Alterations in myocardial uptake of glutamate and release of alanine after propranolol, nifedipine, and glyceryl trinitrate in coronary artery disease.

We examined the effects of antianginal drugs on myocardial uptake of glutamate and release of alanine in patients with chronic effort angina. Thirty-three patients underwent two periods of atrial pacing, the second preceded either by no medication (controls) (n = 8), 0.1 mg/kg i.v. propranolol (n = 8), 30 mg nifedipine sublingually (n = 9) or 0.75 mg glyceryl trinitrate sublingually (n = 8). Before, during, and after each pacing period, coronary sinus blood flow (CSBF), oxygen uptake, and arteriocoronary sinus differences (ACs) of plasma glutamate and alanine were determined. In all groups of patients, arterial alanine concentration fell during the second test. Except for this fall, no metabolic change was seen in controls. Propranolol increased circulating arterial concentration and ACs values of glutamate throughout the test. Nifedipine did not change arterial glutamate concentration but decreased ACs glutamate before and after pacing. Glyceryl trinitrate decreased CSBF, oxygen uptake, and net myocardial uptake of glutamate before pacing despite unchanged arterial level and ACs values. Alterations of myocardial glutamate uptake after drugs may reflect metabolic effects of propranolol primarily exerted on extracardial sites and of nifedipine exerted on the myocardium itself, whereas changes after glyceryl trinitrate seem to be secondary to its cardiac unloading effect. Alterations in myocardial release of alanine were too small and inconsistent to be taken as drug effects.