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The association between obstructive sleep apnea (OSA) and metabolic disorders is well-established; however, the underlying mechanisms that elucidate this relationship remain incompletely understood. Since the liver is a major organ in the maintenance of metabolic homeostasis, we hypothesize that liver dysfunction plays a crucial role in the pathogenesis of metabolic dysfunction associated with obstructive sleep apnea (OSA). Herein, we explored the underlying mechanisms of this association within the liver. Experiments were performed in male Wistar rats fed with a control or high fat (HF) diet (60% lipid-rich) for 12 weeks. Half of the groups were exposed to chronic intermittent hypoxia (CIH) (30 hypoxic (5% O2) cycles, 8 h/day) that mimics OSA, in the last 15 days. Insulin sensitivity and glucose tolerance were assessed. Liver samples were collected for evaluation of lipid deposition, insulin signaling, glucose homeostasis, hypoxia, oxidative stress, antioxidant defenses, mitochondrial biogenesis and inflammation. Both the CIH and HF diet induced dysmetabolism, a state not aggravated in animals submitted to HF plus CIH. CIH aggravates hepatic lipid deposition in obese animals. Hypoxia-inducible factors levels were altered by these stimuli. CIH decreased the levels of oxidative phosphorylation complexes in both groups and the levels of SOD-1. The HF diet reduced mitochondrial density and hepatic antioxidant capacity. The CIH and HF diet produced alterations in cysteine-related thiols and pro-inflammatory markers. The results obtained suggest that hepatic mitochondrial dysfunction and oxidative stress, leading to inflammation, may be significant factors contributing to the development of dysmetabolism associated with OSA.

Obstructive sleep apnea (OSA) during pregnancy is characterized by episodes of intermittent hypoxia (IH) during sleep, resulting in adverse health outcomes for mother and offspring. Despite a prevalence of 8-20% in pregnant women, this disorder is often underdiagnosed.We have developed a murine model of gestational OSA to study IH effects on pregnant mothers, placentas, fetuses, and offspring. One group of pregnant rats was exposed to IH during the last 2 weeks of gestation (GIH). One day before the delivery date, a cesarean section was performed. Other group of pregnant rats was allowed to give birth at term to study offspring's evolution.Preliminary results showed no significant weight differences in mothers and fetuses. However, the weight of GIH male offspring was significantly lower than the controls at 14 days (p < 0.01). The morphological study of the placentas showed an increase in fetal capillary branching, expansion of maternal blood spaces, and number of cells of the external trophectoderm in the tissues from GIH-exposed mothers. Additionally, the placentas from the experimental males were enlarged (p < 0.05). Further studies are needed to follow the long-term evolution of these changes to relate the histological findings of the placentas with functional development of the offspring in adulthood.

The carotid body (CB) acts as a chemoreceptor which, when stimulated by arterial hypoxia, hypercapnia or acidosis, releases transmitters which stimulate sensory afferents that signal to the nucleus tractus solitarius (NTS). Acting through the rostral ventrolateral medulla (RVLM), this initiates a chemoreflex, stimulating autonomic efferents that orchestrate compensatory cardiorespiratory responses. Unfortunately, chronic intermittent hypoxia (CIH), which occurs in obstructive sleep apnoea (OSA), subverts the beneficial homeostatic function of this chemoreflex, causing increases in basal and hypoxia-induced transmitter release by the CB and sensitizing the cardiorespiratory centres it acts through. This causes a chronic sympathetic overdrive, contributing to the pathophysiological consequences of OSA such as heart failure, resistant hypertension and insulin resistance.

