Long-term aerobic swimming training by rats reduces the number of aberrant crypt foci in 1,2-dimethylhydrazine-induced colon cancer.

We determined the effect of long-term aerobic swimming training regimens of different intensities on colonic carcinogenesis in rats. Male Wistar rats (11 weeks old) were given 4 subcutaneous injections (40 mg/kg body weight each) of 1,2-dimethyl-hydrazine (DMH, dissolved in 0.9% NaCl containing 1.5% EDTA, pH 6.5), at 3-day intervals and divided into three exercise groups that swam with 0% body weight (EG1, N = 11), 2% body weight (EG2, N = 11), and 4% body weight of load (EG3, N = 10), 20 min/day, 5 days/week for 35 weeks, and one sedentary control group (CG, N = 10). At sacrifice, the colon was removed and counted for tumors and aberrant crypt foci. Tumor size was measured and intra-abdominal fat was weighed. The mean number of aberrant crypt foci was reduced only for EG2 compared to CG (26.21 +/- 2.99 vs 36.40 +/- 1.53 crypts; P < 0.05). Tumor incidence was not significantly different among groups (CG: 90%; EG1: 72.7%; EG2: 90%; EG3: 80%). Swimming training did not affect either tumor multiplicity (CG: 2.30 +/- 0.58; EG1: 2.09 +/- 0.44; EG2: 1.27 +/- 0.19; EG3: 1.50 +/- 0.48 tumors) or size (CG: 1.78 +/- 0.24; EG1: 1.81 +/- 0.14; EG2: 1.55 +/- 0.21; EG3: 2.17 +/- 0.22 cm(3)). Intra-abdominal fat was not significantly different among groups (CG: 10.54 +/- 2.73; EG1: 6.12 +/- 1.15; EG2: 7.85 +/- 1.24; EG3: 5.11 +/- 0.74 g). Aerobic swimming training with 2% body weight of load protected against the DMH-induced preneoplastic colon lesions, but not against tumor development in the rat.