Melatonin reduces changes to small intestinal microvasculature during systemic inflammation.

BACKGROUND: Systemic inflammation is known to impair the microcirculation in intestine and other organs as a result of multifactorial events. Here, we show that melatonin selectively reduces changes to the small intestinal microvasculature during systemic inflammation. MATERIALS AND METHODS: Lipopolysaccharide (LPS) was infused at a rate of 0.5 mg/kg × h to induce systemic inflammation in male Wistar rats. Melatonin (single dose: 3 mg/kg × 15 min) was intravenously administered before as well as 120 and 240 min after the beginning of the LPS infusion. Systemic parameters were determined in regular intervals. Small intestine, liver, and kidney were histologically (structure of the microvessels, intravascular blood accumulation, and hemorrhages) and immunohistochemically (mast cells, granulocytes, and macrophages) analyzed. RESULTS: Continuous infusion of LPS resulted in dilated microvessels with intravascular blood accumulation (congestion) in liver and small intestine, the latter being particularly pronounced. Blood vessel walls remained intact, there were no hemorrhages. Melatonin significantly reduced these changes to the microvasculature in small intestine, but not in liver. It further reduced mast cell and granulocytes count in small intestine enhanced by LPS. However, except for the systemic blood pressure, melatonin neither improved LPS-dependent changes to systemic parameters nor mortality. CONCLUSIONS: Changes to the microvasculature during systemic inflammation are most pronounced in small intestine. Melatonin selectively diminishes these changes to small intestinal microvasculature, probably by reducing the local immune cells recruitment. However, changes to the small intestine are not decisive for the survival. We assume that the therapeutic benefit of melatonin is more likely in local intestinal inflammation.

Melatonin does not affect disseminated intravascular coagulation but diminishes decreases in platelet count during subacute endotoxaemia in rats.

INTRODUCTION: Inhibitory effects of exogenous melatonin (MLT) on plasma coagulation and platelet aggregation have already been observed in vivo and in vitro under normal conditions. Here, we studied whether MLT also diminishes the lipopolysaccharide (LPS)-induced disseminated intravascular coagulation (DIC) during subacute endotoxaemia. MATERIALS AND METHODS: Subacute endotoxaemia was induced in male Wistar rats by an intravenous infusion of LPS over a period of 300min (0.5mg LPS/kg×h). MLT was administered intravenously 15min before and 120min and 240min after starting of the LPS infusion (3×3mg MLT/kg×15min). The kinetic of clot formation was analysed by thromboelastometry. RESULTS: Infusion of LPS led initially to a significant reduction of clotting time (120min, LPS: 150±21s vs. SHAM: 292±36s), and finally a significant increase of clotting time (300min, LPS: 2768±853s vs. SHAM: 299±67s) and a slight increase of clot formation time (300min, LPS: 1038±657s vs. SHAM: 98±14s) as well as a significant decrease of alpha-angle (300min, LPS: 35±15° vs. SHAM: 72±3°), maximum clot firmness (300min, LPS: 22±6mm vs. SHAM: 68±3mm), and area under the curve (300min, LPS: 1657±552mm×100 vs. SHAM: 6849±307mm×100). Simultaneously, a decrease of platelet count (300min, LPS: 55±8 vs. SHAM: 180±55) and a release of cell-free haemoglobin (240min, LPS: 46±5µmol/L vs. SHAM: 16±2µmol/L) could be observed in the course of subacute endotoxaemia. The additional administration of MLT did not reduce the LPS-induced alterations in parameters of thromboelastometry, but significantly reduced the LPS-induced decrease of platelet count (300min, LPS+MLT: 130±10) and release of cell-free haemoglobin (240min, LPS+MLT: 29±3µmol/L). CONCLUSION: Melatonin does not affect DIC but diminishes thrombocytopenia and haemolysis during endotoxaemia.