Inhibition by Diltiazem of Norepinephrine Release from Sympathetic Nerves in the Rabbit Pulmonary Artery

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Abstract
In order to determine if the calcium blocker diltiazem could alter excitation-secretion coupling in vascular sympathetic nerves, superfused rabbit pulmonary arterial strips were preincubated with 3H-norepinephrine and stimulated electrically (2–8 Hz) and by KCl (60 mM). Diltiazem significantly inhibited tension development with 4 Hz (1.5 × 10–5 M) and 8 Hz (1.5 × 10–6, 1.5 × 10–5M) stimuli, but only at 1.5 × 10–5M did diltiazem inhibit the 3H overflow evoked by an 8-Hz stimulus. No inhibition of 3H overflow was noted with the 2 and 4 Hz stimuli. With an 8-Hz stimulus the inhibition of tension development (45.4%) by diltiazem (1.5 × 10–5M) was significantly greater than the inhibition of 3H overflow (33.8%). A similar relationship was noted with 60 mM KCl stimulation. These data suggest that excitation-secretion coupling in vascular sympathetic nerves can be inhibited by diltiazem.