Demonstration of oxytocin release by bovine luteal cells utilizing the reverse hemolytic plaque assay

Corpora lutea (CL) of a number of species produce oxytocin (OXT). In the present experiments we studied basal, prostaglandin (PG) F2 alpha-stimulated and ascorbate-stimulated OXT release from individual bovine luteal cells utilizing the reverse hemolytic plaque assay (RHPA). Using a mixture of C- and N-terminus-specific antisera against OXT, we were able to demonstrate OXT plaque formation by individual luteal cells. CL consist of two steroidogenic cell types: large luteal cells (LLC), believed to derive from granulosa cells and to produce and secrete OXT, and small luteal cells (SLC), thought to derive from theca cells. To distinguish between these two cell types, we designated cells greater than 20 microns as LLC and those less than 20 microns as SLC. On the basis of this morphological parameter, OXT release from both LLC and SLC was demonstrable. After an incubation period of 15 h, 7% of both cell types formed OXT plaques. PGF 2 alpha and ascorbate increased the size of plaques surrounding both LLC and SLC to more than 200% and 240%, respectively (basal plaque size = 100%). The number of plaque-forming cells increased only slightly in the presence of either PGF 2 alpha or ascorbate in comparison to basal conditions. We suggest that the RHPA can be used to demonstrate peptide release from luteal cells. It is concluded that LLC may be subdivided into functional subclasses because less than 10% of bovine luteal cells release OXT. Known OXT secretagogues increased the amount of OXT released. It appears that not only LLC but also SLC secrete this peptide.(ABSTRACT TRUNCATED AT 250 WORDS)