Metabolism of Highly unsaturated Fatty Acids to Prostaglandins and their Physiological Activities in Fish.

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It is well known that human platelets convert arachidonic acid (AA) to prostaglandins (PGs), especially to thromboxane A_2 (TXA_2), which is a potent inducer of blood aggregation. Although thrombocytes are considered to be the clotting cells of fish blood similar to mammalian platelets, the syntheses of PGs in fish thrombocytes still remain unclear. Therefore, the present study was designed to clarify the capacity of PG syntheses from exogenous AA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) in carp, rainbow trout, and red sea bream thrombocytes, and compared with that in human platelets.The blood of carp and rainbow trout was collected from dorsal aorta, and that of red sea bream from cuvierian duct. The thrombocyte-rich plasma (TRP) was prepared, mixed with N-hydroxyethylpiperazine-N'-2-ethanesufonic acid (HEPES) buffer, centrifuged, and resuspended. The washed pellets were incubated with ^<14>C-labelled highly unsaturated fatty acids (AA, EPA, and DHA).Washed human platelets mainly converted AA to thromboxane B_2, however, washed carp and red sea bream thrombocytes converted AA to PGF_<2<alpha>>,PGE_2, and PGD_2, and washed rainbow trout AA to these three PGs and EPA to TXB_3. Accordingly, it is assumed that there are differences in PG syntheses between human platelets and fish thrombocytes and even among the fish species, Finally, it is considered that the differences in PG syntheses among human platelets and fish thrombocytes cause the different behaviors in the blood aggregation.