Effects of Time and Duration of Progesterone Administration on Mammary Tumours Induced by 712-Dimethylbenz(a)Anthracene in Sprague-Dawley Rats

摘要

A reduction in tumour yield was apparent when progesterone administration was begun 25 days before feeding 7,12-dimethylbenz(a)anthracene (DMBA). This effect was most obvious when the duration of hormone administration was brief. Continuation of progesterone for some time after feeding DMBA caused a progressive diminution of the inhibitory effect, and 135 days of continuous hormone treatment entirely abolished the effects of 25 days pretreatment with the hormone.In contrast, when progesterone injections were begun 2 days after feeding DMBA, there was a trend towards enhancement of tumour yield. Continuous hormone administration appeared more effective than shorter treatment regimens.