Sex steroid modulation of AT2 receptors in human myometrium

In contrast to the abundant expression of the AT2 subtype of angiotensin II (AII) receptors during fetal development, AT2 receptor in adult life is expressed in few tissues. We now report studies on the presence and hormonal regulation of AT2 receptor in human pregnant and nonpregnant myometrium obtained from a large study population (n = 50). AT2 receptor subtypes have been characterized using self- and cross-competition curves among [125I]CGP42112A (a selective AT2 ligand), [125I](Sar1,Ile8)AII (a unselective antagonist), the corresponding unlabeled ligands, and several peptidic and nonpeptidic analogs with different affinities for the AT1 and AT2 receptor subtypes. We found that the human nonpregnant uterus expresses almost exclusively the AT2 subtype, and that [125I]CGP42112A is a selective probe to study human AT2 receptor. By using [125I]CGP42112A, we demonstrated that the density of AT2 receptor in human myometrium is dramatically affected by the hormonal milieu. Indeed, in the estrogen-dominant uterus of normal cycling women in the proliferative phase and that of perimenopausal women with anovulatory cycles, the density of binding sites was very high [1565 +/- 246 fmol/mg protein (n = 11) and 2176 +/- 429 (n = 7), respectively]. The concomitant presence of progestogens blunted the estrogen effect [term pregnancy, 61 +/- 12 fmol/mg protein (n = 5); secretive phase of the cycle, 453 +/- 154 (n = 10); combined oral contraceptive, 243 +/- 74 fmol/mg protein (n = 6)]. Very low concentrations of binding sites are also present in the sex steroid-deprived uterus of postmenopausal women (100 +/- 12 fmol/mg protein; n = 8) and the uterus of fertile women chronically treated with GnRH agonists (199 +/- 100 fmol/mg protein; n = 3). Hence, these data confirm the presence of AT2 receptors in human uterus and indicate their regulation by sex steroids.