Effects of Opiates and Osmotic Stimuli on Rat Neurohypophyseal Metabolic Activity Monitored with [ ³ H]-2-Deoxyglucose

The metabolic activity of the neural lobe of the rat pituitary gland was measured by autoradiographic estimation of the rate of accumulation of 1-[3H]-2-deoxy-D-glucose ( [3H]-2DG). Replacement of drinking water by 2% saline for 5 days resulted in a 300% increase in [3H]-2DG accumulation in the neural lobe. Morphine (8 mg/kg s.c.) increased [3H]-2DG uptake by 213%, and this effect was antagonized by naloxone. Morphine-tolerant rats also showed an increased uptake of [3H]-2DG, and morphine actually reduced the neural lobe activity in these animals. Rats with monosodium glutamate induced lesions of the circumventricular organs no longer showed any increase in neural lobe activity after morphine. Homozygous Brattleboro rats on an ad libitum water intake showed greater neural lobe activity than normal controls, and replacement of drinking water with 2% saline for 24 h resulted in a massive increase in [3H]-2DG uptake. In none of these studies was any alteration detected in the metabolic activity of the supraoptic or paraventricular nuclei.