CELLULAR RETINOIC ACID-BINDING PROTEIN(II) PRESENCE IN RAT UTERINE EPITHELIAL-CELLS CORRELATES WITH THEIR SYNTHESIS OF RETINOIC ACID

Vitamin A (retinol) and retinoic acid are necessary for the maintenanc e of the female reproductive system of higher animals. Our previous wo rk has demonstrated cell specific expression of cellular retinoic acid -binding protein (CRABP) and cellular retinoic-acid binding protein(II ) [CRABP(II)] in the uterus of the rat. CRABP(II) expression was shown to be induced in the uterine surface epithelial cells by treatment of prepubertal rats with pregnant mare serum gonadotropin (PMSG). Here w e report that, after PMSG treatment, collected uteri had markedly high er levels of retinoic acid than did the uteri of prepubertal rats trea ted with the control vehicle, Smooth muscle, stromal, and epithelial c ells were then cultured from uteri from such animals and provided with retinol or with the retinol/retinol-binding protein complex. Retinoic acid production, analyzed by high-performance liquid chromatography, was observed for the epithelial cells from the uteri of prepubertal an imals treated with PMSG, cells previously shown to express CRABP(LI) a nd confirmed here to continue to express it in culture. Little or no r etinoic acid was produced by cultured epithelial cells from the prepub ertal uteri [shown previously to be negative for CRABP(II)] or by smoo th muscle and stromal cells taken from uteri of prepubertal or PMSG-tr eated rats (shown previously to express CRABP). Retinoic acid producti on by uterine epithelial cells [and CRABP(II) expression] was also obs erved if the prepubertal rat was treated with estrogen before cell col lection. At no time did cells expressing CRABP exhibit significant ret inoic acid synthesis. Thus, this system revealed an important differen ce in retinoid metabolism between cells expressing CRABP and CRABP(II) and suggests CRABP(II) may participate in retinoic acid production an d/or secretion.