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Summary
The effects of serotonin, dopamine, and prostaglandins E2 and F2α (PGE2, PGF2α) on the release of oocytes, as well as reinitiation of meiosis in them, were evaluated for the scallop Argopecten purpuratus. Germinal vesicle breakdown, signalling reinitiation of meiosis in oocytes, occurs just prior to their release to the environment and was seen in histological sections of female gonad and kidney, made at the time when the scallop appeared ready to release the female gametes. Studies of the effects of the amines and prostaglandins were made in vitro with fresh sections of the female gonadal sector using varied concentrations and exposure times. Serotonin (10−6 to 10−4 M) increased the number of oocytes released, and these numbers increased in relation to the time of incubation. Release of oocytes, relative to control, was reduced by dopamine (10−6 to 10−4). The effects of the amines on oocyte release were blocked by pre-incubation with indomethacin, an inhibitor of PG synthesis. PGE2 (10−6M) increased oocyte release; PGF2α (10−6M) did not affect this process. Serotonin and the two prostaglandins increased the rupture rate of germinal vesicles, a process unaffected by the presence of dopamine. The results suggest separate mechanisms for the regulation of the processes of egg release and reinitiation of meiosis in this mollusc.
