bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of lighting cycles on daily rhythms in concentrations of plasma tri-iodothyronine and thyroxine in intact and pinealectomized immature broiler hens (Gallus domesticus)
Authors: Sharp P. J. , Klandorf H. , Lea R. W. 
Published: December 2008

ABSTRACT
The effects of pinealectomy on the daily rhythms of concentrations of tri-iodothyronine (T3) and thyroxine (T4) were investigated in sexually immature female chickens exposed to 21-, 24- and 27-h cycles of light and darkness, or to extended periods of light or darkness for more than 24 h. In pinealectomized and control birds, rhythms in levels of plasma T3 and T4 were entrained by all lighting cycles and decreased in amplitude or disappeared in continuous light or darkness. In pinealectomized and control birds held on 21-h (11 h light: 10 h darkness; 11L: 10D) and 24-h (14L: 10D) lighting cycles, the peak of the T4 rhythm coincided with, or lagged, the trough in the rhythm of T3 while in birds held on a 27-h (14L: 13D) lighting cycle, the peak of the T4 rhythm preceded the trough in the rhythm of T3.
Pinealectomy resulted in significant effects on the phases or amplitudes of rhythms of T3 or T4 in all lighting schedules except 4L: 20D. However, these effects were not consistent in direction between experimental groups and were, therefore, of doubtful physiological significance. Pinealectomy increased the mean level of plasma T4 in birds exposed to continuous light or darkness or to 4L: 20D. A corresponding reduction in mean levels of plasma T3 was seen in birds exposed to continuous light or darkness.
It is concluded that under the lighting conditions investigated pinealectomy had no clear effect on the phases or amplitude of daily rhythms of levels of T4 or T3. However, after the effects of the feeding pattern on thyroid hormone rhythms imposed by the lighting cycle were removed by placing birds in constant lighting conditions, pinealectomy appeared to exert an inhibitory action on thyroid function.
J. Endocr. (1984) 103, 337–345
Conversion and release of an intermediate in vasopressin–neurophysin biosynthesis in the guinea-pig
Authors: Jones P. M. , Saermark T. , Robinson I. C. A. F. 
Published: December 2008

ABSTRACT
Guinea-pig neural lobes contain appreciable amounts of neurophysin with a glycopeptide extension (NPGP) which may represent a partially processed form of the arginine vasopressin (AVP) precursor. We have now studied the turnover and release of the NPGP component using a combination of in-vivo radiolabel incorporation and high pressure liquid chromatography. Measurement of the neural lobe content of 35S-labelled peptides at various times after hypothalamic injection of [35S]cysteine demonstrated that the oxytocin-related products accumulated more rapidly than the AVP-related products. The relative amounts of [35S]cysteine incorporated into NPGP and the AVP-related neurophysin (NPavp) changed markedly with time after in-vivo labelling. In-vitro incubation of neurosecretory granules prepared from neural lobes 4 h after radiolabel injection produced a time- and temperature-dependent conversion of NPGP to NPavp. Incubation at 37 °C for 4 h produced a 30% decrease in [35S]NPGP with a concomitant increase in [35S]NPavp, whilst there were no changes in the other 35S-labelled components. In-vitro stimulation of radiolabelled neural lobes by 56 mm-K+ evoked a Ca++-dependent release of NPGP as well as the other expected neurosecretory components, and the amount of NPGP released reflected its neural lobe content. We conclude that the NPGP component found in guinea-pig neural lobes is a biosynthetic intermediate, most of which is further processed to NPavp. However, some NPGP may also be secreted from the neural lobe in an intact form.
J. Endocr. (1984) 103, 347–354
Sex differences in plasma concentrations of steroids during the sensitive period for brain differentiation in the zebra finch
Authors: Hutchison J. B. , Wingfield J. C. , Hutchison R. E. 
Published: December 2008

