Biliary excretion of tetrodotoxin in the cultured pufferfish Takifugu rubripes juvenile after intramuscular administration.

Marine pufferfish of the family Tetraodontidae accumulate a considerable amount of tetrodotoxin (TTX), mainly in the liver and ovary. The detailed distribution of TTX in pufferfish body tissues, however, remains poorly understood. Here we investigated the tissue distribution and biliary excretion of TTX in cultured pufferfish Takifugu rubripes juveniles (6-month-old, 81.5 ± 2.0 g body weight) for 24 h after intramuscular administration of 0.25 μg TTX/g body weight into the caudal muscle. The blood TTX concentration was 0.53 ± 0.15 μg/mL at 1 h, and gradually decreased to 0.05 ± 0.01 μg/mL at 24 h after administration (p < 0.05). The TTX concentration in the liver declined from 1.59 ± 0.10 μg/g at 1 h to 0.48 ± 0.21 μg/g at 24 h (p < 0.05). In contrast, the TTX concentration in the skin increased from 0.27 ± 0.04 μg/g at 1 h to 0.48 ± 0.08 μg/g at 24 h (p < 0.05). The concentration of TTX in the bile remarkably increased from 0.08 ± 0.03 μg/mL at 1 h to 0.39 ± 0.05 μg/mL at 8 h (p < 0.05) and remained at almost the same level at 24 h. These findings indicate that TTX was excreted from the liver into the gallbladder bile in the pufferfish T. rubripes juveniles.