bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the mechanisms of ACTH-induced inhibition of aldosterone biosynthesis in the rat adrenal cortex
Authors: Abayasekara D. R. E. , Vazir H. , Whitehouse B. J. , Price G. M. , Hinson J. P. , Vinson G. P. 
Published: December 2008

ABSTRACT
In rats, chronic treatment with high doses of ACTH (10–40 μg/100 g body weight per day) leads to a marked reduction in aldosterone synthesis by adrenal capsules. The possibility that this inhibition is secondary to a decrease in plasma potassium levels or in renin angiotensin system (RAS) activity has been explored.
The effects of chronic ACTH treatment were compared in (I) animals in which the endogenous RAS activity was stimulated by restricting dietary sodium intake, (II) animals in which plasma angiotensin II was increased by infusion from implanted osmotic minipumps and (III) animals which received supplementary potassium and in which hypokalaemia was prevented. In all cases, rates of aldosterone biosynthesis in vitro by adrenal capsules were decreased in ACTH-treated animals to an extent similar to those in untreated controls. In addition, ACTH treatment of hypophysectomized rats resulted in a similar inhibition of aldosterone biosynthesis to that found in sham-operated controls. It may be concluded that the ACTH-induced reduction of aldosterone biosynthesis is independent of the secretion of other pituitary hormones, and cannot be simply ascribed to either a reduction in RAS activity or in plasma potassium levels. The results are consistent with the view that the effects of chronic ACTH treatment are mediated by a direct action on the zona glomerulosa cell, which leads to its transformation into a zona fasciculata-like form.
Journal of Endocrinology (1989) 122, 625–632
Effects of altered photoperiod or maternal melatonin administration on plasma prolactin concentrations in fetal lambs
Authors: Bassett J. M. , Curtis N. , Hanson C. , Weeding C. M. 
Published: December 2008

ABSTRACT
During winter (December to March), when late-pregnant ewes were maintained under an artificial long-day photoperiod (16 h light) for 3 weeks or more before insertion of fetal vascular cannulae between 118 and 120 days of gestation (full term, 147 days), plasma prolactin concentrations in their fetal lambs were significantly increased throughout the last 3 weeks of gestation in comparison with values in similar aged fetuses from ewes experiencing only the natural short-day (<9 h light) winter photoperiod. When additional lighting was given only after vascular cannulation, fetal plasma prolactin increased steadily from low values, characteristic of winter pregnancies, to high values, characteristic of long-day (16 h light:8 h darkness) pregnancies. Maternal plasma prolactin concentrations changed in a similar way. During summer pregnancies (>16 h light), plasma prolactin in fetal lambs was significantly reduced within 48 h when ewes were given melatonin by i.v. infusion for 14 h each night to simulate the winter duration of the nocturnal increase in plasma melatonin. Maternal plasma prolactin concentrations also decreased significantly when melatonin was given for 3 weeks, but not in a shorter experiment. Increases in fetal plasma prolactin were proportional to the basal prolactin concentration in fetuses injected i.v. with TRH or a dopaminergic antagonist, metoclopramide, to assess how photoperiod influenced the responsiveness of prolactin secretion to acute stimulation. The results confirm that photoperiod, rather than developmental maturity, is the principal determinant of plasma prolactin in the fetal lamb during the last third of gestation, and provide evidence that photoperiodic information is transmitted to the fetus through the diurnal rhythm of melatonin in the ewe.
Journal of Endocrinology (1989) 122, 633–643
Effects of FSH and testosterone on highly purified rat Sertoli cells: inhibin α-subunit mRNA expression and inhibin secretion are enhanced by FSH but not by testosterone
Authors: Toebosch A. M. W. , Robertson D. M. , Klaij I. A. , de Jong F. H. , Grootegoed J. A. 
Published: December 2008

