IL-6 increases airway resistance in the rat

The end-inspiratory occlusion method was applied in anesthetized, paralyzed, positive pressureventilated rats to assess the possible effects of interleukin IL-6 on respiratory mechanics in normal rats. Measurements were made in control rats and in experimental animals before and after IL-6 intraperitoneal administration (15 ng/100 g), including static respiratory system elastance, the resistance to airflow and to the movement of respiratory system tissues, and the resistance due to lung stress–relaxation and mechanical inhomogeneity. Respiratory system hysteresis was also measured, and total mechanical breathing work rate and its elastic and resistive components calculated. Control rats did not exhibit alteration in respiratory mechanics during the observation period (30 min), while the experimental animals showed an increase in resistive pressure dissipations starting 15 min after IL-6 administration. Dose-dependent effects were also investigated. In a rather delayed effect, IL-6 increased the resistance to airflow and to the movement of respiratory system tissues, the resistance due to lung stress–relaxation and mechanical inhomogeneity, and the related resistive mechanical breathing work rate, and left the elastic pressure dissipation unaltered. The mechanisms by which IL-6 may contribute to the airways resistance increase which is seen in different respiratory diseases are likewise discussed.