bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of [1-(3-mercaptopropanoic acid)]-vasopressin and -vasotocin on the pro-oestrous progesterone surge and ovulation in immature female rats
Authors: Cheesman D. W. , Schlegel R.
Published: December 2008

The desamino analogues of arginine-vasotocin (dAVT) and arginine-vasopressin (dAVP), when administered on the afternoon of pro-oestrus to immature female rats primed with pregnant mare serum, blocked the preovulatory progesterone surge and inhibited ovulation. Statistical analysis revealed no difference in the potency of the two compounds. At a dosage of 2·0 μg, dAVT and dAVP yielded a 70 and 87% block of ovulation respectively. Simultaneous administration of dAVT and the antipressor compound [1-deaminopenicillamine-4-valine-8-d-arginine]-vasopressin had no statistically significant inhibitory effect when compared with saline-treated controls.

These data suggest that the inhibitory effects of dAVT and dAVP on the progesterone surge and subsequent ovulation are mediated through receptor sites similar to those mediating the pressor actions of the parent hormones.
Influence of pinealectomy on the suppression of gonadotrophin secretion induced by hyperprolactinaemia in the adult male rat
Authors: McNeilly A. S. , Lincoln D. W.
Published: December 2008

To investigate the role of the pineal gland in the long-term suppression of gonadotrophin secretion induced by prolactin, the effects of pinealectomy were studied in adult male rats with hyperprolactinaemia produced by the transplantation of two pituitary glands under the kidney capsule.

Pinealectomy had no effect on basal levels of LH, FSH or prolactin. The presence of pituitary transplants induced a significant twofold increase in prolactin levels and a prolonged suppression in both LH and FSH. These changes were not affected by pinealectomy. Castration resulted in a similar rise in plasma levels of LH and FSH in rats with and without pituitary transplants. In control rats this rise in LH and FSH was reduced by testosterone-containing silicone elastomer implants (s.c) of 10 mm in length and delayed by implants of 30 mm. These rises in LH and FSH were significantly delayed (10-mm implant) or abolished (30-mm implant) in rats with pituitary transplants indicating an increase in sensitivity of the hypothalamic-pituitary axis to the negative feedback effects of testosterone in these animals compared to controls. These responses were not affected by pinealectomy.

These results suggest that the pineal gland is not involved in the mechanism whereby pituitary grafts, possibly through their secretion of prolactin, cause long-term suppression of gonadotrophin secretion.
In-vivo hypocalcaemic, hypophosphataemic and hyperlipaemic activities in the common peptide sequence of adrenocorticotrophin, melanocyte-stimulating hormone and lipotrophin
Authors: Drouhault Robert , Valéro Danièle , Baghdiantz Alexandre , Blanquet Paul
Published: December 2008

A heptapeptide solution in acetate buffer (pH = 4, 150 μg/kg) of the amino acid sequence common to ACTH, α- and β-MSH and lipotrophin, when injected intravenously into rabbits produced an increase in total lipids, cholesterol and free fatty acids after 1 h and a decrease in plasma calcium and phosphate after 2 h. No significant modification in the amount of creatinine, uric acid, urea, total proteins, CO2, Cl−, K+ or Na+ was observed.
Changes in testicular blood flow and testosterone production during aspermatogenesis after irradiation
Authors: Wang J. , Galil K. A. A. , Setchell B. P.
Published: December 2008

Exposure of the testes of anaesthetized adult rats to 527 rads of γ-irradiation caused testis weight to fall slowly at first and then more rapidly from 21 days afterwards, reaching a minimum at 52 days, when spermatogenesis was severely disrupted. The weights of the accessory organs and the concentrations of testosterone in peripheral blood were slightly reduced; the concentrations in blood from the testicular veins were lower than control at shorter intervals after irradiation, but at later times tended to be similar or greater than control. Testicular blood flow per testis followed testis weight closely, and as a result the production of testosterone by the smaller testes (calculated as the product of plasma flow and the veno–arterial difference in testosterone concentration) was markedly reduced especially when the rats had been stimulated with human chorionic gonadotrophin (hCG). Serum FSH and LH rose appreciably as testis weight fell but there was a proportionately greater rise in FSH than LH, in comparison with surgically castrated animals. Increased amounts of extratubular, extracellular fluid were found in the aspermatogenic testes, but injection of hCG still caused increases in capillary permeability and the amount of fluid in the testis.

These results indicate that during aspermatogenesis following irradiation (as with heat and efferent duct ligation) the capacity of the testes to secrete testosterone is severely limited by decreased testicular blood flow, not by the ability of the Leydig cells to release testosterone into their immediate environment.
Influence of certain steroids on lymphocyte transformation in sheep and goats studied in vitro
Authors: Staples L. D. , Binns R. M. , Heap R. B.
Published: December 2008

The effect of various steroids on lymphocyte transformation was tested with peripheral blood lymphocytes (PBL) from sheep and goats. Transformation was induced with phytohaemagglutinin, pokeweed mitogen and Concanavalin A, and by allogeneic lymphocytes (mixed lymphocyte culture). Progestagens, androgens and corticosteroids inhibited mitogen-induced transformation of lymphocytes from both species. With sheep PBL, progestagens and androgens inhibited transformation at high concentrations. Progesterone and its less active metabolites 5α-pregnanedione and 20α-dihydroprogesterone were equally inhibitory. Corticosteroids were more effective than other steroids at concentrations of less than 1 μmol/l. Oestrogens had relatively little effect with the exception of diethylstilboestrol which markedly enhanced sheep PBL responses to mitogen. Structural comparisons suggested that the most suppressive C-19 and C-21 steroids possessed 4-en-3-one configuration in ring A, and that inhibitory activity was enhanced by C-17α substitution as in 17α-hydroxyprogesterone.

