bluuebunny/crossref_metadata_2025 huggingface dataset:
LUTEINIZING HORMONE RELEASING FACTOR IN PITUITARY STALK PLASMA FROM LONG-TERM OVARIECTOMIZED RATS: EFFECTS OF STEROIDS
Authors: SARKAR D. K. , FINK G.
Published: December 2008

The concentration of LH releasing factor (LH-RF) was measured by radioimmunoassay in blood collected from the cut pituitary stalk of long-term ovariectomized rats anaesthetized with Althesin. Stalk plasma LH-RF concentrations were increased immediately after ovariectomy (carried out at oestrus) and low at 2 and 4 days after operation. The concentrations then began to increase to reach a level at 24–28 days which was significantly higher than the concentrations during the oestrous cycle except for the time of the ovulatory surge at pro-oestrus. This pattern was similar to that of the concentrations of LH in jugular venous plasma taken from the same animals before exposure of the pituitary stalk. Like peripheral plasma LH concentrations, the concentrations of LH-RF in stalk plasma fluctuated and fell significantly and rapidly after the intravenous injection of 1 μg oestradiol-17β. The release of LH-RF in long-term ovariectomized rats, into which had been implanted an oestradiol-containing Silastic capsule, was similar to the diurnal pattern of LH release; the afternoon increase in stalk plasma LH-RF concentration could be blocked by sodium pentobarbitone administered at 13.00 h and augmented by administering this anaesthetic at 13.00 h of the preceding day. The stalk plasma LH-RF concentrations in animals injec[unk]d with oestradiol benzoate (OB) followed 72 h later with either OB or progesterone were lower than the concentrations in animals injected only with oil.

These data show that in the rat (1) ovarian steroids could moderate LH release ('negative feedback') by inhibiting LH-RF release, and that in long-term ovariectomized animals (2) the oestradiol-induced circadian pattern of LH release is due to a circadian pattern of LH-RF release, and (3) the surge of LH produced by administering OB followed by either OB or progesterone is probably due mainly to a massive increase in the responsiveness of the anterior pituitary gland to LH-RF.
MELATONIN IN THE RETINA OF RATS: A DIURNAL RHYTHM
Authors: PANG S. F. , YU H. S. , SUEN H. C. , BROWN G. M.
Published: December 2008

Melatonin was extracted by chloroform from the retina of the rat and measured by radioimmunoassay. In rats housed under a régime of 12 h light: 12 h darkness, melatonin content in the retina, like that in the pineal, serum and brain tissue, was high from midway through the dark to early in the period of light, and low from half-way through the light period to early in the period of darkness. A similar result was found in a second experiment. The existence of a diurnal rhythm of melatonin in the retina of rats as observed in this study is consistent with the suggestion that melatonin may regulate the diurnal rhythm of eye pigmentation in vertebrates.
A COMPARISON OF THE EFFECTS OF FOUR ERGOT DERIVATIVES ON PROLACTIN SECRETION BY DISPERSED RAT PITUITARY CELLS
Authors: DELITALA G. , YEO T. , GROSSMAN ASHLEY , HATHWAY N. R. , BESSER G. M.
Published: December 2008

The inhibitory effects of dopamine and various ergot alkaloids on prolactin secretion were studied using continuously perfused columns of dispersed rat anterior pituitary cells. Bromocriptine (5 nmol/l) and lisuride hydrogen maleate (5 nmol/l) both inhibited prolactin secretion, the effects persisting for more than 3 h after the end of the administration of the drugs. A similar although less long-lasting effect was observed with lergotrile (50 nmol/l) and the new ergoline derivative, pergolide (5 nmol/l). These effects contrasted with the rapid disappearance of the action of dopamine. The potency estimates of the ergots relative to that of dopamine were: lergotrile, 2·3; bromocriptine, 13; lisuride, 15; pergolide, 23.

The dopamine-receptor blocking drugs, metoclopramide and haloperidol, antagonized the prolactin release-inhibiting activity of the compounds; bromocriptine and lisuride showed the highest resistance to this dopaminergic blockade.

The results suggested that the direct effect of the ergot derivatives on dispersed pituitary cells was mediated through dopamine receptors and emphasized the long-lasting action of bromocriptine and lisuride in vitro.
A PROGESTERONE-DEPENDENT STEP IN OVULATION INDUCED BY HUMAN CHORIONIC GONADOTROPHIN IN IMMATURE RATS PRIMED WITH PREGNANT MARE SERUM GONADOTROPHIN
Authors: KOHDA HEIGO , MORI TAKAHIDE , EZAKI YOJIRO , NISHIMURA TOSHIO , KAMBEGAWA AKIRA
Published: December 2008

In immature rats primed with pregnant mare serum gonadotrophin, antiserum to progesterone could prevent or reduce ovulation in response to injected human chorionic gonadotrophin (HCG). To be effective, antiserum treatment had to be within 6 h of gonadotrophin treatment; antiserum given 9 h after HCG was ineffective. Progesterone restored the antiserum blocked ovulation completely or incompletely when administered intravenously within 6 h of treatment with HCG. The first 6 h was shown to be a progesterone-dependent step in the ovulatory process in this experimental system.
INCREASED SODIUM APPETITE IN ADRENALECTOMIZED OR HYPOPHYSECTOMIZED RATS AFTERINTRACRANIAL INJECTIONS OF RENIN OR ANGIOTENSIN II
Authors: AVRITH D. B. , WISELKA M. J. , FITZSIMONS J. T.
Published: December 2008

Rats given free access to food, water and 2·7% NaCl and injected with either renin or angiotensin II into the preoptic area showed an immediate increase in water intake followed by an increase in intake of 2·7% NaCl. The rats continued to drink the hypertonic NaCl solution throughout the test session of 18 h. Intracranial injections of the dipsogen, carbachol, caused thirst but no sodium appetite. Bilateral adrenalectomy had no effect on either the initial water intake or the delayed intake of NaCl that was induced by intracranial injections of renin or angiotensin II. However, the increased water intake during the 18 h after the administration of renin was reduced to normal levels in adrenalectomized rats. Similar results were obtained with hypophysectomized rats. These results demonstrated that the delayed sodium appetite induced by renin or angiotensin II is not secondary to the stimulation of release of hormones from the pituitary gland or adrenal cortex.
PROGESTERONE LEVELS AFTER INDUCTION OF OVULATION IN DIOESTROUS RATS
Authors: SHIROTA MARIKO , SASAMOTO SHUJI
Published: December 2008

Maximal levels of progesterone in the plasma after premature ovulation induced by either the administration of human chorionic gonadotrophin (HCG) or LH-releasing hormone (LH-RH) to dioestrous (day 0) rats were observed from 33 to 45 h but decreased 3 h earlier than after spontaneous ovulation. This suggested an earlier decline in the secretory activity of corpora lutea formed from premature ovulations than that of corpora lutea formed during a normal oestrous cycle.

