Stimulatory Effects of Retinoic Acid on Tumor Growth and Serum Insulin-like Growth Factor-1 in Rats Bearing Estrogen-responsive Pituitary Tumor MtT/Se

MtT/Se is one of 4 cell lines derived from an estrogen-dependent pituitary tumor, MtT/F84. The main difference between these tumor types is that MtT/F84 secretes both growth hormone (GH) and prolactin (PRL) whereas MtT/Se secretes only GH. MtT/Se grew slowly in ovariectomized (ovex) rats, but tumor growth was much faster in estrogen-treated ovex rats. Effects of dietary retinoic acid (RA) on tumor growth, serum GH and insulin-like growth factor-1 (IGF-1) levels were examined in ovex rats. Latency of tumor growth was shortened, and tumor take and weight were promoted by all- trans RA both in the presence and absence of exogenous estrogen. Serum GH and IGF-1 levels became increased in tumor-hearing rats whereas PRL levels remained unchanged. Serum IGF-1 levels exhibited a good correlation with tumor weights ( r =0.84). Our results suggest a close relationship between increase of tumor weight and stimulation of serum IGF-1 level by RA in tumor-bearing rats.