THE CHANGES OF NUCLEIC ACIDS CONTENT IN THE MOUSE MAMMARY GLANDS IN THE COURSE OF INVOLUTION AND THE EFFECTS OF PREGNANCY, PROLACTIN OR PROGESTERONE ON THEM

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Abstract
The nucleic acid content in the mammary glands were measured in an attempt to estimate the extent of involution during normal lactation, the effect of non-removal of milk and further the effects of administration of progesterone, prolactin or simultaneous pregnancy on the mammary glands in mice undergoing the unilateral ligation of nipples. The results obtained were as follows. 1. The decline of mammary function began to occur from day 14 of lactation to day 26 shown by the quantitative decrease of total amount of mammary parenchymal tissues and also the qualitative decrease of mammary synthetic activity. 2. Mammary gland proliferation might be more susceptible in the declining stage to such an inhibitory factor as accumulation of milk than in the peak stage of secretory activity. 4. Six or 12 days after unilateral ligation of nipples on day 14, involution due to cellular atrophy occurred in the ligated side whereas hyperplasia and hypersecretory function might be evoked in the un-ligated side, supposedly by frequent removal of milk. 5. Although atroph-ic figures otherwise occurring in the ligated side 6 days after unilateral ligation could be reversed by the administration of progesterone and prolactin or concurrent pregnancy, (the latter, most effective), the removal of secretion might be necessary to maintain the mammary gland in a full functional state.