Effect of prolactin, progesterone, pregnancy and lactation on DNA synthesis and DNA polymerase activities in rabbit mammary gland

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Abstract
DNA synthesis and DNA polymerase-α, -β and -γ activities in the rabbit mammary gland were studied during hormone-directed cellular growth. It was found that during pregnancy, early lactation and after injection of prolactin, changes in the activity of DNA polymerase-α paralleled the rate of mammary gland DNA synthesis. It was also found that the amount of polymerase-α activity bound to isolated chromatin depended on the physiological state of the animal. During pregnancy and early lactation changes in the activity of chromatin-bound enzyme correlated directly with the rate of DNA synthesis (r = 0·83). Moreover, in virgin rabbits treated with prolactin the activity of chromatin-bound DNA polymerase-α increased markedly at the same time as the DNA-synthetic rate increased. No correlation of the DNA-synthetic rate was found with the activity of soluble (cytosolic) DNA polymerase-α or with the activity of soluble or chromatin-bound DNA polymerases-β and -γ. On the basis of these results it is suggested that in the developing mammary gland both the activity and cellular distribution of DNA polymerase-α might be subject to hormonal regulation. J. Endocr. (1987) 114, 139–145