The steroid effects on PBL were largely unaffected by the reproductive status of the donor, were exerted during the early pre-replicative phase rather than at the time of new DNA synthesis, and were not attributable to cytotoxicity nor to changes in intracellular thymidine pools. An exception was found with the non-steroidal oestrogen, diethylstilboestrol, which enhanced the response to mitogen-treated cultures of sheep lymphocytes at both early and late phases of the cell cycle.

It is concluded that several naturally occurring steroids affect the responsiveness of PBL to mitogenic stimuli, and that progesterone and/or certain of its metabolites may be effective in vivo when present at the high concentrations found in the utero-ovarian lymphatic network draining the gravid uterus or at the trophoblast-maternal interface in the sheep and goat.
The acute effect of placentectomy and hysterectomy on peripheral plasma progesterone levels and ovarian progesterone secretion in the pregnant rat
Authors: Olynyk J. K. , Bruce N. W. , Waddell B. J.
Published: December 2008

The role of placental luteotrophins in modulating plasma progesterone concentrations and ovarian progesterone secretion was examined in 16-day pregnant rats. In an initial experiment rats were placentectomized and their plasma progesterone concentrations monitored for 24 h; the rats were conscious within 30 min of placentectomy. Relative to control values, progesterone concentrations fell significantly within 0·5 h. A venous outflow technique was then used to monitor rates of progesterone secretion from ovaries of hysterectomized and control rats maintained under anaesthesia. Hysterectomy had no apparent effect on either progesterone secretion or plasma progesterone concentrations for at least 2 h. A final experiment was carried out to compare the effects of hysterectomy on plasma progesterone concentrations in conscious rats with those of placentectomized rats of the first experiment. Progesterone concentrations did not change significantly in hysterectomized rats for 4 h but fell to very low values by 24 h. These results suggest that placental luteotrophins do not have an acute, direct role in the control of plasma progesterone levels but are needed to maintain progesterone secretion in the longer term and possibly inhibit uterine luteolysin release.
Effect of various anaesthetics on resting plasma concentrations of luteinizing hormone, follicle-stimulating hormone and prolactin in ovariectomized ewes
Authors: Clarke I. J. , Doughton B. W.
Published: December 2008

Effects of various anaesthetics on plasma LH, FSH and prolactin levels were studied in ovariectomized ewes. In the first experimental series, conducted between June and November (late breeding season, early anoestrous season), the following treatments were given: saline (i.v.) (n = 7); single thiopentone injection (i.v.) (n = 4); induction of anaesthesia for 2 h with thiopentone (n = 5), ketamine/thiopentone mixture (n = 6), Alphathesin (n = 6) or induction with thiopentone and maintenance with halothane (n = 6). The major findings were: (1) halothane anaesthesia reduced mean plasma LH levels by preventing pulsatile secretion of LH; (2) Alphathesin had the least effect on tonic LH concentration; (3) a single thiopentone injection did not affect LH levels; (4) continuous thiopentone anaesthesia increased LH pulse amplitude; (5) plasma FSH concentration was not affected by any of the treatments; (6) ketamine/thiopentone-induced and Alphathesin-induced anaesthesia increased plasma prolactin levels.

In a second experimental series four ovariectomized ewes were anaesthetized with thiopentone for 3 h in January. In contrast to the results obtained with thiopentone in August, treatment in January reduced plasma LH pulse amplitude and mean plasma LH levels. These latter results support the hypothesis that there may be seasonal variation in responses to barbiturate anaesthesia.
Inhibition of phasic but not tonic pituitary secretion by 2-hydroxyoestrone in the rat: evidence of action as an oestrogen antagonist
Authors: Katayama Shigehiro , Fishman Jack
Published: December 2008

Rats with 4-day oestrous cycles, implanted with intracardiac catheters, were injected with 2-hydroxyoestrone at noon on pro-oestrus and their plasma LH levels monitored at frequent intervals thereafter. A dose of 100 μg 2-hydroxyoestrone completely abolished the preovulatory LH rise in four out of ten animals tested, showing no effect in the six others. When an injection of 10 μg oestradiol 1 h before the 2-hydroxyoestrone administration was given all the rats showed an absence of the preovulatory LH surge, while it remained intact in the controls treated with oestradiol only. The principal metabolite of 2-hydroxyoestrone, 2-methoxyoestrone, exhibited no influence on the pituitary gonadotrophin release. Repeated injections of 100 pg doses of 2-hydroxyoestrone to long-term ovariectomized rats produced no change in plasma LH and prolactin levels. In animals primed with oestradiol benzoate, 2-hydroxyoestrone given 1–2 h after the priming dose blocked the phasic release of the pituitary hormones on the afternoon of the 2 subsequent days. The LH and prolactin surges in the primed animals, however, were not affected when the catechol oestrogen was injected 2 h before their appearance.

These results indicate that in the cyclic rat exogenous 2-hydroxyoestrone inhibits the preovulatory LH surge when its administration is coincident with the preovulatory oestradiol rise. In the ovariectomized rat 2-hydroxyoestrone inhibits the oestrogen-dependent priming step but does not affect either the oestrogen-independent expression of the induced surges or the tonic secretion of these pituitary hormones.

