|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1996 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1995 : ¥1,400,000 (Direct Cost : ¥1,400,000)
(1) Estrogen profile during the reproductive cycle and its biosynthesis in the ovary
Estrone (E1), estradiol-17beta (E2), and a small amount of estriol (E3) were identified in the ovary by HPLC-ECD,while only E2 was found in the testis. The level of E2 in the ovary was consistently higher than E1 and it increased with sexual maturation. These results indicate that E2 may play a role in the reproductive events of the oyster and scallop. In vitro experiments demonstrated the presence of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) in the ovaries of both bivalves. The activity of 17beta-HSD in the ovary was lower in the post-spawning stage than in the early differentiating stage. The evidence for the presence of aromatase activity in the scallop ovary was obtained by 3H-water assay. The immunoreactivity against 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450 aromatase and E2 was detected in the cells along the genital tubule of the scallop ovary. It is concluded that estrogens can
be synthesized in the gonad, that their levels vary with the reproductive cycle, and that they have a role in the development of gametes.
(2) 5-HT receptor formation in the oocyte membrane during oogenesis
Serotonin (5-hydroxytryptamine, 5-HT) is a major neurotransmitter that triggers the spawning of bivalve molluscs, mainly their germinal vesicle breakdown (GVBD). The present study employed [3H] 5-HT binding assay to characterize a putative receptor on the prepared oocyte membrane from scallop and oyster and demonstrated the profile and hormonal control of 5-HT receptor formation during their oocyte growth. The dissociation constants of 5-HT on the surfaces of scallop and oyster oocytes were estimated to be 2.64 muM and 2.01 muM,respectively and the maximal binding capacity of each oocyte surface was 152 pmol/mg protein in scallop and 529 pmol/mg protein in oyster. The inhibition of [3H] 5-HT bound by various agonist and antagonist provided the pharmacological profile of 5-HT receptor in each oocyte ; a mixed profile of 5-HT1/5-HT2 in scallop and a relatively single profile of 5-HT1 in oyster. 5-HT receptor formation on the surface of scallop oocyte was induced by estradiol-17beta (E2), which was suggested to be a main reason for promoting effect of E2 on the sensitivity to 5-HT resulting in the induction of spawning. This formation obviously occurred during oocyte growth under the control by E2.