The next spontaneous ovulation occurred 4 days (day 5) after premature ovulation induced by LH-RH on day 0. A single s.c. injection of 2·5 μg oestradiol-17β (OE2) at 10.00 h on day 2 to these animals advanced the next spontaneous ovulation by 1 day. A normal number of oocytes was shed, indicating that earlier secretion of oestrogen on day 2 had advanced the next spontaneous ovulation. A single injection of 2·5 μg OE2 to normal 4-day cyclic rats at metoestrus failed to advance the next ovulation. An earlier decline of progesterone levels in the plasma of rats after premature ovulation as compared with spontaneous ovulation may explain the greater effectiveness of oestrogen in the former group.

The progesterone surge was observed during the period of premature ovulation in both HCG- and LH-RH-treated groups. This progesterone release in the periovulatory period may be responsible for the inhibition of gonadotrophin surges on the expected day of prooestrus (day 1).
EFFECTS OF MANIPULATING SEROTONIN ON THE INCIDENCE OF OVULATION IN THE RAT
Authors: COEN C. W. , FRANKLIN M. , LAYNES R. W. , MacKINNON P. C. B.
Published: December 2008

Previous studies have shown that while depletion of brain serotonin by the administration of p-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, blocks the daily surge of LH in oestrogen-treated ovariectomized rats, restoration of serotonin synthesis by treatment with its immediate precursor, 5-hydroxytryptophan (5-HTP), at a critical time of day, reinstates the surge. The present study indicates that the experimental procedure involving serotonin depletion and its subsequent replenishment may also be used to control the preovulatory LH surge and ovulation in intact cyclic rats provided that (1) the PCPA is administered subcutaneously rather than intraperitoneally and (2) the 5-HTP is given in conjunction with carbidopa, a peripheral decarboxylase inhibitor: the latter observation providing further evidence for a central role for serotonin in the control of ovulation. These precautions were unnecessary when oestrogen was administered at the same time as the PCPA. It appears that PCPA administered intraperitoneally results in a suppression of the preovulatory rise in oestrogen secretion (and may have additional deleterious effects at the level of the ovaries) and that 5-HTP, in the absence of supplementary oestrogen, may block ovulation by peripheral action after conversion to serotonin. This study indicates the need for caution when using pharmacological 'cocktails' to investigate neuroendocrine events underlying ovulation when the experiments are carried out in the presence of the ovaries.
SYNTHESIS OF DNA IN OESTROGEN-INDUCED PITUITARY TUMOURS IN RATS: EFFECT OF BROMOCRIPTINE
Authors: KALBERMANN L. E. , MacHIAVELLI G. A. , DE NICOLA A. F. , WEISSENBERG L. S. , BURDMAN J. A.
Published: December 2008

Bromocriptine increased the concentration of prolactin in oestrogen-induced tumours of the rat pituitary gland. Prolactinaemia was significantly reduced and at the same time there was a considerable decrease in the weight of the tumour, in the incorporation of tritiated thymidine into DNA and in the activity of DNA polymerase a. The results suggested that the intracellular content of prolactin controls cell proliferation in this experimental tumour. A hypothalamic disorder is proposed as the primary cause of these tumours.
SPECIFIC HIGH-AFFINITY OESTRADIOL BINDING IN RAT VENTRAL PROSTATE
Authors: GINSBURG M. , JUNG-TESTAS I. , BAULIEU E. E.
Published: December 2008

The presence of a specific saturable oestradiol-binding component was demonstrated in cytosol from rat ventral prostate. Centrifugation of cytosol, previously incubated with [3H]oestradiol at 0 °C, on low salt glycerol—Tris gradients revealed two oestradiol-binding systems with sedimentation coefficients of 8S and 4S. Excess unlabelled dihydrotestosterone (17β-hydroxy-5α-androstan-3-one) did not compete with the oestradiol binding, whereas excess unlabelled oestradiol or diethylstilboestrol abolished the 8S and 4S peaks. The oestradiol binding to these components could not be detected after proteolytic treatment. Scatchard analysis of saturable oestradiol binding in cytosol of prostates from intact rats and from rats 14 days after orchidectomy indicated that the equilibrium dissociation constant (KDeq) was about 10−10 mol/l at 0 °C, and the concentrations of high-affinity binding sites were approximately 10 fmol oestradiol bound/mg protein. Lower concentrations of oestradiol binding (approximately 2 fmol/mg protein) were found in cytosols from prostates obtained 2 and 4 days after castration. The transient decrease of oestradiol binding was not due to the presence in prostate cytosol of a factor that inactivated the oestradiol receptor. It is proposed that the oestradiol receptor in the cytosol from ventral prostate tissue of the rat is under endocrine control.
DAILY RHYTHM IN SECRETION OF PROLACTIN IN ANDROGENIZED FEMALE RATS
Authors: YOGEV LEAH , TERKEL JOSEPH
Published: December 2008

Androgen-sterilized female rats were obtained by administering 10 μg testosterone propionate to pups on day 2 after birth. In contrast with ovariectomized adults, androgenized adult female rats are incapable of responding to cervical stimulation by secreting prolactin in the nocturnal surge pattern. In spite of the loss of this pattern the androgenized female rats still exhibited a daily circadian rhythm of prolactin secretion with afternoon levels three times higher than those after midnight.
IMMUNOREACTIVE HUMAN CALCITONIN-LIKE MOLECULE IN THE NERVOUS SYSTEMS OF PROTOCHORDATES AND A CYCLOSTOME, MYXINE
Authors: GIRGIS S. I. , GALAN GALAN F. , ARNETT T. R. , ROGERS R. M. , BONE Q. , RAVAZZOLA M. , MacINTYRE I.
Published: December 2008

