Adrenal cortex - a newly recognized peripheral site of action of enkephalins

Different patterns of expression of five neuropeptides in the adrenal gland and kidney of two species of frog

The aim of this study was to demonstrate in the adrenocortical and renal tissues of two species of frog, Rana italica and Rana esculenta, the presence and distribution of five neuropeptides: atrial natriuretic peptide (ANP), Leu-enkephalin (Leu-ENK), neuropeptide Y (NPY), substance P (SP) and vasoactive intestinal peptide (VIP). In anurans, the adrenal medulla is the site for the synthesis, storage and secretion of not only catecholamines but also various peptides. These peptides should not be regarded only as neurotransmitters or modulators for the secretion of catecholamines, but also as hormonal substances that induce systemic effects. All the peptides studied (ANP, Leu-ENK, NPY, SP and VIP) are present in both organs. However, different patterns of expression were observed for some of the peptides in two frogs. Immunopositivity to ANP was found in small clusters of chromaffin cells in both frogs whereas a clear strong positivity was present only in Rana esculenta kidney. Large clusters of chromaffin cells were immunoreactive to Leu-ENK in Rana italica but there were approximately 25% fewer compared to the positive cells present in Rana esculenta. Epithelial cells of renal tubules showed strong immunopositivity to Leu-ENK in Rana esculenta but not in Rana italica. A large number of adrenal cells (70-80%) were immunoreactive to NPY in Rana italica, while in Rana esculenta this peptide was localized in small clusters of chromaffin cells. Both frogs showed many NPY-positive cells in kidney. Many chromaffin cells were found positive to SP and VIP. A strong positivity was also observed in kidney in both frogs. These observations suggest a possible role of these peptides in the control of the physiological functions of adrenal glands and kidney of the two species of frogs studied.

Morphological and functional studies of the paracrine interaction between cortex and medulla in the adrenal gland

Within the last years it has become evident that besides the hypothalamo-pituitary-adrenal axis, extrapituitary mechanisms exist that regulate the activity of the adrenal cortex. In this context, intra-adrenal regulatory mechanisms play an important role. Several secretory products from adrenomedullary cells are able to influence adrenocortical steroidogenesis. Since the main blood flow within the adrenal is directed centripetally from the cortex to the medulla, chromatin cells should act on cortical cells in a paracrine manner. The morphological prerequisite for this regulatory pathway is seen in the close apposition of the two tissues. Within the mammalian adrenal, the two endocrine tissues are interwoven to an astonishing degree with cortical cells located within the medulla and vice versa. It is concluded from morphological and functional studies that paracrine interactions between cortex and medulla play an important role in the regulation of adrenocortical steroidogenesis.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

The role of neuropeptides in the regulation of adrenal zona fasciculata/reticularis function. Effects of vasoactive intestinal polypeptide, substance P, neuropeptide Y, Met- and Leu-enkephalin and neurotensin on corticosterone secretion in the intact perfused rat adrenal gland in situ

There is much evidence to suggest that glucocorticoid secretion may be influenced by the splanchnic innervation to the adrenal gland, and that this effect may be mediated by neuropeptides. The present studies investigated the effects of several neuropeptides on corticosterone secretion by the intact perfused rat adrenal gland in situ. Both vasoactive intestinal polypeptide and Met-enkephalin caused a dose-dependent increase in corticosterone secretion, with a maximum response of 450% and 370% increment in corticosterone respectively. Of the other peptides tested, Leu-enkephalin, substance P and neurotensin all stimulated corticosterone secretion, with a maximum response of around 160% increase in each case. Neuropeptide Y on the other hand, had only a minor effect, which was only apparent over a small dose range. These results support the theory that adrenal neuropeptides may have a role in the regulation of glucocorticoid secretion.

In vivo and in vitro effects of β-endorphin and naloxone on corticosterone and cortisol release in male and female water frog, Rana esculenta

1. beta-Endorphin and naloxone effects on corticosterone and cortisol production in male and female Rana esculenta, were studied in vivo and in vitro. 2. The in vivo and in vitro results were in agreement. 3. beta-Endorphin caused a decrease in corticosterone and cortisol release. 4. Naloxone induced an increase in the two corticosteroids at the same times as the decrease caused by beta-endorphin. 5. beta-Endorphin plus naloxone treatment did not change corticosterone and cortisol levels. 6. These results suggest that in Rana esculenta opioids are involved in the regulation of the hypothalamo-pituitary-interrenal axis; in particular, opioids directly modulated interrenal steroidogenesis.

