| Abstrakt: |
The effect of age and of varying the dietary histidine level, with special emphasis on histamine metabolism, was studied in male, white Leghorn chicks. The birds were fed a 19% amino acid diet with histidine supplied from 0 to 0.8% of diet. In Experiment 1, 7-day-old chicks were fed the experimental diets for 7 days. In Experiment 2, chicks were fed the experimental diets for different time intervals to equalize their body weight at time of killing. In Experiment 3, birds were killed at 5, 9, 12 and 15 days of age when their body weights reached 69, 96, 136 and 184 g, respectively. Concentrations of anserine, carnosine, free-histidine and histamine, and activities of histidine decarboxylase (HDC) and histamine methyl transferase (HMT) were assayed in whole brain, pectoralis major muscle and in proventriculus of 3 or 4 chicks per treatment group. The following results were obtained: As the level of dietary histidine increased, (1) tissue concentrations of free-histidine and of carnosine increased; (2) the activity of HMT increased; (3) the concentration of anserine remained constant; (4) the activity of HDC increased in brain and muscle, but decreased sharply in the proventriculus; (5) the concentration of histamine decreased. (6) Free-histidine concentration, HDC and HMT activities increased with an increase in age and body weight; however, histamine concentrations decreased with age and body weight. The results point to the possibility that the relatively greater increase in HMT activity compared to HDC may be responsible for the decrease in histamine concentration with increase in dietary histidine or increased age. The very high HDC activity in the proventriculus of birds fed low histidine diets may have contributed to the higher histamine concentrations in brain and muscle of birds fed low versus higher histidine-containing diets. [ABSTRACT FROM AUTHOR] |
