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1. 1. Fenfluramine is an optically active 5-hydroxytryptamine (5-HT) releaser and re-uptake inhibitor. Increased brain 5-HT mediates appetite suppression, the D enantiomer being more active than L- or DL-fenfluramine. Fenfluramine also stimulates the hypothalamic-pituitary-adrenal (HPA) axis, leading to suggestions that this could act as a marker for its biological actions. However, the D enantiomer appears less active than a comparable DL racemate dose in animals, while effects of D-fenfluramine on the human HPA axis remain unproven. The aim of the present study was to clarify this. 2. Seven healthy human volunteers (three male, four female; 18-58 years) received 30 mg oral D-fenfluramine or placebo, followed by 125 micrograms/kg, i.v. naloxone or placebo, in randomized, double-blinded, placebo-controlled afternoon studies. We measured plasma adrenocorticotropic hormone (ACTH) and cortisol levels in samples taken at intervals throughout the study period. 3. In contrast to previous results with DL-fenfluramine, we found no dynamic responses to D-fenfluramine alone and no augmentation of responses to naloxone. 4. Central pathways to HPA axis activation are apparently not stimulated by D-fenfluramine at this dose in humans, in contrast with DL-fenfluramine, where the L enantiomer may be more selective for proposed corticotropin-releasing hormone-mediated, post-synaptic 5-HT2 or noradrenergic mechanisms. As previously reported, D-fenfluramine significantly blunted the circadian fall in basal plasma cortisol, providing in vivo evidence for serotonergic involvement in circadian regulation.

Myotonic dystrophy (DM) is an autosomal dominant disorder causing myotonia, progressive muscle weakness, and endocrine abnormalities including hypothalamic-pituitary-adrenal (HPA) axis hyperresponsiveness to CRH-mediated stimuli. This ACTH hyperresponsiveness appears directly related to the underlying genetic abnormality. Naloxone (Nal)-mediated CRH release causes ACTH release in normal humans and an ACTH hyperresponse in DM. Alprazolam (APZ) attenuates the ACTH release in response to Nal in normal individuals, probably by inhibiting CRH release. This study investigates the effects of APZ on Nal-induced HPA axis stimulation in DM. The ACTH response to Nal in DM subjects was significantly reduced by APZ. Despite this DM patients have a relative resistance to APZ inhibition of Nal-induced ACTH/cortisol release. APZ caused a smaller percentage reduction in AUC for ACTH in DM compared with controls. These findings provide further insight into the mechanism(s) of the HPA axis abnormalities in DM. In DM, there may be an increase in tonic opioid inhibition to CRH release with compensatory increases in stimulatory pathways. Alternatively, these patients may have a basal increase in pituitary vasopressin levels or an enhanced AVP/CRH synergistic mechanism at the level of the corticotroph.

PGs influence ACTH secretion. However, their specific role in modulating the activity of the human hypothalamic-pituitary-adrenal (HPA) axis remains unclear. Acetylsalicylic acid (aspirin) inhibits the synthesis of PGs from arachidonic acid by blocking the cyclooxygenase pathway. In this study we administered a single, clinically relevant dose of aspirin before HPA axis stimulation by a bolus dose of iv arginine vasopressin (AVP) to seven normal males using a randomized, placebo-controlled, single blinded design. Aspirin significantly reduced the cortisol response to AVP [mean peak increase from basal, 221.1 +/- 20.1 vs. 165.4 +/- 22.5 nmol/L (P = 0.0456); mean integrated response, 11,199.3 +/- 1,560.0 vs. 6,162.3 +/- 1,398.6 nmol.min/L (P = 0.0116) for placebo aspirin/AVP and aspirin/ AVP, respectively]. The ACTH response was reduced, but did not reach statistical significance [mean peak increase from basal, 7.5 +/- 2.2 vs. 4.3 +/- 0.3 pmol/L (P = 0.0563); mean integrated response, 142.6 +/- 36.0 vs. 96.2 +/- 8.7 pmol.min/L (P = 0.12) for placebo aspirin/ AVP and aspirin/AVP, respectively]. PGs may influence ACTH secretion by being stimulatory or inhibitory to the HPA axis at different levels, such as hypothalamic or pituitary. Which effect predominates in vivo during dynamic activation of the axis may depend on the level at which the secretory stimulus acts. We showed that when normal male volunteers were treated with the PG synthesis inhibitor, aspirin, they had a blunted HPA axis response to the pituitary corticotroph stimulator, AVP.

