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The formation of 14C-histamine from orally administered 14C-1-histidine in pigs.

The object of the present study has been to examine to what extent dietary L-histidine is converted to histamine in pigs, a species which excretes large amounts of histamine in the urine. During the first 24 h after oral administration of 14C-L-histidine only, about 1/10 to 1/3 of the adminstered radioactivity was recovered in the urine. Free 14C-histamine accounted for about 1% of the urinary radioactivity while the values for 14C-1.4-mathylhistamine and 14C-1.4-methylimidazoleacetic acid were about 0.5 and 40%, respectively. The values for 14C-histamine may be overestimated, but the high values for the methylated 14C-metabolites of histamine indicate that 4–20% of orally administered 14C-L-histidine is converted to Hi. This is far superior to what has been found in other species. Oral administration of 10 g L-histidine monohydrochloride to pig resulted in the excretion of a much smaller fraction as histamine and as methylated metabolites of histamine than would be expected from the experiments with 14C-L-histidine.