silico. It paves the way of the acute and chronic toxicity for this class of insecticides on mammalian organisms.

We studied histophysiology of the adrenal medulla in adult (70-day-old) male Wistar rats developmentally exposed to low doses of endocrine disruptor DDT. It was found that exposure to DDT during the prenatal and postnatal ontogeny decelerated the development of the adrenal medulla and reduced the synthesis of tyrosine hydroxylase, the rate-liming enzyme of catecholamine synthesis, in chromaffin cells, which led to a decrease in epinephrine secretion into the blood.

Hypoglycemia remains a major barrier to the achievement of target levels of glycemic control for most individuals with insulin-dependent type 1 diabetes (T1D). Both the loss of β cells and an accompanying defect in the α cell response to hypoglycemia predispose patients with T1D to the development of low blood glucose. Increased glucose variability, exposure to hypoglycemia, and impaired awareness of hypoglycemia all contribute to increased risk of experiencing severe hypoglycemia, which is explained by progressive impairment in epinephrine secretion and autonomic symptom generation in response to hypoglycemia leading to defective glucose counterregulation and hypoglycemia unawareness that characterize hypoglycemia-associated autonomic failure (HAAF). Interruption of HAAF requires interfering with the mechanisms of brain adaptation to low blood glucose that affect central glucose sensing and the autonomic response to hypoglycemia, or avoidance of hypoglycemia that may allow for eventual recovery of counterregulatory and autonomic symptom responses. Strategies for hypoglycemia avoidance that include continuous glucose monitoring may reduce, but do not eliminate, clinically significant hypoglycemia, with ongoing counterregulatory defects and impaired awareness of hypoglycemia. Complete avoidance of hypoglycemia can be achieved following pancreatic islet transplantation and allows for the restoration of counterregulatory and autonomic symptom responses that evidences the potential for reversing HAAF in T1D.

In this work, we presented a mathematical model for the dynamics of glucose, insulin and beta-cell mass under the influence of trauma, excitement and/or stress, the model is an improvement on the work by [1]. We defined and incorporated a parameter to represent the effectiveness of epinephrine in suppressing insulin secretion and a parameter Ge representing epinephrine induced glucose increase as the factors that affect glucose and insulin homeostasis. The model which consists of a system of three nonlinear ordinary differential equations was used to investigate the effect of epinephrine on glucose, insulin and beta-cell mass dynamics. The result of the study showed that; In the presence of epinephrine, the blood glucose increased and the blood insulin decreased due to suppression by the hormone, despite the fact that there is an increase in beta-cell mass the system remained extremely hyperglycemic. Furthermore, the result of the numerical experiment carried out indicated that frequent epinephrine secretion into the blood induced prolong and extreme hyperglycemia. Frequent epinephrine secretion increases the risk of diabetes in humans. In view of the findings of this study, we recommend that there should be massive and continuous health education, especially for communities living in the areas where the stated agents (trauma, excitement and stress) of epinephrine secretion are common.

Summary The intestinal microbiota closely interacts with the neuroendocrine system and exerts profound effects on host physiology. Here, we report that nucleotide-binding oligomerization domain 1 (Nod1) ligand derived from intestinal bacteria modulates catecholamine storage and secretion in mouse adrenal chromaffin cells. The cytosolic peptidoglycan receptor Nod1 is involved in chromogranin A (Chga) retention in dense core granules (DCGs) in chromaffin cells. Mechanistically, upon recognizing its ligand, Nod1 localizes to DCGs, and recruits Rab2a, which is critical for Chga and epinephrine retention in DCGs. Depletion of Nod1 ligand or deficiency of Nod1 leads to a profound defect in epinephrine storage in chromaffin cells and subsequently less secretion upon stimulation. The intestine-adrenal medulla cross talk bridged by Nod1 ligand modulates adrenal medullary responses during the immobilization-induced stress response in mice. Thus, our study uncovers a mechanism by which intestinal microbes modulate epinephrine secretion in response to stress, which may provide further understanding of the gut-brain axis., Graphical abstract, Highlights • Nod1 expressed in adrenal chromaffin cells senses intestinal bacteria • Bacterial Nod1 ligand promotes catecholamine storage and secretion • The microbiota-intestine- adrenal medulla axis modulates fight and flight response, Molecular biology; Neuroscience; Microbiome

Although there is strong evidence linking obesity with increased sympathoneural activity, involvement of the adrenal medulla is less clear. We therefore investigated adrenal medullary function under fasting and feeding conditions in normal weight (NW, n=33), overweight (OW, n=28) and obese (OB, n=36) adults (59% women). Ninety-seven healthy adults participated in a cross-sectional study with recruitment stratified according to BMI. Plasma for catecholamines and metanephrines was sampled in the fasting state, at 30-min intervals during a 120-min glucose tolerance test and during an euglycaemic-hyperinsulinaemic clamp (40 mU m−2 min−1 insulin dose). Body composition was determined by leg-to-leg bioelectrical impedance analysis. Obese subjects had the lowest fasting plasma concentrations of epinephrine (NW: 0.17, 95% confidence interval (CI): 0.14–0.20 nmol l−1; OW: 0.16, 95% CI: 0.12–0.19 nmol l−1; OB: 0.11, 95% CI: 0.08–0.13 nmol l−1; P=0.018) and metanephrine (NW: 0.17, 95% CI: 0.15–0.19 nmol l−1; OW: 0.15, 95% CI: 0.13–0.16 nmol l−1; OB: 0.13, 95% CI: 0.12–0.15 nmol l−1; P=0.022), the latter reflecting adrenal medullary store size. Fasting plasma epinephrine (r=−0.437; P

Hypoglycemia activates the counterregulatory response (CRR), a neural-endocrine reflex that restores euglycemia. Although effective if occasionally activated, repeated induction of the CRR leads to a decline in responsiveness and prolonged exposure to hypoglycemia. The mechanism underlying this impairment is not known. We found that the reduction in epinephrine release that characterizes a suppressed CRR involves a long-lasting form of sympatho-adrenal synaptic plasticity. Using optogenetically evoked catecholamine release, we show that recurrent hypoglycemia reduced the secretory capacity of mouse adrenal chromaffin cells. Single activation of the CRR increased the adrenal levels of tyrosine hydroxylase (TH), the rate-limiting enzyme for catecholamine synthesis, but this was prevented by repeated activation. In contrast, the level of neuropeptide Y (NPY), an adrenal cotransmitter, remained elevated after recurrent hypoglycemia. Inhibition of NPY or Y1 signaling, either transgenically or pharmacologically, prevented the attenuation of both TH expression and epinephrine release. These results indicate that impairment of the CRR involves suppressed activity at the adrenal level. Interfering with the peripheral NPY–dependent negative feedback loop may provide a way to avoid the pathophysiological consequences of recurrent hypoglycemia which are common in the diabetic state.

Iatrogenic hypoglycemia in response to insulin treatment is commonly experienced by patients with type 1 diabetes and can be life threatening. The body releases epinephrine in an attempt to counterregulate hypoglycemia, but the neural mechanisms underlying this phenomenon remain to be elucidated. Orexin neurons in the perifornical hypothalamus (PeH) project to the rostral ventrolateral medulla (RVLM) and are likely to be involved in epinephrine secretion during hypoglycemia. In anesthetized rats, we report that hypoglycemia increases the sympathetic preganglionic discharge to the adrenal gland by activating PeH orexin neurons that project to the RVLM (PeH-RVLM). Electrophysiological characterization shows that the majority of identified PeH-RVLM neurons, including a subpopulation of orexin neurons, are activated in response to hypoglycemia or glucoprivation. Furthermore, the excitatory input from the PeH is mediated by orexin type 2 receptors in the RVLM. These results suggest that activation of orexin PeH-RVLM neurons and orexin type 2 receptors in the RVLM facilitates epinephrine release by increasing sympathetic drive to adrenal chromaffin cells during hypoglycemia.

