Stimulation of postjunctional alpha-1 and alpha-2 adrenoreceptors increases proximal urethral perfusion pressure in the pithed rat.

: 1. In pithed rats, the effects of postjunctional alpha-1 and alpha-2 adrenoreceptor stimulation on prostatomembranous urethral perfusion pressure (UPP) were characterized by using selective adrenoreceptor agonists and antagonists. 2. Dose-dependent increases in UPP were elicited by the intravenous administration of selective alpha-1 and alpha-2 adrenoreceptor agonists, phenylephrine (1.0-30.0 micrograms kg-1) and BHT-933 (10-3000 micrograms kg-1), respectively. 3. The effects of phenylephrine on UPP were antagonized, in a dose-related manner, by pretreatment with prazosin (0.1 and 0.5 mg kg-1, iv), a selective alpha-1 adrenoreceptor antagonist. In contrast, pretreatment with rauwolscine 0.1 and 0.5 mg kg-1, iv), a selective alpha-2 adrenoreceptor antagonist, did not alter phenylephrine-induced increases in UPP. 4. BHT-933 elicited increases in UPP that were antagonized, in a dose-related manner, by pretreatment with rauwolscine (0.1 and 0.5 mg kg-1, iv). Neither dose of prazosin altered the effects of BHT-933 on UPP. 5. These results demonstrate increases in the resistance to flow (constriction) through the proximal urethra following selective stimulation of postjunctional alpha-1 and alpha-2 urethral adrenoreceptors. 6. The role of urethral alpha-adrenoreceptor subtypes in the neurohumoral control of the urethra remains to be determined.