Melatonin-induced augmentation of collagen deposition in cultures of fibroblasts and myofibroblasts is blocked by luzindole--a melatonin membrane receptors inhibitor.

BACKGROUND: Melatonin has been proven to have a regulatory influence on collagen accumulation in different types of wound. It was found to inhibit collagen accumulation in the superficial wound model but increase it in the myocardial infarction scar. The aim of the study is to determine the mechanism of melatonin action in the two wound types in rats. METHODS: Cells were isolated from both the superficial wound (subcutaneously inserted polypropylene net) and myocardial infarction scar (induced by ligation of the left coronary artery) and were identified by electron microscopy. RESULTS: Long-shaped cells forming whirl-like structures in culture (mainly identified as fibroblasts) were isolated from the superficial wound model, while myofibroblasts growing in a formless manner were acquired from the infarcted heart scar. Melatonin (10(-7) M) increased collagen accumulation in both fibroblast and myofibroblast cultures. Luzindole (10(-6) M), the blocker of both MT1 and MT2 melatonin membrane receptors, inhibited the effect of melatonin on the two types of cells. CONCLUSION: Regardless of various healing potentials demonstrated by the tested cells (different cell composition, growth and organization), their response to melatonin was similar. Moreover, in the two investigated cultures, augmentation of the collagen content by melatonin was reversed by luzindole, which indicates the possibility of melatonin membrane receptor involvement in that process. The present results suggest that the increased melatonin-stimulated deposition of collagen observed in the infarcted heart of rats could be dependent on activation of the melatonin membrane receptors on scar myofibroblasts.

Melatonin augments expression of the procollagen α1 (I) and α1 (III) genes in the infarcted heart scar of pinealectomized rats.

The pineal gland is involved in the regulation of collagen accumulation in peripheral wounds and scars of the infarcted heart. This study is aimed to provide an explanation of whether the pineal gland and melatonin (MLT) is involved in the regulation of α1 (I) and α1 (III) procollagen gene expression. A secondary aim is the investigation of whether the mechanism of changes could be explained by the direct influence of MLT on myofibroblasts isolated from the scar. Myocardial infarction was induced by left coronary artery ligation in all rats. Animals were divided into groups: control, vehicle-treated rats, those injected with MLT, sham-operated animals, pinealectomized (Px) rats, and Px rats injected with vehicle or treated with MLT. In the second part of the study, cells from the scar of the infarcted heart were isolated and cultured with MLT at concentrations of 10⁻7 and 10⁻9 M. Both α1 (I) and α1 (III) procollagen gene expressions were evaluated by reverse transcription-polymerase chain reaction. Neither MLT given to intact animals nor pinealectomy alone have an influence on procollagen gene expression. However, administration of MLT to the Px animals increased the expression of α1 (I) and α1 (III) procollagen genes. Cells isolated from the heart scar were identified as myofibroblasts. MLT did not influence collagen gene expression in cultured myofibroblasts. The results indicate that MLT has an influence on procollagen gene expression in Px animals. Because the pineal product does not have an influence on the myofibroblast of the scar, the indirect mechanism of MLT action is suggested. This study may have practical implications in patients with a low level of MLT (elderly subjects, patients treated with ß-adrenergic blockers).

Regulatory influence of melatonin on collagen accumulation in the infarcted heart scar.

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.