Angiotensin and single nephron glomerular function in the trout Salmo gairdneri

Glomerular filtration rate (GFR), urine flow (UV), renal tubular transport maximum for glucose (TMG) and single nephron glomerular filtration rate (SNGFR), determined in anesthetized norepinephrine-infused trout (Salmo gairdneri), were 18.51 ± 5.78 μl.min^-1.kg body wt^-1, 5.31 ± 1.38 μl.min^-1.kg body wt^-1, 105.21 ± 46.84 μg.min^-1.kg body wt^-1, and 3.74 ± 1.12 nl/min, respectively, when in seawater (SW) and 140.39 ± 17.24, 76.38 ± 10.41, 626.16 ± 77.46, and 1.31 ± 0.20 in freshwater (FW). Angiotensin II infusions, to reduce UV, GFR, and TMG by 50%, had no effect on the average SNGFR of FW trout, but reduced that of SW fish to 1.42 ± 0.19 nl/min. Infusion of 20% ferrocyanide, visualized as Prussian blue (PB), identified three glomerular populations: filtering (F) with PB in glomerular vessels and tubular lumen; nonfiltering (MF) - PB in glomerular vessels only; nonperfused (MP) - no PB associated with the nephron. SW and FW kidneys contained about 40% NF tubules. In FW, 45% were F tubules compared with 5% in SW, whereas NP tubules comprised 51% of SW tubules and 13% of FW. During angiotensin II infusions the distributions were 9% F and 46% NF in FW and 6% F and 12% NF in SW trout.