Opiate modulation of the pituitary-adrenal axis: effects of stress and circadian rhythm

Redefining the stress cortisol response to surgery

BACKGROUND

Cortisol levels rise with the physiological stress of surgery. Previous studies have used older, less-specific assays, have not differentiated by severity or only studied procedures of a defined type. The aim of this study was to examine this phenomenon in surgeries of varying severity using a widely used cortisol immunoassay.

METHODS

Euadrenal patients undergoing elective surgery were enrolled prospectively. Serum samples were taken at 8 am on surgical day, induction and 1 hour, 2 hour, 4 hour and 8 hour after. Subsequent samples were taken daily at 8 am until postoperative day 5 or hospital discharge. Total cortisol was measured using an Abbott Architect immunoassay, and cortisol-binding globulin (CBG) using a radioimmunoassay. Surgical severity was classified by POSSUM operative severity score.

RESULTS

Ninety-three patients underwent surgery: Major/Major+ (n = 37), Moderate (n = 33) and Minor (n = 23). Peak cortisol positively correlated to severity: Major/Major+ median 680 [range 375-1452], Moderate 581 [270-1009] and Minor 574 [272-1066] nmol/L (Kruskal-Wallis test, P = .0031). CBG fell by 23%; the magnitude of the drop positively correlated to severity.

CONCLUSIONS

The range in baseline and peak cortisol response to surgery is wide, and peak cortisol levels are lower than previously appreciated. Improvements in surgery, anaesthetic techniques and cortisol assays might explain our observed lower peak cortisols. The criteria for the dynamic testing of cortisol response may need to be reduced to take account of these factors. Our data also support a lower-dose, stratified approach to dosing of steroid replacement in hypoadrenal patients, to minimize the deleterious effects of over-replacement.

The physiologic effects of pain on the endocrine system

Severe pain has profound physiologic effects on the endocrine system. Serum hormone abnormalities may result and these serve as biomarkers for the presence of severe pain and the need to replace hormones to achieve pain control. Initially severe pain causes a hyperarousal of the hypothalamic-pituitary-adrenal system which results in elevated serum hormone levels such as adrenocorticotropin, cortisol, and pregnenolone. If the severe pain does not abate, however, the system cannot maintain its normal hormone production and serum levels of some hormones may drop below normal range. Some hormones are so critical to pain control that a deficiency may enhance pain and retard healing.

Anorexia nervosa: a unified neurological perspective

The roles of corticotrophin-releasing factor (CRF), opioid peptides, leptin and ghrelin in anorexia nervosa (AN) were discussed in this paper. CRF is the key mediator of the hypothalamo-pituitary-adrenal (HPA) axis and also acts at various other parts of the brain, such as the limbic system and the peripheral nervous system. CRF action is mediated through the CRF1 and CRF2 receptors, with both HPA axis-dependent and HPA axis-independent actions, where the latter shows nil involvement of the autonomic nervous system. CRF1 receptors mediate both the HPA axis-dependent and independent pathways through CRF, while the CRF2 receptors exclusively mediate the HPA axis-independent pathways through urocortin. Opioid peptides are involved in the adaptation and regulation of energy intake and utilization through reward-related behavior. Opioids play a role in the addictive component of AN, as described by the "auto-addiction opioids theory". Their interactions have demonstrated the psychological aspect of AN and have shown to prevent the functioning of the physiological homeostasis. Important opioids involved are β-lipotropin, β-endorphin and dynorphin, which interact with both µ and κ opioids receptors to regulate reward-mediated behavior and describe the higher incidence of AN seen in females. Moreover, ghrelin is known as the "hunger" hormone and helps stimulate growth hormone (GH) and hepatic insulin-like-growth-factor-1(IGF-1), maintaining anabolism and preserving a lean body mass. In AN, high levels of GH due to GH resistance along with low levels of IGF-1 are observed. Leptin plays a role in suppressing appetite through the inhibition of neuropeptide Y gene. Moreover, the CRF, opioid, leptin and ghrelin mechanisms operate collectively at the HPA axis and express the physiological and psychological components of AN. Fear conditioning is an intricate learning process occurring at the level of the hippocampus, amygdala, lateral septum and the dorsal raphe by involving three distinct pathways, the HPA axis-independent pathway, hypercortisolemia and ghrelin. Opioids mediate CRF through noradrenergic stimulation in association with the locus coeruleus. Furthermore, CRF's inhibitory effect on gonadotropin releasing hormone can be further explained by the direct relationship seen between CRF and opioids. Low levels of gonadotropin have been demonstrated in AN where only estrogen has shown to mediate energy intake. In addition, estrogen is involved in regulating µ receptor concentrations, but in turn both CRF and opioids regulate estrogen. Moreover, opioids and leptin are both an effect of AN, while many studies have demonstrated a causal relationship between CRF and anorexic behavior. Moreover, leptin, estrogen and ghrelin play a role as predictors of survival in starvation. Since both leptin and estrogen are associated with higher levels of bone marrow fat they represent a longer survival than those who favor the ghrelin pathway. Future studies should consider cohort studies involving prepubertal males and females with high CRF. This would help prevent the extrapolation of results from studies on mice and draw more meaningful conclusions in humans. Studies should also consider these mechanisms in post-AN patients, as well as look into what predisposes certain individuals to develop AN. Finally, due to its complex pathogenesis the treatment of AN should focus on both the pharmacological and behavioral perspectives.

Effects of chronic osteoarthritis pain on neuroendocrine function in men

CONTEXT

Chronic pain has been associated with elevated cortisol, reduced LH and testosterone (T), and/or augmented circulating or excreted catecholamines. Most endocrine studies have been conducted in patients in whom the potentially confounding effects of depression, inflammatory disease, or coexistent medication use have not been controlled.

OBJECTIVE

The objective of the study was to test the hypothesis that chronic pain activates ACTH-cortisol and suppresses LH-T.

DESIGN AND SETTING

This was a case control study conducted at a clinical research center.

PARTICIPANTS

Participants included 16 opioid-naive men with chronic osteoarthritis pain, aged 35-65 yr with body mass index 20-30 kg/m2, and 12 healthy, opioid- and pain-free men of similar ages and body mass indexes.

METHODS

We compared circulating concentrations of ACTH, cortisol, LH, and T derived from every 20-min blood sampling (2000-0800 h), and 24-h urinary excretion of cortisol, epinephrine, norepinephrine, and dopamine.

RESULTS

There were no significant differences in mean or integrated concentrations of ACTH, cortisol, LH, or T, or in the corresponding approximate entropy scores in osteoarthritis patients, compared with control subjects. The 0800-h serum LH concentrations were elevated in patients vs. controls (6.42 +/- 1.65 vs. 3.99 +/- 1.54 IU/liter, mean +/- sd, P = 0.02), whereas there were no significant group differences in total or free T, SHBG, cortisol binding globulin, dehydroepiandrosterone sulfate, or urinary cortisol and catecholamines.

CONCLUSIONS

These data suggest that neuroendocrine function is not significantly altered in otherwise healthy men with chronic musculoskeletal pain and that prior reports of such hormonal abnormalities may have resulted from the confounding effects of coexistent illness or medication use.

