Angiotensin-sensitive neurons in the rat paraventricular nucleus: relative potencies of angiotensin II and angiotensin III.

Angiotensin-activated neurons were examined using microiontophoretic methods in the paraventricular nucleus (PNV) of the rat. In all cases angiotensin III (AIII) was more potent than angiotensin II (AII). This greater sensitivity to AIII was manifested by lower thresholds, shorter latencies, and higher spike frequencies/amplitudes of applied current. The superior potency of AIII was further exaggerated in the spontaneously hypertensive rat (SHR) compared with normotensive Wistar Kyoto (WKY) rats. Postactivity for both AII and AIII was greatly prolonged in SHR. This appeared specific since no prolongation in acetylcholine postactivity was seen in SHR. These data support the notion that AIII may be the centrally active form of angiotensin and are consistent with an obligatory conversion of AII to AIII prior to activation. The selective enhancement of postactivity observed in SHR following angiotensin application suggests a possible defect in signal termination.