摘要:

The possible involvement of the serotoninergic system in histamine-induced PRL secretion was studied in urethane anesthetized male rats. Intracerebroventricular infusion of histamine (30 µg) stimulated PRL secretion 10-fold. This effect was mimicked by the H2-receptor agonist dimaprit (300 µg), while the H1-receptor agonist 2-thiazolylethylamine (140 µg) had no effect. Pretreatment with the serotonin receptor blockers methysergide (2.5 mg/kg i.p.) or ketanserin (2.5 or 10.0 mg/kg i.p.) reduced the PRL peak response to histamine 75, 54, or 58%, respectively. During serotonin receptor blockade, dimaprit had a stimulatory effect similar to that of histamine, while 2-thiazolylethylamine had no effect. Intra-arterial infusion of histamine (420 µg) stimulated PRL secretion 6-fold. This effect was mimicked by the H1-receptor agonist 2-thiazolylethylamine (1,900 µg), while the H2-receptor agonist dimaprit (3,000 µg) had no effect. Pretreatment with methysergide (2.5 mg/kg i.p.) or ketanserin (2.5 or 10.0 mg/kg i.p.) reduced the peak response to histamine 54, 54, or 51%, respectively. The effect of histamine was mimicked by 2-thiazolylethylamine, while dimaprit slightly inhibited the PRL secretion. The antiserotoninergic activity of methysergide and ketanserin was demonstrated by their ability to prevent the PRL-releasing effect to serotonin. The effects of methysergide and ketanserin were not due to dopamine-like activity, since none of the drugs affected basal PRL secretion and since the dopamine receptor antagonist pimozide did not prevent the inhibitory effect of methysergide on the histamine-induced PRL release. The findings indicate that histamine-stimulated PRL secretion is mediated in part by serotoninergic ne

ISSN:0028-3835    

DOI:10.1159/000125059

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The sequential changes in the histological pattern of anterior pituitary cytodifferentiation of the rat are described. The first labeled cells were ACTH positive and were detected in the pars tuberalis on postconceptual day 13. On day 14 ACTH cells also appeared in the ventral periphery of the pars distalis. On fetal day 15 the pars tuberalis anlage was characterized by numerous well-stained ACTH cells and by some weakly labeled FSH-β, LH-β, TSH-β, GH and PRL cells while the pars distalis showed only ACTH positivity. On day 16 of gestation the ACTH cells were equally distributed throughout the whole pars distalis, while LH-β, FSH-β, TSH-β, PRL and GH immunoreactive cells were localized either in the ventral region of the pars distalis only or were evenly distributed throughout the pars distalis. The present immunocytochemical data suggest that in the pars distalis the hypophyseal cell differentiation follows a clear rostrocaudal, ventrodorsal direction and that the time sequence of the functional differentiation of the adenohypophysis is pars tuberalis, pars distalis and pars inter

ISSN:0028-3835    

DOI:10.1159/000125060

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Gonadotropin-releasing hormone (GnRH) produces a rapid and concentration-dependent hydrolysis of polyphosphoinositides in rat anterior pituitary cells in culture. Evaluation of the action of the decapeptide by measurement of [3H]-inositol phosphates and of prelabeled phosphoinositides demonstrated an effect on phosphatidylinositol-4,5-bis-phosphate and phosphatidylinositol-4-phosphate earlier than on phosphatidylinositol. The receptor antagonist [D-pGlul, D-Phe2, D-Trp3,6]-luteinizing hormone-releasing hormone blocked the effect of GnRH on [3H]-inositol phosphate production. Protein kinase C activators attenuated GnRH-induced phosphoinositide hydrolysis, while neither cyclic AMP analogs nor cyclic GMP analogs were effective. These results indicate that phosphoinositide hydrolysis represents an important postreceptor transducing mechanism for GnRH action at the gonadotroph and that protein kinase C (but not cyclic nucleotides) may exert a negative feedback control on GnRH receptor-coupling mechanisms.

