Ruthenium red selectively inhibits capsaicin-induced release of calcitonin gene-related peptide from the isolated perfused guinea pig lung.

In the present study the influence of Ruthenium red on capsaicin- and bradykinin-evoked neuropeptide release from primary afferent neurons was investigated in the guinea pig. Perfusion of the isolated guinea pig lung in vitro with a capsaicin (1 microM)-containing physiological salt solution increased the amount of calcitonin gene-related peptide-like immunoreactivity (CGRP-IR) in the outflow more than 20-fold. Ruthenium red (RR: 1 microM, 10 microM) dose-dependently reduced capsaicin-induced release of CGRP-IR. Addition of bradykinin (1 microM) to the perfusate induced a 3-fold increase of CGRP-IR in the outflow, which was not significantly reduced by 10 microM RR. These results suggest that RR represents a rather specific antagonist of capsaicin's action on sensory neurons.