BACKGROUND: Restoration of near-euglycaemia by intensive insulin therapy results in decreased serum levels of inflammatory mediators. The authors investigated whether the anti-inflammatory effect of insulin was independent of its glucose-lowering action and if this effect was intact in insulin-resistant women with the polycystic ovary syndrome (PCOS) characterized by low-grade chronic inflammation.
MATERIALS AND METHODS: Blood was drawn on the third and sixth days after progestin-induced withdrawal bleeding in 20 young non-diabetic women with PCOS and once between the third and sixth days of the menstrual cycle in 21 age-matched lean healthy control women during a 75-g oral glucose tolerance test (oGTT). Serum insulin, glucose and tumour necrosis factor alpha (TNF-alpha) concentrations were measured after 0, 30, 60, 90 and 120 min.
RESULTS: The increase in insulin and glucose concentrations during the oGTT was significantly more pronounced in patients with PCOS (one patient with impaired fasting glucose, one patient with impaired glucose tolerance, three patients with both) compared with healthy controls. The TNF-alpha serum concentrations decreased in patients with PCOS (mean of both days, P = 0.004). In patients and in controls, there was an inverse correlation between the serum concentrations of insulin and of TNF-alpha during oGTT (for patients, a mean of both days, P = 0.009; for controls, P = 0.047), but not between the serum concentrations of glucose and TNF-alpha.
CONCLUSIONS: The decrease in TNF-alpha concentrations during oGTT and the inverse correlation between endogenous hyperinsulinaemia and serum TNF-alpha concentrations suggested an anti-inflammatory effect of moderately-high insulin concentrations. This occurred despite the presence of moderate hyperglycaemia. These findings also demonstrated a preserved responsiveness of inflammatory mediators to insulin in PCOS.