Relative Adrenal Failure in the ICU: An Identifiable Problem Requiring Treatment

Critically ill patients at some stage may develop adrenal insufficiency (AI). This article reviews the mechanisms, diagnosis criteria, consequences, and treatment of AI in various ICU conditions. Glucocorticoid insufficiency may be related to a decrease in glucocorticoid synthesis (ie, adrenal insufficiency) or to a reduced delivery of glucocorticoid to target tissues and cells. Diagnosis relies on clinical suspicion and ACTH test results. The length of cortisol replacement therapy should be at least 7 days and the adjunction of fludrocortisone is recommended.

A study of maternal plasma beta-endorphin in pre-eclamptic women during labour

This prospective study was undertaken to determine the maternal plasma beta-endorphin levels in pre-eclamptic women during labour and to explore any correlation between the levels and the severity of pre-eclampsia. A total of 50 primiparous women at term were recruited over a period of 5 years. Twenty-five with pre-eclampsia and 25 healthy women considered as a control group. The mean concentration of maternal plasma beta-endorphin in pre-eclamptic group (22.73+/-8.02 pmol/l) was significantly lower (p<0.001) than that of the control group (48.38+/-5.94 pmol/l). A highly significant (p<0.001) negative correlation was found between maternal plasma beta-endorphin levels and both systolic and diastolic blood pressures in pre-eclamptic group.

Normal opioid tone and hypothalamic-pituitary-adrenal axis function in chronic fatigue syndrome despite marked functional impairment

OBJECTIVE

To determine whether the functional impairment seen in chronic fatigue syndrome (CFS) is associated with reduced levels of central opioids and/or deficiency of the hypothalamic-pituitary-adrenal (HPA) axis.

DESIGN

Single-blinded case-control study measuring functional and psychological status, basal hormonal parameters and ACTH/cortisol response to naloxone and ovine corticotrophin-releasing hormone (oCRH) vs. placebo in people with CFS and healthy controls.

PATIENTS

Twelve people with CFS and 11 age-matched controls.

MEASUREMENTS

Hormonal parameters: basal levels of 09:00 h plasma cortisol, dehydroepiandrosterone sulfate (DHEAS) and IGF-1. 24-h urinary free cortisol. Plasma ACTH and cortisol response to naloxone 125 microg/kg, oCRH 1 microg/kg and placebo (normal saline). Psychological parameters: SF-36, Hamilton Depression Score, Hospital Anxiety and Depression Scale and Fatigue Scale.

RESULTS

There were highly significant differences between the CFS subjects and the controls with respect to the measures of fatigue and physical functioning. However, there were no differences in basal levels of 09:00 h cortisol (367 +/- 37 vs. 331 +/- 39 nmol/l, P = 0.51), DHEAS (4.2 +/- 0.6 vs. 4.0 +/- 0.5 micromol/l, P = 0.81), 24-h urinary free cortisol (182 +/- 27 vs. 178 +/- 21 nmol/24 h, P = 0.91) or IGF-1 (145 +/- 19 vs. 130 +/- 11 microg/l, P = 0.52) between the CFS group and controls, respectively. There was also no difference between the groups with respect to the ACTH and cortisol response to either oCRH or naloxone.

CONCLUSIONS

Our data do not support an aetiological role for deficiency in central opioids or the HPA axis in the symptoms of CFS.

Normalization of serum cortisol concentration with opioid treatment of severe chronic pain

Serum cortisol concentrations may be altered in severe, chronic pain due to excess stimulation of the hypothalamic-pituitary-adrenal axis. Among 40 consecutive patients with severe, chronic pain 26 (65.0%) demonstrated abnormal serum cortisol concentration. After 90 days of treatment, only 7 (17.5%; p<0.01) continued to show abnormal serum cortisol concentration indicating that serum cortisol and other serologic abnormalities may serve as biologic markers of severe, chronic pain.

Stimulation of the hypothalamic-pituitary-adrenal axis with the opioid antagonist nalmefene

Nalmefene Stimulation of the HPA Axis.

BACKGROUND

The Hypothalamic-pituitary-adrenal (HPA) axis plays a vital role in the body's response to stress. The traditional gold standard for evaluating the HPA axis, the insulin hypoglycemia test (IHT), has several known limitations, and a second test, the standard ACTH stimulation test, can detect severe deficiencies of cortisol, but often misses mild or early cases. Therefore, a better test for the evaluation of the HPA axis is needed. This study evaluated the opiate antagonist nalmefene as a stimulation test of the HPA axis.

METHODS

25 healthy subjects were studied, 9 women and 16 men, mean age 30.4 yr. (range 21-55), and mean BMI 24.1 kg/m2 (range 18.6-34.2). Subjects received one of 3 doses of intravenously administered nalmefene: 2 mg (n = 6), 6 mg (n = 12), or 10 mg (n = 7). Serum cortisol and plasma ACTH were measured before and serially over two hours after the administration of nalmefene.

RESULTS

ACTH and cortisol levels rose significantly and similarly after the 10 mg dose and the 6 mg dose. After the 10 mg dose, mean peak ACTH was 82.4 +/- 22.6 pg/ml and mean peak cortisol was 25.2 +/- 1.8 microg/dl. After the 6 mg dose, mean peak ACTH was 70.3 +/- 7.7 pg/ml and mean peak cortisol was 24.7 +/- 1.7 microg/dl. Cortisol levels rose above 18 microg/dl in all subjects receiving 10 mg of nalmefene, and in all but two of the subjects receiving 6 mg of nalmefene. Side effects to nalmefene were of greater duration and intensity in the subjects receiving 10 mg of nalmefene vs. those receiving 6 or 2 mg. These included most notably fatigue, lightheadedness, nausea and vomiting.

CONCLUSIONS

Of the nalmefene doses we studied, 6 mg achieved the best combination of stimulation of ACTH and cortisol and fewest side effects. If further studies show a concordance between nalmefene and IHT, nalmefene testing could be used to assess the HPA axis in patients at risk for dysfunction of this axis.

Science review: mechanisms of impaired adrenal function in sepsis and molecular actions of glucocorticoids

This review describes current knowledge on the mechanisms that underlie glucocorticoid insufficiency in sepsis and the molecular action of glucocorticoids. In patients with severe sepsis, numerous factors predispose to glucocorticoid insufficiency, including drugs, coagulation disorders and inflammatory mediators. These factors may compromise the hypothalamic–pituitary axis (i.e. secondary adrenal insufficiency) or the adrenal glands (i.e. primary adrenal failure), or may impair glucocorticoid access to target cells (i.e. peripheral tissue resistance). Irreversible anatomical damages to the hypothalamus, pituitary, or adrenal glands rarely occur. Conversely, transient functional impairment in hormone synthesis may be a common complication of severe sepsis. Glucocorticoids interact with a specific cytosolic glucocorticoid receptor, which undergoes conformational changes, sheds heat shock proteins and translocates to the nucleus. Glucocorticoids may also interact with membrane binding sites at the surface of the cells. The molecular action of glucocorticoids results in genomic and nongenomic effects. Direct and indirect transcriptional and post-transcriptional effects related to the cytosolic glucocorticoid receptor account for the genomic effects. Nongenomic effects are probably subsequent to cytosolic interaction between the glucocorticoid receptor and proteins, or to interaction between glucocorticoids and specific membrane binding sites.