These results indicate a dissociation of central and peripheral activities in this oestradiol metabolite and suggest that this catechol oestrogen functions as an oestrogen antagonist in neuroendocrine events. Since catechol oestrogens can be formed in the brain these pharmacological responses may reflect physiological mechanisms.
Reduced adrenocortical function and increased thyroid function in fasted and refed chickens
Authors: Harvey S. , Klandorf H.
Published: December 2008

The deprivation of food for 48 h markedly increased (P< 0·001) the corticosterone concentration in the plasma of 7- to 8-week-old chickens. When fasted birds were refed for 2 min or 5 s the corticosterone concentration fell to the level in fed birds within 30 min of refeeding. In fasted and refed birds the plasma corticosterone concentration remained lowered for at least 150 min after a 2-min period of refeeding, whereas in birds refed for 5 s the concentration had increased within 120 min to that in fasted birds. When fasted birds were refed 1, 5, 15 or 30 g diet the corticosterone level was again markedly reduced (P< 0·001) within 45 min of refeeding. The magnitude of this post-feeding decline was unrelated to the amount of food eaten, although its duration was; the level in birds refed 1, 5 or 15 g food increasing to that in fasted birds within 90, 135 and 225 min respectively. The corticosterone level in birds refed 30 g diet remained reduced for at least 225 min but increased to that in fasted birds 24 h after refeeding. The initial decline in the corticosterone concentration was unrelated to the consumption of food, since a similar reduction in the corticosterone level was observed in fasted birds which were given the sight of food but prevented from eating it by Perspex lids attached to the food troughs. This initial decline in the corticosterone level was not a result of stress, as it did not occur in fasted control birds. These results suggest that the adrenocortical changes in fasted and refed birds is initially mediated by a conditioned neural stimulus (reinforcement) and is maintained as a result of peripheral metabolic effects of ingested food.

In fasted chickens the concentration of plasma tri-iodothyronine (T3) was greatly reduced (P<0·001) in comparison with fed birds. When fasted birds were refed for 2 min or with 5, 15 or 30 g diet, the level of plasma T3 was increased (P < 0·05) 90 min after refeeding although not to the level in birds which had free access to food. The magnitude and duration of this increase was related to the amount of food consumed and was not observed in birds refed for 5 s or with 1 g food or in fasted birds given sight of but not access to food.
Release of corticosterone from the rat adrenal cortex in response to administration of (1–24)adrenocorticotrophin
Authors: Cam G. R. , Bassett J. R.
Published: December 2008

The intraperitoneal injection of (1–24)ACTH (34–170 nmol/kg) in rats pretreated with betamethasone resulted in a biphasic rise in plasma corticosterone; only a single phase-response was observed after lower doses (3·4–17·0 nmol/kg). There was an initial rapid rise to a level of approximately 0·72 μmol corticosterone/l plasma over the first 10 min after injection, followed by a plateau phase in which there was no further significant rise in steroid levels up to 25 min. Between 25 and 30 min after injection there was a second significant rise in plasma corticosterone concentration. The amplitude of the first phase of steroid increase was essentially the same for all doses of (1–24)ACTH administered whereas the amplitude of the second phase was dose-dependent. The administration of the microtubule inhibitor, colchicine, greatly reduced the amplitude of the second phase of the response to (1–24)ACTH while not affecting the first phase. However, a second stimulus with (1–24)ACTH in colchicine-treated animals was without effect on plasma corticosterone concentrations; both the first and second phases of corticosteroid increase being abolished. It is proposed that the first phase of plasma corticosterone increase resulted from the release of corticosteroid from a storage form close to the cell membrane and not requiring microtubular transport, whereas the second phase was the result of transport from more distant storage sites or de-novo synthesis.
Estimation of melatonin in bovine plasma: patterns in Jersey heifers treated with cloprostenol at two times of day
Authors: Martin T. C. , Cunningham N. F. , Saba N.
Published: December 2008

The estimation of melatonin in bovine plasma by radioimmunoassay is described and some aspects of specificity are discussed. Mean values for individual heifers ranged from 0·025 to 0·25 nmol/l during the day and were significantly (P<0·01) raised in each animal to mean values of 0·19 to 1·41 nmol/l at night. The hormonal changes after cloprostenol injections were not affected by the time of day at which the heifers were treated.
Ovine placental lactogen concentrations during premature delivery induced by infusion of dexamethasone or adrenocorticotrophin to the fetus
Authors: Taylor M. J. , Robinson J. S. , Jenkin G. , Thorburn G. D.
Published: December 2008

Premature delivery was induced by intrafetal infusion of dexamethasone or (1–24)ACTH, starting between days 124 and 129 of pregnancy in twelve ewes carrying intact (n = 7) or hypophysectomized (n = 5) single fetuses. Concentrations of ovine placental lactogen (oPL) in maternal plasma were measured by specific radioimmunoassay before and during premature delivery. There was no significant change in oPL concentrations before delivery in ewes carrying either intact or hypophysectomized fetuses.

