1. The half-life (T½) of the disappearance curve of 133Xe from the knee joint has been used as an indirect measure of synovial perfusion.
2. The effects of intra-articularly administered isoprenaline and noradrenaline and their respective blocking agents, propranolol and phentolamine, on the T½ values have been investigated in normal subjects and in patients with osteoarthritis and rheumatoid arthritis.
3. In normal subjects isoprenaline increased the clearance rate and this effect was blocked by propranolol. Noradrenaline decreased the clearance rate and this effect was blocked by phentolamine.
4. The injection of phentolamine in normal subjects caused an increase in synovial perfusion, suggesting the presence of a basal α-constrictor tone.
5. In the patients with osteoarthritis and rheumatoid arthritis quantitative differences were found in the responses to isoprenaline and noradrenaline and their respective blocking agents.
6. There appeared to be a qualitative difference in the case of phentolamine; it is possible that vasoconstrictor tone may be lost in inflamed joints.