Aims: 

Recent studies showed that reactive oxygen species modulate the vasomotor tone of small arteries and arterioles. Much less is known regarding the importance of reactive oxygen species, such as H₂O₂ in the regulation of tone and responses of small vein and venules and the involvement of constrictor prostaglandins. We hypothesized that H₂O₂ increases the basal tone of small venous microvessels of skeletal muscle.

Methods: 

Small veins of gracilis muscle were isolated from Wistar rats, then cannulated and incubated in physiological salt solutions (PSS) in the presence of 10 mmHg of intraluminal pressure at T=37°C, in a special vessel chamber. Changes in diameter were measured in response to increases in H₂O₂ concentrations (10^-9M –10^-5M) and vasoactive agents. To elucidate cellular mechanisms blockers of cyclooxygenases (indomethacin, INDO, 2.5×10^-5 M, 30 min) and PGH₂/TXA₂ receptors (SQ 29,548, 10^-6M, 20 min) were used. The vasomotor effects of arachidonic acid (AA, 10^-7M – 10^-4M) were also investigated.

Results: 

We have found that H₂O₂ elicited concentration dependent constrictions, which were significantly (p<0.05) inhibited by the presence of indomethacin or SQ 29,548 (maximum responses in H₂O₂-Control: 46±8% of PD; H₂O₂+INDO 74±4% of PD; H₂O₂+SQ 29,548 88±6% of PD). AA also elicited concentration dependent constrictions, which were significantly (p<0.05) reduced by the presence of INDO or SQ 29,548 (Maximum responses in AA-Control: 43±5% of PD, AA+INDO 80±5%; AA+SQ 79±5 PD).

Conclusion: 

Both H₂O₂ and AA elicited concentration dependent constrictions in venous microvessels of skeletal muscle mediated by constrictor prostaglandins acting on PGH₂/TXA₂ receptors, suggesting that even in physiological conditions reactive oxygen species have a role in modulation of venous microcirculation.

Support: 

AHA-FA 0855910D, OTKA T48376, K67984