title: Beta-adrenoreceptors of the cat nictitating membrane.
abstract: 1. The relaxant effects of isoprenaline, salbutamol, adrenaline and noradrenaline on the partially contracted isolated nictitating membrane of the cat were determined in the absence and the presence of alpha-adrenoreceptor blockade. 2. It was possible to demonstrate significant relaxant effects of isoprenaline and salbutamol in the absence as well as in the presence of alpha-adrenoreceptor blockade. However, the relaxant effects of adrenaline and noradrenaline could not be demonstrated in the absence of alpha-adrenoreceptor blockade. 3. Molar concentrations (EC30) of isoprenaline, salbutamol and adrenaline causing 30% relaxation of the tone did not significantly differ from each other; EC30 of each of these agents was significantly less than that of noradrenaline. 4. Beta 1-Adrenoreceptor antagonist metoprolol was less potent than beta 2-antagonist H 35/25 in antagonizing the effect of salbutamol; metoprolol was more potent than H 25/35 in antagonizing noradrenaline. Both these agents were effective antagonists of isoprenaline; however, metoprolol and H 25/35 in combination produced greater antagonism of isoprenaline than did each antagonist separately. 5. It is concluded that the cat nictitating membrane possesses both beta 1- and beta 2-adrenoreceptors which are responsible for the relaxant effects of sympathomimetic agents. A study of these receptors is, however, complicated by concomitant stimulation of alpha-adrenoreceptors.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002415:Cats; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009541:Nictitating Membrane / Q000187:drug effects / Q000294:innervation*; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D002217:Carbachol; D000109:Acetylcholine