Role of the beta 2 adrenoceptor in mediating positive inotropic activity in the failing heart and its relation to the hemodynamic actions of dopexamine hydrochloride.

In patients with severe congestive heart failure, it has been suggested that since myocardial beta 1 adrenoceptors are selectively down-regulated, activation of beta 2 receptors may be a preferable approach to augmenting contractility. Accordingly, dopexamine hydrochloride (1, 2 and 4 micrograms/kg/min) and dopamine (2 and 4 micrograms/kg/min) were administered to 8 patients with dilated cardiomyopathy. Left ventricular (LV) dimensions, thicknesses and pressures were obtained using simultaneous high-fidelity pressure measurements and echocardiographic recordings. LV contractility was assessed using the load-independent relation between LV end-systolic wall stress and rate-corrected velocity of fiber shortening. Cardiac index increased in a dose-related manner with both drugs, and was accompanied by a decline in systemic vascular resistance, a measure of peripheral arteriolar tone. LV end-diastolic pressure was unaltered except for a decrease from 29 +/- 6 to 19 +/- 5 mm Hg (p less than 0.017) at the highest dose of dopexamine hydrochloride. Heart rate was unchanged during the infusion of dopamine but increased significantly with dopexamine hydrochloride. LV end-systolic wall stress, a measure of LV internal load, decreased with both drugs. With dopamine, a dose-dependent positive inotropic effect was observed. Dopexamine hydrochloride, at the 4 micrograms/kg/min infusion dose, exerted a mild positive inotropic effect comparable to that noted with dopamine at 2 micrograms/kg/min. Thus, dopamine and dopexamine hydrochloride improved overall LV performance. With dopamine, a substantial positive inotropic effect occurred in association with a reduction in LV afterload. The increased cardiac index observed with dopexamine hydrochloride was due primarily to peripheral vasodilatation and a positive chronotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)