FIGURE 5.

Consumption of a high fat diet at the end of the active/awake phase results in marked elevations in myocardial triglyceride (B), metabolic gene expression (C), myocardial fatty acid gene expression (D), and alterations in myocardial substrate reliance (E). After 16 weeks of diet intervention, myocardial triglyceride levels (B) were measured in hearts isolated at ZT4 and ZT16. Gene expression analyses of dgat2 (C), agpat3 (C), hsl (C), s3-12 (C), ucp3 (D), and pdk4 (D) were performed using quantitative RT-PCR in WT hearts isolated at ZT4. Substrate reliance (E) was measured in hearts perfused ex vivo in the working mode under basal conditions at ZT4. In this study hearts were perfused only with Krebs-Henseleit buffer containing 8 mm glucose, 0.4 mm oleate conjugated to 3% bovine serum albumin, and tracer amounts of [U-¹⁴C]glucose (0.12 mCi/liter) and [9,10-³H]oleate (0.067 mCi/liter) for glucose and oleate oxidation measurements, respectively. Data are represented as the mean ± S.E. Statistical analysis was performed using a two-way ANOVA. * denotes p < 0.05 diet effect; # denotes p < 0.05 time effect within a feeding group (n = 5–6 for gene expression, n = 6 for myocardial triglyceride, and n = 6–7 for ex vivo measurements).