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The role of prostaglandins during sexual maturation, ovulation and spermiation in the goldfish, Carassius auratus Bouffard, Maria Emilia Rachelle

Abstract

The objective of this study was to determine the involvement of prostaglandins in the sexual development of both male and female goldfish. Carassius auratus. A chromatographic method was developed to separate the different prostaglandin groups. To standardize the procedure, extraction and separation recoveries were measured using tritiated-prostaglandins. Radioimmunoassay was used to measure the PGB1, PGE1 and PGF2* in the plasma and gonad. Initially, a seasonal study was undertaken to assess the importance of prostaglandins during sexual maturation. Samples of plasma and gonad were assayed monthly for prostaglandins (from December to March) from two groups of fish, one held under natural photoperiod and the other under long photoperiod (16L:8D). Although monthly variations occurred in all three prostaglandins examined, these changes did not correlate with changes in gonadal maturationi Prostaglandins were then measured in serial plasma samples of non-gravid and ovulating female goldfish. Ovulation was induced in gravid fish by increasing the water temperature from 14° C to 20° C and by injecting human chorionic gonadotropin (HCG) . It was found that: 1) PGF2 increased over 14 fold, 12 hours after the onset of ovulation (from pre-injection levels of 300 pg/ml to more than 4,000 pg/ml); however, this increase appeared to commence immediately after ovulation. There was no change in plasma P1GF20< levels in non-gravid control fish. The concentration of PGF2^in the ovarian fluid was over 9,000 pg/ml. 2) PGE1 decreased almost three-fold between the time of HCG injection (an average of 10 hours before ovulation) and 24 hours later. The plasma PGE 1 levels in the non-gravid females were up to 20 times less than the gravid ovulating females. The concentration of PGE1 in the ovarian fluid was 630 pg/ml. 3) PGB1 levels decreased in the plasma of non-gravid and ovulating goldfish, following HCG injection. The ovarian fluid contained 300 pg/ml of PGB1. Parallel experiments were performed on male goldfish that were spermiating. There were no significant changes in plasma PGF20C within 24 hours of HCG injection, whereas PGB1 decreased slightly (as for the females), and PGE1 increased significantly 10 hours after HCG injection. The findings of this study suggest that PGF2 and PGE1 in the ovarian fluid are the agents controlling ovulation in the female goldfish and that corresponding levels in the blood contribute to other events associated with ovulation. The experiments on males indicate a possible role for PGE1 during spermiation; however, it is difficult to ascertain its precise involvement at present.

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