bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Beta‐Endorphin on Pulsatile Luteinizing Hormone and Prolactin Secretion During the Follicular Phase in the Ewe
Authors: Curlewis J. D. , Naylor A. M. , Rhind S. M. , McNeilly A. S. 
Published: September 2006

AbstractThe present study was undertaken to determine the effects of the endogenous opioid ligandβ‐endorphin on pulsatile luteinizing hormone (LH) secretion and plasma prolactin concentrations during the follicular phase of the ewe. Oestrous cycles were synchronized by injection of prostaglandin analogue and, commencing 13 h later, saline or β‐endorphin (2, 10 or 50 μg) was injected intracerebroventricularly at hourly intervals for 3 h. Treatment with β‐endorphin was followed by a significant reduction in LH pulse frequency at all doses due to almost complete cessation of pulses. There were no significant changes in LH pulse amplitude or mean LH concentrations. At the lowest dose ofβ‐endorphin, LH pulses recommenced within 3 h of the last injection in all animals and pulse frequency was not significantly different from the saline‐injected controls during the 3 h post‐treatment period. Following treatment with 10 or 50 μg β‐endorphin, LH pulse frequency remained suppressed during the 3 h post‐treatment period but was not different from saline‐treated controls on the following day. The time to the onset of the LH surge was not affected by intracerebroventricularβ‐endorphin. Plasma prolactin concentrations were significantly increased following intracereb‐roventricular injection of 10 or 50 μg β‐endorphin, declining to control values soon after treatments stopped. Intravenous administration of 50 μg β‐endorphin had no effect on LH but was accompanied by a small increase in prolactin concentrations.While these results indicate that hypothalamicβ‐endorphin may be involved in the central control of LH and prolactin secretion, they provide no evidence for subtle modulation of LH pulse frequency by this neuropeptide.
Porcine Relaxin Affects the Release of Luteinizing Hormone in Rats
Authors: Summerlee A. J. S. , Mumford A. D. , Smith M. S. 
Published: September 2006

AbstractThe effects of intravenous injection of porcine relaxin on the pulsatile secretion of luteinizing hormone (LH) were investigated in conscious rats. In untreated, ovariectomized animals, relaxin at doses 2.5 to 10/μg/rat caused a dose‐dependent suppression of pulsatile release of LH. At 5μg relaxin, pulses were suppressed for approximately 60 min and there was a significant (P<0.05) fall in mean plasma LH levels. Pulses returned with the same frequency as the pretreatment period but amplitude and nadir of these pulses were significantly (P<0.05) reduced at doses >2.5μg/rat. In ovariectomized rats pretreated with either estradiol or progesterone alone, relaxin did not alter plasma LH levels. In contrast, injection of 5μg relaxin in rats primed with a combination of estradiol and progesterone caused a 90% increase in circulating LH levels. Intracerebroventricular infusion of a specific angiotensin II antagonist blocked the inhibitory effect of relaxin on LH release in untreated, ovariectomized rats and negated the stimulatory effect of relaxin on LH release in estradiol‐progesterone‐primed, ovariectomized rats. The results demonstrate that acute injections of porcine relaxin in ovariectomized rats suppress the pulsatile release of LH. This effect is blocked when the central angiotensinergic system is compromised suggesting that relaxin might act through the central angiotensin system. The findings are in agreement with other studies that indicate relaxin activates the central angiotensin system. It is also possible that relaxin may act at the level of the adenohypophysis to alter secretion of LH but data in the present study suggest that this may not be a significant site of relaxin action.
Identification of a Single Melanin‐Concentrating Hormone Messenger Ribonucleic Acid in Coho Salmon: Structural Relatedness with 7SL Ribonucleic Acid
Authors: Nahon Jean‐Louis , Presset Francoise , Schoepfer Ralf , Vale Wylie 
Published: September 2006

