A reliable, nondestructive animal model for interstitial cystitis: intravesical low-dose protamine sulfate combined with physiological concentrations of potassium chloride

Abstract

Previous attempts to develop an acute animal model for interstitial cystitis (IC) have included intravesical acetic acid (AA), cyclophosphamide (CYP), lipopolysaccharide (LPS), protamine sulfate (PS), and vanilloid receptor agonists (VRA). In our hands, these treatments have led to frank bladder damage (AA and CYP), were extremely unreliable (LPS and PS), or the neurogenic irritative effects desensitize within the study period (VRA). It has been proposed that impaired barrier function of bladder epithelium and subsequent infiltration of urine contents are important initial events in the pathophysiology of IC. We therefore sought to develop a model that would reliably mimic the acute phase of this debilitating disease. To this end, we combined protamine sulfate (PS) treatment, thought to breakdown urothelial umbrella cell barrier function, and physiologic concentrations of potassium chloride (KCl) in an open cystometrogram animal model. Female Sprague-Dawley rats (body weight, 250 to 300 g) were anesthetized with urethane (1.2 g/kg subcutaneously) and transurethral continuous cystometry was performed with normal saline, and 100 mmol/L KCl or 500 mmol/L KCl as control. Either 10 or 30 mg/mL PS was then added to the control solution for a 30-minute period (for modest and severe urothelial barrier breakdown, respectively), after which the control solution was continued for 1 to 2 hours. Bladder contraction amplitudes, durations, frequency, and intercontractile intervals were recorded and analyzed. There were no differences seen between the saline, 100 mmol/L KCl, or 500 mmol/L KCl control periods, indicating that barrier function in these animals was not affected by the physical preparation. Of the treatments tested, 100 mmol/L KCl with 30 mg/mL PS and 500 mmol/L KCl (the physiologic concentration of rat urine) with either 10 or 30 mg/mL PS produced reliable irritation, which continued up to 2 hours after cessation of PS administration. These results indicate that: (1) the historical use of normal saline, instead of the more physiologic 500 mmol/L KCl, for cystometry greatly biases our understanding of the function of the lower urinary tract in animal models of IC; and (2) modest, noncytotoxic insults to urothelial barrier function can result in dramatic irritative responses, given the proper physiological conditions.