Effects of pituitary grafting on plasma and milk levels of prolactin, growth hormone and progesterone in mice.

Plasma and milk levels of prolactin, growth hormone (GH) and progesterone on days 12-13 of lactation were compared between C3H/He female mice grafted with isologous anterior pituitaries each under the kidney capsules 2-3 days after placing with males and intact controls. At the 1st lactation, both plasma and milk levels of prolactin were higher in the experimental mice than in the control, however, at the 2nd lactation, milk prolactin level of the former decreased to about 1/8 of that of the latter, whereas plasma prolactin level further elevated in the former. While plasma GH level was increased by pituitary grafting, milk GH level was slightly affected by the treatment at either the 1st or the 2nd lactation. There was only a small difference between the experimental and the control groups in either plasma or milk level of progesterone at the 1st and the 2nd lactations. Progesterone levels in plasma and milk were higher at the 1st lactation than at the 2nd lactation in both the experimental and the control groups. These results suggest that the transfer of plasma hormones into milk is not always free, but there may be any regulatory mechanism(s) in this process.