Cardiorespiratory and endocrine effects of endogenous opioid antagonism by naloxone in ponies anaesthetised with halothane

Halothane depresses cardiorespiratory function and activates the pituitary-adrenal axis, increasing beta endorphin. In horses, beta endorphin may enhance the anaesthetic-associated cardiorespiratory depression and mortality risk. The authors studied endogenous opioid effects on cardiorespiratory function and pituitary-adrenal activity in halothane-anaesthetised ponies by investigating opioid antagonism by naloxone. Six ponies were anaesthetised three times (crossover design). Anaesthesia was induced with thiopentone and maintained with 1.2 per cent halothane for 2 hours. Immediately after induction, naloxone was administered either intravenously (0.5 mg kg(-1)bolus then 0.25 mg kg(-1)hour(-1)for 2 hours) or intrathecally (0.5 mg) or was replaced by saline as control. Pulse and respiratory rates, arterial blood gases, cardiac output and plasma cortisol and adrenocorticotrophic hormone (ACTH) concentrations were measured. All groups developed cardiorespiratory depression (40 per cent decrease in cardiac output) and plasma cortisol increased. Plasma ACTH concentration was higher in ponies treated with intrathecal naloxone. Endogenous opioids may inhibit ACTH secretion, attenuating the stress response to halothane anaesthesia in equidae.

Hypothalamic-pituitary-adrenal axis sensitivity to opioids in women with polycystic ovary syndrome

OBJECTIVE

To evaluate the influence of the opioid system on the hypothalamic-pituitary-adrenal axis in women with polycystic ovary syndrome (PCOS).

DESIGN

Controlled clinical study.

SETTING

Academic research environment.

PATIENT(S)

Eight lean and 12 obese women with PCOS, and seven lean and 5 obese control subjects.

INTERVENTION(S)

Each patient received an i.v. bolus of naloxone at a dose of 125 microgram per kilogram of body weight; 48 hours later, each patient received 16 mg of loperamide p.o.

MAIN OUTCOME MEASURE(S)

Samples were collected for 2 hours for the naloxone test and for 3 hours for the loperamide test. Levels of adrenocorticotropic hormone (ACTH) and cortisol were measured in all plasma samples.

RESULT(S)

The obese women with PCOS had a greater ACTH and cortisol response to opiate blockade than either the lean women with PCOS or the control subjects, but there was no difference between the lean or obese control subjects and the lean women with PCOS. There was no difference in the responsiveness of the hypothalamic-pituitary-adrenal axis to loperamide between the PCOS and control groups.

CONCLUSION(S)

The data indicate that the sensitivity of the hypothalamic-pituitary-adrenal axis to opioids cannot be altered in women with PCOS. However, abnormalities of the hypothalamic-pituitary-adrenal axis in women with PCOS could be central in origin, as suggested by the effects of naloxone administration, and probably are related to the anthropometric characteristics of these hyperandrogenic patients.

Diurnal variations in endocrine and psychological responses to 0.2 mg/kg naloxone administration in patients with major depressive disorder and matched controls

BACKGROUND

There is evidence that the endogenous opioid system (EOS) is involved in the modulation of mood and neuroendocrine function. Furthermore, the possible involvement of the EOS in major depression has been postulated, although a clear role has not been established.

METHODS

The affective and endocrine responses to naloxone administration in seven female depressives and in seven matched controls and their diurnal variations were investigated. Subjects had an i.v. bolus of either 0.2 mg/kg naloxone or saline at two time points (09:00 or 18:00 h) and for 2 days in a single-blind, cross-over design.

RESULTS

The basal cortisol plasma levels, both in the morning and in the afternoon, showed higher values (P<0.05) in the depressives. There was a naloxone-induced increase in the adrenocorticotrophic hormone (ACTH), cortisol, and luteinizing hormone (LH) plasma levels, plus a subjective dysphoric effect in both groups. The depressives showed a greater dysphoric effect both in the morning and afternoon (P<0.05), and a blunted cortisol response in the afternoon (P<0.05). There were no differences between groups or time of day in the ACTH or LH responses.

LIMITATIONS

The sample size was small, but by studying each patient as their own control, plus a matched control for every patient, softens this effect. Finding patients with a major depressive episode free of medication is difficult, and this aspect contributes to the size of the sample.

CONCLUSIONS

These results suggest that opioid mechanisms may be involved in the HPA axis changes and possibly in mood changes found in depression. The discrepancy between increased sensitivity in depression to mood changes and decreased change in cortisol may indicate a ceiling effect for the latter.

The effect of naloxone on adrenocorticotropin and cortisol release: evidence for a reduced response in depression

BACKGROUND

Endogenous opioid peptides inhibit the hypothalamic-pituitary-adrenal (HPA) axis by influencing the release of hypothalamic corticotropin releasing factors. This study examines whether increased activity of the HPA axis in major depression is associated with reduced opioid tone.

METHODS

We measured the adrenocorticotropin (ACTH) and cortisol responses to an intravenous bolus of naloxone 0.125 microg/kg in 13 depressed outpatients and 13 healthy volunteers.

RESULTS

The mean cortisol response was significantly reduced (P<0.05), and the ACTH response was also non-significantly reduced in the depressed subjects.

CONCLUSIONS

These findings imply that the degree of inhibitory endogenous opioid tone is reduced in depression. Various mechanisms for the finding are discussed, including possible alteration in the function of alpha-adrenergic pathways.

CLINICAL IMPLICATIONS

Reduced endogenous opioid tone may explain why some depressed individuals self-medicate with opiates, and depression is associated with opiate withdrawal. Opioid pathways may have a role in the mechanism of action of antidepressant drugs, and may be of relevance in the development of novel antidepressants.

LIMITATIONS OF THE STUDY

The sample size was small, leading to a failure of the difference of the basal cortisol levels and also the delta ACTH between the groups to reach statistical significance.

Inhibitory effects of electroacupuncture on stress responses evoked by tooth-pulp stimulation in rats

The mechanism of electroacupuncture (EA) on the stress responses induced by tooth-pulp stimulation was investigated in anesthetized adult female Sprague-Dawley rats. The Hoku point in the Chinese meridian was used for acupuncture stimulation. Constant rectangular current (1 mA) pulses of 5-ms duration were delivered at 3 Hz through a pair of needles for 15 min. As for stress response indexes, we have monitored changes in arterial blood pressure and the levels of blood catecholamines, corticosterone, and ACTH. Arterial blood pressure was increased by high frequency stimulation (0.1 mA, 0.5 ms, 100 Hz for 15 s) of tooth-pulp in the control condition. After EA, we did not observe the same responses of the arterial blood pressure changes with the same stimuli. The tooth-pulp stimulation increased the concentrations of plasma norepinephrine (NE), epinephrine (E), dopamine (DA), corticosterone, and ACTH significantly from the levels of those before stress. After treatment with EA, the stress-induced increase in NE, DA, corticosterone, and ACTH but not the rise in E, were inhibited. When naloxone, an opioid antagonist, was administered intraperitoneally before EA, the effects of EA on stress responses were reduced. In this study, it can be suggested that EA has not only an analgesic effect but also suppressive effects on the stress responses primarily through the mediation of an endogenous opioid.

Influence of body mass on the hypothalamic-pituitary-adrenal-axis response to naloxone in patients with polycystic ovary syndrome

OBJECTIVE

To evaluate the influence of body mass on the hypothalamic-pituitary-adrenal (HPA)-axis response to naloxone in polycystic ovary syndrome (PCOS).

DESIGN

Controlled clinical study.

SETTING

Academic research environment.

PATIENT(S)

Ten lean and 10 obese women with PCOS compared with 7 lean and 8 obese control subjects matched for body mass index.

INTERVENTION(S)

Each patient received an IV bolus of naloxone at a dosage of 125 microg/kg.

