- Effects of weaning by surrogate mothers (ACI) on tumor development in SD rats treated with methylnitrosourea (MNU) and/or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Shiraki, K., Lu, H., Ishimura, Y., Kashiwabara, S., Uesaka, T., Katoh, O., Watanabe, H. Hiroshima J. Med. Sci. (2002)