275 PENTOXIFYLLINE ADDED TO FREEZING EXTENDER HAS A DELETERIOUS EFFECT ON POST-THAW BOAR SPERM QUALITY AND IN VITRO FERTILIZATION RATE

Abstract

Pentoxifylline, a methylxanthine derivative, is considered to be a hyperactivation and acrosome reaction-improving agent. The purpose of this study was to test how the addition of pentoxifylline to freezing extender influences post-thaw sperm motility and membrane integrity. The ability of thawed spermatozoa to fertilize in vitro-matured oocytes was also assessed. Pooled ejaculate sperm-rich fractions collected from three fertile boars were frozen in 0.5-mL straws after being diluted in lactose/egg yolk/glycerol/Orvus-ES-Paste extender (0 pentoxifylline = control) or the same extender supplemented with 2, 4, 8, 16, and 32 mM pentoxifylline. To evaluate post-thaw sperm survival, the percentage of total motile spermatozoa and rapid progressive spermatozoa (CASA system) and plasma membrane and acrosome integrity (flow cytometry) were assessed. Data from six replicates were analyzed in a split plot design using a PROMIXED model. The addition of 4, 8, 16, and 32 mM pentoxifylline to freezing extender significantly decreased progressive and total motility (P < 0.001) compared with control (4.5/26.6%, 4.5/24.5%, 2.8/20.5%, 0.6/11.4%, and 13.2/49.7% for the 4, 8, 16, and 32 mM pentoxifylline groups and the control group, respectively). The same was observed for sperm viability; the percentage of viable spermatozoa with intact acrosomes was significantly lower (P < 0.001) in pentoxifylline-treated groups compared with the control group, chiefly in the 16 mm, and 32 mM pentoxifylline groups (54, 11.6, and 6.2% for control, 16 and 32 mM, respectively). To evaluate in vitro fertilization parameters, cumulus-oocyte complexes were matured in BSA-free NCSU23 medium with 10% porcine follicular fluid, 0.1% cysteine, 10 ng EGF, 10 IU/mL eCG, and 10 IU/mL hCG, in a incubator at 39°C and 5% CO₂. After 40-44 h of maturation, oocytes (n = 1067, in three replicates) were denuded of cumulus cells, washed, transferred to droplets (30 oocytes in 50 ¼L) of TBM medium supplemented with 2 mM caffeine and 0.2% BSA, and inseminated (2000 thawed sperm/oocyte). After a co-incubation period of 6 h, oocytes were washed and transferred to droplets (500 ¼L) of NCSU23 with 0.4% BSA for another 10-14 h, then fixed and stained for 72 h, and examined under a phase-contrast microscope. Data were analyzed as split plot design using a PROMIXED model. The addition of pentoxifylline to the freezing extender reduced significantly (P < 0.001) the penetration rate (51.4, 17.5, 15.8, 17.8, 9.5, and 4.8% for the 0, 2, 4, 8, 16, and 32 mM pentoxifylline groups, respectively) and the efficiency (monospermic oocytes/total inseminated oocytes) of fertilization (34.8, 14.6, 14.7, 15.5, 7.9, and 4.8% for the 0, 2, 4, 8, 16, and 32 mM pentoxifylline groups, respectively) as compared with the control group (the first value in each of these two cases). It is therefore concluded that pentoxifylline added to the freezing extender has a deleterious effect on post-thaw boar sperm quality and on their ability to fertilize the oocytes in vitro.

This work was supported by CICYT (AGL05-0471).