ABSTRACT
Changes in plasma concentrations of sex steroids were examined in male and female zebra finch chicks during the sensitive period for differentiation of sexually dimorphic brain nuclei associated with the control of song. Using a chromatographic separation procedure and radioimmunoassay, androstenedione, testosterone and 5α-dihydrotestosterone were detected in plasma at relatively high concentrations immediately after hatching. There were no sex differences in concentrations of these androgens. An oestrogen, oestradiol-17β, which is known to differentiate the song-control system, is raised specifically in the circulating plasma of male zebra finch chicks, and not in females. The surge in oestradiol, which occurs during the first week after hatching, coincides with the period when capacity for differentiation of the song system is maximal. Exposure of the male brain to oestradiol-17β could trigger neuronal differentiation.
J. Endocr. (1984) 103, 363–369
Pituitary and testicular responses in sexually mature bulls after intravenous injections of graded doses of LH-releasing hormone
Authors: D'Occhio M. J. , Setchell B. P. 
Published: December 2008

ABSTRACT
The capacity of the anterior pituitary gland and testes in mature bulls (705±9 (s.e.m.) kg body wt, n = 4) to respond to graded doses of LH-releasing hormone (LHRH) was assessed relative to endogenous profiles of LH and testosterone secretion. Endogenous hormone profiles were determined by bleeding bulls at 20-min intervals for 12 h. Responses to LHRH were assessed on successive days after single intravenous injections of 1, 5, 10, 50 or 100 ng LHRH/kg body wt. Blood samples were taken at −40, −20, 0, 10, 20, 30, 40, 60 and 120 min relative to LHRH injection. During a 12-h bleed bulls showed spontaneous pulses of LH and testosterone which had peak amplitudes of 2·6±0·5 μg/l and 44·5 ± 7·1 nmol/l respectively. Respective peak LH (μg/l) and testosterone (nmol/l) responses to LVRH were as follows: 1 ng LHRH (3·0±0·7: 47·3±4·1); 5 ng LHRH (8·0±1·2; 52·8 ± 6·2); 10 ng LHRH (11·1±2·3; 57·7 ± 9·1); 50 ng LHRH (19·2±2·8; 47·9±8·6); 100 ng LHRH (19·1±4·7; 43·9 ±6·4). A dose of 1 ng LHRH/kg produced LH and testosterone responses which were comparable in amplitude to spontaneous peaks in the respective hormone. There was a linear (y = 0·28x+5·72; r = 0·81) increase in the LH response to doses of LVRH between 1 and 50 ng/kg; corresponding testosterone responses showed no relationship with the dose of LHRH. The capacity of the anterior pituitary gland to release amounts of LH eight to ten times in excess of those secreted during spontaneous peaks suggests that (1) there exists a large releasable store of LH in the anterior pituitary gland and (2) hypothalamic LHRH is a limiting factor in gonadotrophin secretion. In contrast to LH release, the androgenic response of the testes to acute gonadotrophic stimulation is determined largely by prevailing steroidogenic activity.
J. Endocr. (1984) 103, 371–376
Possible roles of calcium and calmodulin in mammary gland differentiation in vitro
Authors: Bolander F. F. 
Published: December 2008

ABSTRACT
In response to insulin, cortisol and prolactin, mammary gland explants from virgin mice will undergo differentiation, as measured by lactose synthetase activity and casein synthesis. W-13 (N-(4-aminobutyl)-5-chloro-2-naphthalenesulphonamide), a calmodulin inhibitor, reduced prolactin-induced differentiation by 80% while inhibiting insulin- and cortisol-induced RNA synthesis only 40%. However, tissue levels of calmodulin did not change during a 3-day culture, with or without prolactin, suggesting that the regulatory component of the calcium–calmodulin system was the intracellular calcium concentration. In support of this hypothesis, verapamil, a calcium channel blocker, also preferentially inhibited prolactin-induced differentiation and prolactin did stimulate calcium accumulation (from a control value of 3·8 ± 1·3 (s.e.m.) pg calcium/mg wet tissue per 15 min to 61·4 ± 7·0). On the other hand, A 23187, a calcium ionophore which mimicked prolactin actions on calcium accumulation, was not able to induce differentiation in the absence of prolactin; in fact, high concentrations of either A 23187 or extracellular calcium actually inhibited lactose synthetase activity, although casein synthesis was relatively unaffected. Therefore, it appears that the calcium–calmodulin system is involved in prolactin-induced differentiation of mammary gland explants but that it cannot be the only mediator of prolactin actions; i.e. it is necessary but not sufficient. There also appears to be another, separate action of calcium on casein synthesis which involves increasing the mammary epithelial sensitivity toward prolactin with respect to casein synthesis but not lactose synthetase activity.
J. Endocr. (1985) 104, 29–34
Effects of hyperprolactinaemia and testosterone on the release of LH-releasing hormone and the gonadotrophins in intact and castrated rats
Authors: Brar A. K. , McNeilly A. S. , Fink G. 
Published: December 2008

