bluuebunny/crossref_metadata_2025_split huggingface dataset:
Androgen feedback-dependent and -independent control of photoinduced LH secretion in male tree sparrows (Spizella arborea)
Authors: Wilson F. E. 
Published: December 2008

ABSTRACT
Photoperiodic control of gonadotrophin secretion in male tree sparrows was studied by examining changes in plasma LH in castrated birds retained on short daylengths and in castrated birds transferred to long daylengths. Plasma LH concentrations were markedly higher in photostimulated birds than in non-photostimulated birds throughout the 25-day experiment, and implantation of the antiandrogen cyproterone (free alcohol), which should have blocked the action of castration-resistant androgens, did not increase plasma LH in either group. Such results, obtained from birds in which testosterone feedback was inoperative, indicate that the gonadostimulatory effect of long daylengths in intact males must be mediated, at least in part, by an androgen feedback-independent mechanism. To determine whether changes in testosterone feedback facilitate gonadotrophin secretion during photostimulation, two feedback performance characteristics (i.e. set point (minimum concentration of testosterone that suppresses plasma LH) and sensitivity (change in plasma LH per unit change in testosterone)) were quantified by evaluating plasma LH responses of non-photostimulated castrated birds and of photostimulated castrated birds to replacement testosterone (0–4·16 μmol). The data indicate that, in addition to stimulating LH secretion by an androgen feedback-independent mechanism, long daylengths reduce feedback inhibition of LH secretion by increasing the putative set point and decreasing the sensitivity of the testosterone feedback mechanism. The feedback-independent effect is the predominant effect of photostimulation on LH secretion in male tree sparrows.
J. Endocr. (1985) 105, 141–152
Nuclear retinoic acid binding protein in human prostate adenomas
Authors: Boyd D. , Chisholm G. D. , Habib F. K. 
Published: December 2008

ABSTRACT
A retinoic acid binding protein has been detected in salt extracts of nuclei obtained from human prostate adenoma. The binding was characterized by competition experiments, temperature/time studies and saturation analysis.
Substantial binding was only observed after sonication of nuclei and charcoal-pretreatment of a salt extract. The binding of radiolabelled all-transretinoic acid was displaced by all-trans-retinoic acid, retinol and to a lesser extent retinal and two synthetic retinoids, RO 10-1670 and RO 13-7410. Testosterone and dihydrotestosterone, at a 100-fold excess, had little effect on the binding.
The association between retinoic acid and nuclear protein was both temperature and time dependent. At 37 °C, equilibrium was rapidly reached (30 min) whereas at 4 and 25 °C, ligand binding occurred at a slower rate. Saturation analysis performed under steady-state conditions yielded a dissociation constant of 15 ±2 nmol/l.
Metabolism studies failed to show conversion of either radiolabelled all-trans-retinol or [3H]retinoic acid in vitro; these data suggest that both acid and alcohol forms of vitamin A are recognized by the extracted nuclear protein.
The effect of three enzyme inhibitors on [3H]retinoic acid binding was studied. Binding was unaltered in the presence of aprotinin and phenylmethylsulphonyl fluoride but sodium molybdate (10 mmol/l) increased binding by 18%.
The presence of a specific retinoid binding protein in prostate nuclei suggests that retinoids may play some role in the function of the gland.
J. Endocr. (1985) 105, 157–162
Effects of low phosphorus and low calcium diets on the production and metabolic clearance rates of 1,25-dihydroxycholecalciferol in pigs
Authors: Fox J. , Ross R. 
Published: December 2008

ABSTRACT
Severe dietary calcium (Ca) or phosphorus (P) deficiency leads to a similar degree of stimulation of (1) plasma and intestinal 1,25-dihydroxycholecalciferol (calcitriol) levels and (2) intestinal Ca absorption. In contrast, P depletion causes a much smaller increase in the renal 25-hydroxycholecalciferol-1-hydroxylase enzyme activity than does Ca depletion. To test the hypothesis that a reduced metabolic clearance rate (MCR) during P depletion might, in part, account for the observed increase in calcitriol levels, we have developed a simple primed-infusion technique to determine the MCR and production rate (PR) of calcitriol, in vivo, in pigs fed low Ca and low P diets. The MCR of calcitriol was unchanged (0·92 ml/min per kg metabolic body size (MBS)) when low P diets were fed, but showed a significant 15% increase (1·06 ml/min per kg MBS) during the feeding of low Ca diets. The PR of calcitriol increased by 2·3-fold when low P diets were fed and by fourfold during Ca depletion. Thus the increase in plasma calcitriol levels during P depletion of pigs is caused by an increase in production rather than a decrease in clearance. In contrast, Ca depletion is associated with a slightly higher PR than indicated by measurement of plasma calcitriol levels because of the increased MCR.
J. Endocr. (1985) 105, 169–173
Pituitary and gonadal response to exogenous LH-releasing hormone in the male domestic cat
Authors: Goodrowe K. L. , Chakrabortyt P. K. , Wildt D. E. 
Published: December 2008

