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Micturition can be characterized experimentally by monitoring both the frequency and volume of micturition. Previous studies demonstrated that the functional capacity of the rat and rabbit bladder, as determined by cystometry, is approximately equal to the maximal single micturition volume as recorded over a 24 hour period. Studies in many laboratories have demonstrated that chronic increases in diuresis induce increases in micturition frequency and capacity, and an increase in bladder mass. The current study compares the temporal relationship among these parameters in three models of diuresis: streptozotocin-induced diabetes in rats, sucrose-induced diuresis in rats, and furosemide-induced diuresis in rabbits. In both sucrose diuresis in rats and furosemide diuresis in rabbits there were immediate increases in both the frequency and volume of micturition. The magnitude of the increases in micturition frequency and micturition volume paralleled the increase in the total volume of urine excreted. Bladder mass increased progressively over the time course of the study. Streptozotocin-induced diabetes resulted in a more gradual (but parallel) increase in micturition frequency and volume, and again a more gradual increase in bladder mass. These studies demonstrate that functional bladder capacity is increased immediately upon the initiation of diuresis with sucrose or furosemide, as is the frequency of micturition. This indicates that functional bladder capacity is probably under neuronal regulation and the change in capacity is not a function of the increased bladder mass which occurs at a later time period.(ABSTRACT TRUNCATED AT 250 WORDS)

The cat and the rabbit are two of the most popular models for the study of lower urinary bladder function. The cat has been used extensively for in vivo studies of spinal and supra-spinal micturition reflexes. In contrast, the rabbit has been used extensively for the in vitro study of bladder function. Although the cat and rabbit bladders are approximately the same mass, the cat bladder can generate approximately 6 times the intravesical pressure than the rabbit bladder at the same volume (in vitro response to field stimulation). In order to determine if the increased pressure generation is related to increased cellular energetics, we compared the intracellular concentrations of ATP and creatine phosphate (CP), and the enzyme activities of three enzymes which have important functions in cellular energetics: creatine kinase, citrate synthase, and malic dehydrogenase between the cat and rabbit urinary bladder. The results can be summarized as follows: (1) The bladder weight of the cat and rabbit are similar. (2) The isolated cat bladder can generate approximately 6 times the intravesical pressure of the isolated rabbit bladder. (3) The ATP and CP concentrations of the rabbit are significantly greater than the concentrations in the cat bladder. (4) The hydroxyproline concentration is significantly greater in the cat than the rabbit. (5) The maximum activities of creatine kinase, citrate synthase, and malic dehydrogenase are significantly lower in the cat than the rabbit. In general, it is clear that the ability of the cat to generate high intravesical pressures is not correlated with increased tissue high energy phosphate concentrations, or high enzymatic activities of three specific cytosolic or mitochondrial enzymes.