P. G. Andreis

Effects of neuromedin U-8 on the secretory activity of the rat adrenal cortex: evidence for an indirect action requiring the presence of the zona medullaris

The acute effect of increasing concentrations (from 10−8 to 10−6M) of neuromedin U-8 (NMU-8) on steroid secretion of rat adrenal gland was investigated in vitro by high-pressure liquid chromatography. The production of the following steroids was measured: pregnenolone (PREG), progesterone (PROG), 11-deoxycorticosterone (DOC), corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18OH-DOC), 18-hydroxycorticosterone (18OH-B) and aldosterone (ALDO). NMU-8 had no effects on either dispersed adrenocortical cells or fragments of adrenocortical autotransplants lacking medullary chromaffin cells. Conversely, NMU-8 exerted concentration-dependent secretagogue effects on adrenal slices, including both cortex and medulla. At all concentrations tested, NMU-8 increased the production of both PREG and total post-PREG steroids. The increase in total post-PREG steroid output induced by low concentrations of NMU-8 (10−8M) was due to similar rises in the production of non-18-hydroxylated steroids (PROG, DOC and B) and 18-hydroxylated hormones (18OH-DOC, 18OH-B and ALDO); conversely, that provoked by higher concentrations of the neuropeptide (10−7 to 10−6M) was almost exclusively caused by the rise in the yield of 18-hydroxylated steroids. The stimulating effect of NMU-8 on PREG output was blocked by both α-helical-CRH and corticotropin-inhibiting peptide, which are competitive inhibitors of CRH and ACTH, respectively. The following conclusions have been drawn: (1) NMU-8 affects adrenal steroid secretion indirectly by acting on the medullary chromaffin cells, which in turn may paracrinally stimulate the cortical ones; (2) at all concentrations tested, NMU-8, by stimulating the intramedullary CRH/ACTH system, causes a net rise in the activity of the early ratelimiting step of steroidogenesis, with the consequent increase in the output of the entire spectrum of post-PREG steroids; and (3) at higher concentrations (over 10−8M), NMU-8 also elicits the release from chromaffin cells of a factor (not yet known) that specifically enhances 18-hydroxylase activity.

Neuropeptide K enhances glucocorticoid release by acting directly on the rat adrenal gland: the possible involvement of zona medullaris

Neuropeptide K (NPK), a member of the kassinin-like tachykinin family, is contained in the rat hypothalamus and is known to stimulate pituitary ACTH release. The intraperitoneal bolus administration of NPK dose-dependently enhanced corticosterone blood level not only in intact rats, but also in hypophysectomized/ACTH replaced animals. NPK did not affect corticosterone secretion of dispersed rat adrenocortical cells; however, it concentration-dependently raised basal corticosterone production by decapsulated adrenal quarters (including both cortical and medullary tissues). Minimal and maximal effective concentrations were 10(-9) and 10(-8) M, respectively. 10(-8) M NPK potentiated corticosterone response of adrenal quarters elicited by 10(-12) M ACTH, but not that evoked by higher concentrations of ACTH. The direct corticosterone secretagogue effect of 10(-8) M NPK is annulled by 10(-6) M alpha-helical-CRH or corticotropin-inhibiting peptide, competitive inhibitors of CRH and ACTH, respectively. In light of these findings, the hypothesis is advanced that NPK exerts a direct stimulatory action on adrenocortical secretion and that the mechanism underlying this effect of NPK may involve the activation of the intra-medullary CRH/ACTH system.

Effects of interleukin-1β on the renin-angiotensin-aldosterone system in rats

SummaryA bolus IP injection of interleukin-1β (IL-1β) (8 μg·kg−1) increased blood pressure and PRA without affecting plasma aldosterone (ALDO) concentration. IL-1β strongly attenuated angiotensin-II (ANG-II, 10−8M)-stimulated ALDO secretion by both isolated zona glomerulosa (ZG) cells and capsular strips. These findings suggest that IL-1β exerts a twofold opposite action on the main components of the rat renin-angiotensin-aldosterone system: simultaneous stimulation of renin release by kidneys and inhibition of the stimulatory effect of ANG-II on ALDO production. At the highest concentrations (10−6/10−5M), IL-1β was found to lower also basal ALDO output by isolated ZG cells, but not by capsular strips. However, in the presence of saralasin 10−8M (a competitive inhibitor of ANG-II) and captopril 10−8M (an angiotensin-I-converting enzyme inhibitor), IL-1β significantly reduced basal ALDO yield of capsular strips. These last results would suggest that IL-1β could also similarly affect the intraadrenal renin-angiotensin system, which seems to be involved in the local regulation of ZG secretory activity.

Pancreatic polypeptide stimulates corticosterone secretion by isolated rat adrenocortical cells

Pancreatic polypeptide (PP) dose-dependently enhanced both basal and submaximally ACTH-stimulated corticosterone production by dispersed zona fasciculata/reticularis cells of the rat adrenal gland. Conversely PP did not affect either basal or ACTH- and angiotensin-II-stimulated aldosterone and corticosterone secretion of zona glomerulosa cells. These findings could throw light on the physiological significance of the marked increase in the pancreatic release of PP during stresses.