AbstractMelanin‐concentrating hormone (MCH) is a cyclic neuropeptide possessing antagonistic function to α‐melanocyte‐stimulating hormone and corticotropin‐releasing factor in the control of melanosome dispersion within melanophores and adrenocorticotropin release in fish. We have isolated and characterized MCH cDNAs from coho salmon (Oncorhyncus kisutch). The precursor protein predicted by the longest cDNA consists of 132 amino‐acids with a characteristic signal peptide at the N‐terminus and the biologically active salmon MCH (sMCH) peptide at the C‐terminus. The coho sMCH mRNA and protein sequences are very similar but not identical to the previously reported chum or chinook salmon counterparts, suggesting the existence of species polymorphism. Sequence similarities were revealed between α‐melanocyte‐stimulating hormone and part of the C‐terminal domain of sMCH precursor. Two sMCH genes were found in coho salmon. By contrast to other salmon species, only one major sMCH mRNA was detected in coho species suggesting that differential MCH gene expression might occur in salmon. In addition, under low stringency oligoprobes complementary to the sMCH RNA recognize a 0.3 kb RNA which was identified as the 7SL RNA. The regions conserved between those RNAs fold in a similar secondary structure. These similarities might reflect common ancestry which may have functional significance.
Further Evidence that the Septum is not part of the Main Pathway of the Milk Ejection Reflex in the Rat
Authors: Boudaba Cherif , Poulain Dominique A. 
Published: September 2006

AbstractThe possible role of the medial septum in the control of oxytocin release and of the milk ejection reflex induced by suckling was investigated in lactating rats by using electrical stimulations and lesions. In anaesthetized animals, brief electrical stimulation of the medial septum at 5 to 50 Hz elicited a single brief milk ejection similar to natural reflex milk ejections, whereas prolonged low frequency stimulations (5 to 10 Hz) induced a prolonged inhibition of the reflex. In acute experiments under anaesthesia, lesions of the medial septum did not impair the amplitude and pattern of reflex milk ejections. In chronic experiments, lesions of the medial septum resulted first in a loss of body weight of the mothers and a parallel reduction in growth of the litters. After a few days, the litters gained weight normally, and the pattern of milk ejections was normal. Thus, the pathways which pass through or originate from the medial septum and which are excitatory for oxytocin release appear not to be involved in the regulation of the milk ejection reflex. In view of these results and those from our previous study on the lateral septum, we conclude that the whole septum is not essential to the milk ejection reflex. However, the effects of septal stimulation suggest that the medial and lateral septum may be involved in a secondary neural circuitry that can inhibit the reflex.
Inhibition of Hypothalamic Aromatase Activity by 5 Beta‐Dihydrotestosterone
Authors: Schumacher M. , Hutchison R. E. , Hutchison J. B. 
Published: September 2006

AbstractA variable amount of circulating testosterone that reaches brain cells is converted to biologically inactive 5β‐reduced metabolites, namely, 5β‐dihydrotestosterone (5β‐DHT) and 5β‐androstane‐3α,17β‐diol (5β,3α‐diol). In avian species, the production of inactive 5β‐DHT and 5β,3α‐diol is highest during embryonic and post‐hatching life. In the present study, we have investigated the possibility that 5β‐reduction may not only correspond to a steroid inactivation pathway, but that 5β‐reduced metabolites of testosterone may exert direct inhibitory effects on enzymatic pathways producing biologically active steroids. When added to hypothalamic homogen‐ates prepared from adult male doves, 5β‐DHT but not 5β,3α‐diol inhibits the activity of the aromatase enzyme, which converts testosterone to 17β‐oestradiol. During the first days after hatching, when the production of 5β‐reduced metabolites is high, the hypothalamic aromatase is also inhibited by 5β‐DHT. We conclude that a high 5β‐reductase activity during sensitive periods for sexual differentiation may protect the avian brain from the differentiating effects of circulating androgens by inhibiting the production of oestrogen.
Simultaneous Monitoring of Cytosolic Free Calcium and Exocytosis at the Single Cell Level
Authors: Chiavaroli Carlo , Vacher Pierre , Vecsey Alice , Mons Nicole , Letari Ornella , Pralong William , Lagnaux Yvan , Whelan Rosemary , Schlegel Werner 
Published: September 2006

