Circadian rhythms of mitotic activity in gastric mucosa of feeding and fasting rats.

The mitotic index of the glandular epithelium of gastric mucosa was studied in fasting and feeding rats. Fifty-four adult Wistar (ICB) rats, both males and females, were randomly divided into two groups of 27, and one of the groups was fasted for 26-34 hr. All rats were kept on an LD 13:11 cycle with natural light from 0530 to 1830 hr. Eight groups of three or four rats each were killed at 3-hr intervals commencing at 0900 hr. All animals were injected intraperitoneally with colchicine, 1 mg/kg body weight, 2.5 hr before sacrifice. At least 5,000 cells were counted per animal in 5-micron sections. The proportion of colchicine-arrested metaphases in the proliferative zone was determined and expressed as a percentage. The animals fed ad libitum showed a peak of mitotic index at 1200 hr and a trough at night. From the single cosinor analysis, a 24-hr rhythm was detected with the following values: amplitude = 1.40, mesor = 1.47, acrophase = -194.7 degrees, and P = 0.010. The fasting rats exhibited lower values of mitotic index but still a peak at 1200 hr. However, the single cosinor analysis did not show a 24-hr rhythm; values were amplitude = 0.36, mesor = 0.73, acrophase = 142.3 degrees, and P = 0.679.