Oxidative damages to the oocyte or follicular cells were suggested to trigger atresia. In water buffalo, loss of the blood-follicle barrier sieving effect on the diffusion of plasma haptoglobin was previously found to be associated with atretic oocytes. The redox status of water buffalo follicles was evaluated by measuring in follicular fluid both the total antioxidant capacity (TAC), expressed as Trolox equivalents, and the concentration of specific free radical scavengers, determined by high-performance liquid chromatography. Among follicles at random stages of the reproductive cycle (n = 74), a number (n = 32) were analyzed also for the cumulus-oocyte morphology or plasma haptoglobin penetration. The haptoglobin follicular concentration compatible with the barrier selectivity function was calculated to be less than 53% of the concentration in plasma. The data on TAC, retinol, α-tocopherol, γ-tocopherol, ascorbic acid, and uric acid fluctuated in a wide range. The relative (follicular vs. plasmatic) levels of α-tocopherol were found to be negatively correlated with those of retinol (p < 0.01). In the follicles, the α-tocopherol levels were 1.25 ± 0.35 or 1.99 ± 0.72 μM when the haptoglobin concentration was <53 or >53% of the concentration in plasma, respectively. The concentration of ascorbic acid or uric acid was higher (up to 10- or 30-fold, respectively) in follicular fluid than in plasma. Fluids containing haptoglobin >53% or associated with cumulus-oocyte complexes of bad quality displayed levels of uric acid about 20-fold higher than in plasma. The results suggest that a high penetration of haptoglobin in the follicle and cumulus-oocyte degradation is associated with alterations of the level of the major antioxidants, particularly with enhancement of the uric acid concentration.

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