bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of dehydration, haemorrhage and oviposition on serum concentrations of vasotocin, mesotocin and prolactin in the chicken
Authors: Nouwen E. J. , Decuypere E. , Kühn E. R. , Michels H. , Hall T. R. , Chadwick A.
Published: December 2008

Serum concentrations of arginine vasotocin (AVT), mesotocin and prolactin were determined by radioimmunoassay in Rhode Island Red chickens during and after dehydration, haemorrhage and oviposition. During dehydration increased circulating levels of AVT, mesotocin and prolactin were found. As water deprivation proceeded, marked differences were observed. After an initial rise in serum AVT, mesotocin and prolactin levels during mild and moderate dehydration, concentrations of both AVT and prolactin tended to normalize during continued water deprivation, while those of mesotocin remained high throughout the whole dehydration experiment with the highest at the end of the water-deprivation period. Removal of 5 ml blood at intervals of 10 min during six consecutive time-periods did not affect serum osmolality and circulating levels of AVT and prolactin, but slightly increased mesotocin. These results suggest an osmoregulatory role for AVT and prolactin, whereas mesotocin may be involved in volume control. Finally, 1 min after oviposition, control values of 19·5 ±3·4 pmol AVT/1 (n=9) were raised more than sevenfold to 142·9±12·5 pmol/l (n=11). Thereafter, a decline occurred with a half-life for AVT of 13 min with raised serum levels up to 31 min after oviposition. In contrast, the serum concentrations of mesotocin and prolactin remained unaffected by oviposition.

J. Endocr. (1984) 102, 345–351
Role of prolactin in the photoperiodic control of moulting in the mink (Mustela vison)
Authors: Martinet L. , Allain D. , Weiner C.
Published: December 2008

Beginning at the summer solstice adult female mink were maintained in long- or short-day photoperiods and treated with bromocriptine or prolactin. In control females kept under natural lighting conditions the moult coincided with the seasonal decrease in prolactin and resulted in the growth of a dense winter coat which was completed by the end of November. Long days, which slowed the decrease in plasma prolactin relative to animals in the natural photoperiod, induced a more or less complete moult followed by growth of a thin summer coat. On the contrary we observed an accelerated decrease in plasma prolactin concentrations followed by an early and brief moult in females kept under long days but treated with bromocriptine and in females under short days. The growth of a dense winter coat was completed by the end of September in all the females of the short-day group and in six of eleven females treated with bromocriptine. In the other five females, moult was followed by the growth of a summer coat. These results may suggest that the decline of prolactin after the summer solstice is responsible for the onset of the autumn moult, but the early, abbreviated moult and the growth of a winter coat observed in females kept under short days and treated with prolactin do not seem to support this hypothesis. However, the huge non-physiological levels of prolactin measured in the plasma of these females and the appearance of abnormal white under-hairs might suggest that the hormonal balance in this group was completely disturbed by the treatment. The physiological role of prolactin in the seasonal moulting cycle in mink is discussed.

J. Endocr. (1984) 103,9–15
Properties and ontogeny of the glucocorticoid receptor in the placenta and fetal lung of the sheep
Authors: Flint A. P. F. , Burton R. D.
Published: December 2008

The cytosolic glucocorticoid receptor of ovine placental zona intima has been characterized and measured between day 51 of pregnancy and term, and levels compared with those in fetal lung. By ion-exchange and gel-filtration chromatography the molybdate-stabilized receptor was found to be an acidic molecule with Stokes radius approximately 8 nm; these physicochemical characteristics of the ovine placental receptor are comparable to those of receptors in glucocorticoid target tissues from non-ruminants. Concentrations of cytosolic receptor in placenta (mean, 139 fmol/mg protein) were lower than those in fetal lung (627 fmol/mg) at all stages of gestation investigated. To some extent this difference was accounted for by a twofold higher concentration of protein in placental cytosols compared with those from fetal lung. In both tissues, cytosolic receptor concentrations were maximal between days 91 and 130, when fetal adrenal steroid secretion is low; receptor concentrations decreased before term. Fetal hypophysectomy, which resulted in prolonged gestation, raised receptor concentrations in placenta, but not in fetal lung. In both tissues, apparent dissociation constants for [3H]dexamethasone binding to glucocorticoid receptors were in the range 0·5–7·1 nmol/l; these dissociation constants did not change consistently between day 100 and term. In whole-cell preparations of placenta and fetal lung incubated in vitro there was time-dependent specific binding of [3H]dexamethasone by nuclei, and binding of labelled cytosolic receptor to isolated nuclei occurred at all stages of gestation investigated. Binding of [3H]dexamethasone by cytosolic receptor from placenta and fetal lung was inhibited by progesterone and 17α-hydroxyprogesterone, as well as by cortisol, cortisone, 11-deoxycorticosterone and 11β-hydroxyprogesterone; 20α-hydroxyprogesterone and 17α,20α-dihydroxypregn-4-en-3-one were less effective. In experiments to evaluate the possible antagonistic action of progesterone in whole-cell preparations, uptake of [3H]dexamethasone by nuclei was increased up to twofold in placental minces incubated with aminoglutethimide or epostane, when progesterone synthesis was reduced by 98 and 92 per cent respectively. Nuclear uptake in minces of fetal lung was blocked by concentrations of progesterone found in placenta. The existence of a placental glucocorticoid receptor confirms that fetal cortisol may act directly on the placenta to induce the enzymatic changes controlling the onset of labour. Its availability early in pregnancy is consistent with the ability of administered glucocorticoid to induce labour at any time after day 90 of gestation. Progesterone in the placenta may act as a glucocorticoid antagonist, protecting the fetus against inappropriate induction of preterm labour resulting from high levels of glucocorticoids in the maternal circulation.

