Ma. Vincent et al., MICROSPHERE INFUSION REVERSES VASOCONSTRICTOR-MEDIATED CHANGE IN HINDLIMB OXYGEN-UPTAKE AND ENERGY STATUS, Acta Physiologica Scandinavica, 164(1), 1998, pp. 61-69
The vasoconstrictors, angiotensin II (All) and serotonin (5-HT) produc
e opposing metabolic effects and appear to control different flow rout
es in the constant-flow perfused rat hindlimb. In the present study th
e association between vascular flow route recruitment and metabolism w
as assessed by selective microsphere embolism of either route. Microsp
heres (MS, 11.9 +/- 0.1 mu m, mean +/- SE diameter) were injected duri
ng All, 5-HT or vehicle infusions(basal conditions) and the effects on
hindlimb (4.7 +/- 0.1 g muscle) oxygen uptake ((C) over dot o(2)) and
indices of energy status CrP/Cr, CrP/ATP and energy charge (EC) of th
e calf muscle group assessed. MS (1.5 x 10(6)) injected during vehicle
, or 5-HT infusion increased (V) over dot o(2) (P < 0.05) but did not
affect energy status. During All, MS decreased (V) over dot o(2). Chan
ge in (V) over dot o(2) correlated positively with CrP/Cr (r = 0.68, P
< 0.0001) and CrP/ATP (r = 0.51, P < 0.001) but not EC (r = 0.08, P =
0.59). MS (1.5 x 10(6)) increased pressure but did not affect the flo
w rate. The metabolic changes resulting from 1.5 x 10(6) microspheres
were intensified by a second injection of 1.5 x 10(6) microspheres but
further injection (>3.0 x 10(6) microspheres) began to inhibit flow.
It is concluded that a finite number (less than or equal to 3.0 x 10(6
)) of microspheres of 11.9 mu m diameter has opposite effects on (C) o
ver dot o(2) depending on the vasoconstrictor present and that these e
ffects result from the occlusion of the different vascular route acces
sed by each vasoconstrictor. The data support the proposal that hindli
mb metabolism can be controlled by vasoconstrictors as a result of sel
ective vascular recruitment.