Regional distribution of angiotensinogen in rat brain

The regional distribution of angiotensinogen, the prohormone of angiotensin I, was examined in rat brain. Quantification of brain angiotensinogen concentration was difficult because of the presence of an endogenous angiotensin I degrading (i.e. angiotensinase) activity which was active at the pH of the renin-angiotensinogen incubation. This degrading activity was unequally distributed throughout the brain, and its presence in homogenates invalidated measured levels of angiotensinogen. Only following removal of the angiotensinase activity by ammonium sulfate precipitation of the prohormone could the distribution of the prohormone be determined. Angiotensinogen was widely distributed throughout 31 brain regions; however there was an approximate 12-fold variation in concentration. Highest levels of the prohormone were found in the dorsal and ventral periventricular hypothalamus, area postrema, organum vasculosum lamina terminalis, periventricular thalamus, dorsal raphe and lateral reticular formation. Significantly lower amounts were found in the parietal cortex, cerebellum, septum and pituitaries. While the majority of regions examined exhibited similar concentrations of angiotensinogen, the demonstration of regions containing either significnatly low or high amounts of prohormone is consistent with a topographical distribution of angiotensinogen in rat brain.