1. Gamma-aminobutyric acid (GABA) and endogenous opioids each inhibit hypothalamic CRH secretion. In humans, the opioid antagonist, naloxone, stimulates the release of CRH, and so of ACTH and cortisol, while alprazolam, an indirect GABAA agonist, blocks naloxone-induced ACTH and cortisol secretion. Sodium valproate (SV) inhibits ACTH release in response to CRH, metyrapone and substance P. We hypothesized that, if this action is GABAA-mediated, SV should also inhibit naloxone-stimulated ACTH release. 2. We studied five healthy volunteers in randomized, double-blind, placebo-controlled afternoon studies with SV 400 mg, given 180 min before i.v. naloxone 125 micrograms/kg bodyweight. Plasma concentrations of ACTH, cortisol and SV were measured at intervals during the experiments. 3. SV had no effect on the mean integrated ACTH and cortisol responses to naloxone; ACTH: 165 +/- 21 versus 284 +/- 40 pmol.min per L, P = 0.08; cortisol: 10.5 +/- 1.9 versus 12.8 +/- 1.2 nmol.min per L-3, P = 0.14, placebo/nal versus SV/nal respectively. Basal ACTH and cortisol levels were also not significantly altered by SV (P > 0.30). Mean SV levels were not significantly different between SV/nal and SV/placebo studies (P > 0.50). 4. In conclusion, SV had no effect on naloxone-induced ACTH and cortisol release in normal humans at the dose and plasma drug concentrations studied. This contrasts with the potent inhibitory effect of alprazolam, and suggests that the effect of SV on the human hypothalamic-pituitary-adrenal axis may not be through a GABAA-mediated mechanism. Alternatively, higher plasma SV levels or more sustained exposure to SV may be necessary to inhibit hypothalamic secretion of CRH.

Desipramine (DMI), a tricyclic antidepressant and norepinephrine (NE) reuptake blocker, is reported to induce ACTH and cortisol release acutely in humans, probably by facilitating central NE neurotransmission. Tricyclic antidepressant therapy, including DMI, normalizes the ACTH and cortisol hypersecretion that often accompanies depression. The mechanism of hypothalamic-pituitary-adrenal (HPA) axis inhibition by DMI in humans is unknown. In rats, DMI reduces the activity of the locus ceruleus, a major source of NE innervation of the hypothalamic paraventricular nucleus, the site of CRH neurons. Naloxone induces ACTH and cortisol release in humans through a noradrenergic-mediated mechanism and a probable consequent stimulation of hypothalamic CRH release. To study the interaction of these drugs on NE neurotransmission and, hence, HPA axis activity in humans, we administered DMI alone and with naloxone in a randomized, double blind, placebo-controlled protocol in eight healthy male volunteers. DMI (75 mg, orally) was given 180 min before naloxone (125 micrograms/kg BW, i.v.). Plasma ACTH and cortisol were measured at frequent intervals from 60 min before to 120 min after naloxone treatment. Plasma cortisol levels were 77% higher 180 min after DMI compared to those after placebo treatment (287 +/- 17 vs. 162 +/- 14 nmol/L; P = 0.000005). DMI reduced the naloxone-induced rise in cortisol (P = 0.02), but there was no change in the integrated cortisol response. The increase in basal plasma ACTH levels after DMI treatment did not reach statistical significance. DMI significantly increased systolic blood pressure and heart rate consistent with an effect on the noradrenergic control of the cardiovascular system. In summary, DMI increased basal cortisol levels consistent with facilitation of NE neurotransmission and, hence, hypothalamic CRH release. However, DMI had no enhancing effect on naloxone-induced cortisol release. This contrasts with the synergy observed when non-antidepressant agents that increase NE neurotransmission are given with naloxone to humans. DMI increases glucocorticoid feedback sensitivity in the rat HPA axis after several weeks through up-regulation of central corticosteroid receptors. However, this slowly developing effect is unlikely to occur during these acute studies. The effect of DMI on naloxone-induced cortisol release is consistent with an inhibitory effect on central noradrenergic control of ACTH release, perhaps at the locus ceruleus. This is the first human study to suggest an inhibitory effect of DMI on central noradrenergic control of ACTH release.

