Oral L-Ornithine Boosts Growth Hormone in Mice via Ghrelin Receptors
Background
L-ornithine is a well-known amino acid recognized for its ability to stimulate growth hormone (GH) release in various mammals. However, the precise temporal patterns of GH secretion and the underlying receptor mechanisms following oral L-ornithine administration have remained unclear, particularly regarding the specific pathways involved.
Results
The study revealed that plasma GH levels in mice began to increase significantly 150 min after oral L-ornithine administration. These elevated levels were sustained for more than 90 min, indicating a prolonged effect. Interestingly, this increase in GH was significantly delayed compared to the reported peak timing of L-ornithine itself in plasma and tissues, suggesting an indirect rather than direct action. The most critical finding was that the L-ornithine-induced increase in GH release was completely blocked by [D-Lys3]-GHRP-6, a ghrelin receptor antagonist, strongly implicating ghrelin receptor-mediated pathways. In contrast, neither cyclosomatostatin (a somatostatin antagonist, which typically inhibits GH) nor JV-1-38 (a GH-releasing hormone antagonist) had any inhibitory effect on the L-ornithine-mediated GH surge, ruling out their direct involvement in this specific mechanism.
Why It Matters
This research uncovers a novel mechanism by which oral L-ornithine stimulates growth hormone (GH) secretion, specifically implicating ghrelin receptor-mediated pathways. Understanding this interaction could open new avenues for therapeutic strategies targeting GH release, potentially benefiting conditions like GH deficiency, sarcopenia (age-related muscle loss), or other muscle wasting disorders. Further research, including detailed dose-response studies, investigations into the upstream signals activating ghrelin receptors, and validation in larger animal models, could pave the way for future human clinical trials to explore L-ornithine's potential as an oral GH secretagogue.