Melatonin, a widespread substance with antioxidant and anti-inflammatory properties, has been found to act as an antidiabetic agent in animal models, regulating the release and action of insulin. However, the molecular bases of this antidiabetic action are unknown, limiting its application in humans. Several studies have recently shown that melatonin can modify calcium (Ca(2+)) in diabetic animals, and Ca(2+) has been reported to be involved in glucose homeostasis. The objective of the present study was to assess whether the antidiabetic effect of chronic melatonin at pharmacological doses is established via Ca(2+) regulation in different tissues in an animal model of obesity-related type 2 diabetes, using Zücker diabetic fatty (ZDF) rats and their lean littermates, Zücker lean (ZL) rats. After the treatments, flame atomic absorption spectrometry was used to determine Ca(2+) levels in the liver, muscle, main types of internal white adipose tissue, subcutaneous lumbar fat, pancreas, brain, and plasma. This study reports for the first time that chronic melatonin administration (10 mg per kg body weight per day for 6 weeks) increases Ca(2+) levels in muscle, liver, different adipose tissues, and pancreas in ZDF rats, although there were no significant changes in their brain or plasma Ca(2+) levels. We propose that this additional peripheral dual action mechanism underlies the improvement in insulin sensitivity and secretion previously documented in samples from the same animals. According to these results, indoleamine may be a potential candidate for the treatment of type 2 diabetes mellitus associated with obesity.

Introduction. Contrast, eccentricity and position of stimuli used on research of attention in human vision strongly vary among studies. Aim. To study how contrast, eccentricity and position affects detection of stimuli in humans. Subjects and methods. In adults with normal vision, we measured response times to stimuli (gray circles of 0.5º of diameter) presented at random at eight polar coordinates, in three eccentricities with respect of fixation point (2.15, 3.83 and 5.53º) and with three levels of contrast (6, 16 and 78%). Results. Stimuli with eccentricity of 5.38º and 6% of contrast showed the longest response times. In all eccentricities studied, longer response times were found with stimuli of 6% of contrast. Response times of stimuli of 16% and 78% of contrast showed similar response times in all eccentricities studied. Response times founded at eight polar coordinates were heterogeneous at eccentricities of 2.15 and 5.53º, but not at 3.83º. Conclusions. Contrast is the factor that most influence detection of visual stimuli used in this study, particularly at the biggest eccentricity employed. Response times among polar coordinates are also affected by eccentricities of 2.15 and 5.53º, suggesting that distance of stimuli to fixation point is critical for visual detection of stimuli.

Se han estudiado los efectos del envejecimiento normal en la atención visual. Han participado un grupo de 38 personas mayores sanas con una edad media de 67.8 años y ungrupo de 39 personas jóvenes sanas con edad media de 19.2 años. En un primer experimento de detección visual, se midieron los tiempos de respuesta, con y sin atención encubierta, a la presentación de estímulos (círculos grises de 0.5º de diámetro) y que aparecen en tres excentricidades (2.15, 3.83 y 5.53º de campo visual) y con tres niveles de contraste (6, 16 y 78%). En un segundo experimento de discriminación visual de la forma, se presentaron círculos y cuadrados con las mismas características que en el experimento anterior, pero en este caso solo se debía responder a la aparición de los círculos. En ambos grupos de edad, la atención encubierta redujo los tiempos de respuesta. En comparación con los jóvenes, el grupo de mayores logró mejores resultados en algunos aspectos de las pruebas de atención y redujo más los tiempos de respuesta en los estímulos de mayor excentricidad. Los datos sugieren que en el envejecimiento existe un mecanismo de adaptación en el que la atención visual favorece especialmente la percepción de aquellos estímulos más difíciles de detectar.

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