For localization of the site of post-prandial mesenteric hyperemia, low-fat, low-protein food was placed in either the stomach, duodenum, or jejunum while blood flow was measured in the celiac artery, superior mesenteric artery (SMA), or jejunal vein of anesthetized dogs. Distribution of flow in the jejunal wall was also measured. After intragastric placement of food, celiac arterial flow increased within 5 min and remained elevated for 30-60 min; SMA flow increased within 30 min and stayed up for at least 3 h. Intra-duodenal infusion of digested food increased SMA flow but did not alter celiac flow or flow to an isolated jejunal segment. Placement of digested food into one jejunal segment increased flow to that segment did not affect flow was localized to the mucosal layer. These studies indicate that during digestion, blood flow increases in the mucosa of the intestine when exposed to chyme and is not changed in other areas of the gastrointestinal tract. Postprandial mesenteric hyperemia induced by low-fat, low-protein food is a local phenomenon.
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. Effects of carotid chemoreceptor stimulation on coronary vascular resistance, left ventricular dP/dt, and strain-gauge arch output were studied at natural coronary blood flow with the chest closed and during constant-flow perfusion of the left common coronary artery with the chest open. Carotid chemoreceptor stimulation slightly increased left ventricular dP/dt and slightly decreased the strain-gauge arch output, while markedly increasing systemic pressure. Coronary blood flow increased; however, coronary vascular resistance wa.as not affected. 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.
Reflex vascular responses to local carotid chemoreceptor stimulation with hypoxic-hypercapnic, hypoxic, or hypercapnic blood were investigated in pentobarbitalized dogs. Bilaterally isolated carotid chemoreceptors were perfused via an extracorporeal lung circuit. Oxygen and carbon dioxide tensions of blood perfusing the carotid bodies were altered by ventilating the isolated lung with various O2-CO2 mixtures. Ventilation of the whole animal maintained normal systemic O2 and CO2 tensions. Perfusion pressures of the isolated kidney, ileum, forelimb, gracilis and hindpaw were measured during constant-flow perfusion. Carotid chemoreceptor stimulation with hypoxic-hypercapnic blood before vagotomy increased renal vascular resistance but caused no change in intestinal or forelimb resistance. Following vagotomy, hypoxic-hypercapnic, hypoxic, or hypercapnic carotid body stimulation increased renal, intestinal, and forelimb vascular resistance. Forelimb skin and muscle vascular beds contributed about equally to the increase in forelimb resistance. Gracilis muscle and hindpaw resistance also increased during hypoxic-hypercapnic stimulation after vagotomy.
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