bluuebunny/crossref_metadata_2025 huggingface dataset:
VARIATIONS IN PLASMA CONCENTRATIONS OF α-MELANOCYTE-STIMULATING HORMONE DURING THE OESTROUS CYCLE OF THE RAT AND AFTER ADMINISTRATION OF OVARIAN STEROIDS
Authors: THODY A. J. , WILSON C. A. , LUCAS P. D. , FISHER C.
Published: December 2008

Plasma concentrations of α-melanocyte-stimulating hormone (α-MSH) were measured by radioimmunoassay at various times during the oestrous cycle of the rat. Variations in plasma α-MSH concentrations occurred throughout the oestrous cycle. Plasma α-MSH concentrations were low during the day of dioestrus 1 and rose during the evening reaching peak levels at around 02.00 and 06.00 h on dioestrus 2. Plasma α-MSH concentrations then fell and remained low throughout the rest of dioestrus 2. A different pattern was observed during pro-oestrus and oestrus. On those days peak α-MSH concentrations occurred during the morning and persisted until the onset of the dark period at around 17.00 h.

Plasma α-MSH concentrations in ovariectomized rats were found to be increased 24 h after administration of a single injection of oestradiol benzoate and at 12 and 36 h after a single injection of progesterone. It is suggested that these ovarian steroids may influence the rhythm in plasma α-MSH concentration that occurs during the oestrous cycle.
POTENCIES OF PORCINE RELAXINS USING TWO BIOASSAYS
Authors: CHAMLEY W. A. , BAGOYO MARLENE M. , BRYANT-GREENWOOD GILLIAN D.
Published: December 2008

Relaxin reference preparations NIH-R-P1 and Warner Lambert W1164-3, and purified relaxin peptides, CM-a′, CM-a and CM-B, were assayed in the mouse interpubic ligament and rat uterine inhibition bioassays. There was evidence that CM-a and CM-B would bind to glass and significant apparent increases in potency in the case of these two peptides alone resulted from the use of silicone-coated glassware. Using treated glassware, CM-a′, CM-a and CM-B were equipotent in the mouse interpubic ligament bioassay with potencies relative to NIH-R-P1 of 3·97-, 4·85- and 3·64-fold respectively. In the rat uterine inhibition bioassay only W1164-3 and CM-a′ gave dose-response curves which were parallel to NIH-R-P1. In this bioassay, potencies relative to NIH-R-P1 for W1164-3 and CM-a' were 0·35-and 19·6-fold respectively.
FURTHER STUDIES ON THE EFFECTIVENESS WITH WHICH EXOGENOUS LUTEINIZING HORMONE AND FOLLICLE-STIMULATING HORMONE STIMULATE THE RELEASE OF ENDOGENOUS FOLLICLE-STIMULATING HORMONE DURING THE RAT OESTROUS CYCLE
Authors: ASHIRU O. A. , RUSH M. E. , BLAKE C. A.
Published: December 2008

The effects of exogenous rat LH or FSH on the release of endogenous FSH in the cyclic rat have been investigated. Rats were administered phenobarbitone to block the spontaneous increases in gonadotrophins in plasma during pro-oestrus and oestrus and then cannulated through the jugular vein or cannulated and hypophysectomized during the late morning or early afternoon of pro-oestrus. Comparison of patterns of plasma FSH in hypophysectomized and intact rats after i.v. injection of 0·5 μg FSH at 17.00 h suggested that exogenous FSH stimulated the release of endogenous FSH in less than 5 h. Intravenous LH (2 μg at 16.00 and at 18.00 h) raised the level of FSH in plasma between 2 and 6 h after the first injection of LH. Both gonadotrophins stimulated FSH release by the pituitary gland during the morning of oestrus. Comparison of patterns of plasma FSH in hypophysectomized and intact rats after i.v. injection of 0·25 or 0·05 μg FSH at 14.00 h suggested that the latency between FSH injection and stimulation of some FSH release by the pituitary gland is as short as 2 h. Intravenous LH (3,4 or 9 μg) at 14.00 h did not increase the level of FSH in plasma within 2 h and was only minimally effective in raising the level within 4 h. Intravenous LH (2 μg at 16.00 and at 18.00 h) on the afternoon of dioestrus day 2 was nearly as effective in increasing the levels of FSH in plasma as it was when administered to pro-oestrous rats. This procedure did not raise the plasma levels of FSH in rats used on dioestrus day 1. The results suggest that in the phenobarbitone-blocked, pro-oestrous rat (1) a small increase (less than that observed spontaneously) in plasma rat FSH during pro-oestrus is effective in stimulating FSH release by the pituitary gland, (2) an increase in plasma rat FSH can exert positive feedback on its own secretion within 2 h and (3) a large increase in plasma rat LH is not very effective in increasing the plasma level of FSH over a period of 4 h. The results also suggest that the spontaneous increase in plasma levels of FSH and, to a lesser extent, of LH is involved in causing the selective phase of FSH release which occurs during late pro-oestrus and the morning of oestrus, and that LH and FSH act differently, but not necessarily by way of a different mechanism, to stimulate release of FSH by the pituitary gland.
STIMULATION BY LOW PHOSPHORUS AND LOW CALCIUM DIETS OF DUODENAL ABSORPTION OF PHOSPHATE IN BETAMETHASONE-TREATED CHICKS
Authors: FOX J. , BUNNETT N. W. , FARRAR A. R. , CARE A. D.
Published: December 2008

