Endocrine Abstracts

Introduction: The activity of the somatotropic system displays a secretory maximum during early sleep which is also a period known to be important for memory consolidation. Blocking of the sleep-onset associated GH-surge by somatostatin did not affect memory performance but the contribution of growth hormone-releasing hormone (GHRH) to memory processes is unclear. Here we assessed the influence of intranasal GHRH on memory function in waking subjects during the early part of the night.

Methods: Fifteen young and healthy men (mean age 23.5 years) were investigated while staying awake throughout the night. At 21.30 hours subjects received 600 μg GHRH or placebo (saline solution) by the intranasal route in a double-blind experiment. Declarative and procedural memory was examined with a word pair learning task and finger tapping, respectively. Mood and sleepiness were measured by questionnaire (MDBF, Stanford sleepiness scale). Also hunger and thirst were monitored by a self-rating scale. Blood for determination of growth hormone, cortisol, ACTH, insulin and blood glucose were collected in close intervals.

Results: GHRH in comparison with placebo did not improve memory consolidation as expressed as difference (mean±SEM) of recall performance between learning before substance administration (20.30 hours) and in the morning after having spent the night awake (09.00 hours): word pairs: GHRH 72.3±4.1%; placebo 81.3±6.4%; finger tapping: GHRH: 105.9±4.7%, placebo: 99.2±4.9%.

Conclusion: Memory consolidation during the early part of the night is not facilitated by the sleep associated peak activity of the somatotropic system which typically parallels this period.