bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF PROGESTERONE AND ITS INTERACTION WITH OESTRADIOL IN HYPOTHALAMIC AND RAPHE NUCLEI ON LUTEINIZING HORMONE IN PLASMA
Authors: WANDSCHEER D. E. , ALESSIO M. L. , LADOSKY W.
Published: December 2008

Microinjection of progesterone into the preoptic area (POA) of the rat on either day 2 of dioestrus or the morning of pro-oestrus inhibited the ovulatory peak of LH which would normally appear during the afternoon of pro-oestrus. However, when progesterone plus oestrogen were used, the inhibition of the surge of LH was observed only if the microinjection was applied on the morning of day 2 of dioestrus. Microinjection of progesterone into the medial basal hypothalamus (MBH) at day 2 of dioestrus advanced the ovulatory peak by 24 h. This effect was also observed when progesterone and oestrogen were simultaneously infused. Progesterone injected into the MBH on the morning of pro-oestrus significantly increased the release of LH during the afternoon. This effect was also observed when progesterone plus oestrogen were simultaneously infused. Application of progesterone alone or with oestrogen to the nucleus dorsalis raphe on the morning of either day 2 of dioestrus or pro-oestrus induced a significant decrease of the levels of LH in plasma and prevented the appearance of the ovulatory peak during the afternoon of pro-oestrus. These findings indicated that these two steroids have differential actions when infused into various hypothalamic and extrahypothalamic nuclei. Consequently, it is concluded that in studies on the effects of ovarian hormones it is important to take into account not only the isolated action of each one of them, but also their interaction on the effects of the diverse neural structures involved in the control of ovulation on each day of the ovulatory cycle.
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.
ROLE OF THE HETEROGENEITY OF THYROGLOBULIN IN THE SECRETION OF THYROID HORMONE IN MICE
Authors: BAGCHI N. , BROWN T. R. , SHIVERS B. , MACK R. E.
Published: December 2008

The rates of thyroglobulin hydrolysis and iodothyronine release from mouse thyroid glands were studied in vitro. Recently iodinated thyroglobulin ('new pool') had been labelled during life by injection of 131I 3 h before removal of the thyroid, 'old pool' thyroglobulin had been labelled by the administration of 125I in the drinking water for 1 week starting 3 weeks earlier. Chromatographic analysis of pronase digests of the thyroid glands showed that the iodothyronine content of the old and new pools were 19·5 and 7·4 per cent respectively. In the basal state the rate of thyroglobulin hydrolysis was lower from the old pool but the rate of hormone secretion was similar from both pools. Thyrotrophin (TSH) increased the rate of thyroglobulin hydrolysis and hormone release from both pools by up to four to six times the basal rate, the effect being maximal 2 h after administration of TSH and lasting for 6–8 h. The rate of thyroglobulin hydrolysis after TSH was similar in both pools but the rate of release of labelled iodothyronines was significantly higher from the old pool. These studies have indicated that although hydrolysis of thyroglobulin proceeds faster in the new pool than in the old ('last come, first served' hypothesis) nevertheless there is no difference in the rate of hormone secretion from the two pools, and hydrolysis in both pools is affected by TSH.
CIRCADIAN VARIATION IN CONCENTRATIONS OF TESTOSTERONE IN THE PLASMA OF MALE MICE: A DIFFERENCE BETWEEN BALB/cBy AND C57BL/6By INBRED STRAINS
Authors: LUCAS LINDA A. , ELEFTHERIOU B. E.
Published: December 2008

