代謝臓器としての肺

抄録

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), PGF_2α, leukotoriene 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, PGF_2α, 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 PGF_1α 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. Various chemical mediators and cells which synthesize and release these mediators were summarized.
It is well known that LTC₄ and LTD₄ deteriorate the circulation in coronary arteries (CA) and these substances are metabolized in the lung. Therefore, the influence of LTC₄ and LTD₄ on the coronary circulation through the lung was studied in anesthetized mongrel dogs. The coronary arthery blood flow was reduced by 90%.
It is well known that cigarette smoking has diverse effects not noly on the airway system but also on the pulmonary and systemic circulatory system. The acute effects of cigarette smoking are induced mainly by nicotine, the main alkaloid in tobacco. We demonstrated that peripheral venous blood levels of complement C3a and C5a showed a marked increase.
Bronchial asthma, idiopathic interstitial pneumonitis (IIP) and other diffuse interstitial lung diseases related to PG, LTS, disaturated phosphatidylcholine (DSPC) and SP-36 of 36KDa were also referred to.