3H‐Adrenaline Release from Rabbit Isolated Aorta by Electrical‐Field Stimulation

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Abstract
The aim of the present work was to study the release of 3H-adrenaline (3H-A) from rabbit isolated aorta. This release was compared with that of 3H-noradrenaline (3H-NA). The stimulation-evoked 3H-overflow from aorta preloaded with 3H-A decreased with repeated stimulation (S1-S3). In contrast, prestimulation enhanced subsequent stimulation-evoked 3H-overflows. For both 3H-amines, the 1H-overflow increased concomitantly to the same degree with the number of pulses (30-1000) at 3 Hz. The time course of 3H-overflows with either 3H-A or 3H-NA was compared. In the case of 3H-A, the 3H-overflow increased with time, while for 3H-NA the 3H-overflow remained unchanged both at 3 and 10 Hz. The stimulation-evoked 3H-overflow from rings preloaded with either 3H-amine was the same at frequencies from 1 to 10 Hz, whereas at 30 Hz the 3H-overflow derived from 3H-A was higher than that using 3H-NA. An analysis of the quantitative aspects of individual stimulation-evoked 3H-overflows showed that the fractional profile did not differ using either amine. In both cases, at least 96% of the 3H-overflow evoked by stimulation at 3 or 10 Hz was contained in the initial four 2-min. fractions. The ratio between stimulation-evoked 3H-overflow and spontaneous 3H-outflow was the same for both amines at 3 Hz, while the ratio was higher for 3H-NA at 10 Hz. Rauwolscine (10-6 M) enhanced the 3H-overflow 6-fold, while (-)-propranolol (10-7 M) had no effect at 3 Hz. It is concluded that 3H-A is released by electrical-field stimulation in much the same manner as 3H-NA. Furthermore, rabbit isolated aorta is a useful preparation for the study of the release of transmitters as well as the modulation of the release mediated via presynaptic adrenoceptors.