Distribution and location of slowly adapting pulmonary stretch receptors in the airways of cats.

The distribution and location of slowly adapting pulmonary stretch receptors (PSRs) that affect respiratory and cardiovascular functions were investigated in anaesthetized, artificially ventilated and thoracotomized cats. The location of the receptors was done by punctate stimulation and local mechanical stimulation after occlusion of the trachea at end-expiration (Exp). 84% of the slowly adapting PSRs were found to be located in the lung parenchyma. The occlusion technique alone was found to be of help only for a limited population of stretch receptors. The intrapulmonary distribution of PSRs revealed a greater percentage of receptors in the diaphragmatic lobe. No correlation was found between conduction velocity and receptor location. Both the slowly and rapidly conducting receptors were found to be scattered throughout the entire lung parenchyma. However, it was observed that while the majority of low threshold (LT) PSRs were located closer to the hilum of the lung, many of the higher threshold (HT) receptors were located farther away. In addition, when veratrine was administered into the pulmonary circulation, 83% of HT PSRs studied were stimulated by the drug, while only 25% of LT PSRs under study could be stimulated this way. The significance of the above findings is discussed.