NPY and Insulin resistance: 2010a; Wiater et al. 2011). Chronic sleep deprivation studies have shown increased expression of hypothalamic NPY (Koban et al. 2006; Martins et al. 2010). Central administration of NPY results in an increase in EGP in rats, probably by increasing hepatic glucose production (Kalsbeek et al. 2010a). The i.c.v. administration of NPY causes insulin resistance via activation of sympathetic output to the liver (van den Hoek et al. 2008).