Although the inhibitory effect of glucocorticoids on the intestinal absorption of calcium is well recognized, their effect on the absorption of phosphate is less well documented. We studied the effect of the oral administration of betamethasone (BM; 25 μg/kg per day) on the duodenal absorption of phosphate in chicks fed normal calcium, normal phosphorus (NCaNP), normal calcium, low phosphorus (NCaLP) or low calcium, normal phosphorus (LCaNP) diets using the ligated loop technique in vivo. The daily oral administration of BM for 8 days significantly reduced the absorption of phosphate in chicks fed the NCaNP diet (21% decrease) but had less effect in chicks fed the NCaLP (14% decrease) or LCaNP (9% decrease) diets in which birds the absorption of phosphate was significantly raised (49 and 87% respectively). In one group of chicks, BM was administered for 9 days before the birds were transferred to the NCaLP or LCaNP diets. Adaptation was again unaffected by the treatment. Thirty-four per cent of the absorbed phosphate was retained in the duodenal tissue. Treatment with BM reduced the amount retained but this may have been caused by the lower weight of the duodenal segment in these chicks as BM administration markedly reduced growth rate. We have concluded that the duodenal absorption of phosphate in the chick can be inhibited by treatment with BM, although this may be secondary to the reduced rate of growth, but the increase in the absorption of phosphate caused by feeding NCaLP or LCaNP diets was unaffected by the steroid.
INHIBITORY EFFECT OF O-ALKYLATED ANALOGUES OF OXYTOCIN AND VASOPRESSIN ON HUMAN AND RAT MYOMETRIAL ACTIVITY
Authors: MELIN P. , VILHARDT H. , LINDEBERG G. , LARSSON L.-E. , ÅKERLUND M.
Published: December 2008

Analogues of oxytocin and vasopressin modified through O-alkylation (methyl, ethyl and butyl) at position 2 of the peptide chain were synthesized and tested for effects on the rat uterus in vivo and on isolated rat and human myometrial preparations. None of the analogues showed any appreciable oxytocic activity. When tested together with oxytocin or vasopressin the analogues inhibited the uterine response to the hormones in a dose-dependent and reversible way. Ethyl-analogues were more powerful antagonists than methyl-analogues but further prolongation of the alkyl-chain (butyl) diminished the antagonistic properties of the compounds. The effect on antagonistic potency of deamination at position 1 of the analogues varied among the analogues and depended on the test system used. The possible clinical value of the antagonists is discussed.
COMPARISON OF BINDING OF BOVINE AND HUMAN THYROID-STIMULATING HORMONE TO RECEPTOR SITES ON HUMAN THYROID MEMBRANES
Authors: KERMODE J. C. , THOMPSON B. D. , EDMONDS C. J.
Published: December 2008

The binding of 125I-labelled bovine TSH (bTSH) to a wide range of human thyroid membrane preparations was compared with that of 125I-labelled human TSH (hTSH). Much higher binding percentages were obtained with the 125I-labelled bTSH. This was because the receptors had a higher binding affinity for bTSH than for hTSH. No differences in tracer purity, nor differences in optimal conditions for the binding of bTSH or hTSH, nor tracer degradation contributed significantly to the better binding of 125I-labelled bTSH.

Good correlation was found between binding percentages for 125I-labelled bTSH and 125I-labelled hTSH over the range of thyroid specimens. Useful information on human TSH receptors is, therefore, obtainable from binding studies with 125I-labelled bTSH.

The TSH displacement curves yielded linear Scatchard plots whenever the tracer and displacing hormones were of the same species. The data were, therefore, consistent with a simple binding reaction between TSH and a single set of independent receptor sites.
EFFECTS OF EPIDERMAL GROWTH FACTOR ON HAIR GROWTH IN THE MOUSE
Authors: MOORE G. P. M. , PANARETTO B. A. , ROBERTSON D.
Published: December 2008

The growth of the first hair coat in male mice was studied during administration of epidermal growth factor (EGF). Injections of 1 or 4 μg EGF/g body weight for 14 consecutive days from birth resulted in the development of curved overhairs (monotrichs), caused a retardation in rate of growth in length of hair and a reduction in hair diameter and length of follicle bulb. Growth rate partially recovered after cessation of EGF treatment. However, some of the effects produced by injections of EGF during the formation of the first coat were detected in the second and third generations of hair. Since EGF also retarded rate of body growth, we compared the effect of EGF on hair growth with that of restricting food intake in neonatal mice during the development of the first coat. Hair growth was slowed in underfed animals but the effects were less marked than those found in EGF-treated mice of similar body weights.
DEPENDENCE ON PROTEIN SYNTHESIS OF THE N6-MONOBUTYRYL CYCLIC AMP PLUS THEOPHYLLINE MEDIATED RELEASE OF LUTEINIZING HORMONE INDUCED BY LUTEINIZING HORMONE RELEASING HORMONE FROM RAT PITUITARY GLANDS IN VITRO
Authors: DE KONING J. , VAN DIETEN J. A. M. J. , TIJSSEN A. M. I. , VAN REES G. P.
Published: December 2008

The involvement of cyclic AMP in the action of LH releasing hormone (LH-RH) on LH secretion was studied by incubating pituitary glands from adult female rats on day 2 of dioestrus with 1 mm-N6-monobutyryl cyclic AMP (mbcAMP) and 10 mm-theophylline for periods of up to 10 h. This treatment induced a pattern of LH release similar to that observed in the presence of a low concentration of LH-RH (0·1 ng LH-RH/ml), i.e. an initial 4 h period during which the release of LH was minimal was followed subsequently by an increased rate of release. In this system inhibition of protein synthesis by cycloheximide (25 μg/ml) did not impair the initial response of the pituitary tissue but the increase in the rate of LH release during the second phase of the response was blocked.

Preincubation with mbcAMP and theophylline increased the responsiveness of the pituitary tissue to LH-RH. This action could be prevented by including cycloheximide during the preincubation period, whereas addition of this drug during the incubation with LH-RH no longer impaired the increased responsiveness. The size of the sensitizing action of mbcAMP and theophylline mediated through the induction of protein synthesis was comparable with that of a high concentration of LH-RH. From the absence of a significant change in total LH during the preincubation period, it was concluded that the increased responsiveness was not the result of newly synthesized LH.

