THE SINGLE-PASSAGE EXTRACTION OF l a F I N RABBIT BONE

Skeletal blood flow, which may amount to 25% of the resting cardiac output in man (Brookes, 1971a), is a variable of fundamental importance in any investigation of bone metabolism. The few quantitative measurements of bone blood flow which have been made in the past have relied on both direct and indirect techniques. These include venous occlusion plethysmography (Edholm, Howarth & McMichael, 1945), observation of the washout of an interstitially injected tracer (Kelly, Yipintosi & Bassingthwaighte, 1971), the indicator fractionation technique (Kane & Grim, 1966), indicator dilution (White, Ter-Pogossian & Stein, 1964) and the plasma clearance of a bone-seeking radionuclide (Frederickson, Honour & Copp, 1955). The distinction between blood flow to bone mineral and blood flow to bone marrow is often unclear. For clinical skeletal blood-flow studies the plasma clearance technique offers most promise, and the principle is already widely applied in tests of liver, renal and thyroid function (Veal1 & Vetter, 1958). However, measurement of skeletal flow by plasma clearance of a bone-