44 EFFECT OF CRYOPROTECTANT AGENTS IN EQUINE OVARIAN BIOPSY FRAGMENTS

Abstract

Studies on ovarian tissue preservation in horses are scarce, and only one research group (Devireddy et al. 2006 Mol. Reprod. Develop. 73, 330–341) has tested the effect of the cryoprotectant agents in equine ovarian tissue. The purpose of this study was to evaluate (1) the effect of cryoprotectant agents in the morphology of equine preantral follicles (PAF) and structure of the ovarian tissue, (2) the relationship between ovarian stromal cell density and PAF density, and (3) the association of ovarian stromal cell density with PAF morphology after exposure to cryoprotectant agents. Three independent experiments with identical methodologies were performed in this study. Each experiment was composed by one cryoprotectant agent (dimethyl sulfoxide, ethylene glycol, propylene glycol) performed in 3 replicates. Ovarian biopsy fragments (1.5 × 1.5 × 10 mm) were harvested from 6 mares and submitted to 4 times of exposure (0, 10, 15, 20 min) at room temperature in a solution of α-minimal essential medium (MEM)⁺ and one cryoprotectant (dimethyl sulfoxide, ethylene glycol, or propylene glycol) at a concentration of 1.5 M. The cryoprotectant removal was performed by a 3-step (5 min each) equilibration process using (1) α-MEM + 0.5 M sucrose, (2) α-MEM + 0.25 M sucrose, and (3) α-MEM alone after each time of exposure. All fragments were fixed in Bouin’s solution for histological analysis. Data were analysed by ANOVA, Fisher’s exact test, Spearman’s rank correlation, and power test. The PAF density, stromal cell density, and area of the fragments were not affected (P > 0.05) by any of the cryoprotectant agents throughout the time of exposure. However, the morphology of the PAF was affected (P < 0.05) by the cryoprotectant agents. In the propylene glycol and dimethyl sulfoxide, higher (P < 0.05) percentages of abnormal PAF were observed at 10 and 20 min of exposure, respectively. However, the PAF morphology in the ethylene glycol treatments was not affected (P > 0.05) throughout the times of exposure. Strong correlations (range, 0.57 to 0.77; power, 96 to 99%) were identified between PAF density and stromal cell density in all experiments. When stromal cells were classified into groups of density (i.e. low, 25.67–34.66; medium, 34.67–43.66; and high, 43.67–52.67 cells/2500 μm²), only the high stromal cell density was positively correlated (P < 0.001) with the PAF density; however, no correlation between stromal cell density and PAF morphology was observed. In conclusion, (1) ethylene glycol seems to be a less harmful cryoprotectant agent to equine PAF, (2) exposure to cryoprotectant agents did not affect the cell density and area of ovarian fragments, (3) PAF density was positively correlated with stromal cell density, and (4) stromal cell density did not affect the morphology of PAF.