The ultrastructure of Paneth cells of African giant rats (Cricetomys g
ambianus), which were captured on the savanna in western Africa, was s
tudied. The Paneth cells of Cricetomys were clustered at the bottom of
crypts of the small intestine, but not of the colon. In the normal st
ate, Paneth cells had a few secretory granules showing high electron d
ensity. Small clear vesicles which are a characteristic in laboratory
albino rats were not conspicuous. Vacuolated Paneth cells and secreted
materials from the Paneth cells were frequently found. This suggests
that the secretion of Paneth cells of Cricetomys is active in the natu
ral state. No phagocytotic figures were observed. After atropine sulfa
te treatment, secretory granules increased in size and number, whereas
the electron density decreased, similar to that of goblet cell granul
es. However, the granules were not stained by alcian blue or by PAS. I
nhibition of secretory stimuli by atropine can alter the intracellular
processing of secretory substances in Paneth cells.