摘要:

We have recently reported that, in the rat pituitary, prolactin (PRL) is synthesized and stored in two different cell types: the typical PRL cell characterized by the presence of large irregular secretory granules and another cell type containing small round secretory granules. Since the secretion of PRL is stimulated by estrogens, we decided to investigate the effect of gonadectomy and estradiol (E2) replacement therapy in female rats on both cell types using a combination of in situ hybridization and immunostaining. Gonadectomy induced a marked decrease in hybridization signal and an almost complete disappearance of the classical PRL cells. The most abundant PRL cells were the small-granule-containing cells and other PRL cells characterized by the presence of both small and large granules. These changes in the PRL cell population were completely prevented by E2 administration to castrated animals. These studies indicate that E2 cannot only regulate PRL mRNA but also induce important morphological changes in PRL cell types.

ISSN:0028-3835    

DOI:10.1159/000125603

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The acute effects of low oral doses of Δ9-tetrahydrocannabinol (THC), cannabinol (CBN) and cannabidiol (CBD) administered alone or in combinations on LH and prolactin (PRL) secretion and on hypothalamic norepinephrine (NE), dopamine (DA) and serotonin (5-HI) dynamics were examined in adult male rats. Plasma LH levels were significantly reduced 60 min after administration of 0.5 mgTHC/kg body weight and 30, 60 and 120 min after administration of THC + CBN or THC + CBD. There were no changes in plasma PRL in response to cannabinoid treatments. The turnover of NE in both the median eminence (ME) and medial basal hypothalamus (MBH) was dramatically affected by all the cannabinoid treatments. Complete suppression of NE turnover occurred 30 min post-THC and 120 min post-THC + CBN in the ME and 120 min post-THC + CBD in the MBH. Cannabinoids did not significantly affect DA turnover in the MBH or the content of NE, DA, 5-HT or 5-hydroxyindole-3-acetic acid in either the ME or MBH. These data demonstrate that treatment of adult male rats with a low dose of THC suppresses LH secretion and that CBN and CBD potentiate this action of THC. Although the mechanisms responsible for the inhibition of LH release by cannabinoids cannot be positively identified from these experiments, the results suggest that alterations in hypothalamic noradrenergic activity may be involved in this effect

ISSN:0028-3835    

DOI:10.1159/000125604

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

This study was performed to determine if epinephrine (EPI) present in hypophysial portal blood has a peripheral or a central origin. Pituitary stalk and femoral arterial EPI plasma levels were simultaneously measured in rats anesthetized with thiopental or urethane. EPI was measured by two different methods: radioenzymatic assay or HPLC followed by electrochemical detection. In thiopental-anesthetized rats, levels were higher in hypophysial portal than in femoral arterial plasma with both methods. In urethane-anesthetized rats, no difference in EPI concentrations was found between peripheral and portal plasma. A rapid blood volume depletion (15 ml/kg in 3 min) evoked a marked elevation of pituitary stalk and arterial EPI plasma concentration while norepinephrine (NE) and dopamine (DA) levels were unaffected. Under both types of anesthesia, the increase of EPI levels was higher in peripheral than in portal plasma. After removal of the adrenal glands, EPI was undetectable or barely detectable in pituitary stalk and arterial plasma. The hemorrhage-induced stimulation of EPI secretion was blunted in portal and peripheral plasma of adrenalectomized rats. These findings indicate that: (1) hypophysial portal EPI plasma concentration is highly dependent on an adrenal source; (2) hypothalamic EPI is not released into portal circulation in response to acute hemorrhage, and (3) anesthesia markedly influences catecholamines plasma levels.

ISSN:0028-3835    

DOI:10.1159/000125605

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The effect of a 4-min secretory stimulation with 10–6M isoproterenol on the peripheral cytoplasmic zone of intermediate lobe cells of the rat pituitary incubated in vitro was studied. Two widths of the peripheral zone, a 450 nm zone and a 250 nm zone, were analyzed with electron-microscopical morphometry. Isoproterenol stimulation did not induce any significant effect on the number of electron-dense secretory granules contained within the 250 or the 450 nm zone. A 50% decrease was, however, noted in the number of electron-lucent granules situated in immediate association with the plasma membrane. The majority of the transection diameters of electron-dense granules in the peripheral zone of control cells fell within a range of 135–230 nm. A relative increase in the number of transections over 230 nm was noted after isoproterenol stimulation. In conclusion, isoproterenol stimulation induced a preferential release of electron-lucent granules from the peripheral cytoplasmic zone of the intermediate lobe cells, indicating that this subpopulation of granules represents the immediately releasable secretory pool of these cells. In addition, large electron-dense granules appeared in the peripheral zone during isoproterenol stimulat

