Effect of calcium on adrenocortical secretion

The authors investigated the effect of calcium on the basal cortisol secretion and on the adrenocortical secretory reserve, the indicator of which is the so-called ACTH stimulation test. They revealed that during acute hypercalcaemia there is a significant increase of the basal cortisol secretion. The adrenocortical secretory reserve is significantly reduced during hypercalcaemia, this being manifested by a smaller rise of cortisolaemia after ACTH. The Synacthen test repeated after a 48-hour interval is fully reproducible under normocalcaemia. The basal values and the response to Synacthen do not differ from the control examination. The stimulatory action of calcium can be explained indirectly via other humoral factors, the production of which is enhanced by calcium but also the function of calcium which acts as the so-called "second messenger" in steroidogenesis. Calcium has, however, probably also a direct corticotropic effect, resembling that of ACTH.     

Neural and hormonal control of Brunner's gland secretion

For many years it has been speculated that the physiological function of Brunner's glands was to secrete mucus to protect the proximal duodenum from the corrosive effects of acidified gastric juice. However the control of Brunner's gland secretion remains an enigma. Some evidence exists which indicates both cholinergic and adrenergic innervation of these glands, but current consensus weighs heavily in favor of a hormonal stimulus for glandular secretion. This is based in part on evidence obtained from denervated Brunner's gland pouches following a feeding stimulus. A number of hormones and hormone-like substances have been investigated as possible mediators in this secretory response, however, no specificity was ever demonstrated. The inability to pinpoint a given substance as a common mediator can be attributed to the fact that most active agents employed also affect duodenal motility. We present evidence that Brunner's gland secretion can be observed to be a diphasic response. The initial, transient response is always observed in the presence of increased duodenal motility. The sustained response does not require duodenal motility and is probably hormonally mediated.     

Adrenergic stimulation of adrenocortical secretion in immature fowl

In 5-6-week-old cockerels the circulating corticosterone concentration was significantly increased in birds i.m. injected 30 and 60 min previously with adrenaline (0.33 mg/kg), noradrenaline (0.33 mg/kg) or a beta-adrenergic agonist (isoprotorenol, 1 mg/kg), but was reduced in birds pretreated with an alpha-adrenergic agonist (phenylephrine, 1 mg/kg). The stimulation of corticosterone secretion induced by a 30 min period of forced exercise (0.04 km/hr; 0 degree incline) was potentiated by noradrenaline, isoprotorenol and phentolamine pretreatment. In response to exogenous adrenocorticotrophin (ACTH, 8 i.u./kg), administered i.v., the increase in the plasma corticosterone concentration was elevated above that in the controls in birds pretreated with adrenaline, noradrenaline, isoprotorenol or phentolamine (an alpha antagonist administered at 1 mg/kg). The corticosterone response to ACTH was suppressed by phenylephrine pretreatment. These results demonstrate that both basal and stimulated levels of adrenocortical activity may be subtly regulated by adrenergic mechanisms acting at a site(s) within the hypothalamo-pituitary-adrenal axis.     

Mechanisms of insulin inhibition of ACTH-stimulated steroid secretion by cultured bovine adrenocortical cells.

Results of previous studies indicated that insulin at levels comparable to those in humans during hyperinsulinemia decreased ACTH-stimulated cortisol and androstenedione secretion by bovine adrenal fasciculata-reticularis cells in primary culture. In the present studies this inhibitory action was examined further by comparing the effects of insulin on ACTH-stimulated corticosteroid secretion with its effects on 8-(4-chlorophenylthio)-cAMP (cpt-cAMP), forskolin- and [5val]angiotensin II (Ang II)-stimulated corticosteroid secretion. Effects on corticosteroid secretion were correlated with effects on cAMP accumulation and rates of cAMP production. Monolayers were incubated for 24 h in the absence or presence of each agonist alone or in combination with insulin. Insulin (1.7 x 10(-9) or 17.5 x 10(-9) M) caused about a 50% decrease in cortisol and androstenedione secretion in response to ACTH (10(-11) or 10(-8) M). Insulin also decreased ACTH-stimulated aldosterone secretion by cultured glomerulosa cells. Cpt-cAMP (10(-4) or 10(-3) M)-stimulated increases in cortisol and androstenedione secretion were inhibited by insulin, but to a lesser extent than those in response to ACTH. The inhibition of cpt-cAMP-stimulated steroid secretion was not related to increased degradation of the cyclic nucleotide. Increases in cortisol and androstenedione secretion caused by a submaximal concentration (10(-6) M) of forskolin were decreased 50-70% by insulin. In contrast, insulin failed to significantly affect cortisol or androstenedione secretion caused by a maximal concentration (10(-5) M) of forskolin. The secretory responses to Ang II (10(-8) M) were also unaffected by insulin. The effect of insulin to inhibit ACTH-stimulated steroid secretion was accompanied by a reduction in cAMP accumulation as well as an apparent inhibition of adenylate cyclase activation. These data indicate that the effect of insulin to attenuate ACTH-stimulated corticosteroid secretion results from both an inhibition of ACTH-stimulated adenylate cyclase activity and an antagonism of the intracellular actions of cAMP.     

