Messenger ribonucleic acid expression for growth hormone receptor, luteinizing hormone receptor, and steroidogenic enzymes during the estrous cycle and pregnancy in porcine and bovine corpora lutea.

Growth hormone (GH) and luteinizing hormone (LH) are pituitary hormones involved in steroidogenesis in the corpus luteum (CL). The objectives of Experiment I were to determine mRNA expression for GH receptor (GHR) and LH receptor (LHR) in porcine luteal tissues during the estrous cycle and pregnancy and to relate changes in these receptor mRNA with changes in steroidogenic enzyme mRNA for cytochrome P450 side-chain cleavage enzyme (P450sec) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). Ovaries were collected from gilts during the estrous cycle (day 10 [n = 3] and Day 19 [n = 3, regressed CL) and pregnancy (Day 25 [n = 3] and Day 44 [n = 3]). Tissues were frozen in liquid nitrogen and sectioned. Messenger RNA was detected by in situ hybridization, and relative mRNA amounts were determined by image analysis. The mRNA for GHR, LHR, P450sec, and 3 beta-HSD were detected in the CL on Day 10 of the estrous cycle. None of these mRNA were specific to cither large luteal cells (LLC) or small luteal cells (SLC). On Day 19 of the estrous cycle (regressed CL), mRNA for GHR, P450sec, and 3 beta-HSD were decreased (P < 0.01) whereas LHR mRNA disappeared (P < 0.01). During pregnancy, mRNA expression increased 2.1-, 1.4-, 1.4-, and 1.2-fold for GHR, LHR, P450sec, and 3 beta-HSD, respectively (P < 0.05). The luteal location of GHR mRNA in the pig did not agree with that found in our previous studies of GHR mRNA or protein in cattle. Therefore, the objective of Experiment 2 was to measure GHR mRNA by the use of in situ hybridization in bovine CL during the estrous cycle (Day 14; n = 2) and pregnancy (Day 25; n = 2). In situ hybridization demonstrated specific expression of GHR mRNA in the LLC of cattle. Furthermore, GHR mRNA increased 1.8-fold in CL on Day 25 of pregnancy compared with GHR mRNA on Day 14 of the estrous cycle (P < 0.01). In adjacent sections, the LHR mRNA was most highly expressed in clusters of SLC with 1.6-fold more mRNA on Day 25 of pregnancy compared with Day 14 of the estrous cycle (P < 0.01). These results suggest that: 1) mRNA for LHR, GHR, P450sec, and 3 beta-HSD are differentially regulated during the estrous cycle and pregnancy and 2) the cellular location of GHR differs for pigs and cattle, with highly specific expression of GHR in bovine LLC but not porcine LLC. This may suggest different functions for GH in the CL of these species.