[Evidence for the existence of inactive brain renin in the rat. Part I. Activating mechanisms and regional distribution of inactive renin in the brain of normotensive rats]

Active and inactive renin-like enzymes in the brain of spontaneously hypertensive rat

Renin-like enzyme(s) in the brain of spontaneously hypertensive rat (SHR) were activated unequivocally by trypsin. The highest concentration of the active renin-like enzyme was localized in the hypothalamus (1.03 +/- 0.25 ng angiotensin I/mg of protein per h, mean +/- S.D.), followed by the striatum (0.51 +/- 0.21), thalamus (0.40 +/- 0.08), midbrain (0.33 +/- 0.04), medulla oblongata (0.25 +/- 0.01), cerebral cortex (0.21 +/- 0.03), and cerebellum (0.14 +/- 0.03), while the highest concentration of the inactive renin-like enzyme was localized in the hypothalamus (0.86 +/- 0.17), followed by the striatum (0.47 +/- 0.15), thalamus (0.32 +/- 0.09), cerebellum (0.29 +/- 0.04), midbrain (0.26 +/- 0.02), cerebral cortex (0.24 +/- 0.04), and medulla oblongata (0.10 +/- 0.03). The active renin-like activity in the thalamus of SHR was significantly lower than that of age- and sex-matched normotensive Wistar-Kyoto (WKY) rats. Furthermore, the inactive renin-like activity in the striatum, thalamus, cerebellum, midbrain, and medulla oblongata of SHR was significantly lower than that in the corresponding areas of WKY rats. Although the precise mechanisms underlying the conversion of inactive to active renin-like enzyme in the brain remain to be resolved, these results may offer a new aspect for the role of the brain renin-angiotensin system in the initiation and/or development of hypertension of SHR.