Diurnal variations in testosterone in plasma were studied in two inbred strains of mice, BALB/cBy and C57BL/6By. Blood was taken every 4 h over 24 h from male mice at 70 days of age using a lighting regimen of 12 h light to 12 h darkness (lights on 07.00–19.00 h). Values of testosterone in plasma were transformed to log(testosterone in ng/ml) to reduce inequality of variance between groups. In both strains, the distribution of pooled values over all times of day was bimodal, and bimodality was present at most times of day. Circadian variation was evaluated by dividing the transformed values into high and low modes at each time of day and testing for significant variation in the number of animals in each mode over time using the chi-squared test. Significant circadian variation was found in the BALB/cBy strain of mice but not in the C57BL/6By strain. The highest number of high mode cases for BALB/cBy mice was at 22.00 h and the lowest number of high mode cases was at 10.00 h. The log transformation and bimodality of these values are presented as biological expressions of blood levels of testosterone and of tissue responses to these levels in the male mouse. The strain difference in circadian variation may be related to reported circadian changes in behaviour and to possible genetic effects on sensitivity to environmental change or capacity to express circadian rhythms.
COMPARISON OF THE REGULATION OF CALCITONIN IN SERUM OF OLD AND YOUNG BUFFALO RATS
Authors: QUEENER SHERRY F. , BELL N. H. , LARSON SARAH M. , HENRY D. P. , SLATOPOLSKY EDUARDO
Published: December 2008

Studies were carried out to characterize the secretion and the effects of calcitonin in the Buffalo rat. Mean basal concentrations of calcitonin and parathyroid hormone were significantly increased in serum of rats older than 6 months of age as compared with rats between 2 and 3 months of age. The mean concentration of calcium in serum was independent of age. In both age groups, serum calcitonin was increased by administration of calcium (1 mmol/kg body wt) or isoproterenol (100 μg/kg body wt), was diminished by β-adrenergic blockade with dl-propranolol (1 mg/kg body wt) and was not altered by either pentagastrin or glucagon (200 and 100 μg/kg body wt respectively). The average weight of the thyroid glands was significantly greater in the old than in the young animals but the mean concentration of calcitonin in the thyroids was the same. Thyroparathyroidectomy produced a transient increase followed by a fall in mean serum calcium in the old rats. In contrast, a progressive decline in the mean concentration of calcium in serum was observed after thyroparathyroidectomy in the young rats. Treatment of old animals with reserpine (2·5 mg/kg body wt) markedly depleted noradrenaline in the thyroid, lowered calcitonin in serum and converted the pattern of response of serum calcium to thyroparathyroidectomy to that observed in young animals. The results provide evidence that hypercalcitonaemia occurs in aged Buffalo rats, as does hyperparathyroidism, and that the concentrations of calcitonin in blood are modulated by β-adrenergic affectors. Glucagon and pentagastrin exhibit little if any effects on calcitonin secretion in this strain of rat regardless of age.
MODULATION OF CYCLIC AMP IN ISOLATED RAT UTERINE TISSUE SLICES BY PORCINE RELAXIN
Authors: JUDSON D. G. , PAY SARAH , BHOOLA K. D.
Published: December 2008

Porcine relaxin produced a rapid, dose-related rise of cyclic AMP values in rat uterine tissue incubated in vitro. In time-course experiments, peak cyclic AMP concentrations were observed in the uterine slices at 5 min; subsequently the values fell, at first rapidly and then more slowly with the tissue concentration remaining significantly raised at 15 min. Levels of cyclic GMP in the same tissue slices were not significantly altered by relaxin. Furthermore, no increase in basal cyclic AMP values was measured in control slices prepared from the rat heart or jejunum. An increase in cyclic AMP concentration comparable to that found in the rat uterus was observed in slices of porcine uterus and cervix but not of vagina when they were stimulated with porcine relaxin. Our results suggest that the hormonal action of relaxin on the uterus and cervix is mediated through receptors linked to the enzyme, adenylate cyclase.
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.
RESPONSIVENESS OF THE PITUITARY GLAND TO ANDROGENS AND OF THE TESTIS TO GONADOTROPHINS FOLLOWING DAMAGE TO SPERMATOGENESIS IN RATS
Authors: MAIN S. J. , SETCHELL B. P.
Published: December 2008

