Endocrine Abstracts

Neuropeptide PACAP 38 expressed in steroidogenic ovarian cells of rat could be an auto- or paracrine regulator of progesterone synthesis. Moreover, it has been shown that PACAP38 can affect ovarian secretion of prostaglandins. The first and rate-limiting step in the biosynthesis of progesterone is the transfer of cholesterol into mitochondria which is facilitated by the cycloheximide-sensitive steroid acute regulator (StAR) protein. StAR protein has been established as an essential factor required for the acute response of steroidogenic cells to trophic stimulation. It seems that PACAP 38 stimulates ovarian progesterone synthesis directly or indirectly influencing on StAR protein activity. In the present study we examined the effects of cycloheximide (an inhibitor of StAR protein synthesis), actinomycine D (an inhibitor of RNA synthesis) and indomethacin (an inhibitor of prostaglandins synthesis) on progesterone release stimulated by PACAP38 from primary culture of ovarian granulosa cells obtained from adult cyclic rat (diestrus). As exogenous substrate for progesterone synthesis 20-hydroxycholesterol, which can readily diffuse across the mitochondrial membranes to the P450 scc was used. Progesterone concentrations in supernatants were assayed by RIA method. After 2 h incubation progesterone release stimulated by PACAP38 was totally inhibited by cycloheximide and partially inhibited by actinomycine D. After 24 h incubation progesterone release stimulated with PACA38 was totally inhibited by actinomycine D and also by indomethacin. These data suggest that ongoing StAR protein synthesis is partially inhibited by actinomycine D during 2 h incubation, but that during 24 h incubation continuing synthesis requires transcriptional activity.

Conclusion: in primary culture of rat ovarian granulosa cells stimulatory effect of PACAP38 on progesterone release is connected with stimulation of StAR protein synthesis and may be mediated by local synthesis of prostaglandins.

This study was supported by CMKP grant 501-1-1-28-32/05