Effects of amphetamine on protein synthesis and energy metabolism in mouse brain: role of drug-induced hyperthermia.

Changes in brain protein synthesis activity, and in brain levels of glucose, glycogen, and several high-energy phosphate metabolites, were evaluated under conditions of amphetamine-induced hyperthermia in mice. Protein synthesis showed a striking dependence on rectal temperature (TR), falling abruptly at TR above 40 degrees C. A similar result was obtained following direct heating of the animals. Protein synthesis activity in liver showed the same temperature dependence observed for brain. Increased synthesis of a protein with characteristics of the major mammalian stress protein, hsp 70, was demonstrated in both brain and liver following amphetamine administration. Brain protein synthesis showed significant recovery within 2 h after amphetamine administration whereas that of liver remained below 30% of control activity, suggesting significant temporal and quantitative differences in the response of individual tissues to elevated temperatures. Brain glycogen levels after amphetamine administration were significantly lower under conditions of ambient temperature which resulted in more severe drug-induced hyperthermia but did not correlate as strikingly as protein synthesis with the temperatures of individual animals. Brain glycogen also fell in animals whose temperatures were increased by brief exposure at high ambient temperature. Brain glucose levels did not consistently change with hyperthermia. Slight decreases in high-energy phosphates with increasing TR were likely the result of fixation artifact. These results demonstrate the fundamental role of hyperthermia in the reduction of protein synthesis in brain and other tissues by amphetamine, and suggest that temperature also constitutes a significant source of variability in the effects of this drug on brain energy metabolism, in particular glycogenolysis.