Interaction of Met-enkephalin and corticosteroids in immunomodulation

The effect of Met-enkephalin (MENK) on several immune functions, corticosterone (CS) and adrenocorticotropin (ACTH) levels in the plasma was studied in adrenalectomized (ADX) and sham-adrenalectomized (SADX) mice. Multiple Met-enkephalin injections (10 mg/kg per day in two injections 12 h apart, for 4 days) increased the plaque-forming cell response to sheep erythrocytes in the spleen and enhanced the proliferation of spleen cells in vitro. These effects were comparable in sham-adrenalectomized and adrenalectomized mice. However, spleen cells of mice immunized with sheep red blood cells and injected with Met-enkephalin, showed suppressed blastogeneic transformation with Con A. The effect was equal in adrenalectomized and sham-adrenalectomized mice. In the absence of Con A in spleen cell cultures, MENK treatment of donor mice resulted in a significant mitogenic effect. NK activity of the spleen cells was suppressed in MENK-treated adrenalectomized mice. Injection of MENK decreased corticosterone levels and increased ACTH levels in the plasma of sham-adrenalectomized mice. In adrenalectomized mice plasma levels of ACTH were decreased by MENK. It seems that corticosteroid secretion, although changed by adrenalectomy and influenced by treatment with MENK, does not influence the modulatory effect of MENK on the PFC response and blastogeneic transformation of mouse spleen cells. However, NK activity of the spleen cells treated with MENK seems to the reflect joint action of MENK and corticosteroids.

Effects of prolonged sodium restriction on the morphology and function of rat adrenocortical autotransplants

Regenerated adrenocortical nodules were obtained by implanting fragments of the capsular tissue of excised adrenal glands into the musculus gracilis of rats (Belloni et al. 1990). Five months after the operation, operated rats showed a normal basal blood level of corticosterone, but a very low concentration of circulating aldosterone associated with a slightly increased plasma renin activity (PRA). Regenerated nodules were well encapsulated and some septa extended into the parenchyma from the connective-tissue capsule. The majority of parenchymal cells were similar to those of the zonae fasciculata and reticularis of the normal adrenal gland, while zona glomerulosa-like cells were exclusively located around septa (juxta-septal zone; JZ). In vitro studies demonstrated that nodules were functioning as far as glucocorticoid production was concerned, while mineralocorticoid yield was very low. Prolonged sodium restriction significantly increased PRA and plasma aldosterone concentration, and provoked a marked hypertrophy of JZ, which was due to increases in both the number and average volume of JZ cells. Accordingly, the in vitro basal production of aldosterone and other 18-hydroxylated steroids was notably enhanced. The plasma level of corticosterone, as well as zona fasciculata/reticularis-like cells and in vitro production of glucocorticoids by regenerated nodules were not affected. These findings, indicating that autotransplanted adrenocortical nodules respond to a prolonged sodium restriction similar to the normal adrenal glands, suggest that the relative deficit in mineralocorticoid production is not due to an intrinsic defect of the zona glomerulosa-like JZ, but is probably caused by the impairment of its adequate stimulation under basal conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Central but not peripheral opiate receptor blockade prolonged pituitary-adrenal responses to stress

Evidence from pharmacological studies suggest that opiate systems may serve either inhibitory or stimulatory functions on stress-induced responses of the hypothalamic-pituitary-adrenocortical (HPA) axis. The objective of these experiments was to determine whether these discrepant findings may result, in part, from differential effects of central or peripheral opiate receptor blockade on HPA axis responses. To this effect, groups of rats received injections of either saline, naltrexone (NHCl) or the quaternary analogue naltrexone methobromide (NMBr). The animals were then exposed to 30 min of a motion stressor and blood samples were obtained from each rat for analysis of ACTH, corticosterone, and prolactin. The data showed that resting and stress-induced levels of prolactin were decreased by NHCl only. Although neither drug affected the magnitude of the stress-induced ACTH and corticosterone responses, treatment with NHCl, but not NMBr, delayed the poststress decline of these responses. Hence, we concluded that central opiate mechanisms may be important for cessation of HPA axis activity, after exposure to stressful situations.

