Immunoreactive SRIH was detected in the rat ovary (15.6 pg/mg wet weight, 520 pg/mg protein) and was localized to the granulosa cells (168 +/- 6 pg/10(6) cells). Serial dilution studies showed parallelism of the inhibition curve for synthetic SRIH-14 and those of extracts of whole ovary and media conditioned by granulosa cells. The quantity of immunoreactive SRIH released into granulosa cell conditioned media decreased with time, while the intracellular content remained relatively constant. Gel chromatography showed peaks of immunoreactivity co-eluting with SRIH-14 (38%), SRIH-28 (31%) and a high molecular weight component. The addition of synthetic SRIH-14 stimulated meiotic maturation in cumulus-enclosed rat oocytes, with dose dependency being observed at SRIH-14 concentrations between 1 and 1000 pmol/l. No evidence of pre-pro-SRIH gene expression could be demonstrated in either rat ovary or testis using both Northern analysis and reverse transcriptase/polymerase chain reaction amplification of polyadenylated RNA. SRIH may be produced in the ovary during a specific stage of ontogeny or by an alternative gene. It is also possible that SRIH is actively taken up and stored by granulosa cells without being produced locally.