The effects of amyl nitrite inhalation on myocardial blood flow and metabolic heat production

The action of nitroglycerine and dipyridamole in normal and ischaemic dog heart

1 Network and post-network resistances were measured together with heat clearance and heat production in the myocardium. 2 Nitroglycerine dilated all resistance vessels but was twice as effective on network as compared with post-network vessels. 3 Dipyridamole dilated network and post-network vessels equally. 4 Nitroglycerine had no effect on heat clearance or heat production in ischaemic myocardium. 5 Dipyridamole increased heat clearance in normal but not in ischaemic myocardium. 6 Dipyridamole depressed heat production in normal and ischaemic myocardium. 7 That the clinical effectiveness of nitroglycerine does not depend entirely on its coronary vasodilator properties is confirmed. 8 It is suggested that the action of dipyridamole in depressing myocardial heat production may be due to an action on the efficiency of oxygen utilization during cardiac contraction.

Studies on the mode of action of hexobendine, a prospective anti-anginal drug

1. In cats anaesthetized with pentobarbitone sodium, hexobendine (0.25 mg/kg) markedly increased myocardial blood flow (measured using a heat clearance technique) and usually decreased myocardial metabolic heat production, without influencing cardiac contractility or systemic arterial blood pressure. These effects lasted for about 45 min.2. Larger doses (0.5 and 1.0 mg/kg) decreased systemic arterial blood pressure and the rate of rise of the left ventricular pressure pulse (dp/dt), although left ventricular end-diastolic pressure was usually increased. This is indicative of a decrease in myocardial contractility.3. In a concentration of 5 x 10(-6) g/ml., hexobendine protected isolated rabbit atria against the decrease in contractility that follows the removal of oxygen.4. Hexobendine did not antagonize the systemic and myocardial effects of infusions of adrenaline and noradrenaline, nor (except in concentrations of 10(-5) g/ml.) the increase in contractility induced by these catecholamines on isolated rabbit atria.