The results suggest that a prepartum decline in oPL is not an essential prerequisite for delivery, and indicate that fetal glucocorticoids are not directly responsible for the prepartum fall in oPL concentrations observed at spontaneous delivery.
Depression of sodium, chloride and calcium ions in the plasma of goldfish (Carassius auratus) and immature freshwater- and seawater-adapted eels (Anguilla anguilla L.) after acute administration of salmon calcitonin
Authors: Wales N. A. M. , Barrett A. L.
Published: December 2008

Goldfish showed a significant reduction in their plasma sodium and calcium levels 1 h after receiving 50 i.u. calcitonin per kg body weight. When 100 i.u. calcitonin were injected there was a significant fall in circulating levels of both sodium and calcium and also of chloride ions compared with those found in untreated control animals. Administration of calcitonin to immature eels adapted to either freshwater or seawater conditions showed no significant change in plasma ion composition at doses of 10 i.u. per kg body weight or less. However, doses of 50 and 100 i.u. caused significant reductions in plasma sodium, chloride and calcium ion levels compared with sham-injected control animals.

When immature eels were given 100 i.u. calcitonin per kg body weight there were significant reductions in the plasma levels of sodium, chloride and calcium ions but the timing of these changes was slightly different. In freshwater-adapted eels, the depression of plasma sodium was seen after 30 min and lasted for up to 2 h, whilst depression of plasma chloride and calcium was not seen until 1 h after injection. In addition, whilst the lowering of plasma chloride ions lasted up to 2 h after injection, the plasma calcium had returned to the preinjection control level by this time.

In seawater-adapted eels the depression of sodium, chloride and calcium levels was seen at 30 min and the effect continued for up to 2 h after injection when the depression was no longer apparent.
Biosynthesis of pro-opiomelanocortin-related peptides in the neurointermediate lobe of the pituitary gland of the rainbow trout (Salmo gairdneri)
Authors: Rodrigues K. T. , Jenks B. G. , Sumpter J. P.
Published: December 2008

This study concerns the biosynthesis of a number of peptides in the neurointermediate lobe of the rainbow trout, Salmo gairdneri. Among the newly synthesized peptides positively identified were four forms of α-MSH, a β-MSH and two forms of endorphin. The identification of two of the products as sequentially distinct endorphins suggests that the trout neurointermediate lobe synthesizes two pro-opiomelanocortin (POMC) molecules. This may account for the large number of peptides synthesized and secreted by the trout neurointermediate lobe. The identification of some of the products is discussed.

Pulse-chase analysis revealed no positive identification of a precursor molecule, which may indicate that trout POMC is very rapidly processed into smaller products. All of the newly synthesized peptides were secreted concomitantly. There was little if any evidence of post-translational modification of any of the peptides during their secretion.
Effects of chronic treatment with oestrogen, an oestrogen antagonist and a potent luteinizing hormone releasing hormone agonist analogue on pituitary responsiveness to luteinizing hormone releasing hormone in the rat
Authors: Hall J. M. , Whitehead S. A.
Published: December 2008

The rise in gonadotrophin release which occurs after ovariectomy is caused by steroid withdrawal resulting in an enhanced pituitary responsiveness to LH releasing hormone (LHRH) associated with increased LHRH release and pituitary LHRH binding. The effects of oestrogen replacement after ovariectomy and chronic treatment of intact rats with an oestrogen antagonist, tamoxifen, on LH release and in-vitro pituitary responses to LHRH have been investigated. Capsules containing crystalline oestradiol, implanted at the time of ovariectomy, completely inhibited the rise in LH release although pituitary responsiveness was greater after 10 days in the oestrogen-treated rats than in untreated ovariectomized controls. On day 4 after ovariectomy pituitary responses to LHRH were comparable in both treated and untreated groups although in both groups the responses were greater than those measured in intact dioestrous rats. Treatment with tamoxifen over a 4-day period also augmented pituitary responsiveness but only at the lowest dose (0·5 mg/kg); no effect on serum LH concentrations was observed. Higher doses of the antagonist (1 and 2 mg/kg) did not affect pituitary responses, although the highest dose did cause a significant rise in serum LH. Treatment with a daily dose of 50 ng [d-Ser(But)6]LHRH(1–9)nonapeptide-ethylamide, starting on the day of ovariectomy, markedly attenuated the LH responses to LHRH ex vivo at days 2, 4 and 10 after ovariectomy. In contrast, the analogue treatment did not abolish the rise in LH release but this was proportionately less than in controls.
Serum levels of growth hormone during the stunted postnatal development of the vasopressin-deficient Brattleboro rat
Authors: Boer G. J. , Rieutort M.
Published: December 2008

Levels of GH in serum were assayed during the development of heterozygous (HET) control and vasopressin-deficient homozygous (HOM) Brattleboro rats. In early postnatal growth no differences in GH concentrations were present between HET and HOM rats for the rapid decline in serum levels of GH in the first week and the constant period up to day 24 of age thereafter. However, higher values were found in 55-day-old HOM rats and lower values at the age of 9 months. It is concluded that the stunted development of the body and brain of HOM rats is not GH-related, and that changes or anomalies in GH secretion appear only after neurogenesis has been completed.
Plasma testosterone levels in adult and neonatal female rats bearing testosterone propionate-filled silicone elastomer capsules for varying periods of time
Authors: Sommerville E. M. , Tarttelin M. F.
Published: December 2008

Testosterone propionate (TP) was administered, by means of subcutaneous implanted silicone elastomer capsules, into adult and neonatal (aged 3 days) female rats.

