Cardiac responses to burn injury in young and adult guinea pigs.

The present study examined functional and biochemical differences in young compared to adult hearts, and determined if developmental differences altered the ability of the young heart to respond to burn injury. Compared to the adult heart, hearts from young sham burns had diminished responsiveness to isoproterenol, extracellular calcium, and increases in either ventricular filling or coronary flow rate. In contrast, there were no age-related differences in maximal calcium uptake (360+/-11 vs. 367+/-14 nmol/mg) or calcium uptake velocity (59+/-2 vs. 60+/-4 nmol/mg/min) in sarcoplasmic reticulum (SR) vesicles isolated from adult and compared to young control hearts. Burn injury (43% TBSA for adults, 35% TBSA for young) impaired myocardial function in all hearts, regardless of age. Age-related differences in adult and young hearts persisted after burn trauma with significantly lower left ventricular developed pressure (49+/-2 vs. 63 +/-3 mmHg, P < 0.01), +dP/dt max (860+/-89 vs. 1151+/-62 mmHg/sec, P < 0.01), and -dP/dt max (790+/-39 vs. 901+/-50 mmHg/sec, P < 0.02) in young vs. adult burn hearts. Burn injury reduced cardiac SR maximal calcium uptake in adults (sham, 360+/-11; burn, 298+/-12 nmol/mg, P < 0.05), but not in young hearts (sham, 367+/-14; burn, 380+/-12 nmol/mg); however, burn trauma increased the SR calcium velocity/capacity ratio in both young and adult burn groups. Our data confirm age-related differences in ventricular performance in young and adult guinea pigs; these differences persisted after burn trauma. The burn-mediated changes in SR Ca2+ transport suggest that disturbances in intracellular calcium handling may contribute, in part, to post-burn cardiac contractile deficits regardless of age.