Competing circadian effects of methylprednisolone and rat weight, light chains, immunocytoma size and survival.

Eighty-four singly housed LOU rats, 43 males and 41 females, were studied (under conditions standardized for rhythmometry) for the effect of methylprednisolone sodium succinate (MP) upon a transplantable immunocytoma. Body temperature was monitored as a host reference rhythm while light chain excretion and tumor size were monitored to determine an effect upon the tumor. The MP, dissolved in a sweet solution, was consumed by the rats without any statistically significant shift in acrophase of the circadian temperature rhythm. Time dependent effects of MP treatment were observed with respect to 1) tumor size decrement and 2) the survival of treated animals, as compared to untreated animals.