ABSTRACT
The effects of FSH and testosterone on inhibin mRNA expression and inhibin production by highly purified Sertoli cell preparations were examined. Sertoli cells were isolated from testes of 22-day-old rats by sequential trypsin, collagenase and hyaluronidase treatments, with subsequent osmotic shock treatment on day 3 of culture. Contamination by peritubular and germ cells was <0·5 and 1–3% respectively. Intracellular and secreted inhibin levels were measured by radioimmunoassay, using Sertoli cells which were incubated for 24 h in the absence or presence of FSH and testosterone from days 4 to 5 of culture. FSH stimulated the cellular inhibin content and the secreted inhibin level by four- and sevenfold respectively, with a half-maximal effective dose of 5–50 ng/ml. Under the present incubation conditions, testosterone (1 μmol/l) had no effect on immunoreactive inhibin levels in either the presence or absence of FSH. Similarly, the expression of inhibin α-subunit mRNA was increased following FSH stimulation, whereas testosterone had no effect. The expression of inhibin βB-subunit mRNAs was not influenced by FSH or testosterone.
It is concluded that highly purified Sertoli cell preparations, with a very low number of peritubular or germ cells, are fully responsive to FSH with respect to inhibin mRNA expression and inhibin production.
Journal of Endocrinology (1989) 122, 757–762
Regulation by ovarian factors of the LHRH-induced LH response in pituitary glands in situ or grafted under the kidney capsule in intact and ovariectomized rats
Authors: van Dieten J. A. M. J. , de Koning J. , van Rees G. P. 
Published: December 2008

ABSTRACT
When pituitary glands from intact female rats are incubated with LHRH, the resulting LH release shows a biphasic pattern: an initial low rate of LH release (lag phase) is followed by a high rate. When pituitary glands from long-term ovariectomized rats are incubated, the rate of LH release is high throughout stimulation with LHRH. The disappearance of the lag phase might be due to increased LHRH release after ovariectomy and/or the disappearance of ovarian factors.
To distinguish between these possibilities, pituitary glands which had been exposed to endogenous LHRH (pituitary glands in situ) or which had been unexposed to endogenous LHRH (pituitary glands transplanted under the kidney capsule) were incubated in the presence or absence of LHRH.
Biphasic LH secretion patterns were observed during incubation with LHRH with the animal's own pituitary gland and with the transplanted pituitary gland from intact, but not from ovariectomized rats. Thus the disappearance of the lag phase after ovariectomy results from the absence of ovarian secretory products, rather than from increased release of LHRH.
Journal of Endocrinology (1989) 123, 41–45
Suppression of pituitary-testis function in rats treated neonatally with a gonadotrophin-releasing hormone agonist and antagonist: acute and long-term effects
Authors: Kolho K.-L. , Huhtaniemi I. 
Published: December 2008

ABSTRACT
The acute and long-term effects of pituitary-testis suppression with a gonadotrophin-releasing hormone (GnRH) agonist, d-Ser(But)6des-Gly10-GnRH N-ethylamide (buserelin; 0·02, 0·1, 1·0 or 10 mg/kg body weight per day s.c.) or antagonist, N-Ac-d-Nal(2)1,d-p-Cl-Phe2,d-Trp3,d-hArg(Et2)6,d-Ala10-GnRH (RS 68439; 2 mg/kg body weight per day s.c.) were studied in male rats treated on days 1–15 of life. The animals were killed on day 16 (acute effects) or as adults (130–160 days; long-term effects). Acutely, the lowest dose of the agonist decreased pituitary FSH content and testicular LH receptors, but with increasing doses pituitary and serum LH concentrations, intratesticular testosterone content and weights of testes were also suppressed (P< 0·05–0·01). No decrease was found in serum FSH or in weights of accessory sex organs even with the highest dose of the agonist, the latter finding indicating continuing secretion of androgens. The GnRH antagonist treatment suppressed pituitary LH and FSH contents and serum LH (P< 0·05–0·01) but, as with the agonist, serum FSH remained unaltered. Testicular testosterone and testis weights were decreased (P <0·01) but testicular LH receptors remained unchanged. Moreover, the seminal vesicle and ventral prostate weights were reduced, in contrast to the effects of the agonists.
Pituitary LH and FSH contents had recovered in all adult rats treated neonatally with agonist and there was no effect on serum LH and testosterone concentrations or on fertility. In contrast, in adult rats treated neonatally with antagonist, weights of testis and accessory sex organs remained decreased (P <0·01–0·05) but hormone secretion from the pituitary and testis had returned to normal except that serum FSH was increased by 80% (P <0·01). Interestingly, 90% of the antagonist-treated animals were infertile.
It is concluded that treatment with a GnRH agonist during the neonatal period does not have a chronic effect on pituitary-gonadal function. In contrast, GnRH antagonist treatment neonatally permanently inhibits the development of the testis and accessory sex organs and results in infertility. Interestingly, despite the decline of pituitary FSH neonatally, neither of the GnRH analogues was able to suppress serum FSH values and this differs from the concomitant changes in LH and from the effects of similar treatments in adult rats.
Journal of Endocrinology (1989) 123, 83–91
Effects of 1,25-dihydroxyvitamin D3 and cortisol on bovine and human parathyroid cells
Authors: Karmali R. , Farrow S. , Hewison M. , Barker S. , O'Riordan J. L. H. 
Published: December 2008

