Bovine Posterior Pituitary Extract Stimulates Prolactin Release from the Anterior Pituitary Gland In Vitro and In Vivo in Cattle

Abstract

It has been reported that the posterior pituitary (PP) gland contains a potent, unknown prolactin (PRL)-releasing factor (PRF) in rats. PRFs are assumed to be produced in neurones located within the hypothalamus, and to be peptidergic in nature. However, little is known about PRFs in domestic animals. To characterize the PRF in the PP of domestic animals, the present study examined the PRL-releasing activity of an acidic extract from bovine PP (bPP) in vitro and in vivo in cattle. First, the PRL-releasing effect of bPP extract was compared with that of PRL-releasing peptide (PrRP), and thyrotropin-releasing hormone (TRH) from cultured bovine anterior pituitary cells. The extract significantly increased PRL concentrations in the culture medium, at doses of 0.002 and 0.02 eq./ml (one eq. is the PP extract from one animal), compared with the control (p < 0.05). PrRP failed to stimulate the release of PRL. TRH significantly increased PRL concentrations in the culture medium, at doses from 10(-9) to 10(-7) M, compared with the control (p < 0.05). The rate of increase in the PRL concentration, by 0.02 eq./ml bPP extract, was significantly greater than that in TRH (p < 0.05). Secondly, plasma PRL responses to the intravenous (i.v.) injection of bPP extract (0.5 eq./head), PrRP [3.59 mug/kg body weight (BW)], TRH (1 mug/kg BW), and a dopamine receptor antagonist (sulpiride, 0.1 mg/kg BW), were examined in calves. PrRP failed to stimulate PRL release; however, plasma PRL increased immediately following the injection of bPP extract, TRH and sulpiride. The PRL-releasing effect of i.v. injections of TRH and sulpiride was more potent than that of bPP extract. Finally, plasma PRL responses to the intra-hypothalamic injection of bPP extract were examined in calves. The intra-hypothalamic infusion (arcuate nucleus) of 0.0625 eq./head of bPP extract strongly stimulated PRL release in calves (p < 0.05). The present results show that PP contains a physiologically potent PRF in cattle.

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

“…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. In cattle, PrRP failed to stimulate PRL release from anterior pituitary cell cultures, and intravenously administered PrRP failed to increase plasma PRL concentrations (Hashizume et al . 2005).…”

“…(2002) suggested that PrRP is unlikely to be an important prolactin‐releasing factor in this species. In cattle, intravenously administered PrRP did not induce plasma PRL release (Hashizume et al . 2005).…”

Effects of the dopamine agonist cabergoline on the pulsatile and TRH-induced secretion of prolactin, LH, and testosterone in male beagle dogs

“…TRH-induced hyperprolactinemia has been shown to last for at least 90 min with slightly decreasing tendency in castrated calves [19], but may have been shorter in the intact dogs, as after 120 min serum prolactin concentrations had almost decreased to basal levels. Whether or not this short prolactin rise is causally related to the slight but not significant decrease of the mean LH concentration 20 min after TRH is questionable and cannot be concluded from the present data.…”

“…In addition, several other prolactin-stimulating factors have been reported, such as serotonin [13] and thyrotrophin-releasing hormone (TRH) [14][15][16][17][18]. In a recent study the strong prolactin stimulating effect of TRH was also demonstrated in cattle in vitro and in vivo when compared with the prolactin release induced by a bovine posterior pituitary extract and prolactin releasing peptide [19]. Nevertheless, the exact role of TRH in the physiological regulation of prolactin secretion and the effect of the dopaminergic tone on TRH-induced prolactin secretion are not completely understood [7].…”

Functions of Two Distinct “Prolactin-Releasing Peptides” Evolved from a Common Ancestral Gene

“…In vivo , intravenous (IV) injection of PrRP-31 induces PRL release dependent on the estrus cycle and estrogen in rats (67, 68). On the other hand, IV injection of PrRP has no effect on PRL secretion in cattle (69), while intracerebroventricular (ICV) injection of PrRP temporarily increases PRL secretion (60). In addition to this, neither IV nor ICV injections induce PRL secretion in female sheep (43), suggesting that PrRP is not important in stimulating PRL secretion in ruminants.…”