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Vol. 84, Issue 3, 884-889, March 1998
Departments of Veterinary Biomedical Sciences and Medical Physiology, The Dalton Cardiovascular Research Center, and Division of Cardiology, College of Medicine, University of Missouri, Columbia, Missouri 65211
Coronary
resistance arteries isolated from exercise-trained pigs have been shown
to exhibit enhanced myogenic reactivity (J. M. Muller, P. R. Myers, and
M. Harold Laughlin. J. Appl. Physiol. 75: 2677-2682, 1993). The purpose of this study was to test the hypothesis that exercise training results in enhanced vasoconstrictor responses of these arteries to all vasoconstrictor stimuli
[specifically acetylcholine (ACh), endothelin-1 (ET-1), KCl, and
the Ca2+ channel-agonist Bay K
8644]. Female Yucatan miniature swine were trained (Trn) on a
motor-driven treadmill (n = 16) or
remained sedentary (Sed, n = 15) for
16-20 wk. Arteries 50-120 µm in diameter were isolated and
cannulated with micropipettes, and intraluminal pressure was set at 60 cmH2O throughout experiments.
Vasoreactivity was evaluated by examining constrictor responses to
increasing concentrations of ACh
(10
9 to
10
4 M), ET-1
(10
10 to
10
8 M), KCl (bath
replacement with isotonic physiological saline solution containing 30 or 80 mM), and Bay K 8644 (10
9 to
10
6 M). Constricted
diameters are expressed relative to the passive diameter observed after
100 µM SNP. All four constrictors produced similar decreases in
diameter in arteries from both groups [ACh: 0.52 ± 0.07 (Trn)
and 0.54 ± 0,06 (Sed); ET-1: 0.66 ± 0.05 (Trn) and 0.70 ± 0.07 (Sed); KCl: 0.66 ± 0.05 (Trn) and 0.70 ± 0.07 (Sed); Bay K
8644: 0.86 ± 0.05 (Trn) and 0.76 ± 0.05 (Sed)]. Present results combined with previous observations indicate that exercise training does not alter vasoconstrictor responses of porcine coronary resistance arteries but specifically increases myogenic reactivity. Thus the underlying cellular mechanisms for myogenic tone are altered
by training but not receptor-mediated mechanisms (ACh and ET-1) nor
voltage-gated Ca2+ channels (KCl
and Bay K 8644) in coronary resistance arteries.
albumin; spontaneous tone; vascular smooth muscle; acetylcholine; endothelin; Bay K 8644; nitroprusside
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