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SUMMARY
A method of estimating the peripheral plasma concentration of 11-deoxycorticosterone (DOC) in man by means of gas-liquid chromatography with electron capture detection is described. Purification requirements for samples and chromatographic media have been simplified by the use of a detector bypass valve which reduces the risk of detector contamination. For this reason the method is relatively short. There was no measurable blank using either plasma from an adrenalectomized subject or water. The normal range was found to lie between 4·1 and 17·2 ng/100 ml (mean 9·8). Dexamethasone administration to one subject resulted in a subnormal plasma DOC concentration.
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ABSTRACT
The refractoriness of guinea-pigs to the growth-promoting actions of exogenous GH has been suggested to be due to a deficiency or defect in tissue GH receptors or in GH-receptor gene expression. GH-receptor mRNA was, however, demonstrated by Northern blot analysis and by the polymerase chain reaction in extracts of guinea-pig liver, adipose tissue, brain, hypothalamus and pituitary gland. High-affinity, low-capacity binding sites for radio-labelled ovine GH were also demonstrated on the plasma membranes of guinea-pig liver and were similar to those in rat liver. These results demonstrate that the unresponsiveness of guinea-pigs to exogenous GH is not due to the absence of GH receptors.
Journal of Endocrinology (1992) 133, 357–362
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'... by analogy to the situation with calcitonin, it appears worthwhile to look for PTH in the brain and for physiological and behavioral effects of the hormone in the central nervous system' (Gennari, 1988)
Introduction
Parathyroid hormone (PTH)-like peptides, mRNA and degradative enzymes are present in hypophysiotropic regions of the hypothalamus, in which PTHbinding sites are located on neural membranes. Since exogenous PTH stimulates hypothalamic dopamine metabolism and the release of pituitary prolactin, PTH-like peptides in the hypothalamus may have neuroendocrine roles in the regulation of pituitary function. However, as PTH is produced peripherally and neurological disorders are symptomatic of hyperparathyroid disease states, parathyroidal PTH may also participate in the neuroendocrine control of the hypothalamo-pituitary axis.
PTH in the hypothalamo-pituitary axis
Unlike other peptides of the 'diffuse neuroendocrine system', PTH production was believed to be solely by the parathyroid gland (Rosenblatt et al. 1989), from which PTH
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SUMMARY
A method for determining the plasma concentrations of six major corticosteroids, aldosterone, 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), corticosterone, deoxycorticosterone (DOC), cortisol and 11-deoxycortisol using gas–liquid chromatography with electron capture detection is described. Esterification of suitable derivatives of these compounds with heptafluorobutyric anhydride (HFB) allowed detection of quantities of steroid, ranging from 0·3 pg for androstenetrione HFB (from cortisol) to 2·3 pg for corticosterone HFB. No detectable reagent blank was obtained for any compound when water was used instead of plasma and this was also the case when plasma from an adrenalectomized subject was analysed, with the exception of 18-OH-DOC where a reproducible but negligibly small blank occurred. Coefficients of variation for replicate determinations ranged from 8% for corticosterone to 17% for aldosterone. Concentrations in a series of normal human plasma samples were as follows: aldosterone, 4·0–18·0 ng/ 100 ml; 18-OH-DOC, 20–160 ng/ml; corticosterone, 0·08–0·80 μg/100 ml; DOC, 2·8–16·0 ng/100 ml; cortisol, 2·5–10·0 μg/100 ml;and 11-deoxycortisol, 40·0–400·0 ng/100 ml. When seven normal subjects were treated with dexamethasone, concentrations of DOC, cortisol and 11-deoxycortisol fell to below the limit of the normal range, those of 18-OH-DOC and corticosterone were at the lower end of the normal range while the concentration of aldosterone was not significantly affected.
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ABSTRACT
Specific hybridization of polyadenylated RNA, extracted from rat, rabbit and human pituitary glands with a 638 bp rabbit GH receptor (rGHR) cRNA was demonstrated by Northern analysis. In-situ hybridization of tissue sections with the probe demonstrated the localization of rGHR mRNA throughout the rat pituitary gland and its presence in the anterior lobe of the rabbit pituitary. Growth hormone binding sites on pituitary membranes were not, however, demonstrated by radioligand binding studies. Thus, although the GH receptor gene is expressed in pituitary tissue, functional GH receptors may not be inserted into pituitary plasma membranes.
Search for other papers by JOAN D. FULLER in
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* Zoology Department, University of St Andrews, Scotland, KY16 9TS, and † Medical Research Council Blood Pressure Research Unit, Western Infirmary, Glasgow, G11 6NT
(Received 2 April 1976)
Although several corticosteroids have been reported to be present in teleost plasma (review by Idler, 1972) relatively few studies have taken adequate steps to ensure that these compounds have been reliably characterized. Methods of establishing the identity of steroids have been discussed by Brooks, Brooks, Fotherby, Grant, Klopper & Klyne (1970) and those related to teleost studies have been reviewed and assessed by Idler (1972). This report describes the analysis of a small number of plasma samples from Salmonidae caught in Loch Lomond, Scotland. Analysis was by a highly specific method based on gas–liquid chromatography (g.l.c.) which satisfies many of the criteria suggested by the above authors.
