Figure 2

24-hour urinary 6-sulfatoxymelatonin excretion rhythms (ng/2 h) for F344 and HSD rats in SD (upper panel) and LD (lower panel). Values shown are means +/- SEM. Bars at the top of the figure indicate periods of light and dark for the SD and LD treatments, respectively. For each treatment group, n = 12 rats.