Hypoxia Does Not Alter Angiotensin Converting Enzyme Activity in Hamster Pulmonary

Studies were initiated to investigate the effects of hypoxia on the conversion of angiotensin I (AI) to angiotensin II (All) in microvessels of the lung. Using the technique of allografting neonatal lung tissue into the cheek pouch of normal hamsters, the microvessels of the lung, pulmonary arterioles, and venules could be visualized and manipulated by direct in vivo microscopy. The microvessels of the lung were studied 7-10 days after allografting by anesthetizing the hamster with pentobarbital (6.0 mg/ 100 g body weight i.p.) and then preparing the lung tissue for observation. The tissue was suffused with a Ringer's bicarbonate solution bubbled with a normal (20 % O2-5 % CO2-75 % NJ or a low (95% N2-5 % COj) oxygen mixture. After equilibration, a pulmonary arteriole or venule was selected for observation, and the vessel geometry was recorded. Then, a micropipette containing either AI or All was positioned alongside the vessel, and the agent was delivered continuously for 2 minutes. Lumen diameter was recorded continually for 8-10 minutes. This procedure was repeated until both angiotensins were tested on pulmonary arterioles and venules under conditions of a normal and low oxygen environment. This protocol was repeated on cheek pouch microvessels that did not contain pulmonary allografts. Both AI and All produced rapid decreases in the lumen diameters of all microvessels tested. This vasoconstriction was greater for All, and the oxygen environment did no