Role of hormones on the induction of retinoic acid binding protein in mouse mammary gland organ culture.

Influence of various hormones on the induction of cellular retinoic acid binding protein (CRABP) was investigated in the mouse mammary gland organ cultures. Thoracic pairs of mammary glands from the BALB/c mice were cultured for seven days in the presence of various hormones in CMRL medium at 37 degrees C under 50% O2, 5% CO2 and 45% N2 atmosphere. There was a modest increase of mammary CRABP by insulin (I) + prolactin (P), however, addition of progesterone (Pg) or estrogen (E) + Pg to the medium resulted in a dramatic increase in the CRABP. Aldosterone (A) + hydrocortisone (F), in addition to I + P, which promotes differentiation to an extent similar to that of I + P + E + Pg did not have any influence on the induction of CRABP. These results indicate that prolactin and/or Pg in the medium can increase the concentration of CRABP in the mammary gland in vitro. From the results presented in this report, as well as previous work by other investigators, it is concluded that the biological response to retinoids in the mammary tissues cannot be correlated with the absolute concentration of CRABP in the cells. However, the biological response may be dependent upon both the ability of the target organ cells to metabolize the retinoid and to have minimal concentration of CRABP for binding to the active metabolite. The functional significance of hormone-induced CRABP is presently unknown.