Intrarenal hypertonic saline infusions in dogs with thoracic caval constriction

Area of Science:

• Nephrology
• Renal Physiology
• Cardiovascular Physiology

Background:

• Intrarenal artery infusions of hypertonic saline activate tubuloglomerular feedback (TGF).
• The TGF response is modulated by salt balance but unstudied in conditions with expanded extracellular fluid volume and avid sodium reabsorption.
• Conditions like ascites involve salt retention and altered renal hemodynamics.

Purpose of the Study:

• To investigate the renal response to intrarenal hypertonic saline infusions in dogs with and without ascites due to thoracic inferior vena cava constriction.
• To determine if the TGF pathway remains functional in pathophysiological states of salt retention.
• To correlate the TGF response with baseline renal function.

Main Methods:

• Intrarenal infusions of hypertonic saline were administered to control dogs and dogs with partial thoracic inferior vena cava constriction (causing ascites).
• Renal blood flow (RBF) and glomerular filtration rate (GFR) were measured.
• Intravenous saline loading was performed in some dogs to assess response attenuation.
• Baseline renal function was assessed prior to infusions.

Main Results:

• Intrarenal hypertonic saline significantly reduced RBF and GFR in both control and ascites groups.
• The magnitude of RBF and GFR reduction was positively correlated with baseline renal function.
• Intravenous saline loading abolished the vasoconstrictor response in normal dogs but not in dogs with ascites.
• Dogs with ascites showed a preserved but diminished TGF response compared to controls.

Conclusions:

• The tubuloglomerular feedback (TGF) mechanism is preserved in early stages of caval constriction syndrome in dogs.
• The potential activity of TGF decreases as basal renal function declines in these conditions.
• These findings highlight the impact of extracellular fluid volume expansion on renal autoregulation and TGF responsiveness.