Effects of the infusion with ACTH or CRH on the secretory activity of rat adrenal cortex

Six-hour infusion with ACTH or CRH induced a dose-dependent rise in the plasma concentrations of ACTH, corticosterone (B) and aldosterone (A). Positive linear correlations between the plasma levels of ACTH and B or A were found in both ACTH-or CRH-infused animals. Regression curves for B were similar in both groups of animals, while the regression line for A was significantly (P less than 0.05) steeper in CRH-than in ACTH-treated rats. These findings suggest that, in the rat, the mechanism underlying the CRH-induced stimulation of A secretion does not exclusively involve the enhancement of ACTH release.

Effect of codeine and oxazepam on afternoon cortisol secretion in men

The objective of this study was to investigate the effects of oral codeine and oxazepam on afternoon cortisol secretion. Nine subjects received either oxazepam (30 mg) or codeine (30 mg) or placebo at 1700h on separate days in a counterbalanced design; the subjects were not aware of the sequence. Blood samples were collected with an indwelling intravenous catheter at 30-min intervals from 1500h to 1630h. Codeine, but not oxazepam, suppressed cortisol secretion. The trend of the declining cortisol values following codeine was significantly linear. These results are consistent with other evidence indicating the presence of an inhibitory opioid mechanism in the human hypothalamo-pituitary-adrenal (HPA) axis. The cortisol response to codeine may be a reliable and potentially useful paradigm for the study of the role of opioidergic mechanisms in HPA axis dysfunction.

Evidence that long-term administration of a methionine-enkephalin analogue stimulates the growth and steroidogenic capacity of rat inner adrenocortical cells

A prolonged infusion with D-ala2-met-enkephalinamide (DALA) caused a significant increase in both basal and ACTH-stimulated corticosterone secretion by dispersed inner adrenocortical cells of rats whose hypothalamo-hypophyseal axis was pharmacologically interrupted. This effect of DALA was associated with a notable hypertrophy of isolated cells. These findings suggest that enkephalins are involved in the stimulation of the growth and steroidogenic capacity of the cells of the inner layers of rat adrenal cortex.

Effects of substance P on the rat adrenal zona glomerulosa in vivo

Substance P (SP) acutely enhanced the plasma concentration of aldosterone in rats whose hypothalamo-hypophyseal-adrenal axis and renin-angiotensin system were pharmacologically interrupted. The maximal response was obtained with a dose of 100 micrograms/kg. A prolonged (7 days) subcutaneous infusion with SP (50 micrograms/kg/hr) caused a notable hypertrophy of zona glomerulosa cells associated with significant rises in both basal and angiotensin-stimulated plasma levels of aldosterone. Zona fasciculata and the blood concentration of corticosterone were not affected. These findings suggest that SP is specifically involved in the stimulation of the growth and secretory activity of the rat zona glomerulosa.

Effects of naloxone on adrenal cortex regulation in patients with primary aldosteronism

Excess production of proopiomelanocortin (POMC)-derived peptides with aldosterone-stimulating activity has been suggested to play a pathogenetic role in idiopathic hyperaldosteronism (IHA). To further investigate this issue, the opiate receptor antagonist naloxone was administered to 14 patients with primary aldosteronism, 6 with an aldosterone-producing adenoma (APA) and 8 with IHA. Clinical and hormonal effects of iv administration of naloxone (10 mg as a bolus) were compared with those obtained in 8 normal subjects. In normals as well as in APA and IHA patients, naloxone caused a significant increase in plasma cortisol, and no change in ACTH, plasma renin activity (PRA) and aldosterone levels. All subjects were retested after 2 mg dexamethasone. ACTH and cortisol were reduced and PRA was unchanged in all groups, without modifications after naloxone. Baseline aldosterone showed no significant changes in all groups. While normal subjects and APA failed to show any aldosterone response to naloxone after dexamethasone, IHA patients demonstrated a significant decrease. beta-endorphin concentrations were in the normal range before and after dexamethasone. In conclusion, naloxone may have a direct action upon adrenal zona fasciculata increasing the cortisol responsiveness to physiological levels of ACTH in either normals or APA and IHA patients. The decrease of aldosterone induced by naloxone in IHA may be due to an intraadrenal opioid control of zona glomerulosa in this disorder.

