Variations in the number of uterine angiotensin receptors following changes in plasma angiotensin levels.

3H-labelled angiotensin II binding to receptor sites was studied in plasma membranes isolated from myometrial homogenates of uterine horns. Removal of the kidneys, which results in the disappearance of plasma angiotensin II, was followed 19 h after nephrectomy by an increase in the number of uterine receptor sites without significant variation in the apparent dissociation constant. Acute pressor i.v. injection of angiotensin II into nephrectomized rats immediately before removing uteri, did not affect the number of uterine angiotensin receptors, whereas long-lasting angiotensin infusion did reduce the number of receptors. These changes cannot be accounted for by variations in the occupancy of receptor sites. These results demonstrate that the number of angiotensin receptors, at least in uterine contractile cells, is affected by chronic variations of endogenous angiotensin levels. The relation between the specific supersensitivity to angiotensin II observed in uteri from nephrectomized rats and the variations at the receptor level is discussed.