MAIN OUTCOME MEASURE(S)

Samples were collected 30 minutes before and 0, 15, 30, 60, 90, and 120 minutes after injection: ACTH and cortisol levels were measured in all plasma samples.

RESULT(S)

No significant differences were found in the ACTH and cortisol responses to opioid blockade between lean women with PCOS and lean as well as obese control subjects; conversely, obese patients with PCOS showed a higher ACTH and cortisol responses to naloxone compared with all other groups.

CONCLUSION(S)

Hypothalamic-pituitary-adrenal-axis abnormalities of PCOS may be central in origin and abdominal obesity seems to play a key role in the HPA-axis hyperactivity of women with PCOS when naloxone is administered.

A comparison of the naloxone test with the insulin stress test in patients following transsphenoidal surgery

OBJECTIVE

To study the reliability of the naloxone test in assessing the hypothalamic-pituitary-adrenal (HPA) axis in patients following transsphenoidal pituitary surgery, by comparison with the insulin stress test (IST). Also, to establish a normal range for the response to naloxone in healthy controls.

DESIGN

All patients had the IST performed, soluble insulin 0.1-0.3 U/kg (usually 0.15 U/kg) being administered intravenously, followed by venous sampling for plasma glucose and serum cortisol at 0, 15, 30, 45, 60, 75 and 90 minutes. Naloxone (125 micrograms/kg body weight) was similarly administered to all patients 6 days later, with sampling at -15, 0, 15, 30, 45, 60, 90 and 120 minutes for plasma glucose, serum cortisol and plasma ACTH. The naloxone test was also performed on control subjects using an identical protocol.

SUBJECTS

Twenty patients (11F/9M) aged 48.8 +/- 2.8 years (mean +/- SE) 4-6 weeks following transsphenoidal pituitary surgery. Twelve normal healthy control subjects (6F/6M) aged 31.5 +/- 3.0 years.

MEASUREMENTS

Serum cortisol was measured by radioimmunoassay and plasma ACTH by immunoradiometric assay.

RESULTS

Adequate hypoglycaemia (< or = 2.0 mmol/l) was achieved in all patients. Peak cortisol was > 550 nmol/l in 17 subjects (range: 572-867 nmol/l) and a subnormal response observed in 3 (peak cortisol 163-498 nmol/l). In the 17 patients with a normal cortisol response to hypoglycaemia the response to naloxone was extremely variable, with serum cortisol falling in 4 and an increment of < or = 100 nmol/l in 6 others. In the 3 patients who failed the IST, two responded to naloxone and one did not. In normal controls, 3 of the 12 had little or no response to naloxone.

CONCLUSIONS

As the naloxone test fails to produce a response in all normal subjects it is impossible to define a 'normal' response. The numerous discrepancies with the IST in patients are further evidence of the test's lack of reliability in assessing the HPA-axis and it is consequently not a viable alternative to traditional dynamic methods such as the IST.

Hypothalamic-pituitary-adrenocortical axis changes in a transgenic mouse with impaired glucocorticoid receptor function

Recently, a transgenic mouse with impaired glucocorticoid receptor (GR) function was created to serve as an animal model for the study of neuroendocrine changes occurring in stress-related disorders, such as major depression. Here, we investigated the hypothalamic-pituitary-adrenocortical (HPA) axis changes in these transgenic mice. There were no significant differences between basal early morning plasma ACTH and corticosterone levels in normal and transgenic mice. When animals were exposed to a mild stressor, an enhanced response in plasma ACTH was observed in the transgenic mice, whereas plasma corticosterone responses were not different. In view of these differences in plasma ACTH and corticosterone responses, we directed our studies toward the regulation of ACTH secretion on the hypothalamic-hypophyseal level in vitro. Therefore, an in vitro model, the pituitary-hypothalamic complex (PHc) was developed and its ACTH release profile was compared with that of the pituitary (PI) alone. The basal ACTH release by PHc and PI from normal and transgenic mice was similar. Regardless of the strain under study, the basal ACTH release by PI was significantly lower than the release by PHc. Stimulation of tissues with either high K+ (56 mM) or CRH (10 or 20 nM) produced an enhanced ACTH release from both PHc and PI, whereas the response in PI was larger than that in PHC. Moreover, the responses to these stimuli were markedly enhanced in tissues from transgenic mice. In tissues of normal mice, corticosterone inhibited both basal and CRH-stimulated ACTH release more potently in PHc than in PI. Furthermore, the feedback capacity of corticosterone to restrain both basal and CRH-stimulated ACTH release was highly impaired in tissues of transgenic mice, whereas the feedback in PHc appeared to be more affected than that in the PI of these animals. In conclusion, the in vitro data on PHc and PI revealed intrahypothalamic mechanisms operating 1) to fine-tune stimulus-evoked ACTH responses; and 2) to facilitate the negative feedback action of glucocorticoids. Moreover, in the transgenic tissues, the impaired GR function was found to cause augmented stimulus-evoked ACTH responses and an impaired glucocorticoid feedback efficacy which appeared to be mainly defective at the hypothalamic level. Thus, in the transgenic mice with life-long central GR dysfunction we found impaired negative feedback combined with "normal" (i.e. noncompensated) in vivo plasma corticosterone responses. This is a condition with potentially grave pathophysiological consequences and, therefore, this transgenic animal may be regarded as a valuable model for the study of functional glucocorticoid insufficiency at the central nervous system level.

Neurohumoral mechanisms in rheumatoid arthritis

The observation that following stroke or peripheral nerve injuries the development of rheumatoid arthritis is either prevented or ameliorated in the affected limb was the first observation of the involvement of the neurological system in the pathogenesis of the disease. Much subsequent work has established that there are intimate and intricate associations between the central nervous system, the endocrine system and immuno-inflammatory mechanisms. The predominant interaction is through the hypothalamic-pituitary adrenal axis which mediates the secretion of corticotrophin releasing hormone which then stimulates the pituitary to release ACTH. A subsequent stimulation of the adrenal cortex leads to glucocorticoid release with their known potent anti-inflammatory effects. Many factors can interact within the central nervous system to modify this pathway. Of particular relevance is the observation that the hypothalamic-pituitary adrenal axis may be defective in rheumatoid arthritis. This has implications not only in terms of pathogenesis but also in the way in which glucocorticoids are used for the treatment of rheumatoid arthritis.

Influence of acute and chronic morphine or stadol on the secretion of adrenocorticotrophin and its hypothalamic releasing hormone in the rat

The effects of acute and chronic treatment with morphine and stadol on the functional activity of the hypothalamo-pituitary-adrenocortical (HPA) system in the rat were studied by investigating their effects on the secretion of adrenocorticotrophin (ACTH) by the pituitary gland and corticotrophin-releasing hormone (CRH) by the hypothalamus. The acute injection of morphine or stadol (3.5 mg/100 g body weight i.p.) caused a rise at 5 and 25 min followed by a fall at 90 and 120 min in the concentrations of ACTH in the plasma and adenohypophysis and in hypothalamic CRH content. It appears that, in the rat, the response of HPA system to acute morphine or stadol administration could change depending upon the time of courses. In addition, chronic morphine or stadol (0.5 mg/100 g body weight i.p. daily) administration for a period of 7 days have little effect on plasma and adenohypophysis ACTH concentrations and hypothalamic CRH content. This may indicate that drug tolerance might have developed. Conversely, repeated daily doses of morphine or stadol (2 mg/ 100 g body weight i.p.) for 7 days cause a significant lowering of plasma and pituitary ACTH concentrations and hypothalamic CRH content. These data suggest that the effect of both drugs is dose related. Overall, the present results are consistent with an increased release of pro-opiomelanocortin-derived peptides after acute morphine or stadol treatment for a short-term, and with a decreased release of these peptides in chronic treatment. However, the results indicate that morphine and stadol change HPA activity by acting on specific receptors in the hypothalamus and raise the possibility that opioid peptides and their receptors are physiologically important in the control of the secretion of CRH.