J. Endocr. (1984) 103, 31–42
Secretion of corticotrophin releasing factor-like activity by a human bronchial carcinoid cell line
Authors: Kirkland S. C. , Ellison M. L.
Published: December 2008

The production of corticotrophin releasing factor (CRF) activity by human tumour cells in monolayer culture was investigated. The secretion of CRF activity by a bronchial carcinoid cell line was demonstrated using a rat pituitary cell monolayer system. The long-term production (5 years) of CRF activity suggested the synthesis and secretion of active factors by the tumour cells.

The CRF activity was concentrated from medium previously exposed to the tumour cells using batchwise extraction on columns packed with ODS. When these extracts were fractionated by analytical high pressure liquid chromatography, the CRF activity was resolved into two molecular forms.

J. Endocr. (1984) 103, 85–90
Heterogeneity of activity of the prolactin-releasing factor in the bovine hypothalamo–neurohypophysial complex
Authors: Yasuda N. , Yasuda Y. , Greer S. E.
Published: December 2008

Fresh samples of bovine hypothalamic median eminence or hypophysial stalk extracted with 0·1 m-HCl and fractionated on Sephadex G-100 had two prolactin-releasing factor (PRF) components, the major one in the void volume (PRF-A) and the minor one in an elution position (partition coefficient (Kav) = 0·333) immediately after PRF-A (PRF-B). Similar fractionation of bovine posterior pituitary extracts showed two PRF peaks: PRF-A and another in a more retarded position than PRF-B (Kav = 0·645; PRF-C). Storage of bovine stalk extract at −20 °C for 1 year caused a shift from higher molecular weight PRF into PRF-C. Thyrotrophin-releasing hormone stimulated prolactin secretion, but its dose–response slope and chromatographic mobility were quite different from those for bovine tissue extracts. Secretion of prolactin induced by extracts of bovine hypophysial stalk is calcium dependent and is inhibited by dopamine.

J. Endocr. (1984) 103, 243–249
Thyroid hormone binding in rat liver cytosol
Authors: Morgan G.
Published: December 2008

Binding of 3,5,3′-tri-iodothyronine (T3) and thyroxine (T4) to components of perfused rat liver supernatant fraction and isolated liver cell cytosol was studied. Of the four binding fractions in supernatant (X, A, Y and Z) separable by gel chromatography, both T3 and T4 bound preferentially to the A-fraction, which was shown to contain albumin as the major binding protein. When cytosol prepared from isolated cells was examined, T4 was again bound mainly in the A-fraction; however, T3 was observed to bind predominantly in the Y-region. Hormone binding to soluble protein in the latter system is thought to reflect the pattern in vivo, better than does binding in supernatant, although the possibility exists that the concentration of albumin observed in cytosol may be artifically high due to transfer of membrane-bound albumin during cell disruption. Nevertheless, albumin (possibly derived from more than one intracellular source) is capable of binding T4 in vivo. The presence of this protein within the hepatocyte may thus contribute to the high T4 binding capacity of the liver compared to other tissues.