Naloxone stimulates pituitary-adrenal function by blocking an endogenous inhibitory opioidergic tone which modulates pituitary adrenocorticotropin (ACTH) release. In animals, this action of naloxone is mediated by increased corticotropin-releasing hormone (CRH) secretion, but such a mechanism is disputed in humans. CRH and arginine vasopressin (AVP) are known to have a synergistic effect on ACTH secretion in both humans and animals. In vitro, this synergism is independent of L-type voltage-dependent Ca2+ channel function. The aims of this study were therefore: (i) to determine if the combined administration of naloxone and AVP is synergistic regarding ACTH release; (ii) to assess the effect of nifedipine, which blocks L-type Ca2+ channels, on the ACTH response to combined naloxone/AVP stimulation. Seven healthy volunteers were studied using a placebo-controlled, single-blind protocol. Naloxone (125 micrograms/kg) and/or AVP (10 units) were given in all four possible combinations, and oral nifedipine (20 mg) was also given with naloxone and AVP as an additional test. The mean AUC and the mean peak change in ACTH levels following combined naloxone/AVP administration were both significantly greater than the arithmetic sum of the ACTH responses to naloxone and AVP given on separate occasions (AUC: 1,576.4 +/- 417.9 vs. 567.1 +/- 106.1 pmol.min.l-1, p < 0.002; peak change: 37.9 +/- 14.0 vs. 11.8 +/- 2.0 pmol/l, p < 0.007). Nifedipine reduced the ACTH response to combined naloxone/AVP stimulation by 43% (AUC: 1,576.4 +/- 417.9 vs. 897.0 +/- 186.2; p < 0.05), but it remained greater than the sum of the individual responses (897.0 +/- 186.2 vs. 576.1 +/- 106.1, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

We previously showed that CRH-mediated stimuli, including exogenous CRH, cause ACTH hypersecretion in many myotonic dystrophy (DM) patients. We confirmed this by giving naloxone, a stimulator of endogenous CRH release, to a large number of DM patients and controls. DM patients, first degree relatives, and normal controls received i.v. naloxone at 1400 h, and blood was taken for ACTH (RIA) and cortisol (high pressure liquid chromatography) measurements from 15 min before to 120 min after naloxone treatment. DM patients had basal ACTH levels approximately twice those of controls, and their ACTH responses were 4 times those of controls. In contrast, DM basal cortisol levels were not significantly different from those of relatives and were slightly higher than those of normal subjects. Cortisol responses were similar in the three groups, probably due to attenuation at high levels of adrenocortical stimulation, although some patients with inappropriately low cortisol responses for their level of ACTH stimulation warrant further investigation. Nineteen of the 36 patients whose ACTH responses were greater than 3 SD above the normal mean were classed as hyperresponders. Seven patients, who were tested more than once, had reproducible responses relative to those of the normal subjects. We conclude that ACTH hypersecretion after CRH-mediated stimuli, including naloxone, is an inherent, but variable, feature of DM, caused by expression of the genetic mutation at the anterior pituitary. The mechanism is probably a defect in the intracellular pathway initiated by CRH-receptor interaction as a result of abnormal levels of a cAMP-dependent kinase, DMPK, the product of the gene undergoing mutation in DM.

