By means of a standardized, single-level ergometric load of 1.5 watt/kg
body weight, the effects of a new
beta-adrenergic receptor blocking agent
bunitrolol (o-(2-hydroxy-3-tertiary butylamino)-propoxy)-
benzonitrile) was compared with the well-known cardiovascular properties of
practolol during an intraindividual therapeutic crossover trial after
intravenous administration. In the absence of any side-effects,
bunitrolol shows a higher degree of
beta-adrenergic receptor bocking activity than
practolol, with a distinct specificity towards myocardial receptors and very low cardiodepressive properties at rest.
Bunitrolol caused a marked reduction (33%) in exercise-induced myocardial work effort, whilst
practolol achieved a reduction of only 17% under equal conditions. Thus, the same physical work load is performed after
bunitrolol more economically by decreasing both heart rate and blood pressure. The circulatory effects of an intravenous dose of 5 mg
bunitrolol seems to be twice as effective as 10 mg
practolol. This implies that
beta-adrenergic receptor blockade by
bunitrolol during work performance is four times as effective as
practolol. The observed marked effect of
bunitrolol on the diastolic blood pressure is discussed.