The existence of a new subtype of alpha-adrenoceptor on the rat anococcygeus is revealed by SGD 101/75 and phenoxybenzamine.
1 Noradrenaline and Sgd 101/75 (4(2-imidazoline-amino)-2-methylindazol-chlorhydrate) acted as full agonists in contracting the rat anococcygeus. 2 Very low concentrations of phenoxybenzamine (0.3 nM for 2-30 min) reduced preferentially the effects of Sgd 101/75. Preparations made insensitive to Sgd 101/75 by phenoxybenzamine still contracted to noradrenaline, this contraction occurring in the presence of high  concentrations (400 microM) of Sgd 101/75. 3 It is concluded therefore that the alpha 1-adrenoceptor in this preparation is not a homogeneous entity and must be subdivided into at least two subtypes.
D000316:Adrenergic alpha-Agonists; D000818:Animals; D003000:Clonidine / Q000031:analogs & derivatives*; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010643:Phenoxybenzamine; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000145:classification*; D011942:Receptors, Adrenergic, alpha / Q000145:classification*
D000316:Adrenergic alpha-Agonists; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010643:Phenoxybenzamine; D003000:Clonidine; C034204:indanidine; D009638:Norepinephrine