J. Endocr. (1984) 103, 265–271
Androgen-binding proteins in sheep epididymis: characterization of a cytoplasmic androgen receptor in the ram epididymis
Authors: Carreau S. , Drosdowsky M. A. , Courot M.
Published: December 2008

An androgen receptor (Rc) was demonstrated in caput, corpus and cauda epididymal cytosols of the ram. This receptor had a high affinity for 5α-dihydrotestosterone (Kd = 5·2 × 10−9 mol/l) and could be distinguished from the androgen-binding protein (ABP) by several characteristics. On polyacrylamidegel electrophoresis, Rc had a mobility of 0·37 and ABP 0·61; Rc sedimented in the 9S region of a linear sucrose gradient whereas ABP migrated in the 4·3S region; the molecular weights were 192 000 and 90 000 for Rc and ABP; their isoelectric points were 5·7 and 4·8–5·0; they were proteinaceous components since they were destroyed by proteolytic enzymes and heating (50 °C for Rc and 60 °C for ABP); they exhibited different half-times of dissociation: 20 h at 0 °C for Rc and 6 min for ABP, which is in agreement with their respective physiological roles, intra- and extracellular transport of androgens. The content of Rc-binding sites in caput epididymis was 18, in corpus 4 and in cauda 22 fmol/mg protein.

J. Endocr. (1984) 103, 273–279
Somatostatin inhibits prolactin release from the lactotroph primed with oestrogen and cyproterone acetate in man
Authors: Gooren L. J. G. , Harmsen-Louman W. , van Kessel H.
Published: December 2008

The present study investigated the effect of administration of somatostatin (SRIF) on the release of prolactin in men. No effect was observed when SRIF was administered to eugonadal men. Release of prolactin was inhibited, however, when SRIF was administered to oestrogen-treated agonadal subjects (male-to-female trans-sexuals) and to an even greater degree when subjects had been pretreated with a combination of oestrogen and cyproterone acetate. This is consistent with findings in the rat. Thus in man, as in the rat, SRIF can inhibit prolactin secretion, but only after treatment with oestrogen.

J. Endocr. (1984) 103, 333–335
Influence of lighting cycles on daily rhythms in concentrations of plasma tri-iodothyronine and thyroxine in intact and pinealectomized immature broiler hens (Gallus domesticus)
Authors: Sharp P. J. , Klandorf H. , Lea R. W.
Published: December 2008

The effects of pinealectomy on the daily rhythms of concentrations of tri-iodothyronine (T3) and thyroxine (T4) were investigated in sexually immature female chickens exposed to 21-, 24- and 27-h cycles of light and darkness, or to extended periods of light or darkness for more than 24 h. In pinealectomized and control birds, rhythms in levels of plasma T3 and T4 were entrained by all lighting cycles and decreased in amplitude or disappeared in continuous light or darkness. In pinealectomized and control birds held on 21-h (11 h light: 10 h darkness; 11L: 10D) and 24-h (14L: 10D) lighting cycles, the peak of the T4 rhythm coincided with, or lagged, the trough in the rhythm of T3 while in birds held on a 27-h (14L: 13D) lighting cycle, the peak of the T4 rhythm preceded the trough in the rhythm of T3.

Pinealectomy resulted in significant effects on the phases or amplitudes of rhythms of T3 or T4 in all lighting schedules except 4L: 20D. However, these effects were not consistent in direction between experimental groups and were, therefore, of doubtful physiological significance. Pinealectomy increased the mean level of plasma T4 in birds exposed to continuous light or darkness or to 4L: 20D. A corresponding reduction in mean levels of plasma T3 was seen in birds exposed to continuous light or darkness.

It is concluded that under the lighting conditions investigated pinealectomy had no clear effect on the phases or amplitude of daily rhythms of levels of T4 or T3. However, after the effects of the feeding pattern on thyroid hormone rhythms imposed by the lighting cycle were removed by placing birds in constant lighting conditions, pinealectomy appeared to exert an inhibitory action on thyroid function.

J. Endocr. (1984) 103, 337–345
Conversion and release of an intermediate in vasopressin–neurophysin biosynthesis in the guinea-pig
Authors: Jones P. M. , Saermark T. , Robinson I. C. A. F.
Published: December 2008

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

J. Endocr. (1984) 103, 347–354
Sex differences in plasma concentrations of steroids during the sensitive period for brain differentiation in the zebra finch
Authors: Hutchison J. B. , Wingfield J. C. , Hutchison R. E.
Published: December 2008

Changes in plasma concentrations of sex steroids were examined in male and female zebra finch chicks during the sensitive period for differentiation of sexually dimorphic brain nuclei associated with the control of song. Using a chromatographic separation procedure and radioimmunoassay, androstenedione, testosterone and 5α-dihydrotestosterone were detected in plasma at relatively high concentrations immediately after hatching. There were no sex differences in concentrations of these androgens. An oestrogen, oestradiol-17β, which is known to differentiate the song-control system, is raised specifically in the circulating plasma of male zebra finch chicks, and not in females. The surge in oestradiol, which occurs during the first week after hatching, coincides with the period when capacity for differentiation of the song system is maximal. Exposure of the male brain to oestradiol-17β could trigger neuronal differentiation.