To test the interaction of androgen and inhibin feedback on the pituitary gland, inhibin-type feedback from the testes was reduced when they were made aspermatogenetic by bilateral ligation of the efferent ducts or local heating (43 °C for 30 min). There were only minor effects on the subsequent response of the pituitary gland to the removal of androgen feedback by the administration of antiserum against testosterone or by castration. However, in the antiserum-injected animals the steroidogenic response of the testis to the increased serum concentrations of LH was less in aspermatogenic than in control rats. Furthermore, unilateral aspermatogenesis was associated with reduced testosterone output by the treated testis and with compensatory increased output by the contralateral control testis, despite the absence of significant changes in serum LH and normal peripheral levels of testosterone. This suggests that the tubules can regulate the responsiveness of the Leydig cells to LH.
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.
EFFECTS OF INHIBITING PROLACTIN SECRETION ON THE MAINTENANCE OF EMBRYONIC DIAPAUSE IN THE SUCKLING RAT
Authors: GOSDEN R. G. , RUSSELL J. A. , CLARKE J. , PIPER I. , McNEILLY A. S.
Published: December 2008

Treatment of rats with bromocriptine between days 5 and 8 after the post-partum mating resulted in suppression of serum prolactin levels and caused luteal regression. Although this treatment led to embryonic resorption when suckling was prevented by removing litters soon after birth, the diapausing embryos of animals nursing a litter of eight pups were unaffected by the treatment. These results suggest that the high levels of prolactin and progesterone in the circulation during lactation are not responsible for maintenance of the diapausing state.
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.
CHANGES IN FOLLICLE-STIMULATING HORMONE, LUTEINIZING HORMONE, PROLACTIN, OESTRADIOL AND PROGESTERONE CONCENTRATIONS IN THE SERA OF ANOVULATORY ANDROGENIZED FEMALE AND CASTRATED MALE PARABIOTIC RATS OF THE FISCHER-344 STRAIN
Authors: JOHNSON D. C.
Published: December 2008

The serum concentrations of FSH, LH and prolactin, as well as oestradiol and progesterone, were measured by immunoassays at various intervals up to 35 weeks after parabiotic union of an anovulatory androgenized female and a castrated male rat of the Fischer-344 strain. Modest increases in FSH (28%) and larger increases in LH (128%), compared to levels found in single adult animals, produced large increases in follicular growth, ovarian weight and oestrogen production in the female partners; thecal and interstitial elements of the ovaries were not heavily stimulated. Prolactin concentrations in the sera increased to exceedingly high levels and massive pituitary tumours were produced in all of the female partners. Development of cystic follicles with loss of granulosa-cell layers and the formation of early stages of granulosa-cell tumours progressed with time in union. Serum LH levels were as high in parabiotic as in single castrated male rats within 2 weeks, but concentrations of FSH remained much below those of the single animals until 27 weeks after castration. The results are consistent with the view that the ovaries of androgenized female rats of the Fischer strain produce some factor which prevents the post-castration rise in FSH of parabiotic male partners.
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.
IMPORTANCE OF THE EPISODIC NATURE OF LUTEINIZING HORMONE SECRETION FOR NORMAL DEVELOPMENT OF THE BOVINE TESTIS DURING PUBERTY: INTERFERENCE WITH OESTRADIOL-17β
Authors: SCHANBACHER B. D.
Published: December 2008

