Sex differences in the tolerance of immature rat myocardium to global ischemia.

Currently there is considerable interest in the metabolism of the immature myocardium and in particular the mechanisms underlying its greater tolerance to ischemia than that of the adult heart. In order to investigate whether this tolerance is sex-related, we compared the recovery of function in isolated hearts from male and female neonatal rats (three to five days old) following 60 min of normothermic global ischemia and 30 min of reperfusion (n = 8 per group). The female hearts exhibited significantly better (p less than 0.05) recovery of rate (81 +/- 5% vs. 65 +/- 5%) and the rate-pressure product (73 +/- 9% vs. 37 +/- 8%), and a tendency towards better recovery of contractile function (left ventricular developed pressure, 89 +/- 9% vs. 59 +/- 12%; dP/dt, 84 +/- 12% vs. 54 +/- 13%). This evidence for greater resistance of female hearts to ischemic injury was supported by a delayed onset of contracture (mean time to onset, 29.4 +/- 2.7 min vs. 24.9 +/- 2.6 min). The loss in left ventricular compliance during ischemia and reperfusion was also smaller in the female hearts (increase in left ventricular end diastolic pressure, 6.5 +/- 1.2 mm Hg vs. 13.6 +/- 3.8 mm Hg). These results suggest that there may be sex-related differences in the tolerance of immature hearts to ischemia, a factor which should be taken into account in the design and interpretation of experimental studies.