Alprazolam (APZ), a triazolobenzodiazepine with unique clinical utility, has potent inhibitory effects on the human hypothalamic-pituitary-adrenal axis. Because APZ inhibits CRH secretion from isolated rat hypothalami and inhibits the probable CRH-mediated effect of naloxone on ACTH release, it is likely APZ acts as an inhibitor of hypothalamic CRH release in humans. The two principal physiological ACTH secretagogues are CRH and arginine vasopressin (AVP). We studied the ACTH and cortisol responses to an ACTH-releasing dose of AVP with and without preadministration of APZ in humans. Our hypothesis was that acute CRH deprivation by APZ would attenuate the ACTH response to vasopressin, as CRH and AVP act synergistically to control ACTH release. This synergy may depend on activation of subpopulations of corticotropes, some of which require both CRH and AVP together to elicit an ACTH response and/or intracellular "cross-talk" between second messenger pathways stimulated by the secretagogues. APZ (2 mg, orally) was given to eight healthy volunteers 90 min before AVP (0.0143 IU/kg BW, iv) in a randomized, double blind, placebo-controlled design during afternoon studies. ACTH and cortisol levels were measured at frequent intervals from 60 min before to 120 min after AVP injection. APZ reduced the mean integrated ACTH and cortisol responses to AVP by 67% and 70% respectively [ACTH, 161.6 +/- 59.7 vs. 53.0 +/- 20.9 pmol/min.L (P = 0.022); cortisol, 9314 +/- 3310 vs. 2763 +/- 1472 nmol/min.L (P = 0.020, AVP vs. APZ/AVP, respectively)]. APZ reduced the mean peak ACTH and cortisol responses to AVP by 57% (P = 0.023) and 40% (P = 0.0012), respectively. AVP levels were not significantly different in those who received APZ or placebo. This study provides further evidence of the potent inhibitory effects of APZ on ACTH and cortisol release in humans and is the first to find that APZ inhibits AVP-stimulated ACTH and cortisol release. This study also suggests that CRH/AVP synergy is an important physiological mechanism for ACTH release in humans, as indicated by the blunted ACTH response to AVP after APZ-mediated acute CRH deprivation. Inhibition of the pituitary-adrenal axis by APZ may explain its unique efficacy in psychiatric disorders thought to be associated with dysregulation of hypothalamic CRH release.

The ACTH response to endogenous or exogenous CRH is increased in patients with myotonic dystrophy (DM), possibly because of abnormal function of cAMP-dependent protein kinases in this condition. Arachidonic acid (AA) metabolites are believed to interact with the cAMP-dependent second messenger system activated by CRH; therefore, drugs that interfere with AA metabolism may alter ACTH secretion in DM. In this study, seven DM patients were given naloxone, which stimulates endogenous CRH release, and aspirin, which inhibits the synthesis of prostaglandins from AA via the cyclooxygenase metabolic pathway. Pretreatment with aspirin reduced the mean integrated ACTH response to naloxone by 33% (P < 0.05). However, the corresponding 18% reduction in cortisol levels was not statistically significant (P > 0.10). These findings are in contrast to those of a previous study using an identical protocol, in which aspirin increased the ACTH response to naloxone in six normal volunteers. This difference between DM and control subjects is consistent with the hypothesis that the interaction between AA metabolites and the cAMP-dependent protein kinase-A second messenger system is abnormal in the corticotrophs of persons with DM.

1. Endogenous benzodiazepine receptor ligands are thought to influence the human hypothalamic-pituitary-adrenal (HPA) axis and naloxone, a known stimulator of adrenocorticotropic hormone (ACTH) release, is thought to act via release of hypothalamic corticotropin-releasing hormone. 2. The aim of the present study was to assess the influence of endogenous benzodiazepine-receptor ligands by administering flumazenil (Ro15-1788), a benzodiazepine antagonist, and measuring ACTH and cortisol release, both basal and during naloxone-stimulation. 3. Nine normal volunteers in a placebo-controlled double-blind design were studied. Flumazenil (0.5 mg, i.v. bolus) was given 2 min before naloxone (125 micrograms/kg bodyweight, i.v. bolus) immunoreactive-adrenocorticotropic hormone (IR-ACTH) and cortisol levels were measured at frequent intervals from 60 min before to 120 min after naloxone injection. 4. Flumazenil had no effect on ACTH and cortisol release when given alone; flumazenil area under the ACTH/time curve (pmol/L.min) = -36.5 +/- 63.5 compared with placebo = -53.5 +/- 31.8, flumazenil area under the cortisol/time curve (nmol/L.min x 10(-3)) = - 2.4 +/- 2.4 compared with placebo -0.56 +/- 1.4. Flumazenil did not change the ACTH and cortisol release achieved with naloxone; naloxone area under the ACTH/time curve (pmol/L.min) = 327.8 +/- 61.7 compared with flumazenil/naloxone = 366.3 +/- 88.1, naloxone area under the cortisol/time curve (nmol/L. min x 10(-3) = 12.2 +/- 3.4 compared with naloxone/flumazenil = 10.5 +/- 2.1. 5. The authors conclude that flumazenil dose not modify basal or stimulated ACTH and cortisol release in healthy humans. This would suggest that endogenous benzodiazepine-like ligands and the benzodiazepine/gamma-aminobutyric acid receptor complex do not tonically influence the hypothalamic-pituitary-adrenal axis.