Adrenal chromaffin cells comprise the neuroendocrine arm of the sympathetic nervous system and secrete catecholamines to coordinate the appropriate stress response. Deletion of the serotonin (5-HT) transporter (SERT) gene in mice (SERT(−/−) mice) or pharmacological block of SERT function in rodents and humans augments this sympathoadrenal stress response (epinephrine secretion). The prevailing assumption is that loss of CNS SERT alters central drive to the peripheral sympathetic nervous system. Adrenal chromaffin cells also prominently express SERT where it might coordinate accumulation of 5-HT for reuse in the autocrine control of stress-evoked catecholamine secretion. To help test this hypothesis, we have generated a novel mouse model with selective excision of SERT in the peripheral sympathetic nervous system (SERT(ΔTH)), generated by crossing floxed SERT mice with tyrosine hydroxylase Cre driver mice. SERT expression, assessed by western blot, was abolished in the adrenal gland but not perturbed in the CNS of SERT(ΔTH) mice. SERT-mediated [(3)H] 5-HT uptake was unaltered in midbrain, hindbrain, and spinal cord synaptosomes, confirming transporter function was intact in the CNS. Endogenous midbrain and whole blood 5-HT homeostasis was unperturbed in SERT(ΔTH) mice, contrasting with the depleted 5-HT content in SERT(−/−) mice. Selective SERT excision reduced adrenal gland 5-HT content by ≈ 50 % in SERT(ΔTH) mice but had no effect on adrenal catecholamine content. This novel model confirms that SERT expressed in adrenal chromaffin cells is essential for maintaining wild-type levels of 5-HT and provides a powerful tool to help dissect the role of SERT in the sympathetic stress response.

K+-channels of the Kv7/KCNQ-family hyperpolarize and stabilize excitable cells such as autonomic neurons and vascular smooth muscle cells (VSMC). Kv7 may therefore play a role in blood pressure (BP) homeostasis, and prevent a high total peripheral vascular resistance (TPR), a hallmark of hypertensive disease. The present study analyzed if Kv7 channels influence catecholamine release and TPR in normotensive (WKY) and spontaneously hypertensive rats (SHR), and if they may contribute to the antihypertensive protection seen in young, female SHR. Tyramine-stimulated norepinephrine release evokes an adrenergic cardiovascular response, and also allows modulation of release to be reflected in the overflow to plasma. The experiment itself activated some secretion of epinephrine. The results show: (1) XE-991 (Kv7.1-7.4-inhibitor), but not chromanol 293B (Kv7.1-inhibitor), increased tyramine-stimulated norepinephrine overflow and epinephrine secretion in both sexes in SHR, but not WKY. (2) Surprisingly, the Kv7-openers retigabine (Kv7.2-7.5) and ICA-27243 (Kv7.2-7.3-preferring) increased catecholamine release in female SHR. (3) The rise in TPR following tyramine-stimulated norepinephrine release was increased by XE-991 but not chromanol in the female WKY only. (4) Retigabine and ICA-27243 reduced the TPR-response to tyramine in the female SHR only. These results suggested: (1) Up-regulation of Kv7.2-7.3 function in sympathetic neurons and chromaffin cells hampered catecholamine release in SHR of both sexes. (2) The increase catecholamine release observed after channel openers in the female SHR may possibly involve reduced transmission in cholinergic neurons which hamper catecholamine release. These two mechanisms may serve to counter-act the hyperadrenergic state in SHR. (3) Kv7.4, most likely in the vasculature, opposed the tension-response to norepinephrine in the female WKY. (4) Vascular Kv7.4-7.5 could be stimulated and then opposed norepinephrine-induced vasoconstriction in the female SHR. (5) Vascular Kv7 channels did not counter-act norepinephrine induced vasoconstriction in male rats, possibly due to different Kv7 channel regulation. Kv7 channels may represent a novel target for antihypertensive therapy.

The metabolic and energy state of the organism depends largely on the availability of substrates, such as glucose for ATP production, necessary for maintaining physiological functions. Deregulation in glucose levels leads to the appearance of pathological signs that result in failures in the cardiovascular system and various diseases, such as diabetes, obesity, nephropathy, and neuropathy. Particularly, the brain relies on glucose as fuel for the normal development of neuronal activity. Regions adjacent to the cerebral ventricles, such as the hypothalamus and brainstem, exercise central control in energy homeostasis. These centers house nuclei of neurons whose excitatory activity is sensitive to changes in glucose levels. Determining the different detection mechanisms, the phenotype of neurosecretion, and neural connections involving glucose-sensitive neurons is essential to understanding the response to hypoglycemia through modulation of food intake, thermogenesis, and activation of sympathetic and parasympathetic branches, inducing glucagon and epinephrine secretion and other hypothalamic-pituitary axis-dependent counterregulatory hormones, such as glucocorticoids and growth hormone. The aim of this review focuses on integrating the current understanding of various glucose-sensing mechanisms described in the brain, thereby establishing a relationship between neuroanatomy and control of physiological processes involved in both metabolic and energy balance. This will advance the understanding of increasingly prevalent diseases in the modern world, especially diabetes, and emphasize patterns that regulate and stimulate intake, thermogenesis, and the overall synergistic effect of the neuroendocrine system.

Neuroendocrine stress response is regulated by several feedback loops. Since it has been suggested that afferent vagal pathways contribute to these feedback loops, we examined the effect of surgical subdiaphragmatic vagotomy on both baseline and stress-induced increases in plasma epinephrine, norepinephrine, and corticosterone levels in vagotomized and sham-operated Sprague Dawley rats. On either the 3rd or 14th day following vagotomy, the animals were exposed to acute immobilization stress and blood from the jugular vein was collected both before and during stress exposure. We found that vagotomy significantly enhanced immobilization-induced increases of plasma epinephrine, norepinephrine, and corticosterone levels on the 3rd day following surgery. However, on the 14th day following surgery, vagotomy enhanced only increase of plasma epinephrine levels in stressed rats. Our data indicate that afferent pathways of the vagus nerve are involved in negative feedback regulation of epinephrine secretion from the adrenal medulla during stressful conditions. We hypothesize that this feedback mechanism might be mediated by the binding of circulating epinephrine on β2-adrenergic receptors localized on sensory endings of the vagus nerve.

As in humans, young, female, spontaneously hypertensive rats (SHR) have a lower blood pressure (BP) than male SHR. In male, normotensive rats (WKY), α2- and β1+2-adrenoceptors (AR) reciprocally controlled catecholamine release and vascular smooth muscle tension. This interaction was malfunctioning in male SHR. The present study analysed if a favourable shift in the α2/β1+2AR-interaction may represent an antihypertensive protection in females. Female SHR (early hypertension, 12-14 weeks) and normotensive rats (WKY) were infused with tyramine (15 min) to stimulate norepinephrine release through the re-uptake transporter, consequently preventing re-uptake. Presynaptic control of vesicular release was therefore reflected as differences in overflow to plasma. The released norepinephrine increased total peripheral vascular resistance (TPR). The results showed that β1>2AR facilitated tyramine-stimulated norepinephrine release in both strains, also in the presence of α2AR-antagonist (L-659,066). βAR-antagonist (atenolol-β1, ICI-118551-β2, nadolol-β1+2) had no effect on the increased secretion of epinephrine after L-659,066 in WKY, but β1>2AR-antagonist augmented the L-659,066-induced increase in the secretion of epinephrine in SHR. Nadolol increased the TPR-response to tyramine with a greater effect in WKY than SHR, whereas β1or2-selective antagonists did not. One βAR-subtype may therefore substitute for the other. When both β1+2AR were blocked, α2AR antagonist still reduced the TPR-response in WKY but not SHR. Thus, α2/β1+2AR reciprocally controlled catecholamine release, with a particular negative β1AR-influence on α2AR-autoinhibition of epinephrine secretion in SHR. Moreover, in these female rats, β1/2AR-independent α2AR-mediated vasoconstriction was seen in WKY but not SHR, but β1/2AR-mediated vasodilation down-regulated adrenergic vasoconstriction, not only in WKY but also in SHR.

