Effects of Hyaluronic Acid on Ca2+ Influx, Lactate Dehydrogenase Activity, and Cyclic AMP Synthesis in Canine Ejaculated Sperm during In Vitro Capacitation

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The effects of hyaluronic acid, which comprises the cumulus intercellular matrix, on Ca2+ influx, lactate dehydrogenase (LDH) activity, and cyclic AMP synthesis in canine sperm during capacitation was investigated. Ejaculated sperm were collected from 10 Beagle dogs and the sperm were incubated for 4 hr in Eagles MEM containing 10 μg/ml of hyaluronic acid. The percentages of actively motile sperm, hyperactivated sperm (HA-sperm), acrosome-reacted sperm (AR-sperm), and sperm labeled with fluoresceinated Ca2+ indicator (Ca2+-labeled sperm) were evaluated to assess Ca2+ influx into the sperm. LDH activity and cAMP concentration were measured in homogenized sperm. The mean percentages of motile sperm, HA-sperm, and Ca2+-labeled sperm in the MEM containing hyaluronic acid were higher than in the control medium (P<0.05, 0.05, and 0.01, respectively), but there was no difference between the percentages of AR-sperm. Mean LDH activity and mean cAMP concentration were also significantly higher than the control values (P<0.05). The percentages of HA-sperm correlated with those of Ca2+-labeled sperm (r2=0.810). The results indicate that hyaluronic acid increases Ca2+ influx, LDH activity, and cAMP synthesis in canine ejaculated sperm during capacitation in vitro.