In the adult rats a dose-dependent increase in plasma testosterone was measured for capsules of three different sizes (5, 10 and 20 mm crystal length). Testosterone levels reached a peak 4–8 h after insertion (5 mm, 24·6±1·4 (s.e.m.) nmol/l; 10 mm, 34·0 ± 3±8; 20 mm, 44·4 ± 3·1) and returned to control levels within 4 h after removal: the calculated half-life of testosterone was 1 h for all sizes of capsule. In neonates, a capsule of 2·5 mm crystal length was removed after 4 h subcutaneous implantation (at day 3 of age) and produced peak testosterone levels of 126·2± 11·8 nmol/l: the calculated half-life was 8·6 h which compared with a half-life of 48 h after a subcutaneous injection of 312 μmol TP (in 0·05 ml arachis oil) which produced peak levels of testosterone in 4–8 h of 84·6 ±11·8 nmol/l. Chronic implants of TP-filled capsules (2·5 mm crystal length) at 3 days of age and left in situ for 15 weeks gave a half-life of 69 h.

Removable silicone elastomer capsules were found to be a versatile vehicle for the administration of TP to rats of all ages where precise hormone treatment for a known period or prolonged administration is required. The duration and magnitude of plasma hormone levels should be established by assay in an in-vivo situation.
The relationship between prolactin secretion and calmodulin activity
Authors: Merritt J. E. , MacNeil S. , Tomlinson S. , Brown B. L.
Published: December 2008

The possible role of calmodulin in the control of prolactin secretion was examined. The effects of a wide variety of agents on inhibition of prolactin secretion from isolated rat anterior pituitary cells and inhibition of calmodulin activity in an in-vitro system (calmodulin-activated cyclic GMP phosphodiesterase) were compared. A number of phenothiazines showed a close correlation of potencies in the two systems, as did the more specific calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalene sulphonamide (W7), suggesting that calmodulin may be involved in the control of prolactin secretion. Some other drugs also inhibited both prolactin secretion and calmodulin activity in addition to their other well-characterized biochemical effects. However, many of these drugs (including two phenothiazines) were more potent inhibitors of prolactin secretion than of calmodulin activity, suggesting that other intracellular systems in addition to calmodulin may be involved in the control of the secretory process.
Activity in the corpora lutea resulting from sterile matings in Clethrionomys glareolus: a histochemical study
Authors: Westlin L. M. , Niklasson Monica
Published: December 2008

The capacity for steroid production in the corpora lutea (CL) of bank voles was examined by enzyme histochemistry for 3β-hydroxysteroid dehydrogenase. The results revealed similar activity in the CL resulting from sterile matings and the CL of pregnancy 2 days after mating. Six days after mating, the CL of pregnancy showed a strong reaction, while there was almost no reaction in the CL from sterile matings, which were clearly regressed at this time. It is suggested that the CL from sterile matings produce progesterone before regression and that this progesterone may prime the luteotrophic complex, increasing fertility of subsequent matings.
Melatonin feeding decreases prolactin levels in the ewe
Authors: Symons A. M. , Arendt Josephine , Laud C. A.
Published: December 2008

Three groups of Suffolk-cross ewes were kept in (A) summer photoperiod plus melatonin feeding in such a way as to mimic the plasma levels found in winter photoperiod, (B) winter photoperiod or (C) natural light/dark from mid-June onwards. Prolactin levels remained high in group C throughout July and August but were dramatically reduced in both groups A and B. The rise in prolactin levels associated with dusk, however, was still apparent in all three groups. Appropriate administration of melatonin can thus influence prolactin secretion in the same way as an extension of the dark phase. This effect is associated with an early onset of the breeding season in the ewe.
Prolactin-binding capacity, prostaglandin synthesis and fluidity of murine hepatic membranes are modified during pregnancy and lactation
Authors: Dave J. R. , Richardson L. L. , Knazek R. A.
Published: December 2008

The objective of these studies was to determine whether the changes observed in prolactin-binding capacity of mouse liver microsomal membranes during pregnancy and lactation correlated with those observed in the fluidity and prostaglandin (PG)-synthesizing activity of these membrane preparations. Prolactin-binding capacity increased with the advance of pregnancy to reach a peak at 16 days of gestation and declined thereafter to non-pregnant, non-lactating (NPNL) levels. Membrane microviscosity, studied by fluorescence polarization, was significantly decreased throughout early gestation but returned to NPNL levels by day 20 of gestation and remained unchanged thereafter. The amount of PGE synthesized in vitro by these membranes increased during gestation to reach a peak at 12 days of gestation but declined thereafter to below NPNL levels on the day of parturition and returned to NPNL levels by day 20 of lactation. Synthesis of PGF2α remained at a higher level from day 12 to day 18 followed by a decline in activity at parturition to NPNL levels. These changes and other data suggest an interrelationship of receptor levels, fluidity and PG synthesis during pregnancy. Such modifications in local PG synthesis may influence the fluidity of these membranes, which ultimately play a significant role in maximal exposure of membrane receptors during pregnancy.
Hypercalcaemic responses to 16,16-dimethyl prostaglandin E2, a stable prostaglandin E2 analogue in chicks
Authors: Kirby G. C. , Dacke C. G.
Published: December 2008

