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  • Author: C. R. W. Edwards x
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B R Walker, B C Williams and C R W Edwards

Abstract

11β-Hydroxysteroid dehydrogenase (11β-OHSD) inactivates glucocorticoids and thereby modulates their access to both mineralocorticoid and glucocorticoid receptors. Since 11β-OHSD activity influences the biological responses of the hypothalamic-pituitary-adrenal axis, it might be regulated by components of this axis. We examined 11β-OHSD activity in adrenalectomized rats treated for 9 days with dexamethasone and with or without ACTH. Adrenalectomy and low-dose (2 μg/day) dexamethasone had no effect on 11β-OHSD activity in renal cortex, hippocampus or heart, and reduced enzyme activity in aorta. High-dose dexamethasone (50 μg/day) had no effect in renal cortex but increased enzyme activity by at least 50% in all other sites. This effect of dexamethasone was unaffected by the co-administration of ACTH. We also examined the metabolism of dexamethasone by 11β-OHSD in homogenized rat tissues. Only in kidney, in the presence of NAD rather than NADP, was dexamethasone converted to a more polar metabolite previously identified as 11-dehydrodexamethasone. We conclude that: dexamethasone induction of 11β-OHSD is tissue-specific, and includes vascular tissues and hippocampus but not kidney; this tissue-specificity may be explained by contrasting metabolism of dexamethasone by the isoforms of 11β-OHSD; fluctuations of glucocorticoid levels within the physiological range may not have a biologically significant effect on 11β-OHSD activity; and the inhibitory effect of ACTH, observed previously in humans, is likely to depend on the presence of intact adrenal glands.

Journal of Endocrinology (1994) 141, 467–472

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J. R. Seckl, R. C. Dow, S. C. Low, C. R. W. Edwards and G. Fink

ABSTRACT

Steroid-metabolizing enzymes modulate the effects of androgens on brain differentiation and function, but no similar enzymatic system has been demonstrated for adrenocorticosteroids which exert feedback control on the hypothalamus. 11β-Hydroxysteroid dehydrogenase (11β-OHSD) rapidly metabolizes physiological glucocorticoids (corticosterone, cortisol) to inactive products, thereby regulating glucocorticoid access to peripheral mineralocorticoid and glucocorticoid receptors in a site-specific manner. Using in-situ hybridization, we found expression of 11β-OHSD mRNA in neurones of the hypothalamic paraventricular nucleus (PVN) where corticotrophinreleasing factor-41 (CRF-41) is synthesized and from where it is released into hypophysial portal blood. Administration of glycyrrhetinic acid (GE), a potent 11β-OHSD inhibitor, decreased CRF-41 release into hypophysial portal blood in the presence of unchanged circulating glucocorticoid levels, suggesting that 11β-OHSD regulates the effective corticosterone feedback signal to CRF-41 neurones. These effects of GE were not observed in adrenalectomized animals, demonstrating dependence on adrenal products. In contrast, GE led to two- to threefold increases in arginine vasopressin and oxytocin release into portal blood, effects also dependent upon intact adrenal glands. These results suggest that 11β-OHSD in the PVN, and possibly other sites, may represent a novel and important control point of corticosteroid feedback on CRF-41 release in vivo.

Journal of Endocrinology (1993) 136, 471–477

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E. Davies, S. Rossiter, C. R. W. Edwards and B. C. Williams

ABSTRACT

Serotoninergic control of aldosterone secretion in vivo was investigated in conscious rats with indwelling arterial cannulae. Serial blood samples were taken from the animals before and after i.p. administration of 1 ml (4 g/l) 5-hydroxytryptophan (5-HTP), the precursor of serotonin, or saline and they were analysed for 5-HTP, serotonin, 5-hydroxyindoleacetic acid, plasma renin activity (PRA), corticosterone, aldosterone, sodium and potassium concentrations. The role of the renin-angiotensin system was investigated in animals pretreated for 1 week with the angiotensin-converting enzyme inhibitor captopril (25 mg/day). 5-HTP caused a significant increase in all parameters within 45 min except for sodium and potassium. Saline administration showed no significant effect. Captopril pretreatment did not impair the increase in any parameter by 5-HTP, with the exception of the aldosterone response which was significantly attenuated, though not completely.

The results show that administration of 5-HTP, which increases serum serotonin levels, stimulates PRA, aldosterone and corticosterone secretion. Captopril pretreatment inhibits the aldosterone response, suggesting that the aldosterone stimulatory properties of 5-HTP require the presence of angiotensin II, although it is unclear whether it acts in a mediatory or permissive capacity. The failure of captopril to inhibit the aldosterone response completely suggests the involvement of other mechanisms such as the hypothalamo-pituitary adrenal axis or a direct action of serotonin on the adrenal.

