RESPONSE OF SEX-HORMONE BINDING GLOBULIN AND INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1 TO AN ORAL GLUCOSE-TOLERANCE TEST IN OBESE WOMEN WITH POLYCYSTIC-OVARY-SYNDROME BEFORE AND AFTER CALORIE RESTRICTION

OBJECTIVE We determined the relationship of short-term changes in circulating insulin concentrations, resulting from an oral glucose load, to those in both sex hormone binding globulin (SHBG) and insulin-like growth factor binding protein 1 (IGFBP-1) and assessed the effect of a short-term low calorie diet on the levels of SHBG and IGFBP-1 during an oral glucose tolerance test. DESIGN A within-group comparison of biochemical indices during an oral glucose tolerance test before and after calorie restriction. PATIENTS AND METHODS Six obese women with polycystic ovary syndrome with mean (SD) BMI 34.2 (3.4) kg/m2 were studied before and after one month on a very low calorie diet (350 kcal/day; Cambridge diet). Each subject was given a 75-g oral glucose load after an overnight fast and blood samples were taken every 30 minutes for 3 hours. These were analysed for glucose, insulin, SHBG, and IGFBP-1. RESULTS All the women lost weight (range 1.7-9.5 kg). The SHBG concentrations did not change significantly during the oral glucose tolerance test but there was a highly significant decline in IGFBP-1 levels both before (0 min, mean (SD) 27.3 (10.6); 180 min, 8.9 (4.2) mug/l) and after (0 min, 28.4 (12.1); 180 min, 6.2 (2.1) mug/l, P < 0.001) dieting. The sum of the SHBG concentrations during the test, however, was significantly lower prior (129.9 (40.5) nmol/l) to calorie restriction than after (164.3 (70 6) nmol/l), whereas there was no significant effect of dieting on the IGFBP-1 response to glucose. CONCLUSIONS The changes in insulin and SHBG concentrations found after dieting have been confirmed. SHBG levels, in contrast to IGFBP-1, do not change in response to a short-term increase in insulin or glucose concentrations. The difference in the response of the two binding proteins may be explained by differences in their half-lives in the circulation or the regulation of mRNA for the peptides by insulin. This study confirms that insulin regulates both SHBG and IGFBP-1 but that there is a difference in the time course of the response of the two proteins to insulin.