Effects of Low O2 on Intestinal Blood Flow, Tonus and Motility

Abstract

Effects of low O2 on intestinal blood flow were studied in blood perfused segments of dog intestine, 1) completely isolated and the low O2 administered by perfusion with hypoxic heparinized dog blood, or, 2) completely isolated except for extrinsic nerves and the low O2 administered either as in 1 or by respiratory gas mixtures via trachea. The local administration of low O2 (10–7%) to either preparation 1 or 2, increased intestinal blood flow remarkably. This, in the absence of any changes in intestinal tonus or motility, must be ascribed solely to dilatation of the intestinal vasculature per se which commonly predominates over the reflexogenic and/or centrogenic vasoconstrictive influence of low O2. Local histotoxic anoxia (0.3 ml of a 1% solution of NaCN) evokes effects similar to those of 7% O2. Low O2 can also prominently affect intestinal blood flow indirectly, a) by its action on intestinal tonus whereby it may enhance or completely nullify the effects of vasodilatation per se; and b) by its depressive action on the rhythmic intestinal contractions and their propulsion of intestinal blood. In passing through the intestinal vasculature the blood acquires potent vasodilatatory properties which must be ascribed to some ‘substance,’ other than CO2 or low O2, whose release into the blood is apparently facilitated by low O2. The data indicate that the intestine contributes to the reflex chemical control of breathing.