An experiment was conducted to determine the importance of episodic LH secretion during pubertal development in beef bulls. Testicular growth, LH secretory patterns and serum testosterone concentrations were monitored in control bulls, and bulls implanted with one or two oestradiol-filled capsules from 26 to 38 weeks of age. Control but not oestradiol-treated bulls showed normal testicular growth and episodic LH secretory patterns. Serum LH and testosterone responses of 38-week-old control and oestradiol-treated bulls to an intravenous challenge of 5 μg LH releasing hormone indicated normal pituitary responsiveness, but steroidogenic responsiveness had not yet developed in oestradiol-treated bulls. Removal of the capsules at 38 weeks of age resulted in a normal episodic release pattern for LH, with concomitant growth of the underdeveloped testes up to 44 weeks of age. Serum concentrations of LH and testosterone were within the range of normal, adult values by 42 weeks of age. These results suggest that oestradiol can interfere with episodic LH secretion and normal pubertal development in beef bulls, and furthermore that episodic LH secretion is commensurate with the establishment of normal development of the bovine testis during puberty.
DISAPPEARANCE OF IMMUNOREACTIVE α-MELANOTROPHIN FROM RAT PLASMA FOLLOWING OCCLUSION OF DIFFERENT REGIONS OF THE VASCULAR BED
Authors: LAMBERT T. R. , WILSON J. F.
Published: December 2008

The half-life for the disappearance of immunoreactive α-melanotrophin in plasma following intravenous injection of synthetic hormone was measured before and after occlusion of the blood supply to certain organs in the anaesthetized rat. Occlusion of the blood supply to the liver, gut, spleen and pancreas, and of the renal circulation caused non-significant increases in half-life of 2·8 and 10·7% respectively. The importance of peripheral tissues in the clearance of α-melanotrophin was demonstrated by the significant 63·4% increase in half-life caused by occlusion of the blood supply to sections of skeletal muscle, fat and skin.
HORMONAL CONTROL OF THE GONADAL REGRESSION AND RECOVERY OBSERVED IN SHORT DAYS IN MALE AND FEMALE DOVES
Authors: BALTHAZART JACQUES , BALTHAZART-RAZE CLAIRE , CHENG MEI-FANG
Published: December 2008

Sexually mature ring doves (Streptopelia risoria) maintained from hatch on a photoperiod of 14 h light: 10 h darkness (14L : 10D) and kept in isolation were transferred to 8L : 16D. This treatment resulted in a partial regression of the ovaries and testes and a fall in the concentration of plasma LH but not of plasma FSH. After 2–3 months exposure to 8L : 16D, the gonads regrew to their original size: this regrowth was accompanied by a parallel increase in the concentration of plasma LH. The responsiveness of the pituitary gland to LH releasing hormone in both sexes after 5 weeks of exposure to 8L : 16D (when the gonads were partially regressed) was similar to the response observed after 15 weeks exposure to this lighting schedule (when the gonads had regrown). It was concluded that the spontaneous recovery of gonadal size in ring doves exposed to 8L : 16D is controlled by the hypothalamus and does not involve changes in the functional capacity of the pituitary gland or of the gonads.
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.
TIME-RELATED EFFECTS OF EN-CLOMIPHENE UPON CENTRAL AND PERIPHERAL OESTROGEN TARGET TISSUES AND CYTOPLASMIC RECEPTORS
Authors: BOWMAN S. P. , LEAKE A. , MORRIS I. D.
Published: December 2008

