Increased Cardiovascular Responses to Norepinephrine and Calcium Antagonists in Essential Hypertension Compared with Normotension in Humans

Abstract

The responses to a supine rest, norepinephrine (NE) and angiotensin II (Ang II) were investigated in the absence and presence of calcium antagonist nifedipine or diltiazem in essential (genetic, arterial) hypertension and normotension in humans. A supine rest significantly decreased blood pressure (BP), heart rate (HR), stroke volume index (SI), and cardiac output index (CI). On the contrary, the rest increased total peripheral vascular resistance index (TPRI) in both normotensives and hypertensives. The decrease in BP was significantly greater in hypertensives than in normotensives. NE significantly increased BP and TPRI, whereas it decreased HR, SI, and CI. The increase in BP was greater in hypertensives than in normotensives. Nifedipine and diltiazem inhibited the NE-induced increases in BP and TPRI. Ang II increased BP and TPRI, but it decreased HR, SI, and CI. Diltiazem did not inhibit the Ang-II-induced increases in both BP and TPRI. The increased responses to a rest and NE were observed in the early stage of essential hypertension. The increased responses may contribute to both the increase in BP and the induction of high blood pressure in essential hypertension. The calcium antagonists inhibited the NE-induced increases in BP and TPR. The results suggest that the antagonists inhibit the NE-dependent calcium influx and calcium release in the arterial smooth muscle. The observed responses to Ang II suggest that the antagonists may not inhibit Ang-II-dependent calcium-channel activity in the smooth muscle.