A comparison of the naloxone test with ovine CRH and insulin hypoglycaemia in the evaluation of the hypothalamic-pituitary-adrenal axis in normal man

OBJECTIVE

It has been suggested that naloxone might be useful in clinical testing of the hypothalamic-pituitary-adrenal (HPA) axis. We have therefore evaluated this non-selective opioid receptor antagonist, as a test of HPA axis function, and compared the results to ovine corticotrophin-releasing hormone (oCRH) and the insulin tolerance test (ITT).

DESIGN

Following i.v. administration at time zero of naloxone 20 mg (n = 12) on day 1, and either oCRH 1 microgram/kg (n = 6) or soluble insulin 0.15U/kg (n = 6) on day 2, venous blood was sampled at times 120, 0, 15, 30, 45, 60, 90 and 120 minutes for cortisol, ACTH and AVP. Peripheral CRH was also measured following naloxone and insulin hypoglycaemia.

SUBJECTS

Twelve normal males (age 20-57 years) with no history of hypothalamic-pituitary-adrenal axis disease.

MEASUREMENTS

Peptide hormones in plasma samples were measured by radioimmunoassay and cortisol by ELISA. Results are expressed as mean +/- SEM.

RESULTS

Following naloxone, there was a highly significant overall rise in ACTH (P < 0.0005) and cortisol(P < 0.0001), but 1 out of the 12 subjects failed to respond. This subject had a normal ACTH and cortisol response to oCRH, indicating normal pituitary-adrenal function. Peripheral levels of CRH also increased significantly following naloxone (P < 0.002), while AVP did not alter significantly (P = 0.38). Maximal levels of CRH were seen following the ACTH peak however, at a time when ACTH was returning to baseline. All six subjects who received oCRH had an increase in ACTH and cortisol, and the ACTH response to oCRH was greater that that to naloxone (P < 0.05). One subject who developed nausea and hypotension following oCRH had a large rise in AVP and very high levels of ACTH and cortisol. Following insulin each subject had symptomatic hypoglycaemia and significant rises in cortisol (P < 0.0001), ACTH (P < 0.0001), AVP (P < 0.0005) and CRH (P < 0.01) were seen. Both cortisol and ACTH responses to ITT were significantly greater than those to naloxone (P < 0.05 for each).

CONCLUSION

The HPA axis response to naloxone is smaller in magnitude overall compared to oCRH or insulin hypoglycaemia and is variable in normal subjects. This variability probably reflects changes in central opioid tone rather than alterations in pituitary responsiveness to CRH. It is unlikely that the naloxone test will replace currently used clinical tests of HPA axis function, particularly in the setting of a possible ACTH deficiency, because some subjects wit ha normal HPA axis appear not to respond to naloxone. As the mechanism involved in the ACTH response to naloxone has not yet been defined with certainty, the naloxone test should not be regarded simply as a test of endogenous CRH release.

The effects of alcoholism on the hypothalamic-pituitary-adrenal axis: interaction with endogenous opioid peptides

BACKGROUND

Abnormal baseline hypothalamic-pituitary-adrenal axis function and dexamethasone suppressibility seen in withdrawing alcoholics returns to normal on abstinence, but some studies report blunting of the ACTH response to CRH persisting during the early abstinence phase. Reduced central levels of endogenous opioid peptides have been postulated to have an aetiological role in alcohol addiction.

AIMS

To evaluate hypothalamic-pituitary-adrenal axis function in a group of recently abstinent alcoholics using basal hormone data, naloxone (an opioid receptor antagonist), and ovine CRH.

SUBJECTS

Nine alcoholics (age 41.4 +/- 3.1 years) studied more than one week after the acute withdrawal period but within 6 weeks of cessation of drinking, and nine age and sex matched non-alcoholic controls.

PROTOCOL

Cortisol, ACTH, CRH and AVP levels were measured every 20 minutes for 2 hours between 0900 and 1100h Twenty mg naloxone i.v. was administered at 1100h (0 minutes) and further samples for the above hormones were taken at 15, 30, 45, 60, 90 and 120 minutes. On a separate occasion, again at 1100h, oCRH 1 microgram/kg (n = 7 alcoholics, n = 6 controls) was administered, with samples for cortisol, ACTH and AVP taken at the same times.

STATISTICS

Results were examined by analysis of variance for repeated measures (ANOVA), while incremental hormone response and area under the secretory curve (AUC) in alcoholics versus controls were compared by the two-tailed Student's t-test. Linear regression analysis was carried out to examine the relation between basal cortisol and hormone responses to naloxone and oCRH.

RESULTS

Basal hormone levels did not differ between the groups. The alcoholics had a blunted ACTH incremental response to naloxone (11.4 +/- 3.0 vs 21.1 +/- 2.5 pmol/l, P < 0.05) but the cortisol response was not significantly different (205 +/- 51 vs 305 +/- 42 nmol/l, P = 0.15). The alcoholics also had a blunted ACTH incremental response to oCRH (28.7 +/- 4.2 vs 41.2 +/- 3.7 pmol/l, P = 0.052) and by ANOVA a significant main effect of group (alcoholic vs control) was seen (P < 0.02) for the ACTH response to oCRH. There was no difference between the groups in the cortisol incremental response to oCRH. In the control subjects, a negative correlation was found between basal cortisol and the cortisol increment (r = -0.82, P < 0.05) and ACTH increment (r = -0.81, P = 0.052) following oCRH, while in contrast, basal cortisol correlated positively with cortisol increment (r = 0.72, P < 0.05) following naloxone. There was also a trend for basal cortisol to correlate positively with ACTH increment following naloxone in the controls (r = 0.63, P < 0.07). In the alcoholics, the normal negative effect of basal cortisol on the cortisol increment after oCRH was reversed, with a positive correlation between basal cortisol and cortisol increment (r = 0.75, P = 0.05).

CONCLUSIONS

Recently abstinent alcoholics with normal basal HPA axis hormone levels have a blunted ACTH response to naloxone and oCRH. While reduced levels of central endogenous opioid peptides may be a factor in the blunted ACTH response to naloxone in the alcoholics, it is proposed that the alcoholics have reduced pituitary responsiveness to CRH. This may be via a direct pituitary effect of the chronic ethanol exposure or by a reduction in hypothalamic-hypophyseal vasopressin levels.

