Characterization of chemically tritiated microcystin-LR and its distribution in mice

Chemically tritiated microcystin-LR (spec. act. 194 mCi/mmol), purified to >95% by C-18 reverse-phase high performance liquid chromatography, exhibited the same retention time and ultraviolet absorption profile as unlabeled toxin. Acid-hydrolyzed [ 3H]-toxin yielded tritiated glutamate and β-methylasparate. Stability of the non-exchangeable [ 3H]-toxin in saline and urine was >93% after 42 days stored at 22°, 4° or −20°C. In blood, the breakdown of toxin was temperature- and time-dependent (63% at 22°C, 28 days). Unlabeled toxin was stable for >42 days stored at either 4° or −20°C in saline. The ld 50 (mouse, i.p.) of [ 3H]-microcystin-LR and unlabeled toxin was the same [75 μg/kg (65–90) and 65 μg/kg (53–80), respectively]. From 3 to 90 min after i.p. injection of 70 μg/kg [ 3H]-microcystin-LR there was a slow absorption of toxin from the peritoneal cavity and efficient accumulation in liver. The elimination half-life of the plasma concentration curve was 29 min. Tritium distribution in tissue at death or 6 hr post injection was similar for all doses (13–101 μg/kg). At 101 μg/kg, liver contained 56±1%, intestine 7±1%, kidney 0.9±0.2% and carcass 10±1% of the injected dose. Heart, spleen, lung and skeletal muscle contained