EFFECT OF DENERVATION OF THE RAT SUPERIOR MESENTERIC ARTERIAL BED ON THE DISTRIBUTION OF RESISTANCE AMONG THE FIRST 4 ORDERS OF BRANCHING

The rat superior mesenteric artery with its first four orders of branc hing has been examined as an isolated perfused preparation. Lumen diam eter and proportional resistance at each level have been determined an d compared under conditions of constant pressure following methoxamine -induced constriction and acetylcholine-induced relaxation in intact a nd denervated preparations. A comparison was also made between intact preparations under conditions of constant pressure and constant now. L umen diameter and segment length were measured by analysis of video-ta ped images. The distribution of resistance among the first four orders of branching was estimated from the measured values using the Poiseui lle formula. Intact first and fourth order branches had a proportionat ely low resistance, with the remaining resistance being fairly evenly distributed between the second and third order branches. No change in the pattern occurred as a result of either methoxamine or acetylcholin e treatment. The pattern of distribution of resistance changed followi ng denervation, so that proportional resistance was high in the first order branches and fell off from the second to fourth order branches. With methoxamine, the first order branches of denervates had a signifi cantly higher resistance than in intact tissues, with the distribution of resistance in the second to fourth order branches following the ba sal resistance pattern. Reduction in the proportion of resistance with acetylcholine was similar in both intact and denervated preparations. Distribution of resistance did not differ between constant flow and c onstant pressure intact preparations.