A radioimmunoassay for measuring 3α-hydroxy-5α-pregnan-20-one in plasma has been developed. Polyclonal antibodies were raised in rabbits against 3α-hydroxy-20-oxo-5α-pregnan-11α-yl carboxymethyl ether coupled to bovine serum albumin. 3α-Hydroxy-5α-pregnan-20-one was purified from ether extracts of plasma by high-performance liquid chromatography. These antibodies were then used for the radioimmunoassay of this centrally active progesterone metabolite in rat and human plasma. 3α-Hydroxy-5α-pregnan-20-one was detected in plasma from female rats on the day ofestrus (2.0 to 9.3 ng/ml) and in the plasma of women during the luteal phase of the menstrual cycle at levels ranging from 0.25 to 2.5 ng/ml. The latter was highly correlated with plasma progesterone levels.
- plasma RIA