Prostaglandins are believed to influence hypothalamic-pituitary-adrenal (HPA) axis function, but their specific effects on ACTH and cortisol secretion in humans are unclear. Acetylsalicylic acid (aspirin) blocks the synthesis of prostaglandins from arachidonic acid. We studied the effects of oral aspirin on the plasma ACTH and cortisol responses to iv naloxone, which increases endogenous CRH release, in six normal volunteers and on the adrenocortical response to synthetic ACTH boluses in seven other healthy subjects, using placebo-controlled, single blinded protocols. Aspirin pretreatment significantly increased the ACTH response to naloxone [mean peak increase from basal, 8.3 +/- 1.2 vs. 5.9 +/- 0.8 pmol/L (P < 0.05); mean integrated response, 431.9 +/- 51.5 vs. 295.1 +/- 26.6 pmol/L.min (P < 0.005); for aspirin/naloxone and placebo aspirin/naloxone, respectively]. However, the corresponding cortisol results did not show statistically significant differences (P < 0.20). The mean integrated ACTH and cortisol responses were 46% and 26% greater with aspirin, respectively. Aspirin did not influence the cortisol responses to synthetic ACTH administration given according to a dose-response protocol. We conclude that aspirin augments the HPA axis response to naloxone stimulation in normal humans without having a direct effect at the adrenal level. The action of aspirin on the human HPA axis is probably mediated via inhibition of cyclooxygenase, resulting in changes in arachidonic acid metabolites, which influence ACTH release from corticotrophs.

In persons with myotonic dystrophy (DM), the ACTH response to CRH is greater than normal, while it is delayed in response to arginine vasopressin. Since influx of extracellular Ca2+ ions is a common step in signal transduction by both of these secretagogues, an abnormality of cellular Ca2+ transport may underlie the disturbances of hypothalamic-pituitary-adrenal axis function in this condition. Seven myotonic patients were given naloxone, which stimulates endogenous CRH release, and nifedipine, which blocks L-type voltage-dependent Ca2+ channels. Each subject underwent three tests, using different drug combinations, in a single blind, placebo-controlled protocol. Pretreatment with nifedipine delayed the time of the peak plasma hormone responses after naloxone [ACTH, 32.1 +/- 2.1 vs. 51.4 +/- 4.5 min (P < 0.05); cortisol, 42.9 +/- 2.1 vs. 70.7 +/- 4.3 min (P < 0.02); for naloxone and nifedipine/naloxone, respectively]. Additionally, nifedipine significantly reduced the proportion of the mean integrated ACTH response that had occurred by 30 min after naloxone administration (32.0 +/- 4.0% for naloxone vs. 17.6 +/- 2.4% for nifedipine/naloxone; P < 0.02) and the proportion of the mean integrated cortisol response by 45 min after naloxone administration (34.7 +/- 3.5% for naloxone vs. 25.0 +/- 2.6% for nifedipine/naloxone; P < 0.02). However, the total integrated responses did not change [ACTH, 1182.6 +/- 548.9 vs. 905.5 +/- 157.0 pmol/min.L (P = NS); cortisol 17,353 +/- 2,984 vs. 18,469 +/- 3,561 nmol/min.L (P = NS); for naloxone and nifedipine/naloxone, respectively]. We conclude that nifedipine delays, but does not reduce, the ACTH and cortisol responses to naloxone in DM. Since nifedipine has a different effect on normal controls (reduced response with unchanged timing), these findings imply an abnormality of dihydropyridine-insensitive Ca2+ transport (such as T-type Ca2+ channels) in the corticotrophs of DM patients.

