The influence of felodipine and diethyl‐stilboestrol on [3H]noradrenaline release in the rat trachea

Abstract
The fractional release of [3H]noradrenaIine was measured in rings from the rat trachea. Transmitter release was induced either by isotonic KC1 (124 mM) or by 2.5 mM Ca added to a Ca‐free depolarizing solution. Felodipine, a Ca antagonist (10‐4M), had no effect on the basal release of [3H]NA whereas it reduced the overflow of transmitter caused by KC1 or Ca. Diethyl‐stilboestrol (25 μM), which also inhibits Ca influx in smooth muscle, had a stronger inhibitory effect than felodipine on [3H]NA release induced by high K and addition of Ca. Basal efflux of [3H]NA was increased by diethyl‐stilboestrol. This increase also occurred in the absence of extracellular Ca.