The temporal effects of the oestrogen antagonist en-clomiphene were studied in the 3 week ovariectomized rat for up to 24 days after a single dose of 0·5 or 50 mg/kg. Cytosol binding of [3H]oestradiol was measured in central and peripheral target tissues. One day after treatment both doses of en-clomiphene decreased binding of [3H]oestradiol to similar levels within tissues. In brain cytosols binding of [3H]oestradiol returned to expected control values by 16 days with the exception of the hypothalamic cytosol after treatment with 50 mg/kg which, paradoxically, achieved control levels by 8 days. However, a single-point saturation assay was inadequate for the measurement of high-affinity oestrogen receptors in brain tissue. Uterine binding of [3H]oestradiol returned to control levels by 2 and 16 days after treatment with 0·5 and 50 mg/kg respectively. Replenishment of [3H]oestradiol binding was slower in pituitary cytosol and was achieved by 8 and 24 days after treatment with 0·5 and 50 mg/kg respectively. En-clomiphene was uterotrophic; the maximal increase was at 4 days and 1 day after 0·5 and 50 mg/kg and was sustained, albeit at a lower level, for 4 and 8 days respectively. En-clomiphene at 50 mg/kg increased total uterine DNA 2 days after treatment. Small dose-related sustained increases in weight of uterine luminal fluid were also observed. En-clomiphene had no effect upon serum FSH. Serum LH was decreased only on day 8 after treatment. Serum prolactin was increased to a similar level by both doses of en-clomiphene; however, the maximum was achieved 2 and 16 days after treatment with 0·5 and 50 mg/kg respectively. Rats were tested for sexual receptivity after 50 mg/kg en-clomiphene and increases were detected between 7 and 9 days of treatment. Progesterone facilitated this effect only on days 8 and 9. En-clomiphene produced dose-related falls in food intake and body weight, the latter remaining below the weights of control rats throughout the period studied. It is apparent that the temporal effects of en-clomiphene upon cytoplasmic [3H]oestradiol binding are diverse, replenishment of binding being dependent upon the dose and the tissue examined. In addition, the changes in biological activity as measured by uterine and neuroendocrine effects also appear temporally unrelated to each other and to the binding of [3H]oestradiol. Thus further studies are necessary to elucidate possible differences in tissue oestrogen receptor mechanisms and the mode of action of the oestrogen antagonists.
EFFECT OF TESTOSTERONE ON NEURONAL REFRACTORY PERIODS, SEXUAL BEHAVIOUR AND LUTEINIZING HORMONE: A COMPARISON OF TIME-COURSES
Authors: KENDRICK K. M. , DREWETT R. F. , WILSON C. A.
Published: December 2008

Measurements of the refractory period of stria terminalis neurones that are sensitive to testosterone propionate, of sexual behaviour and of plasma levels of LH were taken in castrated rats at various times after initiation of treatment with testosterone propionate. Levels of LH dropped within 24 h, before there was any change in neuronal refractory periods. The period of latency to mounting, however, was reduced to its shortest only after 7–8 days and ejaculations first occurred at the same time; these sexual responses correlated in time with the reduction of the neuronal refractory period to its lowest level.
DIFFERENTIAL EFFECTS OF CYCLIC AMP ON DNA SYNTHESIS BY GERM CELLS AND NON-GERM CELLS IN MOUSE TESTICULAR CULTURE
Authors: NISHIMUNE YOSHITAKE , HANEJI TATSUJI , AIZAWA SHIRO
Published: December 2008

The effect of dibutyryl cyclic AMP (dbcAMP) on DNA synthesis in mouse cryptorchid explants with only type A spermatogonia was examined in vitro. Low concentration of dbcAMP (0·08 mmol/l) stimulated DNA synthesis by germ cells but inhibited that by non-germ cells.
ANDROGENIC ACTION OF GLUCOCORTICOIDS ON THE GRANULAR DUCTS OF MOUSE SUBMANDIBULAR GLANDS
Authors: SATO SEIICHI , MARUYAMA SHICHIRO , AZUMA TAKEO
Published: December 2008

The administration of cortisol acetate and dexamethasone to castrated–adrenalectomized mice increased the submandibular gland weight, the granular duct cell size of the gland and the number of androgen-dependent granules detected with the staining for tryptophan in the duct cell. These changes were not as pronounced as when testosterone propionate was given. Similar effects on the duct cells and an increase in androgen-dependent esteroprotease activity of the submandibular glands were observed in castrated mice, but not in mice with testicular feminization which are genetically deficient in androgen receptors. These results suggest that glucocorticoids exert a certain degree of androgenic action on the granular duct cell through androgen receptors when androgens are absent or deficient.
ACTIONS OF CATECHOL OESTROGENS ON CONCENTRATIONS OF SERUM LUTEINIZING HORMONE IN THE ADULT CASTRATED RAT: VARIOUS EFFECTS OF 4-HYDROXYOESTRADIOL AND 2-HYDROXYOESTRADIOL
Authors: FRANKS S. , MacLUSKY N. J. , NAISH S. J. , NAFTOLIN F.
Published: December 2008

