title: An investigation of presynaptic alpha-adrenoceptor subtypes in the pithed rat heart and in the rat isolated vas deferens.
abstract: The presynaptic cardio-inhibitory effects of the alpha-adrenoceptor agonists xylazine, cirazoline and amidephrine and their interaction with the antagonists yohimbine and prazosin were investigated in the pithed rat. The presynaptic inhibitory effects of the alpha 2-selective agonist xylazine were antagonized by the alpha 2-antagonist yohimbine but not by the alpha 1-antagonist prazosin, thus demonstrating the lack of alpha 2-adrenoceptor antagonism by prazosin. The presynaptic inhibitory effects of cirazoline were antagonized equally by yohimbine and prazosin, and the presynaptic inhibitory effects of the selective alpha 1-agonist amidephrine were antagonized by prazosin more potently than by yohimbine. In the nifedipine-treated isolated epididymal portion of the rat vas deferens, both xylazine and amidephrine produced concentration-dependent inhibition of the isometric contraction to single pulse electrical stimulation. The alpha 2-antagonist rauwolscine antagonized the inhibitory effects of xylazine but not of amidephrine . It is concluded that inhibitory alpha 1-adrenoceptors, as well as the already established alpha 2-receptors, are present presynaptically in the pithed rat heart and in the rat vas deferens.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004558:Electric Stimulation; D004983:Ethanolamines / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000145:classification / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects; D014649:Vas Deferens / Q000378:metabolism; D014991:Xylazine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D004983:Ethanolamines; D007093:Imidazoles; D011942:Receptors, Adrenergic, alpha; D014991:Xylazine; D015016:Yohimbine; C016980:amidephrine; D009543:Nifedipine; C014282:cirazoline; D011224:Prazosin