Dominance of type 1 angiotensin II receptor in the nonpregnant and pregnant bovine uterus

The present study was undertaken to characterize, determine and localize an giotensin II receptors in the nonpregnant and pregnant bovine uterus. Ln ad dition, the concentration of active renin, which is responsible for the gen eration of angiotensin, was determined. Autoradiography and angiotensin II receptor binding studies showed that all compartments of the bovine uterus contained high concentrations of angiotensin II receptors. Ln general, the type 1 angiotensin II receptor (AT(1)) predominated over the AT(2) receptor . In the endometrium, the highest density was found in the caruncles and th e AT(1) receptor was always predominant. The density of angiotensin II rece ptors in the endometrium increased at the beginning of pregnancy, but decre ased and reached values similar to those in nonpregnant animals near term. In the myometrium, the density of angiotensin II receptors was highest at o r near the endometrial-myometrial junction. In this area, the predominant t ype of angiotensin II receptor in the uterus of cyclic cows varied, whereas the AT(1) receptor always predominated during pregnancy. Non-AT(1) and non -AT(2) binding sites were found in the same locations as the angiotensin II receptors, but at lower densities. With the exception of the pregnant endo metrium, all compartments contained higher active renin concentrations than found in plasma, indicating local synthesis of renin. This study demonstra tes a difference in the expression of types of angiotensin II receptor in t he bovine uterus compared with other species. The high densities of angiote nsin II receptors localized in several important areas imply that the renin -angiotensin system participates in regulation of growth and tissue functio n in the bovine uterus.