Balish E, Shih C N, Croft W A, Pamukcu A M, Lower G, Bryan G T, Yale C E
J Natl Cancer Inst. 1977 Apr;58(4):1103-6. doi: 10.1093/jnci/58.4.1103.
Germfree and conventional Sprague-Dawley rats were assessed for their susceptibility to intrarectally injected N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N-methyl-N-nitrosourea (MNU). Adenocarcinoma of the colon was induced in germfree and conventional rats by both MNNG and MNU. The colons of germfree rats were more susceptible to the direct-acting carcinogens, as manifested by earlier morbidity and development of colon tumors (50% tumors within 30-35 wk), than were those of conventional rats (50% colon tumors within 48-50 wk). Germfree and conventional male rats were more susceptible to the carconogens than were their female germfree and conventional counterparts. Young (30 days old at the start of the experiment) germfree rats developed colon tumors more quickly (15-20 wk) than did older (60 days) germfree rats after intrarectal injections of MNNG. No colon tumors were observed in germfree and conventional rats after 75 weekly intrarectal injections with a buffer. Transplantation of an adenocarcinoma induced with MNU in a female rat to germfree and conventional rats showed that it was easily transplantable, required no immunosuppression, and had essentially the same morphologic characteristics as did the primary tumor.
对无菌和普通的斯普拉格-道利大鼠评估其对经直肠注射N-甲基-N'-硝基-N-亚硝基胍（MNNG）或N-甲基-N-亚硝基脲（MNU）的易感性。MNNG和MNU均可在无菌和普通大鼠中诱发结肠癌。无菌大鼠的结肠对直接作用致癌物更敏感，表现为比普通大鼠更早发病和出现结肠肿瘤（30 - 35周内50%出现肿瘤），普通大鼠则是在48 - 50周内50%出现结肠肿瘤。无菌和普通雄性大鼠比其雌性无菌和普通对应大鼠对致癌物更敏感。实验开始时30日龄的年轻无菌大鼠经直肠注射MNNG后比60日龄的老年无菌大鼠更快出现结肠肿瘤（15 - 20周）。无菌和普通大鼠每周经直肠注射缓冲液75次后未观察到结肠肿瘤。将一只雌性大鼠中由MNU诱发的腺癌移植到无菌和普通大鼠，结果显示其易于移植，无需免疫抑制，且与原发肿瘤具有基本相同的形态学特征。
