A dramatic late-gestation increase in fetal plasma cortisol concentrations is critical for the timing of parturition in the sheep. This increase appears to depend upon an intact hypothalamo-pituitary unit and is characterised by increasing responsiveness of the fetal adrenal gland to ACTH. ACTH has been postulated as the critical determinant of the late-gestation cortisol increase; however, recent evidence has suggested that other factors, including the ACTH precursor, pro-opiomelanocortin, may also be involved. To further define the role of ACTH in determining the timing of parturition and the responsiveness of the fetal adrenal gland, intact (INT/ACTH) and hypophysectomised (HX/ACTH) fetuses received a continuous infusion of ACTH(1-24) from the time of surgery (approximately 115 days gestational age (GA)) at a rate we have previously shown to generate normal fetal cortisol concentrations and term parturition in HX fetuses. A third group of saline-infused intact fetuses (INT/SAL) served as the control group. Adrenal responsiveness was assessed by cortisol responses to ACTH(1-24) challenges at 120, 130 and 140 days GA. There were no differences between the three groups of fetuses in the timing of parturition, the late-gestation increase in cortisol concentrations or the size of the adrenal cortex. In both INT/SAL and INT/ACTH fetuses, there were significant increases in basal immunoreactive-ACTH concentrations with advancing GA, although no such increase was observed in HX/ACTH fetuses. The proportion of total ACTH immunoreactivity present in low molecular weight (LMW) forms in INT/ACTH fetuses was greater than that in INT/SAL fetuses, while the level of LMW ACTH in HX/ACTH fetuses was intermediate. Both ACTH(1-24)-infused groups of fetuses had dramatically enhanced adrenal responsiveness to ACTH(1-24) at all GAs tested when compared with INT/SAL fetuses and there was a correlation (in rank order) between the proportion of LMW ACTH immunoreactivity and adrenal responsiveness. From these observations it appears that there is a separate regulation of adrenal responsiveness from basal cortisol concentrations and that an increase in basal cortisol concentrations can occur in the absence of an increase in basal ACTH concentrations. Furthermore, an increase in adrenal responsiveness does not appear to predict the timing of parturition nor basal cortisol concentrations. Taken together with previous studies it appears that ACTH plays an essential role in maintaining the growth of the fetal adrenal and enhancing its responsiveness, but a late-gestation increase in ACTH concentrations is not required to regulate basal cortisol concentrations or the timing of parturition.
KR Poore, IR Young, BJ Canny, and GD Thorburn
N. DESHPANDE, V. JENSEN, R. D. BULBROOK, and T. W. DOOUSS
It has been postulated that the increased rate of corticosteroid formation in the adrenal gland after corticotrophin stimulation is due to an increase in the rate of formation of NADPH or an increase in the availability of a corticosteroid precursor (Haynes & Berthet, 1957; Koritz & Peron, 1958). It has also been shown that adrenal tissue has a high level of glucose 6-phosphate dehydrogenase which generates NADPH (Kelly, Nielson, Johnson & Vestling, 1955). In this communication we would like to present evidence that in the human adrenal gland, exogenous NADPH stimulates cortisol synthesis in vivo.
The patients were all cases of advanced breast cancer with widespread metastases undergoing bilateral oophorectomy and adrenalectomy. In nine of them 2 μc of [7α-3H]pregnenolone was injected via the inferior phrenic artery and the adrenal venous blood was collected for 12 min. after the injection. In four patients, 2 μc of radioactive pregnenolone
I. CHESTER JONES and MARGARET H. SPALDING
Male adult rats whose adrenals were enucleated and allowed to regenerate showed in one group normal competence to handle administered water loads, and in another a slow diuresis after this functional test. In the latter case the predisposing factor is cortical insufficiency and not the absence of the medulla. Even those animals with regenerated enucleated adrenals, which gave a normal response to water loads, nevertheless still showed some differences from normal in regard to sodium and potassium metabolism. The histology of the adrenals in the different groups is described.
M M Ho and G P Vinson
This study located the particular cell types involved in the synthesis of growth factors in adult female rat adrenal glands. Non-isotopic in situ hybridization was used and the cellular localizations of the mRNAs of basic fibroblast growth factor (bFGF), IGF-I, and transforming growth factor-β1 (TGF-β1) were studied in adrenals from control animals and from those treated with ACTH or subjected to dietary sodium restriction. The adrenal medulla was the richest source of both bFGF and IGF-1 mRNA in both control and experimental rat adrenals. In the cortex, bFGF and IGF-I mRNAs were found mainly in the zona fasciculata in control animals, although some transcription was also detected in the zona reticularis and zona glomerulosa. Both ACTH and sodium restriction activated bFGF and IGF-I gene expression in the zona glomerulosa. Since cellular proliferation and differentiation occur primarily in the outer cortex, the data are consistent with the view that bFGF and IGF-I act as an autocrine/paracrine mitogen and differentiation regulator respectively in the rat adrenal cortex.
