We previously demonstrated that a serotonin (5-HT) precursor 5-hydroxytryptophan (5-HTP) increases serum leptin levels in mice. It was reported that administration of 5-HTP elicits hypophagia in rodents and humans. In the present study, we examined involvement of leptin in 5-HTP-elicited decreases in the milk intake of fasted mice. Serum leptin levels increased with increases in milk intake in mice, while 5-HTP strongly decreased milk intake in fasted mice compared to that in the control group. Serum leptin levels in fasted mice treated with 5-HTP were similar to those control mice after milk intake. As leptin is a powerful anorectic signal, 5-HTP-induced anorexia may be mediated by facilitation of leptin secretion.
We previously reported that a serotonin precursor 5-hydroxytryptophan (5-HTP) increases serum leptin levels in mice. In this study, we studied the effects of insulin and adrenalectomy on hyperleptinemia induced by 5-HTP. Co-administration of insulin significantly increased hyperleptinemia elicited by 5-HTP. 5-HTP itself increased serum insulin levels. Adrenalectomy, which depletes corticosterone, did not abolish hyperleptinemic effects of 5-HTP. These results suggest that insulin may participate in hyperleptinemic effects of 5-HTP and that the involvement of corticosterone in effects of 5-HTP may be probably small.
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