Rats’ ovulatory function under melatonin receptors’ blockade

The paper investigates the problem of age dynamics of the estrous function in female rats under standard lighting from the time of birth. On the daily basis, 5 days a week, beginning from the age of five months the rats received along with drinking water a blocker melatonin receptor - luzindol (N-Acetyl-2-benzyl-tryptamine) at the concentration level of 10 mg / l. At the age of three, six, nine, twelve, and fifteen months daily, for a period of two weeks, vaginal smears and cytological examination was performed to estimate the length of the estrous cycle and the phase relationship in ovulatory cycle. The number of short, medium and long cycles; the percentage of the phases of the estrous cycle; relative number of animals with irregular cycles were calcultated. As a result, it recorded a decrease in the amount of short cycles and an increase in the amount of long estrous cycles after one month of luzindol application. It was found out that melatonin receptor blockade influence the appearance of premature aging changes in female rats: a significant decrease in the number of regular cycles and stable occurrence of irregular estrous cycles (6 months of age); earlier prolongation of ovulatory cycle (9 months of age). Apparently, melatonin receptor blockade could lead to an increased secretion of gonadotropins and gonadoliberines. This resulted in the activation of the follicles’ growth and ovaries’ development and contributed to a sustained release of estrogen and the phase change in the ovulatory cycle. Despite different mechanisms affecting the failure in melatoninergic system: loss of melatonin (under the influence of constant light) or melatonin receptor blockade (usage of luzindol) - the effects of actions on the ovulatory function is similar. No rodents with the syndrome of persistent estrus were registered under the pharmacological blockade of melatonin receptor. The obtained results point to the presence of hormonal regulation through sexual hormones.