The present results suggest a role or roles for cyclic AMP in the secretion of LH induced by LH-RH. Besides an effect on the formation of a factor related to the synthesis of protein, other than LH which has a permissive role in the acute release of LH, cyclic AMP might also be concerned in the secretion process through a pathway which does not involve synthesis of protein.
AGONIST AND ANTAGONIST ACTIVITY OF EN-CLOMIPHENE UPON OESTROGEN-MEDIATED EVENTS IN THE UTERUS, PITUITARY GLAND AND BRAIN OF THE RAT
Authors: BOWMAN SUSAN P. , LEAKE A. , MILLER M. , MORRIS I. D.
Published: December 2008

The oestrogen agonist and antagonist activity of a single dose of en-clomiphene (0·5–50 mg/kg) was studied in peripheral and brain tissue in the 3 week ovariectomized rat. 17β-Oestradiol benzoate (100 pg/kg) or vehicle was injected 24 h after en-clomiphene administration and data collected at 72 h. En-clomiphene produced a dose-related (agonist) fall in body weight and food intake. Agonist action was not observed upon sexual receptivity and prolactin secretion; oestrogen antagonism of these parameters was only seen at the higher doses. The effects of en-clomiphene upon serum LH and FSH were complex, both agonist and antagonist activity being demonstrated in the absence and presence of oestrogen. En-clomiphene was uterotrophic at all doses tested; however, oestrogen antagonism was only seen at the higher doses. Inhibition of the accumulation of uterine luminal fluid at the higher doses of en-clomiphene was a sensitive index of oestrogen antagonism. The results are discussed in relation to previous studies of the effects of enclomiphene on oestrogen receptors. With the exception of the antagonism of oestrogen-induced sexual receptivity no correlation could be made between biological activity and the status of oestrogen receptors in tissue.
INVESTIGATIONS INTO THE POSSIBLE EFFECTS OF NATURALLY OCCURRING STEROIDS ON BIOSYNTHESIS OF 16-ANDROSTENES AND ANDROGENS IN MICROSOMES OF BOAR TESTIS
Authors: COOKE G. M. , GOWER D. B.
Published: December 2008

The possible interactions between naturally occurring steroids and three enzymes of the biosynthetic pathways of 16-androstenes and androgens in the boar testis were investigated. High concentrations (1 mmol/l) of several steroids reduced the production of 5,16-androstadien-3β-ol when a microsomal fraction of boar testis was incubated with pregnenolone at pH 7·0 (the pH optimum of this reaction was found to be 6·6). When some of these inhibitors were investigated in more detail using Lineweaver–Burk analyses, the apparent inhibition constants, Ki, increased in value with increasing concentrations of inhibitors. When testosterone was added to 5,16-androstadien-3β-ol synthetase assays, the apparent Ki for 0·1 μmol testosterone/l was 0·165 μmol/l whereas those for 1·0, 10·0 and 100·0 μmol testosterone/l were 1·65, 16·5 and 48·7 μmol/l respectively. The apparent Michaelis constant, Km, of the reaction was 0·6 μmol/l. Similar results were obtained when oestrone, 17α-hydroxyprogesterone and 4,16-androstadien-3-one were added as effectors. At physiological concentrations, these steroids would not affect the biosynthesis of 5,16-androstadien-3 β-ol in vivo. Similarly, both 5α-androst-16-en-3β-ol, quantitatively the most important 16-androstene in the boar testis and 5,16-androstadien-3β-ol were examined for their effects on the 17α-hydroxy-C21 -steroid, C-17,20 lyase (C-17,20 lyase) and 17β-hydroxysteroid dehydrogenase (17β-OHSDH) enzymes of androgen biosynthesis. Neither of these enzymes was affected by the 16-androstene steroids even at concentrations of 100 μmol/l, and the apparent Km values were 3·3 and 26·0 μmol/l for C-17,20 lyase and 17β-OHSDH respectively. This lack of interaction between these pathways implies that the high levels of 16-androstene steroids produced by the testis will not interfere with androgen production, and also that the two side-chain cleavage steps from C21 precursors to C19 steroids are catalysed by independent systems.
FAILURE OF SHORT-TERM HYPERPROLACTINAEMIA TO INCREASE THE NUMBER OF GONADOTROPHIN RECEPTORS IN THE RAM TESTIS
Authors: BARENTON BRUNO
Published: December 2008

Hyperprolactinaemia was induced during March in 2-year-old rams which had regressed testes. Five animals were intravenously infused with prolactin for 3 days at a rate that raised concentrations of prolactin in plasma to levels equivalent to those generally found in summer. Five untreated animals acted as controls.

The treatment did not change plasma levels of LH and FSH and had no effect on testicular content of LH and FSH receptors. These results indicate that prolactin is not directly involved in the acute regulation of gonadotrophin receptors in the ram testis.
EFFECT OF BROMOCRIPTINE ON DNA SYNTHESIS, GROWTH AND HORMONE SECRETION OF SPONTANEOUS PITUITARY TUMOURS IN THE RAT
Authors: PRYSOR-JONES R. A. , JENKINS J. S.
Published: December 2008

The 'spontaneous' development of pituitary tumours has been studied in the Wistar–Furth strain of rat. In females aged 64–135 weeks the incidence was as high as 69% whereas in males aged 72–116 weeks only 6% developed tumours. Hyperprolactinaemia was invariably associated with these spontaneous pituitary tumours but excessive secretion of growth hormone (GH) was found in one animal only. Bromocriptine inhibited secretion of prolactin and DNA synthesis of the tumours. In a mixed GH- and prolactin-secreting tumour transplanted to a peripheral site, bromocriptine reduced the size of the tumour as well as the secretion of both hormones. Oestradiol reversed the inhibitory action of bromocriptine on prolactin secretion and tumour growth but failed to influence the reduction in GH secretion caused by the drug.
PHARMACOKINETICS OF PROGESTERONE IN LAYING AND NON-LAYING HENS (GALLUS DOMESTICUS)
Authors: JOHNSON A. L. , VAN TIENHOVEN A.
Published: December 2008

