A cytochemical section bioassay for plasma trilostane: an orally active inhibitor of 3 beta-hydroxysteroid dehydrogenase activity.

Trilostane is a competitive inhibitor of 3 beta-hydroxysteroid dehydrogenase activity in vitro and an orally active inhibitor of steroidogenesis in vivo. A cytochemical section bioassay for this drug (4 alpha, 5-epoxy-17 beta-hydroxy-3-oxo-5 alpha-androstane-2 alpha-carbonitrile) in human plasma has been developed. The assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the corpus luteum of unfixed tissue sections (6 micron) of the mature dioestrous rat ovary. Trilostane is extracted from plasma by a simple chloroform procedure. The standard curve (0.15-2.5 mumol/l pure trilostane) exhibits a four-fold change in 3 beta-HSD activity and is constructed in the presence of extract from control plasma pools. The detection limit of the plasma assay is 2 mumol/l trilostane after allowing for dilution effects and recovery losses. This level gives a significantly different response from the zero quality control (P less than 0.05) and has an inter-assay coefficient of variation of less than 15%. No false positives have been recorded to date and the majority of samples from subjects receiving therapeutic doses of the drug have levels of greater than 2 mumol/l. Intra- and inter-assay coefficients of variation using both plasma quality controls and unknown samples are 4% (n = 15) and 13.9% (n = 27) respectively. Recovery is 80 +/- 9% (n = 13) and 79 +/- 10% (n = 10) for plasma quality controls containing 12 and 4.8 mumol/l trilostane respectively. Dilutions (up to 1:5) of plasma extracts are parallel to the standard curve and the assay throughput is approximately 16 samples/week technician.(ABSTRACT TRUNCATED AT 250 WORDS)