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Atropine: no effect on exercise muscle hyperemia in conscious rats
Abstract:
The purpose of this study was to test the hypothesis that muscarinic cholinergic receptors are involved in the initial vasodilation in red muscle vascular beds of conscious rats performing slow locomotory exercise. Atropine sulfate (1 mg/kg, ia) was administered to one group of rats in which distribution of cardiac output was estimated with radiolabeled microspheres immediately before exercise while the animals were standing on the treadmill and at 30 s and 5 min of treadmill walking at 15 m/min. Blood flows within and among muscles in the atropine-treated animals were compared with flows in control rats that were given a sham injection of an equal volume of physiological saline. Heart rates were elevated above those of control animals in the atropinized rats during preexercise (+17%) and at 30 s of exercise (+15%). However, distributions and magnitudes of blood flows in nonmuscular tissues and within and among skeletal muscles were the same (P greater than 0.05) in atropinized and control rats during preexercise and at both exercise times, indicating that atropine had no effect on the distribution of cardiac output in the rats. It is concluded that muscarinic cholinergic receptors do not play a significant role in elevating muscle blood flow in conscious rats, either during the preexercise anticipatory phase or during slow locomotory exercise.
Insights
Muscarinic cholinergic receptors do not significantly impact muscle blood flow during exercise. This study found atropine did not alter blood flow distribution in rats during treadmill exercise.
Area of Science:
- Exercise Physiology
- Cardiovascular Physiology
- Neuropharmacology
Background:
- Understanding the mechanisms regulating skeletal muscle blood flow during exercise is crucial for exercise physiology.
- The role of muscarinic cholinergic receptors in exercise-induced vasodilation remains incompletely understood.
Purpose of the Study:
- To investigate the involvement of muscarinic cholinergic receptors in the initial vasodilation of red muscle vascular beds in rats during slow locomotion exercise.
Main Methods:
- Conscious rats were administered atropine sulfate or a saline control.
- Cardiac output distribution was measured using radiolabeled microspheres before and during treadmill exercise.
- Muscle and non-muscular tissue blood flows were compared between groups.
Main Results:
- Atropine administration did not alter the distribution or magnitude of blood flow in muscular or non-muscular tissues.
- Heart rates were slightly elevated in atropinized rats, but this did not affect blood flow distribution.
- No significant differences in blood flow were observed between atropine-treated and control rats.
Conclusions:
- Muscarinic cholinergic receptors do not play a significant role in increasing muscle blood flow during the anticipatory phase or during slow locomotory exercise in conscious rats.
- The findings suggest other mechanisms are primarily responsible for exercise-induced vasodilation in skeletal muscle.