Effect of somatostatin on the zona glomerulosa of rats treated with angiotensin II or captopril: stereology and plasma hormone concentrations

Demystifying "Steroid Withdrawal" During Remission in Cushing's Disease: Is Mineralocorticoid Replacement the Answer?

OBJECTIVE

To study renin-angiotensin-aldosterone axis status (RAAS) in patients of Cushing's disease (CD) at baseline and 6 weeks after curative trans-sphenoidal surgery and evaluate the role of mineralocorticoid replacement in the resolution of "steroid withdrawal syndrome" (SWS). Postoperative RAAS status had not been evaluated in previous studies, although aldosterone levels have been shown to be suppressed during medical therapy with pasireotide and cabergoline.

MATERIALS AND METHODS

This was a prospective, single-center study. Patients with CD, aged between 15-75 years, undergoing curative pituitary surgery were recruited. An 8 am and 11 pm cortisol and adrenocorticotropic hormone (ACTH) were measured at baseline. An 8 am cortisol was measured 6 weeks after surgery to demonstrate remission. Plasma-renin activity and plasma-aldosterone concentration were measured at baseline and 6 weeks after curative surgery.

RESULTS

A total of 14 patients (11 female, 3 male) were recruited initially, of these 8 patients completed the study. The plasma-renin activity was not suppressed at baseline and did not rise significantly after surgery (P = 0.717). However, plasma-aldosterone concentration was in the low-normal range at baseline and had risen significantly 6 weeks after surgery (P = 0.013). No difference was noted in subgroups with or without hypertension.

CONCLUSION

Curative pituitary surgery leads to normalization of plasma-aldosterone concentration in patients with CD just 6 weeks after surgery. Hence, mineralocorticoid replacement may not prove beneficial in alleviating the "SWS" in postsurgical CD patients who have achieved remission.

Cushing's disease and hypertension: in vivo and in vitro study of the role of the renin-angiotensin-aldosterone system and effects of medical therapy

OBJECTIVE/METHODS

Cushing's disease (CD) is often accompanied by hypertension. CD can be treated surgically and, given the expression of somatostatin subtype 5 and dopamine 2 receptors by corticotroph pituitary adenomas, pharmacologically. Indeed, we recently observed that stepwise medical combination therapy with the somatostatin-analog pasireotide, the dopamine-agonist cabergoline, and ketoconazole (which directly suppresses steroidogenesis) biochemically controlled CD patients and lowered their blood pressure after 80 days. Glucocorticoids (GC) modulate the renin-angiotensin-aldosterone system (RAAS) among others by increasing hepatic angiotensinogen expression and stimulating mineralocorticoid receptors (MR). This study therefore evaluated plasma RAAS components in CD patients before and after drug therapy. In addition, we studied whether cabergoline/pasireotide have direct relaxant effects in angiotensin II (Ang II)-constricted iliac arteries of spontaneously hypertensive rats, with and without concomitant GR/MR stimulation with dexamethasone or hydrocortisone.

RESULTS

Baseline concentrations of angiotensinogen were elevated, while renin and aldosterone were low and suppressed, respectively, even in patients treated with RAAS-blockers. This pattern did not change after 80 days of treatment, despite blood pressure normalization, nor after 4 years of remission. In the presence of dexamethasone, pasireotide inhibited Ang II-mediated vasoconstriction.

CONCLUSIONS

The low plasma renin concentrations, even under RAAS blockade, in CD may be the consequence of increased GC-mediated MR stimulation and/or the elevated angiotensinogen levels in such patients. The lack of change in RAAS-parameters despite blood pressure and cortisol normalization suggests persisting consequences of long-term exposure to cortisol excess. Finally, pasireotide may have a direct vasodilating effect contributing to blood pressure lowering.

Adrenal cortex in peripubertal and adult female rats after neonatal treatment with SRIH-14

Neonatal female rats (3-7 days old) were injected subcutaneously twice daily with 20 ?g of SRIH-14/100g b.w. for five consecutive days. The animals were sacrificed in the peripubertal (38 days old) or adult (80 days old) periods of life. Control rats were treated in the same way with identical volumes of saline. SRIH-14 led to significant reduction (p<0.05) of the absolute and relative volumes of the ZG in peripubertal animals, by 11 and 22%, respectively in comparison with the controls. The total number and volume of ZG cells and their nuclei were also significantly decreased (p<0.05) in peripubertal SRIH-14-treated rats as compared to the controls. There were no significant (p>0.05) changes in the morphometric parameters of adult adrenal cortex after SRIH-14 treatment compared with control females. It can be concluded that subcutaneously applied SRIH-14 in the neonatal period inhibits growth of adrenal ZG cells in female rats only up to the peripubertal stage, while the adrenal gland cortex recovers before mature adulthood is reached.