The pharmacological effect of 2-hydroxyoestradiol (2-OHE2) and 4-OHE2 on concentrations of LH in the chronically castrated rat have been compared with that of oestradiol in order to determine whether the in-vivo activity is altered by insertion of a hydroxyl group at position 2 or 4 of the aromatic A ring; these derivatives are naturally occurring oestrogen metabolites. Four groups of six adult male rats were used 4 weeks after bilateral orchidectomy. The right jugular vein was exposed under ether anaesthesia and a basal blood sample taken (10.00 h) immediately before an intravenous injection of vehicle alone (0·1 ml ethanol with 0·01 % ascorbic acid), oestradiol, 2-OHE2 or 4-OHE2 (10 μg of each in 0·1 ml vehicle). Blood was taken from each animal at 2, 4, 6, 8 and 24 h after treatment and serum assayed for LH. Baseline LH levels were similar in the four groups. At 2 h there was no change in 2-OHE2-treated rats but there was a significant decrease of serum levels of LH in rats treated with oestradiol and 4-OHE2 compared with vehicle-treated controls. The decrease in LH was quantitatively similar in oestradiol- and 4-OHE2-treated groups and was sustained at 4, 6 and 8 h, returning to control values at 24 h. In subsequent experiments the effects of lower doses of these two steroids were compared and the potency of 4-OHE2 was estimated to be about 25% that of oestradiol. In a further experiment, 2-OHE2 (100 μg) had no effect when given alone, but when injected i.v. immediately before treatment with 1 μg oestradiol, it was able to inhibit the suppression of LH by oestradiol. In conclusion, 4-OHE2 had a potent effect in lowering plasma LH levels whereas 2-OHE2, even at a high dose (100 μg), did not suppress LH but it was able to inhibit the effect of oestradiol. These differences in biological activity may reflect more rapid metabolism of 2-OHE2 or differences in binding properties of these catechol oestrogens to the oestrogen receptor.
ROLE OF THE MEDICAL–BASAL HYPOTHALAMUS IN THE SECRETION OF GROWTH HORMONE DURING PREGNANCY AND LACTATION IN EWES
Authors: WRÓBLEWSKA BARBARA , DOMAŃSKI E.
Published: December 2008

The main aim of this study was to examine the role of the hypothalamus in controlling the secretion of GH in the ewe. This was evaluated by studying the effect of lesions placed either in the anterior or the posterior medial–basal hypothalamus (MBH) on the concentration of GH in the peripheral circulation during pregnancy and lactation, i.e. when the levels would be high in normal ewes. Simultaneously, the level of prolactin in the peripheral blood of these animals was followed. Lesions of the MBH resulted in a marked decrease in circulating GH as well as disturbances in the mammogenic and lactogenic processes during the periods of periparturition and lactation respectively. The changes were particularly evident if the anterior MBH was lesioned. The present experiments confirm our previous findings that a stimulatory centre is localized in the anterior MBH of sheep whilst in the caudal MBH there is an inhibitory centre regulating the release of prolactin. The results also confirm the important role of GH during lactation in ewes, especially during lactogenesis. The results indicate a differentiated but synchronizing and synergistic role of the MBH regulating the patterns of GH and prolactin secretion in late pregnancy and lactation.
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.
DIMINUTION OF THYROTROPHIN RELEASING HORMONE-INDUCED GROWTH HORMONE SECRETION IN ADULT DOMESTIC FOWL (GALLUS DOMESTICUS)
Authors: HARVEY S. , STERLING R. J. , PHILLIPS J. G.
Published: December 2008