J. Endocr. (1984) 103, 363–369
Pituitary and testicular responses in sexually mature bulls after intravenous injections of graded doses of LH-releasing hormone
Authors: D'Occhio M. J. , Setchell B. P.
Published: December 2008

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

J. Endocr. (1984) 103, 371–376
Possible roles of calcium and calmodulin in mammary gland differentiation in vitro
Authors: Bolander F. F.
Published: December 2008

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

J. Endocr. (1985) 104, 29–34
Effects of hyperprolactinaemia and testosterone on the release of LH-releasing hormone and the gonadotrophins in intact and castrated rats
Authors: Brar A. K. , McNeilly A. S. , Fink G.
Published: December 2008

We have investigated the effect of hyperprolactinaemia on the secretion of LH-releasing hormone (LHRH), LH and FSH in male rats of the PVG strain which were left intact, castrated or castrated and then implanted with either a 10 or 30 mm silicone elastomer capsule containing testosterone (T10 and T30 respectively). Hyperprolactinaemia was produced by pituitary grafts under the kidney capsule. Pituitary stalk blood, for LHRH estimation, and peripheral blood, for LH, FSH and prolactin, were collected under alphaxalone anaesthesia. Pituitary stalk blood was collected during three consecutive periods of 30 min each before, during and after the application of an electrical stimulus to the median eminence (ME).

Hyperprolactinaemia significantly reduced the plasma concentrations of FSH in intact rats and the post-castration increase in the plasma concentrations of both LH and FSH. Neither hyperprolactinaemia nor castration had any significant effect on the spontaneous output of LHRH, but castration alone or castration plus implantation of a T30 capsule did significantly reduce the increment in LHRH output produced by ME stimulation, an effect not seen in rats bearing pituitary grafts. The T30, but not the T10 capsules suppressed the post-castration increase in the gonadotrophins, and the inhibitory effect of testosterone was not significantly affected by hyperprolactinaemia. An incidental but important finding was that the presence of pituitary grafts under the kidney capsule reduced the anaesthetic dose of alphaxalone by 63%.

These results show that (i) in the male rat the inhibitory effect of hyperprolactinaemia on gonadotrophin secretion is not due to a decrease in the spontaneous release of LHRH, (ii) in contrast to the female rat the post-castration increase in gonadotrophin secretion is not accompanied by an increase in the output of LHRH, (iii) the output of LHRH in response to ME stimulation is affected by castration and testosterone but not by hyperprolactinaemia and (iv) the anaesthetic effects of alphaxalone are potentiated by hyperprolactinaemia, and this may explain in part the potentiation of alphaxalone anaesthesia by oestrogen.

J. Endocr. (1985) 104, 35–43
Differential effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour in rams
Authors: D'Occhio M. J. , Galil K. A. A. , Brooks D. E. , Setchell B. P.
Published: December 2008

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

J. Endocr. (1985) 104, 69–75
Lactic acid and steroid production by intact mouse adrenal glands and cell suspensions: effects of nucleotide derivatives and substrates
Authors: Hinson J. , Birmingham M. K.
Published: December 2008

The effects of the dibutyryl derivatives of cyclic GMP and cyclic AMP on lactic acid and steroid production were compared in intact mouse adrenal glands at concentrations of 0·5–1 mmol/l and in mouse adrenal cell suspensions at concentrations of 0·01–1 mmol/l. The dibutyryl derivative of cyclic GMP had little or no effect on lactic acid production in either tissue preparation. It caused a slight stimulation of corticosteroid output in intact glands at a concentration of 1 mmol/l, amounting to one-tenth of the response observed with 1 mm-dibutyryl cyclic AMP. Dose-dependent increases in lactic acid and steroid production were obtained with dibutyryl cyclic AMP in cell suspensions. AMP and GMP increased lactic acid but not steroid production.

All the substrates tested (glucose, glucose-6-phosphate, fructose, fructose-6-phosphate, fructose-1,6-diphosphate, 10 mmol/l; pyruvate and glycerol, 20 mmol/l) stimulated basal glycolysis in intact glands and cell suspensions and none affected basal steroid production significantly. By far the greatest increase in lactic acid production was noted with fructose-1,6-diphosphate. However, only glucose and, in unsectioned glands, pyruvate exerted a potentiating effect on the glycolytic response to ACTH. Glucose potentiated the steroidogenic response to ACTH also, but only in intact glands.