ABSTRACT
To determine the influence of exogenous LH-releasing hormone (LHRH) on serum LH and testosterone, ten adult male domestic cats received three treatments on a rotating schedule at 10-day intervals as follows: (I) 0·1 ml saline i.m. (control); (II) 10 μg LHRH i.m., single injection; (III) 10 μg LHRH i.m., two injections given at a 2-h interval. Serial blood samples collected over a 360-min interval were analysed by radioimmunoassay for LH and testosterone. Although baseline serum LH values in saline-treated animals (treatment I) varied markedly among individual cats (2·2–29·2 μg/l), there was no evidence of pulsatile LH release or alterations in testosterone over time within individual males. In treatment II, the single injection of LHRH induced a rapid rise in mean serum LH within 30 min in all cats (mean peak, 88·2 ±9·8 μg/l), which returned to baseline by 120 min after LHRH. Mean testosterone increased within 30 min in this group (from 6·03 ±2·18 to 18·55 ±3·36 nmol/l), peaked at the 60-min collection (19·76 ± 2·77 nmol/l) and returned to baseline by the 150-min sample. After treatment III, serum LH peaked at 131·6±13·6μg/l within 30 min of the initial LHRH injection. A second injection of LHRH produced another LH surge within 30 min, but in all cats this second response was of a lower magnitude (mean peak, 69·0±14·5μg/l) and shorter duration (P<0·05). The second LHRH injection sustained peripheral testosterone levels for approximately 1 additional h. The increase in testosterone response was negatively correlated with pretreatment serum testosterone concentrations in both treatment groups (treatment II, r = −0·46; treatment III, r = −0·72). These results which provide an endocrinological data base for the male domestic cat: (1) demonstrate the acute sensitivity of the male pituitary-gonadal axis to a single injection of LHRH; (2) indicate that an additional LHRH challenge within 2 h results in a more attenuated LH surge, suggesting pituitary refractoriness to repeated LHRH administration; (3) suggest that gonadal sensitivity to LHRH administration is influenced by circulating testosterone.
J. Endocr. (1985) 105, 175–181
Effect of inhibition of prostaglandin synthesis on cervical softening and uterine activity during ovine parturition resulting from progesterone withdrawal induced by epostane
Authors: Ledger W. L. , Webster M. A. , Anderson A. B. M. , Turnbull A. C. 
Published: December 2008

ABSTRACT
The effects of an inhibitor of 3β-hydroxysteroid dehydrogenase (epostane) on uterine activity and cervical softening have been studied in eight sheep during late pregnancy. Treatment with epostane led to a rapid decline in the concentration of progesterone measured in utero-ovarian venous plasma, to less than 10% of the pretreatment value within 30 min of bolus injection. This was followed by a significant (P<0·02) increase in the concentrations of metabolites of prostaglandins E and F in utero-ovarian venous plasma and uterine activity similar to that seen in the final stages of normal labour. Measurements of cervical tissue extensibility made ex vivo showed the cervix to have softened considerably. These changes occurred without any significant change in the concentration of oestradiol-17β in utero-ovarian venous plasma. Infusion of mefenamic acid, an inhibitor of prostaglandin synthesis, prevented the changes in uterine activity and cervical softening that occurred after injection of epostane alone. Mefenamic acid also reduced the increase in concentrations of metabolites of prostaglandins E and F in plasma, although the concentration of progesterone in these animals showed the same abrupt fall which occurred in sheep after injection of epostane alone. These results suggest that progesterone withdrawal, in the absence of any subsequent rise in circulating oestrogen concentrations, is sufficient stimulus to induce cervical softening in the ewe. Cervical softening following progesterone withdrawal can be prevented by inhibition of prostaglandin synthesis.
J. Endocr. (1985) 105, 227–233
Opioid peptides of the pituitary and hypothalamus: changes in pregnant and lactating rats
Authors: Petraglia F. , Baraldi M. , Giarrè G. , Facchinetti F. , Santi M. , Volpe A. , Genazzani A. R. 
Published: December 2008

