Bovine luteal prolactin receptor expression: Potential involvement in regulation of progesterone during the estrous cycle and pregnancy

In the present study, we performed quantitative reverse-transcription PCR (qPCR) to examine changes in gene expression of prolactin receptor (long form: l-PRLR; short form: s-PRLR) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD; EC 1.1.1.149) in the bovine corpus luteum (CL) throughout the estrous cycle and pregnancy. Western blotting was used to determine protein abundance. Bovine CL were collected and luteal stages (n = 6/stage) were classified by macroscopic observation as early (d 1 to 4 after ovulation), mid (d 5 to 10), late (d 11 to 17), and regressing (d 18 to 20). A CL of pregnancy (n = 6) was determined by the presence of conceptus (d 28 to term). The mRNA for both forms of PRLR were expressed at all the luteal stages. Expression of s-PRLR and l-PRLR mRNA was less (P < 0.01) during early and regressing luteal stages compared with mid and late stages. Expression of s-PRLR mRNA in CL of pregnancy was greater (P < 0.01) than early, mid, and regressing CL and did not differ from late luteal stage expression. A greater (P < 0.01) expression of l-PRLR mRNA was observed in pregnant vs. early and regressing CL. In addition, qPCR showed the presence of 20 alpha-HSD mRNA during all luteal stages of the estrous cycle, with the greatest (P < 0.01) expression observed in the regressing luteal stage. Western blotting revealed protein abundance of both PRLR isoforms during all luteal stages and pregnancy, with a predominance of the s-PRLR protein. Densitometry analysis indicated that protein abundances of s-PRLR were greater (P < 0.05) than l-PRLR during early, mid, and late luteal stages and did not differ during the regressing luteal stage. Protein abundances of 20 alpha-HSD were least (P < 0.05) during the early luteal stage. In conclusion, results of the current study suggest a possible involvement of PRLR, especially s-PRLR, in the regulation of progesterone secretion and metabolism during the bovine estrous cycle and pregnancy.