Bovine corpus luteum is an extrapituitary site of prolactin production

Abstract

Prolactin (PRL) is known to be synthesized not only in the anterior pituitary, but also in other organs including the ovary. Among its various functions, PRL is regarded as the most important constituent of the luteotropic complex in rodents and pigs. The purpose of the present study was to determine whether PRL is produced locally in bovine corpus luteum (CL) and to determine its possible roles in CL. In the present study, we examined changes during the luteal phase in (1) the expressions of PRL and PRL receptors (long form: l-PRLR, short form: s-PRLR) in CL and (2) the localization of PRL in CL. We also measured the levels of PRL mRNA in cultured luteal cells and luteal endothelial cells. Furthermore, the effect of PRL on progesterone (P4) and prostaglandin (PG) F2alpha production by cultured bovine luteal cells was examined. Semiquantitative RT-PCR analysis revealed that the mRNAs for PRL and its two receptors, l- and s-PRLR, were expressed in all luteal stages examined. PRL mRNA expression was less in the regressed stage (days 19-21 after ovulation) than in the other stages. Both l-PRLR and s-PRLR mRNA expressions were higher in the late luteal stage (days 15-17) than in the other stages, while the ratio of l-PRLR to s-PRLR was less in the regressed stage than in the other stages. PRL mRNA was also detected in cultured luteal cells and luteal endothelial cells. PRL protein was immunohistochemically detected only in CL of the mid- and regressed stages. It was detected in smooth muscle cells of the intraluteal arterioles and endothelial cells but not in luteal cells and other cell types of CL. Exposure of cultured luteal cells obtained from mid-stage CL (days 8-12) to bovine PRL (100, 200 ng/ml) for 24 hr did not affect P4 and PGF2alpha production by the cells. The present study demonstrates for the first time the expressions of PRL and PRLR mRNA in bovine CL throughout the luteal phase. The overall results strongly suggest that the bovine CL is an extrapituitary site of PRL production.

Ovarian and PGF2α responses to stimulation of endogenous PRL pulses during the estrous cycle in mares

“…In cows, a luteal role for PRL has not been demonstrated, despite the presence of PRL receptors and the expression of PRL mRNA in the CL [7]. In mares, specific PRL binding sites are uniformly distributed in the mature CL [8], but a luteal role of PRL has not been demonstrated in vitro or in vivo.…”

Dinâmica hormonal durante o processo luteolítico nas espécies equina e bovina; com ênfase sobre o papel da prolactina

“…No tecido luteal in vitro, a PRL é clivada por catepsina D gerando fragmentos antiangiogênicos, os quais podem mediar a regressão luteal. Os receptores para PRL estão presentes tanto na musculatura lisa de artérias luteais quanto em células endoteliais (SHIBAYA et al, 2006). Em éguas, não há indicação de um envolvimento da PRL sobre a função luteal (BECKER; JOHNSON,1990).…”

“…Além disso, em bovinos foi identificada a expressão de PRL e mRNA de receptores de PRL (SHIBAYA et al, 2006), sugerindo uma possível regulação tanto local quanto sistêmica do CL pela PRL (THOMPSON et al, 2011).…”

“…Prolactin perfusion of bovine ovaries increases the secretion of P4 in vitro , but no effect on P4 was observed in vivo (SMITH; MCSHAN;CASIDA, 1957;HOFFMAN et al, 1974;. The bovine CL has binding sites for PRL (POINDEXTER et al, 1979) and expression of PRL and PRL-receptor mRNA (SHIBAYA et al, 2006), suggesting that PRL may be involved in systemic and local regulation of the CL (THOMPSON et al, 2011). Moreover, PRL protein acts as a vasoactive factor (ERDMAN et al, 2007), and PRL proteins are present in the smooth muscle of intraluteal arterioles and endothelial cells (SHIBAYA et al, 2006), suggesting that PRL may mediate development and regression of luteal vessels.…”

“…Prolactin is a constituent of the luteotropic complex in rodents and carnivores , may be part of the luteotropic complex in swine , and may (KANN; DENAMUR, 1974) or may not ) have a luteal role in sheep. In cattle, binding sites for PRL (POINDEXTER et al, 1979) and messenger RNA for PRL ligand and for PRL receptors (SHIBAYA et al, 2008) have been demonstrated in the CL. Protein for PRL is immunohistochemically detectable in the endothelial cells and smooth muscle cells of the intraluteal arterioles (SHIBAYA et al, 2008).…”