Intravenous injection of 6·7–60 μg of a stable prostaglandin E2 analogue, 16,16-dimethyl prostaglandin E2, into 10-day-old chicks caused profound, long-lasting hypercalcaemia. Simultaneous i.v. loading with 50 μmol Ca/bird enhanced the peak response. The responses were accompanied by sedation and lowered skin temperature. Use of acute (simultaneous) 45Ca labelling indicated that the hypercalcaemic responses were due primarily to inhibition of Ca exit from extracellular fluid pools, while chronic (6-day) 45Ca labelling indicated a slower but distinct increase in mobilization of bone Ca pools.
Influence of the pituitary-adrenal axis on the induced release of luteinizing hormone in rams
Authors: Fuquay J. W. , Moberg G. P.
Published: December 2008

Treatment of intact rams with ACTH increased plasma corticosteroids and significantly reduced the ability of LH releasing hormone (LHRH) to elicit the release of LH. Infusion of cortisol at a rate which increased plasma corticosteroid concentrations to above that observed after injection of ACTH did not affect the ability of LHRH to induce the release of LH. In adrenalectomized rams LH release in response to LHRH was inhibited during ACTH treatment but was not affected in the absence of ACTH. Therefore, ACTH reduced the responsiveness of the anterior pituitary gland to LHRH through a mechanism not involving the adrenal gland.
The use of heterologous radioimmunoassays for the measurement of follicle-stimulating hormone and luteinizing hormone concentrations in horse and donkey serum
Authors: Urwin Valerie
Published: December 2008

Heterologous double-antibody radioimmunoassays were developed for the measurement of FSH and LH concentrations in the serum of both horses and donkeys. The FSH assay employed a rabbit anti-ovine FSH serum which showed a complete lack of cross-reaction with equine chorionic gonadotrophin (eCG) and negligible cross-reaction with equine LH. The LH assay utilized an antiserum raised against highly purified eCG. This similarly showed negligible cross-reaction with equine FSH but its high cross-reactivity with eCG prevented the measurement of equine LH concentrations in serum when eCG was also present. In both assays serial dilutions of horse and donkey serum were parallel to the standard.

The assays were used to monitor changes in serum concentrations of FSH and LH during the first 100 days of pregnancy in pony mares and jenny donkeys. In both species during pregnancy LH levels reached a peak 1–2 days after ovulation. They then decreased rapidly to baseline levels where they remained until days 35–40 when the commencement of eCG production prevented their further measurement. Serum FSH concentrations, on the other hand, continued to fluctuate markedly throughout the first 100 days of pregnancy in both the ponies and donkeys. Pronounced surges in FSH levels occurred at regular intervals in some animals but the pattern of release was quite irregular in the others.

The results of this study support the concept that it is continued pituitary FSH release, not eCG secretion, which is responsible for stimulating the secondary follicles which develop during early equine pregnancy. However, it appears likely that it is the LH-like activity of eCG which causes the subsequent ovulation and/or luteinization of these secondary follicles to produce accessory corpora lutea.
Changes in the concentration of thyroxine in the plasma of rat fetuses during late gestation: influence of ligation of the maternal uterine vein and artery
Authors: Wrutniak Chantal , Cabello Gérard
Published: December 2008

Plasma thyroxine levels were detectable in rat fetuses from day 17 of pregnancy and increased exponentially from 3·48 ± 0·13 (s.e.m.) nmol/l to 11·33 ±0·90 nmol/l at birth. Ligation of the maternal uterine vein and artery, performed on day 17 of pregnancy, significantly reduced both the fetal growth rate, observed initially on day 19 of pregnancy (controls: 2·24 ± 0·02 g; fetuses from ligated horns: 1·71 ±0·03 g, P<0·001) and plasma thyroxine levels, observed initially on day 20 of pregnancy (controls: 6·56± 0·13 nmol/1; fetuses from ligated horns: 5·41 ±0·13 nmol/l, P<0·001). In addition we observed positive relationships between plasma thyroxine levels and body weights of the two groups on days 20 and 21 of pregnancy and at birth. These results suggest that relationships observed between plasma thyroxine levels and body weight in fetuses or newborn animals may be explained by the common effect of the placental blood flow mediated by fetal nutrition.
Prostaglandin D2 induces release of luteinizing hormone from the rat pituitary gland without the modulation of hypothalamic luteinizing hormone releasing hormone
Authors: Tasaka K. , Miyake A. , Sakumoto T. , Aono T. , Kurachi K.
Published: December 2008

The effect of prostaglandin D2 (PGD2) on release of LH and LH releasing hormone (LHRH) was studied in a sequential double-chamber superfusion system using the medial basal hypothalamus (MBH) and the pituitary gland from female rats at dioestrus. Infusion of PGD2 (5·7 or 57μmol/l) caused a significant (P <0·05) increase in LH release to values 40–60% above the preinjection values from the pituitary gland superfused either alone or in series with the MBH. No release of LHRH in response to PGD2 was observed from the superfused MBH. These data demonstrate that PGD2 causes LH release from the pituitary gland not by inducing release of hypothalamic LHRH but by a direct action on the gland.
Evidence for the involvement of central conversion of testosterone to oestradiol-17β in the regulation of luteinizing hormone secretion in the cockerel
Authors: Wilson S. C. , Knight P. G. , Cunningham F. J.
Published: December 2008

Treatment of intact cockerels with the synthetic antioestrogen tamoxifen caused a significant increase in the plasma concentration of LH. In contrast, passive immunization with an antiserum raised against oestradiol-17β did not lead to an increase in plasma LH. A pronounced depressive effect of injections of 0·1 mg testosterone propionate (TP) or 0·1 mg oestradiol benzoate (OB) on plasma concentrations of LH was prevented by tamoxifen. Furthermore, a pronounced rise in the concentration of LH releasing hormone in the posterior hypothalamus after the injection of cockerels with OB was completely inhibited by tamoxifen. Neither 0·1 nor 0·5 mg androstenedione modified the concentration of LH in plasma.

