Calcitonin gene-related peptide produces skeletal muscle vasodilation following antidromic stimulation of unmyelinated afferents in the dorsal root in rats.

In anesthetized rats, the contribution of calcitonin gene-related peptide (CGRP) to antidromic vasodilation of skeletal muscle blood flow (MBF) following electrical stimulation of muscle afferent was investigated by measuring biceps femoris MBF using laser Doppler flowmetry. Repetitive antidromic electrical stimulation of unmyelinated C fibers in ipsilateral dorsal roots at the 3rd-5th lumbar segments for 30 s caused an increase in MBF for 3-15 min (mean 4.5 min) without significant change in systemic arterial blood pressure. The increase in skeletal MBF started about 10 s after the onset of stimulation, and peaked at approximately 130% of the control value at about 30 s after the end of the 30 s period of stimulation. The MBF response was totally abolished by topical application of hCGRP (8-37), a CGRP receptor antagonist. It is concluded that antidromic vasodilation in skeletal muscles following stimulation of unmyelinated C afferents in dorsal roots is independent of systemic blood pressure and is mediated essentially by CGRP. It is suggested that this CGRP-related antidromic vasodilation may be important in the clinical improvement of skeletal MBF produced by physical therapy, e.g. acupuncture.