bluuebunny/crossref_metadata_2025_split huggingface dataset:
RELEASE, DISTRIBUTION AND HALF-LIFE OF α-MELANOTROPHIN IN THE RAT
Authors: WILSON J. F. , HARRY FRANCES M. 
Published: December 2008

Concentrations of α-melanotrophin in the plasma of anaesthetized rats were measured by radioimmunoassay at intervals of 2–10 min. Although significant increases of three to ten times in the concentration of α-melanotrophin occurred over periods of 15–35 min, levels of hormone could also be stable for periods of greater than 1 h. The data did not indicate separate secretory episodes but rather a continuous release of α-melanotrophin by the pituitary gland. A very rapid pulsatile secretion operating over periods of less than 5 min cannot be excluded.
Intravenous injection of synthetic α-melanotrophin was followed by a biexponential decline in levels of hormone in plasma indicating a rapid distribution to the extracellular fluid and a slower elimination by metabolism. The apparent volume of distribution of α-melanotrophin was 210 ml/kg, the half-life for elimination 7·1 min and the estimated clearance 1·55 nmol/day per kg.
EFFECTS OF ANDROGENIC AND OESTROGENIC HORMONES ON MATING BEHAVIOUR IN RAMS CASTRATED BEFORE OR AFTER PUBERTY
Authors: D'OCCHIO M. J , BROOKS D. E. 
Published: December 2008

Adult sheep which had been castrated either before or after puberty were treated with a variety of steroids. The administration of testosterone propionate, oestrone, oestradiol-17β or diethylstilboestrol to animals castrated before puberty caused them to mount oestrous ewes. Oestradiol-17α was less effective than these hormones in this regard, whilst oestriol, hexoestrol and 5α-dihydrotestosterone were ineffective. The response to oestradiol-17β was not altered by the concurrent administration of dexamethasone to block the pituitary–adrenal axis which suggests that oestradiol-17β was not exerting its effect indirectly by causing the release of adrenal steroids. When 5α-dihydrotestosterone was administered in conjunction with oestradiol-17β intromission and ejaculation were observed in addition to mounting behaviour.
When rams were castrated as adults their mating behaviour slowly declined over the course of 2 years. After this time, mounting behaviour was rapidly restored by the administration of oestradiol-17β but not by 5a-dihydrotestosterone. These results are consistent with the hypothesis that oestrogens are the ultimate agents responsible for promoting mating behaviour in male animals and hence aromatizable androgens, such as testosterone, are effective whereas non-aromatizable androgens, such as 5α-dihydrotestosterone, are not.
DIFFERENTIAL EFFECTS OF ESTRAMUSTINE PHOSPHATE UPON CELL PROLIFERATION IN MOUSE ACCESSORY SEX GLANDS
Authors: ALISON M. R. , WRIGHT N. A. 
Published: December 2008

The effects of estramustine phosphate (EMP) have been measured during the proliferative response of the seminal vesicle and coagulating gland of the castrated mouse after continuous treatment with testosterone. Daily subcutaneous injections of 60 μg testosterone were begun 14 days after castration. Three daily injections of EMP (100 mg/kg body wt) were begun on either day 11 or day 13 after castration. Cell proliferation was monitored by [3H]thymidine-labelling techniques combined with autoradiography, and by determinations of mitotic index.
Treatment with EMP on days 11, 12 and 13 after castration almost completely blocked the testosterone-induced proliferative response in the coagulating gland. Treatment with EMP commencing on day 13 after castration was less effective. Estramustine phosphate had a small stimulatory effect on DNA synthesis and mitosis in the seminal vesicle. Measurements of 5α-reductase activity in vitro did not reflect the dynamic cell kinetic changes observed in both tissues in vivo. We have concluded that previous assay systems using the Coffey model are unsuitable for the assessment of antiandrogens and prostatic anti-cancer drugs.
ADRENALECTOMY HAS A DIFFERENTIAL EFFECT ON THE OVARIAN RESPONSE OF TWO STRAINS OF RAT
Authors: JACOBS J. J. , PEPPLER R. D. 
Published: December 2008