The relative ineffectiveness of dibutyryl cyclic GMP is in accord with the species-dependent differing responses to the free form of the cyclic nucleotides noted in mouse and rat adrenal glands. The substrate requirements are in keeping with a rate-limiting role of phosphofructokinase and an action of ACTH at some site between the entry of glucose into the cell and the formation of fructose-1,6-diphosphate.

J. Endocr. (1985) 104, 105–111
Influence of angiotensin II on the concentration of arterial plasma electrolytes in anaesthetized sheep
Authors: Osborn E. C. , Sugden P. L. , Mackenzie J. C. , Aitken D. M. , Chapman I. D. , Howes S. , Mason O. F. , Rigby G. V. , Wilson J.
Published: December 2008

Angiotensin II and I significantly raised potassium and lowered sodium and chloride ion concentrations in arterial plasma, with peak changes occurring in the first 2 min of a 6-min infusion period. The octapeptide increased the arterial K+ level in a dose-dependent manner, but the response showed tachyphylaxis when multiple infusions of 6-min duration were administered after a recovery interval of only 5 min. Raising the arterial blood pressure by 20–33 mmHg with adrenaline and noradrenaline failed to account for the increase in arterial plasma K+ concentration produced by the two peptides. These findings, in particular the rise in K+ concentration, are discussed in relation to possible mechanisms by which angiotensin II affects arteriolar tone.

J. Endocr. (1985) 104, 143–148
Phenytoin and thyroid hormone action
Authors: Franklyn J. A. , Davis J. R. E. , Ramsden D. B. , Sheppard M. C.
Published: December 2008

Circulating free thyroid hormone concentrations are reduced in subjects taking long-term phenytoin, a finding at variance with their euthyroid clinical state and normal serum TSH concentration. It is suggested, therefore, that phenytoin may modify the cellular effects of thyroid hormones.

In order to examine the influence of phenytoin on thyroid hormone action in the pituitary gland we studied its effect on the binding of tri-iodothyronine (T3) to isolated nuclei prepared from rat anterior pituitary tissue. Phenytoin inhibited the nuclear binding of T3 in a dose-dependent fashion. Phenytoin also partially inhibited thyrotrophin-releasing hormone-stimulated TSH release from cultured rat anterior pituitary cells. These studies provide evidence for a direct effect of phenytoin on the thyrotroph mediated via nuclear T3 receptor binding.

J. Endocr. (1985) 104, 201–204
Effects of antiserum to thyrotrophin-releasing hormone on the concentrations of plasma prolactin, thyrotrophin and LH in the pro-oestrous rat
Authors: Horn A. M. , Fraser H. M. , Fink G.
Published: December 2008

The possible role of thyrotrophin-releasing hormone (TRH) in causing the pro-oestrous surge of prolactin was investigated in conscious female rats by passive immunization with a specific anti-TRH serum raised in sheep. Blood samples were withdrawn through a previously implanted intra-atrial cannula. The i.p. injection of 1 ml anti-TRH serum, but not non-immune sheep serum, at 13.00 h of pro-oestrus delayed by about 1 h the onset of the prolactin surge, but the peak of the surge was similar to that in animals injected with the non-immune serum. The plasma concentrations of TSH were significantly reduced by the anti-TRH serum, but plasma concentrations of LH were not significantly affected. These results show that TRH may play an important role in the timing and initiation, but not the maintenance of the prolactin surge in the pro-oestrous rat.

J. Endocr. (1985) 104, 205–209
Induction of precocious puberty in the female rat after chronic naloxone administration during the neonatal period: the opiate 'brake' on prepubertal gonadotrophin secretion
Authors: Sirinathsinghji D. J. S. , Motta M. , Martini L.
Published: December 2008

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

J. Endocr. (1985) 104, 299–307
Social factors and puberty in female rats
Authors: Slob A. K. , van Es G. , van der Werff ten Bosch J. J.
Published: December 2008

The effects of postweaning social conditions on the age of puberty were studied in female rats from an early-and a late-maturing strain. The postweaning living conditions consisted of the presence or absence of an adult rat (intact or gonadectomized male, or intact female), or of bedding soiled by adult males. The infantile females exposed to these conditions were caged either singly or with three peers. Puberty was studied in terms of first ovulation, verified always by ovarian histology.

