| Abstract: | Pharmacological and radio-ligand binding studies have recently indicated the existence of beta 2-adrenoceptors in the human heart. Their physiological role, however, remains to be elucidated. The present study investigated in 17 normal, young volunteers the effect on resting left ventricular (LV) function of two types of beta-blockers; a predominant beta 1-adrenoceptor antagonist (atenolol, 50 mg once daily) and ICI 118,551 (20 mg t.i.d.), a new, predominant beta 2-antagonist. LV function was assessed using M-mode echocardiograms and systolic time intervals. Atenolol, ICI 118,551, and placebo were given according to a randomized, double-blind, cross-over protocol. As compared with placebo, both drugs caused a decrease in resting heart rate, but the reduction by ICI 118,551 was less pronounced. Systolic blood pressure was only reduced by atenolol 8 mm Hg on average. Cardiac output was decreased to the same extent following treatment with atenolol (-20%) as after ICI 118,551 (-17%). These decreases in cardiac output were related to the beta-blocker-induced bradycardia, since stroke volumes were not affected during either selective beta 1- or beta 2-blockade. In addition, all other echocardiographic variables reflecting LV pump function, such as fractional shortening, velocity of diameter change and of displacements, pre-ejection period, and the ratio of PEP/LVET, were not different from placebo. We conclude that in normal young subjects, global LV pump function is not affected by beta 1- or by beta 2-blockade, despite the negative chronotropic effect of both drugs.(ABSTRACT TRUNCATED AT 250 WORDS) |
