Nongonadal LH/hCG receptors in pig: functional importance and parallels to human.

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) share a common receptor in gonadal cells; however, the presence of these receptors has also been detected in several nongonadal but reproduction-associated tissues of pig, human, and other species. There are no data about the ontogeny of the human LH/hCG receptor. The expression of the porcine LH receptor gene in the uterus starts about 10 days after the appearance of this gene in gonads. LH/hCG receptors were found in uterus (myometrium, endometrium), oviduct, cervix, fetal membranes, and umbilical cord in humans and pigs. The main role of LH/hCG receptors in myometrium is stimulation of growth and hyperplasia and relaxation of uterine motility. hCG also increases blood flow in the uterine artery. LH and hCG can increase production of prostaglandins in endometrium, oviduct, and blood vessels. It is suggested that the preovulatory surge of LH plays an important role in controlling oviductal contractions. Human and pig mammary glands also possess LH/hCG receptors through which gonadotropins can affect the metabolism of steroid hormones in this tissue and may play an inhibitory role in mammary carcinogenesis and in the growth of breast tumors.