Objective: To assess whether the phase of the menstrual cycle influences the counter-regulatory response to hypoglycemia.
Design: Prospective randomized euglycemia-hypoglycemia clamp studies in the follicular and luteal phases of the menstrual cycle in the same woman.
Settings: Clinical Research Center, Yale University School of Medicine.
Patients: Eight regularly menstruating nonobese women.
Main outcome measures: Counter-regulatory hormonal response to hypoglycemia-epinephrine, norepinephrine, glucagon, cortisol, GH, and PRL; glucose homeostasis: rates of whole-body glucose appearance and utilization, and the rate of hepatic glucose production.
Results: In the follicular and luteal phases of the cycle fasting glucose levels (88 +/- 1 and 85 +/- 2 mg/dL, mean +/- SEM, respectively; conversion factor to SI units, 0.05551), basal glucose turnover (2.37 +/- 0.20 and 2.63 +/- 0.13 mg/kg per minute), basal insulin levels (10 +/- 1 and 9 +/- 1 microU/mL; conversion factor to SI units, 6.0), and insulin levels during the clamp study (53 +/- 3 and 45 +/- 4 microU/mL) were not significantly different. During the euglycemic phase of both studies, glucose utilization rose twofold (to 4.73 +/- 0.31 and 4.39 +/- 0.31 mg/kg per minute): hepatic glucose production was suppressed; and counter-regulatory hormones remained unchanged. Induction of hypoglycemia produced increases in the concentrations of counter-regulatory hormones that were indistinguishable in both phases of the cycle. Similarly, the increase in hepatic glucose production provoked during hypoglycemia was similar in each phase of the cycle (1.20 +/- 0.24 and 1.28 +/- 0.36 mg/kg per minute).
Conclusion: The counter-regulatory hormonal response to hypoglycemia, as well as the metabolic sequelae of these hormonal changes, are similar in the follicular and luteal phases of the menstrual cycle.