LOCALIZATION AND QUANTITATION OF ANGIOTENSIN AT(1) AND AT(2) RECEPTORS IN THE PREGNANT AND NONPREGNANT SHEEP UTERUS

The two angiotensin II receptor subtypes, AT(1) and AT(2), have been r eported to be differentially expressed in the myometrial membrane prep arations of nulliparous and pregnant sheep, however, their distributio n in the sheep reproductive tract has not been reported, The aim of th is study is to map the distribution of AT(1) and AT(2) receptors in th e anoestrus reproductive tract of the sheep by quantitative in vitro a utoradiography and to investigate if the density and distribution of t he receptors change during pregnancy. The AT(2) receptor is abundant i n a discrete layer in the myometrium of the anoestrus sheep uterus, wh ilst the AT(1) receptor is expressed at lower levels, predominantly in the endometrium. Near-term pregnant uteri, show a marked change in th e expression of angiotensin II receptors: the myometrium no longer exp resses detectable AT(2) receptors but rather, expresses low levels of AT(1) receptors. Angiotensin converting enzyme is found in high concen trations in the blood vessels of the pregnant and non-pregnant sheep r eproductive system and on the epithelial cells of the fallopian tubes of the non-pregnant sheep. These studies reveal marked reciprocal chan ges of angiotensin II receptors, with myometrial AT(1) receptors incre asing during pregnancy, whilst AT(2) receptors fall markedly. These ch anges suggest that angiotensin II may be involved in regulating change s of uterine structure and function during pregnancy by interaction wi th multiple receptor subtypes.