ABSTRACT
Immunoreactive (Ir) β-endorphin concentrations were determined in plasma, anterior pituitary (AP), neurointermediate pituitary lobe (NIL) and mediobasal hypothalamus (MBH) of pregnant (12–14 and 18–20 days) and fertile control rats, during labour and lactation. Immunoreactive Met-enkephalin concentrations were also evaluated in the MBH.
Concentrations of Ir β-endorphin in plasma, AP and NIL of rats during early and late pregnancy were significantly higher than in controls, the plasma and AP contents showing an increasing pattern in the second half of gestation. During labour, Ir β-endorphin concentrations in plasma and AP reached the highest values, whereas those in NIL remained unchanged. Lactating rats showed Ir β-endorphin concentrations in NIL and plasma in a range similar to that found in pregnant rats, resulting in concentrations in the AP not significantly different from those of non-pregnant controls.
Immunoreactive β-endorphin and Ir Metenkephalin concentrations in MBH of pregnant rats were almost twice as high as in controls, rising markedly during labour; during lactation levels were in the same range as in non-pregnant controls.
These results indicate that pregnancy and labour are characterized by high plasma, pituitary and hypothalamic concentrations of Ir β-endorphin as well as by high hypothalamic Ir Met-enkephalin levels, and that Ir β-endorphin concentrations vary differently during pregnancy, lactation and labour in the two pituitary lobes, supporting the existence of different control mechanisms in the AP and NIL.
J. Endocr. (1985) 105, 239–245
Effects of growth hormone-releasing factor(1–44) on growth hormone release from human somatotrophinomas in vitro: interaction with somatostatin, dopamine, vasoactive intestinal peptide and cycloheximide
Authors: White M. C. , Daniels M. , Kendall-Taylor P. , Turner S. J. , Mathias D. , Teasdale G. 
Published: December 2008

ABSTRACT
The effect of GH-releasing factor(1–44) (GRF) alone, or together with somatostatin (SRIF), dopamine (DA), vasoactive intestinal peptide (VIP) or cycloheximide was studied in a total of ten human somatotrophinomas using a static cell culture system. Growth hormone-releasing factor (2·0×10−8 mol/l) significantly (P<0·05) stimulated GH release from nine out of ten tumours over 4-h incubations, and a dose-related effect (2·0×10−10−2·0×10−8 mol/l) was observed in five tumours thus studied.
Repeated GRF (2·0×10−8 mol/l)-mediated GH release was seen during 96% (n = 25) of experiments performed on six tumours over 4 h and up to 27 days in culture. Growth hormone-releasing factor (2·0×10−8 mol/l) also stimulated GH release from five out of seven somatotrophinomas during 60-min incubations.
Somatostatin (6·1×10−9 mol/l) completely inhibited GRF-induced GH secretion from four tumours studied over 4 h, but in each case there was significant (P<0·05) 'rebound' of GH release from cultures exposed to both GRF and SRIF during a subsequent recovery period. Dopamine suppressed basal GH release from two out of four tumours, but in each case had a greater inhibitory effect on GRF-mediated GH release. Vasoactive intestinal peptide directly stimulated GH release from two out of three tumours, and the effects were additive to maximal stimulatory doses of GRF. Cycloheximide significantly (P< 0·01) enhanced GRF-stimulated release of GH during a 60-min incubation, but inhibited both basal and GRF-stimulated release over 4 and 8 h. We conclude that a static cell culture system can be used successfully to study the action of GRF on human somatotrophinoma tissue for up to 27 days in culture. Human somatotrophinomas seem to be only rarely unresponsive to the stimulatory action of GRF, which is itself significantly modulated by SRIF, DA and VIP. De-novo protein synthesis appears to be necessary for the full expression of GRF activity on human somatotrophinoma tissue.
J. Endocr. (1985) 105, 269–276
Hypothalamo-pituitary regulation of thyrotrophin secretion in chronically catheterized Brattleboro rats
Authors: Wolf B. A. , Hugues J.-N. , Aratan-Spire S. , Reinberg A. , Voirol M.-J. , Czernichow P. 
Published: December 2008

