THE ROLE OF SPECIFIC MACRONUTRIENT AVAILABILITY IN THE EFFECT OF FOODRESTRICTION 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 restr iction or the reduced availability of a specific macronutrient. In Exp eriment 1 lactating rats nursing litters of eight pups were assigned t o one of four conditions: 1) ad lib. fed; 2) protein-restricted; 3) ca rbohydrate-restricted; and 4) fat-restricted. Animals in all the restr icted conditions were given access to 50% of ad lih. intake of the app ropriate nutrient for Days 1-14 postpartum and ad lib. access to the o ther two macronutrients. In Experiment 2, ad lib. supplementation from one macronutrient source was provided to lactating rats given restric ted access to a composite diet. No differential effect of specific mac ronutrient deprivation or supplementation on length of lactational die strus was observed in these studies. Thus, the results of both studies are consistent with the hypothesis that caloric restriction plays a p rimary role in inducing the prolongation of lactational diestrus in fo od-restricted rats. (C) 1998 Elsevier Science Inc.