Nutritional effects on neurotransmitter metabolism in the broiler chicken

Two experiments were conducted with broiler chickens to determine various nutritional effects on neurotransmitter metabolism. In Experiment 1, 21-day old chickens were fasted for 24 hr, fed on an ad libitum basis, fed a diet containing 450 g crude protein/kg (high-protein) or fed a diet containing 80 g crude protein/kg (high carbohydrate) to examine nutritional regimens that may alter neural factors regulating growth. Chickens were injected (250 mg/kg BWt) with a tyrosine hydroxylase inhibitor, alpha-methyl-DL-p-tyrosine (AMPT), to inhibit catecholamine synthesis and to estimate turnover constants as functions of these treatments. In Experiment 2, 7-day old chickens were fed diets containing 120, 180, 240, and 300 g crude protein and 1 mg T3/kg diet for 21 days to determine the effects of both dietary protein and thyroid status on catecholamine concentrations. Norepinephrine (NE) and dopamine (DA) in the brains and NE and DA in the hearts and pancreases were separated by HPLC and determined by electrochemical detection. Fractional turnover of DA in the brains of both fed and fasted chickens was equal but was over twice as great as that of NE. Fractional NE turnover in hearts of both fed and fasted chickens was 12.3%/hr although fractional NE turnover in pancreas was greater (P < 0.05) in fasted than in fed chickens (9.0%/hr vs 5.1%/hr). These same rate constants were also seen in brains of chickens fed high-carbohydrate or high-protein diets. In contrast, a protein diet increase pancreatic and cardiac NE turnover compare to a high-carbohydrate diet.