ISSN:0028-3835    

DOI:10.1159/000125061

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

These studies were undertaken to characterize the secretion of adrenocorticotropin (ACTH), immunoreactive (ir) β-endorphin (ir-β-EP) and ir α-melanocyte-stimulating hormone (ir-α-MSH) from the surgically isolated ovine pituitary in response to an audiovisual stress (barking dog, 3 min) and insulin hypoglycemia. The studies were performed in 4 ovariectomized, hypothalamo-pituitary-disconnected (HPD) and 4 sham-HPD ewes bearing indwelling jugular venous catheters. Basal concentrations of the three pro-opiomelanocortin (POMC) peptides and plasma cortisol were significantly increased in the HPD animals. When the control ewes were exposed to the audiovisual stimulus, plasma ACTH, ir-β-EP and ir-α-MSH levels were increased 2.5-, 10-, and 5-fold 1 min after the stress; plasma cortisol attained maximal values at 5 min. In contrast, plasma levels of the three POMC peptides were not significantly increased in the HPD animals, although a rise in plasma cortisol occurred. The administration of regular insulin (5 units/kg i.v.) to control ewes caused plasma ACTH, ir-β-EP, and ir-α-MSH levels to increase 17-, 22-, and 67-fold at 50 min; plasma cortisol values were maximal at 60 min. In contrast, the elevated basal levels of POMC peptides in the HPD animals were not significantly increased by the hypoglycemia, but a significant elevation of plasma cortisol was seen. We conclude that: (1) the increase in ACTH in intact animals after an audiovisual emotional stress and hypoglycemia, and the abolition of this increase by HPD, indicates that both stimuli, each acting through distinct neuroanatomical pathways, increase the net corticotropin-releasing activity of the hypothalamus; (2) the rise in plasma cortisol in HPD animals after stress suggests that peripheral humoral factors may release additional small amounts of ACTH from the anterior pituitary, and (3) the finding of increased basal ACTH levels after HPD suggests that POMC peptide synthesis and secretion by the anterior pituitary is tonically regulated by an inhibitory factor of hypothalamic

ISSN:0028-3835    

DOI:10.1159/000125062

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

In this study, changes in individual proteins in the ventromedial hypothalamus (VMN) and the preoptic area (POA) of the female rat brain were quantitatively assessed following either a short treatment (2 h) or a discontinuous schedule of estradiol. Ovariectomized (OVX) rats were implanted with estradiol capsules or sham-implanted for the appropriate paradigm and sacrificed by decapitation. Punches of brain tissue containing the VMN and POA were incubated with 35S-methionine and 35S-cysteine, and the labeled proteins separated by two-dimensional gel electrophoresis. Estradiol-induced changes were quantitatively assessed by computerized optical densitometry and subjected to a normalization procedure between pairs of estradiol-treated and OVX control gels. A number of proteins within the VMN and POA were found to be positively or negatively affected in labeling after either hormone administration paradigm. In both brain regions, the population of proteins affected in labeling after 2 h of estradiol treatment were markedly different from those affected after the discontinuous hormone paradigm. Comparison of the VMN and POA also indicated that the populations of proteins affected in labeling by either hormone treatment paradigm were different, with there being only 3 proteins (from a total of 39) affected in the same direction and 2 affected in the opposite direction by the hormone in both regions. These findings lend support to the hypothesis that administration of estradiol results in a molecular cascade of events within brain regions involved in the control of reproductive behavior. The differential effects of estradiol on proteins in the VMN and POA correlate with the dichotomy of function of these two brain regions and provide further evidence that gonadal steroids accomplish their action on neurons via mechanisms that are, in part, unique to the brain region.

ISSN:0028-3835    

DOI:10.1159/000125063

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The response of folliculo-stellate (FS) cells of the anterior pituitary to estrogen has been studied in two strains of rat which differ in estrogen responsiveness. Fischer 344 (F344) rats are highly estrogen-responsive in comparison to Sprague-Dawley (S-D) rats. Ovariectomized adults were implanted with silastic capsules containing 17β-estradiol benzoate. Control and experimental animals were sacrificed 10 and 20 days after implantation of the silastic capsules. Most FS cells of F344 rats revealed dramatic changes, i.e. activation as phagocytes, after 10 and 20 days of estrogen treatment. These activated FS cells separated themselves from adjacent parenchymal cells and frequently contained phagosomes which included portions of granulated cells, mostly somatotrophs and lactotrophs. They also contained a variety of lysosomal dense bodies and dilated cisterns of endoplasmic reticulum. Endfeet processes abutting the parenchymal basal lamina contained large aggregates of dumbbell-shaped granules and tubulo-vesicles. Subjacent to the endfeet processes the basal lamina was often discontinuous, and profiles suggesting uptake of fragments of the basal lamina by FS cells were evident. Most FS cells of estrogen-treated S-D rats either were identical to those of controls or were only minimaly modified. However, a few activated FS cells were present and these contained a variety of lysosomal dense bodies and phagosomes, as well as lipid inclusions and dilated endoplasmic reticulum. Endfeet projections at the parenchymal basal lamina contained very few dumbbell-shaped granules or tubulo-vesicles, and the basal lamina was intact. Estrogen sensitivity of F344 rats appears, at least in part, to be associated with activation of FS cells as phagocytes and in degradation of the parenchymal basal lamina. This specific cellular response may thus contribute to, or underlie, the vascular reorganization and angiogenesis which occur during onset stages of estrogen-induced tumors of the anterior pituitary

ISSN:0028-3835    

DOI:10.1159/000125064

出版商:S. Karger AG    

年代:1988

数据来源: Karger