ABSTRACT
Plasma renin activity (PRA) and systolic time intervals (STI), including total electromechanical systole (QS2), left ventricular ejection time (LVET), pre-ejection period (PEP) and isovolumetric contraction time (ICT), were measured in patients with borderline hypertension (n = 23) before and after oral treatment with atenolol and propranolol. Both beta blockers caused a similar fall in blood pressure and heart rate (P less than 0.001). QS2, PEPc and PEP/LVET values did not change after treatment. Propranolol prolonged ICT (p less than 0.001) and reduced LVET (p less than 0.001). No significant changes were detected in PRA after atenolol while a reduction was found after treatment with propranolol (p less than 0.001). No relationship was found between PRA and STI, however a linear correlation was recorded between systolic pressure and PRA (r = 0,91; p less than 0.01) before beta-blockade. These results suggest that: a) only beta 2-adrenoceptors are involved in the release of renin; and b) the effect of beta-blockers on STI follows a reduction of blood pressure and heart rate which in turn affect afterload.
