Hemodynamic reactions under various stimuli before and during chronic beta-blockade.

Chronic beta-blockade with the cardioselective blockers practolol and atenolol had no attenuating effect on blood-pressure increases provoked by cold pressor test or by plasma expansion. Reports in the literature of an exaggerated cold pressor test reaction under propanolol therapy could be confirmed with practolol and atenolol. This may be regarded as an advantage of cardioselective blockade. The increase of the cardiac output after plasma expansion is enhanced during cardioselective beta-blockade. This could result from a reduced action of cardioselective blockers on the capacitance vessels. Concerning the mechanisms of antihypertensive action of beta blocking agents our findings do not support the cardiac output hypothesis. Before and during beta blocking therapy baroreflex sensitivy was not significantly different. So the baroreflex theory can't be strengthened neither.