Effect of Prolactin on the Secretion of Hypothalamic GnRH and Pituitary Gonadotropins

Abstract

In order to clarify the mechanism by which excess PRL inhibits gonadotropin release, in vivo and in vitro studies were performed with adult female rats. First, we examined the effect of hyperprolactinemia, produced by implantation of anterior pituitary glands under the kidney capsule, on catecholamine turnover in the medial basal hypothalamus (MBH) and on GnRH concentrations in MBH and hypophyseal portal blood. Rats bearing pituitary transplants exhibited increased turnovers of dopamine (DA) in the MBH, decreased concentrations of GnRH in the MBH and in plasma of hypophyseal portal blood and impaired gonadotropin release from the pituitary gland. Second, we examined the effects of PRL on DA release and of DA on GnRH release from rat hypothalamic cells. We observed that PRL stimulated [³H] DA release, and DA inhibited ionophore-induced GnRH release from dispersed hypothalamic cells. Third, we examined the effect of PRL on estrogen-induced LH release using the in vitro perfusion system. We found that administration of PRL suppressed estrogen-induced LH release by suppressing GnRH release from the hypothalamus. These findings suggest that chronic hyperprolactinemia may increase dopaminergic tone in the MBH that may inhibit GnRH secretion from the MBH and LH release from the pituitary and that these processes may be responsible for disturbances of cyclic hypothalamic pituitary-ovarian activity.

Prolactin regulation of testosterone secretion and testes growth in DLS rams at the onset of seasonal testicular recrudescence

“…Unlike in the rat (Voogt et al 1987, Koike et al 1991, PRL treatment does not appear to suppress hypothalamic GNRH secretion in sheep. Infusion of PRL into the third ventricle of the brain has little or no effect on episodic LH release in either rams (Lincoln & Tortonese 1997, Romanowicz et al 2004 or ewes (Curlewis & McNeilly 1991, Misztal et al 2005.…”

Ectopic macroprolactinoma mimicking a chordoma: a case report.

“…That high prolactin suppresses GnRH even if secreted ectopically and with no direct contact between the hypothalamus and the ectopic prolactinoma, is illustrated in the present case. This has also been found in rat studies where prolactin-secreting cells were transplanted outside the pituitary (Smith & Bartke 1987, Koike et al 1991.…”

Promoter Usage and Estrogen Regulation of Prolactin Receptor Gene in the Brain of the Female Rat

“…In addition, PRL acts at the cellular level to regulate GnRH secretion [8, 9, 10], the firing rate of hypothalamic neurons [11], the metabolism of neurotransmitters and neuropeptides [12], oxytocin release [13], enzyme activities in neurons [14]and glial cellular proliferation [15]. The physiological actions of PRL on the brain are suggested to be mediated by cognate PRL receptors (PRL-R) which belong to the superfamily of cytokine receptors [16].…”