Enhanced epinephrine secretion from adrenal chromaffin cells (ACCs) is an important homeostatic response to severe systemic inflammation during sepsis. Evidence suggests that increased activation of ACCs by preganglionic sympathetic neurons and direct alterations in ACC function contribute to this response. However, the direct effects of sepsis on ACC function have yet to be characterized. We hypothesized that sepsis enhances epinephrine secretion from ACCs by increasing intracellular Ca2+ signaling. Plasma epinephrine concentration was increased 5-fold in the lipopolysaccharide-induced endotoxemia model of sepsis compared with saline-treated control mice. Endotoxemia significantly enhanced stimulus-evoked epinephrine secretion from isolated ACCs in vitro. Carbon fiber amperometry revealed an increase in the number of secretory events during endotoxemia, without significant changes in spike amplitude, half-width, or quantal content. ACCs isolated up to 12 hours after the induction of endotoxemia exhibited larger stimulus-evoked Ca2+ transients compared with controls. Similarly, ACCs from cecal ligation and puncture mice also exhibited enhanced Ca2+ signaling. Although sepsis did not significantly affect ACC excitability or voltage-gated Ca2+ currents, a 2-fold increase in caffeine (10 mM)-stimulated Ca2+ transients was observed during endotoxemia. Depletion of endoplasmic reticulum Ca2+ stores using cyclopiazonic acid (10 μM) abolished the effects of endotoxemia on catecholamine secretion from ACCs. These findings suggest that sepsis directly enhances catecholamine secretion from ACCs through an increase in Ca2+ release from the endoplasmic reticulum. These alterations in ACC function are likely to amplify the effects of increased preganglionic sympathetic neuron activity to further enhance epinephrine levels during sepsis.

Several neural peptides have been demonstrated to influence central nervous system control of nutrient metabolism. The principal mechanism by which these peptides influence peripheral nutrient metabolism is by altering the secretion of adrenal epinephrine. Bombesin or its mammalian counterpart, gastrin releasing peptide, and TRF act within the brain to stimulate the secretion of epinephrine from the adrenal gland. Associated with these changes in epinephrine secretion is a reduction of plasma insulin and elevation of plasma glucagon and glucose. Somatostatin and various somatostatin analogs act in the brain to inhibit adrenal epinephrine secretion stimulation by a variety of stimuli.

The risk of hypoglycemia with anti-hyperglycemic agents is an important limiting factor in the management of type 1 (T1DM) and type 2 (T2DM) diabetes mellitus. While hypoglycemia is more common in T1DM, the incidence is high in T2DM patients who use insulin or secretagogues, particularly patients with longer duration of diabetes. The underlying cause of hypoglycemia in diabetes is a complex interaction between hyperinsulinemia and compromised physiologic and behavioral responses to falling glucose levels. Pancreatic dysfunction also causes loss of normal therapeutic response to hypoglycemia--a reduction in circulating insulin (in T2DM only) and an increase in glucagon secretion. In T1DM and advanced T2DM, the third defense against hypoglycemia is increase in adrenomedullary sympathoadrenal epinephrine secretion, which is also compromised, causing the syndrome of defective glucose counterregulation. Diminished increase in epinephrine, also called hypoglycemia-associated autonomic failure (HAAF), is largely responsible for defective glucose counterregulation. HAAF can result in recurrent hypoglycemia and lowering of glycemic threshold that typically triggers sympathoadrenal response to hypoglycemia. This results in hypoglycemia without warning symptoms, or "hypoglycemia unawareness," which increases the risk of severe hypoglycemia associated with substantial morbidity and mortality. Long-term effects of severe hypoglycemia, aside from causing accidents, may include adverse cardiovascular outcomes and cognitive impairment. To reduce the impact of hypoglycemia, it is important to identify patients at risk and use careful consideration when choosing antidiabetes medications. Newer insulin analogs that more accurately replicate endogenous insulin secretion and incretin therapies that cause glucose-sensitive insulin secretion may ultimately reduce the risk of hypoglycemia.

Background Corticotropin-releasing factor (CRF) signaling induced by stress is well established to delay gastric emptying (GE) and stimulate colonic functions. The somatostatin receptor (sst1–5) agonist, ODT8-SST acts in the brain to inhibit stress-induced adrenocorticotropic hormone and epinephrine secretion. We investigated whether ODT8-SST acts in the brain to influence stress-related alterations of gastric and colonic motor function and sst receptor subtype(s) involved. Methods Peptides were injected intracerebroventricularly (i.c.v.) under short isoflurane anesthesia and GE, fecal pellet output (FPO) and distal colonic motility monitored in conscious mice. Key Results The stress of acute anesthesia/vehicle i.c.v. injection reduced GE by 67% and increased defecation by 99% compared to non-injected controls. Both responses were abolished by ODT8-SST (1 μg = 0.75 nmol) or sst1 agonist (0.65–1.95 nmol). The sst1 agonist (1.95 nmol) also prevented the abdominal surgery-induced delayed GE. Octreotide (sst2 > sst5 > sst3) and the sst2 or sst4 agonists (1 μg = 0.78 or 0.70 nmol, respectively) injected i.c.v. did not influence FPO while i.c.v. somatostatin-28 mimicked ODT8-SST’s effect. The ODT8-SST-induced increased food intake was inhibited by i.c.v. sst2 antagonist while the reduced FPO was unchanged. ODT8-SST i.c.v. reduced distal colonic motility in semi-restrained mice compared with vehicle and blocked water avoidance- and i.c.v. CRF (0.5 μg = 0.09 nmol)-induced stimulated FPO while a similar colonic secretomotor response to i.p. 5-hydroxytryptophane (10 mg kg−1 = 36.4 μmol kg−1) was unaltered. Conclusions & Inferences ODT8-SST counteracts stress/i.c.v. CRF-related stimulation of colonic motor function and delayed GE which can be reproduced mainly by activation of sst1 receptors. These data opens new insight to brain somatostatinergic signaling pathways interfering with brain circuitries involved in gut motor responses to acute stress.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved pleiotropic neuropeptide that functions as a neurotransmitter, neuromodulator and neurotrophic factor. Accumulating evidence implicates PACAP as an important regulator of both central and/or peripheral components of the stress axes, particularly exposure to prolonged or traumatic stress. Indeed, PACAP and its cognate receptors are widely expressed in the brain regions and peripheral tissues that mediate stress-related responses. In the sympathoadrenomedullary system, PACAP is required for sustained epinephrine secretion during metabolic stress. It is likely that PACAP regulates autonomic function and contributes to peripheral homeostasis by maintaining a balance between sympathetic and parasympathetic activity, favoring stimulation of the sympathetic system. Furthermore, PACAP is thought to act centrally on the paraventricular nucleus of the hypothalamus to regulate both the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Intriguingly, PACAP is also active in brain structures that mediate anxiety- and fear-related behaviors, and the expression of PACAP and its receptors are dynamically altered under pathologic conditions. Thus PACAP may influence both hard-wired (genetically determined) stress responses and gene-environment interactions in stress-related psychopathology. This article aims to overview the molecular mechanisms and psychiatric implications of PACAP-dependent stress responses.

Iatrogenic hypoglycemia is a problem for many people with diabetes (1). It causes recurrent morbidity in most people with type 1 diabetes and many with advanced type 2 diabetes and is sometimes fatal. It generally precludes maintenance of euglycemia over a lifetime of diabetes and therefore full realization of the benefits of glycemic control. It impairs defenses against subsequent falling plasma glucose concentrations and causes a vicious cycle of recurrent hypoglycemia. Hypoglycemia in diabetes is typically the result of the interplay of therapeutic insulin excess—caused by treatment with insulin, a sulfonylurea, or a glinide—and compromised physiological and behavioral defenses against falling plasma glucose concentrations (1,2). Compromised physiological defenses include loss of the normal decrease in β-cell insulin secretion and increase in α-cell glucagon secretion and attenuation of the normal increase in adrenomedullary epinephrine secretion during hypoglycemia. The compromised behavioral defense is failure to ingest carbohydrates because of loss of symptoms due to attenuation of the normal increase in sympathoadrenal, largely sympathetic neural, activity. The concept of hypoglycemia-associated autonomic failure (HAAF) in diabetes posits that recent antecedent hypoglycemia (or sleep or prior exercise) causes both defective glucose counterregulation (by attenuating the epinephrine response in the setting of absent insulin and glucagon responses) and impaired awareness of hypoglycemia (by attenuating sympathoadrenal and the resulting symptomatic responses) and thus a vicious cycle of recurrent hypoglycemia. Although additional intraislet mechanisms may be involved, it is reasonable to attribute both loss of the insulin and of the glucagon responses to hypoglycemia, the prerequisites to HAAF, to β-cell failure. Insulin normally restrains glucagon secretion and a decrease in insulin normally stimulates glucagon secretion during hypoglycemia. In the setting of absolute endogenous insulin deficiency—β-cell failure—there is …

