Exp Clin Endocrinol Diabetes 2008; 116 - N18
DOI: 10.1055/s-0028-1096345

Intranasal growth hormone-releasing hormone (GHRH) impairs declarative memory consolidation and GH secretion during nocturnal wakefulness

M Hallschmid 1, I Wilhelm 1, C Michel 2, H Lehnert 2, J Born 1, B Perras 1, 2
  • 1Department of Neuroendocrinology, University of Lübeck, Germany
  • 2Department of Internal Medicine I, University of Lübeck, Germany

Context and aim: The activity of the somatotropic system displays a secretory maximum during early sleep which is a period known to be essential for memory consolidation. While blocking the sleep-onset associated surge in growth hormone (GH) secretion does not affect memory performance, the contribution of growth hormone-releasing hormone (GHRH) to memory formation is unclear. We assessed the influence of intranasal GHRH on memory consolidation in waking men. Design and subjects: Twelve healthy young men (mean age 23.3+/-1.0 years) were investigated twice (GHRH and placebo) during nocturnal wakefulness. Declarative and procedural memory consolidation was examined by means of a word pair and a finger tapping task, respectively. Learning took place around 2030h, i.e., before subjects were intranasally administered 600µg GHRH and saline solution, respectively. Recall was tested at 0900h in the morning. Levels of GH, ACTH, cortisol, catecholamines, insulin and blood glucose were assessed throughout the night. Results: The number of word pairs recalled in the morning (expressed as the percentage of word pairs acquired at learning) was reduced in the GHRH condition (72.3±4.1%) compared to placebo (81.3±6.4%; p<0.05). Finger tapping was not influenced. A small but distinct GH peak observed in the control condition around 2330h was blunted by intranasal GHRH administration. Conclusion: Intranasal GHRH administration impairs declarative but not procedural memory consolidation during nocturnal wakefulness. GHRH treatment also impairs GH release during the first night-half, suggesting that the effects of intranasal GHRH are mediated via an ultrashort negative feedback loop that controls GH secretion.