Inhibition by diltiazem of norepinephrine release from sympathetic nerves in the rabbit pulmonary artery

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 KG (60 mM). Diltiazem significantly inhibited tension development with 4 Hz (1.5 × 10^-5M) and 8 Hz (1.5 × 10^-6, 1.5 × 10^-5 M) stimuli, but only at 1.5 × 10^-5 M 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^-5 M) 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.