Aims: 

The pressure-induced myogenic response has been well characterized in small arteries and arterioles. Less is known regarding its presence in small venous vessels, especially because in previous in vivo studies in anaesthetized animals small veins and venules did not exhibit appreciable myogenic tone. We hypothesized that isolated small veins develop myogenic tone in response to elevation of intraluminal pressure.

Methods: 

Small veins were isolated from gracilis muscle of male Wistar rats, then cannulated and incubated in physiological salt solution (PSS) in the presence of 10 mmHg of intraluminal pressure at T=37°C, in a special vessel chamber. Changes in diameter in response to increase in the pressure (1–12mmHg) and effects of vasoactive agents were measured by videomicroscopy. The nonselective blocker of cyclooxygenase enzymes (indomethacin, INDO, 2.5×10^-5M, 30min) and the blocker of PGH₂/TXA₂ receptor (SQ 29,548, 10^-6 M, 20min) and the H₂O₂ metabolizing enzyme (catalase, CAT, 120U/ml, 20min) were used.

Results: 

Isolated rat gracilis muscle venules developed substantial tone in response to increases in intraluminal pressure (active diameter: 260 ± 19mm, whereas passive diameter (PD): 370 ±12mm at 10 mmHg). Presence of indomethacin or SQ 29,548 or catalase reduced significantly the pressure-induced myogenic tone (control: 67±5% vs. +INDO 81±8% of PD; +SQ 29,548 88±7% of PD; +CAT 81±11% of PD at 10 mmHg pressure).

Conclusion: 

Small veins of skeletal muscle develop spontaneous myogenic tone in response to increases in intraluminal pressure. This myogenic response is mediated by H₂O₂ and constrictor prostaglandins, acting on PGH₂/TXA₂ receptors. Thus pressure sesitivity, reactive oxygen species and constrictor prostaglandins may have important physiological and pathological roles in the regulation of blood flow in venous microcirculation.

Support: 

AHA-FA 0855910D, OTKA T48376, K67984