METHODS

Male rats (Osborn-Mendel strain), weighing 350-450 g, were anesthetized with sodium pentobarbital (35 mg-kg-*, ip). Polyethylene catheters, filled with 100 IU sodium heparin and 0.009 g NaCl per milliliter of water, were tied into the lefi femoral artery and vein. The skin was sutured and infiltrated with 2% butacaine sulfate (Abbott, North Chicago, Ill.). The hindquarters of the animals were covered with surgical hose and then wrapped loosely in a fast-setting plaster bandage (Johnson and Johnson, New Brunswick, NJ), with hindlimbs and catheters protruding. The bandage was tied down on a lead block, and the animals were allowed to recover from anesthesia for 4 h. Butacaine sulfate was applied periodically to the sutured skin. In their harness, the conscious rats could freely move their forequarters and head and neck, and appeared