A Humoral Sensitizing Factor for Norepinephrine in the Spontaneously Hypertensive Rat

Abstract

The vasopressor effect of exogenous norepinephrine was compared before and after iv injection of sera from Aoki-Okamoto spontaneously hypertensive rats into bioassay animals. Changes in the pressor responses were compared to those produced by the sera of normotensive Sprague-Dawley-derived rats. The systolic blood pressures of serum donor animals were periodically taken via a cuff over the caudal artery. The animals were decapitated and trunk blood was collected. The mean systolic blood pressure of the spontaneously hypertensive group was 184 ± 4 mm Hg just prior to killing. A separate group of normotensive rats was bilaterally nephrectonized and after 24 hr was ganglionically blocked with hexamethonium and used as bioassay animals. Bioassay animals were given standardized doses of norepinephrine iv at 6-min intervals both before and after iv injection of 15-25 μl of either normotensive or spontaneously hypertensive rat serum. Spontaneously hypertensive rat serum increased the average pressor response to norepinephrine 22 ± 7% (P < 0.02). Normotensive serum did not increase the pressor response to norepinephrine. These data suggest there is a humoral factor in spontaneously hypertensive rat serum that potentiates the pressor effect of norepinephrine when injected into bioassay animals.