Expression of adrenomedullin mRNA in adrenocortical tumors and secretion of adrenomedullin by cultured adrenocortical carcinoma cells

Immunoreactive-adrenomedullin concentrations and the expression of adrenomedullin mRNA were studied in the tumor tissues of adrenocortical tumors. Northern blot analysis showed the expression of adrenomedullin mRNA in tumor tissues of adrenocortical tumors, including aldosterone-producing adenomas, cortisol-producing adenomas, a non-functioning adenoma and adrenocortical carcinomas, as well as normal parts of adrenal glands and pheochromocytomas. On the other hand, immunoreactive-adrenomedullin was not detected in about 90% cases of adrenocortical tumors (<0.12 pmol/g wet weight (ww)). Immunoreactive-adrenomedullin concentrations ranged from 0.44 to 198.2 pmol/g ww in tumor tissues of pheochromocytomas and were 9.2 ± 1.2 pmol/g ww (mean ± SD, n = 4) in normal parts of adrenal glands. Adrenomedullin mRNA was expressed in an adrenocortical adenocarcinoma cell line, SW-13 and immunoreactive-adrenomedullin was detected in the culture medium of SW-13 (48.9 ± 1.8 fmol/10⁵ cells/24h, mean ± SEM, n = 4). On the other hand, immunoreactive-adrenomedullin was not detectable in the extract of SW-13 cells (<0.09 fmol/10⁵ cells), suggesting that adrenomedullin was actively secreted from SW-13 cells without long-term storage. These findings indicate that adrenomedullin is produced and secreted, not only by pheochromocytomas, but also by adrenocortical tumors. Undetectable or low levels of immunoreactive-adrenomedullin in the tumor tissues of adrenocortical tumors may be due to very rapid secretion of this peptide soon after the translation from these tumors.     

Feedback control of pancreatic secretion in rats. Role of gastric acid secretion.

Pancreatic secretion in rats is regulated by feedback inhibition of cholecystokinin (CCK) release by proteases in the gut lumen, but little is known about the role of gastric acid in this regulation. This study, carried out on conscious rats with large gastric fistulas (GF) and pancreatic fistulas, shows that diversion of pancreatic juice results in the progressive stimulation of pancreatic secretion only in rats with the GF closed. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl instilled into the duodenum in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice. Pretreatment with omeprazole (15 mumol/kg) to suppress gastric acid secretion or with L-364,718 (5 mumol/kg) to antagonize CCK receptors in the diverted state, resulted in the decline in pancreatic secretion similar to that observed after opening the GF. CCK given s.c. (20-320 pmol/kg) failed to cause any significant rise in the post-diversion pancreatic secretion in rats with the GF closed, but stimulated this secretion dose-dependently when the GF was open. Camostate (6-200 mg/kg) in rats with pancreatic juice returned to the duodenum caused dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 75%. This study provides evidence that gastric acid plays a crucial role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteases, and that factors that eliminate gastric acid secretion reduce this response.     

Effects of glucagon and glucagon-like peptide-1 on glucocorticoid secretion of dispersed rat adrenocortical cells.