A molecule very closely resembling human calcitonin immunologically and chromatographically was extracted from the nervous systems of several protochordates and a cyclostome, Myxine. The presence of human calcitonin-like molecules in the nervous systems of primitive chordates suggests that they have some function in the nervous system of these species and that the bone-regulating function of the calcitonins may have arisen much later in the vertebrates.
A DOSE-RESPONSE COMPARISON OF THE ACTIONS OF ANGIOTENSIN II AND ANGIOTENSIN III IN SHEEP
Authors: BLAIR-WEST J. R. , COGHLAN J. P. , DENTON D. A. , FEI D. T. W. , HARDY K. J. , SCOGGINS B. A. , WRIGHT R. D.
Published: December 2008

Comparisons of aldosterone responses to [des-Asp1]-angiotensin II and angiotensin II, often at single dose levels, have shown a wide range of potency ratios. Therefore four-point dose–response comparisons were performed in sodium-replete sheep, using i.v. infusion rates of angiotension II and angiotensin II amide that reproduced the physiological range of blood concentration of angiotensin II for sheep. Angiotensin III was infused i.v. at the same rates. Effects on arterial blood pressure, cortisol secretion rate, adrenal blood flow and plasma levels of Na+ and K+ were also compared. The potency ratio, angiotensin III: angiotensin II amide, was 0·87 for actual aldosterone secretion rate and 0·90 for the calculated increase in aldosterone secretion. For angiotensin III: angiotensin II the ratios were 0·80 and 0·91 respectively. These ratios were not significantly different from 1·00 but the tendency for angiotensin II to be slightly more potent was probably due to a contribution from derived angiotensin III during infusion of angiotensin II. Angiotensin II or angiotensin II amide was ∼ four times as potent as angiotensin III in raising arterial blood pressure. Cortisol secretion rate was slightly but significantly increased by all peptides at the higher infusion rates. Infusions had no effect on adrenal blood flow or plasma levels of Na + but raised plasma levels of K + slightly. These results confirm the conclusion from adrenal arterial infusion experiments that angiotensin II and III are almost equipotent in stimulating aldosterone secretion in sheep.
INHIBITION OF SECRETION OF LUTEINIZING HORMONE INDUCED BY ELECTROCHEMICAL STIMULATION OF THE ANTERIOR CINGULATE CORTEX MEDIATED BY A β-ADRENERGIC MECHANISM
Authors: CACERES A. , TALEISNIK S.
Published: December 2008

Release of LH occurred in ovariectomized, oestrogen-primed rats when the medial preoptic area (mPOA) was electrically stimulated with monophasic square pulses of 1 ms duration (50 Hz, 150 μA, 15 s on and 15 s off for 30 min). Electrochemical stimulation of the anterior cingulate area applied immediately after the first 15 min period of stimulation in the mPOA completely prevented the rise in LH normally observed during the following 15 min. This effect was suppressed either by selective blockade of noradrenaline synthesis with diethyldithiocarbamate, or following systemic or intraventricular injection of the βadrenergic blocker, propranolol, whereas it did not change after systemic atropine, pimozide or phenoxybenzamine. Isoprenaline, a β-adrenergic agonist, injected into the third ventricle of rats stimulated in the mPOA mimicked the effect of the cortical stimulation, this effect was also blocked by propranolol. Intraventricular administration of propranolol or of isoprenaline had no effect on the release of LH induced by the injection of gonadotrophin releasing hormone, showing that their action is not directly on the pituitary gland. Intraventricular injection of noradrenaline, which failed to affect the release of LH induced by stimulation in the mPOA, inhibited this release when animals were pretreated with phenoxybenzamine. On the other hand, the LH-releasing potency of noradrenaline was greatly increased if the β-receptors were blocked.

From these results it may be concluded (1) that inhibition of the secretion of LH evoked by electrochemical stimulation of the anterior cingulate cortex is mediated by an adrenergic mechanism involving a β-receptor and (2) that noradrenaline exerts an inhibitory effect on the secretion of LH through a β-receptor in addition to the known facilitatory action through an α-receptor.
EPISODIC FLUCTUATIONS IN CONCENTRATIONS OF ANDROGEN IN SERUM OF MALE RATS: POSSIBLE RELATIONSHIP TO SEXUAL BEHAVIOUR
Authors: SÖDERSTEN P. , ENEROTH P. , EKBERG P.-H.
Published: December 2008

Serum levels of androgen were higher during the late part of the light phase of the light: darkness (LD) cycle than during the late part of the dark phase during three consecutive days in intact male rats. The serum concentration of androgen in blood samples obtained at hourly intervals from individual male rats fluctuated markedly with occasionally as much as a tenfold difference between the highest and lowest values. Evidence was presented that endogenous pulses in the concentrations of androgen in serum of male rats occur during the late part of the light phase and the early and middle parts of the dark phase of the LD cycle. Induction of sexual behaviour by injections of testosterone in castrated rats depended on the time of injection, and the period of maximum behavioural sensitivity to testosterone coincided with the time of the LD cycle when pulses in androgen levels in serum normally occurred in intact rats. Injection of testosterone produced extremely high concentrations of androgen in serum within 0·5 h of injection but these levels declined rapidly thereafter. Testosterone implants, which produced low levels of androgen that did not vary with the LD cycle, were considerably more potent than testosterone injections in stimulating sexual behaviour in castrated rats.
SUPRACHIASMATIC LESIONS DISRUPT THE DAILY RHYTHMICITY IN THE SEXUAL BEHAVIOUR OF NORMAL MALE RATS AND OF MALE RATS TREATED NEONATALLY WITH ANTIOESTROGEN
Authors: SÖDERSTEN P. , HANSEN S. , SREBRO B.
Published: December 2008

