Endogenous concentration of progesterone and 2 slpha -pregnane-3,20-dione in rat decidula tissue.

The endogenous concentration of progesterone (P) and 5 alpha-pregnane-3,20-dione (5AP) were determined in the dedicual tissue of mature rats by radiommunoassay. On the 4th day of pseudopregnancy the uterine concentration was 281 +/- 28 ng/g for P and 266 +/- 41 ng/g for 5AP. Horns were traumatized on the 4th day of pseudopregnancy. On the 4th day following trauma the endometrial concentration of P was 100 +/- 7 ng/g and for 5AP was 104 +/- 10 ng/g. Plasma concentrations were 35.5 +/- 4.1 ng/g. For P and 16.1 +/- 4.9 ng/ml for 5AP. When one horn was removed and the contralateral horn was traumatized, there was direct correlation between the endogenous concentrations of P and 5AP in the previously removed utraumatized horn and the amount of decidual tissue in the contralateral horn 4 days following trauma (r2 = .8949). These experiments indicate the endometrial response to progesterone is a complex process determined in part by local metabolsm and the ability of the uterus to concentrate P.