Hypothalamo-pituitary-interrenal responses to opioid substances in the trout. II. Effects of morphine and D-Ala2, Met5-enkephalinamide on plasma cortisol titres in vivo

The influence of morphine, D-Ala2, Met5-enkephalinamide (DALA), and naloxone on plasma cortisol titres has been studied in vivo in fingerling and adult trout. The responses were complex and variable. A single ip injection of morphine or DALA into fingerlings usually resulted in a rise in plasma cortisol after 0.5 hr followed by a fall below control values within 2 hr. In similar experiments with adult trout, only an inhibitory effect was observed. Naloxone reduced the rise in plasma cortisol following saline injection, but only when the hypothalamo-pituitary-interrenal response was intense. The antagonist also blocked the morphine-induced rise in cortisol secretion. Prolonged morphine treatment diminished both the postinjection and stress-induced secretion of cortisol in adult fish. Morphine had no effect on the spontaneous or ACTH-induced secretion of cortisol by interrenal tissue incubated in vitro. The results support the concept of inhibitory and stimulatory sites of action by opiates and opioid substances on the hypothalamo-pituitary-interrenal axis. These findings are discussed with reference to the action of morphine on hypothalamic and pituitary tissue of the trout in vitro and with the opioid control of hypothalamo-pituitary-adrenal function in mammals.

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.

Neuropeptide-Y acutely stimulates rat zona glomerulosa in vivo

Neuropeptide-Y (NPY) acutely enhanced the plasma concentration of aldosterone (but not that of corticosterone) in both normal animals and in rats whose hypothalamo-hypophyseal axis and renin-angiotensin system were pharmacologically interrupted. The maximal response was obtained with a dose of 150 micrograms/kg. This dose of NPY raised the activity of 11 beta-hydroxylase and 18-hydroxylase in the capsular adrenal (zona glomerulosa), but not that of 11 beta-hydroxylase in the inner adrenocortical layers (zonae fasciculata and reticularis). These findings seem to indicate that NPY is specifically and directly involved in the acute stimulation of the late steps of the secretory activity of the rat zona glomerulosa.

Effects of naloxone on the pituitary-adrenal axis in patients with dexamethasone-suppressible hyperaldosteronism

Endogenous opioids may normally modulate the function of the hypothalamo-pituitary-adrenal axis. We investigated whether opioid peptides play any role on aldosterone secretion in dexamethasone-suppressible hyperaldosteronism (DSH). Clinical and hormonal effects of i.v. administration of naloxone (10 mg as a bolus) in two siblings affected by this disease and in eight normal volunteers were studied. In normals, naloxone caused a significant increase in plasma cortisol compared with placebo, an insignificant increase in ACTH and no change in plasma renin activity (PRA) and aldosterone level. In DSH patients there was a slight increase in plasma cortisol, no change in PRA and a marked rise of aldosterone level. In five normals retested after dexamethasone 2 mg, baseline ACTH and cortisol were reduced and no response to naloxone was observed compared to naloxone alone. After dexamethasone, aldosterone levels were suppressed in DSH patients and unchanged in normals, and did not respond to naloxone in any case. In conclusion, naloxone may increase the responsiveness of adrenal zona fasciculata to physiological levels of ACTH in normals, since the slight increase in ACTH seems inadequate to explain per se the marked cortisol elevation. The marked aldosterone rise after naloxone indicates an underlying adrenal rather than pituitary abnormality in patients with DSH, and possibly implicates endogenous opioids.