The effects of glucagon and glucagon-like peptide-1 (GLP-1) on the secretory activity of rat adrenocortical cells have been investigated in vitro. Neither hormones affected basal or agonist-stimulated aldosterone secretion of dispersed rat zona glomerulosa cells or basal corticosterone production of zona fasciculata-reticularis (inner) cells. In contrast, glucagon and GLP-1 partially (40%) inhibited ACTH (10(-9) M)-enhanced corticosterone secretion of inner cells, maximal effective concentration being 10(-7) M. The effect of 10(-7) M glucagon or GPL-1 was suppressed by 10(-6) M Des-His1-[Glu9]-glucagon amide (glucagon-A) and exendin-4(3-39) (GPL-1-A), which are selective antagonists of glucagon and GLP-1 receptors, respectively. Glucagon and GLP-1 (10(-7) M) decreased by about 45-50% cyclic-AMP production by dispersed inner adrenocortical cells in response to ACTH (10(-9) M), but not to the adenylate cyclase activator forskolin (10(-5) M). Again this effect was blocked by 10(-6) M glucagon-A or GLP-1-A. The exposure of dispersed inner cells to 10(-7) M glucagon plus GLP-1 completely suppressed corticosterone response to ACTH (10(-9) M). However, they only partially inhibited (by about 65-70%) both corticosterone response to forskolin (10(-5) M) or dibutyryl-cyclic-AMP (10(-5) M) and ACTH (10(-9) M)-enhanced cyclic-AMP production. Quantitative HPLC showed that 10(-7) M glucagon or GLP-1 did not affect ACTH-stimulated pregnenolone production, evoked a slight rise in progesterone and 11-deoxycorticosterone release, and markedly reduced (by about 55%) corticosterone secretion of dispersed inner adrenocortical cells. In light of these findings the following conclusion are drawn: (i) glucagon and GLP-1, via the activation of specific receptors, inhibit glucocorticoid response of rat adrenal cortex to ACTH; and (ii) the mechanism underlying the effect of glucagon and GLP-1 is probably two-fold, and involves both the inhibition of the ACTH-induced activation of adenylate cyclase and the impairment of the late steps of glucocorticoid synthesis.     

Serotonin stimulates corticosteroid secretion by frog adrenocortical tissue in vitro

The mode of action of serotonin (5-HT) in the regulation of frog adrenal steroidogenesis was studied in vitro using the perifusion system technique. Graded doses of 5-HT (from 10(-8) to 10(-6) M) increased both corticosterone and aldosterone production in a dose-dependent manner. Short pulses (20 min) of 10(-6) M 5-HT, administered at 130 min intervals within the same experiment, did not cause any desensitization phenomenon. Indomethacin (IDM; 5 microM), a cyclooxygenase inhibitor which induced a dramatic decrease in the spontaneous secretion of corticosteroids, did not impair the stimulatory effect of 5-HT on corticosterone and aldosterone production. In the absence of calcium, 5-HT (10(-6) M) was still able to stimulate corticosteroid production. Dantrolene (5 x 10(-5) M), a blocker of calcium mobilization from intracellular pools which significantly inhibited the spontaneous production of corticosteroids, did not suppress 5-HT-evoked corticosteroid secretion. These results show that 5-HT, stored in adrenal chromaffin cells, may act as a paracrine factor to stimulate adrenal steroidogenesis in the frog. Our data also indicate that the mechanism of action of 5-HT does not depend on prostaglandin biosynthesis.     

Significantly increased cortisol secretion in normal adrenocortical cells transfected with K-ras mutants derived from human functional adrenocortical tumors

Our previous study showed that the mutation hotspots of the K-ras proto-oncogene in human functional adrenocortical tumors are in codons 15, 16, 18, and 31, thus differing from the sites in other tumors. In addition, analyzing the K-Ras protein by a recombinant DNA technique showed that the activity of endogenic GTPase and the GTPase-activating protein (GAP)-binding ability were significantly decreased in patients with these tumors. The aim of this study was to understand whether those K-ras mutants, which were found only in human adrenocortical tumors, play an important role in these tumors. Thus, the mutant K-ras cDNA was constructed with mammalian expression vectors and transfected into normal adrenocortical cells. The amount of cortisol secreted by the transfected cells was 20 to 30 times that of normal cells. Furthermore, Northern blot analysis revealed that the expression of the three steroidogenesis-related genes P450(scc) (cholesterol side-chain cleavage enzyme), P450(C17) (17alpha-hydroxylase/17, 20-lyase), and P450(C21) (steroid 21-hydroxylase) gene increased in the transfected cells. The K-ras oncogene significantly increases cortisol secretion by normal adrenocortical cells.