Acute action of polypeptide YY (PYY) on rat adrenocortical cells: In vivo versus in vitro effects

Polypeptide YY (PYY), a 36-amino-acid peptide contained in high concentration in the chromaffin granules of adrenal medullary cells, significantly raised aldosterone (but not corticosterone) plasma level, when acutely administered intraperitoneum to rats at a dose of 25 microM.kg-1. Conversely, the exposure to PYY (10(-6) M) notably and specifically depressed both basal and ACTH-stimulated production of 18-hydroxylated steroids (aldosterone, 18-hydroxy-corticosterone and 180H-DOC) by isolated rat zona glomerulosa cells. The discrepancy between in vivo and in vitro results is tentatively explained by assuming that the direct inhibitory effect of PYY on aldosterone secretion by rat zona glomerulosa is masked in vivo by the interference of this peptide with one or more of the various factors that are involved in the multifactorial regulation of zona glomerulosa function.

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.

Comparison of ACTH and corticotropin-releasing hormone effects on rat adrenal steroidogenesis in vitro

SummaryThe effects of equimolar concentrations (10−9M) of ACTH and corticotropin-releasing hormone (CRH) on the secretory activity of zona glomerulosa (ZG) and zonae fasciculata and reticularis (ZF/ZR) of rat adrenals were investigated in vitro by high-pressure liquid chromatography. ACTH enhanced the output of all the post-progesterone steroids (11-deoxycorticosterone, 18-hydroxy-11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone, and aldosterone) both by isolated ZG or ZF/ZR cells and by adrenal slices. CRH raised the secretory activity exclusively of adrenal slices, and its effect was less than half that of ACTH. However, the extents to which the various post-progesterone hormones contributed to the ACTH- or CRH-induced rises in the overall adrenal secretory activity were similar. The hypothesis is discussed that CRH acts on the rat adrenal gland by eliciting a local production of ACTH.

Morphology and functional responses of isolated zona glomerulosa cells of streptozotocin-induced diabetic rats

Streptozotocin-induced diabetes significantly decreased plasma aldosterone concentration in rats whose renin-angiotensin system had been pharmacologically interrupted. Isolated zona glomerulosa cells showed a marked atrophy, coupled with a reduced basal secretion of aldosterone and corticosterone. The secretory response to the three main physiological stimuli (ACTH, angiotensin II and potassium) was also notably impaired. The hypothesis is advanced that the chronic lack of insulin may directly impair the growth and steroidogenic capacity of rat adrenal zona glomerulosa.

Structure-activity relationships of adrenomedullin in the adrenal gland.

Human adrenomedullin (ADM) is a 52-amino acid hypotensive peptide, originally isolated from human pheochromocytomas, which is expressed in a wide array of tissues, including blood vessels and adrenal medulla (1). Like other regulatory peptides contained in the adrenal medulla (2), ADM affects the secretory activity of the adrenal cortex probably acting in a paracrine manner. It has been demonstrated that ADM specifically inhibits angiotensin-II (ANG-II)-stimulated aldosterone secretion of dispersed human adrenocortical cells, through a mechanism which is likely to involve the impairment of Ca2+ influx (3,4). ADM possesses a disulfide bridge-formed six-memberedring in 16–21 position, which, along with the N-terminal and C-terminal amino-acid sequences, seems to play a key role in its vascular effects (5–7). Analogous strcture-activity relationship studies are not available as far as the antimineralocorticoid action of ADM is concerned. This prompted us to investigate the effects of several ADM fragments (s...

Effects of cyclosporine-A on steroid secretion of dispersed rat adrenocortical cells.

The acute effect of cyclosporine-A (CSA), a potent immunosuppressive agent, on the secretory activity of dispersed rat adrenocortical cells was investigated. The production of the following steroid hormones was assayed by high performance liquid chromatography: pregnenolone (PREG), progesterone (PROG), 11-deoxycorticosterone (DOC), corticosterone (B), 18-hydroxy-11-deoxycorticosterone (18OH-DOC), 18-hydroxycorticosterone (18OH-B) and aldosterone (ALDO); B and ALDO outputs were also measured by radioimmunoassay. Low concentrations of CSA (0.1-0.2 mg/ml) enhanced basal, but not ACTH- or angiotensin-II (ANG-II) 10(-8) M-stimulated, secretions of PREG, non-18-hydroxylated steroids (PROG, DOC and B) and 18-hydroxylated steroids (18OH-DOC, 18OH-B and ALDO) of both zona glomerulosa (ZG) and zonae fasciculata and reticularis (ZF/ZR) cells. Middle concentrations of CSA (from 0.3 to 0.5 mg/ml) did not affect PREG yield, nor did they alter basal and ACTH-stimulated post-PREG output of both ZG and ZF/ZR cells; however, they elicited a marked decrease in ANG-II-enhanced production of 18-hydroxylated steroid by AG cells. Concentrations of CSA higher than 0.5 mg/ml strikingly reduced either basal and agonist-stimulated over-all steroidogenesis of both ZG and ZF/ZR cells. These findings suggest that CSA at low concentrations strongly stimulates the conversion of cholesterol to PREG (i.e. the rate-limiting step of steroidogenesis), while at middle concentrations it did not affect this early step, but specifically interferes with the intracellular events which transduce the stimulatory signal of ANG-II on the late steps of mineralocorticoid production (i.e. the conversion of B to ALDO). At higher concentrations, CSA probably exerts a cytotoxic effect.