Perinatal Regulation of Mitochondrial and Cytoplasmic Enzymes in Rabbit Liver

Abstract

Extract: The control of postnatal development of the activities of cytoplasmic and mitochondrial malate dehydrogenases and of the purely mitochondrial enzyme, cytochrom oxidase, has been studied in rabbit liver. Each of the three enzymes increased 1.6–1.8-fold in activity during the first 2 days of life. Delivery of animals at varying stages of maturation demonstrated (table II) that the increase in all cases occurred when delivery was effected and was a result of some aspect of the process of birth itself.

Maturation affects cytoplasmic malate dehydrogenase (MDH) differently than the two mitochondrial enzymes. Cytoplasmic MDH is relatively constant in activity in utero and increases approximately 80% whenever delivery is effected (table II, figure 1). In contrast, both the mitochondrial (20–40%) following premature delivery is considerably smaller than the large (1.5-fold) increase following postmature delivery.

Using the artificial feeding procedure developed for this study, newborn animals were maintained for 48 h in an hypoxic environment. Preliminary results suggested that development of enzyme activity was affected by hypoxia.

Speculation: Normal alterations in perinatal enzyme activity are probably a result of various aspects of maturation and the birth process. Varying the time of delivery and the extrauterine environment makes possible experimental study of the physiologic control of this and other perinatal processes.

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