Efferent limb of the coronary vasoconstrictor reflex elicited by distension of the descending colon in anesthetized dogs

Distension of the descending colon elicits reflex coronary vasoconstriction. To study the efferent branch of this reflex, experiments were performed on 5 dogs anesthetized with pentobarbitone. A pouch was formed from the distal 15 cm of the descending colon and distended at constant pressure (54 ± 8.9 mmHg) with warm Ringer solution from a pressurized bottle. During distensions of the colon, arterial blood pressure and heart rate were kept constant by the withdrawal of blood and pacing of the heart, respectively. Experiments were performed before and after intravenous bretylium tosylate (10 mg/kg), a compound which prevents the outflow of catecholamines from the sympathetic postganglionic neurons. Before chemical sympathectomy, colon distension at constant heart rate and blood pressure caused a decrease in mean coronary blood flow by 7 ± 3.3% (mean ± SD, p < 0.0005). This response was abolished after the administration of bretylium (-0.07 ± 0.95%, p > 0.40). We conclude that the efferent branch of the reflex coronary vasoconstriction elicited by colon distension is through sympathetic nerves.