Enhancement by caffeine of mammary gland lobulo-alveolar development in mice: a function of increased corticosterone

Previously we have reported that the stimulatory effect of caffeine on lobulo-alveolar development in the mammary glands of female Balb/c mice is not due to a direct action of the drug on the mammary gland but appears to be due to a caffeine-induced alteration of a yet to be defined systemic physiological process (VanderPloeg et al., J Environ Pathol Toxicol Oncol 11:177-189, 1992). In the present study, we administered caffeine (via the drinking water, 500 mg/L) to ovariectomized, estrogen- and progesterone-treated Balb/c mice. After 30 days of caffeine treatment, a significant (p < 0.001) enhancement of lobulo-alveolar development in the mammary glands of the hormone-treated mice, compared with hormone treated control mice, was observed. Six blood components, that is, total free fatty acids (FFA), glucose, IGF-1, insulin, prolactin and corticosterone, each known to enhance normal or neoplastic mammary gland growth processes in mice or rats, were quantitatively assessed in the blood of these mice. Of these six blood components, only corticosterone (p < 0.001) increased significantly in the caffeine-treated mice. These results provide evidence that the enhancement of mammary gland lobulo-alveolar development in mice by chronic consumption of caffeine appears to be a result of caffeine-enhanced secretion of corticosterone.