By: Robert T. Chatterton, Jr., Linda Hrycyk and Robert C. Hickson
Official Journal of the American College of Sports Medicine (1995)
This paper aimed to provide more information on the possible mechanism by which ovulation and fertility are adversely affected in females due to physical stress. In addition, the stage of the rat estrous cycle was previously determined through cytology with vaginal lavage, however former studies showed that the vaginal lavage was an indirect measure of potential ovulation. Therefore, this new study wanted to test the stage of ovulation based on histological measure of newly formed corpora lutea on the ovary, along with the presence of ova in the oviducts. The overall purpose of the study was to determine the effects of endurance exercise on ovarian progesterone secretion and ovulation, and to test the consistency with which effects occur in individual animals.
To test this, female Sprague-Dawley rats were used and divided into two groups: exercise and sham-exercise. The exercise group underwent a rigorous 90 minute exercise period every day for a length of time equivalent to three of their estrous cycles (equated to around 21-22 days). The rats in the sham-exercise group were placed on stationary treadmills for the same amount of time each day and for the same number of days. Both groups were subject to a small electrical shock behind them to keep them on the treadmill for the required period of time. After the period of sham-exercise or exercise, the rats were sacrificed on the morning of the estrus stage of their cycles. If the rat had an irregular cycle or was acyclic, the rat was sacrificed after the prolonged diestrus stage. In addition, plasma progesterone levels were measured in the blood after each rat was sacrificed. This was done in order to determine the proper function of the ovary. Ovaries were then removed for histological examination to determine the presence of the corpora lutea, and ultimately to confirm ovulation.
The results showed that the sham-exercising rats maintained a consistent 4-5 day cycle. However, 9 of the 17 exercising rats had cycles greater than 5 days. In addition, based on the histological study, 17 of the 19 sham-exercising rats ovulated, while only 7 of the 17 exercising rats ovulated. In terms of progesterone levels, there was no difference between the sham-exercise vs. the exercise rats despite there being a difference in the number of rats that ovulated based on the presence of corpora lutea. However, within the exercise group itself, the rats that did ovulate had significantly higher progesterone levels compared to those rats that were anovulatory.
These findings show that a high percentage (almost half) of the female rats that ran daily for 90 minutes developed changes in their estrous cycles that included a significantly extended diestrus stage. Additionally, they found that studying the ovaries and oviducts for ova is a better indication for ovulation rather than the presence of cornified epithelial cells in vaginal cytology. In the rats that experienced prolonged diestrus stages, old corpora lutea were present, and this could be similar to the mechanism of pseudopregnancy in rats. The stress of running may have either decreased plasma LH (leutenizing hormone) concentrations or increased plasma prolactin levels. A decrease in plasma LH concentrations is usually observed in human females during endurance training. However, it is unknown if the maintained progesterone levels that occurred within the prolonged diestrus stage were due to secretion by the old corpora lutea or by the adrenal gland, since the adrenal gland is a significant source of progesterone in rats (but not in humans). Overall, reduced ovulation did occur in susceptible female rats that underwent endurance training.
-L. Matus
No comments:
Post a Comment