Role of Cyclic AMP in Stimulation‐Evoked Release of3H‐Noradrenaline from Rabbit Isolated Ear Artery

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Abstract
The possible involvement of cyclic AMP in the stimulation‐evoked3H‐overflow from rabbit isolated ear artery preloaded with3H‐noradrenaline was studied. Cyclic AMP (10–5–3x10–4M), 8–bromo‐cyclic AMP (3x10–4M) and adenosine (10–5–3X10–4M) enhanced stimulation‐evoked3H‐overflow. Dibutyryl‐cyclic AMP (10–5–3x10–4M) had no effect. Theophylline (3X10–5M) and the phosphodiesterase inhibitor AH 21–132 (3X10–5M) did not alter the enhancement of3H‐overflow caused by either cyclic AMP or adenosine. Forskolin (3X10–6M) and the phosphodiesterase inhibitors ICI 63 197 (10–4M) and AH 21–132 (3x10–6–3x10–5M) increased stimulation‐evoked3H‐overflow. Forskolin (10–6M) enhanced the effect of ICI 63 197 (3x10–5M) but it did not alter the effect of AH 21–132. It is concluded that cyclic AMP is involved in the stimulation‐evoked release of noradrenaline from postganglionic sympathetic nerves in the rabbit ear artery.