Investigations on the effects of long-term administration of a methionine-enkephalin analogue on the adrenal zona fasciculata of rats treated with dexamethasone or dexamethasone and ACTH

Prolonged (7 days) methionine-enkephalin (DALA) treatment provoked a dose-dependent increase in the volume of zona fasciculata cells of dexamethasone-administered rats, along with a notable rise in the plasma concentration of corticosterone and the activity of 11 beta-hydroxylase. Comparable dose-dependent effects were observed after chronic administration of ACTH to dexamethasone-suppressed rats. The chronic administration of the maximum dose of DALA (500 micrograms/kg/day) was found to significantly further the trophic action of ACTH on the zona fasciculata of dexamethasone-treated animals. It is suggested that enkephalins act independently of and synergistically with ACTH in stimulating the growth and steroidogenic capacity of the rat adrenal zona fasciculata.

Effects of chronic administration of a methionine-enkephalin analogue on the zona glomerulosa of the rat adrenal cortex

The effects of D-ala2-met-enkephalinamide (DALA) on the zona glomerulosa of dexamethasone-ACTH-treated rats were investigated by coupled radioimmunologic and morphometric techniques. Short-term DALA administration provoked a significant increase in the aldosterone plasma level along with a notable lipid droplet depletion in zona glomerulosa cells. Long-term DALA treatment induced a striking hypertrophy of zona glomerulosa cells and a further rise in the blood concentration of aldosterone. These findings seem to indicate that DALA is involved not only in the acute enhancement of aldosterone output but also in the stimulation of the growth and steroidogenic capacity of rat adrenal zona glomerulosa.

Evidence that long-term methionine-enkephalin administration stimulates rat adrenal zona fasciculata

Short-term methionine-enkephalin (DALA) treatment did not induce evident changes in the adrenal zona fasciculata and in the basal corticosterone output of dexamethasone-treated rats administered with maintenance doses of ACTH. Conversely, prolonged (5 days) DALA treatment caused a notable hypertrophy of zona fasciculata cells, along with a significant increase in the plasma concentration of corticosterone. It is suggested that enkephalins exert a trophic action on the rat zona fasciculata.

Responses of rat adrenal glomerulosa and inner zone cells to synthetic ACTH analogs and proopiomelanocortin-derived peptides

A comparison of the responsiveness of isolated rat adrenal decapsular and glomerulosa cells to corticotrophin 1-39 (ACTH 1-39), synthetic ACTH analogs (characterized by a shorter amino acid chain length, the substitution of certain amino acids in the natural sequence by other amino acid residues, the replacement of the C-terminal carboxyl group by an amide), and proopiomelanocortin-derived peptides was performed by measuring corticosterone and aldosterone production, respectively. The potencies of the synthetic ACTH analogs correlated closely with the length of the peptides, similarly in both zones. No activity was observed with the proopiomelanocortin-derived peptides in either zone, with the exception of beta-LPH and alpha-MSH.

The Met-enkephalin analog D-Ala2-Met-enkephalinamide decreases the adrenocortical response to ACTH in dispersed rat adrenal cells

The effects of the Met-enkephalin analog D-Ala2-Met-enkephalinamide (DALA) on basal and ACTH-stimulated corticosterone secretion from dispersed adrenal cells were investigated. Low doses (10(-10) and 10(-12) M) of DALA resulted in no apparent alteration in the response to ACTH (8 X 10(-9), 3.2 X 10(-8) or 1.6 X 10(-7) M). High doses of DALA (10(-8) and 10(-6) M) produced a decline in the steroidogenic response to ACTH. The opiate receptor antagonist naloxone (10(-4)-10(-10) M) did not influence the basal production of corticosterone or the stimulating action exerted by ACTH. However, the presence of naloxone reversed the blocking action on corticosterone production that was exerted by DALA. These findings indicate that enkephalins may decrease adrenocortical responsiveness to ACTH.

