Influence of cholera toxin on the growth and development of N-methyl- N-nitrosourea-induced rat mammary carcinomas

Abstract

Daily injections of cholera toxin (2.0 μg/rat/day) for 4 weeks to female Sprague-Dawley rats did not significantly affect the growth of palpable N-methyl- N-nitrosourea (MNU)-induced rat mammary carcinomas. Percent increase in tumor volume was + 78.8% for control animals and + 72.8% for cholera toxin treated animals. Daily treatment for 16 weeks of female Sprague-Dawley rats with cholera toxin (1.0 μg/rat/day), commencing 3 days after MNU treatment, resulted in a significant ( P < 0.05) increase in mean mammary carcinoma weight per rat at the termination of the study; mammary carcinoma incidence was not significantly affected by cholera toxin treatment. Retinyl acetate feeding (1.0 mM/kg diet) for 16 weeks significantly ( P < 0.05) reduced mammary carcinoma incidence and weight of mammary carcinoma per rat at the termination of study; feeding of retinyl acetate to cholera toxin treated rats blocked the stimulatory effect of cholera toxin on mammary carcinoma development. Thus, the reported striking inhibitory effect of cholera toxin on the growth of dimethylbenzanthracene (DMBA)-induced rat mammary carcinomas was not duplicated in our study, using the MNU-induced rat mammary carcinoma; indeed, the toxin appeared to enhance the early developmental stage of this neoplastic process.