Chronic sustained hypoxia (CSH), as found in individuals living at a high altitude or in patients suffering respiratory disorders, initiates physiological adaptations such as carotid body stimulation to maintain oxygen levels, but has deleterious effects such as pulmonary hypertension (PH). Obstructive sleep apnea (OSA), a respiratory disorder of increasing prevalence, is characterized by a situation of chronic intermittent hypoxia (CIH). OSA is associated with the development of systemic hypertension and cardiovascular pathologies, due to carotid body and sympathetic overactivation. There is growing evidence that CIH can also compromise the pulmonary circulation, causing pulmonary hypertension in OSA patients and animal models. The aim of this work was to compare hemodynamics, vascular contractility, and L-arginine-NO metabolism in two models of PH in rats, associated with CSH and CIH exposure. We demonstrate that whereas CSH and CIH cause several common effects such as an increased hematocrit, weight loss, and an increase in pulmonary artery pressure (PAP), compared to CIH, CSH seems to have more of an effect on the pulmonary circulation, whereas the effects of CIH are apparently more targeted on the systemic circulation. The results suggest that the endothelial dysfunction evident in pulmonary arteries with both hypoxia protocols are not due to an increase in methylated arginines in these arteries, although an increase in plasma SDMA could contribute to the apparent loss of basal NO-dependent vasodilation and, therefore, the increase in PAP that results from CIH.

Oxygen is such an essential element for life that multiple mechanisms have evolved to maintain oxygen homeostasis, including those which detect decreases in arterial O2 and generate adaptive responses to hypoxia. In mammals, oxygen sensing mechanisms are found in erythropoietin-producing cells, peripheral chemoreceptor cells (carotid and aortic bodies), pulmonary artery smooth muscle cells, pulmonary neuroepithelial cells, chromaffin cells, and some specific types of neurons.

Several studies demonstrated a link between obstructive sleep apnea (OSA) and the development of insulin resistance. However, the main event triggering insulin resistance in OSA remains to be clarified. Herein, we investigated the effect of mild and severe chronic intermittent hypoxia (CIH) on whole-body metabolic deregulation and visceral adipose tissue dysfunction. Moreover, we studied the contribution of obesity to CIH-induced dysmetabolic states. Experiments were performed in male Wistar rats submitted to a control and high-fat (HF) diet. Two CIH protocols were tested: A mild CIH paradigm (5/6 hypoxic (5% O2) cycles/h, 10.5 h/day) during 35 days and a severe CIH paradigm (30 hypoxic (5% O2) cycles, 8 h/day) during 15 days. Fasting glycemia, insulinemia, insulin sensitivity, weight, and fat mass were assessed. Adipose tissue hypoxia, inflammation, angiogenesis, oxidative stress, and metabolism were investigated. Mild and severe CIH increased insulin levels and induced whole-body insulin resistance in control animals, effects not associated with weight gain. In control animals, CIH did not modify adipocytes perimeter as well as adipose tissue hypoxia, angiogenesis, inflammation or oxidative stress. In HF animals, severe CIH attenuated the increase in adipocytes perimeter, adipose tissue hypoxia, angiogenesis, and dysmetabolism. In conclusion, adipose tissue dysfunction is not the main trigger for initial dysmetabolism in CIH. CIH in an early stage might have a protective role against the deleterious effects of HF diet on adipose tissue metabolism.

Oxygen is an essential requirement for metabolism in mammals and many other animals. Therefore, pathways that sense a reduction in available oxygen are critical for organism survival. Higher mammals developed specialized organs to detect and respond to changes in O2 content to maintain gas homeostasis by balancing oxygen demand and supply. Here, we summarize the various oxygen sensors that have been identified in mammals (carotid body, aortic bodies, and astrocytes), by what mechanisms they detect oxygen and the cellular and molecular aspects of their function on control of respiratory and circulatory O2 transport that contribute to maintaining normal physiology. Finally, we discuss how dysregulation of oxygen availability leads to elevated signalling sensitivity in these systems and may contribute to the pathogenesis of chronic cardiovascular and respiratory diseases and many other disorders. Hence, too little oxygen, too much oxygen, and a malfunctioning sensitivity of receptors/sensors can create major pathophysiological problems for the organism.

