The Hyperglycaemic Effect of Morphine

1. In the unanaesthetized cat, an injection of 0.75 mg of morphine into a lateral cerebral ventricle produced strong hyperglycaemia; on intravenous injection, 10 to 30 times larger doses were required. Other effects produced with both injections were shivering, pupillary dilatation, opening of the eyes, miaowing, periods of excitation, and analgesia. Between the periods of excitation the cat did not react to objects moving in front of its eyes and it had a vacant stare.2. Noradrenaline, adrenaline, and 5-hydroxytryptamine (5-HT) injected intraventricularly (250 mug, twice) depressed the hyperglycaemia due to intraventricular morphine, and noradrenaline also depressed the hyperglycaemia due to intravenous morphine. Adrenaline produced the strongest and 5-HT the weakest depression. 5-HT did not depress the other effects of morphine, but the catecholamines depressed most of them; only analgesia and the vacant stare appeared to be unaffected.3. Reserpine injected intraventricularly (0.5 mg, twice) greatly accentuated the hyperglycaemia as well as the other effects produced by intraventricular morphine, but pupillary dilatation and opening of the eyes no longer occurred; the protrusion of the nictitating membranes produced by the reserpine persisted.4. Pentobarbitone sodium injected intraperitoneally in an anaesthetizing dose practically abolished the morphine hyperglycaemia, but injected intraventricularly in a dose of a few milligrammes, it had a two fold effect: depression followed by enhancement of the morphine hyperglycaemia. The enhancement may be due to sensitization of the effect of the adrenaline released by morphine, since adrenaline hyperglycaemia was enhanced as well.5. Morphine did not seem to act on structures in the walls of either the lateral or third ventricle when producing its hyperglycaemic effect on intraventricular injection. The action may therefore be on more caudally situated parts of the neuro-axis, on the central grey, on structures in the floor of the fourth ventricle or of the lateral recesses, or even on structures near the ventral surface of the brain stem.