Morphological observations of diarrhea in mice caused by aplysiatoxin, the causative agent of the red alga Gracilaria coronopifolia poisoning in Hawaii.

Diarrhea caused by the red alga Gracilaria coronopifolia poisoning was investigated in mice. The target site of a lethal dose was the whole small intestine where the toxin caused bleeding, resulting in hemorrhagic shock. With a sublethal dose, diarrhea appeared about 4.5 h after i.p. injection and continued for about 4 h intermittently. The site of diarrhea was the large intestine, where the submucosa first accumulated fluid from edema. Then the fluid moved into the lamina propria, the surface epithelial cells were broken and the fluid flowed into the lumen. Finally, diarrheic components apparently originating from capillaries were secreted directly into the lumen. The cecum was the main target of the diarrhea. After the diarrhea ended, the number of goblet cells was increased remarkably and many fine cracks were left on the surface of the epithelium.