ACUTE HAEMODYNAMIC EFFECTS OF MEPHENTERMINE IN MAN

The circulatory effects of single intravenous injections of 0.75 mg/kg mephentermine were investigated in five healthy volunteer subjects. Ninety min after the first injection, atropine 1–2 mg was administered i.v. and the injection of mephentermine repeated. Cardiac output was measured beat-by-beat with an analogue computer-ballistocardio-graph system, validated by dye-dilution cardiac outputs. The first injection of mephentermine increased mean arterial pressure, systemic vascular resistance, and left ventricular minute work, with no change in the other variables. The injection of atropine produced a sudden marked increase in heart rate, cardiac output, arterial pressure, and left ventricular work, and a fall in stroke volume. The repeat injection of mephentermine caused considerably smaller changes in the circulation than either previous injection. Atropine thus unmasked the beta-adrenergic stimulating effects of mephentermine, as well as a surprisingly prolonged action of the agent. It is suggested that the combination of atropine plus mephentermine be investigated as an approach to improved pressor therapy. Mephentermine is relatively slow in onset, with prolonged peak effects. For a given increase in arterial pressure, it produces much less drastic changes in other cardiovascular variables than does methoxamine.