INACTIVATION OF PROGESTERONE BY CELLULAR FRACTIONS OF RAT LIVER AND KIDNEYIN VITRO1

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Abstract
Fresh rat liver and fresh rat kidney were rapidly minced and homogenized. Repeated refrigerated centrifugations of each homogenate, each time at higher speeds, yielded fractions which consisted, respectively, chiefly of nuclei and coarse debris, mitochondria, microsomes, and final supernatant. Each fraction as well as an aliquot of the original homogenate was incubated at 37° C with progesterone. After 60, 30, or 5 minutes the incubation was ended and the residual progestin was extracted and bio-assayed. In general, most of the hormone had been inactivated, the liver nuclear fraction being the only one in which as much as 50–75% of the original hormonal activity consistently remained. Separate assay of the protein “bound” fraction revealed that “binding” was not a significant mechanism of inactivation. In vitro inactivation of progesterone by rat kidney as well as by rat liver was demonstrated.