AbstractQuinacrine, a fluorescent basic molecule, accumulates in secretory granules of pituitary cells, as was revealed by its colocalization with immunoreactive prolactin. Thus quinacrine fluorescence may be used to monitor secretory activity at the single cell level. Rat pituitary cells in primary culture were loaded with quinacrine and stimulated with physiological secretagogues, such as thyrotrophin‐releasing hormone or bradykinin, which induced a multiphasic lowering of fluorescence, corresponding to the loss of quinacrine contained in exocytosed granules. Quinacrine was further used in combination with the fluorescent calcium probe fura‐2, in order to monitor simultaneously exocytosis and variations in the cytosolic free calcium concentration, [Ca2+]i. With an appropriate selection of the excitation wavelengths, in dual excitation microfluorimetry experiments, it was possible to distinguish between fluorescence changes due to altered [Ca2+]i versus quinacrine exocytosis. Transient elevations of [Ca2+]i were provoked in individual pituitary cells by enhancing calcium influx through voltage gated channels. In part of the cells an initial increase in [Ca2+]i coincided with stimulated quinacrine release. The approach was also applied to cells of the neuroblastoma line NCB20, where stimulation with bradykinin caused a transient rise in [Ca2+]i, concomitantly with enhanced exocytosis. No increase in exocytosis was ever detected without an elevation of [Ca2+]i, suggesting that in both cellular systems, an increase in [Ca2+]i, is absolutely necessary, but not sufficient to induce secretion.
Production of the Neurosteroid 3alpha‐Hydroxy‐5alpha‐pregnan‐20‐one in Man
Authors: Hiemke Christoph , Banger Markus , Knuppen Rudolf , Haupt Otto , Jussofie Astrid 
Published: September 2006

AbstractThe narcotically active progesterone metabolite 3α‐hydroxy‐5α‐pregnan‐20‐one (HPO) modulates γ‐aminobutyric acid (GABA) neurotransmission by direct actions on the GABAA‐receptor complex. In the present investigation, the formation of HPO was quantified in man. Twenty‐four h urine samples were collected during the night (2300 to 0700 h) and day (0700 to 2300 h) from 11 healthy subjects (31 ± 5 years) for two consecutive days. The concentration of HPO was measured after enzymatic hydrolysis of conjugated HPO and multiple chromatographic separation steps by gas chromatography‐mass spectrometry. The mean excretion rates of HPO were 14.8 ± 11.8 μg/24 h with high inter‐individual variations. There were no significant differences in the production of HPO during the night and day. It seemed unlikely that HPO was primarily formed in the adrenals or gonads since the excretion rates of HPO poorly correlated with the formation of 17‐ketosteroids or 17‐hydroxycorticosteroids that are widely used as indices of adrenal and gonadal steroid production. The data showed for the first time that HPO is produced in male subjects in concentrations similar to that of classical steroid hormones.
Possible Role of Neurokinin A in the Control of Prolactin Secretion in Rats and Hamsters
Authors: Pisera D. , Debeljuk L. , Seilicovich A. , Afione S. , Duvilanski B. , Diaz M. C. , Lasaga M. , Traktemberg R. , Bartke A. 
Published: September 2006

AbstractThe possible role of neurokinin A (NKA) in the control of prolactin secretion was studied in vivo, by injecting anti‐NKA serum to ovariectomized rats treated with estrogens and to proestrous rats and hamsters. Injections of an anti‐NKA serum to ovariectomized rats treated with two doses of 80 μg 17ß‐estradiol 24 h apart, or treated chronically with estradiol implants induced a significant decrease of serum prolactin levels as compared with those of similarly treated rats injected with normal rabbit serum. In proestrous rats, the anti‐NKA serum did not modify the afternoon surge of prolactin or luteinizing hormone, but when the antiserum was injected the day before, on diestrus II, it significantly reduced the prolactin surge during the afternoon of proestrus.As in these results obtained in the rat, injections of anti‐NKA serum to golden hamsters on diestrus II also significantly decreased the prolactin surge in the afternoon of proestrus.These results suggest a possible physiological role of NKA on prolactin secretion, exerting a stimulatory influence on the release of this hormone.
Luteinizing Hormone Responses to N‐Methyl‐D,L‐Aspartate During a Photoperiodically‐lnduced Reproductive Cycle in the Ram
Authors: Lincoln G. A. , Wu F. C. W. 
Published: September 2006

