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

The significance of ruminal histamine for the induction of epithelial damage 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 ruminal epithelia under shortcircuit conditions. In contrast, mucosal acidification to pH 5.1 induced pronounced effects on tissue conductance (Gt) and short-circuit current (Isc). Using [3H]histamine for flux determination (hist-rad fluxes), significant net absorption of hist-rad (.40+/-.07 nmol x cm(-2) x h(-1); n = 6) was evident under short-circuit conditions in the presence of a mucosal-to-serosal (ms) histamine gradient (80 microM:12 microM). In comparison to hist-rad, absorption of native histamine (ms histamine gradient 80 microM:0 microM) measured with HPLC under open circuit conditions was smaller (.010+/-.003 nmol x cm(-2) x 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 x cm(-2) x h(-1); n = 6) and a dramatic increase (P<.01) in the absorption of native histamine (to .27+/-.04 nmol x cm(-2) x h(-1); n = 10). Absorption of ruminal histamine should be considered an important cause of systemic histaminosis in acidotic ruminants. Histamine absorption is linked to ruminal epithelial damage, which is primarily induced by luminal acidity and not by histamine.