ABSTRACT
Incubation of bovine parathyroid cells with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) decreased both preproparathyroid mRNA levels and parathyroid hormone (PTH) secretion. There was a fall to 56·6 ± 13·7% (mean ± s.e.m.) and 65·1 ± 9·3% in mRNA levels and PTH secretion respectively at 1 nmol 1,25-(OH)2D3/l, and 41·1 ± 13·6% and 42·0 ± 12·1% at 10 nmol 1,25-(OH)2D3/l after 24 h. After 48 h in 0·1 nmol 1,25-(OH)2D3/l, mRNA levels had fallen to 35·3 ± 12·6% and PTH secretion to 32·1 ± 5·0%. In human adenomatous cells, however, incubation with 1,25-(OH)2D3 (10 nmol/l) had no effect on either mRNA levels or PTH secretion even after 48 h. This lack of sensitivity of adenomatous cells to 1,25-(OH)2D3 was not due to an absence of receptors (3847 ± 39 receptors/ng cytosolic protein in adenomatous cells compared with 4068 ± 371 in bovine cells) or receptors being of low affinity.
Cortisol (1 μmol/l) caused a reduction in the number of receptors for 1,25-(OH)2D3 in bovine parathyroid cells of approximately 20% within 24 h of incubation, but no change in affinity. This decrease was accompanied by abolition of the response to 1,25-(OH)2D3 and was reversible, in that withdrawal of cortisol for the final 24 h of incubation was sufficient for the response to return, the number of receptors having returned to control values.
These results suggest that only a small percentage of receptors for 1,25-(OH)2D3 in bovine parathyroid cells may be functional at any one time. Furthermore, the insensitivity of human adenomatous cells to 1,25-(OH)2D3 does not seem to be due to a lack of receptors but may be due to a defect in the interaction between the receptor protein and the PTH gene.
Journal of Endocrinology (1989) 123, 137–142
Specific effect of oestrone sulphate on protein synthesis and secretion by cultured epithelial cells from guinea-pig endometrium
Authors: Chaminadas G. , Alkhalaf M. , Rémy-Martin J. P. , Propper A. Y. , Adessi G. L. 
Published: December 2008

ABSTRACT
Patterns of induced protein synthesis and secretion in guinea-pig endometrial epithelial cell cultures in response to oestrone sulphate alone and oestrone sulphate plus progesterone were investigated. Epithelial cells were cultured for 3 days in growth medium, then washed three times in a steroid-free medium. For each experiment, anticytokeratin immunostaining was used to discriminate the epithelial cells from the stromal cells. Only experiments in which the control dishes displayed more than 80% of anticytokeratinimmunostained cells were further processed. After this period oestradiol-17β (20 nmol/l; control), oestradiol-17β (20 nmol/l) plus progesterone (0·5 μmol/l), oestrone sulphate (1 μmol/l) or oestrone sulphate (1 μmol/l) plus progesterone (0·5 μmol/l) were added to the medium for 48 h. An immunocytochemical progesterone receptor assay showed that oestradiol-17β increased the progesterone receptor content of cells, and progesterone added to cultured cells in the presence of oestradiol-17β induced a significant increase in oestrogen sulphotransferase activity assessing the hormone responsiveness of the cultured cells.
In these culture conditions and after 16 h of incubation, oestradiol-17β induced a 1·7-fold increase in [3H]thymidine incorporation into DNA, and [35S]methionine incorporation into cellular proteins was linearly increased up to 8 h. Biochemical changes induced by the different hormone treatments were studied by labelling the proteins with a 6-h pulse of [35S]methionine. The proteins present in the medium and in cells were analysed by two-dimensional polyacrylamide gel electrophoresis, followed by fluorography. Addition of oestrone sulphate alone or with progesterone produced a change in the patterns of cellular and secreted proteins compared with those in cells cultured with either oestradiol-17β or oestradiol-17β plus progesterone. Three cellular proteins (Mr < 14 000, isoelectric point (pI) 5·2 and 5·3; Mr 75 000, pI 4·9) and one secreted protein (Mr 155 000, pI 5·6–5·9) were specifically induced and could serve as markers of oestrone sulphate action.
Journal of Endocrinology (1989) 123, 233–241
Direct pituitary inhibition of prolactin secretion by dopamine and noradrenaline in sheep
Authors: Thomas G. B. , Cummins J. T. , Doughton B. W. , Griffin N. , Smythe G. A. , Gleeson R. M. , Clarke I. J. 
Published: December 2008

