Fate of Ingested Histamine in Sheep

Abstract

Histamine ingested with the food or given by mouth disappeared much faster from the rumen than an inert marker (polyethylene glycol), whereas the inactivation of histamine by rumen contents was slow in vitro. This indicated that histamine was absorbed unchanged from the rumen. But when G¹⁴-histamine was administered in the same way together with carrier, the biological activity disappeared more rapidly from the rumen than the radioactivity, thus indicating transformation of histamine to inactive metabolites. This study gave no clue as to the reason for the apparent discrepancy between the in vitro and the in vivo experiments.

The in vitro inactivation of histamine in rumen contents was related to the time of feeding, the inactivation in rumen contents aspirated just after feeding being considerably slower than in those aspirated about 3 hrs. after feeding. By inactivation of histamine by rumen contents, formation of small amounts of conjugated histamine was demonstrated both in vivo and in vitro. In vivo experiments indicated that conjugated histamine was absorbed from rumen.

A small flux of radioactivity into the rumen was demonstrated subsequent to subcutaneous injection of C¹⁴-histamine.