Abstract
Effects of nanomolar to submillimolar carteolol, a non-selective β-antagonist, on the evoked release at 1 Hz and the spontaneous release in the absence and presence of uptake1 and uptake2 blockers were studied in pulmonary arteries, isolated from guinea pigs, and then preloaded with [3H] noradrenaline. dl-Carteolol at 10-8, 10-7 and 10-6 M applied at the increasing concentrations inhibited the evoked [3H]-release in untreated arteries and in desipramine and corticosterone-treated arteries. The spontaneous [3H]-release slightly but significantly increased or tended to increase in untreated arteries. dl-Carteolol at 10-5 and 10-4 M clearly and concentration-dependently increased the spontaneous [3H]-release in untreated and cocaine-treated arteries. This increase was markedly inhibited by further pretreatment with normetanephrine. The evoked [3H]-release was not altered by dl-carteolol at 10-5 M, but increased at 10-4 M. This increase was not modified by cocaine and by cocaine and normetanephrine. d-Carteolol at 10-5 and 10-4 M produced effects similar to those of dl-carteolol. Nanomolar to micromolar dl-carteolol inhibits the evoked [3H]-release, which supports our previous conclusion that this inhibition is due to blockade of tonically functioning presynaptic β2-adrenoceptors. Carteolol at the higher concentrations seems to become a substrate for an uptake2 mechanism and to produce an unknown sympathomimetic activity in guinea pig pulmonary arteries.
