Effects of diet and body fat content on cold-induced anestrus in Syrian hamsters.

Mammalian reproduction is inhibited by food shortages, increased foraging requirements, and other factors that decrease the energy available for biological processes. Cold-induced inhibition of reproduction may result from a depletion of available metabolic energy due to the increased requirements for thermogenesis or, alternatively, from mechanisms unrelated to energy expenditure. We examined the relationship between energy availability (in the diet and the body fat stores) and cold-induced anestrus in Syrian hamsters. In experiment 1, hamsters were housed in the cold (5 degrees C) and fed diets that differed in the amount of effort required to ingest them. The number of consecutive estrous cycles was positively correlated with caloric intake and negatively correlated with body weight loss in the cold. In experiment 2, hamsters were fed these diets for several weeks, so that they differed dramatically in body weight and fat content before cold exposure. Half of each group retained the same diet during cold exposure, whereas the other half were fed a regular chow diet. The effects of body weight before cold exposure were less pronounced than the effects of caloric intake during cold exposure. In experiment 3, females were fed different diets before cold exposure, then, during cold exposure, all were fed in a manner that decreased food intake and increased the effort required to obtain food. This energetic challenge exaggerated the effect of prior body weight on the latency to cold-induced anestrus. Thus the latency to cold-induced anestrus in Syrian hamsters is primarily a function of the availability of metabolic energy.(ABSTRACT TRUNCATED AT 250 WORDS)