Involvement of opioid and nicotinic receptors in rectal and anal reflex inhibition of urinary bladder motility in cats.

The present study was performed to investigate mechanisms involved in urinary bladder relaxation during reflex activation of the pelvic nerves in the cat. Electrical stimulation of the pelvic nerves produced a contraction of the urinary bladder (P less than 0.05) and colon (P less than 0.05). Reflex activation of the pelvic nerves by rectal distension or mechanical stimulation of the anus induced relaxation of the bladder (P less than 0.05), while a colonic contraction was elicited (P less than 0.05). Naloxone (1.5 mg kg-1, i.v.) abolished the reflex inhibition of bladder motility elicited by rectal distension or mechanical stimulation of the anus (P less than 0.05). However, the urinary bladder and colonic contraction produced by electrical stimulation of the pelvic nerves were not affected. Hexamethonium (10 mg kg-1, i.v.) or severing of the pelvic nerves completely abolished the responses of the urinary bladder and colon to electrical stimulation or reflex activation of the pelvic nerves. The results indicate that inhibitory reflexes from the rectum and anal canal to the urinary bladder are conveyed via efferents of the pelvic nerves, and involve both nicotinic and opioid receptor mechanisms.