ELEVATION OF BRAIN HISTAMINE CONTENT IN PROTEIN‐DEFICIENT RATS1

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Abstract
—Male rats of the Sprague‐Dawley strain (80–250 g body wt) were fed either an adequate protein diet (18% lactalbumin) or a protein‐deficient diet (0.5% lactalbumin). After 5–8 weeks of receiving the low protein diet, some of the malnourished rats were rehabilitated with an adequate protein diet. The malnourished rats exhibited significant elevations in brain levels of histidine (+415%) and homocarnosine (+100%) in comparison to findings in the control animals of similar age. Associated with the elevated brain levels of histidine in malnutrition was a prominent increase in brain content of histamine (+ 150‐+ 238%). The mean brain histamine levels (ng/g) in the control rats varied from 45.96 to 56.15 in several experiments. In the protein‐deficient rats, values ranged from 115 to 190. Refeeding the malnourished rats with adequate protein diet elicited reversal of histidine and histamine levels to near normal values within 1 week. The increased brain content of histamine in malnutrition was attributed to enhanced rate of production resulting from increased availability of the precursor amino acid, a conclusion consistent with elevation also of the brain content of homocarnosine (γ‐aminobutyryl‐l‐histidine) which is another major route of disposal of histidine in the brain. The relevance of these neurochemical alterations to the behavioural changes often associated with protein malnutrition, deserves some intensive examination.