Synthesis and catabolism of progesterone in placentas from normotensive and severely hypertensive patients before and after parturition.

We measured the synthesis of progesterone (P) from pregnenolone and its conversion into 20 alpha-dihydroprogesterone (20 alpha-DHP) in placentas obtained from 12 patients with severe pregnancy-induced hypertension and from 24 normotensive patients. There was no significant difference between placentas from hypertensive and normotensive patients with respect to mitochondrial 3 beta-hydroxysteroid dehydrogenase: delta 5-isomerase activity both before and after labor, indicating that the capacity of this organ to synthesize P remains unchanged during labor in both groups of patients. There was a significant (p less than 0.05) difference in 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH) activity in placental supernatants obtained from normotensive patients before (853.58 +/- 293 pmoles of 20 alpha-DHP/mg of protein/hr) and after (1,156.66 +/- 280 pmoles/mg of protein/hr) labor. In contrast, 20 alpha-HSDH activity in placental supernatants obtained from hypertensive women before (644.30 +/- 236 pmoles/mg of protein/hr) and after (697.17 +/- 524 pmoles/mg of protein/hr) labor was not significantly different. As a consequence, the endogenous 20 alpha-DHP concentration, which was significantly increased after labor in placentas from normotensive women, remained unchanged in placenta from women with pregnancy-induced hypertension. These results indicate that premature activation of the P to 20 alpha-DHP pathway causing "in situ" P withdrawal does not seem to be an adequate explanation for the increased contractility and the tendency to preterm labor commonly exhibited by patients with pregnancy-induced hypertension