Are the prejunctional alpha 2-adrenoceptors of the rat vas deferens and submandibular gland of the alpha 2A- or alpha 2D-subtype?
We have investigated the effects of antagonists at functional prejunctional alpha 2-adrenoceptors of rat was deferens and rat submandibular gland and compared potencies with affinities for the alpha 2A-, alpha 2B- and putative alpha 2D-ligand binding sites of human platelet, rat kidney, and rat submandibular gland, respectively. Prejunctional potency of antagonists was expressed as an EC30 (concentration producing a 30% increase in stimulation-evoked release of tritium in tissues pre-incubated with [3H]noradrenaline) in rat vas deferens and submandibular gland, and also as a pA2 (antagonist concentration producing a 2-fold shift in the inhibition by the alpha 2-adrenoceptor agonist xylazine of the electrically-evoked isometric twitch) in rat vas deferens. The functional prejunctional alpha 2-adrenoceptors of rat vas deferens and submandibular gland are alpha 2A-like since there was a good correlation between affinity for the alpha 2A-ligand binding site in human platelet and prejunctional potency in rat vas deferens (r = 0.90, n = 7, P less than 0.001), and submandibular gland (r = 0.84, n = 7, P less than 0.05). However, there was a better correlation between affinity for the alpha 2-ligand binding site of rat submandibular gland and prejunctional potency in rat vas deferens (r = 0.95, n = 7, P less than 0.001), and submandibular gland (r = 0.97, n = 7, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Smith
K
K
Department of Physiology, Royal College of Surgeons in Ireland, Dublin.
Docherty
J R
JR
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008297:Male; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000145:classification* / Q000378:metabolism; D013363:Submandibular Gland / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D014649:Vas Deferens / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha