COMPARISON OF URINARY-BLADDER FUNCTION IN RATS WITH HEREDITARY DIABETES-INSIPIDUS, STREPTOZOTOCIN-INDUCED DIABETES-MELLITUS, AND NONDIABETIC OSMOTIC DIURESIS

In vivo and in vitro bladder function were studied in three different models of increased diuresis: 1) Brattleboro rats with hereditary diab etes insipidus (di/di), 2) Sprague-Dawley rats with streptozotocin-ind uced diabetes mellitus (STZ), and 3) Sprague-Dawley rats with increase d diuresis due to 5% sucrose added to the drinking water. When compare d with controls, all three models showed bladder mass, increased water consumption and urine output, higher mean and maximal increased mictu rition volumes, and greater bladder capacity and compliance by in vitr o cystometry. The changes were more extensive in di/di rats than in ST Z and sucrose-drinking rats. The concentration of bladder collagen dec reased in all three rat models when compared with controls. However, t he collagen concentration of STZ bladders was significantly lower than the collagen concentration of di/di and sucrose bladders, suggesting that the decrease in bladder collagen concentration associated with ex perimental diabetes mellitus is only partly related to the increased d iuresis. Contractile function was studied using a whole bladder model. Responses of whole bladders from control and diabetic rats to electri cal field stimulation, carbachol and KCl were identical. Volume-pressu re relations of the isolated whole bladder showed that the magnitude o f the contractile response to KCl is constant at intravesical volumes ranging from about 10 to 95% of cystometrical bladder capacity. Bladde rs from Brattleboro di/di rats and STZ rats showed a rightward shift o f volume-passive pressure curves when compared with appropriate contro ls. Bladders from sucrose-drinking rats had volume-passive pressure cu rves similar to the bladders from controls. This study suggests that w hile contractile function remains intact with increased diuresis, the passive function changes, with the bladder becoming more distensible.