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 by an increase in the number of uterine receptor sites without significant variation in the apparent dissociation constant, which became significant 15 h after nephrectomy. Acute pressor intravenous 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 results provided an explanation for the specific supersensitivity to angiotensin II, observed in uteri excised from nephrectomized rats, which cannot be accounted for by variations in the occupancy of receptor sites. These results also demonstrate that the number of angiotensin receptors, at least in uterine contractile cells, is affected by chronic variations of endogenous angiotensin levels.