Endogenous brain angiotensin II-mediated sympathetic nerve responses are not augmented in mature spontaneously...

Conjugated estrogens injected into the lateral brain ventricle in awake rats elicited behavioral excitation and vasopressor responses. Magnitude of pressor responses was greater in spontaneously hypertensive rats (SHR) than in normotensive Kyoto Wistar rats (WKY). Pressor responses in SHR were abolished by central pretreatments of either captopril or angiotensin II analog. Under urethane anesthesia, conjugated estrogens still produced greater pressor responses in SHR, but accompanying increases in sympathetic nerve firings were the same in both WKY and SHR. These results suggest that while centrally-administered estrogens may activate the brain renin-angiotensin system to increase sympathetic nerve firing and thereby elevated blood pressure, SHR have larger pressor responses only because peripheral vascular reactivity has been increased.