ISSN:0028-3835    

DOI:10.1159/000125615

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Studies were performed in guinea pigs to elucidate alterations in endogenous uterine norepinephrine (NE) levels and changes in the contractile response to exogenous NE following local sympathetic denervation, oophorectomy, or treatment with sex steroids. Both in intact and oophorectomized animals the myometrial NE concentration was reduced after sex steroid treatment (0.5 µg 17-β-estradiol, or 0.1 µg estradiol plus 2 mg progesterone, during 2 weeks), mainly as a result of increased uterine weight. After surgical removal of the hypogastric nerves and section of the suspensory ligaments, a similar response to sex steroids was seen if the animals had previously been oophorectomized. The myometrial contractile activity induced by exogenous NE was measured in vitro. The EC50 values (NE concentration giving 50% of the maximal response) showed a similar pattern of variations after hormonal treatment and oophorectomy as did the concentration of endogenous NE. Thus, exposure to the steroids leading to a reduction of neuronal NE also caused an increased sensitivity of the myometrial smooth musculature to exogenous NE, and in the various experimental groups the two parameters showed a close and significant relationship. The underlying mechanism may induce a denervation supersensitivity to NE induced by exposure to estrogen and progestero

ISSN:0028-3835    

DOI:10.1159/000125616

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Secretion of the growth hormone (GH) in spontaneously hypertensive (SH) male rats has been determined and compared with that of normotensive Wistar-Kyoto (WKY) controls. In a first set of experiments, plasma GH concentration and pituitary GH content were measured in SH rats 30, 60 and 90 days old. 30-day rats showed reduced GH plasma and pituitary levels, whereas in 60- and 90-day-old rats no differences in GH plasma concentration and increased GH pituitary content were observed. In a second set of experiments, 90-day-old SH male rats anesthetized with sodium pentobarbital and intravenously injected with growth hormone-releasing factor (GRF) showed an amplitude and duration of response to injected hormone higher than WKY controls. In a third set of experiments, hemipituitaries of 90-day-old SH males were incubated for 2 h in Krebs-Ringer-bicarbonate either in the presence or in the absence of GRF. In the absence of GRF stimulation, the in vitro release of GH was higher than in WKY controls, whereas in the presence of GRF the sensitivity and the maximum response to GRF was reduced in comparison with normotensive male rats. These results indicate that SH rats have decreased pituitary content and plasma GH concentration before puberty. Besides, they showed increased pituitary GH content in adulthood and opposite changes in the in vivo and in vitro response to GRF.

ISSN:0028-3835    

DOI:10.1159/000125617

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Growth hormone (GH) secretory patterns are influenced by sex steroids, at least in part, through modulation of the secretion of hypothalamic somatostatin (SS) and GH-releasing hormone. Neurons in the periventricular nucleus (PeN) expressing the messenger RNA (mRNA) for SS are modulated by physiological levels of testosterone. However, it is uncertain whether testosterone’s action is mediated directly by androgen receptor activation or indirectly through aromatization to estradiol and subsequent binding to the estrogen receptor. We examined this question by evaluating the effectiveness of 17β-estradiol and the nonaromatizable androgen, dihydrotestosterone (DHT), to mimic the effects of testosterone. Adult male rats were castrated and implanted subcutaneously with a Silastic capsule that contained either testosterone, 17β-estradiol or DHT, or a sham capsule. Intact animals were sham-operated. We used in situ hybridization to assess the effect of these treatments on SS mRNA signal levels in individual neurons of the hypothalamus. Following castration, SS mRNA content was reduced in cells of the PeN (intact, 195 ± 12 grains/cell, vs. castrated, 139 ± 4 grains/cell). Replacement with physiological levels of testosterone prevented the decline in SS mRNA signal levels (castrated testosterone-replaced, 214 ± 15 grains/cell) as did replacement with the nonaromatizable androgen DHT (castrated DHT-replaced, 213 ± 16 grains/cell). Treatment with 17β-estradiol failed to prevent the postcastration decline in SS mRNA content (castrated estrogen-replaced, 145 ± 4 grains/cell). Castrated 17β-estradiol-treated animals were not significantly different from the castrated sham-treated animals (castrated, 139 ± 4 grains/cell, vs. castrated estrogen-replaced, 145 ± 4 grains/cell). These results show that, whereas testosterone and DHT prevented the postcastration decline in SS mRNA signal levels, 17β-estradiol had no such effect. Based on these observations, we conclude that the ability of testosterone to stimulate SS gene expression in neurons of the PeN is likely to be mediated through activation of androgen receptors and not through aromatization

