EFFECTS OF DIURESIS ON MICTURITION

Micturition can be characterized experimentally by monitoring both the frequency and volume of micturition. Previous studies demonstrated th at the functional capacity of the rat and rabbit bladder, as determine d by cystometry, is approximately equal to the maximal single micturit ion volume as recorded over a 24 hour period. Studies in many laborato ries have demonstrated that chronic increases in diuresis induce incre ases in micturition frequency and capacity, and an increase in bladder mass. The current study compares the temporal relationship among thes e parameters in three models of diuresis: streptozotocin-induced diabe tes in rats, sucrose-induced diuresis in rats, and furosemide-induced diuresis in rabbits. In both sucrose diuresis in rats and furosemide d iuresis in rabbits there were immediate increases in both the frequenc y and volume of micturition. The magnitude of the increases in micturi tion frequency and micturition volume paralleled the increase in the t otal volume of urine excreted. Bladder mass increased progressively ov er the time course of the study. Streptozotocin-induced diabetes resul ted 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 imme diately upon the initiation of diuresis with sucrose or furosemide, as is the frequency of micturition. This indicates that functional bladd er capacity is probably under neuronal regulation and the change in ca pacity is not a function of the increased bladder mass which occurs at a later time period. The exact stimulus for the increase in bladder m ass cannot be determined from these studies, but may be related to one or more of the following factors: micturition volume, filling rate, o r frequency of stimulation. (C) 1995 Wiley-Lies, Inc.