Carbohydrate metabolism of mammary tissue II. Levels of oxidised and reduced diphosphopyridine nucleotide and triphosphopyridine nucleotide in the rat mammary gland

Abstract

1. 1.The DPN +, DPNH, TPN + and TPNH contents of rat and rabbit mammary glands have been determined, in the rat at different stages of the lactation cycle and in the rabbit during full lactation. 2. 2.DPN is present mainly in the oxidised form whereas TPN is present chiefly in the reduced form. The pyridine nucleotide content of the rat mammary gland increases from late pregnancy and reaches its maximum level towards the end of lactation when high concentrations of TPN and DPN are found. 3. 3.The intracellular distribution of pyridine nucleotides has been measured in mammary gland tissue from lactating rats. Of the total pyridine nucleotide content of the homogenate about 80% was recovered in the soluble fraction, the remainder being fairly evenly distributed between the nuclei, mitochondria and microsomes. The mitochondria contained very small amounts of TPN and TPNH. 4. 4.The total activity of diphospyridine nucleotidase has been shown to remain remarkably constant in the rat mammary gland throughout the period from pregnancy to early involution. 5. 5.TPNH-cytochome c reductase and pyridine nucleotide transhydrogenase activities have been measured in rat mammary gland at mid-lactation and the relative activities of some of the enzymes concerned with the reduction and oxidation of TPN in the mammary gland have been compared. 6. 6.These results are discussed in relation to factors controlling the levels of oxidised and reduced coenzymes in the mammary gland.