The effects of epinephrine on bone blood flow in dogs and rabbits

This thesis is a report of a study on bone blood flow in adult dogs and rabbits. The effects of epinephrine and some other factors were investigated: (1) by direct observation of bone bleeding through drill holes and in the medullary cavity; (2) by measurement of changes in intramedullary pressure of long bones; and (3) by quantitative estimation of bone blood flow by the Fick principle. A technique was developed for measurement of the initial Sr⁸⁵ clearance by bone by dividing the bone uptake of Sr⁸⁵ by the integrated average concentration of Sr⁸⁵ in the systemic arterial blood. This clearance will represent at least a minimum bone blood flow. It should be equivalent to effective bone blood flow on the assumption that bone clears Sr⁸⁵ rapidly and almost completely from blood circulating through bone by exchange with calcium in bone, just as PAH clearance gives a measure of effective renal blood flow. The normal rate of bone blood flow in adult rabbits by the rate of initial Sr⁸⁵ clearance appeared to be at least 16 ml. per minute per 100 gm. of fresh bone which would represent about 5-10% of the resting cardiac output. The average intramedullary pressure of the femur in dogs was about 55 mm Hg, about 1/2 of the systolic systemic arterial blood pressure. Epinephrine caused a profound reduction in bone blood flow as indicated by reduced bone bleeding, a marked (65%) reduction in intramedullary pressure of bone marrow in the presence of persistently increased systemic blood pressure, and a significant (75%) reduction in Sr⁸⁵ clearance by bone. The changes in intramedullary pressure and in Sr⁸⁵ clearance by bone thus appear to correlate very well with changes in bone blood flow.Medicine, Faculty ofCellular and Physiological Sciences, Department ofGraduat