The role of specific macronutrient availability in the effect of food restriction on length of lactational diestrus in rats

In lactating rats, food restriction for the first two weeks postpartum extends the period of lactational diestrus by about 1 week. In these studies we investigated whether this effect results from caloric restriction or the reduced availability of a specific macronutrient. In Experiment 1 lactating rats nursing litters of eight pups were assigned to one of four conditions: 1) ad lib. fed; 2) protein-restricted; 3) carbohydrate-restricted; and 4) fat-restricted. Animals in all the restricted conditions were given access to 50% of ad lih. intake of the appropriate nutrient for Days 1-14 postpartum and ad lib. access to the other two macronutrients. In Experiment 2, ad lib. supplementation from one macronutrient source was provided to lactating rats given restricted access to a composite diet. No differential effect of specific macronutrient deprivation or supplementation on length of lactational diestrus was observed in these studies. Thus, the results of both studies are consistent with the hypothesis that caloric restriction plays a primary role in inducing the prolongation of lactational diestrus in food-restricted rats. (C) 1998 Elsevier Science Inc.