The relationship between insulin sensitivity and insulin-like growth factor-binding protein-1

Abstract

Insulin has been shown to regulate insulin-like growth factor-binding protein-1 (IGFBP-1) in vivo and in vitro. Insulin resistance is a feature of the polycystic ovary syndrome (PCOS). We have studied the relationship between insulin sensitivity (S₁) and the circulating concentration of IGFBP-1 in a group of young women and in some who had PCOS. A case-control study has been carried out comparing reproductively normal women with women with PCOS (defined as women with oligo- or amenorrhea associated with androgen excess). Fifteen women with clinical PCOS and ten age- and weight-matched controls were studied. S₁ was measured by the frequently sampled intravenous glucose tolerance test (FSIGF) using the minimal model technique. IGFBP-1, insulin-like growth factor-I (IGF-I) and growth hormone levels were measured before and during the FSIGT. Circulating testosterone, dehydroepiandrosterone (DHFA) and its sulfate (DHFAS) levels were measured while the subjects were fasting. S₁ and IGFBP-1 levels were significantly lower in the PCOS group than in controls (S₁ [10₋₅ min₋₁/pM] mean ± SE 3.8 ± 0.8 vs. 8.5 ± 1.3, p < 0,613; IGFBP-1 [ng/ml] mean ± SE 26.6 ± 4.2 vs. 56.0 ± 5.9, p < 0.005). In women with PCOS, IGFBP-1 concentrations related negatively to the body mass index (BMI) (r = -0.11, p < 0.003) and positively to S₁ (r – 0.76, p < 0.003). S₁ remained a significant predictor of IGFBP-1 concentrations when controlled for BMI (combined r² = 0.35, p <0.05). No relationship was found between androgen levels and IGFBP-1. Insulin sensitivity contributed to the difference in IGFBP-1 levels found in women with PCOS. Whether the reduced concentrations of IGFBP-1 play a role in the pathophysiology of PCOS is uncertain, but it may act to alter delivery of IGF to peripheral tissues in insulin-resistant individuals.

Key Words:

• Polycystic Ovary Syndrome
• Insulin Sensitivity
• Insulin-Like Growth Factor-I
• Insulin-Like Growth Factor-Binding Protein-1