ABSTRACT
We have investigated the effect of hyperprolactinaemia on the secretion of LH-releasing hormone (LHRH), LH and FSH in male rats of the PVG strain which were left intact, castrated or castrated and then implanted with either a 10 or 30 mm silicone elastomer capsule containing testosterone (T10 and T30 respectively). Hyperprolactinaemia was produced by pituitary grafts under the kidney capsule. Pituitary stalk blood, for LHRH estimation, and peripheral blood, for LH, FSH and prolactin, were collected under alphaxalone anaesthesia. Pituitary stalk blood was collected during three consecutive periods of 30 min each before, during and after the application of an electrical stimulus to the median eminence (ME).
Hyperprolactinaemia significantly reduced the plasma concentrations of FSH in intact rats and the post-castration increase in the plasma concentrations of both LH and FSH. Neither hyperprolactinaemia nor castration had any significant effect on the spontaneous output of LHRH, but castration alone or castration plus implantation of a T30 capsule did significantly reduce the increment in LHRH output produced by ME stimulation, an effect not seen in rats bearing pituitary grafts. The T30, but not the T10 capsules suppressed the post-castration increase in the gonadotrophins, and the inhibitory effect of testosterone was not significantly affected by hyperprolactinaemia. An incidental but important finding was that the presence of pituitary grafts under the kidney capsule reduced the anaesthetic dose of alphaxalone by 63%.
These results show that (i) in the male rat the inhibitory effect of hyperprolactinaemia on gonadotrophin secretion is not due to a decrease in the spontaneous release of LHRH, (ii) in contrast to the female rat the post-castration increase in gonadotrophin secretion is not accompanied by an increase in the output of LHRH, (iii) the output of LHRH in response to ME stimulation is affected by castration and testosterone but not by hyperprolactinaemia and (iv) the anaesthetic effects of alphaxalone are potentiated by hyperprolactinaemia, and this may explain in part the potentiation of alphaxalone anaesthesia by oestrogen.
J. Endocr. (1985) 104, 35–43
Differential effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour in rams
Authors: D'Occhio M. J. , Galil K. A. A. , Brooks D. E. , Setchell B. P. 
Published: December 2008

ABSTRACT
Castrated sheep were used to study the effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. In the first experiment serum LH and FSH concentrations were determined in intact rams, recently castrated (2 days and 3 weeks) and long-term castrated animals (> 2 years, wethers) during intravenous testosterone infusion at physiological and supraphysiological levels. In intact rams, testosterone infusions effectively suppressed serum LH whilst FSH levels were suppressed only after prolonged infusion at the supraphysiological dose. Recently castrated sheep, which had higher gonadotrophin levels than intact rams, were less sensitive to testosterone feedback. Neither rate of testosterone infusion had any effect on the raised gonadotrophin levels in wethers. In a second experiment gonadotrophin concentrations and mating behaviour were determined in wethers bearing subdermal polydimethylsiloxane implants of testosterone, dihydrotestosterone and oestradiol. Testosterone implants stimulated mating behaviour in all wethers but suppressed gonadotrophins in only a proportion (three out of seven) of the animals. Both oestradiol and dihydrotestosterone suppressed LH and FSH in all wethers, whilst oestradiol, but not dihydrotestosterone, also stimulated mating behaviour. The present findings indicate that testosterone imposes continuing negative feedback on gonadotrophin secretion and that changes in the gonadotrophin regulatory system, which lead eventually to a loss in sensitivity to testosterone feedback, develop soon after gonadectomy. The results also provide the first direct evidence that long-term gonadectomy in male sheep has differential effects on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. A loss in sensitivity to testosterone feedback in castrated animals may involve a lesion in 5α-reductase, the enzyme required for conversion of testosterone to dihydrotestosterone.
J. Endocr. (1985) 104, 69–75
Lactic acid and steroid production by intact mouse adrenal glands and cell suspensions: effects of nucleotide derivatives and substrates
Authors: Hinson J. , Birmingham M. K. 
Published: December 2008

