Effects of intracerebroventricular infusion of genistein on the secretory activity of the GnRH/LH axis in ovariectomized ewes.

Phytoestrogens, plant derived estrogen like-compounds exert numerous effects on the reproductive functions of animals. The present study was designed to demonstrate if exogenous genistein infused during the breeding season into the third ventricle of the brain of ovariectomized ewes could affect the secretory activity of the GnRH/LH axis. Two-year-old ovariectomized ewes (n=8) were infused with vehicle (control, n=3) or genistein (10 microg/100 microl/h, n=5) into the third ventricle.

Genistein, a phytoestrogen, effectively modulates luteinizing hormone and prolactin secretion in ovariectomized ewes during seasonal anestrus.

Through binding with estrogen receptors, phytoestrogens, plant-derived estrogen-like compounds, affect numerous reproductive functions. It is not known whether these compounds are capable of evoking effective changes in luteinizing hormone (LH) and prolactin (PRL) secretion in ewes by acting directly within the central nervous system (CNS). The hypothesis studied was that genistein, infused for several hours into the third ventricle, could immediately affect LH and PRL secretion in ovariectomized (OVX) ewes during seasonal anestrus.

The effects of intracerebroventricular infusion of prolactin in luteinizing hormone, testosterone and growth hormone secretion in male sheep.

This study tested a hypothesis that the enhancement of the prolactin (PRL) concentration within the central nervous system (CNS) disturbs pulsatile luteinizing hormone (LH) and growth hormone (GH) secretion in rams that are in the natural breeding season. A 3h long intracerebroventricular (icv.) infusion of ovine PRL (50 microg/100 microl/h) was made in six rams during the daily period characterized by low PRL secretion in this species (from 12:00 to 15:00 h); the other six animals received control infusions during the same time.

Effects of melatonin on luteinizing hormone secretion in anestrous ewes following dopamine and opiate receptor blockade.

In the present investigation we have examined the ability of melatonin to modify the pulsatile LH secretion induced by treatment with a DA antagonist (sulpiride, SULP) or opioid antagonist (naloxone, NAL) in intact mid-anestrous ewes. The experimental design comprised the following treatments-in experiment 1: (1) intracerebroventricular (i.c.

Melatonin--a modulator of the GnRH/LH axis in sheep.

The nocturnal secretion of pineal melatonin provides information to vertebrates on changes in day length under the circumstances in which they live. In sheep, which are seasonal breeders, the secretion of melatonin is also a signal to the neural structures controlling the secretion of gonadotropins from the pituitary gland to drive their activity in accordance with the season of the year. The sites and mechanisms of melatonin action on GnRH/LH secretion has been the subject of intensive studies in the last decade.

Effect of prolactin infused into the third ventricle on LH secretion in follicular-phase and ovariectomized ewes.

This study tested a hypothesis that an acute enhancement of prolactin concentration within the central nervous system (CNS) would affect the LH secretion in ewes, depending on the level of endogenous estrogens in the organism. A 3-h long intracerebroventricular (icv.) infusion of ovine prolactin was made in late follicular-phase ewes, experiment 1, and in ovariectomized (OVX) ewes (experiment 2).

Effect of melatonin on daily LH secretion in intact and ovariectomized ewes during the breeding season.

This study was conducted to find out whether daily LH secretion in ewes may be modulated by melatonin during the breeding season, when the secretion of both hormones is raised. Patterns of plasma LH were determined in luteal-phase ewes infused intracerebroventricularly (icv.) with Ringer-Locke solution (control) and with melatonin (100 microg/100 microl/h).