Abstract

Cardiovascular actions of diazepam were studied in cats under chloralose-urethane anesthesia or immobilized by decamethonium and in decerebrate preparations. In the anesthetized group, the cardiovascular effects appeared to be most prominent in the anesthetized group. Diazepam, 0.1 mg/kg i.v., caused a slight reduction of the resting blood pressure, heart rate and cardiac contractile force. It also caused an average reduction of the hypothalamic pressor responses of 18 mm Hg from the control of 37 mm Hg or -49%, of the medullary pressor responses of 11 mm Hg from the control of 46 mm Hg or -24%, of the medullary depressor responses of 13 mm Hg from the control of 28 mm Hg or -46% and of the carotid occlusion responses of 24 mm Hg from the control of 106 mm Hg or -23%. Intravertebral or intracarotid injection of diazepam, 0.01 to 0.02 mg/kg, produced an equal or greater diminution of the hypothalamic and, also, to a lesser extent, the medullary presser responses. Diazepam in excess of 1 mg/kg i.v. reduced the contraction of the nictitating membrane on stimulation of the preganglionic but not the postganglionic fibers. The responses on stimulation of the stellate ganglion were essentially unaltered with intravenous doses of up to 6 mg/kg. Diazepam, 0.15 to 0.3 mg into the femoral artery, caused an instantaneous but transient increase of the blood flow, independent of the sympathetic innervation or of cholinergic receptor participation. These findings suggest that diazepam exerts some depressant effects on the central nervous system cardiovascular control mechanisms, the hypothalamic being most susceptible.