CELLULAR MECHANISMS FOR ORTHOVANADATE-STIMULATE PHORBOL ESTER-STIMULATE, AND CALCIUM IONOPHORE-STIMULATED PROSTAGLANDIN PRODUCTION IN BROOKTROUT (SALVELINUS-FONTINALIS) FOLLICLES

Previous studies have shown that prostaglandin (PG) production in broo k trout (Salvelinus fontinalis) follicles can be stimulated by sodium orthovanadate, phorbol-12 myristate 13-acetate ester (PMA), and the ca lcium ionophore, A23187. In the present study, the mechanisms by which these activators stimulate PG production in follicles were specifical ly investigated by examination of their effects on the release of H-3- labeled arachidonic acid (AA) from prelabeled follicles (AA release) a nd on the capacity to convert exogenous H-3-AA into prostanoids (AA co nversion) by follicle walls. 'rhe release of AA from follicles was sig nificantly stimulated by orthovanadate and A23187 after 4 h of incubat ion. Although AA release was not stimulated by PMA alone, levels of AA release in incubations with both PMA and A23187 were greater than in those with A23187 alone. In contrast, AA conversion in follicle walls was significantly increased by PMA and orthovanadate but not by A23187 alone. The results showed that 1) the calcium ionophore A23187 stimul ated ovarian PG production mainly through its effects on the release o f AA from follicles; 2) PMA enhanced follicular PG production through an increase in AA conversion in the follicle walls; and 3) orthovanada te mediated PG production by increasing both AA release and AA convers ion. In addition, PMA-, A23187-, and orthovanadate-stimulated increase s in AA release or conversion were significantly reduced by the transl ational inhibitor, cycloheximide, and the transcriptional inhibitor, a ctinomycin- These results indicate that PMA-, A23187-, and orthovanada te-stimulated AA release and AA conversion require protein synthesis a nd pretranslational activation in the follicles. Thus, the inhibition of PMA-, A23187-, and orthovandate-stimulated PG production in trout f ollicles by actinomycin and cycloheximide, demonstrated in previous st udies, may involve the inhibition of both AA release and AA conversion in the follicles.