Denervation and beta-adrenoreceptors of the cat nictitating membrane

1. Dose-response curves to the relaxant effects of isoprenaline, salbutamol, adrenaline and noradrenaline were determined on the partially contracted smooth muscles of the cat nictitating membrane following alpha-adrenoreceptor blockade in order to test the hypothesis of a causal relationship between the inhibition of neuronal uptake and denervation supersensitivity. 2. Denervation did not produce supersensitivity of the nictitating membrane to the beta-adrenoreceptor-mediated relaxant effects of any of the four agents studied. 3. The sensitivity of the inferior muscle was greater than that of the medial muscle to agents which were good substrates for neuronal uptake (adrenaline and noradrenaline) as well as to those which were not (isoprenaline and salbutamol). 4. Denervation did not alter the antagonist activity of beta-adrenoreceptor blockers propranolol (nonselective) and metoprolol (beta 1-blocker) against isoprenaline or of H 35/25 (beta 2-blocker) against salbutamol. 5. These results do not support the hypothesis of a casual relationship between inhibition of neuronal uptake and supersensitivity to sympathomimetic amines.