Morphine inhibits cortisol and stimulates prolactin secretion in man

The role of opioids in endocrine regulation has been the subject of numerous studies. Surprisingly, however, the acute endocrine effects of morphine on basal hormonal levels in man have not been adequately documented. We report here the effects of intravenous morphine (5 mg) on plasma cortisol and prolactin. Fourteen healthy volunteers (nine male, five female) received morphine at 0930 hr. Blood samples were collected immediately before and 30, 60, 90, 120 and 180 min after the injection. In six of the male subjects the procedure was repeated with a placebo (normal saline) injection. Morphine stimulated prolactin release. There was a trend for a greater response in females compared to male subjects. Cortisol secretion was markedly suppressed by morphine. In sharp contrast to the results obtained with placebo, cortisol levels following morphine declined progressively at a rate consistent with the half-life of cortisol. This downward trend of cortisol values continued uninterrupted for the duration of the experiment in all 14 subjects. These results are consistent with the presence of an inhibitory opioid mechanism in the human hypothalamo-pituitary-adrenal axis.

Naloxone potentiates ACTH and angiotension II but not potassium stimulated aldosterone secretion, in vitro

The effects of naloxone on basal and ACTH, Angiotensin II (AII) and [K+] o stimulated aldosterone secretion from superfused rat adrenocortical tissue were investigated. A high dose (10(-6) M) of naloxone inhibited while a smaller dose (10(-10) M) potentiated and doses of 10(-8) or 10(-12) M naloxone were without an effect on ACTH stimulated aldosterone secretion. A potentiation of AII stimulated aldosterone secretion was observed beginning 2 hrs after 10(-6) or 10(-10) M naloxone was administered while no effect was observed with 10(-4) M naloxone. No effects of 10(-6), 10(-8), 10(-12) M naloxone were detected on aldosterone secretion stimulated by transiently elevating extracellular potassium. Naloxone from 10(-4) to 10(-12) M did not appear to significantly influence basal steroidogenic activity under these conditions. These findings demonstrate that the "opioid antagonist" naloxone has prominent actions on adrenocortical tissue. Both the specificity and lack of specificity of the action of this agent to influence the activity of the 3 secretagogues suggest that naloxone and possibly a naturally occurring endogenous ligand interacts with one or more membrane receptor distinct from the ACTH receptor. A naturally occurring ligand for this receptor could play a prominent role in the physiological regulation of adrenal steroid secretion.

Naloxone has a local effect on the testis of immature rats

Local effect of naloxone on testicular weight, compensatory hypertrophy, and differentiation of the testis and serum testosterone level has been studied in immature rats. A single injection of naloxone in a dose of 2 micrograms/testis under the testicular capsule significantly increased the testicular weight, promoted testicular differentiation and enhanced the rate of compensatory hypertrophy of the remaining testis in unilaterally orchidectomized animals. Data suggest that naloxone has a direct effect on the testis of immature rats.

The met-enkephalin analog FK 33-824 and naloxone do not directly influence cortisol secretion by cultured human adrenocortical cells

Systemic administration of the enkephalin analog FK 33.824 was previously shown to inhibit ACTH secretion in man. In this study, the direct action of this analog on cortisol release was studied. The enkephalin analog (1 microM and 10 microM) did not influence basal or ACTH-stimulated cortisol production by cultured isolated adrenocortical cells prepared from the hyperplastic adrenal glands from three patients with Cushing's disease. Naloxone (10 microM) had also no direct effect on cortisol release. It is concluded that the met-enkephalin analog used in this study and naloxone do affect the hypothalamo-pituitary-adrenal axis via a central effect.

Co-localization of vasoactive intestinal peptide (VIP) and enkephalins in chromaffin cells of the adrenal gland of amphibia. Stimulation of corticosteroid production by VIP

Recent studies have shown that biologically active peptides and monoaminergic neurotransmitters coexist in certain neuronal cell populations. Using the immunofluorescence technique, we have examined the localization of enkephalins, vasoactive intestinal peptide (VIP) and tyrosine hydroxylase in the adrenal gland of the frog Rana ridibunda. Most chromaffin cells which stained for tyrosine hydroxylase contained VIP-like immunoreactivity, whereas methionine- (Met-) and leucine- (Leu-) enkephalin-like immunoreactivity was detected in about 40% of the cells revealed by the anti-tyrosine hydroxylase serum. No VIP- or enkephalin-like immunoreactive nerve fibres were observed. Since in the frog, the chromaffin cells are in close contact with the adrenocortical (interrenal) tissue, a possible action of VIP and opiates on corticosteroidogenesis has been investigated. At doses 10(-6) and 10(-5) M, 20-min infusions of synthetic porcine or chicken VIP elicited a significant increase in corticosterone and aldosterone production by perifused frog adrenals, in a dose-dependent manner. As compared to ACTH, VIP was several orders of magnitude less effective in stimulating corticosteroid production. Morphine, Met- and Leu-enkephalins (10(-5) M) had no effect on spontaneous secretion of corticosteroids. In addition, Met- and Leu-enkephalins (10(-5) M) did not alter the production of corticosterone induced by ACTH. THese results suggest that VIP contained in the chromaffin cells of the frog adrenal gland may exert a local action in stimulating corticosteroid production by the interrenal tissue.