ABSTRACT
Plasma TSH rhythms were measured in Brattleboro (DI) and control Long–Evans (LE) rats with an intracardiac catheter allowing repeated sampling in conscious unstressed animals. The TSH response to thyrotrophin-releasing hormone (TRH; 500 ng/100 g body weight) was also determined. Finally, hypothalamic and pancreatic TRH concentrations and TRH-degrading activity (TRH-DA) were measured by specific radioimmunoassay. Long–Evans rats had a 24-h rhythm with a major modulatory 8-h component. In DI rats, only the 24-h rhythm was detected. The mean 24-h rhythm-adjusted mean TSH level was higher in DI than in LE rats (1·38±0·05 and 1·14 ± 0·06 μg/l respectively, P<0·01). The peak TSH response to TRH was significantly increased in DI rats while the pituitary concentration of TSH was also higher (0·93 ± 0·09 vs 0·39± 0·06 μg/mg wet weight in LE, P<0·001). Hypothalamic TRH and TRH-DA were similar in both strains. The response to propyl-thiouracil-induced hypothyroidism was identical in both strains. We conclude that DI rats have a normal pituitary sensitivity to tri-iodothyronine but a central dysfunction in the pituitary environment leading to some alterations of TSH secretion.
J. Endocr. (1985) 105, 277–283
Physiological control of growth hormone secretion by thyrotrophin-releasing hormone in the domestic fowl
Authors: Klandorf H. , Harvey S. , Fraser H. M. 
Published: December 2008

ABSTRACT
Immature cockerels (4- to 5-weeks old) were passively immunized, with antiserum raised in sheep, against thyrotrophin-releasing hormone (TRH). The administration of TRH antiserum (anti-TRH) at doses of 0·5, 1·0 or 2·0 ml/kg lowered, within 1 h, the basal concentration of plasma GH for at least 24 h. The administration of normal sheep serum had no significant effect on the GH concentration in control birds. Although the GH response to TRH (1·0 or 10·0 μg/kg) was not impaired in birds treated 1 h previously with anti-TRH, prior incubation (at 39 °C for 1 h) of TRH (20 μg/ml) with an equal volume of anti-TRH completely suppressed the stimulatory effect of TRH (10 pg/kg) on GH secretion in vivo. These results suggest that TRH is physiologically involved in the hypothalamic control of GH secretion in the domestic fowl.
J. Endocr. (1985) 105, 351–355
Volumetric control of arginine vasotocin and mesotocin release in the frog (Rana ridibunda)
Authors: Nouwen E. J. , Kühn E. R. 
Published: December 2008

ABSTRACT
Adult male frogs (Rana ridibunda) were subjected to several volumetric and osmometric stimuli and the influence on circulating concentrations of arginine vasotocin (AVT) and mesotocin was studied by the use of highly specific radioimmunoassays. During progressive blood withdrawal (haemorrhage group) urine flow decreased to zero, whereas no change occurred in the plasma and urine osmolality. Control levels of 34·3±7·3 pmol AVT/1 gradually increased up to 638·3±179·1 pmol/l (P<0·001) after a blood loss of up to 50–60% of the blood volume. Plasma mesotocin concentrations also increased from 42·4±9·2 to 70·8±12·0 pmol/l (n = 7). Hypervolaemia, produced by the repeated intravenous injection of isotonic Ringer solution, increased the urine flow and osmolality compared to controls but had no influence on the plasma levels of AVT and mesotocin. Hypernatraemia without volume change profoundly increased the urine osmolality but the urine flow was not affected; the plasma concentrations of AVT and mesotocin remained at the control level. Finally, during a 1-h immobilization stress a pronounced antidiuresis occurred in the presence of a constant plasma and urine osmolality and control plasma levels of AVT and mesotocin.
It is concluded that the release of AVT and, to a smaller extent, of mesotocin is under volumetric control.
J. Endocr. (1985) 105, 371–377
Effect of theophylline on nuclear retention of oestrogen-receptor complexes: correlation with oestrogen responses
Authors: Steinsapir J. , Rojas A. M. , Bruzzone M. E. , White A. , Alarcón O. , Fuentes I. , Fierro C. , González O. , Ampuero R. , Fuentes M. , Bitrán J. 
Published: December 2008

ABSTRACT
In the ovariectomized adult rat uterine oedema induced by 0·01 and 0·1 μg oestradiol-17β/100 g body weight increased further in the presence of theophylline. Nuclear retention of oestrogen-receptor complexes also increased in response to theophylline both in vivo and in vitro. Theophylline decreased the number of eosinophils in the blood and concurrently decreased oestrogen-induced uterine eosinophilia at doses of 0·001, 0·01, 0·1, 1, 10 or 30 μg oestradiol/100 g body weight, through a mechanism independent of glucocorticoids. There was, therefore, no correlation between changes in the number of uterine eosinophils and changes in uterine wet weight induced by theophylline and oestrogen. It is suggested that the presence of oestrogen-receptor complexes in the nucleus for at least 4 h is a prerequisite for the induction of uterine oedema and growth in the presence of theophylline and oestradiol-17β.
J. Endocr. (1985) 105, 397–403
Studies of the heterogeneity of human pituitary LH by fast protein liquid chromatography
Authors: Stockell Hartree A. , Lester J. B. , Shownkeen R. C. 
Published: December 2008

