Presentations

Abstract

Introduction: Galactic cosmic radiation (GCR), the radiation found in space, is between 3-100 times more potent than X-rays and poses a significant risk to astronauts. NASA will be sending female astronauts on the Mars missions, but currently there is little information on the short-term and long-term effects that space radiation may have on female reproductive health. By assessing each of the four stages of follicular growth in the ovary, we can attempt to identify which stages are most vulnerable to radiation exposure, which will highlight the specific risks involved. Decreased follicle numbers could lead to short-term fertility issues or even cause premature ovarian failure which may send the females into early menopause, leading to potential operational consequences. There may also be long-term health implications like osteoporosis and cardiovascular disease. We hypothesize that exposure to GCR will damage ovarian health by reducing the number of ovarian follicles and decreasing overall ovarian volume.

Methods: As part of ongoing studies, female Wistar rats (7-months old) were exposed to space radiation (SR) at Brookhaven National Laboratory. After completion of cognitive testing (~ 4 months post exposure), the rats were euthanized and their ovaries recovered and fixed in 10% formalin. For the present study, ovaries from sham (n=3) and rats exposed to three types of SR exposure (10 cGY of GCR/GCR (n=2), 10 cGY of GCR/He (n=3), 10 cGY of Fe10 (n=2)), were embedded in paraffin wax and sectioned at 5 µm. Every fifth slide was stained with hematoxylin and eosin, and the primordial, primary, and secondary follicles with a visible oocyte nucleus were counted. Follicle counts were multiplied by five to account for assessing every fifth section. Antral follicles are larger than the other follicles and could be directly counted without adjustment. To calculate ovarian volume, an ellipsoid volume formula was used: V = 4/3*π*rh*rl*rw. Radii included the longest and widest sections of each ovary, while the height was determined by counting the number of sections containing ovarian tissue and multiplying by 5 µm.

Results: Ovaries from sham irradiated animals contained all four follicle classes. Primordial follicles were present in large numbers, with smaller numbers of primary and secondary follicles, and fewer antral follicles. When compared to sham irradiated animals, irradiated animal ovaries contained similar numbers of primordial, primary, and antral follicles. Our preliminary data suggests that SR exposure reduces (by approximately two-fold) the abundance of secondary follicles compared to that observed in sham rats. There was an average count of 100 secondary follicles in the sham group, whereas GCR/GCR had 48, GCR/He had 53, and Fe10 had 38. There was also an apparent decrease in ovarian volume with radiation treatment, with the sham average volume measuring 15.54 μL, and the GCR/GCR, GCR/He, and Fe10 measuring 11.97 μL, 13.18 μL, and 8.57 μL respectively.

Conclusion: These data, while preliminary, support our hypothesis that space radiation negatively affects the ovary. Our findings show secondary follicle numbers were decreased by all types of radiation. Further investigation is needed to determine why these follicles specifically were affected and what implication that may have on female reproductive health. Irradiated ovaries were also smaller than the sham ovaries. Typically, a larger ovary is thought to be more active because the antral follicles make up the most volume in the ovary. If an ovary is healthy and active, it will therefore contain more antral follicles and the overall volume will be larger. The diminished secondary follicle counts could also potentially explain the difference in size between radiation and sham groups. Future studies could compare the size of antral follicles between irradiated and sham ovaries to assess whether the follicles are growing to adequate size for ovulation after radiation exposure. Moving forward, studies like this will help inform the need for protective measures against GCR exposure to prevent the negative health consequences of follicular loss.