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 circ ulating insulin concentrations, resulting from an oral glucose load, t o those in both sex hormone binding globulin (SHBG) and insulin-like g rowth 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 a n oral glucose tolerance test. DESIGN A within-group comparison of bio chemical indices during an oral glucose tolerance test before and afte r calorie restriction. PATIENTS AND METHODS Six obese women with polyc ystic 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; C ambridge 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. RE SULTS All the women lost weight (range 1.7-9.5 kg). The SHBG concentra tions did not change significantly during the oral glucose tolerance t est 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 af ter (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 sign ificantly lower prior (129.9 (40.5) nmol/l) to calorie restriction tha n after (164.3 (70 6) nmol/l), whereas there was no significant effect of dieting on the IGFBP-1 response to glucose. CONCLUSIONS The change s in insulin and SHBG concentrations found after dieting have been con firmed. SHBG levels, in contrast to IGFBP-1, do not change in response to a short-term increase in insulin or glucose concentrations. The di fference in the response of the two binding proteins may be explained by differences in their half-lives in the circulation or the regulatio n of mRNA for the peptides by insulin. This study confirms that insuli n regulates both SHBG and IGFBP-1 but that there is a difference in th e time course of the response of the two proteins to insulin.