El cuerpo carotídeo (CC) tiene un papel fundamental en la génesis de las modificaciones que participan en el síndrome de apnea obstructiva del sueño debido a la activación y sensibilización de este órgano quimiorreceptor por la hipoxia crónica intermitente (HCI). Dichos fenómenos conducen a la activación secuencial de centros nerviosos troncoencefálicos y del simpático que tratarán de mantener la homeostasis del organismo al aumentar la ventilación y generar una respuesta vasopresora. Sin embargo, su activación permanente produce efectos adversos que conducen a la hipertensión sistémica. Por otra parte, otros mecanismos independientes de la sensibilización del CC se han propuesto como mecanismos patogénicos que también conducen a la hipertensión a través fundamentalmente de la disfunción endotelial. En esta tesis se han utilizado dos modelos animales de HCI, rata joven y vieja y cobaya joven, con el objetivo de avanzar en el conocimiento sobre los efectos de la HCI mediados y no mediados por el CC. Los principales resultados encontrados en el modelo de HCI de rata joven y vieja son la sensibilización del CC similar en ambas edades después de 15 días de exposición a HCI. Estos resultados no se correlacionan con una sensibilización del reflejo respiratorio, medido como aumento de la respuesta ventilatoria hipóxica en ninguna de las edades analizadas. Las ratas jóvenes muestran una alteración hemodinámica presentando hipertensión. Estos resultados se ajustan en parte a las características de los pacientes que sufren AOS, los cuales muestran un aumento en la respuesta respiratoria y una actividad nerviosa simpática elevada frente a la hipoxia aguda, lo que les hace propensos a desarrollar hipertensión sistémica. El envejecimiento produce un declive gradual en la función de los órganos y sistemas corporales; en este sentido la edad per se en las ratas produce hipertensión sin que la HCI lo modifique. Estos animales presentan una tendencia a sufrir disfunción endotelial e

Carotid body (CB) chemoreceptor cells sense arterial blood PO2, generating a neurosecretory response proportional to the intensity of hypoxia. Hydrogen sulfide (H2S) is a physiological gaseous messenger that is proposed to act as an oxygen sensor in CBs, although this concept remains controversial. In the present study we have used the H2S scavenger and vitamin B12 analog hydroxycobalamin (Cbl) as a new tool to investigate the involvement of endogenous H2S in CB oxygen sensing. We observed that the slow-release sulfide donor GYY4137 elicited catecholamine release from isolated whole carotid bodies, and that Cbl prevented this response. Cbl also abolished the rise in [Ca2+]i evoked by 50 µM NaHS in enzymatically dispersed CB glomus cells. Moreover, Cbl markedly inhibited the catecholamine release and [Ca2+]i rise caused by hypoxia in isolated CBs and dispersed glomus cells, respectively, whereas it did not alter these responses when they were evoked by high [K+]e. The L-type Ca2+ channel blocker nifedipine slightly inhibited the rise in CB chemoreceptor cells [Ca2+]i elicited by sulfide, whilst causing a somewhat larger attenuation of the hypoxia-induced Ca2+ signal. We conclude that Cbl is a useful and specific tool for studying the function of H2S in cells. Based on its effects on the CB chemoreceptor cells we propose that endogenous H2S is an amplifier of the hypoxic transduction cascade which acts mainly by stimulating non-L-type Ca2+ channels.

[Rationale & Aim]: Experimental evidences indicate a correlation among chronic intermittent hypoxia (CIH), increased carotid body (CB) activity, enhanced sympatho-respiratory coupling and arterial hypertension. The recurrent hypoxia/reoxygenation episodes in CIH models produce CB sensitization increasing secretory response and chemoreceptor input to the brainstem, exaggerating the sympathetic reflex. CIH effect in the guinea pig CB, with a hypofunctional CB and lack of ventilatory responses to hypoxia, has not been studied., [Methods]: Guinea pigs were exposed to CIH (21%O2-80s / 5%O2-40s 8h/day; 30 days) and CB secretory response, pletismographic parameters, systemic arterial pressure and sympathetic activity were measured and compared to control animals., [Results]: Ventilatory data showed that only intense hypoxia induced significant increase of minute ventilation in both groups of animals. CB response to hypoxia (catecholamine (CA) secretion or Ca2+i changes) were not observed in C or CIH animals. Plasma CA, heart rate and mean arterial blood pressure were significantly increased in CIH guinea pigs., [Conclusion]: CIH induced hypoxic activation of the sympathetic system non-dependent of CB chemoreceptors, promoting cardiovascular adjustments. Guinea pigs can be a model to study the CB-dependent and nondependent effects induced by CIH.

