EFFECTS OF HYPOCHLOROUS ACID AND ASCORBIC-ACID ON CONDUCTANCE, PERMEABILITY, AND STRUCTURE OF EQUINE COLONIC MUCOSA IN-VITRO

Objectives-To study effects of hypochlorous acid (HOCl) on equine colo nic mucosa in vitro, and determine whether addition of ascorbic acid p rotects against the effects. Animals-6 healthy horses and ponies. Proc edure-Short-circuit current was measured in mucosa mounted in Ussing c hambers. Incubation conditions were: control (no additions); 5 mM HOCl ; 1 mM HOCl; same and 5 mM ascorbic acid; 3 mM HOCl; 3 mM HOCl and 5 m M ascorbic acid; 7 mM HOCl; and 7 mM HOCl plus 5 mM ascorbic acid. Per meability was measured with [H-3]mannitol and, at the conclusion of ea ch experiment, tissues were examined microscopically to assess the eff ects of HOCl and ascorbic acid, alone or in combination. Results-Short circuit current and conductance increased transiently in response to 1 mM HOCl. Tissues had mild surface epi epithelial damage, as evident by swelling and separation of isolated cells. These changes were aboli shed when tissues were coincubated with 5 mM ascorbic acid and 1 mM HO Cl. At 3 and 7 mM concentrations, HOCl caused marked increase in tissu e conductance, short circuit current, and permeability to mannitol; th ese changes were associated with histologic damage. Again, coincubatio n with 5 mM ascorbic acid protected against these changes. Additional studies indicated that the effects of HOCl and the protective effects of ascorbic acid were not mediated through changes in pH. Conclusions- HOCl in low concentrations is capable of increasing the short-circuit current in equine colon, possibly by increasing secretions; however, h igher concentrations can cause tissue damage. The addition of 5 mM asc orbic acid blocks these changes. Clinical Relevance-The concentration of HOCl produced by activated neutrophils could damage equine colonic mucosa and potentially contribute to or cause reperfusion injury. The ability of ascorbic acid to ameliorate this injury in an in vitro sett ing offers a potential method for pharmacologic evaluation of this inj ury and for treatment.