Effect of fasting and refeeding on mesenteric autoregulation in conscious rabbits

To determine whether feeding improves the efficacy of mesenteric autoregulation in conscious animals, rabbits were instrumented with pulsed-Doppler flow probes on the superior mesenteric artery and distal abdominal aorta to record mesenteric and hindquarters blood flow velocity. Hydraulic occluders were placed on the abdominal aorta (just below the celiac artery) and the thoracic vena cava to vary mesenteric and hindquarters arterial pressure (MAP), which was monitored via a catheter positioned in the distal abdominal aorta. Heart rate (HR) and lumbar sympathetic nerve activity (LSNA) were monitored as indexes of sympathetic nervous system activity. Pressure-velocity curves were obtained by aortic and caval occlusions on two consecutive days; first after a 24-h fast and after approximately 24 h of ad libitum refeeding. In the fed state, mesenteric velocity was significantly increased and MAP was decreased slightly; the slight decrease in MAP was counteracted by significant increases in HR and LSNA, whereas hindquarters perfusion was unchanged. The mesenteric and hindquarters pressure-velocity curves were all highly linear (r greater than or equal to 0.9) and showed no evidence of autoregulation in the fasted or fed state when pressure was changed by either the aortic or the caval occlusions. We conclude that autoregulation plays a minor role in the short-term regulation of mesenteric blood flow in the conscious rabbit.