Investigations of prejunctional alpha 2-adrenoceptors in rat atrium, vas deferens and submandibular gland.
We have examined the effects of a series of alpha 2-adrenoceptor antagonists on the stimulation-evoked release of tritium from rat atrium, vas deferens and submandibular gland pre-incubated with [3H]noradrenaline, and correlated these potencies with affinities for the alpha 2A-ligand binding site of human platelet and the alpha 2B-ligand binding site of rat kidney. The alpha 2B-selective adrenoceptor antagonists prazosin and ARC 239 showed significantly higher, and the alpha 2A-selective antagonist BRL 44408 showed significantly lower, potency in atrium than in vas deferens and submandibular gland. Yohimbine and BDF 8933 failed to distinguish between prejunctional alpha 2-adrenoceptors or between ligand binding sites. It is concluded that the prejunctional alpha 2-adrenoceptor of rat atrium resembles the alpha 2B-ligand binding site, and differs from the prejunctional alpha 2-adrenoceptors of rat vas deferens and submandibular gland, which resemble the alpha 2A-ligand binding site.
Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin.
K
K
Smith
S
S
Connaughton
J R
JR
Docherty
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D013363:Submandibular Gland / Q000187:drug effects / Q000378:metabolism*; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha