Abstract
The mammary gland lipase activity of the mouse mammary gland increased to 45-fold of that in unmated gland at 15th day of pregnancy and reached to 65-fold at 20th day of pregnancy. After parturition, the activity abruptly decreased during 3 days to 38% of that at 20th day of preagnancy. On the other hand, only a very small lipoprotein lipase activity was observed in the pregnant gland, but after parturition, that activity increased to 15-fold of that in 20-day-pregnant one at 3rd day of lactation. These facts suggest that the mammary epithelial cells (the mammary gland lipase activity was detected only in epithelial cells) utilizes the fat reserved in the gland in preagnancy, but the lactating mammary epithelial cells utilizes the fat supplied from the blood circulation. The mammary gland lipase activity was decreased by the treatment with epinephrin which increases the fat mobilization in other adipose tissues. In addition, no hormone-sensitive lipase activity was observed in the mammary gland. Thus, the control of fat mobilization must be different in the mammary gland from that in other adipose tissues. Insulin decreased the mammary gland lipase activity in the gland of the unmated mouse. Prolactin increased the enzyme activity and the effect of prolactin was enhanced in the presence of insulin. Hydrocortisone and prolactin decreased the activity in the glands of pregnancy and lactation. The difference in the responsibility to these hormones in the gland of unmated mouse and in those of pregnant and lactating one may due to the fact that the glands in latter two stages already received the hormone actions.
