摘要:

AbstractA perifusion system of anterior pituitary (AP) tissue was used to investigate the temporal interaction of growth hormone‐releasing factor (GRF) and somatostatin (SRIF) in the control of GH secretion in two pig breeds, Göttingen Miniature Pig (GMP), a small obese breed, and German Landrace (GLR), a conventional lean breed. AP tissue pieces derived from sexually mature ovariectomized animals were perifused (6 replicates per treatment) and fractions were collected at 10 min intervals. Basal GH release (ng‐mP‐1mg‐1AP) in GLR was twice that of GMP (P<0.001). Exposure to 10 min pulses of 1 nM GRF repeated 3 times at 2 h intervals resulted in rapid stimulatory GH responses (area under the curve) which became attenuated (P<0.05) over time in GMP but not in GLR. Surprisingly,duringand following the exposure of AP tissue from GMP to 10‐, 20‐, or 40‐min pulses of 10 nM SRIF alone, GH release was markedly stimulated (P<0.05), while AP tissue from GLR only showed a weak rebound GH release after SRIF pulses. With AP tissue from GLR low concentrations (0.1 nM SRIF) amplified GRF‐induced GH release, whereas 1 nM or 10 nM SRIF inhibited GRF‐induced GH release. However, concomitant exposure of AP tissue from GMP to 0.1, 1 or 10 nM SRIF during a GRF pulse markedly enhanced the GH response (P<0.05), compared to 1 nM GRF alone, except for 1 nM SRIF which inhibited the GH response to the first GRF pulse. Thus the presence of SRIF, and not only its withdrawal, is an important factor in setting the timing and duration of GH pulses in both breeds. In GLR the concentration of SRIF is more important than the duration and/or type of SRIF pulse. In contrast, in GMP type and/or duration of SRIF pulses seem to be crucial to optimize pulsatile GH release and even determine peak height of GH pulses caused by GRF. These findings indicate clear breed differences in the role of SRIF and in the control of GH release by the interplay of GRF and SRIF. The ‘paradoxical’ effect of SRIF suggests that the role of SRIF is much more complex than that of a mere inhibitor and whose real role could be a modulator either of GH pulse and/or GR

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00817.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractMaternal nest‐building in rabbits, expressed across the last third of pregnancy, consists of: digging a burrow, collecting straw and shaping it into a nest inside the burrow, plucking body hair and lining the straw nest with it. The sequential expression of these activities is correlated with specific changes in the plasma concentration of estradiol, progesterone (P), and prolactin (PRL). To further substantiate the participation of these hormones in the control of maternal nest‐building we explored in ovariectomized (ovx) New Zealand white rabbits the capacity of several combinations of such hormones to stimulate digging, straw‐carrying, and hair‐pulling. Does given estradiol benzoate (EB; 5 μg/day from days 3 to 21) plus P (2 or 10 mg/day from days 4 to 16) dug into a substrate from the fourth day of the P treatment until withdrawal of this hormone. The intensity of this effect was greater in the group treated with the high dose of P. Straw‐carrying and hair‐pulling occurred after P withdrawal in a dose‐response way. Food intake, which declines in pregnant females shortly before parturition, decreased to the same extent in both groups of ovx EB‐treated does after P withdrawal. A significant increase in PRL plasma levels was observed on day 9 in does given EB plus 2 mg P/day and at two days following P withdrawal in does given EB plus 10 mg P/day. When such ovx EB/P‐treated does were given bromocriptine to block PRL release (1 or 3 mg/Kg/day, from days 11 to 21) the expression of digging was unmodified. By contrast, bromocriptine abolished the display of straw‐carrying and hair‐pulling, and also prevented the decline in food intake normally following P withdrawal. The addition of ovine PRL to ovx EB/P‐treated does given bromocriptine reduced the expression of digging, did not restore straw‐carrying or hair‐pulling, and provoked a sharp decline in food intake. The possible mechanisms of interaction between PRL and steroid hormones for the regulation of specific aspects of the pregnant doe's physiolog

