The influence of weather and climate on the incidence of gastric ulcers after reserpine in rats

Each month over a period of 22 months two groups of female rats were given i.p. 2.5 mg reserpine/kg BW and the number of gastric ulcers/rat were counted 24 h later. One group (n = 40) was kept for 17 days under environmentally controlled conditions (temperature, humidity, light intensity, length of photoperiod) while the other group (n = 40) was maintained for the same 17 days in a room near the open window under uncontrolled conditions. Under uncontrolled conditions gastric ulcer rate was negatively correlated with T_a (r=–0.87), T_a+T_wb(r=–0.84), and T_eq=T_a+2e (r=–0.83) of the last 24 hours. The correlation coefficients were higher with meteorological data of the 24 hours after administration of reserpine than with the data of the previous 16 days. No seasonal variation of ulcer morbidity was observed in the rats kept under controlled conditions. Hence, in rats, reserpine increases the gastric ulcer rate in the cold. Serious errors might arise in the interpretation of experiments when the rats are not housed under environmentally controlled conditions.