A new method has been developed for the simultaneous measurement of inulin and PAH clearance in small laboratory animals (rats). A double-chambered Teflon capsule (capacity: 3 ml) is implanted intraperltuneally. One of the chambers is filled with inulin solution and the other with PAH solution. Both solutions are iso-osmotie. The open ends of the capsule are sealed with double dialysis membranes. Sufficiently high serum and urine levels of both substances can thus be maintained for 72 h. By adapting suitable methods, it proved possible to estimate inulin and PAH in 500 #1 of blood or urine. The advantage of the method is that it can be used for renal clearance tests in small conscious animals, able to move freely within their cages without anaesthesia or intravenous infusions.The feasibility of the technique was tested by monitoring the behaviour of various parameters of renal function after administration of the following nephrotoxic agents: puromycin aminonucleoside, 100 mg/kg s.c.; uranyl nitrate, 2 mg/kg s.c.; mercuric chloride, I mg/kg i.p. The following factors were measured or calculated: urine output, GFR, fractional water reabsorption, PAH clearance, serum urea concentration and clearance, reabsorbed/secreted urea (percentage of filtered urea), Na + clearance and fractional Na + reabsorption, urine glucose concentration, glucose clearance and fractional reabsorption, and urine protein concentration. After the dose of aminonucleoslde there was a significant rise in plasma urea together with significant protelnuria reaching their peak on the eighth day. Uranyl nitrate poisoning caused an approximately 25% reduction in GFR, a drastic reduction in PAH clearance, a definite rise in plasma urea and a reduction in fractional glucose reabsorption from 99 to 55%, all these changes reaching their maximum on the sixth day. After mercuric chloride poisoning the changes reached their peak on the third day; GFR was reduced by approximately 60% and at the same time fractional water reabsorption fell from 97 to 90%. PAH clearance was reduced to 25% of normal and urea concentration rose to 231 mg/100 ml -an extremely high level. Fractional glucose reabsorption was 70.9~ as Part of this work was presented at the 18th and 19th Spring Meetings of the German Pharmacological Society in Mainz, 1977 and1978. compared with 99.7% in the controls. From these results it is apparent that the renal lesion induced by aminonueleoside is situated exclusively in the glomeruli, while the damage caused by uranyl acetate is entirely or almost entirely eonfined to the tubules. The nephrotoxle action of mercuric chlorlde involves both glomerular and tubular functions. However, such an interpretation disregards the fact, established by histological examination, that in mercuric chloride poisoning a large proportion of the proximal tubuli are consistently blocked with cell debris. Under the light microscope the glomerull appear to be intact so that the reduction in GFR cannot be ascribed to glomerular damage, but must be the result of ...

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