Effects of time and duration of progesterone administration on mammary tumours induced by 7,12-dimethylbenz(a)anthracene in Sprague-Dawley rats.
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.
D000818:Animals; D001551:Benz(a)Anthracenes / Q000037:antagonists & inhibitors; D003864:Depression, Chemical; D004357:Drug Synergism; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
D001551:Benz(a)Anthracenes; D011374:Progesterone