Melatonin increases serum growth hormone and insulin-like growth factor I (IGF-I) levels in male Syrian hamsters via hypothalamic neurotransmitters.
In male Syrian hamsters daily evening melatonin injections resulted in increased circulating levels of growth hormone (GH), as well as a modest increase in body weight. A substantial increase in serum levels of insulin-like growth factor I (IGF-I) was observed in all hamsters receiving evening injections of melatonin for 10 weeks. The melatonin-induced increase in serum IGF-I levels was interpreted as a result of increased release of GH during the 10 week period of melatonin administration. The increase in serum GH and IGF-I was associated with significantly decreased hypothalamic turnover of norepinephrine (NE). Since blocking NE synthesis with alpha methyl-p-tyrosine reduced serum GH, the melatonin-induced increase in GH could not readily be attributed to decreased NE turnover. Highly significant increases in 5-hydroxyindole acetic acid (5HIAA) concentrations and in ratios of 5HIAA to serotonin (5HT) were noted in extracts of hypothalamus and in extracts of brain stem, suggesting a serotonergic component to melatonin-induced increase in GH-induced IGF secretion and subsequent growth.
Vriend
J
J
Department of Anatomy, University of Manitoba, Winnipeg, Canada.
Sheppard
M S
MS
Borer
K T
KT
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D006224:Cricetinae; D013006:Growth Hormone / Q000097:blood*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007279:Injections, Subcutaneous; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D008647:Mesocricetus; D018377:Neurotransmitter Agents / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D013737:Testis / Q000187:drug effects; D013963:Thyroid Hormones / Q000378:metabolism
D018377:Neurotransmitter Agents; D013963:Thyroid Hormones; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D008550:Melatonin; D009638:Norepinephrine