Pressor and depressor responses after cholinergic blockade in humans.

To determine whether cholinergic mechanisms contribute to blood pressure responses during arterial baroreflex inhibition and stimulation, we assessed the effects of atropine on pressor and depressor responses during and after release of the Valsalva maneuver, upon administration of intravenous phenylephrine and nitroglycerin, and during neck suction in 12 healthy people. Atropinization augmented the depressor response during the Valsalva maneuver (269%), the pressor response after release of the maneuver (544%), the pressor response to phenylephrine (109%), and the depressor response to nitroglycerin (76%), whereas the depressor response to externally applied neck suction was attenuated or abolished in all subjects. Cardiac output as indicated by impedance cardiography was unchanged during carotid baroreceptor stimulation. The results are best explained by inhibition by atropine of compensatory cholinergic heart rate, vasodilator, and negative inotropic responses.