A dose of 0·05 mg TP, which failed to depress the concentration of LH in plasma of intact cockerels, caused a marked fall in plasma LH in castrated cockerels. Tamoxifen itself exhibited weak oestrogen agonist activity in castrated cockerels by causing a reduction in the concentration of LH in plasma. However, tamoxifen prevented any further depressive effect on LH resulting from the injection of TP. These findings suggest that testosterone exerts an inhibitory influence on LH secretion at the central neural level, partially at least, by means of the product of its aromatization, oestradiol-17β.
Follicular steroids as a prognosticator of successful fertilization of human oocytes in vitro
Authors: Fishel S. B. , Edwards R. G. , Walters D. E.
Published: December 2008

Oocytes were collected by aspiration of preovulatory follicles from 55 women. The preovulatory rise in LH was monitored in urine using the Hi-Gonavis (Mochida Pharmaceuticals) technique. Patients were treated either during the natural cycle or after the induction of ovulation with clomiphene citrate. After collection and culture, the oocytes were inseminated with the spermatozoa of the husband. The levels of progesterone, oestradiol-17β and androstenedione in the clear follicular fluid were measured by radioimmunoassay. A multivariate analysis containing these three hormone levels together with two ratios of progesterone with each of the other hormones indicated reasonable discrimination between the oocytes which fertilized and those which remained unfertilized after insemination. The discriminant analysis suggested that the fertilization of the oocytes could have been predicted on the basis of these hormonal profiles with a success rate which exceeded 90%.
Role of the ovary in sexual differentiation of lactotrophs and somatotrophs in the mouse adenohypophysis: a stereological morphometric study by electron microscopy
Authors: Sasaki F. , Sano M.
Published: December 2008

To study the effect of the ovary on sexual differentiation of somatotrophs and lactotrophs, the anterior pituitary glands of castrated adult male mice which had received an ovarian transplant during postnatal development were studied using a stereological morphometric technique with an electron microscope. In adult male mice which were castrated neonatally and given ovarian transplants at the age of puberty (NCT-males), the ovaries contained follicles and corpora lutea. The percentages (∼40) and numbers (∼2 × 105) of lactotrophs were similar in normal dioestrous females and NCT-males, but were higher than the percentage (9·3) and number (4·6 × 104) in normal males. Ovarian grafts in adult male mice which were simultaneously castrated and given an ovarian transplant just before puberty (PCT-males) contained numerous follicles of various sizes but no corpora lutea. The percentage (46·8) and number (3·9 × 105) of lactotrophs were greater in these mice than in dioestrous females. The percentage of somatotrophs in NCT-males (34·7) was less than in normal males (52·6), but was similar to that in dioestrous female mice (37·4). The percentage of somatotrophs in PCT-males (27·4) was less than in normal male and dioestrous female mice. These data indicate that lactotrophs and somatotrophs differentiate to the female phenotype when a cyclically functional ovary is present after puberty.
Comparison of the biological effects of tamoxifen and a new antioestrogen (LY 117018) on the immature rat uterus
Authors: Wakeling A. E. , O'Connor K. M. , Newboult E.
Published: December 2008

The uterotrophic and antiuterotrophic activities of tamoxifen and 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- <2-(1-pyrrolidinyl) ethoxyphenyl ketone (LY 117018) in the immature rat uterus have been evaluated. The antioestrogens were administered alone, concurrently or sequentially with or without oestradiol. LY 117018 administered alone was less uterotrophic (oestrogenic) than tamoxifen. At high doses, when administered concurrently with oestradiol, LY 117018 was more antiuterotrophic (antioestrogenic) than tamoxifen. When uterine growth was maximally stimulated by prior treatment with oestradiol, tamoxifen and LY 117018 were equally effective in reducing uterine weight. However, when uterine growth was induced with a dose of oestradiol producing an oestrogenic effect equivalent to that of tamoxifen (but less than that produced by LY 117018) LY 117018 was more effective than tamoxifen in reversing the uterotrophic effect of oestradiol. In animals pretreated with LY 117018 a further increase in uterine weight occurred on treatment with tamoxifen. The increase in uterine weight after tamoxifen was progressively reversed by increasing doses of LY 117018. The hypothesis that tamoxifen and LY 117018 may act by different mechanisms, based on the apparent failure of LY 117018 to antagonize the uterotrophic action of tamoxifen, is not supported by these studies.
Antioestrogenic and antitumour activities of a series of non-steroidal antioestrogens
Authors: Wakeling A. E. , Valcaccia B.
Published: December 2008

