Development of NADPH-consuming pathways in heart, brain and liver of the rat

The behavior of the principal NADPH-consuming pathways, fatty acid synthesis (-ATP-citrate lyase), transhydrogenase, glutamate dehydrogenase, glutathione reductase, NADPH-cytochrome c reductase and mitochondrial and cytoplasmic thioredoxin reductases were studied during the development of the heart, brain and liver of the rat. The liver is the tissue with highest NADPH-consuming activities. Transhydrogenase activity is highest in the heart; it undergoes two steep increases of activity, one at birth and another between 15 and 25 days. Liver cytoplasmic glutathione reductase activity increases mainly at birth. The activities in heart and brain are lower and the brain enzyme activity slightly increases throughout development. Liver NADPH-cytochrome c reductase activity greatly increases at weaning. The heart activity is the lowest, no changes taking place in the developmental period. Heart mitochondrial and brain cytoplasmic thioredoxin reductases undergo increases in activity at birth. The ratios of NADPH-producing/NADPH-consuming activities are constant in all tissues studied, and oscillate between congruent to 4 in fetuses to congruent to 2 in adults, the only exception being the adult heart ratio (congruent to 23). This otherwise constancy confirms that both processes are closely correlated.