The mRNA expression of insulin receptor isoforms (IR-A and IR-B) and IGFR-2 in the bovine corpus luteum during the estrous cycle, pregnancy, and induced luteolysis.

Isoform A of the human insulin receptor and the IGF-receptor type 2 (IGFR-2) are both receptors for insulin- like growth factor II (IGF II), which plays a major role in luteal development and function in bovine species. The objective of this study was to determine if both insulin receptor isoforms and IGFR-2 were expressed in the bovine corpus luteum (CL) and if they were regulated during the estrous cycle, pregnancy, and induced luteolysis. CL were collected at the slaughterhouse. For induced luteolysis, CL were obtained by transvaginal ovariectomy at 2, 4, 12, 48, and 64 h after prostaglandin (PG) F2alpha-injection. Real-time RT-PCR was applied to investigate mRNA expression. Two alternatively spliced transcripts encoding the insulin receptor were detected in bovine CL. These two isoforms corresponded to the known isoforms A (IR-A) and B (IR-B) in humans. IR-A mRNA predominated in bovine CL and was significantly down-regulated on d 5-7. IR-B mRNA was significantly up-regulated in the late luteal stage and during early pregnancy. IR-A showed a significant down-regulation at 48 h after PGF2. IGFR-2 mRNA was significantly up-regulated in mid and late luteal stages (d 8-18). It is proposed that the differential mRNA expression of IR-A and IGFR-2, both binding IGF II, may play a role in the development and function of the bovine corpus luteum.