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Palmitate has been shown to stimulate glucose transport, translocation of GLUT4 and insulin receptor autophosphorylation in isolated rat adipocytes (Biochem Biophys Res Commun 177:343-49, 1991). Here we further characterize the ability of short-term treatment with free fatty acids to stimulate glucose transport in isolated rat adipocytes and demonstrate that prolonged treatment induces insulin resistance. Treatment of adipocytes for 15 min with 1 mM myristate (14:0), palmitate (16:0), or stearate (18:0) stimulates glucose transport by 119 +/- 33, 89 +/- 29, and 114 +/- 30%, respectively. In contrast, oleate (cis 18:1), 1), elaidate (trans 18:1), and linoleate (cis 18:2) do not stimulate glucose transport. Palmitate stimulates glucose transport in a concentration-dependent manner, demonstrating saturation at 1 mM and half-maximal stimulation at 0.25-0.5 mM. Prolonged treatment (4 h) of rat adipocytes with 1 mM palmitate induces insulin resistance. After a 4-h preincubation with palmitate (1 mM), insulin stimulates glucose transport in rat adipocytes by 4.4-fold +/- 0.8, vs. 8.8-fold +/- 0.8 in controls (n = 3). Palmitate-induced resistant cells demonstrated a 40% inhibition in maximal insulin responsiveness with little change in insulin sensitivity. Insulin binding is only slightly decreased (8%) in palmitate-pretreated cells. These studies indicate that saturated fatty acids stimulate glucose transport acutely and on prolonged exposure induce insulin resistance via a post-insulin binding defect. The underlying molecular mechanisms of insulin resistance induced by prolonged treatment with saturated fatty acids may now be investigated using this unique cellular model.
Hunnicutt et al. (1994) studied this question.