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1 Dalton Cardiovascular Research Center, 2 Department of Veterinary Biomedical Sciences, and 3 Department of Physiology, and University of Missouri, Columbia, Missouri 65211
Received 7 May 1996; accepted in final form 4 April 1997.
Parker, Janet L., Mildred L. Mattox, and M. Harold Laughlin.
Contractile responsiveness of coronary arteries from exercise trained rats. J. Appl. Physiol. 83(2):
434-443, 1997.
The purpose of this study was to determine whether
exercise training alters vasomotor reactivity of rat coronary arteries.
In vitro isometric microvessel techniques were used to evaluate
vasomotor properties of proximal left anterior artery rings (1 ring per
animal) from exercise-trained rats (ET;
n = 10) subjected to a 12-wk treadmill training protocol (32 m/min, 15% incline, 1 h/day, 5 days/wk) and
control rats (C; n = 6) restricted to
cage activity. No differences in passive length-tension characteristics
or internal diameter (158 ± 9 and 166 ± 9 µm) were observed
between vessesls of C and ET rats. Concentration-response curves to
K+ (5-100 mM), prostaglandin
F2
(10
8-104
M), and norepinephrine
(108-104)
were unaltered (P > 0.05) in
coronary rings from ET rats compared with C rats; however, lower values
of the concentration producing 50% of the maximal contractile response
in rings from ET rats (P = 0.05)
suggest that contractile sensitivity to norepinephrine was
enhanced. Vasorelaxation responses to sodium nitroprusside (109-104
M) and adenosine
(109-104
M) were not different (P > 0.05)
between vessels of C and ET rats. However, relaxation responses to the
endothelium-dependent vasodilator acetylcholine (ACh;
1010-104
M) were significantly blunted (P < 0.001) in coronary rings from ET animals; maximal ACh relaxation
averaged 90 ± 5 and 46 ± 12%, respectively, in vessels of C
and ET groups. In additional experiments, two coronary rings (proximal
and distal) were isolated from each C
(n = 7) and ET
(n = 7) animal. Proximal coronary
artery rings from ET animals demonstrated decreased relaxation
responses to ACh; however, ACh-mediated relaxation of distal coronary
rings was not different between C and ET groups.
NG-monomethyl-L-arginine
(inhibitor of nitric oxide synthase) blocked ACh relaxation of all
rings. L-Arginine (substrate for
nitric oxide synthase) did not improve the blunted ACh relaxation in proximal coronary artery rings from ET rats. These studies suggest that
exercise-training selectively decreases endothelium-dependent (ACh) but
not endothelium-independent (sodium nitroprusside) relaxation responses
of rat proximal coronary arteries; endothelium-dependent relaxation of
distal coronary arteries is unaltered by training.
vascular smooth muscle; potassium; norepinephrine; prostaglandin
F2
; adenosine; nitroprusside; acetylcholine; L-arginine; NG-monomethyl-L-arginine; nitric oxide synthase; flow
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