Angiotensin and single nephron glomerular function in the trout Salmo gairdneri

Area of Science:

• Comparative physiology
• Renal physiology
• Fish osmoregulation

Background:

• Understanding kidney function in fish is crucial for osmoregulation.
• Trout (Salmo gairdneri) are a model organism for studying renal adaptations.
• Norepinephrine and Angiotensin II are key hormones influencing renal function.

Purpose of the Study:

• To investigate the effects of norepinephrine and Angiotensin II on renal function in trout.
• To compare glomerular filtration rate (GFR), urine flow (UV), and tubular transport in freshwater (FW) and seawater (SW) trout.
• To characterize glomerular populations (filtering, nonfiltering, nonperfused) and their response to hormonal stimulation.

Main Methods:

• Measurements of GFR, UV, renal tubular transport maximum for glucose (TMG), and single nephron GFR (SNGFR) in anesthetized trout.
• Infusions of norepinephrine and Angiotensin II to assess hormonal effects.
• Use of ferrocyanide (Prussian blue) to identify and quantify different glomerular populations.

Main Results:

• Seawater trout exhibited significantly lower GFR, UV, TMG, and SNGFR compared to freshwater trout.
• Angiotensin II reduced UV, GFR, and TMG by 50% in both FW and SW trout, but only reduced SNGFR in SW trout.
• Trout kidneys contain filtering (F), nonfiltering (NF), and nonperfused (NP) glomerular populations, with SW fish having a higher proportion of NF and NP tubules.

Conclusions:

• Significant differences in renal function exist between FW and SW trout, reflecting adaptations to different environments.
• Angiotensin II plays a role in regulating SNGFR, particularly in seawater-acclimated fish.
• The heterogeneity of glomerular populations contributes to the overall renal response to environmental and hormonal changes.