Effect of hypothermia on intestinal adaptation and carcinogenesis in the rat

Postoperative hyperplasia enhances experimental intestinal carcinogenesis, but the effects of nonsurgical adaptation are uncertain. The tropic and tumour-promoting potentials of moderate hypothermia were tested in two groups of male Sprague-Dawley rats housed at 10 degrees C for 30 weeks. One group (n = 10) received a 6-week course of azoxymethane (total dose 90 mg kg-1). The second group (n = 7) acted as hypothermic controls. Another 2 groups maintained at 22 degrees C received azoxymethane (n = 15) or served as normothermic controls (n = 15). Overall food intake was 42% higher in the hypothermic groups, yet at sacrifice mean body weight was 13% lower (P less than 0.01). Hypothermia and azoxymethane combined to produce the following increases in crypt cell production rate (CCPR), as determined stathmokinetically: duodenum 170%, jejunum 172%, ileum 74%, proximal colon 227% (P = 0.05-0.01). Independently hypothermia had no effect, but azoxymethane produced 76-156% increases in CCPR throughout the large intestine. Although hypothermia did not affect overall tumour yield, the mean diameter of proximal colonic tumours was increased by 65% (P less than 0.05). In rats receiving azoxymethane, hypothermia stimulates cell proliferation in the small bowel as well as in the proximal colon, where it has a correspondingly mild cocarcinogenic effect.