The metabolic clearance rate (MCR), volumes of distribution (Vd), production rate (PR) and half-life (t½) of progesterone were measured in laying hens 8 h before, during and 8 h after the preovulatory surge of progesterone, and in non-laying hens (pullets and moulting hens) after a single injection of [1,2,6,7-3H]progesterone. A curve-fitting computer program showed that the data of [3H]progesterone metabolism best fit a two-compartment model. The MCR of non-laying birds (163·2±6·4(s.e.m.) ml/min) was significantly greater than that of laying hens (122·4±6·1 ml/min). The mean PR of progesterone in laying hens measured 8 h before and 8 h after the preovulatory peak of progesterone (42·498±6·509 ng/min per kg0·75) was comparable to that of moulting hens (61·771±14·363 ng/min per kg0·75). However, the PR of progesterone in hens when measured during the preovulatory surge of progesterone (254·335±53·972 ng/min per kg0·75) was significantly greater than 8 h before and 8 h after the surge. There were no significant differences among groups in the t½ of the distribution phase (combined mean, 1·03±0·05 min), biologically active t½ (combined mean, 10·93±0·31 min) or Vd of the central compartment (VdA; combined mean, 609·4±46·7 ml). However, the Vd in the peripheral compartment (VdB) was significantly greater in non-laying birds (combined mean, 3891·3±399·5 ml) compared with that of laying hens (combined mean, 2879·2±154·4 ml). There was no significant difference for MCR (ml/min) and PR (ng/min) of progesterone for non-laying pullets between methods using a single injection or continuous infusion. However, when body weight differences between the two groups of pullets were taken into account and the values adjusted by covariance analysis, the MCR obtained with the continuous infusion method was significantly (P<0·05) higher than the value obtained with the single injection method.

It is concluded that (a) the preovulatory surge of progesterone is the result of an increase in the PR and not of a decrease in the MCR; (b) the lower MCR in laying hens compared with pullets and moulting hens is reflected by a smaller Vd B, likely to be due to the presence of progesterone receptors of higher affinity and/or binding capacity in laying hens and to differences in extraction efficiency by progesterone-metabolizing organ systems; (c) t½ in the hen would appear to be shorter than that reported for mammalian species.
ELECTRICAL ACTIVITY OF ANTIDROMICALLY IDENTIFIED TUBEROINFUNDIBULAR NEURONES DURING STIMULATED RELEASE OF LUTEINIZING HORMONE AND PROLACTIN IN PRO-OESTROUS RATS
Authors: DYER R. G. , SAPHIER D. J.
Published: December 2008

Extracellular activity was recorded from tuberoinfundibular neurones in 28 urethane-anaesthetized pro-oestrous rats. In each rat the electrical activity of one antidromically identified neurone was analysed before and during electrical stimulation in the preoptic/anterior hypothalamic areas (PO/AH). This stimulation (50 Hz, 30 s on and 30 s off for 15 min) resulted in significant increases in plasma concentrations of prolactin (from 46±11 (s.e.m.) ng/ml before stimulation to 86 ±17 ng/ml 20 min later; P<0·02) and LH (27 ± 6 to 48±11 ng/ml; P<0·01). A substantial proportion (11 out of 28) of the tuberoinfundibular neurones was inhibited by PO/AH stimulation. If such cells are directly involved with the secretion of anterior pituitary hormones it is probable that they synthesize and secrete inhibitory factors. We have suggested that cells inhibited by stimulation of the PO/AH are possibly the neurones which secrete prolactin inhibitory factor. The excited cells (eight out of 28) gave complex and variable responses to hypothalamic stimulation and were unable to follow applied stimuli at a ratio of more than one extra action potential for every ten stimulus pulses. We propose that this may explain why it is necessary to stimulate the PO/AH at ten times the frequency required for ovulation to occur following stimulation in the median eminence in anaesthetized pro-oestrous rats.
EVIDENCE THAT PROGESTERONE DOES NOT INHIBIT THE INDUCTION OF SEXUAL RECEPTIVITY BY OESTRADIOL-17β IN THE RAT
Authors: SÖDERSTEN P. , ENEROTH P.
Published: December 2008

Progesterone-filled constant-release implants facilitated the induction of sexual receptivity in ovariectomized rats given implants of oestradiol-17β precisely 32 h before testing, irrespective of the time of implantation. Inhibition by progesterone implants of the behavioural response to an injection of progesterone occurred after the facilitation 32 h after oestradiol implantation. Sexual receptivity could be induced in pseudopregnant rats in the absence of progesterone treatment by injection of 1 μg oestradiol 32 and 16 h before testing at a time when endogenous serum levels of oestradiol were low and progesterone levels were high. The behavioural response of ovariectomized rats implanted with oestradiol and tested daily was unaffected by implantation of progesterone at the time of oestradiol implantation, although serum levels of progesterone varied with the number of progesterone implants inserted. Inhibition by progesterone implants of the behavioural response to an injection of progesterone 6 h before behavioural testing occurred only if the progesterone implants were present for at least 32 h of a 48 h period. Serum levels of progesterone were raised within 1 h of progesterone implantation and declined within a 6 h period after implant removal. It is concluded that progesterone does not inhibit the behavioural effect of oestradiol and that progesterone does not play an inhibitory role in the regulation of the behavioural oestrous cycle in our strain of rats.
BROMOCRIPTINE AND α-ERGOCRYPTINE DO NOT INHIBIT OXYTOCIN SECRETION IN THE LACTATING RAT
Authors: RUSSELL J. A. , HARRISON D. J. , McNEILLY A. S.
Published: December 2008

Two experiments were performed to study the effects of bromocriptine and α-ergocryptine on oxytocin secretion in lactating rats. In both experiments, after overnight separation from their litters, rats were injected with either vehicle alone or ergot alkaloid plus vehicle; 4 h later the litters were returned.

