SPATIAL VARIATION IN SYMPATHETIC INFLUENCES ON THE VASCULATURE OF THESYNOVIUM AND MEDIAL COLLATERAL LIGAMENT OF THE RABBIT KNEE-JOINT

1. Laser Doppler perfusion imaging was used to assess the role of the sympathetic nervous system in the control of blood flow to the medial collateral ligament and capsule (synovium and overlying fibrous tissue s) of the rabbit knee joint. 2. Electrical stimulation of the saphenou s nerve (width 1 ms; amplitude 20V; 1-30 Hz) produced a frequency-depe ndent vasoconstriction of knee joint vasculature. The response was max imal at 30 Hz and gave the greatest fall in perfusion at the femoral i nsertion of the ligament (by 33.8 +/- 7.4%, mean +/- S.E.M.; n = 5-6) and the smallest decrease at the tibial insertion of the ligament (by 10.6 +/- 2.9%). 3. Topical application of phentolamine (10(-6) mol) ha d no significant effect on basal knee joint blood flow. However, it ab olished the nerve-mediated constrictor responses in all regions of the medial collateral ligament and synovium at all frequencies. 4. Topica l administration of adrenaline (10(-14) to 10(-7) mol) caused a dose-d ependent decrease in knee joint blood flow with the highest dose produ cing > 75% reduction in perfusion at all areas. 5. There was no eviden ce of a reactive hyperaemia in the 5 min following a 5 min period of f emoral artery occlusion. Artificial manipulation of arterial blood pre ssure by intravenous infusion or withdrawal of blood caused a proporti onal change in ligament and synovial blood flow. These observations ma y indicate a lack of autoregulation in the joint and its exclusion fro m baroreflex modulation. 6. These results suggest a potential role for the sympathetic nervous system in the control of knee joint blood flo w. Neuromodulation of ligament perfusion appears to predominate at the femoral insertion and this could prove to have functional significanc e.