The lung as a metabolic organ

Abstract

The fundamental importance of the lung in providing oxygen and eliminating carbon dioxide is well known. However the lung has another critical role as the site of numerous and important metabolic events. Some of these metabolic activities are essential to the normal performance of pulmonary gas exchange. Impairment of pulmonary metabolic activities can, therefore, have far-reaching repercussions on many organ systems. Special features of pulmonary vascular beds which are helpful for the metabolism of various vasoactive substances through pulmonary circulation are described. The lung can uptake or metabolize various vasoactive substances including acetylcholine, serotonin, bradykinin, prostaglandin E2 (PGE2), PGF2 alpha, leukotriene C4 (LTC4), LTD4 and LTE4. On the other hand the lung can synthetize and release various vasoactive substances including histamine, serotonin, LTC4, LTD4, LTE4, thromboxane A4 (TXA4), PGD2, PGE2, PGF2 alpha, PGI2, LTB4, and PAF (platelet activating factor). We also investigated the metabolism of LTC4 and LTD4 through isolated perfused guinea pig lung lobes. And it is clarified that the infused LTC4 was converted to LTD4 and LTE4, while the infused LTD4 was converted to LTE4. Seventeen years ago, we demonstrated the release of prostaglandins from the lung during mechanical ventilation at large tidal volumes in anesthetized mongrel dogs. We thought this PG is PGE2 which dilates pulmonary vasculatures. In the present study we investigated the release of PG from healthy volunteers by spontaneous hyperventilation. We demonstrated that serum levels of 6-keto PGF1 alpha and PGE2 showed a marked increase following the spontaneous hyperventilation. Various humoral factors related to the pulmonary vascular responses and various humoral factors which related to the tracheobronchial responses were also presented.(ABSTRACT TRUNCATED AT 250 WORDS)