[Changes in lipase activity during pregnancy and lactation in the mouse mammary gland]

Mammary gland lipase activity of the mouse increased 45-fold compared to that in unmated gland at the 15th day of pregnancy and was 65-fold at the 20th day of pregnancy. After parturition, the activity abruptly decreased during 3 days to 38% of that at the 20th day of pregnancy. On the other hand, only a very small lipoprotein lipase activity was observed in the pregnant gland, the activity increased to 15-fold that of 20 day pregnancy at the 3rd day of lactation. These facts suggest that the mammary epithelial cells (mammary gland lipase activity was detected only in epithelial cells) utilize the fat reserved in the gland during pregnancy, but the lactating mammary epithelial cells utilize the fat supplied from the blood circulation. Mammary gland lipase activity was decreased by treatment with epinephrine which increased the fat mobilization in other adipose tissues. Hydrocortisone and prolactin decreased the mammary gland lipase activity in the glands of pregnancy and lactation. In addition, no hormone-sensitive lipase activity was observed in the mammary gland. Thus, the control of fat mobilization in the mammary gland must be different from that in other adipose tissues.