EXERCISE DURING PUBERTY AND NMU INDUCED MAMMARY TUMORIGENESIS IN RATS

Previously we have shown that exercising rats prior to administration of 50 mg NMU/kg (high dose) significantly decreased tumor multiplicity , but not incidence or latency. We hypothesized that the dose of NMU s aturated the system such that the exercise intervention was overshadow ed. Therefore, the purpose of this investigation was to determine if e xercise would have a more pronounced effect with a moderate dose of 37 .5 mg NMU/kg. Female Sprague Dawley rats were, divided into sedentary and exercised groups. The rats were exercised five times per week from 21 to 50 days of age on a progressive treadmill training program with a final workload of 18 m/min at 15% incline for 60 min a day. At 50 d ays of age all rats were given an i.p. injection of NMU at 37.5 mg/kg body weight. The experiment was terminated 22 weeks post carcinogen ad ministration. Although there was no difference in terms of tumor incid ence, multiplicity, or latency be tween the two groups, the tumor grow th rate (0.107 +/- 0.025 vs. 0.043 +/- 0.009 g/day) and final tumor we ight (3.2 +/- 0.74 vs. 1.2 +/- 0.34 grams) were significantly higher i n the exercised animals. IGF-I receptor (9.4 +/- 96 vs. 10.5 +/- 57 pe r mu g protein) and estrogen receptor (18.4 +/- 1.14 vs. 19.6 +/- 1.6 per mu g protein) levels were not significantly different in tumors fr om exercised animals compared to those from sedentary animals. For bot h sets of tumors, correlation be tween estrogen receptor content and g rowth rate is positive, while the correlation between IGF-I receptor c ontent and growth rate is negative. The results of this study suggest that exercise prior to NMU administration does not affect tumor burden but does alter tumor growth rate, which is not due to differences in estrogen receptor or IGF-I receptor content.