Cardiovascular effects of eating, atenolol and their interaction: β1-adrenergic modulation does not play a predominant role in the genesis of postprandial effects

Abstract 1. Eight healthy subjects were investigated on four occasions at least 1 week apart when they either ate a standard 3100 kJ cold meal or fasted. One hour earlier, either 50 mg atenolol or placebo was administered. 2. Eating was followed by prominent changes of systolic cardiovascular function: a rise of heart rate (+7, 95% CI: 4 to 9 beats min(-1)), systolic BP (+5, CI: 1 to 8 mmHg), a drop of diastolic BP (-6, CI:-9 to -3 mmHg), shortening of the pre-ejection period PEP (-11, CI: -13 to -9 ms) and electromechanical systole QS2c (-13, CI: -17 to -8 ms), a rise of the estimated cardiac output CO (+1.3, CI: 1.0 to 1.6 1 min(-1)) and a reduction of the calculated total peripheral resistance TPR (-306, CI: -389 to -222 dyn s cm(-5)). 3. Eating was also followed by an increase of the non-renal clearance of sorbitol (as a measure of hepatic blood flow) and this change was larger than proportional to the increase of CO. The plasma renin activity rose after the meal but the venous plasma noradrenaline and adrenaline concentrations were not affected. 4. The postprandial effects peaked over the first 1-2 h after the meal but remained well detectable up to 4 h after eating. 5. The administration of 50 mg atenolol before the meal reduced the postprandial effects to the same extent as the atenolol effects in the fasting state. This lack of interaction (or mere arithmetic additivity) indicates that the efferent beta1-adrenergic tone does not play a predominant role in the modulation of postprandial cardiovascular changes.