Abstract: 214

ROLE OF PROGESTERONE AND CHOLESTEROL IN ACROSOME REACTION OF CRYOPRESERVED SPERM.

Rajaduri Rajamahendran^{1 *}, 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.