AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 1 39-R44, Copyright © 1979 by American Physiological Society
Sympathetic hyperresponsiveness to hypothalamic stimulation in young hypertensive rats
R. D. Bunag and K. Takeda
The possible occurrence of central sympathetic dysfunction during
development of spontaneous hypertension was studied by recording aortic
pressure and sympathetic nerve activity concurrently during electrical
stimulation of the posterior hypothalamus in 9-wk-old Kyoto-Wistar rats.
Even at this early age, basal levels for both measurements were already
elevated significantly in those with spontaneous hypertension. Increases in
sympathetic neural firing induced by graded hypothalamic stimulation were
always followed by corresponding increases in blood pressure; magnitude of
both effects was appreciably larger in spontaneously hypertensive than in
normotensive rats, as was the vasodepression caused by blocking autonomic
ganglia with pentolinium. By contrast, pressor responses to injected
norepinephrine were almost equal thereby suggesting that cardiovascular
reactivity was unaltered and that enhanced responsiveness to hypothalamic
stimulation was directly due to the concomitant increase in sympathetic
nerve activity. Although the exact site from which sympathetic
hyperactivity originates was unidentified, our results support the
interpretation that sympathetic mechanisms involving the posterior
hypothalamus participate in elevating blood pressure during development of
spontaneous hypertension in rats.
