The American journal of physiology
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We have recently shown that 5% CO2/95% O2 in the serosal bathing solution, with 100% O2 in the mucosal solution, results in CO2-diffusion limitation of acid secretion in bullfrog gastric mucosa. Changing to 10% CO2/90% 02 on both surfaces doubles the acid secretory rate. We calculate that, were the rate of oxygen consumption to increase significantly as a result of secretory stimulation, the tissue would now be oxygen limited. ⋯ Since no change in acid secretory rate or potential difference was observed upon changing from PO2 = 0.9 to PO2 = 1.9 atm, we conclude that the tissue is not O2 limited at normal pressure. Decreasing PO2 below 0.9 atm, by contrast, decreases the acid secretory rate and raises both PD and resistance. We infer that the rate of oxygen consumption did not rise significantly when acid secretion was increased by supplying sufficient CO2.
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Stripped duodenal mucosa of rabbits was mounted in Ussing chambers containing a Ringer solution gassed with 100% O2. The disappearance of acid or alkali from the mucosal solution of short-circuited tissue was measured with a pH stat while the serosal pH was kept at 7.4. The duodenum rapidly disposed of both acid and alkali; neither property was altered by gassing with N2 while iodoacetate was in the perfusing solutions. ⋯ While acid disposal progressively decreased with time for the in vitro gut sacs, the in vivo gut sac showed no fatigue in this respect. Luminal acidification in the Ussing chamber was associated with a profound reduction in short-circuit current (Isc), partially reversible by elevation of the mucosal pH but not by luminal glucose. Our data suggest that acid disposal occurs in part by intraluminal neutralization and in part by diffusion into the mucosa.
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Adenosine is a possible mediator of myocardial and skeletal muscle blood flow regulation. Whether adenosine plays a similar role in modulating the pulmonary pressor response to acute alveolar hypoxia is not known. Adenosine levels (nmol/g tissue) in lung in six dogs ventilated with 95% N2, and 5% CO2 for a period of 3 min increased nearly 10-fold. ⋯ Dipyridamole produced similar responses. These data indicate that adenosine is a pulmonary vasodilator and that it may modulate the pulmonary pressor response to acute alveolar hypoxia. The findings suggest that the use of adenosine or dipyridamole may be beneficial in patients with pathologic elevations of the pulmonary vascular resistance which are a result of an exaggerated pulmonary pressor response to hypoxia, as seen in high-altitude pulmonary edema or that following cerebral injury.
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Coronary vascular and myocardial responses to selective hypoxic and/or hypercapnic carotid chemoreceptor stimulation were investigated in constantly ventilated, pentobarbital or urethan-chloralose anesthetized dogs. Bilaterally isolated carotid chemoreceptors were perfused with autologous blood of varying O2 and CO2 tensions via an extracorporeal lung circuit. Systemic gas tensions were unchanged. ⋯ These studies show that local carotid body stimulation increases coronary blood flow but has little effect on the myocardium. The increase in coronary blood flow results mainly from an increase in systemic arterial pressure. Thus these data provide little evidence for increased sympathetic activity of the heart during local stimulation of the carotid chemoreceptors with hypoxic and hypercapnic blood.