Factors that influence upper gastrointestinal motility in 8-week-old male and female mice, as measured by the distribution of FITC-dextran 30 minutes after gastric gavage. A-C, experiments performed with C57BL/6J mice after a short fast of 4-7 hours (left column) or a long fast of 15-18 hours (right column). D, MGC increases with increasing time of day and duration of fast in testing performed with C57BL/6J mice in the morning after a short fast. E, experiments performed during a precise 1-hour window around 9:00 or 12:00 following a precise fast of 4 or 7 hours reveal that MGC in females is more sensitive to time of day than to duration of fasting. F, experiments performed in the morning after a short fast with three strains of mice reveal sexual dimorphism in C57BL/6J and CD-1, but not BALB/c, mice. Bars represent mean ± SD and are representative of three identical experiments; *** adjusted P < 0.001; ** adjusted P < 0.01; * adjusted P < 0.05 (pairwise comparisons in panel F represent unadjusted P values); N = 7-9 mice per sex per group; AM, experiments performed between 9:00-12:00; PM, experiments performed between 13:00-16:00; FITC = fluorescein isothiocyanate; segment 0 = stomach, 1 = proximal duodenum, 10 = terminal ileum.