Very small amounts of TGF-β1 mRNA were detected, predominantly in the zona fasciculata of control rats. There were no observable differences in amounts and localization of TGF-β1 mRNA between the adrenals of control rats and those treated with ACTH for 1 day. TGF-β1 mRNA was very weak or undetectable in the adrenals from rats treated with ACTH for three and five days or from sodium-restricted rats. Although TGF-β1 immunoreactive protein has been shown to be present in the zonae fasciculata and reticularis and to modulate negatively the steroidogenic activities in the adrenal cortex of other species, its gene is not actively expressed in rat adrenals.
The present results showed that ACTH administration or dietary sodium restriction, both important adrenal mitogens in vivo, significantly altered the spatial patterns of the distribution of bFGF and IGF-I mRNAs and also increased the amount of bFGF mRNA in the adrenal cortex. This suggests that growth and differentiation of the adrenal cortex are partly mediated by bFGF and IGF-I.
Journal of Endocrinology (1995) 144, 379–387
K. Rácz, J. Fehér, G. Csomós, I. Varga, R. Kiss, and E. Gláz
Because human adrenocortical cells from different adrenal disorders exhibit pathologically altered corticosteroid synthesis, and free radical mechanisms may induce pathological changes in the activities of corticosteroid biosynthetic enzymes (cytochrome P-450), we examined the effect of an antioxidant, silibinin, on basal and ACTH-stimulated secretion of several corticosteroids in isolated adrenal cells from an aldosterone-producing adenoma, atrophied adrenal tissues surrounding the adenoma, and hyperplastic adrenals from Cushing's syndrome. In the presence of a high concentration (100 μmol/l) of silibinin, variably diminished secretion of basal aldosterone, corticosterone, cortisol, 18-OH-corticosterone and 11-deoxycorticosterone was found. In contrast, the addition of 0·01 μmol silibinin/l, which failed to produce a clear effect on basal corticosteroid secretion, resulted in a potentiation of ACTH-stimulated secretion of several corticosteroids in the adenomatous and hyperplastic adrenocortical cells. These results suggest that the dose-dependent dual effect of silibinin on corticosteroid secretion may be attributed to corresponding changes in the activities of cytochrome P-450 enzymes, and that stimulation of ACTH-induced corticosteroidogenesis by silibinin is presumably due to the antioxidant property of the drug.
Journal of Endocrinology (1990) 124, 341–345
A M Carter, J R G Challis, and P Svendsen
To ascertain whether repeated hypoxic stress would alter the response of the adrenal cortex to adrenocorticotropic hormone (ACTH), by premature activation of the hypothalamic–pituitary–adrenal axis, we studied fetal sheep subjected to daily reduction of arterial oxygen content by embolization of the fetal placental circulation with 15 μm microspheres for 8 days from about day 124 of gestation (term ∼147 days) and sham-embolized controls. Starting before the final embolization (or shamembolization) on day 8, and continuing for 24 h, the fetus was given an intravenous infusion of ACTH1–24 (0·5 μg/h) or vehicle. Fetal and maternal blood samples were taken for determination of immunoreactive cortisol, and regional adrenal and fetal placental blood flows were measured by the microsphere technique at three time points: 1 h before infusion, 3 h after the start of the infusion (1 h after embolization), and after 24 h of infusion. Prior to infusion of ACTH or vehicle, fetal placental blood flow was lower in microsphere-embolized fetuses than in sham-embolized controls (199 ± 15 vs 292 ± 25 ml/min per 100 g tissue; mean ± s.e.; P<0·01). However, plasma cortisol and adrenal cortical blood flow did not differ between embolized fetuses and controls. Adrenal vascular responses to the 24-h infusion of ACTH were similar in embolized and shamembolized fetuses. Adrenal cortical blood flow increased 3-fold (P<0·05) due to decreased vascular resistance (P<0·01), with no change in adrenal medullary blood flow. Thus, while daily embolization of the fetal placental circulation caused a sustained decrease in cotyledonary blood flow, no evidence of altered responsiveness of the adrenal cortex to ACTH was found in these experiments.
Journal of Endocrinology (1996) 148, 517–522
F S Raza, M Okamoto, H Takemori, and G P Vinson
In the light of studies suggesting that transcription of the gene coding for manganese superoxide dismutase (MnSOD) is induced by ACTH in the rat adrenal gland, northern blot analysis was used to determine its mRNA distribution. It was found that mRNA coding for MnSOD is primarily present in the inner zones of the rat adrenal cortex, and not the glomerulosa. To investigate the functional relationships between MnSOD activity and expression and adrenocortical function, adrenals and blood were taken from animals pretreated with corticotrophin or betamethasone (Betnesol), or subjected to a low-sodium diet. MnSOD activity in inner zone mitochondrial fractions was enhanced by corticotrophin and by a low-sodium diet, but suppressed by betamethasone. Apparent cytosolic MnSOD activity, total cytosolic MnSOD and CuZnMn-SOD, and glomerulosa mitochondrial MnSOD all were unaffected. Steroid assays showed a clear correlation between circulating corticosterone and inner zone mitochondrial MnSOD, but none between aldosterone and glomerulosa MnSOD.
