Intestinal blood flow is controlled by both feed arteries and microcirculatory resistance vessels in freely moving rats.

1. In freely moving rats, intestinal blood flow, aortic blood pressure and blood pressure at the base of mesenteric arcades were measured simultaneously so as to determine the role of feed arteries and of the microcirculation in the control of intestinal vascular resistance. Segmental resistances of feed arteries (Rfeed) and of microcirculatory vessels (Rmicro) were calculated. 2. At rest, Rfeed and Rmicro were 32 and 68%, respectively, of the total intestinal vascular resistance. 3. Injection of noradrenaline (2 micrograms i.v,) increased Rfeed by 151% and Rmicro by 243%. Angiotensin II (400 ng i.v.) did not increase Rfeed significantly, but increased Rmicro by 239%. Conversely, serotonin (15 micrograms i.v.) increased Rfeed by 414% but did not affect Rmicro significantly. 4. Spontaneous physical activity increased Rfeed by 29% and Rmicro by 39%, while sudden environmental stress increased Rfeed by 116% and Rmicro by 129%. Infused noradrenaline (1 microgram min-1 i.v.) or adrenaline (0.8 microgram min-1 i.v.) reduced intestinal flow by 21 and 16% respectively, while noradrenaline, but not adrenaline, increased intestinal resistances. 5. alpha 1-Blockade with prazosin (0.1 mg i.v.) reduced Rfeed and Rmicro by 43 and 16%, respectively. Thereafter, environmental stress decreased Rfeed by 24% while Rmicro was unaffected. Intravenous noradrenaline and adrenaline responses were attenuated. 6. We conclude that in freely moving rats, mesenteric feed arteries, as well as microcirculatory vessels, are true resistance vessels, and that both participate in the control of intestinal blood flow.