Feedback regulation of norepinephrine release from sympathetic nerves is essential to control blood pressure, heart rate and contractility. Recent experiments in gene-targeted mice have suggested that alpha(2C)-adrenoceptors may operate in a similar feedback mechanism to control the release of epinephrine from the adrenal medulla. As heterozygous polymorphisms in the human alpha(2C)-adrenoceptor gene have been associated with cardiovascular disease including hypertension and chronic heart failure, we have sought to characterize the relevance of alpha(2C)-gene copy number for feedback control of epinephrine release in gene-targeted mice.Adrenal catecholamine release, basal hemodynamics and susceptibility to develop heart failure after transverse aortic constriction were tested in mice with two copies (+/+), one copy (+/-) or no functional alpha(2C)-adrenoceptor gene (alpha(2C)-/-).Heterozygous alpha(2C)-receptor deletion (alpha(2C)+/-) resulted in a 43% reduction of adrenal alpha(2C) mRNA copy number and in a similar decrease in alpha(2)-receptor-mediated inhibition of catecholamine release from isolated adrenal glands in vitro. Urinary excretion of epinephrine was increased by 74+/-15% in alpha(2C)+/- and by 142+/-23% in alpha(2C)-/- mice as compared with wild-type control mice. Telemetric determination of cardiovascular function revealed significant tachycardia but no hypertension in alpha(2C)-adrenoceptor-deficient mice. alpha(2C)+/- mice were more susceptible to develop cardiac hypertrophy, failure and mortality after left-ventricular pressure overload than alpha(2C)+/+ mice.Adrenal alpha(2)-mediated feedback regulation of epinephrine secretion differs fundamentally from sympathetic feedback control. A single adrenoceptor subtype, alpha(2C), operates without a significant receptor reserve to prevent elevation of circulating epinephrine levels. This genetic model may provide an experimental basis to study the pathophysiology of alpha(2C)-adrenoceptor dysfunction in humans.

Hypoglycemia unawareness is defined as the onset of neuroglycopenia before the appearance of autonomic warning symptoms.1 It is difficult to study in its natural form because of its paroxysmal and unpredictable nature; therefore, well-controlled trials are limited. However, much is known regarding risk factors, biochemical causes, and populations at greatest risk for the development of hypoglycemia unawareness. Less is known regarding the impact of medications on the development or recognition of this condition in patients with diabetes. Several medications are thought to worsen or promote hypoglycemia unawareness, whereas others may have an attenuating effect on the problem. This article will review hypoglycemia unawareness and summarize the effects of medications that may influence it. In individuals without diabetes, a predictable, organized response occurs when blood glucose declines to hypoglycemic levels (Figure 1). First, insulin secretion is suppressed as glucose falls to < 81 mg/dl.1 The suppression of insulin secretion has two effects: peripheral glucose utilization is reduced and hepatic glucose output is induced. This action typically terminates the episode. However, if glucose decline continues to < 68 mg/dl, glucagon secretion from α-cells and epinephrine secretion from the adrenals are stimulated.1 These actions promote hepatic glucose production via gluconeogenesis and glycogenolysis. Growth hormone and cortisol are released as glucose levels decline even further (to ∼ 63 mg/dl) but are probably best characterized as responders to prolonged hypoglycemia rather than acute responders. The central nervous system triggers autonomic symptoms of hypoglycemia at plasma glucose levels between 54 and 90 mg/dl (Table 1). These symptoms are aimed at encouraging consumption of calories and are the harbinger of impending neuroglycopenia. If unchecked, the hypoglycemia will cause neuroglycopenic symptoms (Table 1) and eventually seizures and coma. View this table: Table 1. Symptoms of Hypoglycemia The glycemic threshold at which this counterregulatory response occurs is predictable in people without …

Canine compulsive disorder (CD) is a condition in which dogs display repetitive, exaggerated, or sustained behavior out of original context. It is believed to occur in dogs subjected to stressful situations resulting in conflict or frustration (Hewson and Luescher., 1996). Among 63 dogs that were diagnosed with CD, 24% of the CD dogs were observed to have hematocrit values higher than the clinical pathology laboratory's reference range. The average CD dog's hematocrit (51%) was significantly higher than the normal average hematocrit (46%) from the reference range. The facts led us to construct two hypotheses to explain why dogs with CD had relatively high hematocrit values and almost one quarter of the CD dog population in the study had polycythemia. The first hypothesis is the stress hypothesis, which states that stress, conflict, and frustration lead to epinephrine secretion and compulsive behavior, with subsequent splenic contraction resulting in polycythemia. The second is the primary polycythemia hypothesis, which states that polycythemia results from primary pathologic processes such as cardiovascular disease or elevation of erythropoietin resulting from kidney problems, including neoplasia or bone marrow disease. The study found that a large proportion of CD dogs observed had a mild elevation in hematocrit. This finding warrants further investigation to determine if it is a cause or an effect of CD in dogs.

Hypoglycemia elicits an integrated array of CNS-mediated counterregulatory responses, including activation of the hypothalamic-pituitary-adrenal axis. The role of antecedent adrenocortical hypersecretion in impaired glucose counterregulation remains controversial. The present studies utilized the selective, nonsteroidal glucocorticoid receptor antagonist, CP-472555, as a pharmacological tool to investigate the hypothesis that hypoglycemic hypercorticosteronemia modulates CNS efferent autonomic and neuroendocrine motor responses to recurring insulin-induced hypoglycemia via glucocorticoid receptor-dependent mechanisms. Groups of adult male rats were injected s.c. with either one or four doses of the intermediate-acting insulin, Humulin neutral protamine Hagedorn (NPH), on as many days, while controls were injected with diluent alone. Animals injected with four doses of insulin were pretreated by i.c.v. administration of graded doses of the glucocorticoid receptor antagonist or vehicle alone prior to the first three doses of insulin. Repeated daily injection of NPH exacerbated hypoglycemia, attenuated patterns of glucagon and epinephrine secretion, and diminished neuronal transcriptional activation in discrete CNS metabolic loci, including the lateral hypothalamic area, dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, and nucleus of the solitary tract. While i.c.v. delivery of 25 or 100 ng doses of CP-472555 did not alter any of these parameters, animals treated with 500 ng exhibited circulating glucose, glucagon, and epinephrine levels that were similar to those in rats injected with one dose of insulin, as well as a reversal of recurring insulin-induced hypoglycemia-associated reductions in Fos immunolabeling in the lateral hypothalamic area, dorsomedial hypothalamic nucleus, and paraventricular hypothalamic nucleus. These results provide unique pharmacological evidence that antecedent activation of central glucocorticoid receptor is required for exacerbation of hypoglycemia during recurring insulin-induced hypoglycemia, and that these receptors mediate modulatory effects of hypoglycemic hypercorticosteronemia on autonomic efferent responses to recurring insulin-induced hypoglycemia. The data also suggest that neurons in central loci characterized here by antagonist-mediated overturn of recurring insulin-induced hypoglycemia-induced decreases in neuronal transcriptional activation may be direct or indirect substrates for this hormonal modulation action.

Subcutaneous (s.c.) injection of formalin into rats is frequently used as a painful stressor that produces a three-phase nociceptive response. We have shown previously that s.c. administered formalin (0.2 ml of 4% solution per 100 g body weight) unexpectedly attenuated the increase of plasma epinephrine levels in rats exposed to exteroceptive stressors (handling, immobilisation). To clarify the mechanism(s) responsible for this phenomenon, the effect of formalin applications on epinephrine plasma levels was investigated in various experimental conditions. Subcutaneous application of formalin combined with exposures of animals to an interoceptive stressor, insulin-induced hypoglycaemia, significantly attenuated the stress-induced increase in plasma epinephrine levels, whereas plasma norepinephrine levels remained highly elevated. Moreover, administration of formalin to unstressed animals also manifested signs of an attenuated epinephrine secretion. Interestingly, intraperitoneal administration of formalin did not reduce the elevated levels of plasma epinephrine. We suggest that formalin attenuates epinephrine secretion from the adrenal medulla most probably via irritation of s.c. somatosensory receptors. We hypothesise that the irritation of the primary sensory afferents fibres might reduce the activity of the sympathetic preganglionic neurones innervating adrenal medullary chromaffin cells. Further investigations are required to establish whether the observed reduction of epinephrine secretion from the adrenal medulla is controlled by either spinal or supraspinal neuronal circuits.

