INHIBITION OF STEROID 17-ALPHA-HYDROXYLASE AND C-17,C(20)-LYASE IN THE HUMAN TESTIS BY EPITESTOSTERONE

Epitestosterone (17alpha-hydroxy-4-androsten-3-one) inhibited competitively 17alpha-hydroxylation of pregnenolone and subsequent C-17, C-20-side chain cleavage of resulting 17alpha-hydroxypregnenolone using microsomal preparations from the human testis. The inhibition constants for 17alpha-hydroxylase and C-17, C-20-lyase with 5-ene-precursors of C21-steroids were 96 and 12.4 mumol/l, respectively.