| Abstract: | We prepared an experimental system to study the effects of drugs on urinary bladder contraction and micturition simultaneously in rats anesthetized with urethane (1 g/kg, s.c.) and alpha-chloralose (25 mg/kg, s.c.). When Tyrode's solution was infused at a constant rate (0.8-1 ml/10 min) through a needle inserted into the bladder from the left ureter, the bladder pressure gradually and then steeply rose, and micturition took place. These changes in bladder pressure and micturition were constantly repeated. In this model, drugs which partially inhibited the bladder contractile force, e.g., atropine (0.01-1 mg/kg, i.v.) and hexamethonium (C6, 5 mg/kg, i.v.) increased the frequency of bladder contraction instead of decreasing the amount of solution excreted from the penis by bladder contraction. The rate of afferent discharges during bladder filling was increased after injection of atropine or C6, and this increase was considered to be responsible for the induction of the increase in the frequency of bladder contraction. Drugs which inhibited the bladder contraction and interrupted micturition, e.g., C6 (20 mg/kg, i.v.) raised the bladder pressure until the solution leaked from the penis. As phentolamine (5 mg/kg, i.v.) or propranolol (1 mg/kg, i.v.) did not facilitate bladder motility but rather inhibited it, the inhibitory action of sympathetic nerves on bladder motility was considered to be weak in rats. This model was useful for studying the effect of drugs on bladder motility and micturition reflex. |