The link between the human sympathoadrenalmedullary system and the adipocyte hormone leptin is controversial. We measured total and regional norepinephrine spillover, epinephrine secretion rate, and extra-adipocyte leptin release in 22 lean [body mass index (BMI) 28) normotensive men who underwent arterial and central venous catheterization. Because plasma clearance of leptin is primarily by renal removal, for men at steady state we could estimate whole body leptin release to plasma from renal plasma leptin extraction. Whole body leptin release was 1,950 ± 643 (means ± SE) ng/min in obese men and 382 ± 124 ng/min in lean men ( P < 0.05). Total and renal norepinephrine spillover rates correlated directly with whole body leptin secretion rate. Leptin is released from multiple nonadipocyte sites, which we tested by use of simultaneous arteriovenous blood sampling. We found a surprisingly large contribution of brain leptin release to the plasma leptin pool, 529 ± 175 ng/min (>40% whole body leptin release), with greater leptin release in obese than in lean men, 935 ± 321 vs. 160 ± 59 ng/min ( P = 0.045). In parallel with leptin measurements, we also quantified brain serotonin turnover and jugular overflow of neuropeptide Y (NPY). Brain serotonin turnover was higher in obese than in lean men, 227 ± 112 vs. 21 ± 14 ng/min ( P = 0.019), as was overflow of NPY from the brain, 12.9 ± 1.4 vs. 5.3 ± 2.2 ng/min ( P = 0.042). These results suggest that leptin is released within the brain and at an increased rate in obese humans, in whom activation of brain serotonergic and NPY mechanisms also exists.

The sympathetic nervous system (SNS) is an important element of the autonomic nervous system which has an essential role in the maintenance of body homeostasis. SNS activation involves norepinephrine release by noradrenergic fibres and epinephrine secretion by adrenal medulla. SNS controls a number of physiological events including metabolic processes, cardiac and vascular activities, gastrointestinal functions and endocrine secretions. The SNS has a major role in the control of adipose tissue function through a direct effect on adipocytes and adipose tissue vessels, and by an indirect effect on pancreatic hormones secretion. Various alterations of SNS effects on metabolism have been implicated in the development and the maintenance of obesity. This review provides an overview of physiological aspects of the SNS involvement in normal and obese subjects. Physiological and pathological changes in SNS activity are summarized. Modifications occurring in adipose tissue function and fat cell responsiveness to norepinephrine and epinephrine are also considered.

Recurrent hypoglycemia can occur as a major complication of insulin replacement therapy, limiting the long-term health benefits of intense glycemic control in type 1 and advanced type 2 diabetic patients. It impairs the normal counter-regulatory hormonal and behavioral responses to glucose deprivation, a phenomenon known as hypoglycemia associated autonomic failure (HAAF). The molecular mechanisms leading to defective counter-regulation are not completely understood. We hypothesized that both neuronal (excessive cholinergic signaling between the splanchnic nerve fibers and the adrenal medulla) and humoral factors contribute to the impaired epinephrine production and release in HAAF. To gain further insight into the molecular mechanism(s) mediating the blunted epinephrine responses following recurrent hypoglycemia, we utilized a global gene expression profiling approach. We characterized the transcriptomes during recurrent (defective counter-regulation model) and acute hypoglycemia (normal counter-regulation group) in the adrenal medulla of normal Sprague-Dawley rats. Based on comparison analysis of differentially expressed genes, a set of unique genes that are activated only at specific time points after recurrent hypoglycemia were revealed. A complementary bioinformatics analysis of the functional category, pathway, and integrated network indicated activation of the unfolded protein response. Furthermore, at least three additional pathways/interaction networks altered in the adrenal medulla following recurrent hypoglycemia were identified, which may contribute to the impaired epinephrine secretion in HAAF: greatly increased neuropeptide signaling (proenkephalin, neuropeptide Y, galanin); altered ion homeostasis (Na+, K+, Ca2+) and downregulation of genes involved in Ca2+-dependent exocytosis of secretory vesicles. Given the pleiotropic effects of the unfolded protein response in different organs, involved in maintaining glucose homeostasis, these findings uncover broader general mechanisms that arise following recurrent hypoglycemia which may afford clinicians an opportunity to modulate the magnitude of HAAF syndrome.

In 1941, writing in the Lancet, R. D. Lawrence (1) noted that “[hypoglycemic] reactions differ so much from the original ones that patients become dangerously unaware of their onset.” This clinical description of impaired hypoglycemia awareness is still recognizable today, and we have become increasingly alert to its development after the publication of the landmark Diabetes Control and Complications Trial (DCCT) in 1993. The DCCT demonstrated that good glycemic control with intensive insulin therapy markedly reduced the risk of long-term microvascular complications of type 1 diabetes (T1D) (2) but that this came at the expense of a significant increase in the risk of biochemical and symptomatic hypoglycemia, whereas the risk of severe hypoglycemia increased 3-fold (3). Intensive insulin therapy was shown to reduce the glucose level at which hypoglycemic counterregulatory and symptomatic defense responses were initiated, significantly contributing to an individual’s risk of severe hypoglycemia (4). A number of studies in humans and animals then showed convincingly that prior exposure to hypoglycemia increased the threshold (lower glucose level) for hormone and symptom responses to subsequent hypoglycemia, which when combined with other counterregulatory defects in T1D (primarily the loss of pancreatic -cell glucagon secretion) was called the syndrome of hypoglycemia-associated autonomic failure (HAAF) (5). Studies, largely in animal models, have since helped inform us about how and where hypoglycemia is sensed in the body (6). However, as pointed out by Amiel (7) in a recent review, our ability to actually prevent the development of HAAF other than through strenuous efforts to avoid hypoglycemia is very limited, more often than not just leading to a period of more relaxed glucose control. In light of this, the report by Vele et al. (8) in this issue of the JCEM, in which the nonspecific opioid receptor antagonist naloxone prevented the development of HAAF in individuals with intensively treated T1D who were studied using an established experimental model, is an important one. Eight subjects with T1D (age, 34 7 yr; duration of diabetes, 12 3 yr), all treated with insulin pumps and with good glycemic control (glycosylated hemoglobin, 7.3 1.1%), took part in three different studies in random order and each separated by at least 5 wk. Each study required the subject to attend on 2 consecutive days. On d 1, each subject underwent two 90-min hyperinsulinemic glucose clamp studies separated by 60 min. The conditions induced were euglycemia (90 mg/dl) or hypoglycemia (60 mg/dl), the latter with (N ) or without (N ) a concomitant infusion of naloxone. On d 2, all subjects underwent a stepped (90, 80, 70, and 60 mg/dl) hypoglycemic clamp study where each glucose plateau was maintained for 50 min, and blood samples were taken for measurement of counterregulatory hormones and glucose turnover. The investigators found as expected that two episodes of antecedent hypoglycemia (control euglycemia vs. N ) resulted in a significant suppression of the epinephrine response to d 2 hypoglycemia, and this was associated with reduced whole body glucose production and increased glucose uptake, hallmarks of HAAF in T1D. In contrast, coinfusion of naloxone during d 1 hypoglycemia (N ) completely prevented the hypoglycemia-induced decrements in epinephrine secretion and hepatic glucose production, as well as the increase in whole body glucose uptake. These findings to a large extent replicate those of a similar study in nondiabetic subjects reported previously in this journal by the same group (9), and the authors

Patients with long-standing type 1 diabetes (T1D) may exhibit defective glucose counterregulation and impaired hypoglycemia symptom recognition that substantially increase their risk for experiencing severe hypoglycemia. The purpose of this study was to determine whether intrahepatic islet transplantation improves endogenous glucose production (EGP) in response to hypoglycemia in T1D patients experiencing severe hypoglycemia. We studied longitudinally subjects (n = 12) with ∼30 years, disease duration before and 6 months after intrahepatic islet transplantation using stepped hyperinsulinemic-hypoglycemic and paired hyperinsulinemic-euglycemic clamps with infusion of 6,6-2H2-glucose and compared the results with those from a nondiabetic control group (n = 8). After islet transplantation, HbA1c was normalized, and time spent while hypoglycemic (

