Effects of Prolactin-Releasing Peptide on Tuberoinfundibular Dopaminergic Neuronal Activity and Prolactin Secretion in Estrogen-Treated Female Rats

Abstract

Both systemic and central effects of a newly discovered prolactin (PRL)-releasing factor (PRF), prolactin-releasing peptide (PrRP), were determined in this study. Systemic injection of PrRP (1 and 10 µg/rat, i.v.) stimulated PRL secretion in ovariectomized, estrogen-treated rats similar to the effect of another PRF, thyrotropin-releasing hormone (TRH). Pretreatment with a dopamine D₂ receptor antagonist, sulpiride (1 µg/rat, i.v.), potentiated the stimulatory effect of both PrRP and TRH on PRL secretion. Using the double-labeling immunohistochemical method, PrRP-immunoreactive terminals were found in close contact with tyrosine-hydroxylase-immunoreactive neurons in the hypothalamic arcuate nucleus. Central administration of PrRP (0.1–1,000 ng/rat, i.c.v.) stimulated tuberoinfundibular but not nigrostriatal dopaminergic neuronal activity in 15 min. Levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in the median eminence and striatum were used as indices for tuberoinfundibular dopaminergic (TIDA) and nigrostriatal dopaminergic neuronal activities, respectively. The serum PRL level, however, was not significantly changed. Similar treatment with TRH (10 ng/rat, i.c.v.) stimulated and inhibited TIDA neuronal activity and serum PRL, respectively, at 30 min. In summary, PrRP may play a role in both the central and peripheral control of PRL secretion.

Effect of intracerebroventricular injections of prolactin‐releasing peptide on prolactin release and stress‐related responses in steers

“…ICV PrRP did not increase peripheral PRL concentrations in rats (Samson et al 2003) or sheep (Curlewis et al 2002). In rats, the PrRP receptor is expressed abundantly in the anterior pituitary (Roland et al 1999), and the effect of PrRP on stimulation of PRL release was reported both in vitro and in vivo (Hinuma et al 1998;Matsumoto et al 1999;Yuan et al 2002). PrRP was previously shown to stimulate PRL secretion from anterior pituitary cell cultures of rats (Hinuma et al 1998) and sheep, although the response was very weak in sheep (Curlewis et al 2002).…”

“…PrRP was previously shown to stimulate PRL secretion from anterior pituitary cell cultures of rats (Hinuma et al 1998) and sheep, although the response was very weak in sheep (Curlewis et al 2002). Intravenously administered PrRP was also shown to increase plasma PRL concentration in rats (Matsumoto et al 1999;Yuan et al 2002) but not in sheep (Curlewis et al 2002). These evidences suggest that PrRP might regulate PRL release from the anterior pituitary in rats which is still debatable, and that PrRP is unlikely to be an important regulator of PRL release in sheep.…”

“…Intravenously administered PrRP was also shown to increase plasma PRL concentration in rats (Matsumoto et al . 1999; Yuan et al . 2002) but not in sheep (Curlewis et al .…”

“…2005). In rats, PrRP immunoreactive terminals exhibited close apposition with tyrosine hydroxylase immunoreactive neurons in the arcuate nucleus and centrally administered PrRP stimulated tuberoinfundibular dopaminergic neurons while serum PRL levels remained unchanged (Yuan et al . 2002), which suggests the indirect regulation of PRL release from the anterior pituitary.…”

Biomedical Vignette

“…Although many candidates have been proposed, none fulfils all the required criteria. Yuan et al [21] reported that a newly discovered candidate, prolactin-releasing peptide (PrRP), stimulates prolactin secretion in ovariectomized, estrogen-treated rats. The blockade of dopamine D 2 receptors potentiates this stimulatory action.…”