0023-6152

AA00697606

1434389

Unrefereed

We recently demonstrated that prostaglandin E_2 (PG_2) increases osteoclastic activity and induces bone resorption in both in vitro and in vivo experiments using goldfish. In the fish reproductive period, the plasma calcium (Ca) level in female teleosts increases remarkably to make vitellogenin, which is a major component of egg protein and a Ca–binding protein. In this period, however, there is no reported relationship between PGE_2 and Ca metabolism in fish. To clarify the Ca metabolism in fish reproduction, we examined plasma PGE_2 and Ca levels and measured tartrate–resistant acid phosphatase (TRAP) activities as an indicator of osteoclastic activity in goldfish. Plasma PGE_2 levels in the reproductive stage significantly increased as compared with those in non–reproductive stages. Also, both plasma Ca and TRAP increased in the reproductive stage. Significant positive correlations were recognized between plasma Ca and the gonad somatic index (r=0.81, p<0.001), plasma Ca and plasma PGE_2 levels (r=0.635, p<0.05), and plasma Ca and plasma TRAP activities (r=0.584, p<0.05) from the analysis using samples of both reproductive and non– reproductive stages. Taking these data into consideration, we suggested that PGE_2 acts on osteoclasts and increases plasma Ca as a result of osteoclastic bone resorption, and we concluded that PGE_2 is an important hormone in Ca metabolism during fish reproduction.