Role of spinal alpha(1)-adrenoceptor subtypes in the bladder reflex in anesthetized rats

The contribution of different subtypes of alpha (1)-adrenoceptors in the lu mbosacral spinal cord to the control of the urinary bladder was examined in urethane-anesthetized rats. Bladder pressure was recorded via a transureth ral catheter under isovolumetric conditions. Drugs were administered intrat hecally at the L6-S1 segmental level of spinal cord. RS-100329 (an alpha (1 A)-antagonist) in doses of 25, 50, and 100 nmol significantly decreased bla dder-contraction amplitude by 38%, 52%, and 95%, respectively, whereas (+)- cyclazosin (an alpha (1B)-antagonist) significantly decreased bladder-contr action amplitude (48% reduction) only in a 50-nmol but not a 100-nmol dose. Fifty nanomoles of RS-100329 and (+)-cyclazosin increased bladder-contract ion frequency by 54% and 44%, respectively. BMY7378 (an alpha (1D)-antagoni st), in doses of 25, 50, and 100 nmol, did not change bladder activity. The se studies suggest that reflex-bladder activity is modulated by two types o f spinal alpha (1)-adrenergic mechanisms: 1) alpha (1A)- or alpha (1B)-inhi bitory control of the frequency of voiding reflexes presumably mediated by an alteration in the processing of bladder afferent input and 2) alpha (1A) -facilitatory modulation of the descending efferent limb of the micturition -reflex pathway. Spinal alpha (1D)-adrenoceptors do not appear to have a si gnificant role at either site.