[Aortic baroreceptor function in narcotized rabbits during alpha-adrenoceptor blockade with prazosin].

Since alpha-adrenoceptor blockade alters the mechanical vessel wall properties, the arterial baroreceptor function is to be changed also by this type of blockade. In 13 rabbits narcotized with chloralose and urethan, therefore, the aortic baroreceptor function was tested together with the baroreceptor heart reflex prior to and after intravenous administration of prazosin (0.005, 0.01, 0.05 mg per kg BW). By inflation and respective deflation of a balloon catheter lying with its tip in the thoracal aorta the arterial blood pressure level ahead was changed over a range as much as 30 to 50 mm Hg. The arterial blood pressure in the aortic arch, the heart rate and the electroneurogram from the peripheral stump of the left aortic nerve were registered. Intravenous administration of prazosin slowed down the arterial blood pressure in a dose related manner, and the heart rate remained similar. After having applied any doses of prazosin the baroreceptor heart reflex was completely abolished. The baroreceptor sensitivity was remarkably increased by prazosin. The characteristic curve describing the baroreceptor function was shifted to the left and was steeper. It was concluded that the baroreceptor heart reflex is directly blocked by the action of prazosin against the transmission in the parasympathetic pathway, and, mediated by the influence of prazosin on the vessel wall properties, the arterial baroreceptor becomes more sensitive.