Differential influence of the calcium antagonist nitrendipine and the vasodilator hydralazine on normal and elevated blood pressure.

The relationship between pre-treatment blood pressure and its reduction by the calcium antagonist nitrendipine (NIT) and the vasodilator hydralazine (HYD) was studied in conscious normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). In SHR the correlation was linear and similar after NIT and HYD. In WKY, however, the hypotensive effect of HYD was greater than that of NIT. As revealed by the dose-response curves in SHR both drugs produce similar maximal drops in blood pressure by about 54%. In WKY, HYD also caused a similar relative reduction in blood pressure. In contrast, after NIT initial blood pressure was reduced by only 27% at maximum. The greater hypotensive effect of HYD in WKY is not caused by impaired sympathetic counterregulation since in both substrains tachycardia was more prominent after HYD. Possible mechanisms of the enhanced depressor action of NIT in hypertension are discussed.