The control of macro- and microcirculation in the mesentery and intestine.

The total blood flow and microvessel blood flow in the mesentery and the intestine anesthetized rabbits were measured while systemic hemodynamics were altered by baroreceptor stimulation and by noradrenaline injection. The percent change of the total peripheral resistance (Rt) was greater than the change in resistance in the intestinal vascular bed (Ri) during baroreceptor stimulation. The capillary blood flow in the intestinal muscle layer (Qs) and villus (Qv) increased slightly while the intestinal arterial flow (Qa) and the arteriolar flow in the mesentery (Qm) decreased. These data indicated that Qs and Qv were not controlled by the sympathetic vasoconstrictor system. The percent change of Ri was greater than that of Rt during noradrenaline injection. Noradrenaline decreased Qa, but Qs and Qv were decreased while Qm was increased. These results show that noradrenaline stimulates alpha-adrenoceptors on small arteries and arterioles in the intestine. The observed Qm changed was in response to the systemic hemodynamic change caused either by the baroreceptor input or by noradrenaline.