THE UPTAKE OF SIMULTANEOUSLY ADMINISTERED [3H]OESTRADIOL AND [14C]PROGESTERONE BY DIMETHYL BENZANTHRACENE-INDUCED RAT MAMMARY TUMOURS

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Abstract
SUMMARY: The uptake of simultaneously injected [3H]oestradiol and [14C]progesterone by dimethylbenzanthracene-induced mammary tumours in the rat was compared with that obtained when oestradiol was injected alone. Progesterone was not taken up and/or retained by hormone-responsive adenomata and fibroadenomata to the same extent as oestradiol, and it is suggested that the mechanism of action of progesterone is different from that of oestradiol and does not involve retention by the target tissue. Progesterone did not affect the uptake of oestradiol by hormone-responsive adenomata and fibroadenomata but there was a tendency for progesterone to increase the uptake of oestradiol and/or its free steroid metabolites by hormone-unresponsive adenomata. This could be due either to the timing of the experiments or to progesterone altering the equilibrium between oestradiol levels in blood and hormone-unresponsive tumours.