Actions of gonadotrophins on the uterus.

Binding sites for LH/hCG are found in the uterus of several species, including humans. In cattle and pigs, the LH receptor, its mRNA and LH receptor protein are present in the uterus throughout the oestrous cycle, and maximum expression occurs at the luteal phase. GnRH receptor is also expressed maximally in the human endometrium at the luteal phase. LH activates both the adenylate cyclase and phospholipase C pathways and increases the concentrations of cyclooxygenase and its products. Activation of LH receptors in the endometrium is associated with PGF production. In contrast, bovine uterine vein LH receptor mRNA and LH receptor concentrations are greatest during pro-oestrus-oestrus and LH increases the production of both PGE and PGF. FSH receptor and its mRNA are present in the bovine cervix and the concentrations are greatest at the time of the FSH peak value in the blood, indicating a physiological role for FSH in the relaxation and opening of the cervix. The presence of gonadotrophin and releasing factor receptors with a dynamic pattern in the endometrium, myometrium, oviduct and cervix of different species provides evidence that gonadotrophins and GnRH play a substantial role as molecular autocrine-paracrine regulators of the oestrous cycle and implantation.