Journal of Endocrinology (1991) 130, 347–355

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D. B. Jones, D. Marante, B. C. Williams and C. R. W. Edwards

ABSTRACT

The possible involvement of the lipoxygenase pathway of arachidonic acid metabolism in the events which take place during ACTH-induced stimulation of corticosterone secretion has been studied using an isolated rat adrenal cell system. Incubation with arachidonic acid resulted in an inhibition of ACTH-stimulated corticosterone production. The lipoxygenase pathway inhibitors nordihydroguaretic acid (NDGA), eicosatetraynoic acid (ETYA) and compound BW755C also produced inhibition of ACTH-stimulated corticosterone synthesis. The concentrations of the inhibitors at which 50% inhibition occurred were 15, 34 and 37 μmol/l respectively. The inhibitions produced by NDGA and ETYA were independent of cyclic AMP output. NDGA also inhibited corticosterone production induced by dibutyryl cyclic AMP but had no effect on corticosterone synthesis induced by pregnenolone.

Preincubation of adrenal cells with the lipoxygenase products 5, 12 and 15 hydroxyeicosatetraenoic acid (HETE) and with leukotrienes A4, B4, C4, D4 and E4 resulted in significant inhibitions of corticosterone production in response to ACTH with leukotriene A4 (LTA4) and with 15HETE and 5HETE. Conversely, incubation with glutathione (GSH), which is known to reduce intracellular LTA4 levels, produced stimulation (at 5 mmol GSH/1) and inhibition (at 50 mmol GSH/1) of corticosterone output. These studies suggest that the lipoxygenase pathway may be involved in ACTH-stimulated corticosterone synthesis.

J. Endocr. (1987) 112, 253–258

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S C Low, K E Chapman, C R W Edwards, T Wells, I C A F Robinson and J R Seckl

Abstract

11 β-Hydroxysteroid dehydrogenase (11β-HSD) catalyses the reversible metabolism of corticosterone to inert 11-dehydrocorticosterone. At least two isoforms exist. 11β-HSD-1, the first to be characterised and the only isoform for which a cDNA has been isolated, is highly expressed in liver, kidney and hippocampus. The activity of 11β-HSD in rat liver is higher in males, due to oestrogen repression of 11β-HSD-1 gene transcription in females. Sexual dimorphism in rodent liver proteins is frequently mediated indirectly via sex-specific patterns of GH release (continuous in females, pulsatile in males). We have now investigated whether this applies to 11β-HSD, using dwarf rats (congenitally deficient in GH) and hypophysectomised animals.

11β-HSD activity and 11β-HSD-1 mRNA expression in liver was significantly lower in control female than male rats (50% and 72% of male levels respectively). These sex differences in the liver were attenuated in dwarf rats, with both males and females showing similar levels of 11 β-HSD activity to control males. Administration of continuous (female pattern) GH to dwarf male rats decreased hepatic 11β-HSD activity (30% fall) and mRNA expression (77% fall), whereas the same total daily dose of GH given in the male (pulsatile) pattern had no effect on hepatic 11 β-HSD in female dwarf rats. Continuous GH also attenuated hepatic 11 β-HSD activity (25% fall) and 11β-HSD-1 mRNA expression (82% fall) in hypophysectomised animals. However, oestradiol itself suppressed hepatic 11β-HSD activity (25% fall) and 11β-HSD-1 mRNA expression (60% fall) in hypophysectomised rats.

Renal 11 β-HSD activity showed no sexual dimorphism in control or dwarf rats, although overall activity was lower in dwarf animals. By contrast, 11β-HSD-1 mRNA expression was higher in male than female kidney in both control and dwarf strains. Neither GH pattern had any effect on 11β-HSD activity or 11β-HSD-1 mRNA levels in the kidney of dwarf rats, although continuous GH attenuated 11β-HSD activity (28% fall) and 11β-HSD-1 mRNA expression in kidney (47% decrease) in hypophysectomised animals. Oestradiol attenuated renal 11β-HSD-1 mRNA expression (74% fall) in hypophysectomised rats, but increased enzyme activity (62% rise) in the kidney. None of the manipulations had any effect on hippocampal 11 β-HSD activity or gene expression.

These data demonstrate the following. (i) Sexual dimorphism of hepatic 11β-HSD is mediated, in part, via sex-specific patterns of GH secretion acting on 11β-HSD-1 gene expression. (ii) There is an additional direct repressive effect of oestrogen on hepatic 11β-HSD-1. (iii) Other tissue-specific factors are involved in regulating 11β-HSD-1, as neither peripheral GH nor oestrogen have effects upon hippocampal 11β-HSD-1. (iv) The regulation of 11β-HSD-1 mRNA expression in the kidney broadly parallels the liver. The lack of correlation between changes in expression of the 11β-HSD-1 gene and renal 11β-HSD activity reflects the presence of an additional gene product(s) in the kidney, the expression of which is largely independent of GH.

