Characterization of Chemically Tritiated Microcystin-LR and Its Distribution in Mouse

Chemically tritiated microcystin-LR (specific activity 194 mCi/mmol), purified to 95% by C-18 reverse-phase HPLC, 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 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). Unlabled 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 & unlabeled toxin was the same (75 micrograms/kg 65-90 & 65 micrograms/kg 53-80, respectively). From 3-90 min after i.p. injection of 70 micrograms/kg 3H microcystin-LR there was a slow absorption of toxin from the peritoneal cavity & 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 ug/kg). At 101 micrograms/kg, liver contained 56 plus or minus 1%, intestine 7 plus or minus 1%, kidney 0.9 plus or minus 0.2% & carcass 10 plus or minus 1% of the injected dose. Heart, spleen, lung and skeletal muscle contained 1% of the radiolabel. Microcystin, Radiochemical-labeling technique, distribution, mouse.