In the first experiment the mothers were conscious. Treatment did not affect suckling behaviour, number of stretch reactions or litter weight gain in the first 30 min. Oxytocin injection before the second 30 min period of suckling caused no extra milk to be obtained. In the second experiment the mothers were anaesthetized with ethyl carbamate (1·1 g/kg body weight) at the time of the ergot alkaloid or vehicle injection. Changes in intramammary pressure were recorded during suckling. Ergot alkaloids altered neither the number of milk ejections caused by suckling, nor the proportion of milk ejections equivalent to 0·2 mu. or more oxytocin.

In both experiments treatment with ergot alkaloids suppressed secretion of prolactin. It is concluded that (a) in suppressing lactation, bromocriptine and α-ergocryptine do not inhibit oxytocin secretion as well as prolactin secretion, and that (b) prolactin secretion is not a necessary concomitant of oxytocin secretion.
PROGESTERONE CONCENTRATIONS IN PERIPHERAL PLASMA OF NON-PREGNANT AND PREGNANT GREY SQUIRRELS (SCIURUS CAROLINENSIS)
Authors: TAIT A. J. , POPE G. S. , JOHNSON ELIZABETH
Published: December 2008

Plasma concentrations of progesterone in non-pregnant female grey squirrels were never greater than 3·2 nmol/l and no significant differences were found between levels in anoestrous, pro-oestrous and oestrous animals. During pregnancy, plasma concentrations of progesterone increased significantly and reached a maximum level of 318 nmol/l at around day 35 of the 44 day period of gestation. After parturition, plasma concentrations of progesterone fell sharply. The corpora lutea of pregnancy began to regress in size at about day 30 of gestation, before the maximum levels of progesterone in the plasma were reached, which suggests that there is an extra-ovarian source of progesterone.

Chromatography of pregnancy plasma extracts showed that no significant amount of 5α-or 5β-pregnane-3,20-dione was present and that progesterone accounted for 90% of the assay-positive material in pregnancy plasma from grey squirrels.
CHANGES IN RESPONSIVENESS OF DISPERSED PITUITARY CELLS TO LUTEINIZING HORMONE RELEASING HORMONE AT DIFFERENT TIMES OF THE OESTROUS CYCLE OF THE RAT
Authors: SPEIGHT ALISON , FINK G.
Published: December 2008

Dispersed pituitary cells obtained from female rats with regular oestrous cycles were suspended in Bio-Gel columns and perfused with pulses of luteinizing hormone releasing hormone (LH-RH). There was a close relationship between the amount of LH released and the concentration of LH-RH in the perfusate. It was not possible to elicit the priming effect of LH-RH, but the LH-response changed markedly during the oestrous cycle in a manner similar to that seen in vivo; i.e. the responses of cells prepared from rats killed at pro-oestrus were much greater than the responses of cells prepared from rats killed on other days of the cycle. A similar change in responsiveness was obtained when the columns were perfused with 60 mmol K+/1, suggesting that at least part of the increase in pituitary responsiveness that occurs at pro-oestrus is not dependent upon changes in specific receptors for LH-RH.
ADRENOCORTICOTROPHIC HORMONE IN THE ANTERIOR AND NEUROINTERMEDIATE LOBES OF THE FETAL RAT PITUITARY GLAND
Authors: CHATELAIN ALAIN , DUPOUY J. P.
Published: December 2008

The concentration of ACTH in the pars distalis and pars intermedia of the fetal rat hypophysis from days 17–21 of pregnancy was measured with a specific radioimmunoassay and a bioassay using isolated adrenal cells from adult rats.

In both lobes of the pituitary gland, a significant correlation was observed between immunoreactive and bioreactive values, expressed as pg equivalents synthetic human 1–39 ACTH per μg protein.

In the pars distalis, ACTH concentrations increased steadily from days 17–20 and then remained unchanged to term. At this time they were tenfold higher than on day 17. In the neurointermediate lobe, ACTH was detected only from day 18; the concentration of ACTH increasing between days 18 and 19. At each of the stages of pregnancy examined, the concentration of ACTH in the pars distalis was greater than that in the pars intermedia.

These data have demonstrated that ACTH is present in both anterior and neurointermediate lobes of the fetal rat hypophysis, that the functional differentiation of the pars distalis takes place earlier than that of the pars intermedia, and that the concentrations of corticotrophin in the pars distalis and in the pars intermedia have different patterns of development as gestation progresses.
MACROPODID MARSUPIAL TESTICULAR GONADOTROPHIN RECEPTORS AND THEIR USE IN ASSAYS FOR MARSUPIAL GONADOTROPHINS
Authors: STEWART FRANCESCA , SUTHERLAND R. L. , TYNDALE-BISCOE C. H.
Published: December 2008

The interactions of several mammalian follicle-stimulating hormones and luteinizing hormones with specific gonadotrophin receptors in macropodid marsupial testicular homogenates were investigated with a view to developing radioreceptor assays for marsupial FSH and LH. Testes from Eastern grey kangaroos and tammar wallabies possessed high affinity (dissociation constant ≃10−10 mol/l) saturable receptor sites which were highly specific for LH or FSH. Luteinizing hormone receptor sites bound only highly purified LH preparations (human, ovine and rat) but did not bind highly purified FSH, TSH or prolactin while FSH receptor sites were equally specific for highly purified FSH preparations. These sites demonstrated a degree of species specificity in that marsupial pituitary extracts were relatively more potent in these assays than in assays using gonadotrophin receptors from rat testes. Serum from hypophysectomized female tammar wallabies had little effect on the slope and position of the LH standard curve but significantly depressed the dose–response curve for FSH. For this reason it was not possible to develop a radioreceptor assay for serum FSH using marsupial testicular FSH receptors. However, gonadotrophin receptors from both rat and marsupial testes have been emplpyed in the successful development of radioreceptor assays for marsupial pituitary LH and FSH and marsupial serum LH.
COMBINED EFFECTS OF NEONATAL THYROXINE TREATMENT AND NEONATAL CASTRATION ON SEBUM PRODUCTION IN ADULT MALE RATS
Authors: TOH YEE CHU
Published: December 2008

Newborn Sprague–Dawley rats were castrated within 24 h of birth and control animals were sham-operated. Intact female rats were also included for comparison. One-half of the rats in each group was treated with 28 μg thyroxine (T4) daily for the first week of life. The secretion rate of sebum was measured at the age of 80 days from the amount of skin-surface lipids that could be extracted with acetone and which had been produced during 2 days.

