ABSTRACT
The effect of hypoxia on blood vessel muscle cells is one of the most important chemical factors causing vasodilation. In addition to the autoregulatory mechanisms, the blood vessels supplying skeletal muscles are also provided with sympathetic innervation of both vasoconstrictor and vasodilator types. A non-neuronal non-mast cell pool of histamine located in the media of skeletal muscle blood vessels would be responsible for the histaminergic vasodilation. A more detailed physiological and histochemical analysis of the neurotransmitters involved in the control of blood flow within skeletal muscles demonstrated that norepinephrine is the vasoconstrictor transmitter released by adrenergic nerve fibers. The arteries and arterioles of skeletal muscles are innervated by a rich plexus of noradrenergic fibers located in the adventitial-medial border. Extrinsic denervation of the muscle caused almost complete disappearance of the perivascular adrenergic nerve fibers and the loss of approximately one half of the nonadrenergic nerves associated with large arteries.