Evidence indicates that the ovarian regulatory mechanism of different strains of rat may respond differently to adrenalectomy; this study examined that possibility.
Adult female Sprague–Dawley and Holtzman rats were maintained under constant environmental conditions and each strain was divided into groups: intact; adrenalectomized; unilaterally ovariectomized; adrenalectomized and unilaterally ovariectomized for 30 days; adrenalectomized 30 days previously and then unilaterally ovariectomized followed by one oestrous cycle; adrenalectomized 30 days previously and then unilaterally ovariectomized followed by one oestrous cycle with progesterone treatment (2 mg); adrenalectomized 30 days previously and then unilaterally ovariectomized followed by one oestrous cycle with corticosterone treatment (2·5 mg/100 g). All operations and autopsies were performed at metoestrus. Chronically adrenalectomized rats shed fewer ova per ovary than intact animals. Rats that had been unilaterally ovariectomized or adrenalectomized and unilaterally ovariectomized for 30 days showed compensatory ovulation as compared with intact rats and rats adrenalectomized for 30 days. Only the Sprague–Dawley rats that were adrenalectomized for 30 days and unilaterally ovariectomized for one oestrous cycle demonstrated compensatory ovulation. The remaining ovary in similarly treated Holtzman rats failed to compensate. Neither progesterone nor corticosterone influenced compensatory ovulation in the Sprague–Dawley rats, but both hormones caused an increase in the number of eggs ovulated in the Holtzman animals. In conclusion, the results of this study indicated that there is a strain-specific responsiveness of the ovary to adrenalectomy as assessed by compensatory ovulation.
CHANGES IN THE BINDING OF HUMAN CHORIONIC GONADOTROPHIN/LUTEINIZING HORMONE, FOLLICLE-STIMULATING HORMONE AND PROLACTIN TO HUMAN CORPORA LUTEA DURING THE MENSTRUAL CYCLE AND PREGNANCY
Authors: McNEILLY A. S. , KERIN J. , SWANSTON I. A. , BRAMLEY T. A. , BAIRD D. T. 
Published: December 2008

The changes in the binding of human chorionic gonadotrophin/luteinizing hormone (HCG/LH), follicle-stimulating hormone (FSH) and prolactin to 44 corpora lutea have been assessed during the luteal phase of the human menstrual cycle and early pregnancy. All corpora lutea bound HCG but out of 32 only ten bound FSH and only seven bound prolactin specifically. While binding of HCG increased to maximal levels in the mid-luteal phase, binding of FSH and prolactin was most often found in the early luteal phase. Maximum binding of HCG was associated with maximum serum levels of progesterone. Luteal regression was associated with a decrease in the binding of HCG but a causal relationship could not be established. Very low binding of HCG was found to corpora lutea of pregnancy.
These results show that (1) the changes in binding of HCG during the luteal phase of the human menstrual cycle are similar to those in other species and (2) there are specific binding sites for prolactin and FSH in the human corpus luteum.
CULTURE SENSITIZATION AND INHIBITION OF LUTEINIZING HORMONE RESPONSIVE PRODUCTION OF CYCLIC AMP IN LUTEAL CELLS BY LUTEINIZING HORMONE, PROSTAGLANDIN F2α AND [d-Trp6]-LUTEINIZING HORMONE RELEASING HORMONE
Authors: HALL A. K. , BEHRMAN H. R. 
Published: December 2008

