BLOCKADE OF ENDOGENOUS GRF AT DARK ONSET SELECTIVELY SUPPRESSES PROTEIN-INTAKE

This study examined whether endogenous central GRF activity contribute s to the increase in macronutrient intake shown by rats at dark onset. Animals were habituated to two diets: carbohydrate-fat and protein-fa t. Antiserum raised against GRF(aGRF; 1% and 10% solutions) was microi njected into the suprachiasmatic nucleus/medial preoptic area (SCN/MPO A) at dark onset, and macronutrient intake was determined at 1, 2, and 4 h postinjection. aGRF blocked the increase in protein intake normal ly seen at dark onset, but had no effect on carbohydrate intake. These findings suggest that endogenous GRF activity in the SCN/MPOA region of the brain contributes to the circadian and nutritional organization of food intake.