The effect of diazepam administration on heart rate and mean arterial blood pressure in resting and stressed conscious rats.

In unstressed rats, doses of 1 mg/kg and higher of diazepam produced tachycardia without changing blood pressure. Sub-chronic dosing (10 mg/kg/day for 4 days) resulted in increased magnitude and duration of the tachycardia. This diazepam induced tachycardia was unaffected by reserpine, slightly blocked by propranolol and abolished by atropine pretreatment. In animals anesthetized with ketamine, diazepam did not change heart rate or blood pressure. When animals were stressed by restraint, heart rate and blood pressure increased markedly. Diazepam did not affect the stress-induced tachycardia but reduced the stress-induced hypertension. These studies show that diazepam has no effect on heart rate or blood pressure in anesthetized animals, has no effect on blood pressure in conscious, unstressed animals but increases heart rate significantly probably by central vagal inhibition and, does not antagonize a stress-induced tachycardia but antagonizes stress-induced increases in blood pressure probably by a reduction in peripheral sympathetic tone.