Δ5,3β hydroxysteroid dehydrogenase activity in cat placental labyrinth: Evolution during pregnancy, subcellular distribution

Abstract

The capability of the cat placenta to synthesize progesterone was studied by measurement of the biochemical activity of Δ5-3β-hydroxysteroid dehydrogenase (Δ5, dehydrogenase (δ5, 3β HSD). This activity was assessed by measuring of the rate of [3H]-progesterone formation from [3H]-pregnenolone through use of a double isotope dilution method. The enzymatic activity was distributed equally between mitochondrial and microsomal fractions, although the specific activity was higher in the microsomal fraction as compared to the mitochondrial fraction. The specific activity in the homogenate was 28.2 ± 1.16 nmol/min/mg protein between Days 28-32 of gestation; it increased to 49.3 ± 1 nmol/min/mg protein between Days 50-62. The total enzymatic activity increased greatly in the last stage of gestation due to the increase in placental weight. These results indicate that placental production of progesterone increases significantly during the latter part of gestation and explain the fact that ovariectomy after Day 49 of pregnancy does not alter the duration of pregnancy.