A Humoral Sensitizing Factor for Norepinephrine in the Spontaneously Hypertensive Rat

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Abstract
The vasopressor effect of exogenous norepinephrine was compared before and after i.v. 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 nephrectomized and after 24 h was ganglionically blocked with hexamethonium and used as bioassay animals. Bioassay animals were given standardized doses of norepinephrine i.v. at 6 min intervals both before and after i.v. injection of 15-25 .mu.l 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. There apparently is a humoral factor in spontaneously hypertensive rat serum that potentiates the pressor effect of norepinephrine when injected into bioassay animals.