Urinary calculi in Lewis and Wistar rats

A high incidence (8/892) of urinary tract calculi was encountered during a study involving rats being fed diets supplemented with retinoids. When the incidence was compared to that observed in earlier studies without retinoid supplements and spanning several years (2/2998), the incidence in the current study was significantly higher. Possible causative factors such as age, sex, strain, diet and carcinogen or retinoid treatment have been analyzed without a clear explanation for the increased incidence. The data suggest that retinoid treatment increased the risk of stone formation, but that retinoids were less important than some other unidentified factor(s) that operated during the recent period.