1. Petrosal sinus sampling has been used to establish the source of adrenocorticotropin (ACTH) in ACTH-dependent Cushing's syndrome. Naloxone, an opioid antagonist, stimulates ACTH secretion, probably via release of endogenous hypothalamic corticotropin releasing hormone (CRH). 2. Three patients with hypercortisolism were studied. Two showed suppressed (> 50%) urinary-free cortisol excretion with high-dose dexamethasone treatment (2 mg every 6 h for 2 days), one did not suppress. The patients were subjected to bilateral simultaneous inferior petrosal sinus sampling (BSIPSS) with simultaneous peripheral venous (forearm) samples. Basal (unstimulated) samples were taken and naloxone (125 micrograms/kg bodyweight) was given intravenously with subsequent simultaneous sampling. Plasma ACTH was measured by radio-immunoassay (RIA). 3. All cases exhibited a marked rise in immunoreactive (IR)-ACTH levels (pmol/L) after naloxone injection, basal to peak: case 1, left 11.5-22.1, right 9.8 with no rise, peripheral 9.1-9.5; case 2, left 456-863, right 125-501, peripheral 59-82; case 3, left 12.7-13.0, right 277-431, peripheral 12.1-11.7. All results indicate pituitary Cushing's syndrome, with a central to peripheral ratio > 2.3:1. Pituitary Cushing's syndrome was confirmed on the results of trans-sphenoidal pituitary surgery in cases 1 and 3. 4. It is suggested that naloxone injection during petrosal sinus sampling in Cushing's syndrome may assist in the diagnosis of ACTH source, by enhancing ACTH release from a pituitary micro-adenoma.

Naloxone, which increases endogenous corticotropin-releasing hormone (CRH) release by blocking an inhibitory opioidergic tone on the hypothalamic-pituitary-adrenal (HPA) axis, was administered in a dose-response protocol to seven healthy volunteers and 13 patients with treated posttraumatic stress disorder (PTSD). Six of the PTSD patients showed an increased hormonal response to the lowest naloxone dose (6 micrograms/kg) compared to both the control subjects and the other PTSD patients. This difference persisted on detailed subgroup analysis, although it was less marked at the highest naloxone dose (125 micrograms/kg). The responses of the other seven PTSD patients were indistinguishable from those of the control group. The greater responses of the six PTSD patients could not be explained on the basis of associated psychiatric illnesses or psychotropic drug therapy, and did not correlate with standard psychological testing or severity of PTSD. The results of this preliminary study therefore suggest that a hypersensitivity of the HPA axis to endogenous CRH stimulation may occur in PTSD.

Alprazolam (APZ) is a benzodiazepine with unique antidepressant activity for a drug of its class. There is some evidence of inhibition of the unstimulated hypothalamo-pituitary-adrenal axis by APZ which may be important in its therapeutic action, and could be detrimental in APZ-treated subjects who encounter stressful stimuli. To assess the effect of APZ on stimulated ACTH and cortisol secretion, we studied 14 normal subjects in a randomized, double-blind, placebo-controlled design. APZ or placebo capsule was administered orally in doses of 0.5 mg and 2 mg, 90 min before either naloxone, 125 micrograms/kg body weight i.v. bolus dose, a known stimulator of ACTH and cortisol release, or placebo. After naloxone stimulation, the area under the plasma ACTH/time curves was significantly reduced by APZ, in both the 2 mg (P < 0.0005) and 0.5 mg (P < 0.005) doses, compared to their respective placebo studies; similar reductions in area under the plasma cortisol/time curves occurred after 2 mg (P < 0.00002) and 0.5 mg (P < 0.0005) APZ doses. We conclude that APZ is a potent inhibitor of naloxone-stimulated ACTH and cortisol release in humans. Since APZ has been shown to inhibit CRH release in vitro, and naloxone-induced ACTH secretion is likely to be caused through CRH release, this suggests that APZ inhibition of naloxone action is via the parvocellular CRH neurons of the paraventricular nucleus and/or central neurotransmitter pathways impinging directly or indirectly on these CRH neurons. Thus APZ may exert at least some of its clinical effects through inhibition of central CRH release. APZ treatment could lead to a relative hyporesponse of the pituitary-adrenal axis during stress. APZ may be an important tool for manipulation of hypothalamic CRH release in studies of pituitary-adrenal function.

Sustained CRH-stimulated ACTH release in vitro depends on Ca2+ influx and is inhibited 30-40%, but not delayed, by dihydropyridine Ca2+ channel blockers. In five normal humans, we found that nifedipine pretreatment reduced integrated ACTH responses to the CRH-mediated stimulus of fenfluramine by 28% and cortisol responses by 34%, results comparable with those from in vitro reports. Nifedipine did not alter the timing of peak hormonal responses. We conclude that (1) in humans, nifedipine inhibits ACTH release by fenfluramine by blocking Ca2+ influx via L-type channels in corticotrophs; (2) the magnitude of fenfluramine-stimulated CRH release is probably unaltered by nifedipine and (3) because the timing is unaltered, nifedipine does not affect the rate of CRH delivery to the corticotroph.

