Ventricular noradrenaline concentrations in naïve and morphine-treated rats subjected to acute myocardial ischaemia

Ventricular histamine concentrations and mast cell counts in the rat heart during acute ischaemia

The ventricular histamine concentrations and mast cell counts of naive and disodium cromoglycate-treated rats subjected to acute left coronary artery ligation under pentobarbitone anaesthesia were examined. In naive animals, there was a significant increase in the right ventricular histamine level at 2 min following left coronary artery ligation. Left ventricular histamine concentrations tended to decrease, and were significantly lower than those of the right ventricle at 5 min. However there were no significant changes in mast cell counts of the right or left ventricles after left coronary artery ligation. Treatment with disodium cromoglycate did not significantly alter the ventricular mast cell counts, interfere with the changes in ventricular histamine concentrations, or the occurrence of early ventricular arrhythmias and haemodynamic changes in response to acute left coronary artery ligation. It is suggested that the increase in the right and decrease in the left ventricular histamine concentrations during acute myocardial ischaemia involves mainly the non-mast cell stores, instead of mast cell sources, of cardiac histamine.

Changes in preganglionic sympathetic nerve function following chronic morphine treatment in rats

1. The effects of acute or chronic morphine treatment on the changes in blood pressure and pulse rate in response to ganglionic stimulation or blockade and to vagal stimulation, and of isolated atria to field stimulation or noradrenaline, were studied. 2. In pithed rats, intravenously injected hexamethonium significantly depressed the blood pressure responses to sympathetic nerve stimulation. The ganglionic blocking effects of hexamethonium were significantly greater in chronically morphine-treated rats, but were not significantly affected by acute morphine administration in naive animals. 3. Intravenous administration of nicotine dose-dependently increased blood pressure and pulse rate. The magnitudes of these changes were not significantly affected by acute or chronic morphine pretreatment. 4. Studies with rat isolated atrial preparations revealed that the changes in atrial contractile rate and force in response to noradrenaline or field stimulation were not influenced by either acute or chronic morphine treatment. 5. Cervical vagal stimulation produced voltage- or frequency-dependent decreases in pulse rate and blood pressure. The responses were not significantly affected by chronic morphine treatment. 6. These findings suggest that the site of the changes in sympathetic function following prolonged exposure to the opiate appears to be on the preganglionic nerve fibres.

Arterial catecholamine levels in morphine-treated rats subjected to sympathetic nerve stimulation

1. The effect of acute or chronic morphine treatment on the changes in arterial noradrenaline and adrenaline levels in response to sympathetic nerve stimulation was studied in rats. 2. Rats which had been chronically treated with morphine in their drinking fluid for 21 days were shown to be morphine-tolerant, as revealed by the tail-immersion test for analgesia. 3. It was found that animals given either acute or chronic morphine treatment had similar basal concentrations of arterial catecholamines to their controls. 4. Sympathetic nerve stimulation produced significant increases in arterial noradrenaline and adrenaline levels in both the control and morphine-treated animals. However, the degree of arterial noradrenaline elevation was significantly less in morphine-tolerant animals. 5. This phenomenon was not observed in acutely morphine-treated rats or at 2 weeks following opiate withdrawal in animals which had been treated previously with morphine for 3 weeks. 6. The findings suggest that chronic morphine treatment in rats not only leads to opiate tolerance but also reduces catecholamine release in response to sympathetic nerve stimulation.

Plasma, cardiac tissue and brain morphine concentrations in acute and chronic morphine-treated rats

1. The plasma, cardiac tissues and brain morphine concentrations in rats after acute or chronic morphine treatment were measured by high-performance liquid chromatography. 2. Morphine concentrations in plasma and cardiac tissues were found to be significantly higher than those in brain after acute morphine injection. However, after chronic oral administration, morphine concentrations in plasma, cardiac tissues and brain were similar. 3. Brain concentrations of morphine following chronic administration were higher than those obtained after acute administration although concentrations in plasma and cardiac tissues were lower.