Morphological alterations and NO-synthase expression in the heart after continuous light exposure of rats.

Although exposure to continuous light is associated with hypertension and modulates the outcome of ischemia-reperfusion injury, less attention has been paid to its effects on cardiac morphology. We investigated whether 4-week exposure of experimental rats to continuous 24 h/day light can modify cardiac morphology, with focus on heart weight, fibrosis and collagen I/III ratio in correlation with NO-synthase expression. Two groups of male adult Wistar rats were studied: controls exposed to normal light/dark cycle (12 h/day light, 12 h/day dark) and rats exposed to continuous light. After 4 weeks of treatment the absolute and the relative heart weights were determined and myocardial fibrosis and collagen type I/III ratio were evaluated using picrosirius red staining. Endothelial and inducible NO-synthase expression was detected immunohistochemically. The exposure of rats to continuous light resulted in an increase of body weight with proportionally increased heart weight. Myocardial fibrosis remained unaffected but collagen I/III ratio increased. Neither endothelial nor inducible NO-synthase expression was altered in light-exposed rats. We conclude that the loss of structural homogeneity of the myocardium in favor of collagen type I might increase myocardial stiffness and contribute to functional alterations after continuous light exposure.

The effect of continuous light exposure of rats on cardiac response to ischemia-reperfusion and NO-synthase activity.

Factors modulating cardiac susceptibility to ischemia-reperfusion (I/R) are permanently attracting the attention of experimental cardiology research. We investigated, whether continuous 24 h/day light exposure of rats can modify cardiac response to I/R, NO-synthase (NOS) activity and the level of oxidative load represented by conjugated dienes (CD) concentration. Two groups of male adult Wistar rats were studied: controls exposed to normal light/dark cycle (12 h/day light, 12 h/day dark) and rats exposed to continuous light for 4 weeks. Perfused isolated hearts (Langendorff technique) were exposed to 25 min global ischemia and subsequent 30 min reperfusion. The recovery of functional parameters (coronary flow, left ventricular developed pressure, contractility and relaxation index) during reperfusion as well as the incidence, severity and duration of arrhythmias during first 10 min of reperfusion were determined. The hearts from rats exposed to continuous light showed more rapid recovery of functional parameters but higher incidence, duration and severity of reperfusion arrhythmias compared to controls. In the left ventricle, the NOS activity was attenuated, but the CD concentration was not significantly changed. We conclude that the exposure of rats to continuous light modified cardiac response to I/R. This effect could be at least partially mediated by attenuated NO production.

Ischemia-reperfusion injury--antiarrhythmic effect of melatonin associated with reduced recovering of contractility.

The effect of melatonin on reperfusion arrhythmias and postischemic contractile dysfunction was studied in the isolated rat heart. 25 min global ischemia was induced and followed by 30 min of reperfusion. Melatonin (10 micromol/l) was present in the perfusion solution during the whole experiment. Experiment revealed protective effect of melatonin on reperfusion-induced arrhythmias--arrhythmia score was significantly lower as well as the total time of arrhythmias duration was significantly shorter in melatonin group than in controls. On the other hand, post-ischemic recovering of contractility was significantly reduced in melatonin group.

[Melatonin and the heart]. / Melatonín a srdce.

Evidence gathered during the last years shows that the pineal hormone melatonin participates in the regulation of the heart. Melatoninergic receptors were found in the heart and vessels and also in the higher centers involved in the regulation of cardiovascular system. Melatonin protects the heart against ischaemia-reperfusion injury and also against cardiotoxic effects of adriamycin and alloxan. Lack of melatonin was repeatedly reported in patients with coronary heart disease. Intake of this hormone leads to decrease of blood pressure in normotensive and hypertensive subjects, while pinealectomy induces hypertension. In addition melatonin can probably influence the levels of intracellular calcium in cardiomyocytes. The aim of this review is to summarize available evidence about effects of melatonin on the heart. Mechanisms involved in these effects are also suggested.

The assessment of erythrocyte deformability by filtration rate.

The aim of the study was to monitor the erythrocyte deformability as one of important factors securing the appropriate tissues perfusion in healthy subjects and diabetic patients with insulin dependent diabetes mellitus. Erythrocyte deformability was determined by the method of filtration and centrifugation, and the erythrocyte filtrability was calculated as a percentage of filtered erythrocytes out of the number of erythrocytes counted before centrifugation. Diluted blood suspensions were filtered by centrifugation through membrane filters with pores of 5 microm in diameter. The speed and duration of centrifugation of 1400 rpm and 5 min respectively were selected as the best ones for filtration due to the lowest value of the coefficient of variance. The values of the arithmetic mean and standard deviation of erythrocyte filtrability were 72.2 +/- 7.9% in normal subjects. In the group of diabetic patients with the long history of insulin therapy the values amounted to 69.1 +/- 4.4%. In diabetic patients, the average value of blood glucose was 11.7 mmol x L(-1), and the glycated haemoglobin concentration reached 9.04%. From the viewpoint of reference values, these facts indicate good compensation of diabetes mellitus. Other haematological values, namely erythrocyte count, haematocrit value, haemoglobin concentration and mean cell volume were within normal reference ranges. No difference between the groups of healthy subjects and diabetic patients was found. (Fig. 4, Ref. 18.)

Effect of melatonin on the isolated heart in the standard perfusion conditions and in the conditions of calcium paradox.

UNLABELLED: The effect of melatonin (MLT) on the isolated rat heart was studied using the standard perfusion conditions (Langendorff preparation) and model of calcium paradox (Ca(2+)-paradox). Ca(2+)-paradox was induced by 1 minute perfusion with Ca(2+)-free Krebs-Henseleit (KH) solution and subsequent 20 minutes perfusion with a normal Ca(2+)-containing KH solution. In MLT group, MLT (10 micromol/l) was in the perfusion solution throughout the experiment. In controls, there was no MLT. VARIABLES: heart rate, coronary flow, systolic and diastolic pressure, +dP/dt max (index of contractility) and -dP/dt max (index of relaxation) were measured at the end of stabilization, i.e. after 30 minutes of standard perfusion and then in the 5th, 10th, 15th, 20th minute after perfusion with Ca(2+)-free KH solution. RESULTS: There was no difference between MLT group and controls in the standard perfusion conditions at the end of stabilization. After perfusion with Ca(2+)-free KH solution, systolic-diastolic difference (in the 10th, 15th, 20th minute), +dP/dt max (in the 5th, l0th, 15th, 20th minute) and -dP/dt max (in the 15th minute) were significantly decreased in MLT group in comparison to controls. CONCLUSION: Melatonin didn't influence rat isolated heart in standard perfusion conditions but it made the heart more susceptible to Ca(2+)-paradox.