Postnatal changes in pyridine nucleotides in rat hepatocytes: Composition and O2 dependence

Abstract

Postnatal changes in pyridine nucleotide concentration, composition, and oxidation-reduction characteristics were studied in liver cells front neonatal (newborn, d 4 and d 8) and adult rats to determine the development of hepatic pyridine nucleotide status and 02 dependence of oxidation of reducing equivalents. The results show that the total pyridine nucleotide concentrations in newborn and 4-d-old rat liver were low (30%) but increased to near adult values (80%) by d 8 postpartum. Analyses of the cellular distribution of NAD+, NADH, NADP+, and NADPH reveal that the reduced forms (NADH plus NADPH) accounted for over 50% of the total in the newborn and 4-d-old rats compared to 30% in adult animals. This relatively higher reductive capacity in hepatocytes of younger rats was largely the result of a significantly higher proportion of NADPH in these cells. Examination of the NADPH/ NADP+ and NADH/NAD+ ratios show that they occur in an inverse relationship with postnatal age; the NADPH/ NADP+ ratio was high at birth and decreased with age, whereas the reverse pattern was found for the NADH/ NAD+ ratio. The result, that NADPH represents a significant percentage of the total pyridine nucleotides in neonatal cells in the early postnatal period, is consistent with a higher demand for NADPh for biosynthetic activities in association with tissue growth. A high NADPH concentration coupled with a low NADH concentration in these cells is further consistent with the finding that succinate is a preferred substrate for newborn respiratory function so as to spare NADH for transhydrogenation to NADPH. The half-maximal oxidation of pyridine nucleotides in cells from newborn rats occurred at 0.49 µM O2, as compared to 1.2 and 4.0 µM O2 in cells from 4-d-old and adult rats, respectively. Direct comparison of the 02 dependencies of pyridine nucleotides at different ages with those of cytochrome c + d demonstrates that the oxidation of pyridine nucleotides occurs in concert with the expression of mitochondrial respiratory components during development. © 1991 International Pediatric Research Foundation, Inc.