Distribution of immunoreactive angiotensin II, angiotensin I, angiotensinogen and renin in the central nervous system of intact and nephrectomized rats.

Evidence for an intracellular pathway for angiotensin synthesis in the central nervous system (CNS) was examined using immunohistochemistry to compare the distribution of angiotensin I (AI), AII, angiotensinogen, and renin in the hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON), median eminence (ME), and pituitary gland in intact and nephrectomized rats. In intact rats injected intracerebroventricularly (i.c.v.) with colchicine, AII neurons were found in the parvocellular PVN, and terminals were seen in the external lamina of the ME. In the pituitary gland, AII was localized within cells of the anterior and intermediate lobes, whereas the posterior pituitary was unstained. In contrast, 24 to 48 hours following nephrectomy, AII-labeled neurons were observed in the magnocellular PVN and SON, even without the aid of i.c.v. colchicine. Likewise, axons within the internal layer of the ME were now labeled, but the pituitary was completely devoid of staining except for the intermediate lobe. AI-labeled neurons were observed only in the parvocellular PVN. Angiotensinogen was localized in the mediobasal hypothalamus, but the PVN and SON were not labeled. Immunoreactive renin was localized within the magnocellular PVN, SON, and posterior lobe of the pituitary in nephrectomized and intact animals. Because of the close overlap of AI and AII staining, these results suggest that AI and AII could represent a precursor product relationship in the CNS. In contrast, in the intact animals, renin and angiotensinogen do not appear to be associated with AII. However, a possible relationship between AII and renin may exist in the magnocellular PVN and SON, since labeled neurons were seen in these nuclei following nephrectomy.