EFFECT OF THE LIGHT-DARK CYCLE OVER THE M ALE-RATS GROWTH UNDER DIFFERENT NUTRITION CONDITIONS

The light-dark cycle exerts an influence over the lipostatic mechanism in the superior vertebrate animals promoting an acceleration in the l ipid synthesis rate during the dark period (in the case of rodents) an d a higher lipolitic rate during the day. This cycle, the feeding habi ts, and the awake-sleep cycle are sincronized. The Growth Hormone is a molecule that facilitates the lipolysis and the protein synthesis. Th is hormone is released, by the pituitary gland, during the puberty and during the short wave sleep period. Modifying the light-dark cycle an d in consequence the sleep-awake cycle and the food consumption, we pr etend to study its influence over the growth rate in weight and lenght in animals that consume 100% of its nutritional requirements. Also wa nt to dilucidate if an alteration of the cycle (18h light 6h dark) in the malnourished animals can revert the deficiency of the growth rate expected in these animals.Male Wistar rats (160), 21 days old, adapted to the temperature and to the light-dark cycle (12h-12h) during a wee k. Then, four groups were formed: Group I: Well nourished rats with al ight-dark (12h-12h) cycle; Group II: Well nourished rats with a light- dark(l8h-6h) cycle; Group III: Malnourished rats with a light-dark (12 h-12h) cycle; Group IV: Malnourished rats with a light-dark (18h-6h) c ycle. Its lenght and weight were registered weekly, obtained its growt h rates, and the results were analysed by the ONE-WAY ANOVA and orthog onal contrasts. It was found a significant difference in the growth ra te in weight between the Groups I acid II; the growth rate in weight i n the Group III had a higher slope than the rate in the Groupe IV but we did not find a significant difference. The growth rate in lenght di d not show a significant difference between the Groups III and IV. The last weight in the malnourished animals represented 55% of the contro l animals last weight; and 47% of the Group IV. The last lenght of the animals of the Group III represented 90% of the control value, and th e last lenght in the Group IV represented 82% of the control animals v alue. The feeding habits are modified changing the cycle to 18h light and 6h dark. Modifying the light-dark cycle appears an accelerating ra te in the growth rate in weight in the well nourished animals, but not in the malnourished ones.