Dietary Protein-Induced Changes in Serum Dopamine-β-Hydroxylase Activity, Glucose, Insulin, Cortisol and Pyridoxal-5′Phosphate Levels in Normal and Immobilized Cats

Abstract

Adult cats, adapted for 19 consecutive days to isocaloric semi-purified diets, were used to study the effects of three different levels of two types of dietary protein source (casein and soya) and the effects of a 2h immobilization period on various blood parameters. The ad libitum food intake and the daily dietary protein intake of cats fed casein diets were significantly higher than those of cats fed soya diets. Blood glucose content was not influenced by dietary protein source and daily protein intake, but pyridoxal-5′phosphate was decreased in cats fed the higher casein and soya levels (40.7% and 29.3%, respectively). Blood insulin and cortisol levels were significantly lower in soya than in casein groups, whereas pyridoxal-5′phosphate content increased progressively with the decreasing soya and casein levels in the diet. The serum dopamine-β-hydroxylase activity was found to be significantly higher in cats fed soya diets (22.1% and 25.7%, respectively) than in all cats fed casein diets. Following a 2h immobilization period, glucose and cortisol levels were significantly increased in casein and soya groups, and pyridoxal-5′phosphate content significantly decreased, whereas dopamine-β-hydroxylase activity and insulin levels remained unchanged. These results suggest that dietary protein sources influence blood parameters and that an acute stressful situation such as induced by a 2h immobilization, permits the dissociation on a biochemical basis of the physiological responses of blood pyridoxal-5′phosphate, glucose, and cortisol content from those of insulin level and dopamine-β-hydroxylase activity, whatever the dietary protein source and the protein level of the diet.