Craig A. Winkel

Conversion of progesterone to deoxycorticosterone in the human fetus: Steroid 21-hydroxylase activity in fetal tissues

Steroid 21-hydroxylase activity was assayed in microsome-enriched fractions prepared from homogenates of a number of human fetal tissues. The activity of this enzyme was demonstrable in several tissues in addition to the adrenal, kidney, and gonads. The highest specific activities of the enzyme were found in adrenal, skin, kidney and urinary bladder. In addition, 21-hydroxylation of progesterone was demonstrated in microsome-enriched preparations of pancreas, thymus, spleen, testis and ovary. Thus a number of fetal tissues may contribute to the formation of deoxycorticosterone, which is present in high concentrations in plasma of the human fetus compared with those in men and nonpregnant women. Moreover, the potential for the in situ formation of DOC in presumed tissue sites of mineralocorticosteroid action was demonstrated.

Conversion of progesterone to deoxycorticosterone in guinea pig spleen: an animal model for the study of steroid 21-hydroxylase activity in extra adrenal sites.

Steroid 21-hydroxylase activity has been demonstrated, previously, in microsome-enriched fractions prepared from a number of human fetal tissues. The finding that this enzyme activity was present in thymus and spleen is suggestive of the possibility that deoxycorticosterone is important in regulation of immunological processes. In the present investigation, we characterized steroid 21-hydroxylase activity in microsome-enriched preparations of guinea pig spleen. The activity of the enzyme was linear with time for 40 min and with protein concentrations up to 4.8 mg X ml-1 incubation mixture. The apparent Km of the enzyme for progesterone was 0.405 microM. Thus, the potential exists for the biosynthesis of DOC from progesterone in the spleen of the guinea pig as well as in the spleen of the human fetus. Therefore, the guinea pig may be an appropriate animal model for the study of the regulation of steroid 21-hydroxylase activity in the spleen as well as a model for the study of the role of this enzyme in immunologic processes.

The origin of and metabolic fate of deoxycorticosterone and deoxycorticosterone sulfate in pregnant women and their fetuses.

DOC and DOC-SO4, which are present in large amounts in the blood of pregnant women, are derived from sources other than maternal adrenal. Other investigators demonstrated that treatment of near-term pregnant women with ACTH or dexamethasone did not cause alterations in the blood levels of DOC. To define the source(s) of DOC and DOC-SO4 in plasma of pregnant women, we evaluated the conversion of plasma progesterone (P) to DOC in extraadrenal sites. DOC is formed from plasma P and, provided that the pregnancy is one characterized by the usual large production of estrogen, DOC production in a given woman is proportional to the level of P in plasma. Unlike other steroid conversions or interconversions, however, the fractional conversion of P to DOC among apparently normal persons varied widely 0.011 +/- 0.003 (mean +/- SEM, n = 40, range = 0.001 to 0.030). In women pregnant with a normal living fetus, the product of the production rate of P and the fractional conversion of P to DOC is sufficient to account for the majority of DOC produced in the mother. There may be a second source of DOC, i.e. the transfer of DOC from the fetal to the maternal compartment in a manner that involves (a) direct transfer of DOC by way of trophoblast and (b) by desulfurylation of DOC-SO4 from fetal umbilical arterial plasma in trophoblast and thence transfer of DOC liberated in trophoblast to the maternal compartment. Presently, it is clear that DOC-SO4 in blood of pregnant women is not derived from plasma DOC; and there is little or no evidence in support of the proposition that DOC-SO4 (as a sulfoconjugate) is transferred from the fetal to the maternal compartment because of placental hydrolysis to DOC. Among the extraadrenal tissue sites identified as those in which 21-hydroxylation of plasma P could be effected are some also believed to be tissue sites of mineralocorticosteroid action, viz, kidney, aorta, thymus, and spleen. Quantitatively, the origin of DOC in the fetus is not as clear as in the maternal compartment; yet, many tissues of the fetus have been identified in which both steroid 21-hydroxylase and 21-hydroxysteroid sulfotransferase activity are present. Thus, in the human fetus, extraadrenal as well as adrenal production of DOC and DOC-SO4 are possible.

Mineralocorticosteroids and pregnancy: Regulation of extra-adrenal deoxycorticosterone production by estrogen

During pregnancy, deoxycorticosterone (DOC) in maternal plasma is produced principally by 21-hydroxylation of circulating progesterone in a number of extra-adrenal tissues. Estrogen acts, directly or indirectly, to increase the transfer constant of conversion of progesterone to DOC. In this study, we evaluated the regulation of DOC production during pregnancy by considering the plasma levels of progesterone, the kinetics of extra-adrenal steroid 21-hydroxylase, and the stimulation of the conversion of progesterone to DOC by estrogen.