Effects of centrally applied somatostatin on pituitary adrenocorticotropes in female rats

Effects of intracerebroventricular (i.c.v.) application of somatostatin (SRIH-14 or SRIH-28) on growth and function of pituitary adrenocorticotropes (ACTH cells) were examined in adult female Wistar rats. Animals were subjected to i.c.v. administration of three 1-microg doses of SRIH-14 or SRIH-28 dissolved in 5 microl saline every second day. Controls were treated in the same way with the same volume of saline only. ACTH-producing cells were studied using the peroxidase-antiperoxidase (PAP) immunohistochemical procedure; blood samples were collected for hormone analyses 5 days after the last injection. SRIH-28 treatment decreased (p < 0.05) all morphometric parameters compared to control rats. Volume of ACTH cells decreased by 10%, nuclei by 36% and volume density by 13%. No significant changes (p > 0.05) in these parameters occurred after SRIH-14 treatment. Plasma concentration of ACTH in SRIH-28-treated rats was significantly lower (p < 0.05) than in control rats by 35%. In SRIH-14-treated rats, plasma concentration of ACTH was slightly, but not significantly (p > 0.05) increased by 13% compared to saline treatment. These observations suggest that centrally administered somatostatin-28, but not somatostatin-14, is specifically involved in the control of growth and secretory activity of ACTH cells in female rats. Thus, selective pharmacological manipulation of SRIH-28 receptors reached from CSF may affect ACTH activity without altering actions usually attributed to receptors sensitive to SRIF-14.

Evidence that endogenous somatostatin (SRIF) exerts an inhibitory control on the function and growth of rat adrenal zona glomerulosa. The possible involvement of zona medullaris as a source of endogenous SRIF

The effect of SRIF and its antagonist cyclo(7-aminoheptanonyl-Phe-D-Trp-Lys-Thr magnitude of Bzl)(SRIF-A) were studied in sham-operated and bilaterally adrenalectomized rats bearing ACTH- and angiotensin II (ANG-II)-responsive adrenocortical autotransplants. SRIF-A (10(-5) M) completely annulled SRIF (10(-6) M)-induced inhibition of ANG-II (10(-8) M)-evoked rise in aldosterone (ALDO) secretion by both dispersed zona glomerulosa (ZG) cells and autotransplant slices. A 7-day intraperitoneal infusion with SRIF (0.3 nmol.kg-1.min-1) significantly lowered plasma ALDO concentration (PAC) in both groups of animals, without affecting plasma renin activity and the plasma levels of ACTH and corticosterone. This treatment caused a marked atrophy of adrenal ZG and its parenchymal cells (without inducing any significant change in the zona fasciculata morphology), as well as of ZG-like cells of autotransplants. Isolated ZG cells and autotransplant slices from SRIF-infused rats evidenced a notable decrease in both their basal and maximally ACTH- or ANG-II-stimulated ALDO production. The simultaneous infusion of rats with SRIF-A (3 nmol.kg-1.min-1) completely reversed all these effects of SRIF. The prolonged infusion with SRIF-A alone caused, in sham-operated rats, a marked increase in PAC and a significant hypertrophy of ZG and ZG cells; basal and maximally-stimulated ALDO secretion of dispersed ZG cells was also notably raised. Conversely, SRIF-A infusion did not evoke any appreciable effect in autotransplanted rats. These findings suggest that endogenous SRIF is specifically involved in the negative control of the secretion and growth of the rat adrenal ZG. Since regenerated adrenocortical autotransplants, which are responsive to SRIF but not to SRIF-A infusion, are completely deprived of chromaffin cells, the hypothesis is advanced that adrenal zona medullaris may be the source of endogenous SRIF regulating ZG function.

Calcitonin gene-related peptide depresses the growth and secretory activity of rat adrenal zona glomerulosa

The bolus ip. injection of rat calcitonin gene-related peptide (CGRP) (5 pm. kg-1) significantly lowered plasma aldosterone concentration (PAC) in rats, despite a mild rise in plasma renin activity. Natremia, kalaemia and the blood levels of ACTH or corticosterone were not affected. Similar results were obtained after prolonged (5 days) sc. infusion of rats with CGRP (1 pm. kg-1. h-1). Moreover, CGRP infusion caused a notable atrophy of the zona glomerulosa (ZG) and its parenchymal cells, as well as a clearcut reduction in the surge of PAC evoked by a bolus injection of a high dose of angiotensin-II (100 micrograms. kg-1). From these results it is suggested that CGRP exerts an inhibitory effect on the growth and secretory activity of ZG in rats.

Effects of prolonged cysteamine administration on the rat adrenal cortex: evidence that endogenous somatostatin is involved in the control of the growth and steroidogenic capacity of zona glomerulosa

A week daily administration of cysteamine (CYS, 300 mg kg-1) lowered plasma aldosterone concentration in rats, without affecting PRA, kalaemia and the plasma levels of ACTH and corticosterone. Prolonged CYS treatment caused a notable hypertrophy of adrenal zona glomerulosa (ZG) and its parenchymal cells, without inducing any apparent change in zona fasciculata morphology. Isolated ZG cells from CYS-treated rats evidenced a notable enhancement in their basal and maximally-stimulated productions of aldosterone and corticosterone. All these effects of chronic CYS administration were completely reversed by the simultaneous infusion of rats with somatostatin (SRIF, 12 micrograms kg-1 h-1). CYS exposure was not found to directly affect the secretory activity of isolated ZG cells from normal rats. Since CYS is known to be a specific depletor of SRIF in different organs of rats, these findings suggest that endogenous SRIF may be involved in the modulation of ZG function.

