Angiotensin-(1-7) and nitric oxide synthase in the hypothalamo-neurohypophysial system.

The organization of angiotensin (Ang)-(1-7) immunoreactivity with respect to neurons containing the nitric oxide synthase, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), in the hypothalamo-neurohypophysial (HNS) system was examined. The majority of neurons in this system were single labeled with Ang-(1-7) or NADPH-d and were found localized in two separate populations of neurons within the HNS. A small number of double-labeled neurons were observed in the supraoptic (SO) and paraventricular (PV) nuclei. Double-labeled accessory neurosecretory neurons were also found distributed between the SO and PV. Although a well-defined function for nitric oxide in the magnocellular hypothalamic system has not been determined, the codistribution and limited coexistence of Ang-(1-7), a heptapeptide involved in antidiuresis, and NADPH-d in the HNS suggests a potential role for these substances in mechanisms modulating fluid homeostasis.