Females of the late-maturing strain living without peers reached puberty about 2 days earlier than females that grew up in groups of four, irrespective of the presence or absence of an adult animal. In neither strain was puberty accelerated by the presence of intact males or the soiled bedding of such males.

These results do not support the view that in the rat pheromones from adult males enhance puberty in females, contrary to what is known to happen in the mouse.

J. Endocr. (1985) 104, 309–313
Effects of pregnant mare serum gonadotrophin and oestradiol benzoate on enzymes associated with xenobiotic metabolism in immature and hypophysectomized female rats
Authors: Williams M. T.
Published: December 2008

Treatment of immature (22-day-old) female Sprague–Dawley rats with pregnant mare serum gonadotrophin (PMSG) resulted in a significant increase in hepatic microsomal cytochrome P-450 concentrations when compared with animals treated with 0·9% (w/v) NaCl solution. Cytochrome P-450 concentrations in microsomes from control and PMSG-treated animals were 0·49 ± 0·07 and 0·78 ± 0·18 nmol/mg microsomal protein respectively (mean ± s.d.). When hypophysectomized rats were treated with PMSG no significant difference was observed between saline-treated and PMSG-treated animals (0·84 ± 0·06 vs 0·88± 0·08 nmol/mg microsomal protein). Cytochrome b5 concentration and NADPH–cytochrome c reductase and ferricyanide reductase activities were not significantly affected by PMSG treatment. Similar results were obtained when immature and hypophysectomized rats were treated with oestradiol benzoate.

Hepatic glutathione (GSH) S-transferase activity was significantly stimulated over control values when hypophysectomized or immature animals were treated with PMSG, oestradiol benzoate or 3-methyl-cholanthrene. Treatment of animals simultaneously with PMSG or oestradiol benzoate and 3-methyl-cholanthrene resulted in higher transferase activity than did either treatment alone. Oestradiol benzoate or PMSG treatment of immature female rats resulted in an approximate twofold increase in hepatic aryl hydrocarbon hydroxylase (AHH) activity. However, AHH activity in hypophysectomized animals was not significantly increased by PMSG or oestradiol benzoate treatment.

It is concluded that PMSG or oestradiol benzoate treatment of immature female rats resulted in increased total cytochrome P-450 concentration and AHH activity in hepatic microsomes. Glutathione S-transferase activity was also stimulated. Neither PMSG nor oestradiol benzoate stimulated cytochrome P-450 levels or AHH activity in hypophysectomized rats. However, GSH S-transferase activity was stimulated similar to that in immature animals.

Conceivably, the PMSG effect observed in immature rats may be due to PMSG-stimulated increases in plasma oestradiol concentrations which interact at the hypothalamo-pituitary axis. The ability of oestradiol benzoate to mimic the effects of PMSG and the known action of PMSG to increase plasma oestradiol levels in immature rats would tend to support this hypothesis. The lack of increase in cytochrome P-450 concentrations and AHH activity in hypophysectomized female rats would further support the involvement of the pituitary gland in the response to PMSG rather than a direct effect of PMSG or oestradiol benzoate on the liver. Since GSH S-transferase activity is stimulated in both intact and hypophysectomized rats, this system may be under a different control mechanism.

J. Endocr. (1985) 104, 315–321
Relationship between adrenocorticotrophin bioactivity in blood and cerebrospinal fluid of rhesus monkeys
Authors: Beckford U. , Herbert J. , Jones M. T. , Martensz N. D. , Nicholson S. A. , Gillham B. , Hamer J. D.
Published: December 2008

Adrenocorticotrophin levels, measured by a cytochemical bioassay, were determined in the plasma and cerebrospinal fluid (CSF) of adult female rhesus monkeys which were ovariectomized and receiving oestrogen replacement therapy. In control monkeys, ACTH bioactivity was found in both CSF (10·2±1·8 ng/l) and plasma (186 ± 51 ng/l) in samples taken at 14.00 h (lights on: 07.00–19.00 h). Dexamethasone treatment (0·2 mg/kg) twice daily for 4 days suppressed plasma ACTH levels (52·8 ± 25·2 ng/l) but had no effect on CSF levels (7·6± 2·7 ng/l). Raising plasma ACTH, either by daily injections of a long-acting preparation of ACTH(1–24) for 6 days or by bilateral adrenalectomy (and subsequently withdrawing cortisol replacement therapy) also resulted in no detectable changes in ACTH levels in the CSF. A regression analysis between ACTH in the plasma and CSF from samples taken throughout the experiments showed no correlation. In contrast, measurement of ACTH by radioimmunoassay, whilst satisfactory for determination of this peptide in plasma, could not identify authentic ACTH in the CSF. It is concluded that bioactive ACTH does not enter the CSF in detectable quantities from either the peripheral vascular compartment or from the animal's own pituitary gland, and that reducing ACTH secretion from the pituitary also has no effect on levels of ACTH in the CSF. This is in marked contrast to other pituitary peptide hormones, including prolactin, which is secreted together with ACTH during 'stress' but which, unlike ACTH, enters the CSF relatively easily.