1. The effect of pretreatment with nifedipine on naloxone-stimulated corticotrophin-releasing hormone (CRH)-induced adrenocorticotrophin (ACTH) release in humans was investigated. The mean peak plasma ACTH and cortisol levels and the mean peak change in cortisol levels from basal were significantly lower in the nifedipine/naloxone test than in the naloxone alone test. The integrated areas under the ACTH-time and cortisol-time curves were reduced by 33 and 49%, respectively, in the nifedipine/naloxone test compared with the naloxone alone test. These results correlate well with published in vitro studies. 2. Acute administration of oral nifedipine partially inhibited naloxone-stimulated ACTH and cortisol release, probably by blockade of plasma membrane voltage-dependent L-type calcium channels normally activated following binding of CRH to pituitary corticotroph receptors. 3. Naloxone-induced CRH release may replace insulin hypoglycaemia testing of pituitary ACTH reserve in humans.

Abstract We administered intramuscular arginine vasopressin (AVP) to ten normal controls and eight myotonic dystrophy patients. By measuring plasma AVP levels in five of the myotonics and all the normals, we showed that absorption and distribution of AVP was not delayed or significantly reduced in myotonics. The magnitude of the mean plasma adrenocorticotropin (ACTH) response to AVP in the myotonics was not different from that of normals, although it was significantly delayed (mean peak time, 37.5+/-4.9 versus 17.0 +/- 3.2 min). We propose that this delay was caused by a significantly reduced ACTH secretion rate in myotonics, because the maximum rate of detection of ACTH in plasma is reduced in myotonics (0.6 +/- 0.2 versus 1.7 +/- 0.5 pmol/L/min), whose corticotropes, while having the same capacity to respond to the AVP stimulus, are slower to attain that capacity. The mean integrated cortisol response (AUC) was significantly smaller for myotonics (8072 +/- 2017 versus 13049+/-1630 nmol.min/L). This may be due to the slower rate of ACTH delivery to the adrenal in myotonics. The timing of the adrenal response does not appear to be impaired in myotonic dystrophy, with the cortisol peak following the ACTH peak by approximately 15 min in both groups. The normal magnitude ACTH response to AVP in myotonics is in contrast to that seen to ACTH secretagogues acting via corticotropin- releasing hormone-initiated pathways, where a rapid hypersecretion is seen. We propose a mechanism of defective calcium transport to account for these observations.

Abstract The plasma immunoreactive adrenocorticotropin and cortisol responses to oral fenfluramine hydrochloride (1.5mg/kg body wt) or placebo were examined in 11 patients with myotonic dystrophy, 4 controls with facioscapulohumeral dystrophy, a similarly debilitating muscle wasting disease, and 14 normal controls in single-blind studies performed in mid-afternoon. Mean areas under the adrenocorticotropin response versus time curve were significantly greater in myotonics (2573 + 429 pmol.min/L) than in facioscapulohumeral dystrophy controls (696 + 279 pmol.min/L, P<0.02) and normals (560+/-61 pmol.min/L, P<0.0001). Corresponding cortisol responses were significantly greater in myotonics (35757 + 3949 nmol.min/L) than in normals (21828+/-1669 nmol.min/L, P < 0.001), but not significantly greater than those in facioscapulohumeral dystrophy controls (22830 + 6140 nmol.min/L, P = 0.055). No stressful side-effects which could affect hormone responses, and no significant changes in blood pressure or heart rate were noted. Fenfluramine activates central serotonergic and/or noradrenergic pathways initiating secretion of corticotropin-releasing hormone and possibly arginine vasopressin. We postulate that these fenfluramine-activated pathways are hyperstimulated in myotonics, leading to adrenocorticotropin and cortisol hypersecretion. This may be a manifestation of a general cell membrane defect in myotonic dystrophy. We found a lack of correlation of age (and severity of disease) with adrenocorticotropin response in myotonics, and therefore, the hyperresponse may serve as a useful marker for the disease before development of other overt signs.

