Changes in the sensitivity to hypoxia and glucose deprivation in the isolated perfused rabbit heart during perinatal development.

The isometric contraction of the isolated rabbit myocardium was measured from 24 days post coitum (dpc) to young adulthood. Tension per gram of heart as developed by the isolated perfused hearts remained constant during late foetal life but increased during the first postnatal week. Sensitivity to hypoxia rapidly increased during foetal life from 26 to 28 days post coitum. In young foetal hearts (up to 28 days post coitum), contraction continued for several hours in the absence of glucose. In contrast, from 28 days post coitum onwards foetal hearts became increasingly dependent on external glucose to maintain their contractility. This change was concomitant with a decrease in myocardial glycogen content. Intracellular electrical activity recorded in the absence of glucose showed that during hypoxia in the foetus at term were reduced, whereas normal activity continued in the same hypoxic glucose-free medium in hearts from foetuses 26 days post coitum. The relative role of glycolysis and oxidative metabolism is discussed and the importance of glycogenolytic metabolism in young isolated foetal hearts is pointed out.