Regulation of coronary circulation or pulmonary circulation in the setting of simulated space environments.

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To simulate the space environment, the animals were tilted down by 10degrees.The chronically instrumented dog enabled us to measure coronary blood flow continuously were studied.In the setting of simulated space environment, there was no discernible change in coronary flow reserve assessed by reactive hyperemia created with 20-second occlusion.Although there was little increase in left ventricular volume in the setting of the simulated space environment, the blockade resulted in the augmented response of left ventricular volume to the head-down tilt.This augmentation caused the marked increase in coronary blood flow.This was probably due to increase in oxygen demand of the heart in the setting of simulated space environment.Acetylcholine induced systemic hypotension.This response was partially inhibited by 1-Nitro Arginine Methyl Ester (1-NAME), and was completely inhibited by mucarinic-1 receptor blockade (Pirenzepine).On the other hand, the response of coronary arterial resistance to acetylcholine was hardly inhibited by 1-NAME and strongly inhibited by Pirenzepine.To clarify the effect of high-gravity condition on pulmonary circulation, the determination of EDRF was established and the effects of low alveolar oxygen on the gravity dependent distribution of pulmonary blood flow were studied.Low alveolar oxygen redistributed the blood flow from lower lung field to upper lung field.