Male rats were treated daily with oil or 100 μg of the antioestrogen, ethamoxytriphetol (MER-25), for the first 10 days of life and, when adult, lesions were made in the suprachiasmatic nuclei (SCN) of the hypothalamus or control lesions were made above the SCN and the rats were tested for sexual behaviour. Treatment with MER-25 enhanced the daily rhythmicity in both mounting and lordosis behaviour and SCN lesions disrupted these behavioural rhythms and the rhythm in the mounting behaviour of oil-treated rats. Rats treated with MER-25 and with SCN lesions showed high levels of mounting and lordosis behaviour throughout the light: darkness cycle. These results support the hypothesis that sexual differentiation by perinatal androgen stimulation uncouples the central rhythm generator from the neural substrates of sexual behaviour in rats.
A HORMONAL ASSESSMENT OF BOVINE PARTURIENT PARESIS: EVIDENCE FOR A ROLE OF OESTROGEN
Authors: HOLLIS B. W. , DRAPER H. H. , BURTON J. H. , ETCHES R. J.
Published: December 2008

A comparative assessment was made of the hormonal control of calcium homeostasis in eight dairy cows which developed parturient paresis and in seven normal animals from the same herd. Plasma levels of calcium, phosphorus, magnesium, free hydroxyproline, 25-hydroxycholecalciferol (25-OHD), 1,25-dihydroxycholecalciferol (1,25-(OH)2D), parathyroid hormone, calcitonin, prolactin and oestrogen were monitored from 30 days prepartum to 15 days post partum.

Prepartum levels of plasma calcium, hydroxyproline and calcitonin were depressed in the paretic animals, and plasma levels of phosphorus and oestrogen were elevated. Plasma levels of 25-OHD remained stable in both groups, whereas levels of 1,25-(OH)2D, parathyroid hormone and prolactin rose sharply at parturition.

Plasma hydroxyproline, an index of bone resorption, began to rise 2 days prepartum in the control cows but not until 2 days post partum in the paretic cows. The data indicate that bone resorption was inhibited in the paretic group at the onset of lactation, and that a decreased capacity for bone resorption is a major factor in the susceptibility of some cows to this disease.

The failure of the paretic animals to resorb bone was not associated with an inability to synthesize the calcium-mobilizing hormones parathyroid hormone or 1,25-(OH)2D, or to regulate the production of calcitonin. However, hypocalcaemia in the affected animals was associated with a significantly higher plasma level of oestrogen (a known inhibitor of bone resorption) in the immediate prepartum period. Following parturition, plasma levels of oestrogen fell rapidly and active bone resorption ensued in the paretic animals.
BIOLOGICAL HALF-LIFE AND ORGAN DISTRIBUTION OF [3H]1-DEAMINO-8-d-ARGININE-VASOPRESSIN IN THE RAT
Authors: LÁSZLÓ F. A. , JANÁKY T. , BALÁSPIRI L. , MORGAT J.-L.
Published: December 2008

The biological half-life of synthetic, radiochemically pure, biologically active [3H]1-deamino-8-d-arginine-vasopressin (dDAVP) in rats was found to be 5·33 ± 0·28 (s.e.m.) min in the initial, transitional, fast phase and 56·28 ± 3·27 min in the second, slow phase. The substance accumulated to the greatest extent in the kidney and small intestine and only slightly in the adenohypophysis. The results have suggested that the extended biological half-life may play a role in the more marked and longer antidiuretic effect of dDAVP. The explanation of the poor accumulation in the adenohypophysis may be that dDAVP does not possess an effect similar to that of corticotrophin releasing factor.
CHANGES IN MEMBRANE POTENTIAL OF CULTURED PORCINE AND HUMAN THYROID CELLS IN RESPONSE TO THYROTROPHIN AND OTHER AGENTS
Authors: BOURKE J. R. , CARSELDINE K. L. , FERRIS S. H. , HUXHAM G. J. , MANLEY S. W.
Published: December 2008

Thyrotrophin (TSH), cyclic AMP, cyclic GMP and 1-methyl-3-isobutyl-xanthine (MIX) promoted the reassociation of isolated porcine and human thyroid cells into follicular structures in culture and stimulated the uptake of radio-iodide. Monolayer cells were present in all cultures, but in decreasing proportions as the concentration of stimulator was increased. The resting membrane potential of porcine thyroid cells cultured for 4 days in the presence of TSH was −54 ± 3·6 (mean ± s.d.) mV for follicular cells and −31 ± 2·6 mV for monolayer cells. In the absence of TSH, only monolayer cells were present and their membrane potential was −24 ± 2·0 mV. Removal of hormone by washing resulted in hyperpolarization to −70 ± 2·9 mV (follicular cells) or −59 ± 3·4 mV (monolayer cells). Subsequent replacement of TSH, or addition of cyclic AMP, MIX, prostaglandin E1 (PGE1) or long-acting thyroid stimulator immunoglobulin resulted in depolarization of previously hyperpolarized cells, to approximately the membrane potential observed before washing. Incubation in MIX resulted in enhanced sensitivity to the depolarizing effect of TSH. Cells cultured in the absence of TSH were unresponsive to TSH or other stimulators. The membrane potential of human thyroid cells behaved similarly in response to TSH, to hormone removal and replacement, and to MIX and PGE1.
OESTROGEN RECEPTORS IN RAT MAMMARY TISSUE AND PLASMA CONCENTRATIONS OF PROLACTIN DURING MAMMARY CARCINOGENESIS INDUCED BY OESTROGEN AND IONIZING RADIATION
Authors: BLANKENSTEIN M. A. , MULDER E. , BROERSE J. J. , VAN DER MOLEN H. J.
Published: December 2008

