In the present study we measured PC-1 content, tumour
necrosis factor (
TNF)-alpha gene expression, and
insulin stimulation of
insulin receptor tyrosine-kinase activity in adipose tissue from non-obese, non-diabetic subjects. These parameters were correlated with in vivo
insulin action as measured by the intravenous
insulin tolerance test (Kitt values). PC-1 content was negatively correlated with Kitt values (r = -0.5, p = 0.04) and positively with plasma
insulin levels both fasting (r = 0.58, p = 0.009) and after 120 min during oral
glucose tolerance test (OGTT) (r = 0.67, p = 0.002). Moreover, adipose tissue PC-1 content was higher in relatively
insulin-resistant subjects (Kitt values lower than 6) than in relatively
insulin-sensitive subjects (Kitt values higher than 6) (525 +/- 49 ng/mg
protein vs 336 +/- 45, respectively, p = 0.012). Adipose tissue
insulin receptor tyrosine-kinase activity in response to
insulin was significantly lower at all
insulin concentrations tested (p = 0.017, by two-way analysis of variance test) in
insulin-resistant than in
insulin-sensitive subjects (Kitt values lower or higher than 6, respectively). In contrast to PC-1, no significant correlation was observed between adipose tissue
TNF-alpha mRNA content and Kitt values, and plasma
insulin levels, both fasting and at after 120 min during OGTT. Also, no difference was observed in
TNF-alpha mRNA content between subjects with Kitt values higher or lower than 6. These studies in adipose tissue, together with our previous studies in skeletal muscle raise the possibility that PC-1, by regulating
insulin receptor function, may play a role in the degree of
insulin sensitivity in non-obese, non-diabetic subjects.