Biological half-life, organ distribution and excretion of 125-I-labelled toxic peptide from the blue-green alga Microcystis aeruginosa

M. aeruginosa is a bloom-forming cyanobacterium which is common in fresh-water lakes. It contains a potent hepatotoxin which when purified has been shown to be a heptapeptide of molecular weight 1019. The toxin was iodinated with 125I using the lactoperoxidase method, the labelled toxin administered intravenously to adult female rats and the half-life and organ distribution measured. The blood half-life after redistribution into extracellular pools was 42 min. The liver and kidneys showed accumulation of 21.7 +/- 1.1 and 5.6 +/- 0.2% of the dose respectively after 30 min. Little accumulation was observed in other organs and tissues. Small-intestinal contents and urine contained 9.4 +/- 6.1 and 2.9 +/- 1.2% of the dose respectively after 120 min. It was concluded that the liver is the main target organ for both accumulation and excretion of the toxin.