AJP - Heart and Circulatory Physiology, Vol 232, Issue 4 426-H433, Copyright © 1977 by American Physiological Society
Central angiotensin II-induced responses in spontaneously hypertensive rats
W. E. Hoffman, M. I. Phillips and P. G. Schmid
The brain isorenin angiotensin system has been implicated in the
development of spontaneous hypertension by several investigators. The
experiments reported here were designed to test the responsiveness of
unanesthetized spontaneous hypertensive (SH) rats to
intracerebroventricular angiotensin II injections compared to Wistar-Kyoto
(WK) normotensive controls. The results indicate that there is no
difference between SH and WK animals in drinking responses or antidiuretic
hormone release to central angiotensin II injections; however, an increased
pressor responsiveness to intraventricular angiotensin II in SH as compared
to WK was observed. The results of intravenous infusions of pressor
substances in these experiments and reports by other investigators suggest
that the increased blood pressure effects to central angiotensin are due to
three possible factors: 1) increased vascular responsiveness of SH to
vasoconstrictor substances in general, 2) increased vascular sensitivity of
SH rats to sympathetic outflow, and 3) decreased baroreceptor reflexes to
acute increases in blood pressure. We suggest that the brain
isorenin-angiotensin system may be involved in spontaneous hypertension by
increased production of angiotensin II or by activation of a potentiated
sympathetic system, but not by a generalized increased sensitivity of brain
receptors to central angiotensin.
