Role of lipoxygenase in the mechanism of acrosome reaction in mammalian spermatozoa.
The acrosome reaction (AR) in bull spermatozoa was induced by the Ca2(+)-ionophore A23187, by dilauroylphosphatidylcholine or by arachidonic acid in the presence of Ca2+ in the incubation medium. The occurrence of AR was determined by following the release of acrosin from the cells. Nordihydroguaiaretic acid (NDGA), an inhibitor of both lipoxygenase and prostaglandin-synthetase, caused 35%, 43% and 69% inhibition of AR at concentrations of 1, 10 or 100 microM, respectively. Eicosatetraynoic acid (ETYA), an analogue of arachidonic acid, caused 17%, 61% and 77% inhibition of AR at concentrations of 20, 40 or 80 micrograms/ml, respectively. When AR was induced by arachidonic acid, ETYA, causes 36% and 58% inhibition at concentrations of 2 or 20 micrograms/ml, respectively. Under identical conditions, 100 microM indomethacin, a specific inhibitor of prostaglandin-synthetase, showed no inhibition but rather 35% stimulation at acrosin release rate. The fact that AR is inhibited by NDGA and not by indomethacin indicates that the lipoxygenase, rather than prostaglandin-synthetase, is involved in the mechanism of AR. Since the inhibition by NDGA is seen in the presence of the Ca-ionophore, we suggest that lipoxygenase activity is not involved in enhancing calcium transport into the cell, but rather at other steps in AR mechanism. A thin-layer chromatography revealed the presence of 15-HETE, the classical product of 15-lipoxygenase activity, which was identified by HPLC. Under AR conditions, there is an elevation of lipoxygenase products and the addition of NDGA caused a reduction in their levels. The inhibition of acrosin release by NDGA can be eliminated by adding 15-HETE or 15-HPETE to the incubation medium. In conclusion, we suggest here for the first time, a physiological role for 15-lipoxygenase in the mechanism of AR in mammalian spermatozoa.
Lax
Y
Y
Department of Life Science, Bar-Ilan University, Ramat-Gan, Israel.
Grossman
S
S
Rubinstein
S
S
Magid
N
N
Breitbart
H
H
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000177:Acrosome / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism*; D001091:Arachidonate Lipoxygenases / Q000378:metabolism*; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D016861:Cyclooxygenase Inhibitors; D006893:Hydroxyeicosatetraenoic Acids / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D016859:Lipoxygenase Inhibitors; D008297:Male; D009637:Masoprocol / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000494:pharmacology; D013094:Spermatozoa / Q000502:physiology* / Q000648:ultrastructure
D001095:Arachidonic Acids; D016861:Cyclooxygenase Inhibitors; D006893:Hydroxyeicosatetraenoic Acids; D016859:Lipoxygenase Inhibitors; D010713:Phosphatidylcholines; D015117:5,8,11,14-Eicosatetraynoic Acid; C015153:1,2-dilauroylphosphatidylcholine; D016718:Arachidonic Acid; D000001:Calcimycin; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D009637:Masoprocol; D001091:Arachidonate Lipoxygenases; D001093:Arachidonate 15-Lipoxygenase; D002118:Calcium; D007213:Indomethacin