J. Endocr. (1985) 104, 331–338
Corticosterone storage within the adrenal cortex: evidence for a sulphate conjugate
Authors: Henry F. J. , Bassett J. R.
Published: December 2008

Incubation of homogenized rat adrenal glands with sulphatase for 18 h resulted in a significant increase in the amount of unconjugated corticosterone that could be extracted from the gland and which could not be attributed to de-novo synthesis of corticosterone during the incubation. Therefore corticosterone may be stored within the adrenal gland as a sulphate conjugate rather than as unconjugated hormone. Exposure of animals to footshock stress resulted in an increase in the amount of unconjugated corticosterone in the gland and a disappearance of the conjugate form. The rapid disappearance of the sulphate conjugate may reflect the activation of a steroid sulphatase by ACTH. However, the release of corticosterone from a storage form such as corticosterone sulphate could not explain entirely the initial increase in plasma corticosterone concentration following the stress. It was calculated that a pair of adrenal glands would have to store up to 20 nmole corticosterone in order to account for the initial increase in plasma corticosterone. This level was much greater than that extracted from a pair of glands (4·8 nmol) even after sulphatase pretreatment.

J. Endocr. (1985) 104, 381–386
Parachlorophenylalanine blocks the spontaneous pro-oestrous surge of prolactin as well as LH and affects the secretion of oestradiol-17β
Authors: Horn A. M. , Fink G.
Published: December 2008

The effect of the 5-hydroxytryptamine synthesis inhibitor, parachlorophenylalanine (PCPA), on the spontaneous, pro-oestrous surges of prolactin and LH was investigated in conscious female rats implanted with an intra-atrial cannula. The LH surge was blocked in all animals treated with PCPA, but the prolactin surge was blocked in six out of ten animals and unaffected in four out of ten animals. There was a significant correlation between the plasma concentrations of prolactin and oestradiol-17β, surges of prolactin occurred in animals with plasma oestradiol-17β concentrations of 120 pmol/l and above, and the LH surge was blocked in animals in which the oestradiol-17β concentration was less than 188 pmol/l plasma. These results show that (i) PCPA can block the pro-oestrous prolactin as well as the LH surge, (ii) in addition to a central action PCPA may depend also on its peripheral effect on the secretion of oestradiol-17β and (iii) on average, lower plasma concentrations of oestradiol-17β are required for triggering the prolactin compared with the LH surge.

J. Endocr. (1985) 104, 415–418
SUPPRESSION OF LUTEAL PROGESTERONE SECRETION IN THE STUMPTAILED MACAQUE BY AN ANTAGONIST ANALOGUE OF LUTEINIZING HORMONE RELEASING HORMONE.
Authors: Fraser H.M. , Baird D.T. , McRae G.I. , Nestor J.J. , Vickery B.H.
Published: December 2008

The dependence of progesterone secretion from the corpus luteum on pituitary gonadotrophin was examined in the cyclic stumptailed macaque by studying the effects of a single s.c. injection of a potent LH releasing hormone (LHRH) antagonist, [N–Ac–D–Nal(2)1, D–pCl–phe2, D–Trp3, D–hArg(Et2)6, D–Ala10] LHRH.

A dose of 100 μg antagonist/kg administered on days 9/10 of the luteal phase in three monkeys caused a marked temporary suppression of serum concentrations of LH and progesterone during the following 32 h but levels still remained detectable and after 2 days serum hormone concentrations returned to the normal luteal-phase range. When the same animals were treated with 300 μg antagonist/kg at the same period during a subsequent cycle, serum LH levels were close to or at the limits of detection of the bioassay for the next 48 h and progesterone concentrations declined steadily, reaching non-detectable values by 48 h. In two monkeys the progesterone levels remained suppressed and they menstruated prematurely; in the third monkey the progesterone concentration rose to just above baseline and menstruation occurred at the expected time. Administration of 300μg antagonist/ kg on days 6/7 of the luteal phase in a further three monkeys also suppressed progesterone concentrations but not to baseline values, and after 2 days a normal progesterone profile was regained. These results suggest that the corpus luteum of the stumptailed macaque is largely dependent on pituitary gonadotrophin support during the mid to late luteal phase.
Hypothalamic gonadotrophin-releasing hormone and pituitary and plasma FSH and prolactin during photostimulation and photorefractoriness in intact and thyroidectomized starlings (Sturnus vulgaris)
Authors: Dawson A. , Follett B. K. , Goldsmith A. R. , Nicholls T. J.
Published: December 2008

