Evidence from lack of decentralization-induced supersensitivity that beta 2-adrenoceptors of the cat nictitating membrane are non-innervated

Influence of inhibition of extraneuronal uptake and of O-methylation on the hyperglycaemia caused by sympathomimetic amines in depancreatized rats

This study aimed at testing whether the O-methylating system (extraneuronal uptake + O-methylation) modulates, in-vivo, β-adrenoceptor-mediated responses. The influences of U-0521 (3,4-dihydroxymethylpropiophenone, an inhibitor of catechol-O-methyl transferase (COMT)) and hydrocortisone (an inhibitor of extraneuronal uptake) on the hyperglycaemia evoked by isoprenaline and adrenaline were compared. Both inhibitors enhanced the increase of the plasma glucose level induced by either isoprenaline (0·36 nmol kg−1 min−1) or adrenaline (0·55 nmol kg−1 min−1). The enhancement caused by U-0521 developed faster than that caused by hydrocortisone, but was of the same magnitude. This is the first report of supersensitivity to sympathomimetic amines caused by inhibition of either COMT or extraneuronal uptake in-vivo and for a response not involving smooth muscle cells.