The development of tone in the smooth muscle of guinea-pig isolated tracheal preparations may be influenced by prostanoids released from the adjacent airway cartilage.

Guinea-pig tracheal strip preparations containing cartilage, placed under an applied load in vitro, develop tone spontaneously. The finding that spontaneous tone is reduced by indomethacin suggests that one or more prostanoids are involved in the development of spontaneous tone in this species. In this study we examined the effects of removing the cartilage component of the preparations on changes in tone induced by indomethacin and isoproterenol. In contrast to preparations containing cartilage, tissues devoid of cartilage, did not develop tone after the application of an initial 1 g resting load. Indomethacin (1 microM) reduced resting tone by 0.62 +/- 0.14 g in cartilage-containing tissues but, in contrast, reduced tone by only 0.03 +/- 0.01 g in tissues devoid of cartilage. Furthermore, relaxation responses (0.38 +/- 0.05 g) to isoproterenol (1 microM) could be produced in cartilage-containing preparations but not in cartilage-free preparations. Radioimmunoassays indicated that the release of PGE2, PGF2 alpha and 6-keto PGF1 alpha, the end-product of PGI2 breakdown, was diminished in preparations lacking cartilage. Thus, in guinea-pig airway preparations cartilage is apparently a source of sufficient prostanoids to induce spontaneous tone.