ABSTRACT
The Pharmacia fast protein liquid chromatography system was employed to fractionate a purified preparation of human LH (hLH) on the anion exchanger Mono Q at pH 7·8 into 14 sub-fractions. Each of the sub-fractions was characterized by its behaviour on polyacrylamide gel electrophoresis, sodium dodecyl sulphate (SDS) gel electrophoresis, LH receptor binding activity and sialic acid content. All sub-fractions contained sialic acid, were active in binding to LH receptors, and exhibited components typical of hLH subunits on SDS gel electrophoresis. None of the sub-fractions was homogeneous with respect to charge. There is evidence that part of the heterogeneity results from the presence in some molecules of an internal proteolytic cleavage within the β-subunit, and fractions enriched in species containing such cleavages were prepared by this method.
J. Endocr. (1985) 105,405–413
Possible role of prolactin in the inhibitory effect of testosterone on the hypothalamic-pituitary-testicular axis in the rat
Authors: Tresguerres J. A. F. , Perez Mendez L. F. , Lopez-Calderon A. , Esquifino A. I. 
Published: December 2008

ABSTRACT
To study the role of testosterone on the regulation of the hypothalamic-pituitary-testicular axis, young intact male Wistar rats were given acute (24 h) or chronic (5 days) subcutaneous treatments of 500 μg testosterone propionate (TP) or vehicle alone. Plasma LH, prolactin and testosterone levels were measured both basally and after administration of LH-releasing hormone (LHRH) or human chorionic gonadotrophin (hCG) by means of specific radioimmunoassay systems using materials supplied by the NIADDK. After acute treatment with TP there was an increase in basal plasma testosterone concentrations and no modification in the hCG response when compared with vehicle-treated animals. No difference could be detected in basal plasma testosterone levels after the chronic treatment, but a significant reduction in the hCG response was observed. Both acute and chronic treatments with TP resulted in a significant decrease of basal plasma LH levels. A reduced LH response to LHRH in acutely treated rats and no response in the chronically treated rats was detected. Plasma prolactin levels showed an increase after both acute and chronic treatments. To evaluate the possible role of the increased plasma prolactin levels on the above modifications during TP treatment, another group of animals was treated with TP and bromocriptine (dopamine agonist) simultaneously to avoid the increase in plasma prolactin levels. In this situation, neither basal plasma LH levels nor the response to LHRH were altered when compared to vehicle-treated rats; a normal testosterone response to hCG stimulation was observed in spite of the high basal plasma testosterone levels. All these observations suggest that increased prolactin levels may exert a modulatory role on the negative feedback effect of testosterone both at the testicular and central levels.
J. Endocr. (1985) 105, 423–427
Alteration of prolactin control in adult rats treated neonatally with sex steroids
Authors: Vaticón M. D. , Fernández Galaz M. C. , Tejero A. , Aguilar E. 
Published: December 2008

ABSTRACT
Androgenized, oestrogenized and control female and male rats were used to establish possible differences in the alteration of the prolactin control system. Neonatal treatment involved administration of oestradiol benzoate or testosterone propionate (TP) on days 1 and 5 to the males and on day 5 to the females. Oil-treated animals were used as controls. Plasma prolactin levels were measured in these animals during adulthood (a) before gonadectomy, performed on day 80, and 27 days after gonadectomy and (b) on the 2 days (at 10.00 and 17.00 h) after administration of a single dose of TP to gonadectomized animals. Oestrogenized rats had the highest plasma prolactin concentrations just before and after gonadectomy. Testosterone propionate increased plasma prolactin levels in all groups. This response was more notable in the female than in the male groups, and was highest in the oestrogenized animals. Temporal rhythms of the prolactin response to TP were daily, perhaps circadian, with increased levels in the afternoon compared with those in the morning. This pattern was not present in oestrogenized females and androgenized males. Results suggest (a) that oestrogens and androgens given neonatally differ in their ability to alter the prolactin control system, and (b) that females seem to be more sensitive than males to changes in hypothalamic differentiation induced by neonatal steroid treatment.
J. Endocr. (1985) 105, 429–433