Vasoactive intestinal polypeptide（VIP）と急性低酸素症および急性呼吸性アチドーシス

Release of Vasoactive Intestinal Polypeptide during Acute Hypoxia and Acute Respiratory Acidosis

　近年，肺は単にガス交換を行なうだけでなく，種々の血管作動性物質の産生，放出および代謝に重要な臓器と考えられている。例えば，anaphylaxisの時，histamine，slow-reacting substance of anaphylaxis（SRS-A），prostaglandins（PGs）などが肺より放出されると報告されている。また著者らは急性低酸素症時，PGsの中間代謝産物であるPG endoperoxideより生じるprostacyclin（PGI₂）が肺から放出される可能性があることを報告^1）した。今回，著者らはブタの小腸から発見されたvasoactive intestinal polypeptide（VIP）について，急性低酸素症時および急性呼吸性アシドーシス時に肺より放出されるかどうか検討した。

　VIPはその名が示すよりもはるかに広く体内に分布し，膵臓を含む食道から直腸までの消化管のみならず，中枢神経系や肺にも高濃度に分布することが知られている。

　Vasoactive intestinal polypeptide (VIP), originally discovered and isolated from porcine duodenum, is now known to occur more widely in normal tissues, including the lung, and to have a broader range of biological actions than its name implies. VIP induces vasodilation in the peripheral systemic vessels, the coronary vessels and the pulmonary circulation, and it has a positive inotropic effect on cardiac muscle. VIP shows bronchodilation and augmented ventilation. However, the possible physiologic roles in cardiorespiratory disorders are still unknown.

　We have tried to confirm the release of VIP, especially from the lung, during acute hypoxiaand acute respiratory acidosis in anesthetized dogs with controlled ventilation. Acute hypoxia was induced by ventilation of 10 percent oxygen for 10 minutes, and acute respiratory acidosis by ventilation of 10 percent carbon dioxide for five minutes. We collected blood samples from the aorta, the pulmonary artery or the right ventricle (PA) and the superior mesenteric vein (MV) through indwellt catheters. Plasma VIP levels were measured by a specific radioimmunoassay.