Peripheral norepinephrine release is facilitated by presynaptic β-adrenoceptors, believed to involve the β2-subtype exclusively. However, β1-selective blockers are the most commonly used β-blockers in hypertension. Here the author tested the hypothesis that β1AR may function as presynaptic, release-facilitating auto-receptors. Since β1AR-blockers are injected during myocardial infarction, their influence on the cardiovascular response to acute norepinephrine release was also studied. By a newly established method, using tyramine-stimulated release through the norepinephrine transporter (NET), presynaptic control of catecholamine release was studied in normotensive and spontaneously hypertensive rats. β1AR-selective antagonists (CGP20712A, atenolol, metoprolol) reduced norepinephrine overflow to plasma equally efficient as β2AR-selective (ICI-118551) and β1+2AR (nadolol) antagonists in both strains. Neither antagonist lowered epinephrine secretion. Atenolol, which does not cross the blood–brain barrier, reduced norepinephrine overflow after adrenalectomy (AdrX), AdrX + ganglion blockade, losartan, or nephrectomy. Atenolol and metoprolol reduced resting cardiac work load. During tyramine-stimulated norepinephrine release, they had little effect on work load, and increased the transient rise in total peripheral vascular resistance, particularly atenolol when combined with losartan. In conclusion, β1AR, like β2AR, stimulated norepinephrine but not epinephrine release, independent of adrenal catecholamines, ganglion transmission, or renal renin release/angiotensin AT1 receptor activation. β1AR therefore functioned as a peripheral, presynaptic, facilitating auto-receptor. Like tyramine, hypoxia may induce NET-mediated release. Augmented tyramine-induced vasoconstriction, as observed after injection of β1AR-blocker, particularly atenolol combined with losartan, may hamper organ perfusion, and may have clinical relevance in hypoxic conditions such as myocardial infarction.

Glucocorticoids are required for the normal functioning of chromaffin cells and their capacity to produce epinephrine. This was modeled in a unique clinical syndrome of isolated glucocorticoid deficiency due to unresponsiveness to ACTH. The working hypotheses were that in patients with isolated glucocorticoid deficiency, adrenomedullary epinephrine would be suppressed despite replacement therapy; that norepinephrine might show a compensatory response; and that the physiological response to stress would reflect these changes. Toward these hypotheses, patients with ACTH unresponsiveness on glucocorticoid replacement were subjected to three levels of acute stress: assumption of upright posture, cold pressor, and exercise. Their catecholamine and physiological response were monitored. Patients with isolated glucocorticoid deficiency of this study had severe adrenomedullary dysfunction, characterized by a minimal resting production of epinephrine (6 ± 2 pg/ml compared with 64 ± 22 pg/ml of the controls) and a minimal response to stress. A slight compensatory increase of norepinephrine was found in response to cold pressor test (754 ± 200 pg/ml compared with 431 ± 73 pg/ml of the control). The physiological response is characterized by low systolic blood pressure and high pulse rate in rest and mild stress and in a pressor response to exercise (diastolic 87 ± 5 mm Hg, compared with 73 ± 2 mm Hg of the control). It is concluded that intra-adrenal glucocorticoids are essential for epinephrine secretion, that norepinephrine may be compensatory, and that these result in a distinct physiological response. The implications of the pressor response to exercise, the declining pulse pressure, and the increased pulse response insinuate a lower physical fitness in patients with adrenal insufficiency.

In the adult patient with type 1 or type 2 diabetes, optimal control of glucose concentrations to near the upper end of the normal range will prevent long-term complications. 1,42,83,89,101 Clearly, insulin replacement schemes are unlike normal endogenous insulin secretion, leaving the clinician with the dilemma of how to obtain normoglycemia. Although normoglycemia has a critical role in the prevention of chronic complications, patients with diabetes must constantly walk a tight rope, balancing high and low glucose concentrations. Beyond the question of how to pulse insulin physiologically to cover carbohydrate intake acutely, clinicians are challenged by the lack of accurate background insulin replacement. Declining insulin concentrations that normally occur during postprandial periods are difficult to generate outside of insulin pump therapy and, even then, ramping the insulin infusion rate up and down occurs in the absence of feedback on changes in glucose concentration. In addition to problems with insulin replacement, lack of education in regards to counting the grams of carbohydrate accurately sets the stage for excess insulin administration. Factors under the patient's control and beyond the patient's control are responsible for the frequency of hypoglycemia that is the focus of this article. Early in the development of intensive diabetes treatment strategies, health care providers and investigators noted a diminution in the symptoms of hypoglycemia as patients approached near normoglycemia. 4,5,12 Symptoms were reduced, and the glucose concentration required to trigger them fell also. Amiel and colleagues 4 demonstrated an associated failure in epinephrine secretion that made patients vulnerable to what is now known as hypoglycemia unawareness. 56 Even a single episode of hypoglycemia is sufficient to partially attenuate epinephrine secretion and the symptoms associated with hypoglycemia 63 ; however, generally, and certainly in clinical practice, more than one episode leads to autonomic failure. 35 In the fasted subject, portal vein insulin concentrations determine the endogenous rate of hepatic glucose production. 28 One of the fundamental roles of insulin is to reduce the rate of gluconeogenesis and glycogenolysis. 74 Of the glucose produced from the liver, 55% is consumed by the brain, and the remainder by skeletal muscle and the renal medulla. 85 Of these three tissues, the brain has an absolute dependence on glucose and is incapable of storing more than a few minutes of glucose as glycogen. 85 When the glucose supply is interrupted, the classic symptoms of hypoglycemia stem from neuroglycopenia, which, in turn, triggers many of the hormonal responses (counterregulation). 92 Unfortunately, the counterregulatory responses are often insufficient to stimulate endogenous glucose production to offset the brain's fuel shortage, and a critical threshold is passed beyond which normal brain function is interrupted. For this reason, in more than 1 million patients with type 1 diabetes, hypoglycemia is a common limiting factor preventing them from achieving the tight metabolic control that is necessary to prevent complications. The patient with type 2 diabetes is also at some risk, but the mechanisms leading to low glucose concentrations diverge somewhat in the two forms of the disease. In either case, the net result is that, during critical deficits of glucose provision to the brain, the patient loses consciousness or experiences a seizure. Understanding brain glucose handling is a cardinal requirement to understanding the intricacies of the pathophysiology and treatment of hypoglycemia.

CRH is thought to play a role in responses of the adrenocortical and adrenomedullary systems during stress. To investigate the role of CRH in stress-induced secretions of corticosterone and epinephrine, we subjected wild-type (WT) and CRH-deficient (knockout, KO) mice to restraint, and analyzed plasma corticosterone, plasma catecholamines, and adrenal phenylethanolamine N-methyltransferase (PNMT) gene expression and activity before and during 3 h of restraint. Plasma corticosterone increased over 40-fold in WT mice, but minimally in CRH KO mice. Adrenal corticosterone content tended to increase in CRH KO mice, although to levels 5-fold lower than that in WT mice. CRH KO mice had significantly lower plasma epinephrine and higher norepinephrine than WT mice at baseline, and delayed epinephrine secretion during restraint. Adrenal PNMT messenger RNA content in CRH KO mice tended to be lower than that in WT mice, though the degree of induction was similar in both genotypes. PNMT enzyme activity was significant...

By providing the principal inhibitory regulation of the discharge of sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM), neurons in the caudal ventrolateral medulla (CVLM) play a major role in regulating the level of sympathetic nerve activity (SNA) to cardiovascular targets. To determine whether adrenal medullary secretion of epinephrine (EPI) is also regulated by sympathoinhibitory inputs from the CVLM to the RVLM, we compared levels of plasma EPI obtained after disinhibition of RVLM neurons with levels obtained after inhibition of CVLM neurons, both of which result in sustained elevations in arterial blood pressure (AP), SNA, and heart rate (HR). Plasma norepinephrine (NE) concentrations were significantly elevated following bilateral microinjection either of bicuculline (BIC) into the RVLM or of muscimol into the CVLM of urethane/chloralose-anesthetized, artificially-ventilated rats. In sharp contrast, although plasma EPI concentrations were significantly elevated following disinhibition of neurons in the RVLM, they were unchanged by inhibition of neurons in the CVLM. These results demonstrate that the discharge of sympathetic premotor neurons in the RVLM regulating adrenal secretion of EPI is modulated by a tonic, GABA-ergic inhibition that arises from a source that is different from the sympathoinhibitory neurons in the CVLM that project to RVLM sympathetic premotor neurons controlling vasoconstrictor and cardiac targets.

