Intrarenal Filtrate Distribution, during Saline Infusion in Rats with Unilateral Ureteral Ligation

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Abstract
Six days after unilateral ureteral ligation (UL) the contralateral kidney had increased GFR by 66 % in conscious rats. The average relative single nephron filtration rate (gfr) of superficial nephrons, as measured by the 14C ferrocyanide single injection technique, was 75 % of deep nephron gfr in UL rats compared to 90 % in intact rats. Thus hyperfiltration was more pronounced in deep nephrons. Isotonic saline infused i.v. (15 % BW in 60 min) in a second group of UL rats increased GFR by average 36 % compared to preinfusion GFR. Higher single nephron GFR and lower fractional sodium reabsorption enabled the UL rats to excrete sodium and water at practically the same absolute rates as compared to intact rats previously studied during identical saline infusion experiments. Saline infusion increased superficial gfr in UL rats from 75 % to 96 % of deep gfr. Provided superficial nephrons constitute 70 % of total nephron number these results imply that filtration rate rose by 48 % in superficial and by 16 % in deep nephrons. It is suggested that maximally one third of total sodium excretion in the saline infused UL rats might be due to superficial nephrons not being able to reabsorb their disproportionately increased filtered load.

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