We next tested the kinetics of other fasting-induced hepatic PPARα activity in vivo. We used several measures of PPARα activity, including Fgf21 (figure 5A) and Vanin1, Cyp4a10, Cyp4a14 and Fsp27 mRNAs (figure 6A), since these genes were most sensitive to fasting and to fenofibrate, and were strictly PPARα dependent (see online supplementary files 6–10A). Plasma FFA and glucose levels were also measured during fasting (figure 6B). FFA were markedly increased in the early night (ZT14–ZT16). The FFA pattern was correlated with the PPARα mRNA expression profile and expressions of Fgf21, Vanin1, Cyp4a10, Cyp4a14 and Fsp27 (figures 5A and 6A). This strongly suggested that FFA released from adipocytes during fasting-influenced hepatic PPARα expression and activity without inflammatory response since hepatic Tnfα mRNA expression was not sensitive to fasting. We further determined that acute treatment of fasted mice with the β3-adrenergic receptor agonist CL316243 enhanced circulating FFA levels in WT and Pparαhep−/− mice (figure 6C), and increased expressions of Fgf21, Cyp4a14, Vanin1, Cyp4a10 and Fsp27 in WT mice but not Pparαhep−/− mice (figure 6D) without inducing Tnf α in response to fasting
