Plasma estradiol and prolactin levels and their response to stress in two strains of rat with different sensitivities to 7,12-dimethylbenz[a]anthracene-induced tumors.

Number and development of 7,12-dimethylbenz[a]anthracene (DMBA)-induced tumors are higher in Sprague-Dawley (SD) than Long-Evans (LE) rats and restraint retards tumor development in SD rats. Prolactin levels in LE hooded and SD rats were similar at ages 62 and 93 days whereas estradiol levels were considerably lower in the LE strain at the early age only. After chronic restraint of SD rats, corticosterone levels were unaffected while estradiol levels increased and prolactin levels decreased. The low levels of estradiol, indicative of delayed maturation in the LE rats at the time of DMBA exposure, might be the cause of the resistance of this strain to DMBA-induced tumors. The effects of stress might be mediated by increased levels of estradiol and decreased levels of prolactin in the stressed rats.