Environmental control of energy metabolism in rats.

Food availability was arranged so that episodes of feeding were separated by long periods of deprivation. Distinctly different contexts were associated with each condition. For other animals, relatively short periods of deprivation stood in contrast to relatively long opportunities to free-feed, and were also embedded in widely differing physical contexts. These temporal relationships among the conditions were adjusted to sharpen the saliency of each metabolic condition and thereby enhance its associability with the distinctive environment in which each occurred. To avoid the possibility of circadian entrainment, the feeding or deprivation episodes occurred at unpredictable times according to a variable-time schedule. Following several training cycles and an extended period of free-feeding in a neutral environment, the animals were reexposed to the various contexts and sacrificed for metabolite assays. The environment predictive of feeding elevated adipocyte lipoprotein lipase activity and lowered the levels of serum free fatty acids. The deprivation context boosted serum triglycerides and blood urea nitrogen. The conditioned responses were all of a compensatory nature: Feeding cues resulted in accelerated caloric deposition, deprivation cues elicited conditioned mobilization of stored energy. While protein catabolism and several indices of fat metabolism appear to be conditionable, no evidence of environmental control of glycemic responses was observed.