A reduced Glut 4 content in adipose tissue is not an early defect in the development of human insulin resistance

In order to investigate whether Glut 4 content is reduced in the adipose tissue at an early stage of human insulin resistance, among 30 non-obese (BMI <27) non-diabetic (by oral glucose tolerance test) volunteers, we selected 3 groups of 10 subjects each according to their insulin sensitivity at an i.v. insulin tolerance test (K(itt) values). We then compared the Glut 4 content in the adipose tissue specimens from 7 of the most insulin sensitive and 8 of the most insulin resistant subjects. No difference was observed in the average Glut 4 content between the 2 groups (0.45 ± 0.05 arbitrary densitometric units in insulin sensitive subjects vs 0.61 ± 0.16 in insulin-resistant subjects). No significant correlation was observed between Glut 4 content in adipose tissue nor in vivo insulin sensitivity (K(itt) values), plasma insulin levels 120 min after an oral glucose load, or BMI. In contrast to Glut 4 content, insulin action was already reduced in adipose tissue from insulin-resistant subjects, as shown by the significantly (p <0.05) impaired ability to stimulate receptor tyrosine-kinase activity, a key step in the insulin signalling cascade. In conclusion we demonstrate that, at an early stage, human insulin resistance is not associated to a reduced Glut 4 content in adipose tissue.