[Rationale & Aim]: Chronic sustained hypoxia (CSH) initiates physiological adaptations to maintain oxygen levels but also has deleterious effects as pulmonary hypertension (PH). Chronic intermittent hypoxia (CIH), as found in obstructive sleep apnea, is associated with the development of systemic hypertension and cardiovascular pathologies. Our aim was to compare systemic and pulmonary hypertension and endothelial dysfunction development in rats exposed to CSH vs. CIH., [Methods]: We exposed male rats to sustained hypoxic atmosphere (10%O2; pO2≈70 mmHg, 14 days) or intermittent hypoxia (5%O2 40s, 21%O2 80s, 8h/day, 21 days). We measured pulmonary artery (PA) pressure by right heart catheterization, Fulton index, vasomotor responses in PA using small vessels myography and L- arginine-NO metabolism., [Results]: Systemic and pulmonary hypertension, besides left ventricular hypertrophy, occurs in response to CIH exposure in rats, preserving pulmonary artery endothelial integrity, but decreasing NO production and eNOS protein expression. Conversely, CSH exposure triggers CB mediated respiratory chemoreflex, PH and right ventricular hypertrophy, besides blunted pulmonary vascular relaxation to carbachol and reduced plasma L-arginine: asymmetric dimethyl arginine (ADMA) ratio., [Conclusion]: CSH and CIH point to different targets and different mechanisms to produce endothelial dysfunction and systemic and pulmonary hypertension in the rat.

Guinea pigs (GP), originally from the Andes, have absence of hypoxia-driven carotid body (CB) reflex. Neonatal mammals have an immature CB chemo reflex and respond to hypoxia with metabolic changes arising from direct effects of hypoxia on adrenal medulla (AM). Our working hypothesis is that adult GP would mimic neonatal mammals. Plasma epinephrine (E) has an AM origin, while norepinephrine (NE) is mainly originated in sympathetic endings, implying that specific GP changes in plasma E/NE ratio, and in blood glucose and lactate levels during hypoxia would be observed. Experiments were performed on young adult GP and rats. Hypoxic ventilation (10% O2) increased E and NE plasma levels similarly in both species but PaO2 was lower in GP than in rats. Plasma E/NE ratio in GP was higher (≈1.0) than in rats (≈0.5). The hypoxia-evoked increases in blood glucose and lactate were smaller in GP than in the rat. The AM of both species contain comparable E content, but NE was four times lower in GP than in rats. GP superior cervical ganglion also had lower NE content than rats and an unusual high level of dopamine, a negative modulator of sympathetic transmission. Isolated AM from GP released half of E and one tenth of NE than the rat AM, and hypoxia did not alter the time course of CA outflow. These data indicate the absence of direct effects of hypoxia on AM in the GP, and a lower noradrenergic tone in this species. Pathways for hypoxic sympatho-adrenal system activation in GP are discussed.

Clinical and experimental evidence indicates a positive correlation between chronic intermittent hypoxia (CIH), increased carotid body (CB) chemosensitivity, enhanced sympatho-respiratory coupling and arterial hypertension and cardiovascular disease. Several groups have reported that both the afferent and efferent arms of the CB chemo-reflex are enhanced in CIH animal models through the oscillatory CB activation by recurrent hypoxia/reoxygenation episodes. Accordingly, CB ablation or denervation results in the reduction of these effects. To date, no studies have determined the effects of CIH treatment in chemo-reflex sensitization in guinea pig, a rodent with a hypofunctional CB and lacking ventilatory responses to hypoxia. We hypothesized that the lack of CB hypoxia response in guinea pig would suppress chemo-reflex sensitization and thereby would attenuate or eliminate respiratory, sympathetic and cardiovascular effects of CIH treatment. The main purpose of this study was to assess if guinea pig CB undergoes overactivation by CIH and to correlate CIH effects on CB chemoreceptors with cardiovascular and respiratory responses to hypoxia. We measured CB secretory activity, ventilatory parameters, systemic arterial pressure and sympathetic activity, basal and in response to acute hypoxia in two groups of animals: control and 30 days CIH exposed male guinea pigs. Our results indicated that CIH guinea pig CB lacks activity elicited by acute hypoxia measured as catecholamine (CA) secretory response or intracellular calcium transients. Plethysmography data showed that only severe hypoxia (7% O2) and hypercapnia (5% CO2) induced a significant increased ventilatory response in CIH animals, together with higher oxygen consumption. Therefore, CIH exposure blunted hyperventilation to hypoxia and hypercapnia normalized to oxygen consumption. Increase in plasma CA and superior cervical ganglion CA content was found, implying a CIH induced sympathetic hyperactivity. CIH promoted