Changes in concentrations of hypothalamic gonadotrophin-releasing hormone (GnRH) and pituitary and plasma FSH and prolactin were measured in intact and thyroidectomized female starlings (Sturnus vulgaris) after transfer from short to long photoperiods.

In intact birds, hypothalamic GnRH did not increase significantly during the first 6 weeks of photostimulation, but by 12 weeks, as birds became photorefractory, it had decreased to levels significantly lower than those before photostimulation. In thyroidectomized birds, which did not become photorefractory, hypothalamic GnRH remained high after 12 weeks of photostimulation. Pituitary FSH increased in both intact and thyroidectomized birds; it then decreased to low levels in intact photorefractory birds, but remained high in thyroidectomized birds. Plasma FSH increased to a peak after 2 weeks, but by 6 weeks it had decreased to low levels in both groups. In intact birds there was a 70-fold increase in pituitary prolactin during the first 6 weeks, and levels were still high after 12 weeks of photostimulation. In thyroidectomized birds, pituitary prolactin remained low. The results suggest that while the initial effect of long daylengths is to cause gonadal maturation, the ultimate effect is to switch off the reproductive system.

J. Endocr. (1985) 105, 71–77
A black background facilitates the response to stress in teleosts
Authors: Gilham I. D. , Baker B. I.
Published: December 2008

This work examines the difference in responsiveness to stress which characterizes fish adapted to white and black backgrounds. Trout were maintained in black or white tanks for 2 weeks and then subjected to intermittent intense or moderate noise stress for periods between 1 h and 5 days, or to the stress of being injected daily with a large volume of liquid for 3 days. Plasma cortisol concentrations increased more readily and to a greater extent in fish from black tanks in response to moderate stress or brief intense stress. Dexamethasone suppressed the stress-induced rise of cortisol in white-adapted fish but was only partially effective in trout from black backgrounds. These differences in plasma cortisol between black- and white-adapted fish can be related to the different titres of plasma ACTH, apparently derived from the pars distalis.

Removal of the neurointermediate lobe (NIL) from black-adapted eels markedly depressed the normal rise in plasma cortisol elicited by noise stress. It is suggested that products from the NIL may modulate the stress response of the hypothalamo-pituitary axis although other routes through which background colour could affect the pituitary responsiveness to stress are also considered. In several cases, stress also enhanced the secretion of MSH from the NIL.

J. Endocr. (1985) 105, 99–105
The priming effect of LH-releasing hormone: effects of cold and involvement of new protein synthesis
Authors: Curtis A. , Lyons V. , Fink G.
Published: December 2008

The possible involvement of protein synthesis in the priming effect of LH-releasing hormone (LHRH) has been investigated in vitro using hemipituitary glands from pro-oestrous rats. Cycloheximide (7·1 μmol/l) blocked the priming effect of LHRH (elicited by 8·5 nmol LHRH/1) and protein synthesis (assessed by gel electrophoresis of 35S-labelled pituitary proteins). Pituitary glands were also incubated at 0–1 °C followed by incubation at 37 °C. While incubation at 0 °C for either 1 or 2 h reduced LH release and blocked protein synthesis, the LH response to LHRH in a subsequent 1-h incubation at 37 °C was similar to that during the corresponding period in pituitary glands incubated throughout at 37 °C. Incubation with medium alone at 0 °C during the first hour followed by incubation with LHRH at 37 °C during the second hour resulted in an LH response to LHRH which was similar to that in glands incubated with LHRH for 2 successive hours at 37 °C. Two-dimensional gel electrophoresis showed that LHRH priming was associated with the synthesis of a new protein of approximately 69000 molecular weight and with changes in the isoelectric point of two other high molecular weight proteins. These results suggest that the priming effect of LHRH involves the synthesis of a new protein as well as post-translational changes (possibly phosphorylation) in two other proteins and that exposure to cold may prime the pituitary gland to LHRH possibly by stimulating intracellular Ca2+ release and/or protein phosphorylation.

J. Endocr. (1985) 105, 163–168