Figure 4: Variations of mortality according to the circadian stage (1, 5, 9, 13, 17, and 21 HALO) at various doses (6.0 and 6.6 m/kg, i.p.) of sodium nitroprusside in 2 week old male (a) and female (b) mice. Each point represents the mean SEM of four independent experiments. The black bar corresponds to the dark period. Best drug tolerance occurred, irrespective to the gender, when the drug was injected in the light phase (during the animal's rest span). The ?2 test detected statistically significant differences in mortality rate related both to dosing time (P < 0.0002) and dose (P < 0.02).