Skeletal muscle circulation in animals
Under normal resting condition, blood flow to the skeletal muscle is 15% and this varies according to the activity of the muscle. Blood flow to the skeletal muscle is controlled by the alpha adrenergic sympathetic system tone on the blood vessels.
The neurotransmitter substance involved is the norephinephrine which stimulates alpha receptors in the vascular smooth muscle. These fibres also produce vasoconstriction and decreases the blood flow. This vasoconstriction is reflexely influenced by arterial baroreceptors, chemoreceptors and cardiac baroreceptors.
On the other hand, epinephrine, has a slight to moderate vasodilator effect by stimulating the beta receptors. In certain species like cats and lower animals, sympathetic vasodilator fibres are present that have acetylcholine as the neurotransmitter.
During rest and at exercise, blood flow to the skeletal muscle in autoregulated and is not affected by the level of metabolites. But local metabolites play role in vasodilatation.
Vasodilator factors activated during muscle contraction are anoxia, increased Co2 tension, lactic acid, hydrogen ions, bradykinin, histamine, acetyl choline, ATP, adenylic acid, potassium ions etc.