Interaction between the calcium entry blocker nifedipine with the alpha 1-adrenoreceptor-mediated increase in diastolic pressure elicited by catecholamines.
In the pithed normotensive rat the effect of the calcium entry blocker nifedipine was studied on alpha 1-adrenoreceptor-mediated pressor responses of intravenously administered (-)-noradrenaline, dopamine and (-)-adrenaline as well as of (-)-noradrenaline released from sympathetic neurones by DMPP, tyramine, McN-A-343 and electrical stimulation of the spinal cord at the level Th5-L4. The alpha 1-adrenoreceptor-mediated pressor responses to both intravenously administered and neuronally released catecholamines were moderately antagonized by nifedipine. The alpha 1-adrenoreceptor-mediated increase in diastolic pressure elicited by DMPP was unique in its extreme insensitivity to blockade by nifedipine. The results support the hypothesis that phenylethylamine-like alpha 1-adrenoreceptor agonists induce an increase in diastolic pressure relatively independent of extracellular calcium in contrast to imidazolidine-like agonists. The data may be interpreted as indicating that each alpha 1-adrenoreceptor agonist activates the alpha 1-adrenoreceptor in a unique way.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D002395:Catecholamines / Q000494:pharmacology*; D003655:Decerebrate State; D003971:Diastole / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D002395:Catecholamines; D011942:Receptors, Adrenergic, alpha; D009543:Nifedipine