Renal kallikrein: its localization and possible role in renal function

Area of Science:

• Nephrology
• Renal Physiology
• Biochemistry

Background:

• Kallikrein distribution within the kidney is not fully understood.
• The kallikrein-kinin system's role in renal sodium handling requires further elucidation.

Purpose of the Study:

• To determine the anatomical distribution of kallikrein in the dog kidney.
• To identify the specific site of kallikrein secretion within the nephron.
• To investigate the kallikrein-kinin system's involvement in regulating sodium excretion.

Main Methods:

• Kallikrein distribution was assessed across different kidney regions (cortex, medulla, papilla).
• Stop-flow techniques in dogs were employed to localize kallikrein secretion within nephron segments.
• Urinary kallikrein and circulating kinin levels were measured in response to saline loading and desoxycorticosterone administration.
• Experiments in rats explored the relationship between sodium intake, water excretion, and urinary kallikrein.

Main Results:

• Kallikrein concentration decreased from the outer to the inner cortex, with minimal levels in the medulla and papilla.
• The highest kallikrein concentrations were detected in nephron fluid fractions with the lowest sodium concentrations.
• Urinary kallikrein and circulating kinins increased in saline-loaded dogs.
• Urinary kallikrein levels rose in dogs that escaped the sodium-retaining effects of desoxycorticosterone.
• A correlation between water/sodium excretion and urinary kallikrein was observed in rats with varying sodium intake.

Conclusions:

• Kallikrein is secreted into the urine at the distal tubule level, potentially by the tubule itself or associated structures.
• The kallikrein-kinin system appears to be involved in the regulation of renal sodium excretion.
• These findings suggest a role for the kallikrein-kinin system in regulating renal function at the distal tubule or collecting duct.