Rabbit versus rat urinary bladder: Effects of in vitro hypoxia

Purpose: Studies indicate that bladder hypoxia may be an etiological factor for lower urinary tract dysfunction. Rat and rabbit are two species of exp erimental animals used frequently to study lower urinary tract function and dysfunction. The objective of this study was to compare directly effects o f in vitro hypoxia on contractile responses of rat and rabbit urinary bladd er to different forms of stimulation. Methods: Sexually mature male New Zea land White rabbits and Sprague-Dawley rats were compared. Each bladder was excised while the animal was anesthetized, and longitudinal bladder strips were cut, then mounted in organ baths. A tension of 2 g was placed on all s trips. Effects of 1, 2, 3 and 4 h hypoxia followed by 1 h of reoxygenation on contractile responses of bladder strips to field stimulation (FS), carba chol (100 mu mol/l), ATP (1 mmol/l) and KCl (120 mmol/l) were determined. R esults: Contractility, per unit tissue mass, of rat bladder strips was sign ificantly greater than that of rabbit bladder strips in response to FS (all frequencies), carbachol, KCl and ATP. Hypoxia (followed by reoxygenation) resulted in time-dependent progressive reduction in contractile responses o f bladder strips to all stimuli. Rat bladder was significantly more sensiti ve to hypoxia than rabbit bladder in response to FS and carbachol. Hypoxia induced similar effects on rat and rabbit bladder responses to ATP and KCl. Conclusion: Rat bladder neurogenic and cholinergic responses are significa ntly more sensitive to hypoxia than are those of rabbit bladder, which may be due to the rat bladder's greater contractile force generation and previo usly reported higher Ca2+-ATPase activity.