Comparison of the sympathetic nervous system activity between spontaneously hypertensive and Wistar-Kyoto rats to respond to blood pressure reduction.

Two types of calcium antagonists, diltiazem and nicardipine, were separately infused in 23-28 week-old spontaneously hypertensive (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats (under sodium thiobutabarbital anesthesia and ventilation, n = 4) through the left femoral vein, resulting in the reduction of blood pressure. In each rat, mean arterial blood pressure, heart rate and the concentration of plasma catecholamines (CAs), norepinephrine (NE) and epinephrine (E), were concomitantly determined and the correlations between these three values were studied for each calcium antagonist. Plasma concentration of CAs were measured in blood samples collected during the infusion from the right femoral artery of each rat by the automatic sensitive and selective detection system. The reduction of blood pressure induced by the calcium antagonists brought about an increase in plasma CAs levels. The blood pressure correlated well with the logarithm of plasma NE and E concentration and the relations were expressed as Y = -alpha log(X)+m (Y, blood pressure; X, concentration of plasma NE or E; alpha, slope; and m, intercept). The alpha s of SHR rats were greater than those of WKY rats for the calcium antagonists employed, meaning that the increment of plasma CAs responding to a decrease in blood pressure was smaller in SHR than in WKY rats. It was concluded that the contribution of the sympathetic nervous system to maintaining blood pressure reduced by diltiazem and nicardipine is less in SHR than in WKY rats.