La hipertensión arterial pulmonar (HAP) se caracteriza por el aumento progresivo de la resistencia vascular pulmonar (RVP) que conduce al fallo del ventrículo derecho y puede llegar a provocar la muerte prematura; se considera hipertensión cuando la presión media en la arteria pulmonar es igual o superior a 25mmHg en reposo. Puede estar ocasionada por múltiples patologías como la enfermedad veno-oclusiva pulmonar, hipertensión pulmonar persistente del recién nacido (HPPRN), cardiopatía izquierda o trastornos pulmonares que producen hipoxemia, causa en la que va a estar centrado este trabajo. Entre otros factores que pueden ocasionar esta enfermedad podemos encontrar también la predisposición genética (mutación en el gen que afecta la expresión del receptor BMPR2), la inducción por fármacos o asociada a otras patologías que obstruyen la microcirculación pulmonar como trastornos del tejido conectivo, VIH, hipertensión portal o cardiopatías congénitas.

Mammals have developed different mechanisms to maintain oxygen supply to cells in response to hypoxia. One of those mechanisms, the carotid body (CB) chemoreceptors, is able to detect physiological hypoxia and generate homeostatic reflex responses, mainly ventilatory and cardiovascular. It has been reported that guinea pigs, originally from the Andes, have a reduced ventilatory response to hypoxia compared to other mammals, implying that CB are not completely functional, which has been related to genetically/epigenetically determined poor hypoxia-driven CB reflex. This study was performed to check the guinea pig CB response to hypoxia compared to the well-known rat hypoxic response. These experiments have explored ventilatory parameters breathing different gases mixtures, cardiovascular responses to acute hypoxia, in vitro CB response to hypoxia and other stimuli and isolated guinea pig chemoreceptor cells properties. Our findings show that guinea pigs are hypotensive and have lower arterial pO2 than rats, probably related to a low sympathetic tone and high hemoglobin affinity. Those characteristics could represent a higher tolerance to hypoxic environment than other rodents. We also find that although CB are hypo-functional not showing chronic hypoxia sensitization, a small percentage of isolated carotid body chemoreceptor cells contain tyrosine hydroxylase enzyme and voltage-dependent K+ currents and therefore can be depolarized. However hypoxia does not modify intracellular Ca2+ levels or catecholamine secretion. Guinea pigs are able to hyperventilate only in response to intense acute hypoxic stimulus, but hypercapnic response is similar to rats. Whether other brain areas are also activated by hypoxia in guinea pigs remains to be studied.

The carotid body (CB) is a singular organ which senses variations of the arterial blood PO2, PCO2 and [H+]. In the middle of 1980s, based on our experimental data, our laboratory proposed the membrane hypothesis of acute hypoxic chemoreception formulating that the chemoreceptor cells decrease in arterial PO2 is detected by an oxygen sensor, and the reduction in the opening probability of O2-sensitive K+ channels (Lopez-Barneo et al., 1988) depolarizes chemoreceptor cells. Activation of voltage dependent Na+ and Ca2+ channels increases intracellular free [Ca2+] promoting release of catecholamines and other neurotransmitters, which augment the activity of the carotid sinus nerve producing hyperventilation (Gonzalez et al., 1994). Second messengers, such as cAMP, EPAC, and hydrogen sulphide, are capable to modulate the flow of information in the chemoreception transduction cascade (Rocher et al., 2009; Gallego-Martin et al., 2015). Nowadays, oxygen sensor identity remains unknown. Physiological systemic effects of CB activation have long been studied. In recent years, CB involvement in several pathological processes turns into a field of high interest. Some of these pathological processes are respiratory diseases that involve hypoxic situations, such as chronic sustained hypoxia in chronic obstructive pulmonary disease and chronic intermittent hypoxia (CIH) in obstructive sleep apnea (OSA). As a consequence of CIH, repetitive CB activation produces sympathetic overstimulation and redox imbalance, with high levels of reactive oxygen species (Agapito et al., 2009). CB overexcitation in OSA patients could be related to the appearance of cardiovascular pathologies (endotelial dysfunctions, hypertension, cardio- and cerebrovascular accidents), hepatometabolic alterations (obesity, insulin resistance, non-alcoholic hepatic steatosis), and neuropsychiatric diseases (anxiety, depression, dementia). Recently, it has been proposed a relationship between CIH, the main constitutiv

