The role of endothelial factors in the active hyperemic responses
in contracting canine muscle.
King-Vanvlack, Cheryl E., Scott E. Curtis, Jeffrey D. Mewburn, Stephen
M. Cain, Christopher K. Chapler.
School of Rehabilitation Therapy and Department of Physiology,
Queen's University, Kingston, ON, K7L 3N6 and Department of
Pediatrics and Physiology and Biophysics, University of Alabama at
Birmingham, USA, 35205
APStracts 2:0115A, 1995.
We investigated whether EDRF and prostaglandins, which may be released
under conditions of increased blood flow, contribute to the active
hyperemia in contracting muscle of anesthetized dogs. The venous
outflow from the left gastrocnemius muscle was isolated and measured.
The tendon was cut and placed in a force transducer. One group served
as a control (n=9; CON); EDRF synthesis was inhibited using N_-nitro
-L-arginine methyl ester (L-NAME) in a second group (n=9), and a third
group (n=7) received L-NAME and indomethacin (L-NAME+INDO) to inhibit
prostaglandin synthesis. Following resting measurements, the distal
end of the cut sciatic nerve was stimulated to produce isometric
contractions at 1, 2, 4, and 6 twitches per second (tw/s) for 6-8
min, separated by 25 min recovery periods. Blood flow and O2 uptake
increased linearly from resting values of 11.8+/-2.4 and 0.3+/-0.05
ml x 100g-1 x min-1 respectively to maximal values of 84.2+/-5.1 and
11.1+/-0.7 ml x 100g-1 x min-1 in the CON group; neither these values
nor those for tension development were different from values observed
at comparable contraction frequencies in the L-NAME and L-NAME+INDO
groups. At rest, resistance was greater (p<0.05) in both the L-NAME
and L-NAME+INDO groups as compared to CON; the highest value
(p<0.05) occurring in the L-NAME+INDO group. Muscle resistance
decreased (p<0.05) in all groups at all contraction frequencies;
the values were not different between the 3 groups. Because
differences in resting vascular resistance were abolished even at 1
tw/s, we believe that endothelial factors which modulate vascular
tone at rest, do not contribute to active hyperemia.
Received 22 August 1994; accepted in final form 10 March 1995.
APS Manuscript Number A881-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.