ABSTRACT
The effects of dopamine, noradrenaline and 3,4-dihydroxyphenylacetic acid (DOPAC) on the release of prolactin were examined in ovariectomized ewes. Infusion of dopamine (0·5 or 1 μg/kg per min for 2 h i.v.) reduced plasma prolactin concentrations in a dose-dependent manner, whereas DOPAC (5 or 10 μg/kg per min for 2 h i.v.) had no effect. In a further series of experiments, ovariectomized hypothalamo-pituitary disconnected ewes were given dopamine or noradrenaline (each at 0·5 or 1 μg/kg per min for 2 h i.v.), and both amines reduced mean plasma concentrations of prolactin with similar potency in a dose-dependent manner. These effects were blocked by treatment with pimozide and prazosin respectively. During the infusion of dopamine, the peripheral plasma concentrations of DOPAC and 3,4-dihydroxyphenylethyleneglycol (DHPG) were increased (DOPAC, 22 ± 7 (s.e.m.) to 131 ± 11 nmol/l; DHPG, 2·9 ± 0·3 to 6·4 ± 0·2 nmol/l), but plasma concentrations of dopamine and noradrenaline did not change. Finally, administration of domperidone, a specific dopamine receptor antagonist that does not cross the blood-brain barrier, resulted in a sustained increase in plasma prolactin concentrations in ovariectomized ewes. We conclude that the secretion of prolactin from the pituitary gland is under dual inhibitory regulation by both dopamine and noradrenaline in the sheep.
Journal of Endocrinology (1989) 123, 393–402
Osmoregulation of vasopressin secretion in the insulin-withdrawn streptozotocin-treated diabetic rat
Authors: Charlton J. A. , Thompson C. J. , Palmer J. M. , Thornton S. , Baylis P. H. 
Published: December 2008

ABSTRACT
To investigate whether hyperglycaemic ketoacidotic diabetic rats continue to osmoregulate the secretion of arginine vasopressin (AVP), male Wistar rats were injected with streptozotocin (150 mg/kg body weight). Rats rendered diabetic were maintained on protamine–zinc insulin (PZI) for 11 days (insulin-treated rats; n = 35), after which PZI was withdrawn for 72 h in half the rats (insulin-withdrawn rats). Insulin-withdrawn and -treated rats were divided into two groups; one was injected i.p. with distilled water (20 ml/kg) and the other with hypertonic saline (500 mmol NaCl/l; 20 ml/kg), and killed 30 min after injection. Insulin-withdrawn rats (water loaded and osmotically stimulated) were hyperglycaemic (16·5 ± 0·8 and 16·5 ± 0·9 mmol glucose/l respectively) and ketotic (2077 ± 664 and 1474 ± 170 μmol acetoacetate/l respectively). Insulin-treated rats were euglycaemic and non-ketotic. Osmotic manipulation caused similar changes in plasma sodium in both insulin-withdrawn and -treated rats. Plasma AVP was low in the water-loaded rats (0·6 ± 0·1 and 4·5 ± 0·9 pmol/l in the insulin-treated and -withdrawn rats respectively) and increased in rats injected with hypertonic saline (1·2 ± 1·8 and 35·2 ± 17·9 pmol/l respectively). There was no evidence of hypotension and hypovolaemia in any group of rats. Linear regression analysis defined the functions: plasma AVP = 2·56 (plasma Na – 141), r = +0·63, P < 0·01 for hyperglycaemic ketotic rats; plasma AVP = 0·83 (plasma Na – 146), r = +0·78, P < 0·001 for insulin-treated animals. The slopes and abscissal intercepts were significantly (P < 0·05) different. We conclude that the hyperglycaemic ketotic diabetic rat retains the ability to osmoregulate AVP secretion.
Journal of Endocrinology (1989) 123, 413–419
Ontogeny of ACTH(1–24) receptors in rat adrenal glands during the perinatal period
Authors: Chatelain A. , Durand P. , Naaman E. , Dupouy J. P. 
Published: December 2008