ABSTRACT
The effects of the dibutyryl derivatives of cyclic GMP and cyclic AMP on lactic acid and steroid production were compared in intact mouse adrenal glands at concentrations of 0·5–1 mmol/l and in mouse adrenal cell suspensions at concentrations of 0·01–1 mmol/l. The dibutyryl derivative of cyclic GMP had little or no effect on lactic acid production in either tissue preparation. It caused a slight stimulation of corticosteroid output in intact glands at a concentration of 1 mmol/l, amounting to one-tenth of the response observed with 1 mm-dibutyryl cyclic AMP. Dose-dependent increases in lactic acid and steroid production were obtained with dibutyryl cyclic AMP in cell suspensions. AMP and GMP increased lactic acid but not steroid production.
All the substrates tested (glucose, glucose-6-phosphate, fructose, fructose-6-phosphate, fructose-1,6-diphosphate, 10 mmol/l; pyruvate and glycerol, 20 mmol/l) stimulated basal glycolysis in intact glands and cell suspensions and none affected basal steroid production significantly. By far the greatest increase in lactic acid production was noted with fructose-1,6-diphosphate. However, only glucose and, in unsectioned glands, pyruvate exerted a potentiating effect on the glycolytic response to ACTH. Glucose potentiated the steroidogenic response to ACTH also, but only in intact glands.
The relative ineffectiveness of dibutyryl cyclic GMP is in accord with the species-dependent differing responses to the free form of the cyclic nucleotides noted in mouse and rat adrenal glands. The substrate requirements are in keeping with a rate-limiting role of phosphofructokinase and an action of ACTH at some site between the entry of glucose into the cell and the formation of fructose-1,6-diphosphate.
J. Endocr. (1985) 104, 105–111
Influence of angiotensin II on the concentration of arterial plasma electrolytes in anaesthetized sheep
Authors: Osborn E. C. , Sugden P. L. , Mackenzie J. C. , Aitken D. M. , Chapman I. D. , Howes S. , Mason O. F. , Rigby G. V. , Wilson J. 
Published: December 2008

ABSTRACT
Angiotensin II and I significantly raised potassium and lowered sodium and chloride ion concentrations in arterial plasma, with peak changes occurring in the first 2 min of a 6-min infusion period. The octapeptide increased the arterial K+ level in a dose-dependent manner, but the response showed tachyphylaxis when multiple infusions of 6-min duration were administered after a recovery interval of only 5 min. Raising the arterial blood pressure by 20–33 mmHg with adrenaline and noradrenaline failed to account for the increase in arterial plasma K+ concentration produced by the two peptides. These findings, in particular the rise in K+ concentration, are discussed in relation to possible mechanisms by which angiotensin II affects arteriolar tone.
J. Endocr. (1985) 104, 143–148
Phenytoin and thyroid hormone action
Authors: Franklyn J. A. , Davis J. R. E. , Ramsden D. B. , Sheppard M. C. 
Published: December 2008

ABSTRACT
Circulating free thyroid hormone concentrations are reduced in subjects taking long-term phenytoin, a finding at variance with their euthyroid clinical state and normal serum TSH concentration. It is suggested, therefore, that phenytoin may modify the cellular effects of thyroid hormones.
In order to examine the influence of phenytoin on thyroid hormone action in the pituitary gland we studied its effect on the binding of tri-iodothyronine (T3) to isolated nuclei prepared from rat anterior pituitary tissue. Phenytoin inhibited the nuclear binding of T3 in a dose-dependent fashion. Phenytoin also partially inhibited thyrotrophin-releasing hormone-stimulated TSH release from cultured rat anterior pituitary cells. These studies provide evidence for a direct effect of phenytoin on the thyrotroph mediated via nuclear T3 receptor binding.
J. Endocr. (1985) 104, 201–204
Effects of antiserum to thyrotrophin-releasing hormone on the concentrations of plasma prolactin, thyrotrophin and LH in the pro-oestrous rat
Authors: Horn A. M. , Fraser H. M. , Fink G. 
Published: December 2008

