Hypotensive effect of des-acyl ghrelin at nucleus tractus solitarii of rat

Ghrelin is a gut-brain peptide and its endocrine activities are mediated by GH secretagogue receptor (GHSR)-1a. Des-acyl ghrelin does not activate GHSR-1a and is devoid of endocrine activities. While the microinjection of ghrelin into rat nucleus tractus solitarii (NTS) elicited hypotensive effects, this was not the case upon injection into GHSR-expressing rostral ventrolateral medulla or caudal ventrolateral medulla. To make clear the reason of the discrepancy between receptor distribution and neuronal responses, we examined the cardiovascular response of rats microinjected with des-acyl ghrelin into NTS. Intra-NTS injection of des-acyl ghrelin significantly reduced mean arterial pressure and heart rate. The hypotensive and bradycardic activity evoked by des-acyl ghrelin was not significantly different from that of native ghrelin. These results suggest that des-acyl ghrelin contribute to the regulation of cardiovascular control and that a receptor other than GHSR-1a exists in NTS.