Effects of ovarian hormones on GPR120 mRNA expression in mouse pituitary gonadotrophs

GPR120 is a G-protein-coupled receptor that is activated by long-chain fatty acids. In our previous study, GPR120 expression was detected in gonadotrophs of the mouse anterior pituitary gland. It is well known that the function of anterior pituitary cells is largely under the influence of circulating sex steroids. Thus, in the present study, we investigated the modulatory roles of the ovarian hormones, estrogen (E2) and progesterone (P), on the expression levels of GPR120 mRNA in mouse pituitary glands. GPR120 mRNA expression levels in the pituitary gland were increased after ovariectomy or P treatment, and were decreased after the administration of E2. Simultaneous injection of E2 and P interfered with the action of E2 on GPR120 mRNA expression. The GnRH antagonist, Cetrotide, did not inhibit the increase in GPR120 expression in ovariectomized (OVX) animals. In addition, immunohistochemistry revealed that more than 95.4% of GPR120 immunoreactive cells colocalized with the luteinizing hormone β (LHβ) in the anterior pituitary gland of intact, ovariectomized (OVX), estradiol-primed OVX (OVX+E2), or progesterone-primed OVX (OVX+P) animals. Furthermore, GPR120 mRNA expression levels were not significantly different in the pituitary gland of females throughout the ovarian cycle. It is suggested that low levels of P may mask the inhibitory effect of estradiol on the synthesis of GPR120 in the estrous stage in intact animals. These results demonstrate that ovarian hormones may directly regulate GPR120 expression in the reproductive cycle at the pituitary level.