Evaluation Of Islet β-Cell Function By Botnia Glucose Clamp In Women With Polycystic Ovary Syndrome

Objective: To evaluate islet β-cell function in non-obese and obese women with polycystic ovary syndrome (PCOS), and to explore whether glucose disposition index (DI=I₃₀/ΔG₃₀×Homa-IS) obtained from OGTT is reliable to evaluate islet β-cell function in PCOS patients. Methods: 47 women with PCOS (31 in non-obese group, 16 in obese group respectively) and 20 healthy women (control group) were given oral glucose tolerance tests (OGTT) and Botnia glucose clamp which consisted of an intravenous glucose tolerance test (IVGTT) for 60 minutes followed by an euglycemic-hyperinsulinemic clamp for 2 hours. Insulin sensitivity (IS) was evaluated by homeostasis model (Homa-IS) and Botnia glucose clamp (Clamp-IS) which was calculated as insulin-mediated glucose disposal rate of the euglycemic-hyperinsulinemic clamp divided by the mean of insulin concentrations at 150 min and 180 min (M/I, mg·kg^-1·min^-1 per μU/ml). Islet β-cell function (βF) was reflected through homeostasis model(Homa-βF) and OGTT(ΔI₃₀/ΔG₃₀) and acute insulin response(AIR) of IVGTT. AIR was calculated by three methods (AIR₁, AIR₂ and AIR₃): AIR1, by the incremental mean above basic level of insulin concentrations at 2, 4, 6, 8 and 10min after glucose challenge; AIR2, by the mean of βF index (ΔI/ΔG) at the same time points as described previously; AIR3, by the ratio of area under curve of insulin concentration from zero to ten minutes to that of glucose concentration (INS_AUC10/GLU_AUC10). Glucose disposition index (DI) was calculated as the product of IS and βF (DI=IS×βF). Results: 1. BMI and plasma glucose level at 2h of OGTT were higher in obese PCOS women than those in other two groups, and there were no significant difference between control group and non-obese PCOS group. 2. Clamp-IS was significantly different from each other in three groups (P <0.0001), and Clamp-IS was decreased by 50±25% and 35±19% respectively in non-obese and obese PCOS groups as compared with control group. 3. βF indexes (Homa-βF, AIR₁, AIR₂ and AIR₃) were similar in three groups, but there was a trend of increase in βF indexes in women with PCOS, especially for obese women. 4. DI calculated as Clamp-IS×AIR was lower in non-obese and obese women with PCOS than that in healthy women, and no significant difference was found in PCOS groups. 5. DI obtained from OGTT(ΔI₃₀/ΔG₃₀×ISHOMA)showed positive linear correlation with that of Botnia glucose clamp (AIR₂×Clamp-IS) (r =0.54, P <0.0001), and showed inverse linear correlation with plasma glucose level at 0, 30, 60 and 120min of OGTT (r = -0.31, -0.39, -0.41 and -0.52 respectively, all P <0.05). Conclusion: Regardless of obesity or not, PCOS patients have decreased insulin sensitivity. Acute insulin response to glucose in women with PCOS doesn't decrease, but compensatory ability of β-cell for insulin resistance is deficient. DI obtained from OGTT(ΔI₃₀/ΔG₃₀×ISHOMA)is simple and reliable to evaluate β-cell function in PCOS patients.