Methods

Experiments were performed on 29 mongrel dogs. Dogs were of both sexes, and each dog weighed from 15 to 20 kg. The dogs were anesthetized with sodium pentobarbital and then prepared for micro-puncture and clearance studies as described pre-viously [1, 9—11, 15]. The left jugular vein was cath-eterized to infuse an inulin solution (5%) at a rate sufficient to establish a plasma inulin concentration of approximately 0.8 mg/mi. The left foreleg vein was catheterized for the administration of solutions and to give additional anesthetic as required. Sys-temic blood pressure, measured with a Statham pressure transducer (Statham Lab. Inc., Hato Rey, Puerto Rico) and recorded on a Grass polygraph (Grass Instr. Co., Quincy, Massachusetts) was monitored via a catheter placed in the femoral ar-tery. The femoral catheter was also used for collection of arterial blood samples. The left kidney was exposed, and the renal ar-tery, vein, and ureter were freed of surrounding tis-sue. The ureter was catheterized, and an electro-magnetic blood flow transducer was placed around the renal artery (Carolina Medical Electronics, Inc., King, North Carolina); the flow transducer was not used in three dogs due to the occurrence of double renal arteries. In 21 dogs having a main renal artery of sufficient length, a 22-gauged curved needle was inserted into the artery and kept patent by continuous infusion of heparinized saline at 0.2 mllmin. Renal arterial pressure was measured with a Statham pressure transducer attached to the catheter. An adjustable plastic clamp was placed around the renal artery between the flow probe and the needle. In the remaining eight dogs, a clamp was placed around the aorta, proximal to the left renal artery; femoral arterial pressure was used as a measure of renal arterial pressure. The kidney was then placed on a lucite holder, prepared for micropuncture, and continuously bathed with a warmed, heparinized saline solution.

In group A, 13 dogs were studied at naturally oc-curring plasma COP levels. Group B consisted of nine dogs that were studied following infusion of a volume of 25% albumin solution equivalent to 3% of body weight. Four of the dogs were studied both prior to and after albumin infusion and are included in both groups. In the remaining five dogs of group B, micropuncture procedures were not carried out prior to albumin infusion due primarily to time constraints. A substantial time delay (1 to 2 hours) was involved in the albumin-loading procedure since the concentrated albumin solution had to be infused slowly (2 to 5 mL/min) to avoid undesirable systemic effects. In addition, the plasma COP values were increased to very high values for a period of time