We have investigated the effect of melatonin administration on the cytometric and endocrine functions of the
ovary during aging. Young cyclic (3 months old), middle-aged pre-acyclic (13 months old), and old acyclic (22 months
old) female Wistar rats were used for two months, in both control and melatonin-treated groups. Cell cycle by flow cytometry:
the percentage of ovarian cells in the G0-G1 phase was the highest in both control and melatonin-treated rats.
However, melatonin treatment significantly reduced (P< 0.05) the percentage of cells in the G0-G1 phase compared to
control rats. This reduction of cells in the G0-G1 phase is derived to the S phase in cyclic and acyclic rats. The possibility
that a tumoral process leads to a proliferative effect observed in young and acyclic melatonin-treated rats was ruled out
because no significant differences were found for p53 and Ki67 expression levels between control and melatonin groups.
Density of oocytes: the oocyte number per ovary unit volume was not affected by melatonin treatment in the three age
ranges studied. Melatonin treatment in middle-aged (pre-acyclic) rats resulted in significantly higher (P< 0.05) ovarian
volume; higher oocyte volume, without significant differences, and oocytes in circular form were significantly (P< 0.05)
higher than in control rats. Melatonin treatment during pre-acyclic age range could resynchronize the estrous cycle periodicity.
Melatonin treatment was able to maintain the same levels of estradiol in the pre-acyclic age groups studied as those
observed in the young cyclic rats. The present results indicate that melatonin administration to middle-aged female rats
produces beneficial effects that extend the reproductive function of the ovary.
Keywords: Aging, cell cycle, estradiol, melatonin, oocytes, ovarian aging, ovarian aging, ovary.
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