Ontogenetic development of energy-supplying enzymes in rat and guinea-pig heart

The purpose of the present study was to compare the ontogenetic development of the activity of myocardial energy-supplying enzymes in two mammalian sp ecies, differing significantly in their level of maturation at birth. The a nimals were investigated during the late prenatal period and 2, 7, 14, 21, 25, 30, 63, 120 and 730 days after birth in the rat and 2, 21, 84 and 175 d ays in the guinea-pig. The following enzymes were assayed in the right and left ventricular myocardium: lactate dehydrogenase (LDH, lactate uptake and /or formation), triose phosphate dehydrogenase (TPDH, carbohydrate metaboli sm), glycerol phosphate dehydrogenase (GPDH, glycerol-P shuttle)), hexokina se (HK, glucose phosphorylation), malate dehydrogenase (MDH, tricarboxylic cycle), citrate synthase (CS, tricarboxylic cycle) and hydroxyacyl-CoA dehy drogenase (HOADH, fatty acid breakdown). The rat heart, highly immature at birth, exhibits three different developmental patterns of energy-supplying enzymes, identical in both ventricles: (i) two mitochondrial enzymes of aer obic metabolism (CS, HOADH) and GPDH have a relatively low activity at the end of prenatal life; thereafter their activity steadily increases, approac hing the adult levels between the 3rd and 4th postnatal weeks. A significan t decrease was observed between the 4th and 24th months. (ii) MDH and LDH: prenatal values were significantly higher as compared with the 2nd postnata l day; after this period the activities increased up to adulthood (4 months ) and decreased during senescence. (iii) The activities of HK and TPDH are characterized by only moderate changes during development. HK differs from all other enzymes by the highest prenatal values, which exceed even adult v alues. In contradiction to the rat heart, the developmental differences in more mature guinea-pig heart were significantly less pronounced. The only o ntogenetic differences observed were the lower activities of enzymes connec ted with aerobic metabolism at the end of the prenatal period. Our results point to possible differences in the development of adaptive metabolic path ways in animals with different levels of maturation at birth.