Female Sprague–Dawley rats received a subcutaneous implant containing 2 mg oestradiol at the age of 7 weeks. One week later half of the rats treated with oestrogen and half of the rats in an untreated control group were irradiated with 2 Gy (200 rad) of X-rays. The content of oestrogen receptor of the mammary tissue and the concentration of prolactin in the plasma were studied at intervals of 2 months for a period of 14 months after this treatment. Oestrogen treatment resulted in a decrease in the content of oestrogen receptors in the mammary tissue of both irradiated and non-irradiated rats. In oestrogen-treated rats, plasma prolactin was raised 10–50 times and pituitary tumours were observed. Radiation had no additional effect on the oestrogen-receptor content of mammary tissue or the concentration of plasma prolactin. The changes in the oestrogen-receptor content of mammary tissue and the prolactin concentration of plasma preceded the development of mammary tumours. It is suggested that the synergistic action of oestrogen and radiation on rat mammary tumour development is the result of a stimulation by oestrogen and/or prolactin of the sensitivity of the mammary gland to ionizing radiation.
CONVERSION OF TESTOSTERONE TO 5β-REDUCED METABOLITES IN THE NEUROENDOCRINE TISSUES OF THE MATURING COCKEREL
Authors: MASSA R. , SHARP P. J.
Published: December 2008

The metabolism in vitro of [4-14C]testosterone to reduced derivatives was studied in the pituitary gland, hypothalamus and hyperstriatum dorsale of cockerels from hatch to sexual maturity. The most important metabolites were 5β-dihydrotestosterone (5β-DHT), 5β-androstane-3α,17β-diol (5β-3α-diol) and 5β-androstane-3β,17β-diol. Trace amounts of androstenedione and, in the hypothalamus only, of 5α-DHT were also detected. The amounts of 5β-reduced metabolites produced by all neuroendocrine tissues declined progressively during maturation with the steepest fall occurring during the first 2 weeks after hatch. At all ages studied, 5β-DHT was formed to the greatest extent by the hyperstriatum dorsale, to a lesser extent by the hypothalamus and in the smallest quantities by the pituitary gland. In the three tissues studied, 5β-3α-diol tended to be formed to the greatest extent by the pituitary gland.

No significant change was observed in the metabolism of testosterone to reduced derivatives in any of the neuroendocrine tissues after castration.

It was concluded that in the cockerel, unlike the rat, a change in 5α-reductase activity of the neuroendocrine tissues is unlikely to be involved in the initiation of puberty. The physiological significance of 5β-reductase activity in the neuroendocrine tissues remains to be established.
STIMULATION BY ORNITHINE OF OVINE PLACENTAL LACTOGEN SECRETION
Authors: HANDWERGER S. , GRANDIS A. , BARRY S. , CRENSHAW M. C.
Published: December 2008

Arginine is a potent stimulus to the secretion of placental lactogen (PL) as well as GH and prolactin in sheep. To determine whether other amino acids of the urea cycle also affect PL secretion, ornithine (25 g) and citrulline (20 g) were infused intravenously into four pregnant ewes over a period of 0·5 h. In eight experiments, ornithine stimulated PL secretion by 124 ± 25 (s.e.m.) % with the initial increase occurring by 1 h after the start of each infusion. Plasma GH concentrations increased from 3·4 ± 1·1 to 24·5 ± 5·9 ng/ml and plasma prolactin concentrations increased from 58·8 ± 12·8 to 310·7 ± 88·4 ng/ml. Citrulline, on the other hand, had no consistent effect on PL secretion. Plasma GH concentrations following the infusion of citrulline, however, increased by 15–20 ng/ml in two of four experiments and plasma prolactin concentrations decreased by 73·2 ± 3·2% in all four experiments.The results indicate that ornithine is also a potent stimulus to the secretion of PL, GH and prolactin and suggest that arginine-induced PL secretion may result from the conversion of arginine to ornithine.
EFFECT ON OVULATION OF 20α-HYDROXY-4-PREGNEN-3-ONE AND ITS 5α-REDUCED METABOLITES IN IMMATURE RATS TREATED WITH PREGNANT MARE SERUM GONADOTROPHIN
Authors: GILLES PAMELA A. , KARAVOLAS H. J.
Published: December 2008

The ability of 20α-hydroxy-4-pregnen-3-one (20α-dihydroprogesterone, 20α-DHP) and its 5α-reduced metabolites, 20α-hydroxy-5α-pregnan-3-one and 5α-pregnane-3α,20α-diol, to facilitate ovulation was examined in immature female rats which had been treated on day 22 of age with a non-ovulatory dose (12 i.u.) of pregnant mare serum gonadotrophin. An increased incidence of ovulation occurred in rats treated on the morning of day 24 with 20α-DHP. However, a dose of 20α-DHP three to four times that of progesterone was required to induce ovulation in all animals. In contrast, neither 20α-hydroxy-5α-pregnan-3-one (at doses ranging from 0·5 to 5·0 mg) nor 5α-pregnane-3α,20α-diol (tested at 3·0 or 4·0 mg) facilitated ovulation. Therefore both 20α-DHP and progesterone, the two major progestins of the rat oestrous cycle, have the ability to facilitate ovulation. It is concluded that the ability of 20α-DHP to facilitate ovulation does not appear to be by way of conversion to its 5α-reduced metabolites.
OESTRADIOL-17β INCREASES PITUITARY RESPONSIVENESS BY A MECHANISM THAT INVOLVES THE RELEASE AND THE PRIMING EFFECT OF LUTEINIZING HORMONE RELEASING FACTOR
Authors: SPEIGHT ALISON , POPKIN RACHEL , WATTS A. G. , FINK G.
Published: December 2008

We have investigated the mechanism by which oestradiol-17β augments pituitary responsiveness to luteinizing hormone releasing factor (LH-RF). Adult rats were ovariectomized on the morning of dioestrus and implanted with either an empty silicone elastomer capsule or a capsule containing oestradiol-17β. Twelve hours later the LH response, tested by injecting 50 ng LH-RF/100 g i.v., was significantly greater in animals implanted with an oestradiol capsule compared with that in animals implanted with an empty capsule. The effect of oestradiol was blocked by sodium pentobarbitone administered 4 h before the test, and this block was overcome by infusing LH-RF during the 4 h period at doses which by themselves were not sufficient to evoke a large release of LH. We also measured LH-RF in pituitary stalk blood collected under Althesin anaesthesia between 4–6 and 12–13 h after ovariectomy and capsule implantation. The concentration of LH-RF in stalk plasma fell between these two collection periods in animals implanted with empty but not with oestradiol-filled capsules. The concentrations of LH-RF in stalk plasma, although relatively low, were significantly higher in animals bearing an oestradiol-containing capsule than the concentrations in peripheral plasma from similarly treated animals, and, by comparison with the LH-RF concentrations in peripheral plasma from animals infused with LH-RF, were sufficiently high to increase significantly the responsiveness of the pituitary gland. These data show that as well as acting directly on the pituitary gonadotrophs, oestradiol-17β increases the responsiveness of the anterior pituitary gland by a mechanism that involves the release and the priming effect of LH-RF.
EFFECTS OF AN ANTI-OESTROGEN, TAMOXIFEN (ICI 46,474), ON LUTEINIZING HORMONE RELEASE AND OVULATION IN THE HEN
Authors: WILSON SUSAN C. , CUNNINGHAM F. J.
Published: December 2008

