Abstract
Increased levels of endothelin (ET), an endogenous peptide with profound vasoconstrictor actions that mediates vascular tone, were reported in conditions characterized by increased vascular tone. Also extreme inactivity, such as spinal cordinjury (SCI), leads to an increased vascular tone and elevated levels of ET. PURPOSE To determine the contribution of ET to the increased vascular tone in SCI individuals and the effect of hybrid FES-training on the contribution. METHODS The contribution of ET to basal vascular tone was assessed in 8 SCI individuals (age 38 ± 9 years) by local intra-arterial (right femoral artery) administration of selective ETA- and ETB-receptor antagonist; BQ-123 and BQ-788, respectively. Bilateral thigh blood flow was measured with plethysmography and vascular resistance was calculated as mean arterial pressure/blood flow. 7 SCI individuals followed the same procedure after 6 weeks of hybrid functional electrical stimulation (FES) cycling (12 sessions). RESULTS The ET-blockade resulted in a significantly higher blood flow and right/left-ratio (response in infused leg divided by non-infused leg) and lower vascular resistance of the infused leg (RM ANOVA; p<0.001). After training, resting blood flow was elevated (T-test; p=0.048) and the effect of ET-blocking on blood flow (RM ANOVA; p=0.08) and right/left-ratio (RM ANOVA; p=0.01) was attenuated after training compared to before. Vascular resistance did not change significantly. DISCUSSION The different responses to ET-receptor blocking before and after training emphasizes the altered contribution of ET to basal vascular tone. The marked differences can be caused by a down-regulation of ET-release, its receptors, or ET-sensitivity. CONCLUSION (1) Endothelin seems to contribute to the increased vascular tone in spinal cord-injured individuals, and (2) hybrid FES-cycling decreases the contribution of ET to baseline vascular tone.
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