Prostanoids in regulation of postprandial jejunal hyperemia and oxygen uptake

The role of prostanoids in regulation of jejunal blood flow (JBF) was studied in anesthetized dogs. Intra-arterial infusions of arachidonate produced biphasic changes and dose-dependent decreases in jejunal vascular resistance (JVR) in untreated and aspirin-pretreated dogs, respectively; mefenamate abolished these responses. The jejunum released prostaglandin I2 (PGI2) greater than PGE2 greater than thromboxane A2 (TXA2) (radioimmunoassay) under resting conditions, and food enhanced the release of PGE2 greater than PGI2 greater than TXA2 greater than PGF2 alpha. Addition of arachidonate to food enhanced TXA2 and PGF2 alpha releases and decreased PGI2 and PGE2 releases, while inhibiting the food-induced increases in JBF and O2 uptake; mefenamate inhibited these arachidonate actions. A TXA2 receptor antagonist (SQ-29548) reversed the arachidonate vascular and metabolic actions. Intra-arterial infusions of PGI2 or PGE2 decreased, whereas TXA2 analogue U-44069 or PGF2 alpha increased JVR. A mixture of these prostanoids infused at blood concentrations similar to the increase observed during food placement did not alter JVR. At concentrations similar to the increases observed when arachidonate was added to luminal food, the infusions increased JVR and abolished the food-induced decrease in JVR. In conclusion, jejunal productions of PGI2, PGE2, TXA2, and PGF2 alpha increase during nutrient absorption. Addition of arachidonate to food attenuates the former two and enhances the latter two releases, which act to attenuate food-induced jejunal hyperemia.