Angiotensin II vascular receptors in fetal and neonatal rats

Specific binding sites for angiotensin II in aorta and renal arteries have been studied in rat fetuses (18th day of pregnancy) and 1‐day‐old newborn rats by binding studies in arterial membranes using [¹²⁵I] ileu‐5‐angiotensin II. One type of angiotensin receptor was found both in fetuses and in the newborns; the capacity of this (RT) decreased immediately after birth (from 0·06 ± 0·01 nM to 0·02 ± 0·005 nM; ± SEM) and the affinity (Kd) increased at birth (from 3·5 ± 0·6 nM to 19·5 ± 1·2 nM; ± SEM). Localization of the specific binding sites was studied by autoradiography on arteries from fetal and newborn rats either perfused with iodinated angiotensin II by cannulation of the aorta or in vitro on cryostat sections incubated with the radioactive angiotensin II. Both in fetuses and in the newborn the binding sites were located in the tunica media of the arteries.