In the case of model differences, germline BMAL1 deletion is associated with profound neurohumoral and behavioral alterations (leading to cardiometabolic disease), which are not observed in CBK mice (Turek et al., 2005; Marcheva et al., 2010; Young et al., 2014); neurohumoral factors (e.g., FGF21), behaviors (e.g., feeding/fasting), and cardiometabolic diseases (e.g., obesity) are known to affect GH responsiveness (Beauloye et al., 2002; Inagaki et al., 2008). Here, FGF21 is linked to obesity due to melanocortin 4 receptor deficiency.