AbstractAspartate and glutamate represent a major class of excitatory amino‐acid neurotransmitters in the vertebrate brain, and stimulation of gtutaminergic receptors by the specific agonist N‐methyl‐D, L‐aspartate (NMDA) induces luteinizing hormone‐releasing hormone (LHRH) and LH secretion. In this study, we used NMDA as a probe to investigate the hypothalamic regulation of LH secretion at different stages of a reproductive cycle in Soay rams induced by exposure to alternating 16‐week periods of long and short days. NMDA (20 mg/kg) injected intravenously caused an acute increase in blood plasma concentrations of LH, with a significant increase within 2 to 4 min, and peak levels within 20 min. The magnitude of the response changed markedly during the cycle; it was greatest in the sexually inactive phase under long days (with a linear dose‐response over the range 1 to 20 mg/kg NMDA) and least in the sexually active phase under short days (only 20 mg/kg NMDA produced a small response). Pituitary responsiveness to a standard dose of LHRH (5.3 ng/kg iv) varied only slightly at the different stages and could not account for the observed changes in the LH response to NMDA. There were the expected changes in the endogenous pattern of LH secretion during the cycle, with high frequency LH pulses occurring during the sexually active phase. There was an inverse relationship between the frequency of LH pulses and the LH response to NMDA. Pretreatment of rams with an LHRH antagonist (36 μg/kg iv; Syntex, RS18286) totally blocked the LH response to both NMDA and LHRH, while in a separate study, treatment with dexamethasone (synthetic glucocorticoid, 133.4 μg/kg iv) partially blocked the LH responses. The overall results indicate that NMDA stimulates LHRH secretion in the ram and the response is independent of the activation of the hypothalamo‐pituitary‐adrenal axis. The variation in the LH response during the reproductive cycle may reflect changes in the releasable stores of LHRH in the median eminence. These appear to be depleted in the sexually active phase, when LHRH is secreted in pulses at high frequency. The variation in the response to NMDA may also reflect changes in release of endogenous excitatory amino‐acids, which act via NMDA receptors to form part of the physiological regulation of the reproductive cycle in the ram.
Circadian Variation of Plasma Calcitonin Gene‐Related Peptide in Man
Authors: Wimalawansa Sunil J. 
Published: September 2006

AbstractCalcitonin gene‐related peptide (CGRP) is one of the most potent endogenous vasodilator peptides known so far. Almost all clinical studies using or measuring CGRP are conducted during the day, and hence this study was carried out to see any variations of CGRP levels in the circulation during this period. Three separate studies were conducted. In the first study, following an overnight fast, sequential samples of blood were taken from six healthy volunteers between 0900 and 2100 h and were assayed for CGRP using a highly sensitive and specific radioreceptor assay. A diurnal variation of CGRP in the circulation (P<0.0001) was demonstrated. No difference in the diurnal pattern of CGRP in plasma was seen between males and females. The range of plasma receptor‐active CGRP was 2.8 to 13.0 pmol/l (mean ±SEM, 7.03±0.28 pmol/l). Two peaks of CGRP were observed in the circulation (increases of ∼100% from the basal levels obtained at 0900 h), one around midday (P<0.0001) and the other in the late afternoon (P< 0.005). To assess the contribution of CGRP released from the gut following food, a second study was carried out in which the protocol of the first study was repeated in three volunteers but avoiding any food during the day. Although a similar diurnal variation of receptor‐recognized CGRP was seen in this study (P<0.01), the changes observed were significantly lower than those observed in the first study, suggesting that the effect of a meal exaggerates the response of diurnal variation of plasma CGRP. In a third study, circadian variation of receptor‐recognized CGRP was examined in three volunteers over a 24 h period. In addition to the diurnal pattern seen with the first study, the plasma CGRP levels continued to decrease up to early morning. The lowest levels of CGRP were detected between 0300 and 0600 h. After this time the levels gradually rose towards midday.It is well accepted that the incidence of cardiovascular episodes is high during the early hours of the morning. Separate studies are necessary to determine if these low levels of ‘biologically‐active CGRP’ in the early hours of the morning are a coincidence, or whether they play a role (e.g. relative deficiency of CGRP) in contributing to the occlusion of already diseased arteries. Furthermore, the diurnal variations of monomeric CGRP demonstrated here imply that, with any experiments relying on the measurement or infusion of CGRP, timing of blood sampling and relationship to meals are important and should be strictly adhered to in most physiological studies with CGRP. This is the first study which demonstrates the circadian variation in plasma concentrations of CGRP.
Fine Structural Changes in Explants of the Neural Lobe of the Rat Hypophysis
Authors: Dellmann H.‐Dieter , Gabrion Jacqueline , Privat Alain 
Published: September 2006

