Figure 4.

Circadian Rhythmicity Was Present in Stress Tolerance and Four of Ten Paracrine Secretion Factors

(A) Apoptosis was measured after serum shock, subsequent time periods (as depicted on x axis), and 6 hr of doxorubicin exposure using a Caspase-Glo 3/7 assay. Apoptosis was 27.4% ± 2.0% higher 27 and 51 hr compared with 15 and 39 hr after serum shock (p < 0.001; n = 4 independent experiments). In non-synchronized cells, no circadian rhythm was present (p = 0.396; n = 4 independent experiments).

(B) Circadian rhythm in the excretion of paracrine factor PIGF-1 (placental growth factor).

Data are presented as mean ± SEM; ^∗p < 0.05 for significant circadian oscillation.