PURINERGIC AND CHOLINERGIC COMPONENTS OF BLADDER CONTRACTILITY AND FLOW

The role of ATP as a neurotransmitter/neuromodulator in the urinary tr act has been the subject of much study, particularly whether ATP has a functional role in producing urine flow. Recent studies suggested sig nificant species variation, specifically a variation between cat and o ther species. This study was performed to determine the in vivo respon se of cat urinary bladder to pelvic nerve stimulation (PNS) and to the exogenous administration of cholinergic and purinergic agents. In ane sthetized cats, bladder contractions and fluid expulsion was measured in response to PNS and to the exogenous administration of cholinergic and purinergic agents. Fluid was instilled into the bladder and any fl uid expelled by bladder contractions induced by PNS or exogenous agent s was collected in a beaker. The volume was measured in a graduated cy linder and recorded. PNS, carbachol and APPCP produced sustained contr actions with significant expulsion of fluid. ATP, ACh and hypogastric nerve stimulation did not produce any significant expulsion of fluid. Atropine, a cholinergic antagonist, inhibited PNS contractions and flu id expulsion with no effect on purinergic actions. There was a signifi cant relationship between the magnitude of the contraction, duration o f the contractions and volume of fluid expelled. The data and informat ion from other studies, strongly suggests a functional role for ATP as a cotransmitter in the lower urinary tract different from ACh's role. ATP stimulation of a specific purinergic receptor plays a role in ini tiation of bladder contractions and perhaps in the initiation of urine flow from the bladder. ACh's role is functionally different and appea rs to be more involved in maintenance of contractile activity and