EFFECTS OF HEPARIN, VENOUS STRANGULATION OBSTRUCTION OF THE SMALL-INTESTINE, AND REPERFUSION OF THE SMALL-INTESTINE ON PLASMA DIAMINE OXIDASE ACTIVITY IN HORSES

Diamine oxidase (DAO), an enzyme of small intestinal origin, is releas ed from mucosal storage sites by IV administration of heparin, to yiel d the plasma postheparin DAO (PHD) curve. The PHD curve is diminished when mucosal surface area is lost, and baseline (without heparin) plas ma DAO activity increases when mucosal storage sites are damaged. Plas ma DAO activity was measured after 2 doses of heparin were administere d rv in healthy, conscious horses. In anesthetized horses, the PHD cur ve was studied: during sham small intestinal surgery, and during venou s strangulation obstruction (VSO) of the distal 50% of the small intes tine. In a third group of anesthetized horses, baseline plasma DAO act ivity (without heparin) was measured during VSO of the distal 50% of t he small intestine for 90 minutes, followed by reperfusion for 90 minu tes. Postheparin plasma DAO curves in conscious horses were similar to those reported in other species. Horses with VSO had a similar PHD cu rve as did sham-operated controls at all times, except at 15 minutes, when plasma DAO activity was significantly (P < 0.05) greater in the V SO group. Horses with VSO and reperfusion had no change in baseline pl asma DAO activity throughout the study. Peritoneal fluid DAO activity remained low throughout the study, but increased slightly in horses wi th VSO that received heparin, possibly because of DAO from extravasate d blood in the peritoneal fluid. Results indicated that the plasma DAO response to IV administered heparin in horses is similar to that in o ther mammals, but, unlike other species, baseline and postheparin DAO activities did not change as expected after small intestinal vascular obstruction and mucosal injury. There may be additional sources of DAO in horses, the type of injury induced was not of sufficient magnitude to affect storage sites of DAO, or the circulatory changes induced by VSO might have altered tissue delivery of heparin.