A 45-year-old woman undergoes evaluation for growth hormone excess. Her serum IGF-1 is elevated, and a 75 g oral glucose tolerance test fails to suppress GH below 1 ng/mL. The patient is obese with a BMI of 34 kg/m². Which of the following physiological states is normally associated with the LOWEST serum GH concentration?

• A Stage N3 (slow-wave) sleep
• B Acute hypoglycemia (blood glucose 40 mg/dL)
• C Ingestion of a 100 g oral glucose load ✓
• D Prolonged fasting for 48 hours

Explanation

Oral glucose ingestion raises blood glucose, which stimulates hypothalamic somatostatin release and suppresses GH secretion. This is the physiological basis of the OGTT suppression test used to diagnose acromegaly. In contrast, slow-wave sleep is the strongest physiological stimulus for GH secretion. Hypoglycemia and prolonged fasting both elevate GH via reduced somatostatin and increased GHRH drive. The glucose load therefore produces the lowest GH level among the choices.

Reference: Williams Textbook of Endocrinology, 14th ed.

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