Cyclophosphamide (Cyc) is known to cause ovotoxicity and infertility in women. Our aim is to investigate the possible ovotoxic effects of Cyc and possible antioxidant and protective effects of blue-green algae, Spirulina (Sp), in rat ovaries. Eighteen rats were given: group I ( , control); group II ( , CP), a single dose Cyc; group III ( , Sp+Cyc), 7 days Sp+single dose Cyc. Tissue malondialdehyde (MDA) levels, superoxide dismutase (SOD), and catalase (CAT) activities are assessed biochemically. Normal and atretic primordial and primary follicle counts for all sections obtained for each ovary are calculated. Mean number of follicle counts for each group are compared. In Sp+Cyc group, tissue MDA levels were significantly lower than those in the CP and higher than those in the C group ( + ). Tissue SOD activity was significantly higher in Sp+Cyc group than that in the CP group and lower than that in the C group ( + ). No statistically significant difference was found between the ovarian CAT activities in any group. Histomorphometrically, there was also no significant difference between the mean numbers of normal and atretic small follicle counts. Our results suggest that single dose Cyc has adverse effects on oxidant status of the ovaries and Sp has protective effects in Cyc-induced ovotoxicity. 1. Background Cyclophosphamide (Cyc), one of the most effective alkylating agents, is associated with the greatest risk of female infertility [1, 2]. This is mostly attributed to ovarian toxicity and is thought to be strongly related to the cumulative doses of Cyc . Reproductive functions deteriorate by rapid depletion of the oocyte reserve mediated by apoptotic cell death and ovarian atrophy with disappearance of resting primordial follicles  and also growing follicles  in humans. In other words, apoptosis, which physiologically is an essential event for ovarian function  and development of this organ, would become harmful when the ovary is exposed to Cyc . The toxic metabolites of Cyc and the drug itself also interfere with intracellular antioxidation systems which play an important role in detoxifying the reactive oxygen species (ROS) . Superoxide dismutase (SOD), which converts the superoxide anion to hydrogen peroxide, plays a central role in antioxidation reactions . Catalase (CAT), another antioxidant enzyme, catalyzes exclusively the decomposition of hydrogen peroxide to water and oxygen without an electron donor . It is also shown that the lipid peroxidation in ovaries increases in oxidative stress conditions such as ischemia .
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