The role of oestradiol in the regulation of LH release in the hen was studied by use of the anti-oestrogen, tamoxifen (ICI 46,474).

Intramuscular injection of laying hens with 2 or 4 mg tamoxifen on 2 successive days delayed or prevented the occurrence of the preovulatory release of LH and ovulation expected on day 3. Ovulation could be restored by i.v. injection of 20 pg LH releasing hormone (LH-RH). Tamoxifen at a dose of 1 mg affected neither the timing of the preovulatory release of LH nor ovulation. Treatment with 2 or 4 mg tamoxifen on 2 successive days reduced the effectiveness of an i.m. injection of progesterone to stimulate a release of LH. Injection of 1, 2 or 4 mg tamoxifen on 2 successive days significantly raised basal levels of LH in the blood at 24 h after the last injection. This was associated with an increase in the capacity of the pituitary gland to respond to an injection of synthetic LH-RH by a release of LH.

These studies suggest that oestradiol has at least two roles in the regulation of LH release in the hen. First, it maintains a low basal level of LH in the blood by reducing the responsiveness of the pituitary gland to LH-RH. Secondly, oestradiol has a facilitative role in the mechanism by which progesterone stimulates the preovulatory release of LH.
EFFECTS OF ANDROGEN INJECTIONS AND DECAPITATION ON THE PITUITARY-GONADAL AXIS AND GENITAL TRACT OF FETAL RATS AT THE END OF GESTATION
Authors: NAESSANY S. , HABERT R. , PICON R.
Published: December 2008

The relationships between LH activity in the plasma, testicular and plasma levels of testosterone and prostatic buds were examined on day 21 of gestation in control and experimental male fetal rats. Surgical hypophysectomy by decapitation of the fetus 3 days before death produced a reduction of LH activity in plasma and level of testosterone in the testes; the development of cranial prostatic buds was impaired although plasma levels of testosterone were unchanged. Injections of testosterone propionate (10 mg) on days 18, 19 and 20 of gestation had similar effects on testicular testosterone; this effect was not due to a direct inhibition of androgen synthesis by testosterone, but to a lowering of LH activity and suggests the existence of a feedback mechanism of testosterone on the fetal hypothalamo–pituitary axis.
EFFECTS OF OESTROGEN AND PROSTAGLANDIN F2α ON LUTEINIZING HORMONE RECEPTORS IN HUMAN CORPORA LUTEA
Authors: NAKANO RYOSUKE , YAMOTO MAREO , IWASAKI MASAFUMI
Published: December 2008

The binding of 125I-labelled human LH (hLH) to the 2000 g subcellular fraction of human corpora lutea of the menstrual cycle was examined. Displacement studies demonstrated that 125I-labelled hLH was specifically bound in the 2000 g fraction of human luteal tissue. Specific binding of 125I-labelled hLH was demonstrated in all the corpora lutea examined except for two aged corpora lutea at an early proliferative phase of the cycle. The number of binding sites for hLH increased between the early to mid-luteal phase and decreased towards the late luteal phase. However, the apparent dissociation constant (Kd) in each corpus luteum did not vary throughout the menstrual cycle. In addition, the effects of treatment with diethylstilboestrol diphosphate (DES) and prostaglandin F2α (PGF2α) on the binding of 125I-labelled hLH to the 2000 g fraction of luteal tissue were investigated and the changes in hLH receptors were estimated by Scatchard analysis. The number of binding sites were 1·59 × 10−14 mol/mg protein in control tissue, 0·86 × 10 −14 mol/mg protein in DES-treated luteal tissue and 2·95 × 10−14 mol/mg protein in PGF2α-treated luteal tissue. Thus, the binding sites for hLH decreased as a result of treatment with DES and increased by treatment with PGF2α. In contrast, the apparent Kd in each luteal tissue revealed almost the same value (4·24 × 10−10 to 6·07 × 10−10 mol/l) after treatment with DES or PGF2α. The results of the present study suggest that oestrogen and prostaglandin might have an important role in modulating hLH receptor in human corpora lutea.
MAINTENANCE OF UNIMPLANTED FERTILIZED OVA IN SPAYED RATS: EFFECTS OF CORTISONE ACETATE THERAPY DURING THE PERIOD OF EMBRYONIC DIAPAUSE
Authors: SMALSTIG E. B. , SHAAR C. J. , BENNETT D. R. , POWELL J. G. , COCHRANE R. L.
Published: December 2008

Rat dams were ovariectomized on day 3 of pregnancy and treated with corn oil (0·25 ml/day), progesterone (4 mg/day), cortisone acetate (2 or 10 mg/day), cortisone acetate (10 mg/day) plus progesterone (4 mg/day) or progesterone (4 mg/day) plus oestrone (1 μg/day) from days 2 to 8 or 14, followed by 6 to 11 days of treatment with progesterone (4 mg/day) plus oestrone (1 μg/day). Implantation of ova at the normal time was realized in the animals treated from day 2 with progesterone plus oestrone. Implantation of ova was only realized subsequent to progesterone plus oestrone in the dams treated with progesterone alone, cortisone acetate alone, or progesterone plus cortisone acetate, except for one animal in the latter group. Implantation of ova was not usually realized even after progesterone plus oestrone treatment in the dams treated with corn oil. Even though cortisone acetate maintained unimplanted ova in spayed rats in much the same manner as does progesterone, it was not equivalent to progesterone in efficacy or action.
EFFECT OF ANAESTHESIA ON THE NEGATIVE FEEDBACK ACTION OF GONADAL STEROIDS ON GONADOTROPHIN SECRETION IN THE OVARIECTOMIZED GUINEA-PIG
Authors: KILPATRICK M. J. , DONOVAN B. T.
Published: December 2008

