[Effect of the light-dark cycle over the growth of male rats with different health status]. / Influencia del ciclo luz-oscuridad en el crecimiento de ratas macho con diferente estado de nutrición.

The light-dark cycle exerts an influence over the lipostatic mechanism in the superior vertebrate animals promoting an acceleration in the lipid synthesis rate during the dark period (in the case of rodents) and a higher lipolitic rate during the day. This cycle, the feeding habits, and the awake-sleep cycle are syncronized. The Growth Hormone is a molecule that facilitates the lipolysis and the protein synthesis. This hormone is released, by the pituitary gland, during the puberty and during the short wave sleep period. Modifying the light-dark cycle and in consequence the sleep-awake cycle and the food consumption, we pretend to study its influence over the growth rate in weight and length in animals that consume 100% of its nutritional requirements. Also want to dilucidate if an alteration of the cycle (18 h light 6 h 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 (12 h-12 h) during a week. Then, four groups were formed; Group I: Well nourished rats with a light-dark (12 h-12 h) cycle; Group II: Well nourished rats with a light-dark (18 h-6 h) cycle; Group III: Malnourished rats with a light-dark (12 h-12 h) cycle; Group IV: Malnourished rats with a light-dark (18 h-6 h) cycle. Its length and weight were registered weekly, obtained its growth rates, and the results were analysed by the ONE-WAY ANOVA and orthogonal contrasts. It was found a significant difference in the growth rate in weight between the Groups I and II; the growth rate in weight in the Group III had a higher slope than the rate in the Group IV but we did not find a significant difference. The growth rate in length did not show a significant difference between the Groups III and IV. The last weight in the malnourished animals represented 55% of the control animals last weight; and 47% of the Group IV. The last length of the animals of the Group III represented 90% of the control value, and the last length in the Group IV represented 82% of the control animals value. The feeding habits are modified changing the cycle to 18 h light and 6 h dark. Modifying the light-dark cycle appears an accelerating rate in the growth rate in weight in the well nourished animals, but not in the malnourished ones.