METHODS

Three kidney rats. An extra or third kidney was transplanted into a group of seven adult male isogenic Lewis rats whose average weight was 500 g. The kidneys were taken from littermates and transplanted into the lower abdomen. The transplantation procedure was that described by Silber and Crudop (17). At the same time littermates of the same sex and weight served as a control group. Thus two groups of rats were obtained from a single litter, one group containing three kidneys and the other a group of normal rats. In addition, both preoperatively and 2 mo after the transplant, renal size as estimated by the length of the longitudinal axis was ascertained by direct measurement as well as intravenous pyelography. Simultaneous inulin and PAH clearances (as described below) were performed 2 mo postoperatively on both the three kidney and control rats. Rats cvith hypertrophied kidneys. A group of adult male Lewis rats was anesthetized, and one kidney was removed through a midline incision. These rats were then allowed to recover. Four weeks following unilateral nephrectomy, clearance and size measurements were made. In another group of rats which also underwent unilateral nephrectomy, two rats were anesthetized and the hypertrophied kidney was removed from one and transplanted into the other. Thus each rat in this group had two hypertrophied kidneys. At 6 weeks postoperatively clearance and size measurements were made.

Clearance studies. On the day of the experiment the rats were anesthetized with Nembutal given intraperitoneally, 35 mg/kg. The femoral artery and vein were catheterized for the collection of blood and the infusion of appropriate solutions into the animal. The bladder was catheterized with a polyethylene catheter. The priming solution was injected intravenously; it contained 100 mg of inulin