Investigations on the control of in vitro spontaneous brook trout (Salvelinus fontinalis) ovulation

The possible roles of follicular cyclooxygenase and cAMP in the control of in vitro spontaneous brook trout (Salvelinus fontinalis) ovulation were investigated. Brook trout oocytes that had undergone germinal vesicle breakdown and follicular separation in vivo, were incubated in vitro in the presence of indomethacin. At 3 or 30 microM, indomethacin significantly reduced the levels of PGF and PGE (measured by radioimmunoassay) in the incubation medium but did not inhibit spontaneous ovulation in vitro. Follicular cAMP levels were measured by a competitive protein binding assay, prior to and during spontaneous ovulation. cAMP levels were approximately 3.2 pmol/mg protein prior to incubation and did not fluctuate significantly from this value throughout the 24-hr incubation period. The phosphodiesterase inhibitor, 3-isobutyl-l-methyl-xanthine, significantly increased follicular cAMP levels at 1.0 and 0.1 mM. The combined results suggest that cyclooxygenase metabolites or a decrease in cAMP are not involved in the control of spontaneous brook trout ovulation in vitro. The in vitro effects of primaquine, a putative phospholipase mediator, were also investigated. At lower concentrations (0.1-0.5 mM), primaquine significantly enhanced ovulation above that observed in spontaneous controls. However, at 1.0 mM, primaquine inhibited spontaneous ovulation. Indomethacin at 3 or 30 microM did not block the stimulatory effect of primaquine observed at lower concentrations, indicating that cyclooxygenase metabolites are not involved in the stimulatory effect of primaquine on ovulation.