Short term effects of a tratment with methoprololo (a selective beta1-blocking agent ) in essential hypertension.Changes of haemidynamics,renin ,aldosterone, sodium and potassium balance

The short-term effects of a treatment with methoprolol (a selective β 1-blocking agent) have been studied in 20 adults with essential hypertension that showed non-objective signs of salt-water retention, cardiac failure and nephropathy. During the investigation (a basal period of 8-10 days + 10 days of treatment) the sodium and potassium intake was held constant (80-100 mEq and 50-60 mEq per day, respectively); blood pressure (BP) was evaluated at least four times a day in supine and orthostatic positions with an arm-cuff sphygmomanometer heart rate, and external balance of Na and K were measured daily. PRA, the daily urinary aldosterone excretion and creatinine clearance were measured before treatment and on the 5(th) and 10(th) days of treatment; cardiac output (thermodilution method) was measured before and after ten days of treatment. The administration of methoprolol (3 mg/kg b.w.) effected: a significant fall of systolic and diastolic BP, both in standing and recumbent positions; a significant decrease of the heart rate, with a conservation of postural reflexes; a significant decrease of cardiac output, mainly due to a decrease in the cardiac rate, with no change of systolic volume; and an inhibition of renin secretion, accompanied by insignificant modification of aldosterone production. There was no change of creatinine clearance and no sodium retention in spite of the fall in blood pressure. We conclude that treatment with methoprolol does no trigger any self-limiting effect like sodium retention (beta-blocking agents are the only antihypertensive agents with this property, excluding diuretics) or renin stimulation (which is inhibited). Also, no change would be expected in cation distribution since aldosterone secretion was normal throughout the treatment.