Increased incidence of adjuvant arthritis in Wistar rats

The moderate incidence of arthritis in Wistar rats after inoculation of a suspension of Mycobacterium butyricum in oil increased to nearly 100% by two modifications. Inoculation with 4 week- as compared to 1 week-cultured. M. butyricum raised the incidence from 34 to 63%. Inoculation of this more arthritogenic material into the F1-descendants of M. butyricum sensitive parents raised the incidence of 96%. Also the severity of the arthritis in rats selected in that manner was higher than in non-selected rats. Treatment of arthritic rats of either source with phenylbutazone resulted in a comparable dose-related reduction of the diameters of the hind-limbs. Mating of rats with various degrees of arthritic response showed that sensitivity transmission to the F1-descendants was optimal with the most sensitive parents. Although the exact nature of the transmission has not been defined, the uniform and higher sensitivity of thus selected rats is of great value for quantitative pharmacological studies.