AbstractTo obtain a purified population of pituicytes, pieces of rat neural lobes were dissected free of the pars intermedia, incubated in a variety of media, and fixed at regular intervals between 7 and 56 days of incubation. Many neurosecretory axons survived for up to 21 days without any apparent signs of degeneration. Most axons, however, degenerated and were progressively phagocytosed and subsequently eliminated by pituicytes and microglial cells. Lysed axons that were not eliminated, persisted as dense bodies or paracrystalline inclusions. After 30 days of culture, cluster‐forming pituicytes predominated the explants. Pituicytes underwent morphologic changes such as medium‐dependent decrease or increase of lipid inclusions, Golgi activation, process extension and interdigitation, formation of gap junctions and bundles of intermediate filaments. At the explant surface in contact with the culture medium, pituicytes differentiated into an epithelial layer of ciliated and microvilli‐bearing cells linked by junctional complexes. Long‐term neural lobe explants are a relatively pure source of viable pituicytes and should be useful for further studies on the functional significance of these cells.
A Daily Prolactin Rhythm Persists in the Ewe, Foetus and Newborn Lamb After Maternal Pinealectomy in Late Gestation
Authors: McMillen I. C. , Walker D. W. , Young I. R. , Nowak R. 
Published: September 2006

AbstractWe have investigated the effect of maternal pinealectomy between 104 and 120 days gestation on the daily rhythm in plasma prolactin concentrations in the ewe, foetus and newborn lamb. There was a 24 h prolactin rhythm present in both the intact (n = 4) and pinealectomized (n = 4) ewes. Plasma prolactin concentrations were highest at 2100 h (i.e. 2 h after lights off) and a daily prolactin rhythm was present until at least 24 h before delivery. The mean 24 h foetal plasma concentration of prolactin was significantly higher (P<0.001) in the pinealectomized (35.3 + 1.9 μg/1) than in the intact group (6.9 ± 0.6 μg/1). There was a significant 24 h rhythm in foetal prolactin concentrations and the timing of the daily peak (2100 h) was the same in the foetuses of intact and pinealectomized ewes. During the first 10 weeks after birth there was a significant effect of time of day on prolactin concentrations but the 24 h prolactin profile was significantly different in the lambs delivered to pinealectomized ewes than in the lambs delivered to intact ewes. In the lambs delivered after maternal pinealectomy, plasma prolactin concentrations were higher between 1900 and 2300 h than between 0700 and 1100 h, whereas in lambs delivered to intact ewes, prolactin concentrations were higher at 0100 h than between 1500 and 1700 h. We conclude that the ontogenesis of the daily rhythm in foetal and newborn lamb plasma prolactin concentrations is not dependent on a daily melatonin signal from the ewe.
Interaction of Forskolin and Melatonin on Cyclic AMP Generation in Pars Tuberalis Cells of Ovine Pituitary
Authors: Morgan Peter J. , Lawson Wilfred , Davidson Gary 
Published: September 2006

AbstractThe pineal indoleamine, melatonin, acts on specific secretory cells of the pars tuberalis of the sheep pituitary. Using pars tuberalis cells in primary culture melatonin inhibited forskolin‐stimulated cyclic AMP production in both a time ‐ and dose‐dependent manner, but the nature of the melatonin response was critically dependent upon the stimulatory concentration of forskolin used. Forskolin alone stimulated dose‐dependent cyclic AMP accumulation, which reached an equilibrium state after 15 min. This was maintained for up to 3 h, indicating a lack of desensitization to forskolin. Melatonin (1 μM) inhibited this response by greater than 80% at all doses. However, 100 μM forskolin reduced both the affinity and the number of the melatonin receptors, relative to untreated controls. Consistent with this, melatonin was 100 times less potent at inhibiting forskolin‐stimulated cyclic AMP production, when titrated against 100 μM forskolin as compared to 1 μM forskolin. The response to 1 μM forskolin could be potentiated by 10 μM phorbol 12,13 myristate acetate, but not by calcium ionophore (A23187). This provides evidence for the interaction of the phosphatidylinositol pathway with the cyclic AMP system in these cells. Nevertheless melatonin can inhibit both the potentiated and non‐potentiated response with equal effect.