Effects of naloxone on diurnal rhythms in mood and endocrine function: a dose-response study in man

This study investigated diurnal variations in the affective and endocrine response to opioid blockade in man and whether there were effects related either to the dose of naloxone or the time of day at which it was given. Normal male subjects were given an intravenous bolus of either 0.2 mg/kg (study 1) or 1 mg/kg naloxone (study 2) or control infusions at two time points (0900 or 1800 hours) in a single-blind crossover design. Before and following each infusion, mood was measured by the Profile of Mood States (POMS) and a visual analogue scale (VAS), and blood samples taken at 15-min intervals. Cortisol, LH ACTH and vasopressin (study 2 only) were measured. Blood pressure and heart rate were also monitored. The lower dose of naloxone had no effect on overall mood (POMS), though tension and confusion were increased in the afternoon. The VAS showed increased depression in the afternoon, and heightened tension, sleepiness and reduced ability to concentrate at both times of day. The higher dose increased overall dysphoria at both time points, though the tension and depression subscales were not altered. VAS depression and tension were increased, and there were changes in sleepiness. Subjective reports showed that 45% of the subjects correctly identified the drug treatment at the lower dose compared with 89% at the higher one. ACTH increased after both doses of naloxone irrespective of time of day. Cortisol was also raised by naloxone; the effect was greater in the afternoon for the lower dose, but not the higher.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypersensitivity of the hypothalamic-pituitary-adrenal axis to naloxone in post-traumatic stress disorder

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.

Effect of naltrexone treatment on the treadmill exercise-induced hormone release in amenorrheic women

The effect of an acute physical stress on hormone secretions before and after a 10-day naltrexone treatment in untrained healthy and amenorrheic women was investigated. Plasma levels of pituitary (LH, FSH, prolactin, GH, ACTH, beta-endorphin) and adrenal (cortisol, androstenedione, testosterone) hormones were measured at rest and in response to 60 min of physical exercise. The test was done both before and after a 10-day naltrexone (50 mg/day) treatment. Graded levels of treadmill exercise (50, 70 and 90% of maximal oxygen uptake (VO2) every 20 min) was used as physical stressor. While mean +/- SE plasma LH levels in control women were higher than in amenorrheic patients and increased following the naltrexone treatment (p < 0.01), no significant differences of basal plasma hormonal levels were observed between amenorrheic and eumenorrheic women, both before and after naltrexone treatment. Physical exercise at 90% VO2 induced a significant increase in plasma GH, ACTH, beta-endorphin, cortisol, androstenedione and testosterone levels in controls before naltrexone treatment (p < 0.01). The mean increase in plasma androstenedione and testosterone levels in control women was significantly higher after naltrexone treatment (p < 0.01). In amenorrheic patients before naltrexone, physical exercise induced an increase in plasma prolactin and GH levels, but not in plasma ACTH, beta-endorphin, cortisol, testosterone and androstenedione. After naltrexone treatment, the exercise induced a significant plasma ACTH, beta-endorphin and cortisol levels, while the increase of plasma prolactin levels was significantly higher than before treatment (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 12-hour infusion of naloxone on mood and cognition in normal male volunteers

The effects of a 12-hour naloxone infusion on mood, cognition, and plasma cortisol levels were evaluated in eight normal subjects. The dosage used was a 10 mg dose plus 7 mg/hr (total = 94 mg). Naloxone induced a significant rise in serum cortisol and also induced cognitive impairment, as shown by increased choice reaction time, reduced ability to recall the order of letters and numbers, and reduced accuracy of spatial orientation. The rise in cortisol induced by naloxone was significantly correlated with the rise in the Profile of Mood Scale (POMS) score, indicative of dysphoria. Finally, performance on the spatial orientation task was highly negatively correlated with the peak POMS score after naloxone. From these data and previous studies it is concluded that opioid receptors of low sensitivity to naloxone may mediate a common mechanism regulating the pituitary-adrenal axis' mood, and cognitive function during stress. Personality traits may account for the large individual variability reported in previous studies.

The central effect of methionine-enkephalin on NK cell activity

The central effect of opioid peptide on natural killer (NK) cell activity in BALB/c mice was investigated. Injection of methionine-enkephalin (Met-Enk), 0.02 microgram/mouse or 1 microgram/kg, directly into the cisterna magna (CM) of the brain, resulted in a significant enhancement of NK cell activity. This enhancement was blocked by opiate antagonists, naltrexone and quaternary naltrexone. The same dose of Met-Enk had no effect on NK cell activity when given to the mouse intraperitoneally or intravenously. Moreover, des-tyrosine-methionine-enkephalin injected into the CM at 1 microgram/kg, had no effect on NK cell activity. The results indicate that activation of an opioid-mediated pathway in the central nervous system is capable of activating the pathways that stimulate the NK cell response in the periphery.

Abnormal adrenal gland metabolism in opioid addicts: implications for clinical treatment

Adrenal gland metabolism is markedly altered in heroin addicts. During daytime hours, the addict may suffer corticoid deficiency of the addisonian type, and in the evening, an excess of the cushingoid type. The high plasma levels of cortisol that are found in the evening in addicts antagonize endogenous opioids in a manner similar to naloxone. In the present study, 72% of the heroin addicts who sought treatment demonstrated reduced adrenal cortisol reserve. Effective immune and stress responses are dependent on adrenal cortisol reserve. This finding provides an explanation for the heroin addict's vulnerability to AIDS and other infectious diseases. One of methadone's greatest attributes is that it helps normalize adrenal metabolism. Clinical methods to at least partially correct adrenal metabolism may enhance current opioid addiction treatment modalities.

Stress and morphine mediated changes in pituitary-adrenal axis in guinea-pigs

1. Changes in plasma levels of B-END and cortisol were investigated in guinea-pigs receiving either stressful stimuli for various lengths of time or i.p. injections of morphine or saline. 2. A decrease in B-END levels occurred when animals were stressed, whereas cortisol was not affected. 3. Morphine (50 mg/kg i.p.) enhanced B-END and cortisol levels 5 min after injection, whereas a decrease in B-END was seen at 30 min. 4. Saline (i.p.) produced a decrease of B-END levels 30 min after injection and an increase in cortisol 5 and 10 min after injection. These findings suggest that in the guinea-pig the response of pituitary-adrenal axis to stress or morphine could change depending upon the time of sampling.

Stimulation of kappa opiate receptors in intestinal wall affects stress-induced increase of plasma cortisol in dogs

In dogs, an acoustic stress (A.S.) produced by hearing of intense music (less than or equal to 90 dB) through earpieces for 1 h induced a 520% maximal rise in plasma cortisol 15-30 min after the beginning of stress. Oral administration of the specific kappa agonists, U-50488 (0.1 mg/kg) and PD 117302 (0.05 mg/kg), 30 min before the A.S. session reduced significantly (P less than 0.01) by 71.2% and 80.9% the maximal increase of plasma cortisol but did not affect the increase observed after intracerebroventricular administration of ovineCRF (100 ng/kg). These effects which are not reproduced by intravenous administration of the drugs at similar doses, were blocked by previous treatment with MR 2266 (0.1 mg/kg) or local anesthesia and vagotomy, suggesting that kappa opioid agonists inhibit the stress-induced activation of the hypothalamo-pituitary-adrenocortical (HPA) system by acting selectively on specific receptors located in the wall of the proximal gut.

