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ABSTRACT
The effects of the γ-aminobutyric acid receptor agonists muscimol and baclofen were investigated on the secretion of GH, LH, ACTH and TSH from the anterior pituitary in vitro using a rapid superfusion system. A bicuculline-sensitive stimulatory effect of muscimol was demonstrated on the secretion of GH, LH and ACTH but not TSH. Baclofen had no effect on the basal secretion of any of the hormones, but inhibited LH-releasing hormone-stimulated release of LH and K+- and Ba2+-stimulated release of ACTH. The benzodiazepine Roll-6896 and the barbiturate secobarbital were found to potentiate the effect of muscimol on GH secretion. These results demonstrate the presence of GABAA receptors on somatotrophs, gonadotrophs and corticotrophs, and the presence of GABAB receptors on gonadotrophs and corticotrophs. Thyrotrophs appear devoid of GABA receptors.
J. Endocr. (1986) 108, 1–8
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Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, Ducane Road, London w12 0hs
received 30 December 1985
INTRODUCTION
Banting & Best (1922) used what is now a classical endocrinological technique in their discovery of insulin. They pulverized pancreas with buffer, filtered the crude tissue extract and found that it produced hypoglycaemia when injected into an experimental dog. One would have thought that within a few years most bodily tissues would have been treated similarly in a search for further circulating hormones. This has not been the case. As recently as 1981 de Bold and his colleagues prepared an extract of rat cardiac atria in a fashion not dissimilar to that of Banting & Best (1922) and found that injection into a donor rat produced a dramatic diuresis and natriuresis. Indeed the urine flow increased tenfold whilst sodium and chloride excretion increased more than 30-fold (de Bold, Borenstein, Veress &
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SUMMARY
One hundred and twenty albino female rats (Sprague-Dawley-Rolfsmeyer) were divided into five equal groups. Rates of thyroxine secretion (TSR) and food consumption were determined during the control period, and 10 and 25 days after initiation of dietary treatment. Animals in each group served as their own controls for the following modifications of their diet: (1) protein-free diet, (2) 5% protein (casein) diet, (3) 10% protein diet, (4) 15% protein diet, and (5) 20% protein diet. Purina lab chow (23·4% protein) and the 20% casein diet served as control diets. The TSR, the body weight and amount of food consumed were depressed significantly in the group fed on a protein-free diet for 10 and 25 days. The group fed 5% protein diet had a non-significant decrease in TSR as compared with the controls. Similarly, TSR was not reduced by 10, 15 or 20% protein diets. Food consumption decreased significantly in the groups fed a 5, 10 and 15% protein diet, but not in the group on 20% casein. Body weight decreased significantly in the groups on a protein-free diet and on a 5% protein diet.
It would appear from these results that protein content of the diet does not become a limiting factor for TSR until it is lower than 5%. It is suggested that the calorie intake plays a more important role in regard to TSR than a low protein content of the food.
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ABSTRACT
Plasma samples were obtained at weekly intervals from the peripheral circulation of 12 women in the last 2–7 weeks of pregnancy. The concentrations of oestradiol and progesterone (isolated by chromatography) were measured by radioimmunoassay; the proportion of each hormone which was not bound to protein was measured by steady-state gel filtration. From these, the apparent concentration of the non-protein-bound form of each hormone was calculated.
The mean proportion of oestradiol not bound to protein varied from 0·84 to 2·71% in the different subjects, but within each subject variation was within experimental error. For progesterone, the mean proportion not bound to protein in the different subjects varied from 1·76 to 2·77%; within individuals the proportion remained essentially constant.
There was no consistent, recognizable trend as labour approached in (i) the concentration of oestradiol; (ii) the concentration of progesterone; (iii) the concentrations of non-protein-bound oestradiol or non-protein-bound progesterone; (iv) the ratio of the concentrations of progesterone and oestradiol; (v) the ratio of the concentrations of non-protein-bound progesterone and oestradiol. In nine out of 12 subjects, the ratio of the concentration of non-protein-bound progesterone to that of non-protein-bound oestradiol was greater than the corresponding ratio based on total hormone concentrations.
These results therefore provide no support for the hypothesis that human labour is preceded by alteration in the progesterone to oestradiol ratio which can be detected by measurement of these hormones in peripheral blood.