Immunoblot analysis of MnSOD showed two apparent isoforms, at approximately 25 kDa and 75 kDa. There was a partial relationship between expression of the 75 kDa isoform and MnSOD activity, in that it was induced by corticotrophin. However, there was also a slight induction with betamethasone, and a low-sodium diet had no effect. The 25 kDa MnSOD isoform was unaffected by the treatments. The results suggest that MnSOD may have a specific role in the steroidogenic function of the fasciculata/reticularis of the rat adrenal, but not in that of the glomerulosa.
F.-P. Chou, S. Gallant, and A. C. Brownie
Circulating levels of 11-deoxycorticosterone are increased during the development of adrenal-regeneration hypertension. The present studies were undertaken to examine the mechanisms involved in this increase. Plasmids containing cDNA inserts coding for cytochrome P-45011β, cytochrome P-450scc and adrenodoxin were used to determine, by Northern blot analysis, mRNA levels at 1, 2 and 3 weeks of adrenal regeneration. There was a striking decrease in mRNA transcripts for all three enzymes during the first week of regeneration when compared with intact adrenal tissue. Over the next 2 weeks the mRNA levels increased to 64% for P-450 11β, to 80% for P-450scc and to 82% for adrenodoxin. Actin mRNA levels were 70% of control levels in the first week but were back to control levels by the second week. The present findings suggest that decreased expression of steroid 11β-hydroxylase could contribute to the increased secretion of 11-deoxycorticosterone during the early stages of adrenal regeneration.
Journal of Endocrinology (1989) 122, 403–408
Salvatore Valiante, Marina Prisco, Rosaria Sciarrillo, Maria De Falco, Anna Capaldo, Flaminia Gay, Piero Andreuccetti, Vincenza Laforgia, and Lorenzo Varano
Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are regulatory neuropeptides of the hypothalamus–hypophyseal–adrenal axis, acting via the common receptors VPAC1 and VPAC2 and the selective PACAP receptor PAC1. In the adrenal glands of the Italian wall lizard, Podarcis sicula, the presence of VIP in chromaffin cells, and the VIP-stimulated release of catecholamine and aldosterone in vivo, was previously shown. To examine the localization of both peptides and receptors and their mRNAs in the adrenal gland of P. sicula, immunohistochemistry and in situ hybridization were performed: PACAP and its mRNA were detected in chromaffin cells, VPAC1 was found associated with steroidogenic tissue, VPAC2 and PAC1 with chromaffin tissue. Using ‘far western blot’ technique, we showed the presence of specific binding sites for VIP/PACAP in the adrenal glands of the lizard. The effects of both VIP and PACAP on the adrenal cells of the lizard were examined in vitro in adrenal cell co-cultures: both VIP and PACAP enhanced catecholamine, corticosterone and aldosterone release from adrenal cell co-culture in a time- and dose-dependent manner. The catecholamine release was inhibited by PAC1 antagonist and in VPAC2 immunoneutralized adrenal cells. The effects of VIP and PACAP on aldosterone secretion were counteracted by VPAC1 antagonist administration in vitro. Corticosterone secretion elicited by VIP was not blocked by VPAC1 antagonist, while the PACAP-induced release of corticosterone was blocked by the antagonist. Overall, our investigations indicate that these neuropeptides of the secretin superfamily can act not only as neurotransmitters but also as autocrine and paracrine regulators on chromaffin and cortical cells, being important mediators of the non-cholinergic system in the lizard adrenal gland.
GA Braems, VK Han, and Challis JR
Hypoxemia represents a major stress for the fetus, and is associated with alterations and adaptations in cardiovascular, metabolic and endocrine responses, which in turn may affect tissue growth and differentiation. To determine the effects of hypoxemia on fetal adrenal activity and growth, we subjected sheep fetuses at days 126-130 and 134-136 (term 145 days) to reduced PaO2 by reducing the maternal fraction of oxygen for 48 h (mean reduction of 6.8 mmHg), without change in arterial pH or PaCO2. This stimulus resulted in similar increases in the plasma immunoreactiveACTH response at both ages. Among adrenal steroids, plasma cortisol (C21Delta4) rose in both groups of animals, but plasma androstenedione (C19Delta4) declined marginally, resulting in a pronounced increase in the cortisol:androstenedione ratio in the plasma that was greater and more sustained in the older fetuses. In the younger fetuses, after 48 h of hypoxemia, there were no significant changes in mRNAs encoding steroidogenic enzymes in the fetal adrenal gland. However, in the older fetuses, hypoxemia resulted in significantly increased levels of mRNAs encoding P450scc, P450C21 and 3beta-hydroxysteroid dehydrogenase, but not for P450C17, in the fetal adrenal gland. Levels of IGF-II mRNA in the fetal adrenal gland fell in both groups of fetuses, and this response was greater at the later gestational age. We conclude that sustained hypoxemia is a potent stimulus which activates adrenal steroidogenesis in the late gestation fetal sheep. The resultant increase in cortisol synthesis is associated with decreased expression of adrenal IGF-II mRNA. We speculate that this relationship might influence patterns of fetal organ growth and differentiative function in response to fetal stress such as hypoxemia.