Stimulation of prostaglandin synthesis in fish follicles by a phorbol ester and calcium ionophore

The effects of the phorbol ester, phorbol 12‐myristate‐13‐acetate (PMA), and the calcium ionophore, A23187, on prostaglandin E (PGE) and F (PGF) levels were investigated using incubates of brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) ovarian tissue. The combination of PMA (0.1 μg/ml) and A23187 (0.1 μg/ml) synergistically stimulated an increase in PGE and PGF levels in incubates of brook trout follicles obtained from females prior to germinal vesicle breakdown, prior to ovulation and postovulation. The highest levels were observed in incubates of follicles taken just prior to ovulation. By itself, PMA also stimulated PGE and PGF accumulation while A23187 was much less effective. A23187, but not PMA, stimulated in vitro ovulation of brook trout follicles. Both cycloheximide and actinomycin inhibited PGE and PGF accumulation in incubates of preovulatory brook trout follicles stimulated with PMA but these inhibitors did not block ovulation induced by A23187 or PMA/A23187. The effect of PMA and A23187 were tested on the following 3 yellow perch tissue preparations: 1) isolated follicles [free of extrafollicular tissue (EF)], 2) EF tissue, and 3) intact tissue (containing undissected follicles attached to EF tissue). Incubates with all tissue types were performed in the presence or absence of 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐PG, 0.1 μg/ml). PMA (0.1 μg/ml) in combination with A23187 (0.01 μg/ml) stimulated PGE and PGF accumulation in all tissue types though the greatest increase was generally observed in intact preparations. There was a lower accumulation of PGE in intact and EF tissue incubates stimulated with 17,20β‐PG and PMA. In addition, in incubates of ovarian tissue from several perch there was a higher accumulation of PGF in intact preparations stimulated by PMA or PMA/A23187 in the presence of 17,20β‐PG. The results for both species indicate that phorbol esters (PEs) can stimulate prostaglandin synthesis in follicles and, given that PEs have been shown to stimulate protein kinase C, it is possible that this enzyme is naturally involved in the control of ovarian PG synthesis in fish. It also appears that the stimulation is related to maturational stage in brook trout and steroid stimulation in yellow perch.