Sphingolipid were quantified as described previously by LC/ESI/MS/MS using a TSQ Quantum Ultra-triple quadrupole mass spectrometer (Thermo Fisher) equipped with an electrospray ionization (ESI) probe and interfaced with an Agilent 1100 HPLC (Agilent Technologies) (Holland et al., 2011; Li et al., 2009). Glucose was measured by Alpha Trak glucometer (Abbott Labs). Insulin and Adiponectin were quantified by ELISA (Millipore). Adiponectin distribution was measured as previously described (Schraw et al., 2008). To prevent contamination of MS equipment with 3H-containing samples, ceramides and diacyglycerols were measured on samples obtained following hyperinsulinemic euglycemic clamps using established enzymatic methods (Perry et al., 2000).