ABSTRACT
Binding of ACTH to receptors was studied on crude adrenal membranes from fetal and newborn rats. 125I-Labelled ACTH(1–24) was used as the radioligand, the steroidogenic potency of which was 100-fold lower than that of unlabelled ACTH(1–24). Binding was specific, rapidly equilibrated and temperature dependent. Scatchard analysis of the binding data revealed a single class of binding sites with a dissociation constant of about 100 nmol/l at all stages of development studied. The concentration of ACTH receptors expressed per mg membrane proteins decreased in fetuses between days 17 and 21 of gestation and remained stable in newborn rats from weeks 1 to 4. The number of ACTH receptors expressed per adrenal increased regularly in fetal and newborn rats. The perinatal evolution of these concentrations of ACTH receptors is related to the increase in the size of the adrenals and the changes in cytoplasmic structures of the adrenocortical cells. When the number of ACTH-binding sites was expressed per μg DNA, maximum values occurred in fetuses on day 19 of gestation, and minimum values in newborn rats, 1 week after birth. There was an excellent correlation between the plasma levels of immunoreactive ACTH and corticosterone and the number of ACTH receptors per μg DNA during the perinatal period. Other results suggest that ACTH is able to up-regulate the number of its own receptors.
Journal of Endocrinology (1989) 123, 421–428
Human growth hormone treatment of hypophysectomized rats increases the proportion of type-1 fibres in skeletal muscle
Authors: Ayling C. M. , Moreland B. H. , Zanelli J. M. , Schulster D. 
Published: December 2008

ABSTRACT
The studies describe alterations after hypophysectomy in the proportion of the type-1 and type-2 fibres in rat skeletal muscles, and the effects of replacement treatment with pituitary human (h) GH.
Cytochemical analysis of myosin ATPase, succinate dehydrogenase and lactate dehydrogenase activities in sections of rat hind limb muscles were used as markers of fibre type and revealed that hypophysectomy reduced the proportion of type-1 fibres by 50% in soleus and in extensor digitorum longus muscles. This reduction in the proportion of type-1 fibres was accompanied by the appearance of transitional fibres (type 2C/1B).
Following seven daily injections of hGH (60 mIU/day) to hypophysectomized rats, the proportion of type-1 fibres in both soleus and in extensor digitorum longus was increased with a concomitant reduction in the number of transitional fibres. After 11 days of treatment, all these transitional fibres had reverted back to type-1 fibres. Only hGH was observed to elicit this effect; injections of other pituitary hormones had no effect on the proportions of these transitional fibres.
These alterations in fibre type occurred more rapidly than the changes reported after prolonged electrical stimulation of muscle or following extended exercise.
These findings suggest that hypophysectomy and GH injection can result in a rapid alteration in the fibre composition of skeletal muscle, which may have important implications in terms of the resistance to fatigue and speed of contraction of the muscle.
Journal of Endocrinology (1989) 123, 429–435
Metabolic clearance of insulin-like growth factor-II in sheep
Authors: Hodgkinson S. C. , Davis S. R. , Moore L. G. , Henderson H. V. , Gluckman P. D. 
Published: December 2008

ABSTRACT
The metabolic clearance of ovine insulin-like growth factor-II (IGF-II) was examined in sheep using 131I-labelled IGF-II. Following i.v. administration the tracer was distributed in a volume similar to that of the vascular space (58-5 ±3.3 ml/kg; mean ± s.e.m., n = 5) and demonstrated a triphasic pattern of clearance. Size-exclusion chromatography of a plasma sample collected 1 min after injection revealed peaks of radioactivity corresponding to hormone complexed to binding proteins of 150 and 40–50 kDa (relative abundance 21 and 65% respectively), a high molecular weight binding protein (>200 kDa; 5%) and 'free' tracer (9%). Chromatography of sequential plasma samples revealed different patterns of clearance for these constituents. Half-lives of 131I-labelled IGF-II complexed to the 150 and 40–50 kDa binding proteins, as calculated from rate constants for their decay, were 351 ± 30 and 9.6 ± min respectively (n = 5). These differ markedly from estimates for the clearance of IGF-I (545 ± 25 min, n = 8, and 34 ± 2.3 min, n = 6) associated with carrier proteins of the same apparent molecular weights. This was reflected in calculated metabolic clearance rates for IGF-I (3.9 ± 0.5 ml/min) and IGF-II (7.8 ±1.0 ml/min). Chromatography also revealed that free IGF-II was reduced to negligible levels by 12 min. In contrast, radioactivity eluting in the position expected for the > 200 kDa binding protein was cleared from the circulation very slowly. However, the small proportion of total radioactivity eluting in these molecular weight regions precluded calculation of decay constants for these species. Tracer degradation was monitored throughout the clearance study and estimated to be <20% at 800 min following i.v. administration. Less than 20% of tracer was cleared into urine over the 24 h of sampling, concurrent with a >90% fall in plasma radioactivity. Tracer in urine was completely degraded.
Journal of Endocrinology (1989) 123, 461–468