Many cells are able to regulate their sensitivity to hormones. In order to investigate the mechanism(s) by which rat luteal cells regulate their sensitivity to LH, we have developed and characterized a cell culture model. Cultures of dispersed rat luteal cells were exposed to graded doses of bovine LH, an analogue of LH releasing hormone (LH-RH) ([d-Trp6]-LHRH), and prostaglandin F2α (PGF2α) for 3 h. The media containing these hormones were then replaced with fresh hormone-free medium and the cells cultured for 24 h. In order to test the sensitivity of these cultures after 24 h, the medium was discarded and replaced by medium alone, or medium containing a standard dose of bovine LH for 1 h. The amount of cyclic AMP accumulated during this hour was used as an index of the sensitivity of the cells to LH.
Control cultures became 'supersensitive' to LH with augmented production of cyclic AMP during culture but LH-receptor binding activity was not increased. During the first 2 h of culture, LH (100 ng/ml) increased accumulation of cyclic AMP by fourfold, but after 5 h of culture, stimulation of cyclic AMP accumulation by the same dose of LH was increased 32-fold, 299-fold at 13 h and 359-fold at 21 h of culture. The increase in LH-responsive accumulation of cyclic AMP with culture was severely impaired by early exposure of cells to LH, LH-RH analogue or PGF2α during the first 2 h of culture. Also, both LH-RH analogue and PGF2α acutely inhibited LH-stimulated accumulation of cyclic AMP. Inhibition of culture-induced sensitization of LH responsiveness was not altered by the addition of 3-isobutyl-l-methylxanthine. Scatchard analysis of LH binding sites indicated that pretreatment of luteal cells with LH (or human chorionic gonadotrophin at an equivalent dose) reduced the number of free LH receptors when measured after 24 h of culture, but total receptor binding activity was not changed. However, a similar effect was not seen with cells treated with PGF2α or LH-RH analogue.
It is suggested that 'culture-induced' supersensitivity may represent either recovery of preisolation sensitivity or result from the loss of an endogenous factor(s) which retards the coupling of the LH receptor and adenylate cyclase. Although PGF2α and LH-RH analogue have been shown to directly prevent the occupied LH receptor from activation of adenylate cyclase, the present observations have indicated that this inhibitory process was continued even when these agents were removed from the culture medium.
EFFECTS OF TREATMENT WITH ADRENOCORTICOTROPHIN ON THE HYPOTHALAMO-PITUITARY-ADRENAL SYSTEM
Authors: STARK E. , KÄRTESZI M. , RAPPAY GY. , MAKARA G. B. 
Published: December 2008

Long-term treatment with adrenocorticotrophin (ACTH) inhibited the stress-induced response of the hypophysial-adrenocortical system 24 h after the final ACTH injection. The mechanism of this phenomenon was studied in both normal and adrenalectomized rats, the latter receiving corticosterone at various doses.
The effect of electrical stimulation of the medial basal hypothalamus on the concentration of corticosterone in plasma (an indicator of ACTH secretion), the corticotrophin releasing factor (CRF) content of the stalk median eminence (SME), the ACTH content of the pituitary gland and the in-vitro release of ACTH by the pituitary gland incubated with or without addition of SME extract were investigated.
Electrical stimulation of the medial basal hypothalamus failed to induce a rise in concentrations of corticosterone in plasma of normal rats treated with ACTH; moreover the levels of hypothalamic CRF and hypophysial ACTH were significantly decreased.
Hemipituitary glands of ACTH-treated rats released markedly less ACTH in vitro in response to SME extract than did the control glands. This indicated that long-term hormone administration caused a serious impairment of the responsiveness of the corticotrophic cells toward CRF.
Pituitary ACTH content and in-vitro responsiveness of pituitary glands obtained from ACTH-treated, adrenalectomized rats receiving corticosterone replacement seemed to be dependent on the amount of exogenous corticosteroid, but not on that of exogenous ACTH.
Our previous and present findings suggest that long-term treatment with ACTH elicits repeatedly increased secretion of endogenous corticosterone, impairing the stress-induced CRF–ACTH release at both the hypothalamic and hypophysial levels. Our data challenge the view that ACTH itself is able to inhibit its own secretion.
INDEPENDENT DOWN-REGULATION OF INSULIN AND CALCITONIN RECEPTORS ON A HUMAN TUMOUR CELL LINE
Authors: FINDLAY D. M. , DE LUISE M. , MICHELANGELI V. P. , MARTIN T. J. 
Published: December 2008