The effects of urethane or sodium pentobarbitone anaesthesia on the feedback effects of oestradiol or progesterone on gonadotrophin secretion in the ovariectomized guinea-pig have been investigated. In the control experiments in which no steroids or vehicles were given the concentration of LH and FSH in samples of peripheral blood collected at intervals of 15 min varied in a random episodic manner. The mean level of LH was significantly greater in sodium pentobarbitone- and urethane-anaesthetized animals when compared with conscious animals, and in the conscious animals there was a progressive fall in mean LH level during the course of serial sampling. This effect was not observed in anaesthetized animals.

Oestradiol benzoate (2 μg s.c.) inhibited LH secretion in conscious animals and in those anaesthetized with sodium pentobarbitone, but not in urethane-anaesthetized guinea-pigs. Progesterone (200 μg s.c.) progressively depressed plasma LH levels in conscious and urethane-anaesthetized animals, but not in guinea-pigs anaesthetized with sodium pentobarbitone. The effect of anaesthesia was the converse of that observed with oestradiol treatment.

Significant changes in FSH secretion were not observed under any experimental conditions.

These findings point to the existence of a mechanism in spayed guinea-pigs that restrains LH secretion, the action of which is reduced by anaesthesia and modified by oestradiol and progesterone.
DELAY OF THE SELECTIVE SURGE OF FOLLICLE-STIMULATING HORMONE BY BOVINE FOLLICULAR FLUID DURING THE PERIOD OF OVULATION INDUCED BY HUMAN CHORIONIC GONADOTROPHIN IN DIOESTROUS RATS
Authors: SASAMOTO SHUJI , OTANI TSUYOSHI , SHIROTA MARIKO
Published: December 2008

When bovine follicular fluid (BFF) was given i.p. three times at intervals of 3 h from 17.00 to 23.00 h to dioestrous rats pretreated with 10 i.u. human chorionic gonadotrophin (HCG) at 17.00 h on the day of dioestrus (day 0), the selective surge of FSH at 02.00 h on day 1 was suppressed in a dose-dependent manner. Three i.p. injections of 0·5 ml BFF completely suppressed the FSH rise in plasma at 02.00 h on day 1, but the time of premature ovulation induced by HCG was not altered. In these animals treated with HCG and BFF, however, the selective surge of FSH occurred as a delayed surge from 05.00 to 23.00 h on day 1. After seven i.p. injections of 0·5 ml BFF (from 17.00 h on day 0 to 11.00 h on day 1) the delayed surge of FSH took place from 17.00 h on day 1 to 11.00 h on day 2, indicating that waning of BFF with a decrease in inhibin secretion by the ovaries may be responsible for the delay of the FSH surge.

The next spontaneous ovulation in rats treated with HCG and BFF occurred on day 5, a delay of ovulation of 1 day compared with animals given HCG on day 0 with no BFF. Initiation of follicular maturation or selection of growing follicles for the succeeding oestrous cycle appeared to be retarded by the delay of the FSH surge in HCG- and BFF-treated animals.

The pituitary content of FSH in animals given HCG and three i.p. injections of 0·5 ml BFF increased strikingly until 11.00 h on day 1, when the delayed FSH surge was already in progress. These results suggest that the ability of the pituitary gland to synthesize FSH is high during the period of ovulation.
PLASMA LEVELS OF ANDROSTENEDIONE, EPITESTOSTERONE, TESTOSTERONE AND OESTROGENS IN COWS AT PARTURITION
Authors: MÖSTL E. , MÖSTL K. , CHOI H. S. , DREIER H. K. , STÖCKL W. , BAMBERG E.
Published: December 2008

The concentration of total unconjugated oestrogens in the peripheral plasma of cows increased from 2·00±0·20 (s.e.m.) ng/ml 7 days before to 3·87±0·50 ng/ml 1 day before parturition and declined to values below 0·30 ng/ml on day 2 post partum. The concentrations of androstenedione, epitestosterone and testosterone remained approximately constant at 0·90±0·10,0·92±0·08 and 0·40±0·20 ng/ml respectively during the last week of pregnancy. After parturition the concentration of the three androgens declined rapidly.

Similar to data obtained in goats we did not find a marked increase in androgen levels in the peripheral blood of cows before parturition.
VARIATIONS IN PLASMA CONCENTRATIONS OF VASOPRESSIN DURING THE MENSTRUAL CYCLE
Authors: FORSLING MARY L. , ÅKERLUND M. , STRÖMBERG P.
Published: December 2008

Plasma vasopressin concentrations, determined by radioimmunoassay, were followed throughout the menstrual cycle in eight healthy women. The concentrations were found to depend on the day of the menstrual cycle. The mean concentration on day 1 was 0·5±0·08 (s.e.m.) μu./ml, while that on days 16–18 was 1·1±0·16 μu./ml. These values were significantly (P <0·02) different. Vasopressin release in women may thus depend on the hormonal changes during the menstrual cycle.
EFFECT OF BOVINE GROWTH HORMONE AND A PARTIALLY PURE PREPARATION OF SOMATOMEDIN ON VARIOUS GROWTH PARAMETERS IN HYPOPITUITARY DWARF MICE
Authors: HOLDER A. T. , SPENCER E. M. , PREECE M. A.
Published: December 2008

