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

Chemically tritiated microcystin-LR (spec. act. 194 mCi/mmol), purified to greater than 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 beta-methylasparate. Stability of the nonexchangeable [3H]-toxin in saline and urine was greater than 93% after 42 days stored at 22 degrees, 4 degrees or -20 degrees C. In blood, the breakdown of toxin was temperature- and time-dependent (63% at 22 degrees C, 28 days). Unlabeled toxin was stable for greater than 42 days stored at either 4 degrees or -20 degrees C in saline. The LD50 (mouse, i.p.) of [3H]-microcystin-LR and unlabeled toxin was the same [75 micrograms/kg (65-90) and 65 micrograms/kg (53-80), respectively]. From 3 to 90 min after i.p. injection of 70 micrograms/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 micrograms/kg). At 101 micrograms/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 less than 1% of the radiolabel.