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Rajaduri Rajamahendran1 *, Afsaneh Motamed Khorasani1 , Chi Yu Gregory Lee2
Animal Science Dept., University of British Columbia, Vancouver, Canada 1
OB/GYN Dept., University of British Columbia, Vancouver, Canada 2
Progesterone (P4) is known to induce mammalian sperm acrosome reaction (AR) in vitro, whereas cholesterol (CH) one of the major components in seminal plasma, inhibits AR. Our objectives were to study the effects of P4 and CH on frozen-thawed bovine sperm AR, as well as the mechanism of CH action on P4-induced AR. Swim-up separated sperm from six bulls were incubated in modified Tyrodes' for 0, 2, 4, 6 h (38.5°C, 5% CO2). AR was induced with P4 (0.1, 1, and 10 µg/ml for 30 min), either in the presence or absence of CH (1 µg/ml). In a parallel experiment, the effects of -sitosterol (1 µg/ml), a CH plant analog, and CH on P4-induced AR were compared. Dibutyryl cyclic adenosine monophosphate (db c-AMP, 1 mM/ml) and Ca2+ ionophore (10 µM/ml) were also incubated, with and without CH. Percent sperm AR was determined using Fluorescein-labeled lectin, from pisum sativum (FITC-PSA), and a fluorescent microscope. AR was induced by P4 at 0 h after sperm were thawed. The optimal AR induction was achieved by 10 µg/ml P4 in 30 min (34.4± 2.5%, P<0.05) and it was not different at 0, 2, 4, and 6 h. CH (95.6% inhibition) and -sitosterol inhibited P4-induced AR. db-cAMP-induced AR was inhibited by CH but this was not the case with Ca2+ ionophore-induced AR. The results suggest that frozen-thawed bovine sperm are capacitated at thawing. P4 induces frozen-thawed bovine sperm AR effectively, but with individual variations. CH inhibits P4-induced AR completely. It appears that the effect of CH is not receptor-mediated. It is proposed that CH restricts the movement of proteins in bilayers and prevents the exposure of P4 surface receptor sites.
This abstract is being presented on Monday, August 2 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.