Acetylcholine stimulation of bovine chromaffin cells results in increased norepinephrine and epinephrine secretion accompanied by a corresponding increase in synthesis. The addition of neuropeptide Y (NPY) to the culture medium prevents the increase in catecholamine synthesis but not secretion. Treatment of chromaffin cells with nicotine produces a concentration-dependent increase in tyrosine hydroxylase activity (IC50 = 1.2 microM) that is reduced if NPY is present during stimulation. Tyrosine hydroxylase activity decreases in a concentration-dependent fashion if increasing amounts of NPY are included in the culture medium, IC50 = 0.2 nM. Treatment with pertussis toxin completely prevents the effect of NPY. The rank order of potency for inhibition of tyrosine hydroxylase activity is NPY > or = [Leu31,Pro34]NPY > or = peptide YY > NPY2-36 > NPY13-36 > NPY18-36 > or = NPY26-36 >> NPY1-30, suggesting a NPY-Y1 receptor subtype. Examination of the effect of NPY on nicotine stimulation of chromaffin cell protein phosphorylation showed that NPY produces a concentration-dependent decrease in a 60-kDa protein, IC50 = 6.4 nM. The effect of NPY is pertussis toxin-sensitive. The rank order of potency is [Leu31,Pro34]NPY > or = NPY >> NPY18-36. Immunoprecipitation confirmed the identity of the 60-kDa protein as tyrosine hydroxylase.

The purpose of this investigation was to determine the effects of transdermal estradiol (E2) replacement on substrate utilization during exercise. Amenorrheic females (N = 6) performed three exercise trials following 72 h of placebo (C 72) and 72 and 144 h of medicated transdermal estradiol (E2) treatment (E2 72 and E2 144). Exercise involved 90 min of treadmill running at 65% VO2max followed by timed exercise to exhaustion at 85% VO2max. Resting blood samples were obtained for glucose, insulin, free fatty acids (FFA), and E2. Exercise blood samples were obtained for E2, lactate, epinephrine, and norepinephrine. Rates of appearance and disposal were calculated for glucose and glycerol using a primed, continuous infusion of [6,6-2H] glucose and [2H5] glycerol. Medicated transdermal placement increased E2 significantly at rest, before exercise (35.03 +/- 12.3, 69.5 +/- 20.1, and 73.1 +/- 31.6 pg.mL-1 for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). Resting FFA increased significantly following E2 treatment (0.28 +/- 0.16, 0.41 +/- 0.27, and 0.40 +/- 0.21 mmol.L-1 for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). Glucose Ra was significantly decreased during exercise as a result of E2 replacement (21.9 +/- 7.7, 18.9 +/- 6.2, and 18.9 +/- 5.6 mumol.kg-1.min-1 for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). Average glucose Rd also decreased during exercise as a result of E2 replacement (21.3 +/- 7.8, 18.5 +/- 6.4, and 18.6 +/- 5.8 mumol.kg-1.min-1 for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). However, the estimated relative contribution of plasma glucose and muscle glycogen to total carbohydrate oxidation was similar among the trials. Epinephrine values were significantly lower late in exercise during the E2 72 and E2 144 trials, compared with the C 72 trial (P < 0.05). These results indicate that elevated E2 levels can alter glucose metabolism at rest and during moderate intensity exercise as a result of decreased gluconeogenesis, epinephrine secretion, and/or glucose transport.

1. 1. Endocrine and thermoregulatory responses to acute heat (34°C) and cold (10°C) exposures were determined in eight pigs at 6 months of age. Half of the pigs had been reared in a cycling upper thermal environment (27–32°C) for the first 28 days of life, while the others had been reared in a lower thermal environment (21°C). 2. 2. Concentrations of cortisol increased significantly during both acute heat and cold thermal exposures (P = 0.0001) although the response was greater in the heat than in the cold (P = 0.003). A prolactin response occurred during acute heat exposure (P = 0.004). Growth hormone secretion increased during acute cold exposure (P = 0.001). There was a strong tendency for increased epinephrine secretion during both acute heat and cold exposures (P = 0.06). No significant effects of either exposure were found on plasma norepinephrine (P = 0.9), or triiodothyronine (P = 0.11). 3. 3. Neonatal environment did not affect daily core body temperature (Tc) before acute heat or cold exposures, but did alter amplitude of the 24-h Tc cycle. The amplitude was significantly greater in animals reared in the lower thermal environment (P < 0.001). 4. 4. Acute heat exposure resulted in significant increases in Tc (P < 0.001) and heat production (P < 0.01). Neonatal thermal environment had no significant effect on Tc and heat production responses to acute heat and cold thermal exposures.

Recent studies show that mononuclear cells release a small peptide (molecular weight < 3,000) that stimulates chromaffin cell epinephrine secretion (1). The present study demonstrates that endotoxin (ETX) enhances this mononuclear cell-mediated epinephrine secretion and examines the potential mechanism for regulation of this peptide. Mononuclear cells from bovine spleen were cultured 24 h in serum-free media after which the supernatant (conditioned media, CM) was harvested and filtered to remove molecules with a molecular weight greater than 3,000. In vitro epinephrine secretion from bovine chromaffin cells was used as a test system and CM-secretion expressed as a percentage of total cell content. ETX challenge (1 microgram/mL) of mononuclear cell cultures significantly enhanced bioactivity of CM (control-CM = 11.8 +/- .7, ETX-CM = 17.7 +/- 2.8). Separation of cell populations by adherence to plastic revealed that T cell and/or B cell populations were the main source of the bioactive peptide(s) in unstimulated cell cultures (T/B cell = 12.9 +/- .7, M phi = 6.2 +/- .8). In contrast, ETX induced significant bioactive peptide release from the macrophage population (M phi = 6.2 +/- .8, ETX-M phi = 15.9 +/- 2.8). Polyacrylamide gel analysis revealed a small peptide in nonadherent cell CM that was present only in ETX-challenged macrophage cultures. Additionally, data are presented that demonstrate a correlation between CM bioactivity and protease activity in CM. Proteases secreted from mononuclear cells in response to ETX is hypothesized to cleave the bioactive peptide from a larger "parent" protein. This peptide may play a role in the elevation of plasma catecholamines observed in the setting of critical injury and illness and contribute to development of the systemic inflammatory response syndrome (SIRS) and subsequent shock states.

An important facilitating effect of angiotensin II on adrenal catecholamine release has been demonstrated in several species. To determine whether specific AT1 receptor blockade affects medullary epinephrine secretion and musculocutaneous norepinephrine release during insulin-induced hypoglycemia, 16 healthy volunteers received losartan vs. placebo followed by an intravenous insulin bolus and measurement of effect variables at short intervals for 150 min. AT1 receptor blockade was effective, as evidenced by substantially increased circulating renin and angiotensin II levels, a 60% inhibition of circulating aldosterone, and an 8.5% decrease of mean arterial pressure over time compared with placebo. Arterial glucose concentration fell to a nadir of 1.9 mM, arterial epinephrine concentration increased 23-fold, forearm musculocutaneous norepinephrine release increased 4-fold, heart rate increased 40%, and forearm blood flow increased 3-fold. All absolute values and the time course of these changes were independent of AT1 receptor blockade. It is concluded that a putative interaction between angiotensin II and the sympathoadrenal axis may not be mediated by AT1 receptors in humans.

Impaired epinephrine secretion and symptom unawareness are characteristic of severe hypoglycemia in individuals with long-standing type I diabetes. Recently, the avoidance of clinical hypoglycemia has been reported to improve epinephrine and symptom responses to hypoglycemia in type I patients. However, the extent to which these defects can be restored in individuals with long-standing type I diabetes and autonomic neuropathy has not been assessed, nor has it been determined whether pancreas transplantation, which not only obviates hypoglycemia but also prevents hyperglycemia, results in the complete recovery of either epinephrine response or symptom awareness during insulin-induced hypoglycemia. We performed stepped hypoglycemic clamp studies in successful pancreas transplantation recipients to assess epinephrine and other counterregulatory hormone responses during hypoglycemia and to determine the degree to which hypoglycemic symptom recognition could be restored. Thirteen pancreas transplant recipients and matched control subjects were studied utilizing stepped hypoglycemic clamp protocol to achieve target glucose levels of 3.9, 3.3, 2.8, and 2.2 mmol/l (70, 60, 50, and 40 mg/dl, respectively). Plasma epinephrine response was significantly greater in healthy control subjects and pancreas transplant patients compared with type I subjects at the glucose plateaus of 3.9, 3.3, and 2.8 mmol/l. However, epinephrine response in pancreas transplant recipients was significantly less than that seen in either healthy control subjects or nondiabetic kidney transplant recipients at each of these glucose plateaus. The magnitude of the epinephrine response in pancreas transplant type I patients did not correlate with either the duration of diabetes, the duration of transplantation, or the measures of autonomic nerve function. Hypoglycemic symptom recognition was significantly greater in pancreas transplant subjects than type I patients and did not differ between pancreas transplant and control groups. No improvement in norepinephrine response was observed after pancreas transplantation, while glucagon responses to hypoglycemia were normalized in pancreas transplant patients. In conclusion, these studies uniquely demonstrate that successful pancreas transplantation improves epinephrine response and normalizes hypoglycemia symptom recognition in patients with long-standing diabetes and established autonomic neuropathy. No correlation was observed between the severity of autonomic neuropathy or the duration of diabetes and the recovery of either the epinephrine or symptom responses to hypoglycemia.

