Estrogen effect on the seasonal levels of catecholamines in the scallop Patinopecten yessoensis

1. Seasonal variations of catecholamine levels in the various tissues of Patinopecten yessoensis and the effect of in vivo administration of estradiol-17β (E₂) on those levels were investigated using high performance liquid chromatography (HPLC). 2. No significant differences between endogenous noradrenaline and dopamine levels in the female and those in the male were observed. Their gonadal levels showed the lowest value during the active spawning period and increased after spawning, and continued to increase through the early differentiating stage. 3. A significant decrease in catecholamine levels were observed 22 hr after E₂ administration in the gonad. 4. These results suggest that seasonal variations of catecholamine levels in P. yessoensis are implicated in the reproductive cycle and that E₂ may play a role in the regulation of catecholamine levels in the gonad.