Peripheral antagonistic action of trimebutine and kappa opioid substances on acoustic stress-induced gastric motor inhibition in dogs

The effects of intracerebroventricular (i.c.v.), intravenous (i.v.) and oral (p.o.) administration of trimebutine on the gastric motor inhibition induced by acoustic stress were investigated in fasted dogs fitted with strain-gauge transducers on the antrum and proximal jejunum. Started 40-50 min after the last migrating motor complex, a 1 h acoustic stress delayed by 111% the occurrence of the next gastric migrating motor complex without affecting the jejunal motor pattern. This inhibition of gastric migrating motor complex induced by acoustic stress was abolished by previous p.o. administration of trimebutine (1 mg/kg) but not by its i.v. (0.1 mg/kg) or i.c.v. (0.01 mg/kg) injection. The trimebutine blockade of gastric motor alterations induced by acoustic stress was suppressed after previous i.v. treatment with MR 2266 (0.3 mg/kg) but was unaffected by naloxone (0.3 mg/kg). Furthermore oral administration of U-50488H (10 micrograms/kg) and ethylketocyclazocine (10 micrograms/kg) respectively abolished and reduced the acoustic stress-induced delay of the occurrence of the gastric migrating motor complex. We concluded that trimebutine is able to antagonize the gastric motor disturbances induced in dogs by acoustic stress, probably by acting selectively on peripheral kappa receptors located in the wall of the proximal gut and directly stimulated from a mucosal site.

Adrenal steroid responses to naloxone in polycystic ovarian disease

In order to investigate the role of the adrenal gland in the pathogenesis of polycystic ovarian disease (PCOD), we evaluated the adrenal steroid response to an opiate receptor blockade. Six healthy menstruating volunteers and 6 patients with PCOD were given a saline or naloxone (4 mg i.v.) injection in the early follicular phase. Blood samples were taken prior to the injections and every 15-30 minutes in the following 2 hours. Cortisol, androstenedione (A) and dehydroepiandrosterone (DHA) plasma levels were determined by RIA after extraction (cortisol) and celite chromatography (A and DHA). While in controls naloxone increased only cortisol concentrations, in PCOD patients DHA plasma levels also were stimulated by the opiate receptor antagonist. In PCOD patients the increase of cortisol (p less than 0.05) and of DHA (p less than 0.001) levels resulted significantly higher than in controls. In both groups A plasma levels remained unchanged after naloxone administration. These data confirm that endogenous opioids exert an inhibitory control on the pituitary-adrenal axis. In PCOD patients the response to naloxone led to a hypersecretion of adrenal delta 5-androgens, which could account for the development of the syndrome.

Mu-, delta-, kappa- and epsilon-opioid receptor modulation of the hypothalamic-pituitary-adrenocortical (HPA) axis: subchronic tolerance studies of endogenous opioid peptides

In opiate-naive rats, the endogenous opioid peptides, beta-endorphin, dynorphin(1-13) and Met-Enk-Arg-Phe (MEAP) and the synthetic enkephalin analogue D-Ala2-D-Leu5-Enk (DADLE) potently stimulated plasma corticosterone in a dose-dependent, naloxone reversible manner. To characterize their in vivo affinities, the effects of these peptides on plasma corticosterone release were tested in rats made tolerant to morphine, U50488H, DADLE/morphine or beta-endorphin. These cross-tolerance studies showed that dynorphin and MEAP exerted their action on plasma corticosterone release at kappa-opioid receptors. The action of DADLE occurred at delta-opioid receptors, while the action of beta-endorphin occurred principally at another receptor site. These results indicate that there is independent modulation of the hypothalamic-pituitary-adrenal axis by endogenous opioid peptides at mu-, delta- and kappa-opioid receptors. In addition there may be modulation by beta-endorphin at a separate site that we suggest could be a central epsilon-receptor site. This cross-tolerance paradigm, using a neuroendocrine model, provides in vivo evidence for the action of centrally active endogenous opioid peptides at multiple and independent opioid receptors.

Effect of central naloxone on hormone and blood pressure responses to hemorrhage in conscious sheep

The role of the brain opioid system in the control of hypothalamic-pituitary-adrenal activity was studied in 10 conscious sheep with an indwelling cannula in a cerebral lateral ventricle. On separate days, sheep received infusions of artificial CSF (control) and the opiate antagonist, naloxone (100 micrograms/hr) before and during acute moderate hemorrhage (15 ml/kg over 10 min). Infusion of naloxone before hemorrhage raised plasma ACTH and resulted in a significant increase in cortisol compared to the control infusion. In contrast, ACTH and cortisol responses to hemorrhage tended to be blunted by central naloxone infusion. The responses of vasopressin, aldosterone and the catecholamines remained unaffected by naloxone. The fall in blood pressure and the rise in heart rate accompanying hemorrhage were likewise unaltered. These results suggest that brain opioid peptides have an inhibitory effect on basal ACTH secretion but do not play a major role in modulating the hemodynamic or pituitary-adrenal responses to acute moderate hemorrhage in conscious sheep.

Potentiation of the hCRF-induced release of ACTH in man by an opioid antagonist

Administration of synthetic human corticotropin-releasing factor (hCRF; 2 micrograms/kg body weight) to six normal male subjects produced a significant rise in plasma ACTH, followed by an increase in circulating cortisol. Simultaneous treatment with the opioid antagonist naloxone (1.6 mg i.v. bolus, followed by an infusion at a rate of 1.2 mg/h) significantly potentiated the hCRF-induced rise in ACTH and enhanced the cortisol response to hCRF. It is suggested that naloxone acts by antagonizing an inhibitory ultra-short-loop feedback effect of coreleased beta-endorphin on pituitary corticotrophs, thereby amplifying the net effect of hCRF, i.e., the release of ACTH.

Stress and the pituitary-adrenal axis

The hypothalamo-pituitary-adrenal axis is controlled by complex regulatory mechanisms. Numerous factors such as CRF, vasopressin, oxytocin, angiotensin II and conceivably other hormones--all controlled by various substances acting on central locations--stimulate the release of the stress hormone ACTH. On the other hand, glucocorticoids inhibit the secretion of ACTH by acting at the hypothalamic and/or pituitary level. The release of ACTH is therefore the final outcome of the interactions between the hypothalamus, the adrenal gland and possibly other organs. The multimolecular nature of the factors responsible for the control of the pituitary-adrenal axis is an attractive hypothesis because of the great variety of stress stimuli. The various factors could have specific roles in various stress situations. They provide a highly sensitive mechanism regulating very finely the stress hormone in response to a whole variety of endogenous and exogenous stimuli. Depending on the type of stress, they may therefore singly or in combination affect the amount and duration of ACTH and steroid secretion. The released glucocorticoids may then produce their numerous effects on inflammatory and immunological processes, carbohydrate metabolism, shock and water balance. It has been postulated that these effects may be important in order to prevent host responses from over-reacting to stress and threatening homeostasis. However, proof of the necessity of the glucocorticoid hypersecretion in response to stress remains elusive.

An analogue of met-enkephalin attenuates the pituitary-adrenal response to ovine corticotrophin releasing factor

The met-enkephalin analogue, DAMME, suppresses the pituitary-adrenal axis in normal subjects; it is not clear whether this occurs at the level of the pituitary or above. We therefore administered synthetic ovine corticotrophin releasing factor (CRF-41) 100 micrograms i.v. to a group of normal male subjects, with or without pretreatment with DAMME 250 micrograms i.v., and monitored the response of plasma ACTH and serum cortisol. CRF-41 caused a marked stimulation of ACTH and cortisol release, but this was significantly attenuated by pretreatment with DAMME. It is therefore concluded that DAMME either directly inhibits the corticotroph at the level of the pituitary, or that it suppresses release of an additional factor which normally potentiates the action of CRF-41 on the pituitary.

