RADIOIMMUNOASSAY OF SERUM AND OVARIAN PREGNENOLONE IN IMMATURE RATS

Antiserum was generated in a rabbit against pregnenolone-16α-car-boxyethyl thioether conjugated to bovine serum albumin. The antibody, used for the assay of pregnenolone in extracts of serum and tissue homogenates, proved sufficiently specific to allow direct assay of extracts without chromatography. Sensitivity, defined as that point on the standard inhibition curve equal to the lower value 2 SD from the mean radioactivity bound to antibody in the buffer control (zero hormone) tubes, was 0.02 ng. The accuracy was confirmed by the recovery of known amounts of pregnenolone added to serum and aqueous buffer medium. The inter- and intra-assay coefficients of variation were respectively 10.6% and 9.1%. Specificity was confirmed by checking cross reactivity of various steroids and by finding comparable pregnenolone levels in samples before and after chromatography. The administration of aminoglutethimide to rats resulted in the reduction of ovarian and serum pregnenolone levels. Administration of isoxazole, on the other hand, caused an increase in both serum and tissue pregnenolone levels. These findings are in agreement with accepted views of the action of these two metabolic blocking agents. © 1979.