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00818.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00819.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe anterior pituitary gland is a site of nitric oxide (NO) production and action, suggesting a local regulatory function. We recently reported that NO inhibitsin vitroprolactin release. The aim of the present study was to establish the mechanism of action of NO on prolactin release and to determine whether NO is involved in the inhibitory effect of GABA on prolactin release. Since NO exerts its action through cGMP by activating guanylate cyclase in different tissues, we examined the effect of sodium nitroprusside (NP), a NO releaser, on intrapituitary cGMP levels. Incubation of anterior pituitary glands with 0.5 mM NP 4‐fold increased intrapituitary cGMP content, but decreased intrapituitary cAMP levels. In addition, we studied the effect of NP on prolactin release in the presence of LY 83583, an inhibitor of guanylate cyclase activity and 3‐lsobutyl‐1‐methylxanthine (IBMX), an inhibitor of phosphodiesterase activity. 10μM LY 83583 and 0.5 mM IBMX blocked the inhibitory effect of NP on prolactin release. (10‐3M) 8Br‐cGMP, an analogue of cGMP, mimicked the effect of NP on prolactin release. On the other hand, NO seems to be involved in the inhibitory effect of GABA on prolactin release since hemoglobin, a scavenger of NO, and Nw‐nitro‐L‐arginine methyl ester, an inhibitor of NO synthase (NOS), blocked the pituitary response to GABA. Moreover, GABA (106M) stimulated NOS activity by almost 50%. GABA increased intrapituitary cGMP levels and decreased cAMP. Dopamine stimulated NOS activity weakly.These observations suggest that NO, acting through the guanylate cyclase‐cGMP pathway, inhibits prolactin secretion. In addition, NO may be involved in the inhibitory effect of GABA and dopamine

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00820.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstractlnterleukin‐1β stimulates oxytocin and vasopressin release in conscious, male rats and causes a rise in blood pressure. These experiments were done to: A) examine the effect of i.c.v. interieukin‐1 β (1 ng/μl) on circulating levels of vasopressin in female rats at different stages of lactation and B) determine if α‐adrenergic mechanisms and/or prostaglandins were involved as mediators. Urethane‐anaesthetized non‐lactating rats and rats at Day 7, 10, 20 and 26 of lactation were set up for arterial blood sampling and i.c.v. injections. One mL blood samples were obtained in one min periods before, and at 1, 2.5, 5, 10, 30, 60 and 120 min after the following treatments: i.c.v. treatment with either interleukin‐1β (1 ng in 1 μl PBS‐BSA) or PBS‐BSA (1 μl) as a vehicle control; or i.c.v. treatment with interleukin‐1β following pretreatment with either phentolamine (1.7 ng/μl i.c.v.) or indomethacin (1 ng/μl i.c.v.). As blood was sampled, isotonic saline was infused (1 mL per min) and blood pressure was monitored to minimize any hypovolemic effects due to sampling. Extracted plasma was assayed using a specific vasopressin radioimmunoassay, lnterleukin‐1 β i.c.v. stimulated the release of vasopressin above that elicited by PBS‐BSA alone in non‐lactating rats resulting in an approximate 1.2 to 2‐fold increase in plasma hormone levels. Throughout the first half of lactation, vasopressin responsiveness to i.c.v. interleukin‐1β treatment was markedly attenuated. In latter stages of lactation, the response recovered and resembled that of non‐lactators around the time of weaning. Prostaglandins consistently mediate a stimulatory action of interleukin‐1β on vasopressin release whereas α‐adrenergic mechanisms mediate a depression of interleukin‐1β‐induced vasopressin release during the early to middle stages of lactation. It is possible that the depression in interleukin‐1β‐stimulation of vasopressin release in early to mid‐lactation is conducive for nursing to occur and that the increase in vasopressin responsiveness towards the latter stages

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe neural pathways responsible for conveying the steroid feedback signals that ultimately affect reproductive neuroendocrine function remain largely undefined. One possibility involves a direct projection from estrogen receptor (ER)‐containing neurons to the median eminence (ME), a site of neuroendocrine peptide release. To examine this possibility, 8 ewes received stereotaxic injections of the retrograde neuronal tract‐tracing compound cholera toxin‐β subunit (CTβ) into the ME. Neurons sending projections to the ME and containing ER were identified using a dual‐label immunoperoxidase method. Double‐labeled cells were found in distinct regions: (1) the ER‐rich arcuate nucleus (ARC) that contained the greatest number of double‐labeled cells, and (2) the organum vasculosum of the lamina terminalis (OVLT) which contained a very consistent, but low, number of double‐labeled cells. While a fairly large number of retrogradely‐labeled ARC neurons containing ER were identified, the majority of ER‐containing ARC neurons were unlabeled and thus send projections elsewhere. Other regions containing high concentrations of ER‐positive cells such as the medial preoptic area (MPOA), anterior hypothalamic area, and ventrolateral portion of the ventromedial hypothalamic nucleus, were devoid of double‐labeled cells. Similarly, regions rich in neuroendocrine neurons such as the periventricular hypothalamus and paraventricular and supraoptic hypothalamic nuclei contained no double‐labeled cells. These results suggest that modulation of neuroendocrine secretory activity may occur directly at the level of the ME by ER‐containing neurons located within restricted regions of the hypothalamus and forebrain. However, the relatively low proportion of ER‐containing neurons projecting to the ME suggests that the influence of estradiol upon neuroendocrine function also may include

