Possible Involvement of Ganglionic Blocking Effects of Diltiazem in Regulation of Blood Pressure and Heart Rate of the Rabbit

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Under pentobarbitone anesthesia, arterial blood pressure and heart rate were recorded in rabbits. The elevation in systemic blood pressure and increased heart rate induced by electrical stimulation of the right thoracic sympathetic nerve trunk were depressed by either an intravenous injection of diltiazem (300μg/kg) or by placing cotton pledgets soaked in 2mM diltiazem solution onto the right stellate ganglion. These inhibiting effects of diltiazem were statistically significant with high sympathetic stimulation frequencies (10-20Hz), but not when lower frequencies (1-5Hz) were used. On the other hand, hexamethonium (10mg/kg i.v. or 100mM applied topically) depressed cardiovascular responses to sympathetic stimulation over a wide range of frequencies (1-20Hz). Present results reveal a frequency-dependent inhibition of ganglionic transmission by diltiazem, and suggest that diltiazem may depress excessive sympathetic activity without affecting normal ganglionic transmission.