Discrepancy between alpha 1-adrenoceptor-mediated contraction and the occupation theory in rat vas deferens--possible existence of a 'silent' receptor.
The relation of the amount of alpha 1-adrenoceptors (alpha 1-R) with contraction to norepinephrine (NE) through alpha 1-R in rat vas deferens was examined by means of radiobinding assays. Treatment with dibenamine decreased the maximal contraction to NE with a decrease in the amount of alpha 1-R but the relation was not linear. The contractile response disappeared completely when 20% of the alpha 1-R still remained. Moreover, culture of dibenamine-pretreated muscle restored the contraction to NE without a significant increase in the amount of alpha 1-R in the muscle. These findings suggest that some alpha 1-R are 'silent' in the contraction of rat vas deferens in response to NE under physiological conditions.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003983:Dibenzylchlorethamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D009924:Organ Culture Techniques; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000032:analysis* / Q000502:physiology; D014649:Vas Deferens / Q000187:drug effects
D011942:Receptors, Adrenergic, alpha; D003983:Dibenzylchlorethamine; D002118:Calcium; D009638:Norepinephrine