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 tempxal relationship among these parameters in three models of diuresis: streptozotocininduced 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. The exact stimulus for the increase in bladder mass cannot be. determined from these studies, but may be related to one or more of the following factors: micturition volume, filling rate. or frequency of stimulation. o IWS WIICY-L~SS. Inc.