Levels of antioxidant defenses are decreased in bovine spermatozoa after a cycle of freezing and thawing
Bibliographic record
Abstract
Growing evidence suggests that the generation of reactive oxygen species (ROS) and their detoxification by antioxidants plays a very important role in fertility. However, the relationship between the level of antioxidants in spermatozoa and the decreased fecundity following a freeze/thaw cycle remains poorly understood. We assessed the activities of antioxidant enzymes such as catalase, glutathione peroxidase (GPx), superoxide dismutase (SOD), and levels of reduced/oxidized glutathione (GSH/GSSG) in bovine semen. Sperm cells were isolated using a Percoll gradient to avoid contamination from seminal plasma, cellular debris, and other cell types. We found that bovine spermatozoa are poorly adapted to metabolize the toxic hydrogen peroxide (H(2)O(2)). Indeed, very low levels of GPx and an absence of catalase were observed. We also studied the effect of freezing and thawing bovine spermatozoa in a egg yolk-Tris-glycerol extender (EYTG). Cryopreservation significantly reduced sperm GSH levels by 78% and SOD activity by 50%. We also investigated whether the decrease in GSH level could be linked to oxidative metabolism and found that a greater reduction in intracellular GSH level occurred when fresh sperm cells were incubated in EYTG for 6 hr at 38.5 degrees C under aerobic conditions than when incubated under restricted oxygen availability. Our results strongly suggest the involvement of an oxidative stress during a freeze/thaw cycle and are consistent with the hypothesis that ROS generated during such a cycle are detrimental to sperm function.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".