Effects of a Potent Catatoxic Steroid, 16α‐Cyanopregnenolone, on Microsomal Metabolism of Steroid Hormones, Sterols and Bile Acids in Rats

The effect of administration of the potent catatoxic steroid 16α‐cyanopregnenolone on the microsomal hydroxylation of 4‐[4‐¹⁴C]androstene‐3,17‐dione, 4‐[4‐¹⁴C]pregnene‐3,20‐dione, [4‐¹⁴C]‐cholesterol, 7α[6β‐³H]hydroxy‐4‐cholesten‐3‐one, and tritium‐labelled taurodeoxycholic acid was studied in rats. The 6α‐, 16α‐ and 18‐hydroxylation of 4‐androstene‐3,17‐dione increased 1.5–2 times and 6β‐hydroxylation of the same substrate increased about 5 times after administration of 16α‐cyanopregnenolone to male rats. With 4‐pregnene‐3,20‐dione as substrate 2α‐hydroxylation increased twice, 2β‐ and 16α‐hydroxylation four times, and 6β‐hydroxylation nine times in male rats; the corresponding figures for stimulation of microsomal hydroxylation of 4‐pregnene‐3,20‐dione in female rats were: 2β‐hydroxylation twice, 6α‐hydroxylation nine times, 7α‐hydroxylation four times and 6α‐hydroxylation five times. 16α‐cyanopregnenolone administration led to a significant increase (1.5 times) in male rats of the activity of 17β‐hydroxysteroid oxidoreductase active on 4‐androstene‐3,17‐dione and to a significant decrease (to about 50% of the control value) in female rats of the activity of 5α‐reductase with 4‐pregnene‐3,20‐dione as substrate. The activities of 3α‐ and 3β‐hydroxysteroid oxidoreductases were not affected. After treatment with 16α‐cyanopregnenolone the 7α‐hydroxylation of cholesterol seemed to diminish but this effect was not statistically significant; no effect was seen on the microsomal 12α‐hydroxylation of 7α‐hydroxy‐4‐cholesten‐3‐one. 7α‐Hydroxalation of taurodeoxycholic acid was stimulated about twice. It is concluded that the effects of 16α‐cyanopregnenolone administration closely resemble the effects of treatment with phenobarbital and it is suggested that these drugs have a common mechanism of enzyme induction.