The incorporation of [2-14C] glycine and [6-14C] orotic acid into the acid-soluble ribonucleotides and ribonucleic acids of the rat mammary gland.

It has been reported (Wang & Greenbaum, 1960) that there is an increase in both the total amount and the concentration of the acid-soluble ribonucleotides of the rat mammary gland over the period from pregnancy to late lactation and it was thought that these changes probably reflected the increase of metabolic activity associated with the onset of lactation. Over the same period the RNA of the gland also increases, particularly in the microsome fraction (Slater & Planterose, 1958). It was suggested that this increase was related to the greater rate of protein synthesis consequent on the greater rate of milk production. However, there are, as yet, no data available on the turnover rates of the RNA and acid-soluble ribonucleotides of the gland. The data presented here indicate that, over the period studied, there is an increased synthesis of the acid-soluble purine and uracil nucleotides, and also an initial increase in the total incorporation of the two precursors used into RNA at parturition, but later there follows a decrease as lactation advances.