Intravenous glucose tolerance test-derived insulin sensitivity changes during the menstrual cycle

Area of Science:

• Endocrinology
• Metabolic Physiology
• Reproductive Science

Background:

• Insulin sensitivity during the menstrual cycle is debated, with conflicting results from previous studies.
• Minimal model analysis of intravenous glucose tolerance tests (IVGTT) can assess insulin sensitivity and glucose effectiveness, but hasn't been applied to menstrual cycle phases.

Purpose of the Study:

• To investigate the impact of the menstrual cycle on insulin sensitivity (SI) and glucose effectiveness.
• To apply minimal model analysis to tolbutamide-modified IVGTTs to evaluate these parameters across different cycle phases.

Main Methods:

• Eight cycling women underwent tolbutamide-modified IVGTTs during the early follicular, midcycle, and midluteal phases.
• Minimal model analysis was used to derive insulin sensitivity (SI) and glucose effectiveness from IVGTT data.

Main Results:

• Insulin sensitivity (SI) showed a stepwise decrease from the follicular to the luteal phase (p < 0.007).
• Mean SI was highest in the follicular phase (6.20 ± 0.91), lower at midcycle (4.95 ± 0.73), and lowest in the luteal phase (3.20 ± 0.25).
• No significant changes in glucose effectiveness were observed across the menstrual cycle phases.

Conclusions:

• A significant decrease in insulin sensitivity occurs during the luteal phase of the normal menstrual cycle.
• Midcycle insulin sensitivity did not show significant changes compared to the follicular phase.
• Glucose effectiveness remains stable throughout the menstrual cycle.