A human lung cancer cell line (BEN cells) with a calcitonin receptor and calcitonin-responsive adenylate cyclase also possesses an insulin receptor. This has been characterized and found to have properties similar to those of other mammalian cell insulin receptors. A receptor number of 58 000 per cell was calculated from curvilinear Scatchard plots, and dissociation of bound labelled insulin by dilution was facilitated by the addition of unlabelled insulin, consistent with negatively co-operative interactions among binding sites.
Preincubation of cells with either calcitonin or insulin led to loss of hormone binding in washed cells. In the case of calcitonin this was associated with loss of adenylate cyclase response. For each hormone the state of down-regulation was characterized by a decrease in receptor number, and for calcitonin there was also a loss in sensitivity of adenylate cyclase. Down-regulation to calcitonin was more rapid than that to insulin and in each case recovery had occurred by 16 h after removal of the hormone. Induction of down-regulation was specific, in that preincubation with one hormone did not influence the subsequent binding or response of the other. Such data are consistent with independent modulation of peptide receptors in the same cell.
EFFECTS OF HISTAMINE IMPLANTS IN SEVERAL BRAIN REGIONS ON THE RELEASE OF PROLACTIN IN CONSCIOUS ADULT MALE RATS
Authors: ALVAREZ E. O. , DONOSO A. O. 
Published: December 2008

The levels of prolactin in the plasma of conscious male rats were determined at various times after an acute administration of histamine or a histamine releasing agent, compound 48/80, in three brain regions. The brain structures that were examined were, the caudal part of the preoptic area and anterior part of the anterior hypothalamic area (POA–AHA), the arcuate nucleus–ventromedial nucleus region (ARC–VMN) and the medial–basal amygdaloid nucleus of the limbic system (AME).
A marked increase in plasma levels of prolactin was observed when implants of histamine were in the POA–AHA region. A more consistent increase was found when 1 μg histamine was injected in the same region; values of prolactin were about 3·6 times greater than in their controls injected with 0·9% saline. Such increased hormone levels lasted up to 2 h. A similar rise in prolactin level was found when the implants of histamine were located in the ARC–VMN region. When compound 48/80 or empty cannulae were placed in those brain regions that were examined, no changes in plasma levels of prolactin were induced.
Both histamine and compound 48/80 elicited a delayed and long-lasting decrease of the high plasma level of prolactin present in rats bearing cannulae in the AME region.
The results suggest that in the male rat, histaminergic sites, located in rostral and mediobasal hypothalamus and in the central area of the amygdala, are involved in the mechanisms controlling prolactin secretion.
ROLE OF PROGESTERONE IN THE CONTROL OF SECRETION OF FOLLICLE-STIMULATING HORMONE IN THE IMMATURE FEMALE RAT
Authors: MEIJS-ROELOFS H. M. A. , KRAMER P. , GRIBLING-HEGGE L. 
Published: December 2008

