Crystal accumulation and very high short-circuit currents in rabbit urinary bladder

Area of Science:

• Nephrology
• Urology
• Physiology

Background:

• A condition in rabbits characterized by calcium carbonate (CaCO3) crystal accumulation in the urinary bladder was observed.
• High incidence in rabbits housed for two months or longer in vivarium conditions.

Purpose of the Study:

• To characterize a rabbit bladder condition involving CaCO3 crystal accumulation and elevated short-circuit current (Isc).
• To investigate the physiological and biochemical factors associated with this condition.

Main Methods:

• Observation of crystal mass, urine consistency, and stone formation in rabbits over time.
• Measurement of short-circuit current (Isc) using Ussing chamber techniques.
• Amiloride sensitivity testing and noise analysis to investigate ion transport mechanisms.
• Analysis of plasma aldosterone, GFR, and urinary composition (Na+, Ca2+, pH, osmolality).

Main Results:

• Crystal mass increased with age, occupying up to one-third of bladder volume and causing sludgy urine.
• Excreted urine had 20x lower crystal content than bladder urine, indicating retention.
• Short-circuit current (Isc) in rabbits with sludgy urine was significantly higher (up to 46 microA/cm2, average 12 microA/cm2) and entirely amiloride-sensitive, attributed to increased channel density.
• No kidney stones were detected in rabbits with bladder crystals, and vice versa.
• No clear explanation found in bacterial infection, plasma aldosterone, GFR, or major urinary parameters, except for a potentially missing urinary component in sludgy urine.

Conclusions:

• A rabbit condition involves bladder CaCO3 crystal accumulation and markedly increased, amiloride-sensitive sodium transport.
• Crystal retention in the bladder appears significant.
• The underlying cause for the condition and the relationship between crystal accumulation and high Isc remain undetermined.