Capsaicin-Induced Calcitonin Gene-Related Peptide Release from Isolated Rat Stomach Measured with a New Chemiluminescent Enzyme Immunoassay

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Abstract
The peripheral capsaicin-sensitive afferent nerve has been reported to play an important role in gastroprotection and to release a calcitonin gene-related peptide (CGRP). We developed a new chemiluminescent enzyme immunoassay (CLEIA) for CGRP and measured capsaicin-induced CGRP release from the isolated and inverted rat stomach. The basal CGRP release from the stomach was 0.40 +/- 0.02 pg/mg wet weight in a 30-min incubation. Capsaicin (1 x 10(-8)-1 x 10(-5) M) stimulated CGRP release in a concentration-dependent manner. In the stomach from rats with defunctionalization of afferent neurons, the levels of the basal and capsaicin-induced CGRP release were below the limit of detection. On the other hand, the capsaicin-induced CGRP release was not blocked by tetrodotoxin treatment. The gangliosym-pathectomy abolished the increase in the CGRP levels. However, the capsaicin-induced CGRP release was not affected by pretreatment with 6-hydroxydopamine, a neurotoxin that causes a complete degeneration of adrenergic nerve terminals. In conclusion, the CLEIA system may be useful for detecting the released CGRP and studying the activity of capsaicin-sensitive nerves, particularly the CGRP-containing nerves. Our results also confirmed that although the CGRP-containing nerve runs in the sympathetic nerve trunk, the activity of the nerve is not affected by adrenergic nerves, and the capsaicin-induced CGRP release may be attributable to the tetrodotoxin-resistant component.