Castration of rats at birth decreased the rate of sebum secretion and neonatal castration plus neonatal thyrotoxicosis produced an even lower level of sebum which more nearly approached that seen in female rats with neonatal T4 treatment. It was concluded that a reduction in the response of the sebaceous glands in adult rats made thyrotoxic with high doses of T4 in the early stage of life is not due to a decreased secretion of gonadal steroids.
SKIN-COLOUR CHANGES IN THE LIZARD, ANOLIS CAROLINENSIS, IN RESPONSE TO LOCALIZED ELECTRICAL STIMULATION AND LESIONS IN THE DIENCEPHALON
Authors: HEMER J. H. , SALAS M. A. , LAPOINTE J. L.
Published: December 2008

A study was made of changes in skin colour in the lizard, Anolis carolinensis, in response to deep electrical stimulation at 0·2 mm intervals throughout the periventricular region of the diencephalon and the anterior brain stem. Double-barrelled glass microelectrodes with tip diameters of 3 μm were used. A 20 μA pulse-train consisting of a 500 Hz signal lasting for 1 s yielded localized responses. Skin darkening occurred only in response to stimulation delivered in the anterior and dorsal region of the diencephalon and skin lightening only in response to stimulation in a small area in the posterior and ventral region of the hypothalamus. Electrical lesions in the latter region resulted in permanent skin darkening. Surgical interruption of the hypothalamo–hypophysial neurosecretory tract did not block skin-colour change in response to dark or light backgrounds.

It was concluded that MSH release is under tonic inhibitory control by hypothalamic neurones in Anolis. Both inhibitory and stimulatory neurones can be localized stereotaxically in the diencephalon and neither type corresponds with the neurosecretory neurones of the hypothalamo–hypophysial tract. The functional relationship between the stimulatory neurones and the inhibitory neurones and pars intermedia remains unclear.
BINDING OF GLUCOCORTICOSTEROIDS TO HEPATIC ERYTHROPOIETIC CELLS OF THE RAT FETUS
Authors: BILLAT C. , FELIX J. M. , MAYEUX P. , JACQUOT R.
Published: December 2008

A role for glucocorticosteroids in the evolution of the fetal liver erythron in vivo has been proposed. If direct, such an intervention implies the presence of receptor sites in the cells of the erythroid cell lines. To test this hypothesis cell suspensions were prepared from liver haematopoietic tissue obtained from rat fetuses aged 13, 14, 17 and 20 days. Their composition was determined by light microscopy. The populations consisted essentially of cells of the erythroid line: juvenile cell types (progenitor and basophilic cells) predominated in tissue collected at 13 and 14 days of gestation, more mature types (polychromatic and acidophilic cells) became more abundant at 17 and 20 days of gestation. Suppressible binding of glucocorticosteroid at 4°C was studied on these suspensions, using [3H]dexamethasone. Binding sites were found at all stages of gestation studied. The mean number per cell (for the entire erythroid population) was roughly 3600, 3500, 2300 and 1700 at 13, 14, 17 and 20 days of gestation respectively, without any change in the apparent equilibrium dissociation constant (Kd: 5·5 × 10−9 to 6·5 × 10−9 mol/l). Suspensions containing essentially progenitor cells were prepared from erythropoietic cells from livers obtained at 14 and 16 days of gestation, using a rabbit immune serum against rat erythrocytes in the presence of an excess of complement. These cells had 1800 and 1600 receptor sites per cell respectively (same Kd as above). No receptors were found on circulating adult or fetal erythrocytes.

The results strongly suggest that there is an uneven distribution of the number of the glucocorticosteroid binding sites per cell amongst the different cell types of the erythroid line. These sites were present in progenitors, increased in number in the basophilic cells and then progressively disappeared as the cells matured.
ACUTE EFFECTS OF HYPOTHALAMIC LESIONS UPON GONADOTROPHIN SECRETION IN THE FERRET
Authors: DONOVAN B. T. , TER HAAR M. B.
Published: December 2008

The changes in FSH and LH secretion after placement of lesions in the hypothalamus were traced in ferrets serially bled at 15 min intervals. Passage of the lesioning current through platinum electrodes in anoestrous females was associated with an immediate surge in LH and FSH output. Damage to the hypothalamus of oestrous females also caused an immediate surge of LH secretion, but then a long-lasting second rise in blood LH content set in. High concentrations of LH were never sustained overnight. The response of long-term spayed females to the placement of hypothalamic lesions was similar to that of anoestrous ferrets, while that of anoestrous or oestrous ferrets was not altered by acute removal of the ovaries. Manipulation of the ovaries appeared to facilitate FSH and LH secretion. The response of males was similar to that of anoestrous females. Marked increases in FSH and LH release were also seen in females when lesions were made with steel electrodes, but had subsided on the following day.
EFFECTS OF NEONATAL EXPOSURE TO MONOSODIUM GLUTAMATE ON THE ELECTRICAL ACTIVITY OF NEURONES IN THE MEDIOBASAL HYPOTHALAMUS, AND ON THE PLASMA CONCENTRATIONS OF THYROID-STIMULATING HORMONE AND PROLACTIN, FOLLOWING STIMULATION OF THE ROSTRAL HYPOTHALAMUS IN ADULT FEMALE RATS
Authors: SAPHIER D. J. , DYER R. G.
Published: December 2008

