Localization and quantitation of angiotensin AT1 and AT2 receptors in the pregnant and non-pregnant sheep uterus.

The two angiotensin II receptor subtypes, AT1 and AT2, have been reported to be differentially expressed in the myometrial membrane preparations of nulliparous and pregnant sheep, however, their distribution in the sheep reproductive tract has not been reported. The aim of this study is to map the distribution of AT1 and AT2 receptors in the anoestrus reproductive tract of the sheep by quantitative in vitro autoradiography and to investigate if the density and distribution of the receptors change during pregnancy. The AT2 receptor is abundant in a discrete layer in the myometrium of the anoestrus sheep uterus, whilst the AT1 receptor is expressed at lower levels, predominantly in the endometrium. Near-term pregnant uteri, show a marked change in the expression of angiotensin II receptors: the myometrium no longer expresses detectable AT2 receptors but rather, expresses low levels of AT1 receptors. Angiotensin converting enzyme is found in high concentrations in the blood vessels of the pregnant and non-pregnant sheep reproductive system and on the epithelial cells of the fallopian tubes of the non-pregnant sheep. These studies reveal marked reciprocal changes of angiotensin II receptors, with myometrial AT1 receptors increasing during pregnancy, whilst AT2 receptors fall markedly. These changes suggest that angiotensin II may be involved in regulating changes of uterine structure and function during pregnancy by interaction with multiple receptor subtypes.