Changes in integrated vagal afferent activity induced by model lung diseases in rats

An attempt has been made in the present report to evaluate quantitatively the sensory activity in both vagal nerves of control rats and rats with experimental lung inflammation, by employing the integration technique. We evaluated background vagal nerve activity, resting respiration and activity during inflation at constant pressures of 5 to 20 cm of water. It was found that integrated vagal respiratory activity cannot be assessed in absolute units under our experimental conditions, because of the large scatter of data. However, when the integrated values were related, for example, to resting respiration (in percentage), it was possible to compare some respiratory parameters in control, healthy rats of the Wistar strain and rats with lung inflammation. While background activity in control rats represents 75.9% of resting respiration, this parameter is significantly higher both in rats with 2-day carrageenin lung inflammation and those intoxicated with paraquat. Lung inflation at pressures 5, 10, 15, 20 cm H2O increased vagal activity linearly both in control and the two experimental groups with the degree of lung inflation. However, values in experimental animals corresponding to those of the control group were not reached until higher inflation pressures. From the functional aspect, experimental rats had characteristic tachypnoea which returns to control values after bilateral vagotomy. Since it was found that lung compliance was significantly decreased in both carrageenin and paraquat lung processes, it is being suggested that the diminished activity from lung receptors during inflation is due to mechanical properties of the lung tissue, namely lowered lung compliance.