The relative oestrogenic and antioestrogenic activities in the immature rat uterus of the antioestrogens tamoxifen, trioxifene, 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- <2-(1-pyrrolidinyl) ethoxyphenyl ketone (LY 117018) and 6-hydroxy-2-(p-hydroxyphenyl)-benzo(b)thien-3-yl p- <2-(1-piperidinyl) ethoxyphenyl ketone (LY 139481) were compared. The efficacy of these compounds in inhibiting the growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary carcinomas was also measured. Tamoxifen and trioxifene were equipotent antioestrogens (ED50 =dose required to produce 50% reduction in oestradiol-stimulated uterine growth = 0·1 mg/kg); both compounds also demonstrated a maximal partial agonist (uterotrophic) effect of 40% that of oestradiol. LY 117018 and LY 139481 were less potent antioestrogens (ED50 = 0·7 and 0·25 mg/kg respectively) than tamoxifen but both compounds were also less oestrogenic (partial agonist activities 20 and 10% respectively compared with oestradiol). The differences in partial agonist activity were reflected by differences in maximum antioestrogenic effects. High doses of tamoxifen or trioxifene produced 60% inhibition of oestradiol-induced uterine growth whereas LY 117018 (80% inhibition) and LY 139481 (90% inhibition) were both more antioestrogenic because of their reduced partial agonist activity. In rats bearing DMBA-induced mammary tumours tamoxifen was the most effective inhibitor of tumour growth. In tamoxifen-treated animals only 7% (8/111) of hormone-dependent tumours showed progressive growth, compared to 60% in controls. The other antioestrogens were less effective; in trioxifene-treated animals 42% (18/43) of tumours continued to grow during treatment. Similarly, for LY 117018, 39% (14/36) and for LY 139481, 26% (10/38) of tumours showed progression. High doses of trioxifene and LY 117018 were markedly less efficacious than low doses. The increased separation between oestrogenic and antioestrogenic activity in the rat uterus, exemplified by LY 117018 and LY 139481 compared to tamoxifen and trioxifene, did not lead to increased antitumour efficacy.
Response of transcortin and α2u-globulin to turpentine-induced inflammation in the rat: influence of corticosteroids and prolactin
Authors: Faict D. , Vandoren G. , De Moor P. , Lesaffre E. , Verhoeven G.
Published: December 2008

Evidence is presented that transcortin and α2u-globulin react as negative acute-phase proteins in the rat. Thirty-six hours after turpentine injection, the serum concentration of these proteins showed a two- to threefold decrease. Thereafter, transcortin rapidly returned to normal values, whereas α2u-globulin remained low.

This reaction pattern was still present after adrenalectomy, adrenalectomy and administration of glucocorticoids, and after treatment with bromocriptine, a suppressor of prolactin secretion. It is concluded that changes in the secretion of glucocorticoids and prolactin are not required for the observed turpentine-induced decrease of transcortin and α2u-globulin.
Sustained oestrogen-induced hyperprolactinaemia results from a pituitary defect
Authors: Willoughby J. O. , Pederick H. J. , Jervois P. M. , Menadue M. F.
Published: December 2008

Pituitary enlargement and hyperprolactinaemia were induced in male rats by a single subcutaneous injection of 2 mg oestradiol benzoate in oil. Two months after treatment, when oestrogen levels were normal, serial blood samples for determination of plasma concentrations of prolactin were obtained from undisturbed animals through an indwelling right atrial cannula which had been implanted 7–10 days before.

Basal concentrations of prolactin were obtained in treated and control rats, and responses of prolactin to intravenous injections of thyrotrophin releasing hormone (TRH), apomorphine, butaclamol and fenfluramine were measured.

Sustained hyperprolactinaemia with pituitary hyperplasia was achieved in only 20% of animals. Responses of prolactin to TRH were the same in control, oestrogen-treated hyperprolactinaemic and non-hyperprolactinaemic rats, indicating normal pituitary responsiveness to one prolactin releasing factor.

Complete suppression of prolactin concentrations by apomorphine occurred in hyperprolactinaemic animals, whereas no suppression could be demonstrated in animals with normal (low) basal prolactin levels, indicating good responsiveness of hyperplastic pituitary glands to dopamine inhibition.

Dopamine receptor blockade by butaclamol resulted in a vigorous prolactin response in animals with sustained hyperprolactinaemia, indicating that dopaminergic prolactin inhibitory mechanisms remain qualitatively intact, but the response was quantitatively less than in controls, suggesting insufficient hypothalamic release of dopamine.

Responses of prolactin to certain doses of fenfluramine were completely abolished in hyperprolactinaemic animals, indicating diminished sensitivity of serotoninergic prolactin releasing factor mechanisms.

Prolactin releasing factor unresponsiveness and relative insufficiency of dopaminergic activity could be regarded as physiologically appropriate responses to chronic hyperprolactinaemia. Thus oestrogen-induced chronic hyperprolactinaemia appears to be entirely of pituitary origin.
Changes in testosterone metabolism by the brain and cloacal gland during sexual maturation in the Japanese quail (Coturnix coturnix japonica)
Authors: Balthazart J. , Schumacher M.
Published: December 2008

Testosterone metabolism in the brain and pituitary and cloacal glands of male and female Japanese quail was studied in vitro during sexual maturation (from 1 day to 5 weeks after hatching).

The production of 5α-dihydrotestosterone in the hyperstriatum and cloacal gland and that of androstenedione in the cloacal gland of males was highest at 1 day after hatching, which could be related to the peak of plasma androgens previously demonstrated in neonatal quail. 5β-Reductase activity was very high in the brain, but not the pituitary or cloacal glands of young chicks and decreased markedly, especially in the hypothalamus, during sexual maturation. As 5β-reduced metabolites of testosterone are inactive androgens, it is suggested that the decrease of 5β-reductase activity with age corresponds to a potentiation of the effects of testosterone at the level of the brain.

J. Endocr. (1984) 100, 13–18