AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 3 430-G435, Copyright © 1990 by American Physiological Society
Thromboxane plays a role in postprandial jejunal oxygen uptake and capillary exchange
A. Alemayehu and C. C. Chou
Department of Physiology, Michigan State University, East Lansing 48824-1101.
The effects of a thromboxane A2 (TxA2)-endoperoxide receptor antagonist, SQ
29548, on jejunal blood flow, oxygen uptake, and capillary filtration
coefficient (Kfc) were determined in anesthetized dogs under resting
conditions and during the presence of predigested food in the jejunal lumen
in three series of experiments. In series 1, 2.0 micrograms intra-arterial
administration of SQ 29548 was found to abolish completely the
vasoconstrictor action of graded doses (0.05-2.0 micrograms) of
intra-arterial injection of a TxA2-endoperoxide analogue, U44069. SQ 29548
(2.0 micrograms ia) per se did not significantly alter resting jejunal
blood flow, oxygen uptake, capillary pressure, or Kfc. Before SQ 29548,
placement of food plus bile into the jejunal lumen increased blood flow +42
+/- 9%, oxygen uptake +28 +/- 7%, and Kfc +24 +/- 6%. After SQ 29548, the
food placement increased blood flow +37 +/- 8%, oxygen uptake +52 +/- 11%,
and Kfc +63 +/- 20%. The food-induced increases in oxygen uptake and Kfc
after SQ 29548 were significantly greater than those induced before the
blocking of TxA2-endoperoxide receptors by SQ 29548. Our study indicates
that endogenous thromboxane does not play a role in regulating jejunal
blood flow, capillary filtration, and oxygen uptake under resting
conditions. However, it plays a role in limiting the food-induced increases
in jejunal oxygen uptake and capillary exchange capacity without
influencing the food-induced hyperemia.