The extracellular calcium-sensing receptor (CaSR) is a unique G protein–coupled receptor (GPCR) activated by extracellular Ca2+ and by other physiological cations including Mg2+, amino acids, and polyamines. CaSR is the most important master controller of the extracellular Ca2+ homeostatic system being expressed at high levels in the parathyroid gland, kidney, gut and bone, where it regulates parathyroid hormone (PTH) secretion, vitamin D synthesis, and Ca2+ absorption and resorption, respectively. Gain and loss of function mutations in the CaSR are responsible for severe disturbances in extracellular Ca2+ metabolism. CaSR agonists (calcimimetics) and antagonists (calcilytics) are in use or under intense research for treatment of hyperparathyroidism secondary to kidney failure and hypocalcemia with hypercalciuria, respectively. Expression of the CaSR extends to other tissues and systems beyond the extracellular Ca2+ homeostatic system including the cardiovascular system, the airways, and the nervous system where it may play physiological functions yet to be fully understood. As a consequence, CaSR has been recently involved in different pathologies including uncontrolled blood pressure, vascular calcification, asthma, and Alzheimer's disease. Finally, the CaSR has been shown to play a critical role in cancer either contributing to bone metastasis and/or acting as a tumor suppressor in some forms of cancer (parathyroid cancer, colon cancer, and neuroblastoma) and as oncogene in others (breast and prostate cancers). Here we review the role of CaSR in health and disease in calciotropic tissues and others beyond the extracellular calcium homeostatic system.

Chronic Intermittent Hypoxia (CIH) is considered to be one of the main causes of systemic arterial hypertension observed in the obstructive sleep apnea syndrome. It is thought that repetitive episodes of hypoxia/re-oxygenation produce oxidative stress, inflammation and sympathetic hyperactivity, generating endothelial dysfunction and systemic hypertension. It has been proposed that the repeated carotid body (CB) stimulation produced by CIH would induce CB sensitization, increasing chemoreceptor input to the brainstem that originates an exaggerated sympathetic reflex with a rise of circulating catecholamine (CA) and hypertension. Unlike other rodents, preliminary data show a lack of CB sensitivity to acute hypoxia in guinea pigs, in which case, CIH would not induce CB sensitization and the effects derived from the CB hyperactivity would not be observed. Therefore, guinea pigs could be a negative control model to study the effects of CIH mediated by CB. In this study, experiments were performed on adult male Hartley guinea pigs (475±10 g; n=32) control or exposed to CIH (21% O2-80 s/5% O2-40s 8h/day; 30 days). Ventilatory parameters (tidal volume and respiratory rate) were measured in freely moving animals by whole body plethysmography; other measurements were performed on animals anaesthetized with a mixture of ketamine (100 mg/Kg) and diazepam (2 mg/Kg; ip.). Control and CIH guinea pig respiratory minute volume exhibited similar changes when acute hypoxic test was applied (399±5 vs 411±5 in air and 417±15 vs 456±17 ml/min/Kg in 10% O2; n=16). Values are means ± S.E.M. compared by ANOVA. There were no in vitro CB responses to acute hypoxia (CA secretion or Ca2+i changes) in either group of animals. No differences were found in mean arterial blood pressure (37±2 vs 43±3 mmHg; n=8), or in plasma and tissue CA levels (CB, adrenal medulla, renal artery) measured after exposure to CIH. The fact that the guinea pig CB is hypo-functional and is not sensitized by CIH would r