Effects of substance P and calcitonin gene related peptide (CGRP) on guinea pig nasal mucosal secretion in vivo.

Trigeminal sensory nerves contain and release the neurotransmitters substance P (SP) and calcitonin gene related peptide (CGRP) in nasal mucosa. The effects of SP and CGRP on nasal secretion were tested in an in vivo model of guinea pig nasal mucosal secretion by topically applying the peptides directly to turbinates, and then lavaging the nostrils 10 min later. Concentrations of total protein, albumin, and 125I-bovine serum albumin (25I-BSA, injected intravenously at time 0 of the studies) were measured in lavage fluid. SP (beginning at 10(-8) M) and CGRP (beginning at 10(-6) M) stimulated the secretion of 125I-BSA indicating stimulation of plasma protein exudation. SP and CGRP increased total protein concentration at 10(-6) M indicating stimulation of glandular secretion. Topically applied thiorphan (1 microgram), an inhibitor of neutral endopeptidase, did not potentiate the maximal response to SP. However, thiorphan significantly prolonged the duration of 125I-BSA, total protein, and albumin secretion in response to SP indicating that the vascular and glandular responses were enhanced. This implies the presence of neutral endopeptidase, and demonstrates a regulatory role for this enzyme in vivo. These findings are consistent with the concept that SP and CGRP released by nociceptive sensory nerve axon responses in guinea pig nasal mucosa lead to plasma extravasation, albumin exudation, and glandular secretion, and that these mechanisms contribute to nasal responses to injury in this species.