Tupaias (tree shrews)--a new animal model for gallstone research; first observations of gallstones.

In tupaias, rat-sized mammals with phylogenetic affinities to insectivores and primates, gallstones can be induced by diet. Twenty per cent butter, 20% sucrose, and 1% cholesterol, added to the standard diet, caused massive stone formation in 11 of 16 male tupaias. In the other five animals the bile contained cholesterol crystals or few stones, liquid crystals, and fat droplets. The stones were composed almost totally of cholesterol and closely resembled those described in squirrel monkeys, which had been fed a similar diet. The diet caused neither a change in body weight nor serious diarrhea or any other conceivable illness of the experimental animals. Only liver weight and liver fat content increased. No spontaneous gallstones were found in 200 healthy animals, which had been fed standard diet. In sick animals cystine stones or a soft concrement of undefined organic material were observed. Tupaia, thus, represents a suitable and convenient animal model for gallstone research.