Action potentials were recorded from 174 neurones in the mediobasal hypothalamus of ovariectomized adult female rats exposed neonatally to monosodium glutamate (MSG) and from 145 neurones in control rats. All of the animals, which were anaesthetized with urethane, had been ovariectomized for at least 3 weeks and received two injections of oestradiol benzoate (20 μg/100 g body weight, i.m.) 72 h and immediately before the recording experiments. The response of each neurone to electrical stimulation of the median eminence and rostral hypothalamus (preoptic and anterior hypothalamic areas; PO/AH) was analysed. The most striking feature of the results obtained was the significant (P < 0·001) loss of inhibitory responses in those neurones remaining in the adult rats after neonatal treatment with MSG. The loss of inhibitory responses applied to both stimulation sites.

In each rat the response of one neurone, which was antidromically identified as projecting to the median eminence, was recorded before and during stimulation of the PO/AH at 50 Hz for 30 s in every min for 15 min. Before and after this stimulation blood was collected from a jugular vein for estimation by radioimmunoassay of concentrations of prolactin and TSH. In the MSG-treated rats significantly (P < 0·05) fewer neurones were inhibited by the 50 Hz stimulation than in control rats. In control rats the plasma concentrations of prolactin nearly quadrupled as an immediate consequence of this treatment, whereas in MSG-treated rats plasma concentrations barely doubled. However, in the MSG-treated rats plasma concentrations of prolactin continued to rise after stimulation ceased, possibly as a consequence of enhanced secretion of thyrotrophin releasing hormone.
EFFECT OF GONADECTOMY ON THE CONCENTRATIONS OF CATECHOLAMINES IN DISCRETE AREAS OF THE DIENCEPHALON OF THE DOMESTIC FOWL
Authors: KNIGHT P. G. , GLADWELL R. T. , CUNNINGHAM F. J.
Published: December 2008

Concentrations of dopamine, noradrenaline and adrenaline in discrete areas of the diencephalon in male and female domestic fowl were correlated with changes in the plasma concentrations of LH induced by gonadectomy. Gonadectomized birds of both sexes exhibited raised plasma concentrations of LH and in castrated cockerels the daily administration of testosterone propionate was completely effective in preventing the post-castration rise in LH. Although no significant alterations in the brain concentrations of noradrenaline or adrenaline were observed in cockerels, the concentration of dopamine in the paraventricular nucleus (PVM), dorsomedial thalamic nucleus and mediobasal hypothalamus (MBH) were significantly raised in castrated compared with sham-operated birds by 136, 182 and 52% respectively. In each case the increase was partially suppressed by testosterone replacement therapy. In pullets, ovariectomy resulted in significant increases in the concentrations of dopamine (83%) and noradrenaline (78%) in the MBH and noradrenaline (35%) and adrenaline (34%) in the PVM. These findings suggest that in the fowl at least part of the negative feedback effect of gonadal steroids on LH secretion may be mediated by catecholaminergic mechanisms at the level of the hypothalamus.
INHIBITION OF OXYTOCIN- OR PROSTAGLANDIN F2α-DRIVEN MYOMETRIAL ACTIVITY BY RELAXIN IN THE RAT IS OESTROGEN-DEPENDENT
Authors: PORTER D. G. , DOWNING SANDRA J. , BRADSHAW JANE M. C.
Published: December 2008

Relaxin in doses of 5 μg i.v. completely but reversibly abolishes 'spontaneous' myometrial activity in anaesthetized ovariectomized rats. Similar levels of myometrial activity, evoked in oestrogen-treated rats (which normally have quiescent uteri) by infusions of oxytocin or prostaglandin F2α (PGF2α), were also reduced to complete quiescence by relaxin in small doses. However when spontaneous myometrial activity in untreated ovariectomized rats was slightly stimulated by oxytocin the uterus became completely refractory to the inhibitory effects of relaxin even at doses of 50 μg. Relaxin was also ineffective in reducing myometrial activity in similar rats during intra-arterial infusion of PGF2α. It is suggested that the ability of relaxin to inhibit uterine smooth muscle during exogenous stimulation is oestrogen-dependent.
EFFECT OF REDUCED EXTRACELLULAR SODIUM CONCENTRATION ON THE FUNCTION OF ADRENAL ZONA GLOMERULOSA: STUDIES IN CONSCIOUS RATS
Authors: BALLA T. , NAGY K. , TARJÁN ÉVA , RENCZES G. , SPÄT A.
Published: December 2008

The present experiments were designed to study the effect of extracellular hyponatraemia on aldosterone secretion. Hyperaldosteronism was induced by peritoneal dialysis with 5% glucose solution in dexamethasone-pretreated rats. In the narrow physiological range of 135–142 mmol/l, as well as in the whole range of the study (122–142 mmol/l), the plasma concentration of sodium showed a close negative correlation with the serum concentration of aldosterone (r = −0·71 and −0·83, respectively). Plasma renin activity increased after peritoneal dialysis; however, no close correlation was observed either between sodium concentration and plasma renin activity or plasma renin activity and serum aldosterone concentration within the dialysed group. The ratio of serum concentration of aldosterone to plasma renin activity showed no considerable change between 132 and 142 mmol/l but rose steeply below 132 mmol sodium/l suggesting that a factor(s) other than angiotensin may also contribute to the induction of hyperaldosteronism.
FEEDBACK EFFECTS OF STEROIDS ON GONADOTROPHIN RELEASE IN HYPERPROLACTINAEMIC, OVARIECTOMIZED RATS
Authors: CARTER D. A. , WHITEHEAD S. A.
Published: December 2008

