Comparison of the responses of fetal and adult cardiac muscle to hypoxia.

Su, JUDY Y., AND WILLIAM F. FRIEDMAN. Comparison of the responses of fetal and adult cardiac muscle to hypoxia. Am. J. Physiol. 224(6): 1249-1253. 1973.-The responses of cardiac tissue isolated from fetal and adult sheep were compared after selective inhibition of aerobic and anaerobic metabolism. The frequency of contraction of adult right atria was significantly more depressed by oxygen deprivation or exposure to dinitrophenol than the fetal atria. Fetal right atria were more sensitive to inhibition of glycolysis by iodoacetate than the adult. No differences were observed in the ability of fetal and adult ventricular myocardium to generate tension with either oxygen or glucose deprivation. Both fetal and adult atria1 and ventricular myocardium were more sensitive to the combination of oxygen deprivation and iodoacetate than either intervention alone. In the absence of glucose, oxygen deprivation depressed adult atria1 and ventricular tissue to a greater extent than observed in the presence of glucose In contrast, when fetal myocardium was exposed to the combination of oxygen and glucose deprivation, a secondary, positive chronotropic and inotropic response was observed that could be blocked by the beta-adrenergic blocking agent, propranolol (10 + M). The results suggest that the fetal heart is more dependent on glycolytic than aerobic metabolism as an energy source when compared to the adult heart. The secondary, positive chronotropic and inotropic response of fetal heart to the combination of glucose and oxygen deprivation is compatible with a preferential agedependent release of cardiac catecholamines and a supersensitivity of fetal myocardium to norepinephrine when compared to the adult.