RESUMO
The regulatory influence of the pineal gland on superficial wound healing and collagen content is documented. The aim of the present study was to determine whether the pineal gland and its secretory product melatonin regulate collagen accumulation in the scar of the infarcted heart and to explain the mechanisms of its action. To induce myocardial infarction in rats the left coronary artery was ligated. Metoprolol at the dose of 0.2 mg/100 g body weight (b.w.) was injected intraperitoneally to inhibit melatonin secretion. Pinealectomy was performed on some animals. For the in vitro study, cells were isolated from the heart scar and cultured in Dulbecco's modified Eagle medium with 3% fetal calf serum and antibiotics. Collagen content was evaluated as hydroxyproline content according to the Woessner method. Melatonin subcutaneously injected into the rats at the doses of 30 microg/100 g or 60 microg/100 g b.w. increased collagen accumulation in the heart scar. The doses of 3 microg/100 g b.w. and 300 microg/100 g b.w. were not effective. Surgical and pharmacological pinealectomies had opposite effects and reduced collagen content in the scar. However, melatonin administration (60 microg/100 g b.w.) to pinealectomized rats reversed the effect of pinealectomy and normalized collagen levels in heart after infarction. Cells isolated from the heart scar were identified as myofibroblasts. Melatonin (10(-7)-10(-8) m) increased collagen accumulation in the cultures. Collagen accumulation in the scar of the infarcted heart is regulated by melatonin and it exerts effects directly on the myofibroblasts of the infarcted area. Therefore, melatonin-induced collagen accumulation in the infarcted heart could be considered as the event improving the tensile strength of the scar and retarding the development of complications.