Summary: in this; study we examined the effects of long-term treatment of 19 patients with primary hypertension with the sr adrenoceptor antagonist atenolol on norepinephrine and epi­ nephrine kinetics, at rest and during sympathoadrenal stimula­ tion by lower body negative pressure. Norepinephrine and epinephrine kinetics were measured by using the radioisotopedi luti on technique by steady-state infusion of tritiated norepi­ nephrine and epinephrine. The patients were studied before and at the end of 3 months of treatment with atenolol (50 or 100 mg daily). A control group of four normotensive subjects was stud­ ied before and after 3 months without any drug treatment. In this group, only arterial blood samples were collected without infu­ sion of the tritiated catecholamines. Atenolol decreased blood pressure and heart rate, but forearm vascular resistance was not affected by atenolol. During atenolol, baseline arterial plasma epinephrine decreased from 0.23 ± O.02 to U.17 ± O.Oi nM (p < 0,05), and this was accompanied by a decrease in total body ep­ inephrine spillover from 0,50 ± 0.05 to 0.35 ± 0.04 nmol/min (p < 0.05), In the control group, arterial plasma epinephrine had not decreased after 3 months. In addition, the increment of arterial plasma epinephrine during lower body negative pressure at-40 mm Hg was attenuated during atenolol. Atenolol had no effect on total body and forearm norepinephrine spillover rates, either at rest or during lower body negative pressure. Clearance ivtes of epinephrine and norepinephrine were not significantly ef­ fected by atenolol. These results suggest that treatment of pa­ tients with primary hypertension with the s j-adrenoceptor blocker atenolol inhibits the adrenomedullary secretion of epi­ nephrine, but it does not affect the biochemical indices of sympathoneural activity, It remains speculative whether this selec­ tive effect of atenolol on epinephrine secretion contributes to its hypotensive action and to its cardioprotective effects in the long term. KeyWords: s (-Adrenergic— Sympathoadrenal activity— Hypertension— Catecholamines.

Recently, it was demonstrated that colorectal cancer HT-29 cells can secrete epinephrine (adrenaline) in an autocrine manner to auto-stimulate cellular growth by adrenoreceptors activation, and that this secretion is enhanced by nicotine, showing an indirect relation between colorectal cancer and tobacco. The electrochemical behaviour of human colon adenocarcinoma HT-29 cells from a colorectal adenocarcinoma cell line, the hormone and neurotransmitter epinephrine, and nicotine, were investigated by cyclic voltammetry, using indium tin oxide (ITO), glassy carbon (GC) and screen printed carbon (SPC) electrodes. The oxidation of the HT-29 cells, previously grown onto ITO or SPC surfaces, followed an irreversible oxidation process that involved the formation of a main oxidation product that undergoes irreversible reduction, as in the epinephrine oxidation mechanism. The effect of nicotine stimulation of the HT-29 cells was also investigated. Nicotine, at different concentration levels 1, 2 and 15 mM, was introduced in the culture medium and an increase with incubation time, 0 to 3 h and 30 min, of the HT-29 cells oxidation and reduction peaks was observed. The interaction of nicotine with the HT-29 cells stimulated the epinephrine secretion causing an increase in epinephrine release concentration, and enabling the conclusion that epinephrine and nicotine play an important role in the colorectal tumour growth.

α2-Adrenoceptor-activation lowers central sympathetic output, peripheral, vesicular norepinephrine release, epinephrine secretion, and modulates vascular tension. We previously demonstrated that α2-adrenoceptor-mediated inhibition of basal norepinephrine release was not reflected in plasma unless re-uptake through the norepinephrine transporter (NET) was blocked. Tyramine activates reverse norepinephrine transport through NET. Here we tested the hypothesis that tyramine, by engaging NET in release, also blocks re-uptake, and therefore allows manipulation of pre-junctional α2-adrenoceptors to directly regulate norepinephrine overflow to plasma. We compared in anesthetized spontaneously hypertensive rats (SHRs) and normotensive controls (WKYs), the effect of α2-adrenoreceptor antagonist (L-659,066) and/or agonist (clonidine) on norepinephrine overflow and increase in total peripheral vascular resistance (TPR) evoked by tyramine-infusion (1.26 μmol/min/kg, 15 min) and epinephrine secretion activated by the surgical stress. TPR was computed as blood pressure divided by cardiac output, recorded as ascending aortic flow. Plasma catecholamine concentrations after tyramine were higher in SHRs than WKYs. Pre-treatment with L-659,066 increased the catecholamine concentrations in WKYs, but only if combined with clonidine in SHRs. Clonidine alone reduced tyramine-induced norepinephrine overflow in SHRs, and epinephrine in both strains. Tyramine-induced increase in TPR was not different after clonidine, eliminated after L-659,066 and L-659,066 + clonidine in WKYs, but only after L-659,066 + clonidine in SHRs. We conclude that tyramine-infusion does allow presynaptic regulation of vesicular release to be accurately assessed by measuring differences in plasma norepinephrine concentration. Our results indicate that presynaptic α2-adrenoceptor regulation of norepinephrine release from nerve vesicles and epinephrine secretion is dysfunctional in SHRs, but can be restored by clonidine.

The sympathetic nervous system is of major importance in the regulation of numerous physiological functions. While it is clearly established that there is a decreased noradrenergic status in people with autonomic neuropathy, the epinephrine secretion is much more controversial. Basal and mental stress-stimulated plasma catecholamine levels were measured in 42 diabetic patients with and without pathological cardiovascular function tests and in 13 healthy, non-diabetic control subjects. In addition, the excretion of catecholamines was measured in a 24 h urine collection and compared with the stress stimulated plasma levels. During mental stress exposure a diminished epinephrine secretion was found in diabetic patients with autonomic neuropathy compared with diabetic patients without neuropathy and the healthy control group (p < 0.05: respectively). The decreased epinephrine response to mental stress was strongly correlated with a diminished urinary excretion of this "neurotransmitter' (r = 0.46; p < 0.01). Diabetic patients suffering from cardiovascular autonomic neuropathy exhibit a diminished sympatho-adrenal response following mental stress exposure. Both measurement of urinary and mental stress stimulated plasma epinephrine levels following mental stress provide reliable information regarding sympatho-adrenal activity in diabetic patients.

Previously, we have shown that novel mononuclear-cell-derived factor(s) [molecular weight (MW) < 3,000] stimulate the release of epinephrine (EPI) from adrenal medullary chromaffin cells to levels comparable to that of maximal cholinergic stimulation. The present study provides evidence that the observed bioactivity is due to the action of a single peptide of 627 Da apparent MW. The peptide nature of the bioactive component was suggested by a decreased bioactivity after acid hydrolysis as well as altered bioactivity subsequent to peptidase (carboxypeptidase Y, leucine aminopeptidase) treatment. The bioactive conditioned-medium (CM) peptide(s) were isolated and further characterized using SDS-PAGE analysis. SDS-PAGE separation of G-25 Sephadex purified CM shows that bioactivity resides in a single peptide band. Additional studies revealed that CM also mediates norepinephrine release from sympathetic ganglia cells. Regulation of peptide production was shown to involve negative feedback in that incubation with mononuclear cells with EPI prevented further bioactive peptide release. This feedback inhibition was partially blocked by the beta-adrenergic receptor antagonist propranolol. These findings suggest a novel and potentially important mechanism by which the immune system can alter neuroendocrine function.