Intrahepatic lipid, not visceral or muscle fat, is correlated with insulin resistance in older, female Rhesus macaques

OBJECTIVE: Little is known of the effect of body composition on glucose metabolism in the aging female non-human primate. We studied these variables in older female Rhesus macaques. DESIGN AND METHODS: Female Rhesus macaques (Macacamulatta, n = 19, age range 23–30 yrs) underwent magnetic resonance imaging and (1)H spectroscopy to quantify total abdominal fat, visceral fat (VF), subcutaneous fat (SF) area, extramyocellular lipid (EMCL), intramyocellular lipid (IMCL) and intrahepatic lipid (IHL) content, and DEXA scan for whole body composition. A subgroup (n=12) underwent a fasting blood draw and intravenous glucose tolerance test. RESULTS: SF correlated with homeostatic model assessment of insulin resistance (HOMA(IR)) and quantitative insulin sensitivity check index (QUICKI), but not after adjustment for fat mass. IHL demonstrated the strongest correlation with HOMA(IR), QUICKI and calculated insulin sensitivity index (CS(I)), and remained significant after adjustment for fat mass. VF, IMCL, and EMCL did not correlate with any of our measures of insulin sensitivity. CONCLUSIONS: Despite a greater amount of VF compared to SF, VF was not associated with markers of insulin resistance (IR) in the older female monkey. Instead, IHL is a marker for IR in the fasting and post-prandial state in these animals.