AJP - Regulatory, Integrative and Comparative Physiology, Vol 236, Issue 3 147-R152, Copyright © 1979 by American Physiological Society
Diminished sympathetic silent period in spontaneously hypertensive rats
L. P. Schramm and G. N. Barton
To determine if elevated sympathetic activity occurs in spontaneously
hypertension, the silent period induced in splanchnic nerves following
electrical stimulation of dorsal medullary sympathoexcitatory sites was
compared in anesthetized normotensive Wistar Kyoto rats (WKYs) and Okamoto
spontaneously hypertensive rats (SHRs). The strength of silent periods was
defined as the degree of inhibition of responses to testing stimuli
delivered at various latencies following conditioning trains, and it was
assumed to be inversely related to the level of sympathetic activity.
Weanling SHRs exhibited weaker silent periods than weanling WKYs although,
at that age, the arterial pressures of the strains were not significantly
different. Silent periods were also weaker in adult SHRs than in adult
WKYs. This difference persisted after arterial pressures, which fell under
anesthesia, were raised by phenylephrine infusions to the respective
"normal" levels in each strain. These results support the hypothesis that
elevated sympathetic activity exists during both the development and
maintenance of spontaneous hypertension in rats.
