The effects of a single
intravenous infusion of
prenalterol, a beta 1 selective agonist, on haemodynamics (echocardiography) and venous plasma
catecholamine concentration were studied in 8 patients with severe
congestive heart failure. In these patients, age-adjusted plasma
norepinephrine (NE) and
epinephrine (E) levels before
prenalterol infusion were higher compared to values found in 10 control healthy subjects (both P less than 0.01). In
heart failure patients, circulating NE levels were not dissimilar in 2 samples drawn 60 and 0 minutes before commencing
prenalterol infusion (772.0 +/- 131 ng/l [mean +/- SD] and 775.5 +/- 130.0 ng/l respectively).
Prenalterol induced a significant improvement in the cardiac index,
stroke index, ejection fraction and velocity of circumferential fiber shortening, associated with a moderate but significant decrease in peripheral vascular resistance. All these changes persisted for 60 minutes after the end of infusion. Circulating NE levels were 604.0 +/- 125 ng/l at 60 min. after start of infusion (P less than 0.01 vs pre-infusion levels) and 526.1 +/- 108 ng/l at 60 min. after the end of infusion (P less than 0.01 vs pre-infusion levels). Plasma E showed a slight decrease, which did not attain statistical significance. Heart rate and diastolic blood pressure remained unchanged during and after infusion, while systolic blood pressure increased by 10-15 mmHg during and after infusion. We conclude that a single 1-hour
prenalterol infusion in patients with severe
congestive heart failure induces an haemodynamic improvement associated with a reduction of previously elevated circulating NE levels. This reduction could indicate a lowering in the intensity of the afferent stimulus for the reflex sympathetic overactivity.