Effect of Age on Specific Angiotensin II-Binding Sites in Rat Brain

Abstract

Specific angiotensin II-binding sites were studied in isolated rat brain membranes. In 6- to 8-week-old rats, the highest [l25I]angiotensin II binding was found in thalamus, midbrain, and hypothalamus. Scatchard plots indicated a single class of binding site in each region, and regional differences were due to differences in the number of binding sites rather than to variations in affinity. Angiotensin II binding to brain membranes was studied in rats of different ages between birth and 6 weeks. Significant changes in the number of brain angiotensin II-binding sites occurred during this time, reaching maximum levels of up to 10 times the adult levels at 1–2 weeks of age. Levels of binding sites in midbrain and thalamus-hypothalamus peaked at 2 weeks, while those in the brain stem, cerebrum, and cerebellum were highest at 1 week. [¹²⁵I]angiotensin II binding to brain membranes was measured after peripheral infusion of rats with [Sar¹, Ala⁸]angiotensin II (saralasin; 15 μg/kg-min for 30 min). While there was no difference in binding between saralasin-infused and control rats at 6–8 weeks of age, there was a significant decrease in binding after saralasin infusion in 2-week-old rats. It is postulated that circulating angiotensin II may be able to reach brain angiotensin II receptors in newborn rats, and that the high levels of specific binding sites in these rats may indicate a physiological role for angiotensin in the brain during the first few weeks after birth. (Endocrinology106: 995, 1980)