ISSN:0028-3835    

DOI:10.1159/000125618

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The binding of 3H-RO 5-4864 to the peripheral-type benzodiazepine receptors (PBZDR) in rat testicular interstitial cells (TIC) was characterized. The binding was saturable, reversible and showed a single high-affinity (Kd = 5.02 ± 0.86 nM) class of binding sites. The maximal binding capacity (Bmax) in crude mitochondrial fractions (77.6 ± 9.1 pmol/mg protein) represents the highest density of PBZDR in tissues thus far studied. In comparison with the crude mitochondrial fraction the subcellular fractionation of TIC revealed a 2-fold enrichment of 3H-RO 5-4864 binding sites to the purified mitochondria (Bmax = 140 ± 23 pmol/mg protein). The ability of various drugs to displace 3H-RO 5-4864 from TIC binding sites was examined and the inhibition constants (Ki) for RO 5–4864, PK 11195, diazepam and flunitrazepam were 3.5, 4.4, 159, and 353 nM, respectively, whereas clonazepam and RO 15-1788 were inefficient in displacing 3H-RO 5-4864 (Ki 10 µM). This pharmacological profile is characteristic of PBZDR described in other tissues. In conclusion, rat TIC possess a very high concentration of PBZDR primarily associated with mitochondrial memb

ISSN:0028-3835    

DOI:10.1159/000125606

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

γ-Aminobutyric acid (GABA) neurones are present in the zona incerta (ZI) where other systems have been shown to influence gonadotrophin release. This report investigates the effect of GABA agents in the ZI on ovulation and luteinizing hormone (LH) release. In intact females under Saffan anaesthesia, bilateral stereotactic injections into the ZI of two GABA transaminase inhibitors [amino(oxy)acetic acid and γ-acetylene GABA] on the morning of pro-estrus or two GABA agonists on the afternoon of pro-estrus inhibited ovulation. The selective GABA B agonist baclofen was effective at 0.05 nM; muscimol, a mixed GABA A and B agonist, was 50-fold less potent, while the selective GABA A agonist isoguvacine had no effect at 500 nM. Administration of baclofen at 0.05 and 5 nM into the ZI significantly reduced plasma LH concentration in untreated ovariectomized rats and also prevented the rise in LH normally induced in ovariectomised rats primed with 5 µg oestradiol benzoate (OB) plus 0.5 mg progesterone. In ovariectomised rats primed with 5 µg OB alone, administration of the selective GABA A antagonist bicuculline (200 and 260 pg/side) had no effect on plasma LH, while the GABA B antagonist phaclofen (10 pg/side) stimulated a rise in plasma LH, 40 and 60 min after injection. These results indicate that GABA activity in the ZI exerts an inhibitory effect on LH release and ovulation and this is preferentially exerted via GABA B recept

ISSN:0028-3835    

DOI:10.1159/000125607

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

[l25I]-neuropeptide Y receptors were characterized in the rat pituitary gland using quantitative autoradiography. Scatchard analysis of saturation isotherms showed high affinity (Kd 8.5 × 10–11M) and single class of binding sites (Bmax 0.22 pmol/mg of protein) in the posterior lobe of the pituitary gland, with no specific binding in the intermediate or anterior lobe. Increasing concentrations of guanine nucleotide analogues and peptide YY inhibited neuropeptide Y binding. In addition, neuropeptide Y binding was pertussis-toxin-sensitive. These results add additional information about a possible neuronal (through neuropeptide Y) and hormonal (through peptide YY) regulation of posterior pituitary function, which is most probably GTP-depende

ISSN:0028-3835    

DOI:10.1159/000125608

出版商:S. Karger AG    

年代:1990

数据来源: Karger