ABSTRACT
The possible role of thyrotrophin-releasing hormone (TRH) in causing the pro-oestrous surge of prolactin was investigated in conscious female rats by passive immunization with a specific anti-TRH serum raised in sheep. Blood samples were withdrawn through a previously implanted intra-atrial cannula. The i.p. injection of 1 ml anti-TRH serum, but not non-immune sheep serum, at 13.00 h of pro-oestrus delayed by about 1 h the onset of the prolactin surge, but the peak of the surge was similar to that in animals injected with the non-immune serum. The plasma concentrations of TSH were significantly reduced by the anti-TRH serum, but plasma concentrations of LH were not significantly affected. These results show that TRH may play an important role in the timing and initiation, but not the maintenance of the prolactin surge in the pro-oestrous rat.
J. Endocr. (1985) 104, 205–209
Induction of precocious puberty in the female rat after chronic naloxone administration during the neonatal period: the opiate 'brake' on prepubertal gonadotrophin secretion
Authors: Sirinathsinghji D. J. S. , Motta M. , Martini L. 
Published: December 2008

ABSTRACT
Studies were undertaken using the opiate receptor antagonist naloxone to examine the hypothesis that endogenous opiates may have a restraining effect on prepubertal gonadotrophin secretion and may be involved in the maturation of the central nervous system mechanisms regulating the onset of puberty in the female rat. Naloxone (2·5 mg/kg) administered intraperitoneally every 6 h to female rats from day 1 to day 10 of postnatal life significantly (P <0·001) advanced the age of onset of puberty assessed in terms of the day of vaginal opening and first oestrus (32·3 ± 0·2 vs 40·8 ± 0·4 days in control saline-treated animals). Animals so treated with naloxone showed significantly (P < 0·001) higher levels of FSH (761·4 ± 87·6 vs 483·8± 57·2 μg/l in control animals) and LH (562·8 ± 57·4 vs 351·3 ± 43·3 μg/l in control animals) at the first late pro-oestrus and a significantly (P < 0·001) higher number of ova released at first oestrus (12·4 ± 0·4 vs 8·1±0·3 in controls). Body weight at first oestrus was significantly (P <0·001) lower in the naloxone-treated animals, an indication that these animals were much younger. The weights (per 100 g body wt) of the ovaries and uteri at the first oestrus were significantly (P <0·01) higher in the naloxone-treated rats than in the controls. However, there were no significant differences in the weights of the adrenals and anterior pituitary glands between the two groups of animals. A study of the cyclic patterns of the neonatally naloxone-treated animals performed for 15 consecutive cycles after the first oestrus showed normal 4- or 5-day cycles similar to those occurring in the saline-treated animals. The lengths of the first and second cycles in the naloxone-treated animals were not significantly different from controls. No significant differences in body weight or in organ weights at oestrus or in the levels of LH and FSH determined during the various stages of the oestrous cycle were found between naloxone- and saline-treated animals when these parameters were examined at 3 months of age. Naloxone had no effect on onset of puberty when administered during the other stages of prepubertal life. The mechanisms by which naloxone acts specifically during the neonatal period to induce precocious puberty are at present not known but are being investigated; they may be related to naloxone-induced alterations in the inhibitory synaptic arrangements between opiatergic and gonadotrophin-releasing hormone (GnRH) neurones, with a resulting decrease in the inhibitory influence exerted by endogenous opioids on GnRH neurones during this period of intense neurological development. The results suggest that the endogenous opiate peptides could play a key role in the central mechanisms which trigger the onset of puberty in the female rat.
J. Endocr. (1985) 104, 299–307
Social factors and puberty in female rats
Authors: Slob A. K. , van Es G. , van der Werff ten Bosch J. J. 
Published: December 2008

ABSTRACT
The effects of postweaning social conditions on the age of puberty were studied in female rats from an early-and a late-maturing strain. The postweaning living conditions consisted of the presence or absence of an adult rat (intact or gonadectomized male, or intact female), or of bedding soiled by adult males. The infantile females exposed to these conditions were caged either singly or with three peers. Puberty was studied in terms of first ovulation, verified always by ovarian histology.
Females of the late-maturing strain living without peers reached puberty about 2 days earlier than females that grew up in groups of four, irrespective of the presence or absence of an adult animal. In neither strain was puberty accelerated by the presence of intact males or the soiled bedding of such males.
These results do not support the view that in the rat pheromones from adult males enhance puberty in females, contrary to what is known to happen in the mouse.
J. Endocr. (1985) 104, 309–313