The growth-promoting effects of a partially purified preparation of somatomedin (12·7 units/mg) were compared with those of various doses of bovine GH (5, 20 and 80 μg/day) when injected into hypopituitary dwarf mice. Growth parameters studied were body-weight and tail-length velocities (calculated as the slope of a regression line fitted to daily measurements against time), uptake of 35SO2−4 into costal cartilage in vivo and organ weights (heart, liver and kidney). In the first experiment somatomedin (6·4 units/day), bovine GH and 0·9% NaCl were injected once daily in a volume of 0·1 ml for 10 days. Treatment with bovine GH promoted a significant dose-dependent increase in body-weight and tail-length velocities and 35SO2−4 uptake into costal cartilage in vivo. Somatomedin also promoted a significant increase in body-weight velocity and 35SO2−4 uptake, both responses were between that observed with the lowest dose of bovine GH and control values. Somatomedin did not promote increase in tail-length velocity. Organ weights did not differ significantly between any of the treatment groups when expressed as mg/g body weight. In the second experiment somatomedin (a daily total of 21·6 units/day) and 0·9% NaCl were injected three times per day in a volume of 0·033 ml, bovine GH was again injected once daily in a volume of 0·1 ml, and the treatment period was 12 days. As in the first experiment all doses of bovine GH and somatomedin promoted a significant increase in body-weight velocity. These results are consistent with the somatomedin hypothesis.
CONVERSION OF [4-14C]PROGESTERONE TO ANDROSTENEDIONE IN VITRO BY THECAL TISSUE FROM THE OVARY OF THE DOMESTIC FOWL (GALLUS DOMESTICUS)
Authors: LLEWELYN CHARLOTTE A.
Published: December 2008

The conversion of [4-14C]progesterone to androstenedione by thecal tissue homogenates from the large yellow follicles of the hen ovary was measured at two periods of the ovulatory cycle after incubation for 1 h in the presence of cofactors. Production of androstenedione by the largest follicle, F1, was reduced significantly 1–2 h before ovulation compared with 15 h before ovulation, whereas production of an unidentified androgen increased. These differences were not observed in the next largest follicles, F2 and F3. Thecal tissue homogenates from all the follicles converted [4-14C]progesterone to 17 α-hydroxyprogesterone, androstenedione and testosterone.
MAINTENANCE OF SECRETION OF CALCIUM AND MAGNESIUM DURING INFUSIONS OF PARATHYROID HORMONE TO LACTATING GOATS
Authors: HOVE K. , TOLLMAN R.
Published: December 2008

Hourly secretion of calcium and magnesium by goat mammary glands was studied following infusions of bovine parathyroid hormone (PTH) into the mammary artery in amounts (6–15 ng/kg per min) giving rise to levels of PTH in mammary venous blood commonly observed during spontaneous hypocalcaemia (2·4–13 μg/l). In two series of experiments a 3 h infusion of PTH was given. The first series was carried out at a normal level of plasma calcium, while the availability of calcium was increased by a 20 h infusion of CaCl2 in the other series. No changes in mammary secretion of calcium or magnesium could be observed during the hormone infusions. A decrease in the urinary excretion of calcium occurred, thus demonstrating the activity of the infused PTH.

In a third experiment an 18·5 h infusion of PTH (6 ng/kg per min) into the mammary artery was given to study possible effects of a more prolonged increase of PTH concentrations. This infusion caused a gradual increase in plasma levels of calcium. Average concentrations of calcium in milk increased slightly (about 5% in both glands (P<0·05). The hourly yield of milk was not significantly changed in the infused gland after 18·5 h of PTH infusion. A small but significant increase occurred in the non-infused gland. Yields of magnesium were not influenced by the infusion of PTH. It was concluded that losses of calcium into milk are independent of the PTH concentration in the circulation.
CORRELATION OF ENDOGENOUS SOMATOSTATIN, GASTRIC INHIBITORY POLYPEPTIDE, GLUCAGON AND INSULIN WITH GASTRIC FUNCTION IN THE CONSCIOUS CALF
Authors: BELL F. R. , WEBBER D. E. , WASS J. A. H. , REES LESLEY H. , EVANS JOAN , MARGAN LINDA M. , MARKS V. , LEWIS JANE
Published: December 2008

Levels of endogenous somatostatin, gastric inhibitory polypeptide (GIP), glucagon and insulin were measured during gastric (abomasal) emptying in the conscious calf. Isotonic NaHCO3 infused into the duodenum increased rates of emptying of a saline test meal and of gastric acid secretion, but had no effect on basal levels of blood glucose, somatostatin, GIP, insulin or glucagon. By contrast, intraduodenal infusion of 60 mm-HCl caused complete inhibition of gastric emptying, reduction of acid secretion, and an immediate increase in plasma somatostatin from 121·3 ± 9·4 (s.e.m.) to 286·3 ± 16·3 pg/ml (P <0·01) but levels of GIP, insulin, glucagon and glucose were unaltered. Intravenous injection of somatostatin (0·5 μg/kg) suppressed the antral electromyographic recording and gastric efflux so long as plasma somatostatin levels remained above approx. 200 pg/ml. This suggests that somatostatin can be released by intraduodenal acidification and that it inhibits gastric function by an endocrine effect. Since somatostatin retards gastric emptying it may therefore have an indirect role in nutrient homeostasis by limiting discharge of gastric chyme to the duodenum.
EARLY INHIBITION BY PROGESTERONE OF OESTROGEN-INDUCED ORNITHINE DECARBOXYLASE ACTIVITY IN THE CHICK OVIDUCT AND RAT UTERUS
Authors: LEVY CARLOS , MEŠTER JAN , BAULIEU ETIENNE-EMILE
Published: December 2008

The oestradiol-induced increase of ornithine decarboxylase (ODC) activity in the 'withdrawn' chick oviduct was found to be inhibited by progesterone. In vitro (2 h at 37 °C), progesterone (1 μmol/l) abolished the effect of oestradiol (20 nmol/l), progesterone alone having no effect. In vivo, progesterone (3 mg/kg) inhibited ∼70% of the augmentation of ODC activity induced in the oviduct within 2 to 6 h of treatment with oestradiol benzoate (1·5 mg/kg). Administration of progesterone alone in vivo caused an increase in the ODC activity, the maximum level measured after 6 h being similar to that obtained when the chicks were given both oestrogen and progesterone.

In the rat uterus in vivo progesterone also inhibited the rise of ODC activity caused by oestradiol, ∼70% inhibition being observed between 2 and 6 h after treatment. Progesterone alone had no effect on uterine ODC activity during this period.