title: Microsomal preparations of normal bovine iris-ciliary body generate prostacyclin-like but not thromboxane-A2-activity.
abstract: Indomethacin-treated bovine iris-ciliary body microsomes (IBIM) have been studied for their ability to convert PG endoperoxides into either thromboxane-A2 (TxA2)-like or prostacyclin (PGI2)-like activity. The biological activity of the ocular tissue microsomes were compared with either indomethacin-treated human platelet microsomes (for TxA2-like activity) or rabbit aorta microsomes (for PGI2-like activity) under appropriate incubation conditions. No evidence could be found for the formation of TxA2-like activity from PG endoperoxides by the IBIM. In contrast, when the IBIM were incubated with PGH2 for 1 min at 22 degrees C without cofactors, PGI2-like activity was produced, causing profound relaxation of the isolated dog coronary artery preparation without contracting the rabbit aorta and inhibiting arachidonic acid-induced platelet aggregation. Equivalent quantities of boiled IBIM failed to alter the biological activity of PGH2 under identical conditions. Tranylcypromine (500 microgram/ml) completely abolished the appearance of PGI2-like activity. Furthermore, the PGI2-like activity found was stable for 10 min at 22 degrees C at pH 8.5 but completely lost under similar conditions at pH 5.5. It is concluded that microsomal preparations of normal bovine iris-ciliary body can synthesize PGI2-like activity in substantial amounts but not TxA2-like activity.
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects; D002417:Cattle; D002924:Ciliary Body / Q000378:metabolism*; D004285:Dogs; D011464:Epoprostenol / Q000378:metabolism*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007498:Iris / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D011449:Prostaglandin Endoperoxides / Q000378:metabolism; D011453:Prostaglandins / Q000378:metabolism*; D011463:Prostaglandins H / Q000378:metabolism; D011817:Rabbits; D012756:Sheep; D013928:Thromboxane A2 / Q000378:metabolism
chemical_list: D011449:Prostaglandin Endoperoxides; D011453:Prostaglandins; D011463:Prostaglandins H; D013928:Thromboxane A2; D011464:Epoprostenol; D007213:Indomethacin