Ultrastructural distribution of somatostatin-14 and -28 in rat adrenal cells

Previous studies have shown that somatostatin modulates angiotensin-induced aldosterone secretion by adrenal glomerulosa cells. This effect is mediated through specific receptors which do not show any preference for somatostatin-14 (S14) or the N-extended form somatostatin-28 (S28). The study of the distribution of 125I-Tyr [Tyr0, DTrp8] S14- and 125I-Tyr [Leu8, DTrp22, Tyr25] S28-binding in frozen sections of the rat adrenal by autoradiography indicated that both peptides bind to similar loci. High concentrations of binding sites were observed in the zona glomerulosa, and low concentrations were detected in the medulla. At the ultrastructural level, immunocytochemistry after cryoultramicrotomy revealed endogenous S14- and S28-like immunoreactive material in zona glomerulosa and in medulla. In glomerulosa cells, immunoreactive material was localized at the plasma membrane level, in the cytoplasmic matrix, in the mitochondria, and in the nucleus. S14- and S28-like materials were detected in both epinephrine and norepinephrine-storing cells of the adrenal medulla. In these cells, the distribution of either immunoreactive product was similar; it was observed in cytoplasmic matrix, secretory granules and nucleus, but not at the plasma membrane level. In situ hybridization does not reveal somatostatin mRNA in zona glomerulosa or medulla. These results demonstrate that S14 and S28 bind to, and are taken up by zona glomerulosa and adrenal medullary cells, but are not produced by these cells.

Somatostatin analog (SMS 201-995) inhibits the basal and angiotensin II-stimulated 3H-thymidine uptake by rat adrenal glands

The effects of a long-acting somatostatin analog SMS 201-995 injections on the basal and angiotensin II-stimulated [3H]-thymidine uptake by the rat adrenal glands incubated in vitro were examined. It was shown that SMS 201-995 significantly inhibited the [3H]-thymidine uptake and, additionally, suppressed the stimulatory effect of a single angiotensin II injection.

Increased 3H-thymidine incorporation into DNA of organ-cultured adrenal explants from rats injected with corticotropin and/or cysteamine

The effect of a single injection of cysteamine /CySH/ - a sulfhydryl substance, known to deplete tissue content of somatostatin /SS/ - on 3H-thymidine incorporation into DNA of rat adrenal explants incubated in vitro was investigated. It was shown that: 1/ Single in vivo injection of ACTH or of CySH increased 3H-thymidine incorporation into DNA of the organ-cultured adrenals, 2/ Dexamethasone reduced the 3H-thymidine uptake, but that decrease did not attain statistical significance versus controls.

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.

Further investigations on the atrial natriuretic factor (ANF)-induced inhibition of the growth and steroidogenic capacity of rat adrenal zona glomerulosa in vivo

A prolonged infusion with ANF (20 micrograms/kg/h for 7 days) induced atrophy of zona glomerulosa cells and lowering of basal plasma concentration of aldosterone in rats whose hypothalamo-hypophyseal-adrenal axis and renin-angiotensin system had been interrupted by the simultaneous administration of dexamethasone/captopril and maintenance doses of ACTH/angiotensin II. Chronic ANF treatment also caused comparable reductions in the aldosterone response of zona glomerulosa cells to the acute stimulation with angiotensin II, potassium and ACTH. These data are interpreted to indicate that ANF exerts an inhibitory effect on the growth and secretory activity of rat zona glomerulosa, and that the mechanism underlying this action of ANF does not involve blockade of renin release or ACTH secretion.

Long-term stimulatory effect of neuropeptide-Y on the growth and steroidogenic capacity of rat adrenal zona glomerulosa

A prolonged infusion with neuropeptide-Y (NPY) caused a notable hypertrophy of the adrenal zona glomerulosa and its parenchymal cells in rats whose hypothalamo-hypophyseal axis and renin-angiotensin system were pharmacologically interrupted. Zona glomerulosa hypertrophy was associated with a significant rise in both basal and stimulated plasma levels of aldosterone. Zona fasciculata cells and the blood concentration of corticosterone were not affected. These findings suggest that NPY is specifically involved in the stimulation of the growth and steroidogenic capacity of rat adrenal zona glomerulosa.

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.

Further studies on the inhibitory effects of somatostatin on the growth and steroidogenic capacity of rat adrenal zona glomerulosa

Chronic somatostatin administration was found to partially reverse the ACTH-enhanced growth of the rat zona glomerulosa. The effect of somatostatin was completely superposable to that of captopril, a specific inhibitor of the angiotensin-converting enzyme, and the inhibitory actions of these two agents did not cumulate. Neither somatostatin nor captopril counteracted the ACTH-induced stimulation of the growth and steroidogenic capacity of the rat zona fasciculata. These findings support the view that somatostatin acts as an exclusive and specific modulator of the adrenoglomerulotrophic action of the renin-angiotensin system.