Myocardial triglycerides increased by fasting. Effects of hypoxia on contractility and enzymatic release

The effect of fasting on the mechanics of contraction was studied in the isolated perfused rat heart, in oxygenated and hypoxic conditions. Animals were subjected to 48 h of fasting, a condition which produces augmented endogenous triglycerides (TG). Normal and fasted rats were submitted to a 10-min period of hypoxia, which depressed peak tension (Tp), maximal rate of contraction (Tc), and relaxation (Tr); all three parameters recovered with reoxygenation. However, Tp and Tc of hearts of fasted animals were less affected by hypoxia, and Tp, Tc, and Tr attained higher levels during reoxygenation compared with hearts of normally fed animals. These results suggest that as triglycerides are augmented, they might have a beneficial action on the hypoxic heart, though other unknown effects of fasting cannot be discarded. LDH was the only cardiac enzyme whose release in the perfusion medium significantly increased in hypoxic hearts, irrespective of the fasting state of the animal. The positive correlation between LDH and an index of relative recovery (IH) for Tp, Tc, and Tr, indicate that not only hypoxia but a good recovery are necessary to yield high LDH values.