Right ventricle systolic pressure increase following intravenous acetylcholine injection

In order to characterize and compare right ventricle (RV) and left ventricle (LV) and left ventricle (LV) hemodynamic responses to physiological and pharmacological maneuvers, we studied the effect of the intravenous injection of acetylcholine (ACh) in 32 anaesthetized mongrel dogs. After producing a decrease in aortic pressure and in left ventricle systolic pressure (LVSP). ACh always determined a significant increase in the right ventricle systolic pressure (RVSP) preceded or not by a fall in this parameter. Atropine and denervation of carotid and aortic pressure receptors suppressed this rise in RVSP. It is suggested that the RVSP increase is secondary to a sympathetic reflex response parting from the pressure receptors after detecting the aortic hypotension elicited by ACh following peripheral vascular bed vasodilation. Sympathetic discharge could produce a systemic venoconstriction that increases the venous return to the RV, together with a direct inotropic effect on the ventricular muscle. Both actions, peripheral and myocardial, would account for the RVSP increase. We cannot totally disconsider a probable additional pulmonary vasoconstrictor effect included as part of the sympathetic reflex response.