Abstract
The release of calcitonin gene-related peptide (CGRP), neurokinin A (NKA) and substance P (SP) from intralumenally perfused rat trachea was examined in vitro. In accord with the relative tissue levels of the respective peptides, capsaicin (10 −8 to 10 −5 M) and K + (120 mM) added to the perfusate resulted in a concentration-dependent increase in the levels of CGRP and NKA, and to a minor extent SP, in the perfusates. Sequential exposure of the trachea to capsaicin revealed a concentration-dependent tachyphylaxis of CGRP release. Thus, 40 min after the application with capsaicin 10 −5M, a second exposure to capsaicin at the same concentration, or K + 120 mM, did not evoke CGRP release. In contrast, prior stimulat release induced by a second stimulation with K + 120 mM or capsaicin 1 diminished or abolished in the absence of Ca 2+. HPLC analysis of CGRP which eluted in the same fraction as synthetic rat CGRP. These data demonstrate that CGRP, NKA and SP exist in releasable, capsaicin-sensitive pools in terminals which lie within the proximal lumen of the trachea.
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