title: Alpha 1- and alpha 2-adrenoceptors in the smooth muscle of isolated rabbit urinary bladder and urethra.
abstract: The present experiment was undertaken to determine the existence of alpha 1- and alpha 2-adrenoceptors in the smooth muscle of the rabbit bladder dome, trigone and proximal urethra. In the dome pretreated with propranolol (10(-6) M), phenylephrine (10(-5) M-10(-3) M) and norepinephrine (10(-7) M-10(-5) M) caused only a small contraction but norepinephrine, only at high concentrations (10(-4) M-10(-3) M), produced a small relaxation. Clonidine, however, had no effect on the dome. In both trigone and urethra, phenylephrine, clonidine and norepinephrine caused dose-dependent contractions. The contractile response to phenylephrine or norepinephrine was significantly greater than that to clonidine in the trigone but no such difference was observed in the urethra. Prazosin (10(-8) M-10(-6) M, alpha 1-adrenoceptor antagonist) produced a rightward shift of the phenylephrine and clonidine dose-response curve in both the trigone and urethra. Yohimbine (10(-8) M-10(-6) M, alpha 2-adrenoceptor antagonist) inhibited the response to clonidine without significantly affecting the responses to phenylephrine. These studies indicated that alpha 1- and alpha 2-adrenoceptors are present in both the trigone and proximal urethra. In the dome, only alpha 1-adrenoceptors are sparsely distributed.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014521:Urethra / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D011433:Propranolol; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin