M.A.Vincent and M.G. Clark
Biochemistry, University of Tasmania, Hobart, Australia

Agents that cause vasoconstriction in the constant-flow perfused rat hindlimb can either increase (Type A vasoconstrictor) or decrease (Type B vasoconstrictor) metabolism. The opposing metabolic effects of vasoconstrictors may be due to flow re-distribution into nutritive or non-nutritive flow routes. In the present study, microspheres (12Ám, diameter) or FluoSpheres® (10Ám or 15Ám, diameter) were infused, in the presence of vehicle, AII (Type A) or 5-HT (Type B). Metabolic parameters including oxygen consumption (VO2) and tissue high energy intermediates such as creatine phosphate (CrP), creatine (Cr), ATP, ADP and AMP were assessed. When 1.5x106 microspheres (12Ám) were infused, the stimulatory effect of AII on VO2 and CrP/(CrP+Cr) was significantly reversed by 38% and 88% respectively (p<0.05) whereas the inhibitory effect of 5-HT on VO2 and CrP/(CrP+Cr) was reversed by 37% and 34% respectively. In the absence of vasoconstrictors, 1.5x106 microspheres increased VO2 similar to the effects of microspheres with 5-HT, however CrP/(CrP+Cr) was not affected. For all conditions, tissue energy charge (EC) and flow rate did not change. Similarly, the infusion of 1.5x106 (10Ám) FluoSpheres® or 5.0x105 (15Ám) FluoSpheres® partially reversed the effects of 5-HT and AII. In conclusion, microspheres can reverse the pre-constricted metabolic state of the perfused rat hindlimb by changing the vascular flow route and provide a novel method for studying nutritive and non-nutritive flow.

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