Contractile function of heart muscle from burned guinea pigs

Atrial muscle isolated from burned guinea pigs was used to assess myocardial contractile changes associated with thermal injury. Muscle was obtained 16-18 hours after the animals were subjected to sham burn (controls) or to scald burn equivalent to 16% of total body surface area. Isometric contractile tension (CT) and its maximal rate of increase (+dT/dt) were not significantly altered by burn. However, the maximal rate of relaxation (-dT/dt) was uniformly less in muscle from the burned group, and this difference was significant at several time intervals after in vitro contractile responses were elicited. Similarly, -dT/dt responses to increased stimulation frequency (0.1-3.0 Hz) and to increased calcium ion concentration (1.0-10.0 mM) were generally less in the burned group, whereas corresponding CT and +dT/dt responses of the burn and controls groups were not significantly different. Present data indicate that atrial muscle removed from moderately burned guinea pigs exhibits normal contractile capabilities, but may be characterized by impaired relaxation properties.