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

The opiate control of the pituitary-adrenal axis has been investigated in normal subjects. The infusion of 1 mg of the met-enkephalin analogue, DAMME, led to a fall in circulating cortisol in spite of a fall in blood pressure. Conversley, 16 mg of the opiate antagonist, naloxone led to brisk and pronounced elevations in plasma ACTH, lipotrophin (LPH) and cortisol. The rise above basal levels was consistent, irrespective of whether the infusion was given at 09.00, 18.00, or 23.00 h; the peak response obtained was significantly less at 23.00 h than at either 09.00 or 18.00 h. Finally, insulin-induced hypoglycaemia (0.15 u/kg) or naloxone (25 mg) produced a similar rise in plasma cortisol which was no different when the two stimuli were combined. It is suggested that there is a constant tonic inhibition of the pituitary-adrenal axis by endogenous opiates throughout 24 h, and that the circadian rhythm of ACTH/LPH secretion is not due to changes in opiate tone. However, disinhibition of this tone is likely to be responsible, at least in part, for the rise in cortisol in response to hypoglycaemic stress.

In vitro steroidogenic properties of FK 33 824, a stable analog of methionine-enkephalin. Opiate-dopamine interaction in the control of aldosterone production

The steroidogenic properties of a stable analog of the endogenous opioid methionine-enkephalin, FK 33 824, were studied with calf adrenal glomerulosa cells and its effects were compared to those of angiotensin II (A II) and metoclopramide. Metoclopramide, A II, and FK 33 824 induced dose-related increases in aldosterone production. The order of potency in stimulating aldosterone was A II, FK 33 824, metoclopramide. Metoclopramide and FK 33 824 did not increase cortisol production. The response to A II but not to FK 33 824 was inhibited by equimolar concentrations of (Sar1 Ala8) antagonist analog of AII (saralasin acetate). By contrast in the presence of equimolar concentrations of naloxone, an opioid receptor antagonist, FK 33 824-induced aldosterone production was markedly inhibited while the response to A II was unchanged. Increases in cAMP accompanied the steroidogenic response to ACTH but not to A II or FK 33 824. Dopamine at physiological concentrations (10(-10) M) inhibited FK 33 824-induced aldosterone production. These results suggest that FK 33 824 is an aldosterone secretagogue and that it initiates steroidogenesis by mechanisms similar to those of A II. However the inability to block its effect with a specific antagonist of A II provides evidence for its action on a separate site.

ACTH and corticosterone response to naloxone and morphine in normal, hypophysectomized and dexamethasone-treated rats

The effect of opiate receptors blocker naloxone on ACTH and corticosterone secretion in normal, dexamethasone-treated and hypophysectomized rats was studied. A dose-related increase in plasma corticosterone level was found at 45 min after s.c. injection of naloxone in a dose range of 0.25-2.0 mg kg-1. The rise in plasma corticosterone was preceded by a slight increase in plasma ACTH. Acute morphine administration in a relatively low dose (6 mg kg-1 s.c.) induced a significant rise in both plasma ACTH and corticosterone levels. Dexamethasone treatment was followed by low basal corticosterone level, by total inhibition of the stress response and response to morphine injection, while the response to ACTH administration was normal. Under these circumstances as well as in rats 6 days after hypophysectomy, naloxone failed to increase plasma corticosterone levels. It is concluded that a direct stimulation of corticosteroid biosynthesis in adrenal cortex is not involved in the mechanism of naloxone-induced activation of pituitary-adrenocortical function.