MESENTERIC BLOOD-PRESSURE PROFILE OF CONSCIOUS, FREELY MOVING RATS

1. Blood pressure has been measured in the aorta and at four points in the mesenteric circulation of conscious, freely moving rats under phy siological, resting conditions. 2. Using small polythene catheters, bl ood pressure was measured simultaneously in the aorta and either dista lly in the superior mesenteric artery (group A), at the base of a mese nteric arterial arcade (vessel diameter ca 100 mu m) (group B), at the base of a mesenteric venous arcade (group C) or distally in the super ior mesenteric vein (group D). Local blood flow distribution proximal and distal to the measurement point was restored after the cannulation s through appropriate ligations. 3. In conscious animals 5-17 h after surgery, systemic mean blood pressure was 121 +/- 2 mmHg. Local pressu res at the four locations (as a percentage of systemic pressure) were: 95 +/- 1% in group A, 64 +/- 2% in group B, 13 +/- 1% in group C and 7 +/- 1% in group D. Thus, large arteries dissipated 5% of the total p ressure drop, arcade small arteries 31%, the intramural circulation 51 %, arcade veins 6% and the remaining veins plus the hepatic circulatio n 7%. 4. Immediately after surgery, the corresponding pressure drops w ere 4, 16, 66, 5 and 9%, respectively, thus emphasizing that the press ure profile can be profoundly affected by surgery and anaesthesia. 5. The data indicate that under resting conditions in conscious, freely m oving rats, half the mesenteric vascular resistance resides outside th e intramural circulation, primarily in the arcade small arteries.