Temporal comparison of 18:1 fatty acid isomers in liver, heart, and skeletal muscle of ob/ ob mice to their controls. The composition of non-esterified 18:1 fatty acid (18:1 NEFA) isomers was determined in mouse liver (Panel A), heart (Panel B), and thigh skeletal muscle (Panel C) of ob/ ob mice (solid bars) and their controls (open bars) at 10, 12, and 16 weeks of age by MDMS-SL as described in MATERIALS AND METHODS. These isomers include vaccenic (n-7), oleic (n-9), and petroselinic (n-12) acids as indicated.