J. Endocr. (1985) 104, 7–15
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ABSTRACT
The response of plasma atrial natriuretic peptide (ANP) concentration to acute intravascular volume expansion was measured in ten male Wistar rats. An infusion of 3 ml polygelene colloidal solution at 37 °C over 45 s produced peak venous pressure rises of 1·5cm water. A highly significant (P<0·001) rise of immunoreactive plasma ANP from 24·4 ± 2·2 (mean ± s.e.m.) pmol/l to a peak of 70·0±10·5 pmol/l occurred within 2·5 min. Plasma ANP concentrations had virtually returned to basal levels (32·7 ± 2·7 pmol/l) 30 min after this acute volume load. A further infusion of 10 ml polygelene colloidal solution in 2 min produced peak venous pressure rises of 10 cm water and caused a dramatic and significant (P< 0·001) increase of plasma ANP concentration to a peak of 534·8 ± 38·5 pmol/l, occurring 7·5 min after infusion. The plasma ANP concentration had fallen but remained above basal levels 30 min later (137·2 ± 26·4 pmol/l).
Similar results were obtained using an identical protocol but with whole rat blood instead of polygelene solution as the volume-expanding agent. Gel column chromatography suggested that the majority of the immunoreactive ANP in rat plasma was of similar molecular size to rat α-ANP(1–28).
These results support the hypothesis that blood volume expansion is a potent stimulus for the release of ANP into plasma.
J. Endocr. (1986) 109, 9–13
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Relaxin is abundant in porcine corpora lutea during pregnancy and after hysterectomy; the levels increase as the age of the corpus increases (Anderson, Ford, Melampy & Cox, 1973). It declines sharply before parturition and is associated with accumulation and disappearance of granules in the cytoplasm of the lutein cell (Belt, Anderson, Cavazos & Melampy, 1971). Cytoplasmic granules are abundant in rat corpora lutea during late pregnancy (Long, 1973).
Holtzman-derived rats, weighing 150–180 g, were caged singly in an air-conditioned room with a lighting scheme of 12 h light and 12 h darkness. Oestrous cycles were determined daily by vaginal smears. Pseudopregnancy was induced by mechanical stimulation and the animals were killed on days 6, 9, 11 and 13. Hysterectomies were performed on day 6 of pseudopregnancy and the animals killed on days 6, 9, 11, 13, 17, 19 and 21. A decidual response was induced on day 4 and these
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Department of Animal Science, Iowa State University, Ames, Iowa 50011, U.S.A.
(Received 29 August 1975)
A previous investigation on growth in the immature pig indicated that hypophysectomy leads to a markedly reduced growth rate, but not complete cessation of growth (Ford & Anderson, 1967). Results are presented on the effect of exogenous growth hormone (GH) on growth and development in immature hypophysectomized pigs.
Immature male Yorkshire pigs were hypophysectomized by a supraorbital approach (du Mesnil du Buisson, Léglise & Chodkiewicz, 1964). The animals were anaesthetized with sodium thiopentone (0·3–0·8 g; Abbott Laboratories) and surgical anaesthesia was maintained with oxygen (200–500 ml/min) and halothane (1–4%; Ayerst Laboratories). Sham-operations included all surgical procedures except removal of the hypophysis. After surgery the pigs were isolated in individual pens in a postoperative room maintained at 24–25 °C.
Porcine growth hormone (PGH) or rat growth hormone (RGH) was injected intramuscularly at 1·0 mg/day during a
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ABSTRACT
A synthetic version of the human relaxin encoded by the human gene 2 (hRlx-2) was administered to pregnant rhesus monkeys (Macaca mulatta) on gestational days 141–158. Monkeys (three per group) received doses of 100 μg/kg or 2000 μg/kg as a continuous i.v. infusion over 2 h into a radial vein. One monkey in the low-dose group received, along with the unlabelled hRlx-2, 25·5 μCi/kg of the test material internally labelled with [35S]cysteine. Immunoreactive hRlx-2, as measured by enzyme-linked immunosorbent assay, appeared in all fetuses within 30 min (the first sampling time) of beginning the infusions. Peak fetal plasma levels of hRlx-2 were only 0·8–1·5% of the maternal values. Only 8–15% of the fetal serum radioactivity was hRlx-2. Radioactivity from maternal urine pooled over the 4-h experiment did not elute at the volume corresponding to hRlx-2, but near the column volume.
