Haemodynamic Effects of Selective ??1Blockade (Trimazosin) in Essential Hypertension

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Abstract
As a preliminary to a larger clinical trial, the haemodynamic effects of the selective α-adrenoceptor antagonist trimazosin were studied at rest and during bicycle exercise in the upright position in 14 patients with uncomplicated, stable essential hypertension. Rest and exercise studies before the drug was given revealed no evidence of left ventricular pumping deficiency. A single intravenous bolus of trimazosin (2 mg/kg) resulted in a plasma concentration of 13.1 ± 1.0 mg/ml 30 min after injection. This plasma concentration of trimazosin was associated with a reduction in the systemic vascular resistance (p < 0.01); in the absence of any increase in the cardiac output, this resulted in a fall in the systemic blood pressure (p < 0.01) at rest. Heart rate and left heart filling pressure were unchanged. During 4 min of upright dynamic exercise after drug, the increment in systemic blood pressure was similar to that in the control study; i.e., the absolute level of pressure was reduced (p < 0.01). The increases in heart rate, cardiac output, and left heart filling pressure during exercise were also unchanged after drug compared with those measured in the control study. The left heart filling pressure and cardiac output were slower to increase at the onset of exercise after trimazosin, which may imply a degree of venodilatation. There were no hypotensive symptoms or large falls in blood pressure after trimazosin at rest, but following 4 min of submaximal upright bicycle exercise, three of the 14 patients developed postural hypotension. Trimazosin lowers blood pressure solely by reduction of the systemic vascular resistance without inhibiting the cardiovascular response to dynamic exercise.