Circadian-dependent response in DNA synthesis to epidermal growth factor in spleen, bone marrow, and lung and in mitotic index of corneal epithelium in ad libitum-fed and fasted CD2F1 mice.

The effect of epidermal growth factor (EGF) on DNA synthesis in the spleen, bone marrow, and lung and on the mitotic index in the corneal epithelium was investigated in CD2F1 mice that were standardized on an LD 12:12 cycle and either fed ad libitum or fasted for 24-34 hr. EGF brought about decreases in DNA synthesis in both the bone marrow and spleen in ad libitum-fed male mice. Moreover, the degree of response and the duration of time it took for the decreases to become statistically significant were circadian-stage dependent. The response brought about by EGF on DNA synthesis in the lung also was circadian-stage dependent, but it was an increase and occurred much later than in the spleen or bone marrow. The maximum decreases brought about by EGF in spleen and bone marrow occurred at 13 hr after EGF treatment, being 37% and 28%, respectively. The maximum increase in DNA synthesis in the lung was 116% and was recorded 33 hr after treatment, but the first statistically significant increase (35%) was recorded 28 hr after treatment. Under the conditions of this study, fasting diminished the overall level of DNA synthesis in the bone marrow, spleen, and lung. We conclude, however, that sampling was too limited to draw definitive conclusions regarding the persistence of a DNA synthesis rhythm in fasting and the effect that EGF has on the fasting rhythm. There was no apparent effect on fasting on the mitotic index of the corneal epithelium.