Effect and absorption of histamine in sheep rumen: Significance of acidotic epithelial damage

The significance of ruminal histamine for the induction of epithelial damag e and systemic histaminosis during the ruminal lactic acidosis syndrome was investigated using the Ussing chamber technique. Histamine did not affect the electrophysiological characteristics of ovine luminal epithelia under s hort-circuit conditions. In contrast, mucosal acidification to pH 5.1 induc ed pronounced effects on tissue conductance (G(t)) and short-circuit curren t (I-sc). Using [H-3]histamine for flux determination (hist-rad fluxes), si gnificant net absorption of histrad (.40 +/- .07 nmol.cm(-2).h(-1); n = 6) was evident under short-circuit condimine gradient (80 mu M:12 mu M). In co mparison to hist-rad, absorption of native histamine (ms histamine gradient 80 mu M:0 mu M) measured with HPLC under open circuit conditions was small er (.010 +/- .003 nmol.cm(-2).h(-1); n = 10). Mucosal acidification to pH 5 .1 led to an increase (P < .05) in net absorption of hist-rad (to .67 +/- . 06 nmol.cm(-2).h(-1); n = 6) and a dramatic increase (P < .01) in the absor ption of native histamine (to .27 +/- .04 nmol.cm(-2).h(-1); n = 10). Absor ption of ruminal histamine should be considered an important cause of syste mic histaminosis in acidotic ruminants. Histamine absorption is linked to l uminal epithelial damage, which is primarily induced by luminal acidity and not by histamine.