Serial sampling of plasma growth hormone in a healthy young adult shows the single largest daily GH pulse occurs at a predictable time. This peak corresponds to:

• A Immediately after waking, driven by the cortisol awakening response
• B Early in slow wave (stage N3) sleep, shortly after sleep onset ✓
• C Mid-afternoon, coinciding with the postprandial insulin rise
• D During REM sleep episodes in the early morning hours

Explanation

The major GH pulse of the day occurs shortly after the onset of slow wave sleep (stage N3), mediated by increased GHRH release and reduced somatostatin tone. This is why sleep deprivation blunts GH secretion and IGF-1 generation over time. REM sleep is not associated with GH peaks, and the morning cortisol rise is a separate HPA rhythm, which makes options A and D tempting but incorrect.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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