Endocrinology. 1986 Apr;118(4):1266-70.  

The steroid C-17,20-lyase complex in isolated Graafian follicles: effects of
human chorionic gonadotropin.

Eckstein B, Tsafriri A.

Androstenedione synthesis was studied in isolated rat preovulatory follicles and
compared with that of rat testicular tissue using [14C]progesterone together
with 17 alpha-hydroxy-[3H]progesterone as substrates in the presence of NADH or
NADPH as cofactors. The amount of androstenedione formed was measured by
addition of carrier, reisolation, and crystallization to constant specific
activity. The labeling patterns of androstenedione and 17
alpha-hydroxyprogesterone (17-OHP) confirmed that both tissues preferentially
catalyzed the synthesis of androstenedione from progesterone rather than from
17-OHP. It appears, therefore, that free 17-OHP was not an obligatory
intermediate in this reaction. When hCG (5 IU) was administered sc and the
follicles were isolated 3 h later, androstenedione synthesis was inhibited
whether NADH or NADPH was added as cofactors. By contrast, 17-hydroxylase
activity was inhibited only with NADH as cofactor. Hence, the gonadotropin, with
NADH as cofactor, specifically reduced progesterone incorporation into
androstenedione without affecting incorporation of 17-OHP. Thus, hCG appears to
affect androstenedione production from progesterone at two different sites of
the lyase complex.

PMID: 3485044 [PubMed - indexed for MEDLINE]