Effect of hyperinsulinemia on myocardial amino acid uptake in patients with coronary artery disease

Branched-chain amino acids (BCAAs) are oxidative energy substrates for the heart and may exert anabolic effects on myocardial protein. The factors reg ulating their myocardial uptake in patients with ischemic heart disease are therefore of interest. To examine whether myocardial BCAA utilization is i nfluenced by the circulating insulin concentration, in 10 patients with chr onic ischemic heart disease, we measured transmyocardial amino acid balance during fasting and again during a 90-minute euglycemic insulin infusion (p lasma insulin, 218 +/- 25 mu U.mL(-1)) with plasma BCAA concentrations held constant by coinfusion. In the fasting state, the myocardial fractional ex traction of leucine (8%), isoleucine (9%), and valine (5%) from arterial pl asma was slightly greater than that of glucose (3%), while net myocardial B CAA uptake (leucine, 409 +/- 207 nmol min(-1); isoleucine, 220 +/- 144 nmol .min(-1); valine, 407 +/- 326 nmol.min(-1); and total BCAA uptake, 1.0 +/- 0.3 mu mol.min(-1)) was about 13% that of glucose (8 +/- 2 pmol min(-1)). D uring euglycemic hyperinsulinemia, myocardial glucose uptake increased 3-fo ld, but there was no change in the arterial-coronary sinus balance or net m yocardial uptake of any BCAA under conditions where their plasma concentrat ions were held constant. Instead, the myocardial uptake of each BCAA correl ated positively with its concentration in arterial plasma. These results de monstrate that in patients with cardiovascular disease, myocardial utilizat ion of BCAAs is insensitive to the circulating insulin level and is regulat ed instead by their availability in arterial plasma. Hyperinsulinemia reduc ed the magnitude of both net glutamate uptake and alanine release, suggesti ng a possible salutary effect on myocardial oxidative efficiency. Copyright (C) 2000 by W.B. Saunders Company.