Effects of synthetic adrenocorticotrophin on adrenal medullary responses to splanchnic nerve stimulation in conscious calves

Right medullary and various cardiovascular responses to stimulation of the peripheral end of the splanchnic nerve have been investigated in the presence and absence of exogenous adrenocorticotrophin, ACTH1-24, (5 ng min-1 kg-1). The adrenal-clamp technique was employed in conscious calves, after the pituitary stalk had been cauterized and they had recovered from anaesthesia. The intravenous infusion of ACTH1-24 increased the plasma ACTH concentration by about 1100 pg ml-1 and right adrenal venous output of cortisol by about 400 ng min-1 kg body weight-1. Stimulation of the splanchnic nerve at 4 Hz for 10 min had no effect on either arterial plasma ACTH concentration or the adrenal output of cortisol. Closely similar amounts of both adrenaline and noradrenaline were released in response to nerve stimulation in the presence and absence of exogenous ACTH. In contrast, the fall in adrenal vascular resistance of about 40%, which normally occurred in response to splanchnic nerve stimulation, was completely abolished by ACTH. The adrenal produced relatively large quantities of met-enkephalin-containing peptides. During splanchnic nerve stimulation the output of these increased 2-100-fold, at which time free met5-enkephalin accounted for only 10-20% of total. During ACTH infusion the output of free met5-enkephalin was reduced at rest and during nerve stimulation, but that of total met-enkephalin-containing peptides was unaffected. These results indicate that ACTH or an adrenal steroid may alter the processing of proenkephalin in the adrenal medulla acutely but not total opiate secretion. Alternatively, the presence of ACTH could act by influencing the population of chromaffin cells activated by splanchnic nerve stimulation.

Role of beta-endorphins in silent myocardial ischemia

The reason for the absence of pain perception in silent myocardial ischemia is unknown. A role of increased endorphinic activity in patients with silent ischemia has been postulated. To further investigate this hypothesis, 10 men with documented coronary artery disease and previous positive electrocardiographic findings during exercise without anginal pain were studied. Six healthy volunteers served as control subjects. The protocol included 2 bicycle exercise tests, the first test serving as baseline and the second performed after administration of naloxone, a specific opiate antagonist. Plasma beta-endorphin levels were measured by radioimmunoassay in both tests at rest, at peak exercise level and after recovery. All patients underwent thallium-201 scintigraphy after coronary vasodilation to provide an additional independent marker of ischemia. All patients showed stress-induced reversible perfusion abnormalities. No patient reported pain after naloxone application. Exercise duration, blood pressure and heart rate were not significantly altered by naloxone. Plasma beta-endorphin levels ranged from 18 +/- 6 pg/100 microliters (mean +/- standard deviation) at rest to 22 +/- 6 pg/100 microliters during exercise in the patient group and from 20 +/- 5 to 27 +/- 9 pg/100 microliters in the control subjects. Thus, there was no significant increase of plasma beta-endorphins during exercise or after naloxone administration, nor was there any difference observed between patients and control group. These data support the view that endorphinic activity does not play an essential role in the pathophysiology of silent myocardial ischemia.

Loperamide, an opiate analogue, inhibits plasma ACTH levels in patients with Addison's disease

The effects of loperamide, an opiate analogue of the piperidine class on pituitary hormone secretion were evaluated in eight patients with Addison's disease. In all patients loperamide administration (16 mg orally) induced a marked fall in plasma ACTH levels (P less than 0.01), without affecting GH, PRL and LH levels. Plasma ACTH concentration fell significantly from 854 +/- 167 pg/ml (mean +/- SEM) to 460 +/- 123 pg/ml at 60 min (P less than 0.01). The inhibition persisted throughout the whole test period, the nadir being reached at 300 min. Low dose naloxone infusion 180 min after loperamide administration caused plasma ACTH to rise from 181 +/- 61 pg/ml to 539 +/- 99 pg/ml (P less than 0.01). The present data suggest that the opiate analogue loperamide is a potent inhibitor of ACTH secretion in patients with Addison's disease, which may be acting on mu receptors, since its effect is blocked by low doses of naloxone.

Effect of opiate-receptor blockade on normoglycemic and hypoglycemic glucoregulation

By use of the opiate antagonist naloxone, we have examined the hormonal and metabolic responses to opiate-receptor blockade under basal conditions and during insulin-induced hypoglycemia in normal dogs. Naloxone treatment had no measurable effect on glucose concentration, turnover, and norepinephrine levels, but stimulated plasma epinephrine, glucagon, and cortisol and inhibited insulin release. Insulin (7 mU X kg-1 X min-1) decreased plasma glucose to 42 +/- 4 mg/dl due to an initial decrease in glucose production and an increase in glucose disappearance. Glucose production then increased, and plasma glucose plateaued. After 50 min of insulin infusion, epinephrine levels increased 26-fold (P less than 0.05), norepinephrine and glucagon 3-fold (P less than 0.02), and cortisol 4-fold (P less than 0.01). Similarly, plasma beta-endorphin and adrenocorticotropin (ACTH) were elevated (6-fold, P less than 0.01, and 16-fold, P less than 0.05, respectively). When naloxone was given during insulin-induced hypoglycemia, there was earlier release of epinephrine, glucagon, beta-endorphin, ACTH, and cortisol as well as a greater release of glucagon (P less than 0.001) and cortisol (P less than 0.0001). This resulted in a greater increase in glucose production (P less than 0.01), thus lessening the insulin-induced hypoglycemic excursion. In conclusion, in the dog, endogenous opiates may play a small role in the regulation of basal insulin and glucagon release and can inhibit the pituitary-adrenal axis under basal conditions and during hypoglycemia. Thus increased glucose production in response to insulin-induced hypoglycemia is consistent with the excessive response of counterregulatory hormones during opiate-receptor blockade.

No effect of naloxone on plasma oxytocin in normal men

The role of endogenous opiates in the control of the secretion of oxytocin in the basal state in healthy male volunteers was investigated with the opiate antagonist naloxone. There was no change in plasma oxytocin levels, assessed for a 120 min period following the intravenous administration of naloxone (10 mg). Although there was no effect of opiate receptor blockade with naloxone in this basal situation, further studies are needed to evaluate the possible role of opioid regulation of oxytocin during lactation and parturition.

The nature of opioid involvement in the hemodynamic respiratory and humoral responses to exercise

After 30 min rest in the lying position, 12 healthy male volunteers (average age 22 years) received, in a randomized double-blind cross-over protocol, either saline or naloxone (10 mg iv followed by a continuous infusion of 10 mg/hr). Thereafter they rested for a further 30 min in the recumbent position and for 15 min sitting on a bicycle ergometer; they then exercised to exhaustion. At rest plasma levels of adrenocorticotropin (ACTH), cortisol, and aldosterone increased during infusion of naloxone, while body temperature decreased. During exercise the difference in plasma ACTH between naloxone and saline periods was abolished, while the differences in plasma cortisol and aldosterone lost statistical significance. Intra-arterial pressure, heart rate, ventilation, O2 uptake, and CO2 output were continuously monitored throughout the experiment and were not affected by naloxone. This was also the case for several hormonal and biochemical measurements, including those of plasma renin, angiotensin II, norepinephrine, 13,14-dihydro-15-keto-prostaglandin F2 alpha, glucose and lactate, and serum insulin and growth hormone. Exercise performance was not changed by naloxone. In conclusion (1) during exhaustive graded exercise of short duration opioidergic inhibition of the pituitary-adrenocortical axis is probably not sustained, (2) apart from the latter mechanism, the present study does not support the hypothesis that endogenous opioids are involved in various hemodynamic, respiratory, and hormonal responses to this type of exercise.