Effect of Dietary Histidine Deprivation in Two Rat Strains on Hemoglobin and Tissue Concentrations of Histidine-containing Dipeptides

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Abstract
Carnosine, a suggested neurotransmitter in the olfactory pathway, has been shown to be sensitive to dietary histidine manipulation in relation to its concentration in various tissues. There is a question concerning the extent to which olfactory bulb carnosine may be depleted. Thirty male ARS Sprague-Dawley albino rats and 30 male Charles River CD albino rats of similar age (64–66 days) and weight (200–250 g) were used to compare the strains relative to the depletion of olfactory bulb carnosine. Rats from each strain were divided into 2 groups and fed ad libitum either a diet adequate for maintenance (0.07% histidine, 3.7% protein) or an isonitrogenous, histidine-free diet. Rats were killed at the start of the experiment and after 6 and 10 weeks of feeding. Changes in the tissue (olfactory bulb, whole brain, pectoral muscle) concentrations of basic free-amino acids and dipeptides (carnosine, homocarnosine, anserine) as well as of blood hemoglobin were measured. There were no observable differences in the depletion time course of the tissue constituents between the two rat strains. The results indicated that histidine, liberated during the catabolism of imidazole-containing compounds (e.g. hemoglobin, muscle carnosine), was preferentially utilized to maintain olfactory bulb carnosine. This is consistent with carnosine playing an important role in olfaction. In an additional experiment, male Charles River CD albino rats (18 weeks old) were fed restricted amounts (15 g/rat/day) of either a maintenance or histidine-free diet over a 16 week period. Olfactory bulb levels of carnosine and of free-histidine were significantly reduced in the histidine-deprived rats to 24% and 35% of control values, respectively. A significant difference in emotionality, as measured by fecal boluses left during an open field behavior test was observed. It was suggested that the histidine-deprived rats might have altered concentrations of hypothalamic histamine.