Figure 4.

Urethane-anaesthetized female rat: traces showing the effects of i.v. IP₅I (30 nmol kg⁻¹) on bladder and urethra pressure (mmHg) and on raw external urethral sphincter (EUS-EMG) activity during the micturition reflex evoked by distension of the urinary bladder by saline (0.05 ml min⁻¹). The first panel shows the control effects of infusion of saline into the bladder (infusion on) to evoke contractions (increases in bladder pressure); after three similar contractions the infusion was stopped (infusion off) and the bladder allowed to contract isovolumetrically. At 5 min after the saline infusion had been switched off, the bladder was emptied. The second panel shows the same scenario 5 min after administration i.v. of IP₅I. Note that there were no rhythmic contractions during the infusion of saline and this was associated with a maintained relaxation of the urethra and increase in EUS-EMG activity. On turning off the saline infusion, these rhythmic bladder contractions returned although of reduced magnitude.