The significance of serum 17 alpha-hydroxy progesterone as determined by radioimmunoassay

17 α-hydroxy progesterone (17 OH-P), which exists in minute quantities in blood, has been considered to be a difficult substance to determine, and its dynamics and significance have been largely unclarified. We produced a sensitive, highly specific antiserum to 17 OH-P and used it to quantitatively measure by radioimmunoassay the serum 17 OH-P levels in the peripheral blood of both non gravid and gravid females and in umbilical blood. In women with normal menstrual cycles, peripheral serum 17 OH-P levels in the preovulatory period were 309 +- 77 pg/ml, in the luteal phase 757 +- 268 pg/ml and in menopause 158 +- 71 pg/ml. In gravid women, 6 - 20 wk levels were 1.8 +- 0.3 ng/ml, at 26 wk 3.4 +- 0.9 ng/ml, at 30 wks 3.3 +- 0.5 ng/ml, at 34 wks 4.6 +- 0.3 ng/ml, and at 40 wks or term 5.2 +- 0.6 ng/ml. In cases of threatened abortion and toxemia gravidarum, levels were slightly lower than those listed above. At parturition, maternal peripheral levels were 5.9 +- 0.9 ng/ml, umbilical venous levels 16.4 +- 5.2 ng/ml, umbilical arterial levels 10.5 +- 5.8 ng/ml, and retroplacental blood levels 13.2 +- 4.8 ng/ml. From these findings, it is possible to hypothesize that in normal women, the preovulatory 17 OH-P is produced and released by the adrenal cortex, in the luteal phase by the corpus luteum, and in late pregnancy by the placenta. Further, it is possible to identify the ovulatory period, and in pregnancy the placental function. (auth.)