The effect of the extent of hydrolysis in casein on its specific dynamic action in the rat.

1. Adult female rats given a diet containing 200 g casein/kg showed an increase in heat production which reached a maximum in 10--20 min after completion of food intake. 2. Replacement of casein in the diet by enzymic hydrolysates of casein of different extents of hydrolysis (pepsin for 1 or 3 h and pancreatin for 6, 12 or 24 h) resulted in a decrease in metabolic rate (stimulation) in the rat, reaching a maximum of 61.8% of the control value (non-hydrolysed casein). 3. The specific dynamic action of casein and casein hydrolysate was inversely proportional to the amount of amino-nitrogen released. 4. On the basis of the experimental findings it may be concluded that the synthesis and secretion of digestive enzymes were the main causes of the increase in metabolic rate after protein ingestion.