Functional importance of bovine myometrial and vascular LH receptors and cervical FSH receptors

Bovine myometrium and cervix contain luteinizing hormone/human chorionic go nadotropin (LH/hCG) binding sites, LH receptor (LH-R) messenger RNA (mRNA), and LH-R protein. Expression of LH-R is dependent on the stage of the cycl e. LH-R expression is high during the luteal phase but weak during the foll icular phase. In both myometrium and cervix, LH activates both the adenylat e cyclase and phospholipase C pathways, and the effect of LH on both pathwa ys at each stage of the cycle is correlated with the amount of LH-R present in the tissue. Because activation of cyclic AMP (cAMP) is associated with myometrial quiescence, we suggest that LH activation of uterine cAMP could serve to keep the uterus quiescent during the luteal phase. On the other ha nd, in the uterine vein LH-R mRNA and LH-R are maximal during preestrus/est rus as opposed to the luteal phase. In the uterine vein, LH increases the e xpression of cyclooxygenase and production of both prostaglandin E-2 (PGE(2 )) and PCF2 alpha. Because PGF(2 alpha) is the physiological luteolytic sig nal in the cow, we suggest that this increase in prostaglandin production b y the uterine vein is part of the physiological events leading to luteolysi s. In addition to uterine LH-R, the bovine cervix at preestrus/estrus has h igh levels of follicle-stimulating hormone receptor (FSH-R) and its corresp onding mRNA. As with LH-R, activation of FSH-R by FSH is associated with ac tivation of a G protein-coupled receptor family that mediates the cAMP and inositol phosphate signaling pathways. Activation of these signaling pathwa ys is associated with an increase in the expression of cyclooxygenase and p roduction of PGE(2). Because expression of the FSH receptor was maximal at the time of the FSH peak in the blood, we suggest a physiological role for FSH in the cervix relaxation and opening at estrus.