Temperature acclimation in the Mongolian gerbil (Meriones unguiculatus): biochemical and organ weight changes.

1. Adult Mongolian gerbils (Meriones unguiculatus) were acclimated to 5 +/- 1, 24 +/- 1 and 34 +/- 1 degrees C for 6-8 weeks. 2. Body weights of temperature acclimated gerbils did not differ significantly from controls. Organ wt/body wt ratios of liver, kidney and heart increased in cold-acclimated and decreased in heat-acclimated gerbils. Adrenal wt/body wt ratio increased in the cold and was unchanged in the heat. Relative weights of brain, spleen, lungs, brown fat and ovaries + uterus did not change with temperature acclimation. 3. Cold acclimation produced significant increases in specific and total activity of brown fat alpha GPO and liver SO and AAO and in total activity of kidney SO; a significant decrease in liver mitochondrial ADP/O ratio with succinate as substrate; and no change in brown fat SO or liver alpha KGO. 4. Heat acclimation produced significant decreases in specific and total activity of liver and kidney SO, and in total activity of brown fat SO and alpha GPO, and liver AAO and alpha KGO. 5. The combined biochemical and organ wt changes seen in temperature-acclimated gerbils suggest that this species is capable of altering its metabolic thermogenic potential in response to a wide range of ambient temperatures.