GPR30 mediates estrone, estriol, and estradiol to suppress gonadotropin-releasing hormone-induced luteinizing hormone secretion in the anterior pituitary of heifers.

Recent studies demonstrated that G-protein-coupled receptor 30 (GPR30) on the plasma membrane of gonadotroph cells mediates picomolar, but not nanomolar, levels of estradiol (E2) to rapidly suppress gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) secretion in the anterior pituitary (AP). While estrone (E1) and estriol (E3) are considered "weak" estrogens that exert suppressive effects through estrogen receptors α and ß, it is conceivable that they also strongly suppress GnRH-induced LH secretion via GPR30. Both E1 and E3 are likely present within the blood at picomolar or nanomolar concentrations, indicating that such concentrations are sufficient to suppress GnRH-induced LH secretion. To evaluate this possibility, bovine AP cells were cultured under steroid-free conditions and then incubated with various concentrations (0.01 pM to 10 nM) of E2, E1, or E3, prior to stimulation with GnRH. Notably, GnRH-induced LH secretion from AP cells was inhibited by 1-100 pM E2, 1-10 pM E1, and 1-100 pM E3. GnRH-induced LH secretion from AP cells was not inhibited by lower (0.01-0.1 pM) or higher (1-10 nM) concentrations of E2, E1, and E3. These suppressive effects were inhibited by pre-treatment of AP cells with the GPR30 antagonist G36, but not with the estrogen receptor alpha antagonist. Treatment with E1 or E3 also yielded decreased cytoplasmic cAMP levels in cultured AP cells pre-treated with dopamine and phosphodiesterase inhibitors. Therefore, these results suggest that GPR30 mediates the suppressive effects of E1, E3, and E2 on GnRH-induced LH secretion from bovine AP.

Sexual polymorphisms of vomeronasal 1 receptor family gene expression in bulls, steers, and estrous and early luteal-phase heifers.

Vomeronasal 1 receptors (V1R) are a family of receptors for intraspecies chemosignals, including pheromones, and are expressed in the olfactory epithelium (OE) and vomeronasal organ (VO). Even in the well-studied rodents, it is unclear which members of the V1R family cause sexual polymorphisms, as there are numerous genes and it is difficult to quantify their expressions individually. Bovine species carry only 34 V1R homologs, and the OE and VOs are large enough to sample. Here, V1R expression was quantified in the OE and VOs of individual bovines. Based on the 34 gene sequences, we obtained a molecular dendrogram consisting of four clusters and six independent branches. Semi-quantitative RT-PCR was used to obtain gene expression profiles in the VOs and OE of 5 Japanese Black bulls, 5 steers, 7 estrous heifers and 6 early luteal-phase heifers. Ten genes showed significant between-group differences, and 22 showed high expression in VOs than in OE. The bulls showed higher expression of one gene more in OE and another in VOs (both P<0.05) than did steers; both genes belonged to the first cluster. No genes were expressed more abundantly in steers than in bulls. The estrous heifers showed higher expression of a gene of the second cluster in OE, and a gene of the third cluster in VOs (both P<0.05) than did early luteal-phase heifers. These results suggest V1R expression exhibits sexual polymorphisms in cattle.