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe neuroendocrine control of prolactin synthesis and secretion before birth is not well understood. We have measured the changes in the level of prolactin mRNA in the anterior pituitary of the fetal sheep throughout the last 15 days of pregnancy (term = 147 ± 3 days gestation). We have also investigated the effects of surgical disconnection of the fetal hypothalamus and pituitary (HPD) with or without long term Cortisol infusion on pituitary prolactin mRNA levels and plasma prolactin concentrations in the late gestation sheep fetus. Prolactin mRNA levels were measured in anterior pituitaries collected from a series of fetal sheep (130–134 days, n = 6; 135–140 days, n = 6; 141–145 days, n = 6) in late gestation. HPD was carried out in ten fetal sheep at 105–115 days gestation and five intact fetal sheep were used as controls. In the HPD group, either saline (HPD + saline group, n = 5) or Cortisol was infused (3.5mg/24 h) for 5 days from 134–136 days gestation (HPD + Cortisol group, n = 5). There was an increase in the ratio of prolactin mRNA:18S rRNA in the fetal pituitary between 130–134 days (0.46 + 0.08, n = 6) and 135–140 days (1.27 ± 0.17 n = 6) which was maintained after 141 days gestation, (1.27 ± 0.11, n = 6). The mean prolactin mRNA: 18 S rRNA ratio was significantly higher (P<0.05) in intact fetal sheep (1.41 ± 0.16, n = 4) than in the HPD fetal sheep after either saline (0.54 ± 0.14, n = 4) or Cortisol (0.74 ± 0.24, n = 5) administration. The mean plasma concentration of prolactin was also higher in the intact group (28.3 ± 3.9 ng/ml) when compared with the HPD + saline group (8.0±3.3 ng/ml) or the HPD+cortisol group (5.6 ± 1.9 ng/ml). We have demonstrated that there is a strong hypothalamic drive to prolactin synthesis and secretion in the fetus and that Cortisol does not act directly at the fetal pituitary to stimulate prolactin synthesis and secre

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe direct effect of acetylcholine on pituitary growth hormone secretion during the postnatal period of the rat was studied using a superfusion system. Acetylcholine elicited a dose related stimulatory effect on growth hormone (GH) secretion in the pituitaries from 2‐day old rats. M, muscarinic agonist McN A343 mimicked the GH releasing effect of acetylcholine, nicotine was ineffective. The GH release elicited by acetylcholine diminished with postnatal development, it was small by the end of the third postnatal week and was not demonstrable in the adult pituitaries. The effect of acetylcholine was potently antagonized by pirenzepine (M1antagonist) and 4‐DAMP (M3and M1antagonist) but not by methoctramine (M2antagonist). It is concluded that unlike in the adult, in the newborn rat the cholinergic regulation of pituitary GH secretion plays a prominent role directly at pituitary level most likely via M1recept

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe role of hypothermia in the suppression of pulsatile luteinizing hormone (LH) release by the barbiturate sodium pentobarbitone has been investigated in ovariectomized rats. Each animal was fitted with an intraperitoneal miniature radio transmitter to monitor core temperature and with an indwelling intravenous and intraperitoneal catheter. During the 6‐h sampling period the animal's core temperature was recorded automatically every 5 min and a 25 μl blood sample was obtained concurrently using an automated system. After the initial 3 h of sampling either the drug or the vehicle was administered via the intraperitoneal cannula from outside the cage, thus ensuring minimal disturbance to the animal. Administration of sodium pentobarbitone (40 mg/kg) at an ambient temperature of 21°C resulted in a significant hypothermia throughout the 3‐h post‐injection period. During this period there was a significant reduction in mean LH concentration, and in the frequency and amplitude of the LH pulses. When the drug was administered at an ambient temperature of 35°C there was no reduction in core temperature and no significant change in the LH pulse parameters. Vehicle treatment was without significant effect on core temperature or on the LH pulse parameters when administered at an ambient temperature of either 21°C or 35°C. These results indicate that the effects of this barbiturate on the pulsatile release of LH are secondary to the induced hypothermia and suggest that hypothermiaper semay be able to disrupt LH pulses. It is therefore imperative to reassess the significance of previous studies that have implicated particular neurotransmitter systems in the control of LH pulses; unrecognized hypothermic effects of the treatments may have been the primary cause of the pulse suppression, rather than a direct involvement of the neurotransmitter in question in the regulation of LH releasing hormone. The neurophysiological process by which the hypothermic state may inhibit LH pulses remains to be

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0953-8194    

DOI:10.1111/j.1365-2826.1996.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY