11 beta-Hydroxysteroid dehydrogenase (11 beta-OHSD) catalyses the reversible conversion of corticosterone to inactive 11-dehydrocorticosterone, thus regulating glucocorticoid access to mineralocorticoid and perhaps glucocorticoid receptors in vivo. 11 beta-OHSD has been purified from rat liver and an encoding cDNA isolated from a liver library. However, several lines of indirect evidence suggest the existence of at least two isoforms of 11 beta-OHSD, one found predominantly in glucocorticoid receptor-rich tissues and the other restricted to aldosterone-selective mineralocorticoid target tissues and placenta. Here we have examined the effects of chronic (10 day) manipulations of sex-steroid levels on 11 beta-OHSD enzyme activity and mRNA expression in liver, kidney and hippocampus and present further evidence for the existence of a second 11 beta-OHSD isoform in kidney. Gonadectomized male and female rats were given testosterone, oestradiol or blank silicone elastomer capsules, controls were sham-operated. In male liver, gonadectomy+oestradiol treatment led to a dramatic decrease in both 11 beta-OHSD activity (69 +/- 8% decrease) and mRNA expression (97 +/- 1% decrease). Gonadectomy and testosterone replacement had no effect on male liver 11 beta-OHSD. However, in female liver, where 11 beta-OHSD activity is approximately 50% of that in male liver, gonadectomy resulted in a marked increase in 11 beta-OHSD activity (120 +/- 37% rise), which was reversed by oestradiol replacement but not testosterone treatment. In male kidney, gonadectomy+oestradiol treatment resulted in a marked increase in 11 beta-OHSD activity (103 +/- 4% rise). By contrast, 11 beta-OHSD mRNA expression was almost completely repressed (99 +/- 0.1% decrease) by oestradiol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)