Sensory nerve‐mediated vasodilation is reduced in plantar metatarsal arteries from spinal cord injured rats (1170.15)

Abstract

Axon‐reflex mediated vasodilation is reduced in skin of spinal cord injured humans (SCI). This change is suggested to produce altered skin function, an increased risk of pressure sores and slow wound healing. This study investigated the interaction between sympathetic and sensory nerve‐mediated effects in plantar metatarsal arteries (PMAs) from T10 spinal cord transected and sham‐operated (control) rats. Six weeks post‐surgery, PMAs were dissected and mounted isometrically in wire myographs. In control PMAs, activation of the perivascular nerve fibers with trains of 100 pulses at 1 Hz evoked contractions that peaked at ~10th pulse (1.1 ± 0.1 mN/mm) and then declined to ~40% (41 ± 5%) of the peak value at the 100th pulse. In PMAs from SCI rats, the peak amplitude of contraction was ~2‐fold larger (2.1 ± 0.2 mN/mm, P < 0.01) and the decline during the train of stimuli was smaller (declined to 94 ± 5 % of peak value). Treatment with capsaicin to inhibit the vasodilator action of the primary afferent nerve fibers did not greatly change the peak amplitude of nerve‐evoked contractions in PMAs from either control or SCI rats. However, in control PMAs, the decline in contraction during the train of stimuli was markedly reduced, with the contraction measured at the 100th pulse being increased by ~155% (155 ± 40 %). The % increase in amplitude of contractions measured at 100th pulse was much smaller in PMAs from SCI rats (20 ± 6%, P < 0.01). In conclusion, these findings indicate that the decline in sympathetic nerve‐mediated contraction during trains of stimuli is produced by co‐activation of primary afferent nerve fibers and that this effect was greatly reduced in PMAs from SCI rats. This finding may explain why axon reflex‐mediated vasodilation is reduced in skin of SCI humans.Grant Funding Source: Supported by the NHMRC of Australia