Gonadotropin Response to Insulin and Lipid Infusion Reproduces the Reprometabolic Syndrome of Obesity in Lean Women

Abstract

Introduction: The reprometabolic syndrome of obesity is associated with reduced gonadotropins and impaired LH and FSH response to gonadotropin releasing hormone (GnRH). We sought to reproductive the reprometabolic syndrome in normal weight, eumenorrheic women by infusing a combination of insulin and lipid. Materials and Methods: 15 women, mean age 32 (IQR 26,36) and BMI 21.9 (20.2, 22.9) were recruited with intent to perform early follicular phase, 6-hour infusions of insulin (20-40mg/mU/m2/min) and lipid (Intralipid) or saline infusion (controls); 12 women completed both intended studies and an additional 3 women completed only one of the two studies. The first 4 hours of each study assessed endogenous gonadotropins; at 4hrs, a 75 ng/kg GnRH bolus was administered and sampling continued until 6hrs. Linear mixed model analysis was used to determine differences between Intralipid versus saline on endogenous LH pulse amplitude (primary outcomes), mean FSH, and area under the curve (AUC) response to GnRH (secondary outcomes). Results: LH pulse amplitude, mean FSH, and both AUC responses to GnRH were all reduced by Intralipid/insulin; mean FSH (P=0.03) and AUC for LH (P=0.05) were at or near statistical significance. LH pulse amplitude and response to GnRH were significantly reduced (P=0.04 and 0.02) when one participant with very high LH and AMH levels was excluded. Discussion: Acute infusion of insulin/lipid to eumenorrheic, normal weight women recapitulated the reprometabolic syndrome of obesity. These findings imply that specific circulating factors in obese women contribute to their sub fertility and thus may be amenable to discovery and treatment.