Specimens of four salmonid species were collected by means of seine or gill-nets. Coregonus lavaretus,
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SUMMARY
Insulin was infused into the portal vein of four greyhounds previously pancreatectomized; assays on their hepatic venous serum showed thereafter not only a striking rise in total insulin-like activity (ILA), but also a steady rise in 'atypical' ILA (to 200–300% of the pre-infusion level).
For controls in two other pancreatectomized greyhounds, with their livers temporarily excluded from the circulation, insulin was similarly infused into a femoral vein and the brachial vein sampled for assays; no rise in 'atypical' ILA was then seen.
The levels of 'typical' or 'atypical' ILA in the three venous samples were not found to be altered by oxygenation before their plasmas were separated for bioassay.
These experiments suggest that 'atypical' insulin is found in serum because some of the 'typical' insulin secreted by the pancreas is transformed to the 'atypical' form during its passage through the liver.
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SUMMARY
To investigate the role of adrenal and gonadal steroids in the long-term suppression of gonadotrophin secretion induced by prolactin the effects of adrenalectomy or castration on the serum and pituitary levels of LH, FSH and prolactin and the hypothalamic content of LH releasing hormone (LH-RH) have been studied in adult male rats with hyper prolactinaemia produced by the transplantation of pituitary glands under the kidney capsule.
Levels of LH and FSH in serum were significantly suppressed in all intact pituitary-grafted rats. Adrenalectomy on the day of pituitary implantation or 20 days later did not affect this suppression. However, castration on days 0,28 or 49 after pituitary grafting resulted in a rise in levels of FSH in serum indistinguishable from that in control rats. While the rise in levels of LH after castration on day 0 was the same as the controls, this increase was significantly reduced 2 days after castration on days 28 and 49 after pituitary grafting.
Castration resulted in an increase in the pituitary content of LH and a reduction in the hypothalamic content of LH-RH but no change in the pituitary content of FSH. Hyperprolactinaemia did not appear to affect these responses.
The present results showed clearly that the gonad but not the adrenal must be present for prolactin to exert an inhibitory effect on gonadotrophin secretion.
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ABSTRACT
Although GH has no direct effect on GH release from chicken pituitary glands, GH receptor mRNA similar to that in the rabbit liver was identified by Northern blot analysis in extracts of adult chicken pituitaries. Complementary (c) DNA, reverse transcribed from chicken pituitary RNA, was amplified by the polymerase chain reaction (PCR) in the presence of 3′- and 5′-oligonucleotide primers coding for the extracellular domain of the chicken liver GH receptor and was found to contain an electrophoretically separable fragment of 500 bp, identical in size to that in chicken liver. Digestion of this pituitary cDNA with NcoI produced expected moities of 350 and 150 bp. Amplification of chicken pituitary cDNA in the presence of oligonucleotide primers for the intracellular sequence of the chicken liver GH receptor produced an electrophoretically separable fragment of approximately 800 bp, similar to that in chicken liver. This fragment was cut into expected moieties of 530 and 275 bp after digestion with EcoRI. These PCR fragments were identified in extracts of the pituitary caudal lobe, in which somatotrophs are confined and account for the majority of endocrine cell types, and in the cephalic lobe, in which somatotrophs are lacking. Translation of the GH receptor mRNA in the pituitary gland was indicated by the qualitative demonstration of radio-labelled GH-binding sites in plasma membrane preparations, in pituitary cytosol and in nuclear membranes. These results provide evidence for the expression and translation of the GH receptor gene in pituitary tissue, in which GH receptors appear to be widely distributed within cells and in different cell types. GH may therefore have paracrine, autocrine or intracrine effects on pituitary function.
Journal of Endocrinology (1992) 135, 459–468
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ABSTRACT
Freshly isolated bovine adrenocortical cells were pretreated with various concentrations of cholesterol and of high- (HDL) and low-density lipoprotein (LDL) fractions of known cholesterol content and then incubated in medium alone with and without angiotensin II. Preincubation with cholesterol (323 μmol/l) caused basal aldosterone synthesis to increase from 0·89 ± 0·08 to 2·77 ± 0·22 pmol/106 cells per hour (±s.e.m.) but did not significantly affect angiotensin-stimulated synthesis. Human HDL containing cholesterol at a final concentration of 129–647 μmol/l increased both basal and angiotensin-stimulated aldosterone synthesis. In HDL-treated cells, both the threshold response and responses to increasing concentrations of angiotensin were raised. Human LDL had no effect on basal or stimulated aldosterone synthesis nor did LDL alter the effects of HDL when cells were incubated with HDL and LDL in combination. Qualitatively similar results were obtained with bovine lipoproteins.
These studies show that, in short-term incubations of fresh tissue, the supply of cholesterol may be a limiting factor in aldosterone synthesis and that HDL rather than LDL is the preferred source. These observations are discussed in relation first to the mechanisms by which cholesterol/HDL might augment steroid responses and secondly to other studies with cultured cells which have demonstrated a role for LDL.
Journal of Endocrinology (1989) 121,125–131
