Venous adenosine content and vascular responses in dog hind-limb skeletal muscles during twitch contraction.
In dogs anaesthetized with pentobarbitone sodium and chloralose and artificially ventilated, the skeletal muscles of a hind limb were vascularly and neurally isolated and perfused at a constant flow of 150% of the resting blood flow (5.8 +/- 0.3 ml.min-1.100g-1 muscle tissue, mean +/- S.E.M., n = 6) obtained after denervation of the limb. Electrical stimulation of the cut peripheral ends of the femoral and sciatic nerves for 20 min resulted in muscle contraction and a decrease in arterial perfusion pressure to a new steady level (59.7 +/- 8.6% decrease in vascular resistance) within 2 min; the pressure remained constant throughout the remaining 20 min. Similarly venous oxygen tension decreased from 38.2 +/- 1.3 (control) to 16.4 +/- 1.7 mmHg (n = 5) during contractions. The concentration of adenosine in arterial plasma did not change significantly during muscle contraction (122.5 +/- 28 nM, n = 8). However, the adenosine concentrations in venous plasma increased significantly (P less than 0.05) from a control value of 94.8 +/- 33 nM (n = 8) to 256 +/- 82 nM (n = 8) after 10 min and 235 +/- 31 nM (n = 8) after 20 min of muscle contraction. During infusion of adenosine into the femoral artery to give a range of arterial plasma concentrations between 0.17 and 90 microM, 89.2 +/- 2.8% (n = 20) of the infused adenosine was removed (taken up by tissues) from the blood before it reached the vein. Infusion of adenosine caused dose-dependent decreases in vascular resistance ranging between 7 and 79%; 5.58 +/- 1.50 microM adenosine caused a decrease in resistance of 36.1 +/- 7.1% (n = 10) and 51.7 +/- 7.4 microM adenosine caused a decrease of 51.2 +/- 4.1% (n = 9). Comparison of venous plasma adenosine concentrations during adenosine infusions with those seen during contractions suggests that the released adenosine can contribute about 60% of the total vasodilatation seen during contractions of the muscle. These results show that adenosine appears in the venous blood during muscle contraction and is likely to contribute to exercise hyperaemia.
Ballard
H J
HJ
Department of Physiology, University, Leeds.
Cotterrell
D
D
Karim
F
F
D000241:Adenosine / Q000097:blood*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004285:Dogs; D004558:Electric Stimulation; D005267:Femoral Nerve; D006614:Hindlimb / Q000502:physiology; D009119:Muscle Contraction; D009132:Muscles / Q000098:blood supply* / Q000294:innervation; D012584:Sciatic Nerve; D014680:Veins
D000241:Adenosine