Responses of bone and joint blood vessels in cats and rabbits to electrical stimulation of nerves supplying the knee.

1. Experiments were performed to assess the extent to which knee joint blood flow in cats and rabbits is affected by electrical stimulation of the nerve supply to the knee. 2. Absolute changes in blood flow were measured using the radiolabelled microsphere (approximately 15 microns) technique whilst relative changes in blood flow were assessed using laser Doppler flowmetry. 3. Despite deep general anaesthesia, sympathetic nerve fibres innervating cat knee joint blood vessels showed marked 'tone'. 4. Blood flow to the joint capsule (synovium and overlying fibrous and areolar tissues) was substantially reduced (by approximately 90% in the cat and approximately 45% in the rabbit) during electrical stimulation of the articular nerve supply. 5. The percentage change in the laser Doppler flowmeter signal did not differ significantly from the percentage change in blood flow measured by microsphere technique. 6. Blood vessels in the cancellous bone of the distal femur (condyles) and proximal tibia (plateau) appear to be innervated by vasoconstrictor fibres which reach their effectors via the articular nerves. However, the cortical bone and red marrow of the diaphysis of the femur do not receive such innervation. 7. The potency of the vasoconstrictor influences acting on joint blood vessels could be of relevance in the pathogenesis of inflammatory joint diseases.