Age-related changes in the response of GH to administration of thyrotrophin releasing hormone (TRH) have been investigated in the domestic fowl. In two strains of chicken the i.v. administration of TRH (10 μg/kg) to 4-week-old male and female birds markedly increased (> 200 ng/ml) the plasma GH concentration within 10 min of treatment and the concentration remained higher than the pretreatment level for at least a further 20 min. Saline (0·9%) administration had no effect on GH secretion in comparable groups of control birds. The same dose of TRH had no effect on plasma GH concentrations in adult (> 24-week-old) laying hens or cockerels. The administration of TRH at doses of 0·1–100 μg/kg (i.v.) or 0·39–50 μg/bird (s.c.) also had very little, if any, effect on GH secretion in laying hens. In laying hens slight increases (10–20 ng/ml, P < 0·05) in the plasma concentrations of GH were observed in one experiment 60 min after the s.c. injection of 100 μg TRH, and in another 60, 90 and 120 min after the serial s.c. injection of TRH (100 μg/bird) every 30 min over a 150 min period. The poor GH response of the adults to TRH stimulation was not due to high circulating concentrations of endogenous gonadal steroids, as surgical gonadectomy had no effect on the GH response to TRH. These results suggest maturational differences in the control of GH secretion in the fowl.
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.
INTERACTION OF α-MELANOCYTE-STIMULATING HORMONE, MELATONIN, CYCLIC AMP AND CYCLIC GMP IN THE CONTROL OF MELANOGENESIS IN HAIR FOLLICLE MELANOCYTES IN VITRO
Authors: WEATHERHEAD BRIAN , LOGAN ANN
Published: December 2008

In short-term (48 h) cultures of hair follicles α-melanocyte-stimulating hormone (α-MSH) and cyclic AMP stimulated melanogenesis through an increase in tyrosinase activity. In contrast cyclic GMP mimicked the effects of melatonin by inhibiting melanin production without causing a concomitant decrease in tyrosinase activity. Both cyclic GMP and melatonin blocked the stimulatory effects of cyclic AMP and α-MSH on melanin production but they left the increased levels of tyrosinase activity unaffected. Phosphodiesterase inhibitors (3-isobutyl-1-methylxanthine and papaverine) simultaneously stimulated tyrosinase activity and inhibited melanin production, presumably by allowing endogenous cyclic AMP and cyclic GMP to accumulate intracellularly. It is suggested that whereas MSH stimulates melanogenesis through a cyclic AMP-dependent mechanism there must also be an inhibitory cyclic GMP-dependent mechanism, perhaps activated by melatonin, which operates at some post-tyrosinase step in the melanin biosynthetic pathway.
EFFECTS OF TESTOSTERONE, PREGNENOLONE, PROGESTERONE AND CORTISOL ON PITUITARY AND TESTICULAR FUNCTION IN MALE GOLDEN HAMSTERS WITH GONADAL ATROPHY INDUCED BY SHORT PHOTOPERIODS
Authors: BARTKE A. , KLEMCKE H. , AMADOR A.
Published: December 2008

Testicular regression was induced in adult golden hamsters by exposure to a short photoperiod (5 h light: 19 h darkness). The response of these animals to exogenous steroids (ten injections each of 5 mg testosterone, testosterone propionate, pregnenolone, progesterone or cortisol administered s.c. three times/week) was evaluated from weight changes in testes and seminal vesicles, from plasma levels of LH, FSH and testosterone, and from testicular human chorionic gonadotrophin (HCG) binding and testosterone levels. Administration of testosterone or testosterone propionate produced a decrease in plasma gonadotrophins and a three- to fourfold increase in weights of testes and seminal vesicles, thus indicating that the seminiferous tubules, similarly to accessory reproductive glands, retained the ability to respond to androgenic stimulation. Binding of HCG by testicular tissue was dramatically reduced by treatment with testosterone, probably reflecting atrophy of the Leydig cells. Treatment with pregnenolone or progesterone failed to increase testicular weight, seminal vesicle weight or concentrations of testosterone in the testes. This suggests that the atrophic testes of these animals may have a limited capacity to produce biologically significant amounts of androgens from C21 steroids. Administration of cortisol did not alter any of the parameters of reproductive function that were examined.