Gonadotropin-releasing hormone and kisseptin-10 regulate nuclear receptor subfamily 5 group a member 1/catenin beta 1/ nuclear receptor subfamily 0 group B member 1 activity in female rat anterior pituitary gland.

In this study, we tested the hypothesis that modulation of endogenous gonadotropin-releasing hormone (Gnrh) neuronal network activity alters the mRNA expression of nuclear receptor subfamily 5 group A member 1 (Nr5a1), through one of the component of Wnt pathway signaling - catenin beta 1 (Ctnnb1) (its co-activator), and its co-repressor nuclear receptor subfamily 0, group B member 1 (Nr0b1) in the female rat pituitary gland in vivo. Adult ovariectomized rats were given a serial infusion of Gnrh, kisspeptin-10, Gnrh + Gnrh antagonist (Antide), or kisspeptin-10 + kisspeptin antagonist (kisspeptin-234) into the third ventricle of the brain. The anterior pituitary and blood was used to mRNA and protein expression analysis. We demonstrated that Gnrh up-regulates Nr5a1 mRNA expression in the anterior pituitary and induces NR5A1 depletion in gonadotropes. Gnrh administration increased both Ctnnb1 mRNA expression and protein synthesis, and induced activation of cellular Ctnnb1 via translocation from the gonadotropes cytoplasm to nucleus. After kisspeptin-10 treatment, up-regulation of Nr0b1 mRNA and protein expression in the anterior pituitary was observed. These data indicate that Gnrh-neuron-mediated network activity alters Nr5a1 gene transcription and translation in gonadotrope cells and this effect may result from the changes induced in the Ctnnb1 and Nr0b1 gene/protein expression balance.

Involvement of salsolinol in the suckling-induced oxytocin surge in sheep.

During lactation, the main surge of oxytocin is induced by a suckling stimulus. Previous studies have shown that salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline), a dopamine-derived compound, stimulates both the synthesis and the release of oxytocin in lactating sheep. The objective of the present study was to verify the hypothesis that salsolinol is involved in the mechanism that generates the oxytocin surge that occurs during suckling. Thus, a structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), known to antagonize some of its actions, was infused into the third ventricle of the brain of lactating sheep nursing their offspring. Serial 30-min infusion of 1MeDIQ (4 × 60 µg/60 µL) or vehicle were administered at 30-min interval from 10 AM to 2 PM. The experimental period in every ewe consisted of a nonsuckling period (10 AM-12 PM) and a suckling period (12 PM-2 PM). Blood samples were collected every 10 min, to measure plasma oxytocin concentration by RIA. In control sheep, oxytocin surges of high amplitude were observed during the suckling period. The oxytocin surges induced by suckling were significantly (P < 0.01) diminished in sheep receiving 1MeDIQ infusions as compared to those that received control infusions. However, no significant effect of 1MeDIQ was observed on basal oxytocin release, before suckling. Furthermore, oxytocin release, as measured by the area under the hormone response curve (AUC), was significantly decreased by the administration of 1MeDIQ during the suckling period. This study shows that elimination of the effect of salsolinol within the central nervous system of lactating sheep attenuates the oxytocin surge induced by suckling. Therefore, salsolinol may be an important factor in the oxytocin-stimulating pathway in lactating mammals.

Pituitary galaninergic system activity in female rats: the regulatory role of gonadal steroids.

The well-recognized sensitivity of the galanin gene in the anterior pituitary gland to estrogen suggests that estrogen receptor activity may influence the galaninergic system through modulation of galanin receptor (GALR) gene expression. Here, we evaluated the following: (i) the effects of estrogen on GALR mRNA expression; (ii) the estrogen receptor subtype that is specifically involved in this activity; and (iii) the effects of progesterone in the absence or presence of estrogen on galanin concentration in anterior pituitary gland. In the first experiment, ovariectomized 4-month-old rats were pre-treated subcutaneously with 17ß-estradiol (3 x 20 µg), the ESR1 (ERα) agonist propyl pyrazole triol (PPT) (3 x 5 mg), and the ESR2 (ERß) agonist diarylpropionitrile (DPN) (3 x 0.5 mg). In the second experiment, 4-month-old ovariectomized females received daily subcutaneous injections of 17ß-estradiol (3 x 20 µg), progesterone (2 x 5 mg), or combined estradiol (3 x 20 µg) and progesterone (2 x 5 mg). Anterior pituitaries were excised the day after the final 17ß-estradiol injection (experiment I) and 1 hour after receiving the second progesterone dose. Relative GALR1, GALR2, and GALR3 mRNA expression was evaluated using quantitative real-time PCR, and pituitary galanin concentration was determined using a specific radioimmunoassay. The results revealed that estrogen predominantly induced a 5-fold increase in GALR3 gene transcription. To a lesser extent, 17ß-estradiol also increased GALR1 mRNA expression, but had no effect on GALR2 mRNA levels. The estrogen-induced increase in GALR3 gene expression occurred exclusively through ESR1 activation. The increase in GALR1 gene expression occurred through activation of both estrogen receptor subtypes, but the ESR2 subtype was predominantly involved. Furthermore, the results revealed that progesterone regulates the activity of the pituitary galaninergic system by facilitating estradiol-induced galanin synthesis in the female rat anterior pituitary gland.

Salsolinol Up-Regulates Oxytocin Expression and Release During Lactation in Sheep.

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a dopamine-derived compound present in the central nervous system and pituitary gland. Several previous studies on lactating sheep and rats have reported that salsolinol plays a crucial role in the regulation of prolactin secretion. The present study investigated the effects of salsolinol, which was infused into the third ventricle of the brain, on oxytocin expression and release in lactating sheep, 48 h after weaning of 8-week-old lambs. Serial 30-min infusions of salsolinol and vehicle were performed at 30-min intervals from 10.00 to 15.00 h. Blood samples were collected every 10 min. The supraoptic nucleus (SON), paraventricular nucleus (PVN) and posterior pituitary were collected immediately after the experiment. Expression levels of mRNAs for oxytocin and peptidylglycine α-amidating monooxygenase (PAM), the terminal enzyme in the oxytocin synthesis pathway, were measured using a real-time polymerase chain reaction. Oxytocin peptide content in the posterior pituitary was measured by an enzyme-linked immunosorbent assay, and plasma oxytocin concentration was measured by radioimmunoassay. Salsolinol treatment significantly up-regulated oxytocin and PAM gene expression in the SON (P < 0.01 and P < 0.05, respectively), PVN (P < 0.01 and P < 0.05, respectively) and posterior pituitary (P < 0.05 and P < 0.05, respectively). Oxytocin peptide content in the posterior pituitary and the area under the response curve of plasma oxytocin were significantly (P < 0.05 and P < 0.01, respectively) higher in salsolinol-treated sheep than in control animals. The present study shows for the first time that salsolinol stimulates oxytocin secretion during lactation in sheep.