The inhibitory action on FSH secretion of combined oestradiol and progesterone treatment of ovariectomized, immature rats was studied at various ages. At all ages studied (13–35 days) an additional inhibitory action of progesterone, if combined with oestradiol, could be found as compared with the effect of oestradiol alone. Until 20 days of age, the rise in serum FSH concentration as measured 2 days after ovariectomy could be completely prevented by administration of 0·05 μg oestradiol/100 g body weight or by administration of a lower dose of oestradiol (0·01–0·025 μg) combined with progesterone (0·5–1·5 mg/100 g body weight). After 20 days neither oestradiol nor the combined oestradiol/progesterone treatment resulted in an FSH concentration similar to that found in intact rats. However, the lowest FSH concentrations were reached by using combinations of oestradiol and progesterone.
Using progesterone alone, FSH concentration in ovariectomized rats was significantly reduced between 18 and 30 days of age, but not before or after this period.
Taken together with data on uterine weight and serum concentrations of progesterone, these findings suggest that (1) both oestradiol and progesterone exert an age-dependent role in regulating FSH secretion in the immature female rat, and (2) amounts of oestradiol and progesterone capable of maintaining, in ovariectomized rats, uterine weights not different from those in intact rats will maintain near-physiological concentrations of FSH before but not after day 20. Thus, ovarian factors other than oestradiol and progesterone must be involved in the regulation of FSH secretion in the female rat after 20 days of age.
ONTOGENETIC DEVELOPMENT OF THE INHIBITION OF GROWTH HORMONE RELEASE BY SOMATOSTATIN IN THE RAT: IN-VIVO AND IN-VITRO (PERIFUSION) STUDY
Authors: RIEUTORT MICHEL 
Published: December 2008

An in-vitro study of GH secretion by rat fetal and neonatal pituitary glands was conducted using a perifusion system. After a 2 h period the GH content of the effluent was constant. Theophylline, thyrotrophin releasing hormone (TRH) and rat stalk median eminence extract (SME) were effective stimuli of GH release from the pituitary glands of the 19·5-day-old fetuses. Somatostatin, added to the medium (10 μg/ml), had no inhibitory effect on GH release (basal or stimulated by either theophylline or SME) before day 4 after birth. After postnatal day 5, somatostatin always inhibited GH secretion. These findings were consistent with the results of experiments in vivo. In rats tested within 4 days of birth, sodium pentobarbitone-stimulated plasma GH levels were not reduced by somatostatin; on day 4 and thereafter somatostatin depressed the response to pentobarbitone injection.
These results indicate a postnatal maturation of the regulation of GH release by the hypothalamo–hypophysial system in the rat.
IMMUNOREACTIVE GROWTH HORMONE LEVELS DURING THE HORMONAL INDUCTION OF LACTATION AND DURING HAND-MILKING IN EWES
Authors: HOOLEY R. D. , SCHAMS D. , FINDLAY J. K. 
Published: December 2008

Growth hormone was measured by radioimmunoassay in blood samples collected from ewes during the hormonal induction of lactation and during hand-milking post partum. Ovariectomized ewes were induced to lactate with injections of progesterone + oestradiol benzoate every 3 days for 30 days (priming phase) and then daily injections of dexamethasone for 5 days (trigger phase). The ewes were then milked daily. Immunoreactive GH levels fluctuated considerably but were generally in the range 1–15 ng/ml during all phases of lactation and were unaffected by bromocriptine treatment. Milk yield was unrelated to GH levels.
Growth hormone was also measured in blood plasma taken at frequent intervals around the time of milking in lactating ewes approximately 4 weeks post partum. Although a clear prolactin response to milking was observed, there was no indication of a GH response.
Although there is probably a minimum requirement for GH for lactation, a relationship between immunoreactive GH levels and milk yields was not established, perhaps because of limitations of the radioimmunoassay to detect all the biologically active GH.
EFFECTS OF ACUTE NEUROTROPHIC STRESS ON PERIPHERAL METABOLISM OF CORTISOL IN CONSCIOUS MALE GUINEA-PIGS
Authors: MANIN M. , DELOST P. 
Published: December 2008

