The hormonal regulation of cholesterol side-chain cleavage cytochrome P450, adrenodoxin, and their messenger ribonucleic acid expression in bovine small-like and large-like luteal cells: relationship with progesterone production.

The bovine corpus luteum contains two steroidogenic cell types, small and large luteal cells. The present study aimed to examine molecular mechanisms regulating progesterone (P4) production in long term cultures. The content of the side-chain cleavage (SCC) enzymes cytochrome P450scc and adrenodoxin (ADX) and the steady state availability of their mRNAs were determined and compared to P4 production in each of the luteal cell types. Small-like (SLC) and large-like (LLC) luteal cells were obtained by incubating theca interna and granulosa cells with forskolin and insulin. Upon luteinization, LLC expressed 2- to 3-fold higher amounts of both SCC enzyme mRNAs than did SLC. Moreover, 8 days after stimulant removal, LLC retained their P4 production capacity, expressed P450scc and ADX mRNAs, and contained these proteins. Nevertheless, the presence of the luteinizing agents in LLC culture medium was required for maximal expression of SCC enzymes. In the SLC, P4 production, P450scc and ADX content, and their mRNAs showed a much stronger dependence on chronic cAMP (and insulin) stimulation. In SLC, stimulant removal was accompanied by a sharp decrease (95% reduction) in P4 production, P450scc and ADX enzyme content (57% and 90% reduction, respectively), and their mRNAs (90% and 95% reduction, respectively). However, their steroidogenic capacity could be restored by forskolin and insulin replenishment. Interestingly, P4 production by both luteal cells types was reflected better in ADX than in P450scc content. These observations emphasize the contribution of the large luteal cell to P4 output, which may become crucial when hormonal support of the corpus luteum is deficient.