COMPARISON OF THE SYMPATHETIC NERVOUS-SYSTEM ACTIVITY BETWEEN SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS TO RESPOND TO BLOOD-PRESSUREREDUCTION

Two types of calcium antagonists, diltiazem and nicardipine, were sepa rately infused in 23-28 week-old spontaneously hypertensive (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats (under sodium thiobut abarbital 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 ca techolamines (CAs), norepinephrine (NE) and epinephrine (E), mere conc omitantly determined and the correlations between these three values m ere studied for each calcium antagonist, Plasma concentration of CAs w ere measured in blood samples collected during the infusion from the r ight femoral artery of each rat by the automatic sensitive and selecti ve detection system, The reduction of blood pressure induced by the ca lcium antagonists brought about an increase in plasma CAs levels, The blood pressure correlated well with the logarithm of plasma NE and E c oncentration and the relations were expressed as Y = -alpha log(X) + m (Y, blood pressure; X, concentration of plasma NE or E; alpha, slope; and rn, intercept), The alpha s of SHR rats were greater than those o f WKY rats for the calcium antagonists employed, meaning that the incr ement of plasma CAs responding to a decrease in blood pressure was sma ller in SHR than in WKY rats, It was concluded that the contribution o f the sympathetic nervous system to maintaining blood pressure reduced by diltiazem and nicardipine is less in SHR han in WKY rats.