Cortisol metabolism was studied in conscious adult male guinea-pigs subjected to a neurotrophic stress (immobilization and stimulation by light for 3 h).
The disappearance curves of tracer quantities of [3H]cortisol were represented by a two-pool model. In stressed animals, there was a marked increase in the mean plasma level of cortisol (184% of control value; P <0·001) and in the metabolic clearance rate (MCR; 17% of control value; 0·001 <P <0·01). This rise in the MCR of plasma cortisol resulted from an increase in the mean total apparent volume of distribution (49%, P < 0·001). The lack of significant differences in the slopes of the second exponential phase of the disappearance curves indicated that the stress did not significantly increase the half-life of cortisol. The mean binding capacity of transcortin for cortisol (ST) was significantly higher in the animals which had been subjected to the neurotrophic stress than in the control guinea-pigs (0·02 < P <0·05). However, ST values remained very low and accounted for the very high levels of free cortisol found after the stress. The results suggest that the raised concentrations of unbound cortisol found in the plasma of conscious adult male guinea-pigs in response to neurotrophic stress reflect a hypersecretion of corticosteroid.
ELECTROPHYSIOLOGICAL RECORDINGS FROM OXYTOCINERGIC NEURONES DURING SUCKLING IN THE UNANAESTHETIZED LACTATING RAT
Authors: SUMMERLEE A. J. S. , LINCOLN D. W. 
Published: December 2008

A method is described for making extracellular recordings of the spontaneous activity of single hypothalamic neurones in unanaesthetized, freely moving, lactating rats using chronically implanted micro-wire electrodes. Extracellular recordings taken from individual neurones were maintained for periods of between 1 and 12 days. These records were not affected by any normal movement of the animal. As several micro-wires were implanted into each animal it was possible to make simultaneous recordings from several different hypothalamic sites in the same animal. Some recordings were identified as those from magnocellular neurones in the paraventricular nucleus on the basis of antidromic invasion after electrical stimulation of the neurohypophysis.
Milk ejection in response to the prolonged sucking of ten or more pups was intermittent, and individual milk ejections recurred at intervals of 2–10 min throughout each period of nursing. The rise in intramammary pressure at milk ejection was associated with a vigorous extensor response from the pups. This was monitored by radar to provide an index of milk ejection in the unanaesthetized rat.
Eleven antidromically identified neurones were recorded through 321 milk ejections. Eight of these neurones displayed a transient (2–6 s) and very substantial acceleration in discharge at the time predicted for oxytocin release, i.e. 10–12 s before milk ejection. The background discharge of these cells was 0·1–2·6 action potentials/s; this increased to 16–50 action potentials/s during the brief period of accelerated activity. Twenty-five neurones were studied during 365 milk ejections in rats which did not have a stimulating electrode implanted in the neurohypophysis. Thirteen of these neurones displayed a burst of high frequency discharge before each milk ejection, similar to that described for the antidromically identified neurones. Two of the non-responsive cells displayed a phasic pattern of discharge, characteristic of vasopressinergic neurone discharge recorded in anaesthetized rats.
These observations of putative oxytocinergic neurones in unanaesthetized, freely moving rats are identical with those previously made on anaesthetized rats, and establish that the high frequency burst of electrical activity displayed by magnocellular neurones some 10–12 s before milk ejection is responsible for oxytocin release under normal physiological circumstances.
2-HYDROXYOESTRADIOL INHIBITS PROLACTIN RELEASE FROM THE SUPERFUSED RAT PITUITARY GLAND
Authors: LINTON ELIZABETH A. , WHITE NICKI , LIRA DE TINEO OFELIA , JEFFCOATE S. L. 
Published: December 2008

The effects of 2-hydroxyoestradiol (2OH-OE2), dopamine, oestradiol-17β and 2OH-OE2 plus dopamine on prolactin and LH release from the male rat pituitary gland were examined in vitro.
2-Hydroxyoestradiol reduced prolactin secretion by 51% at 10−10 mol/l and by 34% at 10−7 mol/l, while oestradiol-17β had no effect at these doses. Dopamine alone (5 × 10−7 mol/l) decreased prolactin released by 58%, 2OH-OE2 plus dopamine produced a similar inhibition of 60%.
No significant effect on LH release was observed throughout.