Open Access.ALPHA.1B-Adrenoceptor Mechanisms in Rabbit Iris Dilator.
Author(s) -
Issei Takayanagi,
Koji Shiraishi,
Noriko Kokubu
Publication year - 1992
Publication title -
japanese journal of pharmacology/japanese journal of pharmacology
Language(s) - Uncategorized
Resource type - Journals
eISSN - 1347-3506
pISSN - 0021-5198
DOI - 10.1254/jjp.59.301
Subject(s) - methoxamine , dilator , prazosin , agonist , medicine , endocrinology , norepinephrine , alpha (finance) , clonidine , adrenergic receptor , chemistry , receptor , dopamine , antagonist , surgery , construct validity , patient satisfaction
Rabbit isolated iris dilator strips were contracted by norepinephrine, an alpha 1A- and alpha 1B-nonselective agonist, but not by methoxamine, an alpha 1A-selective agonist. The concentration-response curve for norepinephrine was considerably inhibited by chloroethylclonidine. The pA2 values for WB4101 and 5-methylurapidil were 8.16 +/- 0.09 and 7.84 +/- 0.08 (means +/- S.E. of 8-12 experiments), respectively, and significantly smaller than the values reported in the rat renal artery and thoracic aorta, and rabbit bronchus, where the alpha 1A-subtype is predominant. These results suggest that the rabbit iris dilator contains primarily the alpha 1B-subtype. Clonidine and tizanidine did not contract the rabbit iris dilator but shifted the curve for norepinephrine in a parallel manner, suggesting that they interact with the alpha 1B-subtype and act as competitive antagonists in this muscle. Methoxamine (up to 10(-3) M) had no effect on the contractile response to norepinephrine, suggesting that methoxamine does not interact with the alpha 1B-subtype.