[Analysis of the baroreflex activation of the sympathetic system in waking cats induced by urapidil and sodium nitroprusside].

The responses of the sympathetic system to a stepwise decrease of arterial blood pressure by administering sodium nitroprusside or urapidil were studied in experiments on conscious cats with preliminarily implanted transducers and catheters. Adrenaline and noradrenaline concentrations in arterial and venous blood plasma were measured by means of a high performance liquid chromatography. It was shown that when nitroprusside was used for lowering blood pressure there occurred reflex activation of the sympathetic system. That is, an elevation of plasma adrenaline and noradrenaline concentrations, a rise of noradrenaline release in vessels of the skeletal muscles, an increase of the heart rate. Urapidil when given in equihypotensive doses failed to increase catecholamine concentrations and tachycardia that seems to be related to the central inhibition of the baroreceptor reflex.