Vasoconstriction induced by sympathetic stimulation during development of hypertension

Abstract

Vasoconstrictor responses in the perfused hindquarters to lumbar sympathetic chain stimulation and to intra-arterially injected drugs were examined in rats during the development of renal hypertension. Perfusion pressure-flow determinations demonstrated increased vascular resistance in the hindquarters at periods of 2, 6, and 12 wk. in the hypertensive groups. Responses to sympathetic chain stimulation at varying intensities (0.5-10 V) and frequencies (1.25-20 pulses/sec.) were not significantly different in control and hypertensive animals at 1, 6 and 12 wk. Reactivity was increased in hypertensive rats at 2 wk. and the differences occurred mainly at the lower intensities of stimulation. Responses to angiotensin were significantly augmented at 2, 6, and 12 wk. in operated animals, whereas effects of norepinephrine were not increased as consistently. These results indicate that the greater vascular resistance observed in hypertensive rats was not primarily due to increased vascular reactivity to sympathetic impulses.