Angiotensin II in rat brain comigrates with authentic angiotensin II in high pressure liquid chromatography

Indirect evidence has implicated a role for central angiotensin II in blood pressure control. To answer directly the question of whether angiotensin II exists in the brain, independent of blood-borne angiotensin, and to quantify the amounts in different parts of the central nervous system, a sensitive radioimmunoassay was used to measure extracts of male adult rat brain hypothalamus and cortex after purification with high pressure liquid chromatography with a high recovery. The fractions coeluted with authentic angiotensin. Rats were nephrectomized bilaterally, and 24 hours later the brains were extracted in acetic acid and boiled. SepPak C-18 purification preceded reverse phase high pressure liquid chromatography. High pressure liquid chromatography revealed two peaks, one which comigrated precisely with [Ile5] angiotensin II, and another smaller peak which overlapped with [Ile5] angiotensin III. The highest levels were found in the hypothalamus (125 pg/g tissue), pituitary (190 pg/g tissue), spinal cord (199 pg/g tissue), and lower levels were found in cortex (60 pg/g tissue). The results demonstrate that the antibody which was previously used in the immunocytochemical localization of angiotensin in the hypothalamus detects authentic angiotensins. However, the study did not depend on just one antibody. A second antibody which we developed gave the same results. Molecular sieving using Sephadex G-25 with acetic acid revealed a distinct peak in the 1000 MW range and a smaller, higher molecular weight peak which needs further investigation. Spontaneously hypertensive rats did not have higher concentrations of hypothalamic angiotensin II than normotensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)