1. Adrenergic mechanisms play an important role in regulation of ACTH release. We used the alpha 2-adrenergic agonist, clonidine, as a central nervous system inhibitor of ACTH release to see if it would alter naloxone-induced ACTH secretion in normal human volunteers. 2. There was a significant blunting of the mean peak level of ACTH and the mean peak change of ACTH from basal as well as the area under the ACTH-time curve when clonidine was given prior to naloxone. 3. We conclude that clonidine, by blocking central noradrenergic pathways, which stimulate corticotropin-releasing hormone secretion, inhibits naloxone-induced ACTH secretion. This suggests that naloxone causes ACTH release through these same central noradrenergic pathways.

1. This study set out to compare the effect of the combination of fenfluramine (Fen) and naloxone (Nal) on ACTH and cortisol release with each of these agents alone in six normal volunteers. Three protocols were used: 1.5 mg/kg bodyweight oral Fen; 125 micrograms/kg bodyweight i.v. Nal; oral Fen plus i.v. Nal 135 min later. Plasma ACTH and cortisol were measured at intervals of 285 min over each test. 2. The mean peak levels and mean peak changes from basal in plasma ACTH and cortisol were significantly greater in the combination test (Fen/Nal) than in either the Fen alone or the Nal alone tests. Fen and Nal given together cause a synergistic release of ACTH and cortisol as determined by the areas under the ACTH-time and cortisol-time curves for Fen/Nal compared to the sums of Fen alone plus Nal alone curves for ACTH and cortisol. 3. We conclude that Fen and Nal acting synergistically work through different and potentiating mechanisms at the hypothalamic, central nervous system and/or pituitary levels to cause ACTH release.

1. Adrenaline causes ACTH release from cultured rat pituitary corticotrophs (Vale et al. 1983) and there is evidence that it causes ACTH release in rats in vivo (Plotsky et al. 1985). 2. The present study examined the effects of intravenous adrenaline infusion with and without simultaneous administration of the known ACTH secretagogue, arginine vasopressin, in normotensive and mild essential hypertensive men on their plasma ACTH and cortisol levels. 3. Low dose adrenaline infusion (0.013 microgram/kg per min) does not cause ACTH or cortisol release, but appears to blunt the ACTH and cortisol rise caused by arginine vasopressin (0.14 pressor units/kg, i.m.).

1. Clonidine, an alpha 2-adrenergic agonist, is thought to inhibit noradrenergic neuronal activity (NNA) in the central nervous system (CNS) by a presynaptic alpha 2-receptor mechanism. Central NNA is thought to be the primary monoaminergic stimulus to pituitary ACTH release. Fenfluramine, a serotonin releasing agent and uptake inhibitor, causes ACTH release in normal man. 2. The present study investigated the effect of clonidine on fenfluramine-induced ACTH release in six normal volunteers. Four protocols were used: 1.5 mg/kg body weight oral fenfluramine; 4.3 micrograms/kg body weight oral clonidine; oral clonidine + oral fenfluramine 1 h later; placebo clonidine. Plasma ACTH and cortisol were measured at intervals for 5 h after clonidine and for 4 h after fenfluramine. 3. The mean plasma ACTH and cortisol levels and the mean maximal changes in these levels were significantly lower during the clonidine + fenfluramine test than during fenfluramine alone. Plasma ACTH and cortisol levels were not lowered significantly more by clonidine than by placebo. 4. In conclusion, clonidine blocked the ACTH-releasing activity of fenfluramine in normal humans. This inhibition of active ACTH release may result from clonidine blockade of fenfluramine-induced activation of central NNA. Clonidine alone was no more effective than placebo in lowering plasma ACTH and cortisol.

1. The present study investigated the effect of prior administration of nifedipine on AVP-induced ACTH release in seven normal volunteers. Three protocols were used: 20 mg oral nifedipine; 0.14 pressor units intramuscular (i.m.) per kg bodyweight aqueous AVP; oral nifedipine plus i.m. AVP 90 min later. Plasma ACTH and cortisol were measured at intervals for 2.5 h during each test. 2. The mean peak plasma ACTH and cortisol levels and the mean peak changes from basal in these levels were significantly lower in the nifedipine/AVP test than in the AVP alone test. The integrated area under the cortisol time curve was significantly lower for the nifedipine/AVP test than that for the AVP test alone. Nifedipine alone caused no changes in ACTH or cortisol. 3. Acute administration of oral nifedipine caused an inhibition of AVP-stimulated ACTH and cortisol release in normal humans. This effect may be due to blockade of plasma membrane calcium channels normally activated during AVP stimulation of pituitary corticotrophs.