Further evidence for tonically functioning presynaptic beta-adrenoceptors in guinea-pig pulmonary arteries.

Effects of dl- and d-carteolol alone on the release of tritium evoked by transmural field stimulation at 1 Hz were investigated in spirally cut guinea-pig pulmonary arteries preloaded with [3H]-norepinephrine. Cumulatively applied dl-carteolol 10(-8) M, 10(-7) M and 10(-6) M readily inhibited the release of tritium in a concentration-dependent manner, whereas the same concentrations of d-carteolol produced no effect. In conclusion, presynaptic beta-adrenoceptors in guinea-pig pulmonary arteries tonically function to facilitate the release of the transmitter norepinephrine.