Oxygen exchange in the mesenteric microcirculation of the dog

The relationships of O₂ tension in mesenteric lymph (PmlO₂) and mesenteric venous blood (PmVO₂) were examined after graded hemorrhage (10 dogs), stepwise increments in FIO₂ (4 dogs), and regional infusion of papaverine (2 mg/min) or IV glucagon (25 μg/kg) (4 dogs). Measurements included superior mesenteric arterial flow (SMA-Q), PaO₂, PmVO₂, PmlO₂, and arterial and mesenteric venous blood O₂ content (CaO₂, CmVO₂). Intestinal DO₂ was calculated as the product of SMA-Q and CaO₂, and VO₂ was calculated from the Fick equation [SMA-Q x (CaO₂-CmVO₂)]. Graded hemorrhage lowered SMA-Q, DO₂ and DO₂/VO₂ and increased splanchnic O₂ extraction (CaO₂-CmVO₂). Elevation of EIO₂ increased PaO₂, PmVO₂, and PmlO₂. Both PmlO₂ and PmVO₂ varied directly with DO₂/VO₂ and PaO₂, but PmlO₂ showed greater sensitivity to PaO₂. Papaverine and glucagon both increased SMA-Q, DO₂, CmVO₂, and PmVO₂, but PmlO₂ rose after papaverine, indicating greater capillary perfusion, and fell after glucagon, suggesting diversion of mesenteric blood flow through arteriovenous shunts. Thus, either PmVO₂ or PmlO₂ is ordinarily an accurate measure of intestinal tissue oxygenation, but the disparate response after glucagon suggests that PmlO₂ is a more reliable indicator.