Journal of Endocrinology (1991) 130, 339–345
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ABSTRACT
We have studied cortisol and androstenedione secretion by dispersed cells of the outer zona fasciculata (ZF) plus zona glomerulosa, and the inner zona reticularis (ZR) plus medulla of the guinea-pig adrenal. The ZF and ZR were microdissected apart, the cells dispersed and incubated (200 000 cells/ml) for 90 min in the presence of adrenocorticotrophin (ACTH; 500 ng/l), dibutyryl cyclic AMP (dbcAMP; 1 mmol/l), pregnenolone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11-deoxycortisol and 21-deoxycortisol. The steroid concentrations were 5–25 μmol/l. Cortisol secretion was assayed by radioimmunoassay. There was no detectable cortisol secretion ( < 50 nmol/l) from the ZR in the controls (no additive) or after dbcAMP stimulation. Adrenocorticotrophin-stimulated cortisol secretion was also low (range < 50–340 nmol/l). In contrast the ZF secreted 177–379 (control), 828–2052 (dbcAMP) and 2863–9735 (ACTH) nmol cortisol/l. There was no detectable (i.e. < 2 nmol/l) cAMP production by ZR or ZF either basally (no ACTH) or after ACTH stimulation (500 ng/l). Challenge of the ZR cells with each cortisol precursor steroid (5 μmol/l) increased (P < 0·05) cortisol secretion over that seen with the corresponding basal and ACTH-stimulated controls. Thus pregnenolone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11-deoxycortisol and 21-deoxycortisol (converted directly to cortisol by 21-hydroxylase) gave rise to (mean ± s.d., n = 4) 406 ± 86, 680 ± 180, 1307 ± 111, 1141 ± 234 and 3160 ± 419 nmol cortisol/l respectively. The corresponding figures for the ZF prepared from the same adrenal cortex were 3919 ± 309, 4122 ± 97, 5766 ± 615, 5035 ± 260 and 6954 ± 755 nmol cortisol/l. With pregnenolone (25 μmol/l), cortisol secretion increased to 7847 ± 1424 (ZR) and 12880 ± 982 nmol/l (ZF), a ZR:ZF ratio of 0·6 compared with 0·1 for pregnenolone at 5 μmol/l. Androstenedione was secreted in the basal state by both ZF and ZR in similar quantities, i.e. 3·7 ± 0·3 and 3·7 ± 0·4 nmol/l (n = 9 and 14 respectively). Both cell types were ACTH sensitive, with androstenedione secretion increasing to 28 ± 4·8 (ZF) and 12·5 ± 0·9 (ZR) nmol/l.
There was a direct correlation (r = 0·924, P < 0·05) between total adrenal weight and body weight, between the percentage ZR in the cortex and adrenal weight (r = 0·96, P < 0·05) and between the percentage ZR and body weight (r = 0·981, P< 0·05). In a mature animal (800–1000 g) the ZR may occupy > 66% of the adrenal cortex. The mean diameters of cells from the ZF and ZR were 21 and 25 μm respectively.
J. Endocr. (1986) 109, 399–404
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ABSTRACT
Twenty patients with chronic renal failure were studied before and after haemodialysis. Plasma atrial natriuretic peptide (ANP) concentrations were markedly elevated (P < 0·01) before dialysis in comparison with healthy control subjects. After haemodialysis the plasma ANP concentration was lower in 19 patients (P < 0·01) but remained above the normal range in all but three cases. Systolic and diastolic blood pressure and body weight fell during dialysis but none of these changes correlated with the reduction of the plasma ANP concentration. Chromatographic analysis of plasma extracts indicated that α-ANP is the predominant circulating molecular form. The increase in concentration of ANP in plasma between dialyses, at a time when many patients are susceptible to sodium and water overload, and its return towards normal after dialysis supports the putative role of ANP as a circulating factor released in response to sodium and water accumulation.
J. Endocr. (1986) 110, 193–196