Journal of Endocrinology (1994) 143, 541–548

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C. R. W. EDWARDS, T. CHARD, MURIEL J. KITAU, MARY L. FORSLING and J. LANDON

SUMMARY

A radioimmunoassay for vasopressin was developed using antibodies produced against conjugated and non-conjugated arginine vasopressin. Despite the fact that the vasopressin molecule has only eight amino acids, cross reactivity studies showed that these antibodies were specific for different amino acid sequences.

Labelled hormone of high specific activity (350–800 μCi/μg) was produced by a modification of the chloramine-T method. Unreacted iodide was removed by the batchwise addition of an ion-exchange resin. Other techniques of purification produced no advantage over this simple method.

Several methods of separating antibody-bound and free hormone were studied. All except chromatoelectrophoresis proved satisfactory. Ammonium sulphate or ethanol precipitation of bound hormone was chosen because of simplicity, speed and reproducibility.

The lower limit of detection of the assay was 80 pg arginine vasopressin/ml diluent buffer. Therefore an extraction and concentration procedure is necessary for the measurement of basal circulating levels of the hormone.

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S. C. Low, S. N. Assaad, V. Rajan, K. E. Chapman, C. R. W. Edwards and J. R. Seckl

ABSTRACT

11β-Hydroxysteroid dehydrogenase (11β-OHSD) catalyses the reversible conversion of corticosterone to inactive 11-dehydrocorticosterone, thus regulating glucocorticoid access to mineralocorticoid and perhaps glucocorticoid receptors in vivo. 11β-OHSD has been purified from rat liver and an encoding cDNA isolated from a liver library. However, several lines of indirect evidence suggest the existence of at least two isoforms of 11β-OHSD, one found predominantly in glucocorticoid receptor-rich tissues and the other restricted to aldosterone-selective mineralocorticoid target tissues and placenta. Here we have examined the effects of chronic (10 day) manipulations of sex-steroid levels on 11β-OHSD enzyme activity and mRNA expression in liver, kidney and hippocampus and present further evidence for the existence of a second 11β-OHSD isoform in kidney.

Gonadectomized male and female rats were given testosterone, oestradiol or blank silicone elastomer capsules, controls were sham-operated. In male liver, gonadectomy+ oestradiol treatment led to a dramatic decrease in both 11β-OHSD activity (69 ± 8% decrease) and mRNA expression (97 ± 1% decrease). Gonadectomy and testosterone replacement had no effect on male liver 11β-OHSD. However, in female liver, where 11β-OHSD activity is approximately 50% of that in male liver, gonadectomy resulted in a marked increase in 11β-OHSD activity (120 ± 37% rise), which was reversed by oestradiol replacement but not testosterone treatment.

In male kidney, gonadectomy+oestradiol treatment resulted in a marked increase in 11β-OHSD activity (103 ± 4% rise). By contrast, 11β-OHSD mRNA expression was almost completely repressed (99 ± 0·1% decrease) by oestradiol treatment. This effect of oestradiol was reflected in a loss of 11β-OHSD mRNA in all regions of the kidney showing high expression by in-situ hybridization. In female kidney, oestradiol replacement also led to an increase in 11β-OHSD activity (70 ± 15% rise) while mRNA expression fell by 95 ± 3%. None of the treatments had any effect on enzyme activity or mRNA expression in the hippocampus, although transcription starts from the same promoter as liver.

We conclude that (i) sex steroids regulate 11β-OHSD enzyme activity and mRNA expression in a tissue-specific manner and (ii) the concurrence of increased enzyme activity with near absent 11β-OHSD mRNA expression in the kidney following oestradiol treatment suggests that an additional gene product is responsible, at least in part, for the high renal activity observed.

Journal of Endocrinology (1993) 139, 27–35

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R. Benediktsson, J. L. W. Yau, S. Low, L. P. Brett, B. E. Cooke, C. R. W. Edwards and J. R. Seckl

ABSTRACT

The enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD) catalyses the conversion of physiological glucocorticoids to inactive products, thus modifying the access of glucocorticoids to glucocorticoid and mineralocorticoid receptors. Glucocorticoids may affect ovarian function both indirectly and via binding to ovarian receptors. We have demonstrated 11β-HSD bioactivity and mRNA expression in rat ovary in vitro. The enzyme was localized to oocytes and luteal bodies immunohistochemically using two antibodies raised against purified rat liver 11β-HSD. These data are supported by in-situ hybridization studies, which also localized 11β-HSD mRNA expression to oocytes and luteal bodies. The results suggest that 11β-HSD may modulate the effects of glucocorticoid on ovarian function.

Journal of Endocrinology (1992) 135, 53–58