Melatonin Prevents Early but Not Delayed Ventricular Fibrillation in the Experimental Porcine Model of Acute Ischemia.

Antiarrhythmic effects of melatonin have been demonstrated ex vivo and in rodent models, but its action in a clinically relevant large mammalian model remains largely unknown. Objectives of the present study were to evaluate electrophysiological and antiarrhythmic effects of melatonin in a porcine model of acute myocardial infarction. Myocardial ischemia was induced by 40-min coronary occlusion in 25 anesthetized pigs. After ischemia onset, 12 animals received melatonin (4 mg/kg). 48 intramyocardial electrograms were recorded from left ventricular wall and interventricular septum (IVS). In each lead, activation time (AT) and repolarization time (RT) were determined. During ischemia, ATs and dispersion of repolarization (DOR = RTmax - RTmin) increased reaching maximal values by 3-5 and 20-25 min, respectively. Ventricular fibrillation (VF) incidence demonstrated no relations to redox state markers and was associated with increased DOR and delayed ATs (specifically, in an IVS base, an area adjacent to the ischemic zone) (p = 0.031). Melatonin prevented AT increase in the IVS base, (p < 0.001) precluding development of early VF (1-5 min, p = 0.016). VF occurrence in the delayed phase (17-40 min) where DOR was maximal was not modified by melatonin. Thus, melatonin-related enhancement of activation prevented development of early VF in the myocardial infarction model.

Mechanical properties of the pectin hydrogels and inflammation response to their subcutaneous implantation.

We studied the influence of the mechanical properties of pectin hydrogels on acute inflammation and tissue repair after subcutaneous implantation. We used hard and soft pectin hydrogels. The results of histology and the analysis of serum-level cytokines demonstrated that the intensity of acute inflammation increased with increasing hardness of the pectin hydrogels. We also showed that the pectin hydrogels did not inhibit tissue repair. The results of the morphometric and texture analysis of the pectin hydrogels showed that the in vivo biodegradation kinetics of hard hydrogels were greater than those of soft pectin hydrogels. We also observed that on the surface of the hard and soft pectin hydrogels, a network of collagen fibers was formed. The surface of the pectin hydrogel was shown to prevent the adhesion of infiltrating inflammatory cells. The results of the in vitro experiments demonstrated that pectin hydrogels inhibited the functional activity of macrophages and minimally activated the complement system. Therefore, we showed that soft pectin hydrogels have low proinflammatory potential and can be used in surgery as a barrier material as prevention of adhesions in the abdominal cavity. The hard pectin hydrogel can be used in tissue engineering. The hard pectin hydrogels can be used in the reconstruction of skin because are overpopulated with collagen fibers and contribute to the formation of new connective tissue, their elasticity is comparable to the skin and can be adjusted. They are biodegradable, and no additional manipulation is required to remove them.