The effect of hyperprolactinaemia on the progesterone-induced LH surge which occurs in oestrogen-primed, ovariectomized rats has been investigated. Hyperprolactinaemia was produced by implanting pituitary glands under the kidney capsule and levels of LH and prolactin in the circulation were measured at appropriate times during the steroid treatment. Twenty-four hours after oestrogen administration plasma LH levels were significantly reduced in both hyperprolactinaemic and sham-operated control rats. Progesterone induced a surge of LH which peaked 5 h after injection in both groups of rats. However, the peak LH level in the hyperprolactinaemic rats was less than 50% of that observed in the controls. Differences were also found in the effect of oestrogen on prolactin release in the hyperprolactinaemic rats. It is suggested that prolactin reduces the sensitivity to progesterone by a direct action on the hypothalamic–pituitary axis.
EFFECTS OF AN ANTISERUM TO LUTEINIZING HORMONE AND STEROID REPLACEMENT THERAPY ON MAINTENANCE OF PREGNANCY IN THE RAT: SERUM AND LUTEAL LEVELS OF PROGESTERONE, TESTOSTERONE AND OESTRADIOL
Authors: TERRANOVA P. F. , GREENWALD G. S.
Published: December 2008

Pregnant rats were injected s.c. with antiserum to LH (anti-LH) on days 8 or 10 of pregnancy (day 1 = day of sperm-positive vaginal smear) and subsequently given various steroids s.c. to prevent luteolysis and/or abortion. A single injection of 4 mg progesterone on day 8 prevented abortion and luteolysis as shown on day 12 by the presence of fetal swellings and levels of progesterone in serum (88 ±6 (s.e.m.) ng/ml) and corpora lutea (26±3 ng/mg) comparable to control values. After 0·5 ml anti-LH on day 10, a daily dose of 4 mg progesterone prevented abortion in five out of eight animals but by day 13 luteal progesterone was 3·0 ± 0·7 compared with 24±3 ng/mg in controls.

After anti-LH on day 8 or 10, daily injections of 1 or 4 mg testosterone propionate or 10 μg, 100 μg or 1 mg oestradiol failed to prevent abortion or to raise luteal concentrations of progesterone to normal values. However, 4 mg testosterone propionate on day 8 or 100 or 500 μg oestradiol on day 10 maintained serum progesterone levels at approximately half those of control values. Treatment with 4 mg testosterone propionate on days 8–11 led to significant increases in serum and luteal levels of testosterone and oestradiol on day 12; on day 10 exogenous oestradiol (100 or 500 μg) increased serum and luteal levels of oestradiol by day 13.

These results, especially treatments begun on day 8, are difficult to reconcile with the current concept that the luteotrophic action of LH in the pregnant rat is exerted by increasing luteal androgens that are aromatized to oestrogens which then act as the direct luteotrophic stimulus.
INSULIN RELEASE AND STEROID-HORMONE BINDING IN ISOLATED ISLETS OF LANGERHANS IN THE RAT: EFFECTS OF OVARIECTOMY
Authors: EL SEIFI S. , GREEN I. C. , PERRIN D.
Published: December 2008

Ovariectomized rats showed a 30% increase in body weight and food intake over a 9 day period after operation. When pair-fed with normal controls, they had comparatively higher fasting serum levels of glucose and lower levels of insulin and progesterone than the normal rats. Treatment with oestradiol reversed these results. Insulin release from islets isolated from ovariectomized rats was significantly lower than from those of normal controls; the secretory responses were improved after administration of oestradiol to ovariectomized rats.

Cytosol receptors for progesterone and oestradiol were measured in a 105 000g supernatant fraction of islets from normal, ovariectomized and oestrogen-treated ovariectomized rats. Progesterone-receptor binding was dramatically reduced after ovariectomy but was restored to normal levels by oestradiol treatment of the rats. Oestradiol-receptor binding was not significantly affected by ovariectomy but was increased several fold by oestrogen treatment of ovariectomized rats.

These results suggest that islets of Langerhans contain receptors for both progesterone and oestradiol, and that this receptor population is subject to change. Progesterone—but not oestradiol—receptor measurements could be correlated with alterations in the rates of secretion of insulin from islets. Oestrogen administration in vivo had profound effects on subsequent insulin release from islets, though this may have been mediated by way of an increase in the quantity of the progesterone receptor.
TIME-RELATED SECRETION OF GONADOTROPHINS AFTER A SINGLE INJECTION OF STEROID-FREE BOVINE FOLLICULAR FLUID IN PREPUBERTAL AND ADULT FEMALE RATS
Authors: HERMANS W. P. , DEBETS M. H. M. , VAN LEEUWEN E. C. M. , DE JONG F. H.
Published: December 2008

The time-related changes in gonadotrophin concentrations after a single injection of steroid-free bovine follicular fluid (bFF), which contains material with inhibin-like activity, were studied in 25-day-old and adult female rats which either were intact or had been ovariectomized 2 days before. In ovariectomized and intact rats administration of bFF caused a selective suppression of FSH after 4–8 h in 25-day-old rats and after 3–4 h in adult rats. No systematic changes in concentrations of LH after bFF injection were observed. Relative suppression of FSH levels in adult rats was more pronounced and of longer duration than in 25-day-old rats. Moreover, the total period of suppression lasted longer in ovariectomized than in intact rats (12 and 8 h for 25-day-old and 24 and 15 h for adult rats respectively). Hypersecretion of FSH was found in intact rats after the initial suppression; this phenomenon was more pronounced and of longer duration in adult than in 25-day-old rats. No clear change in the numbers of healthy growing follicles was observed after injection of bFF into intact rats. These results indicate that the pituitary secretion of FSH responds quickly and selectively after administration of bFF to intact and ovariectomized, 25-day-old and adult female rats. The hypersecretion of FSH in intact rats might compensate for the initial suppression of this gonadotrophin, and may thus ensure the maturation of a normal number of follicles.