Biophysical and Biochemical Studies on the Regulatory Mechanism of Fatty Acids on Blood Platelet Functions

顺式多不饱和脂肪酸如亚油酸和α -亚麻酸抑制ADP和其他激动剂诱导的血小板聚集。由于抑制激动剂诱导的细胞质Ca^<2+>的增加，它们抑制了聚集。因此，我们随后观察了脂肪酸对细胞内环AMP水平的影响，环AMP是调节细胞内Ca^<2+>的物质之一。放射免疫分析研究表明，在茶碱存在的情况下，添加这些脂肪酸增加了环AMP的含量，这与它们对聚集的抑制作用相一致。在完全抑制聚集的浓度范围内，这些脂肪酸诱导环AMP的基础浓度增加1.6% - 1.8倍。另一方面，饱和脂肪酸，硬脂酸，既不影响聚集也不影响环AMP水平。顺式多不饱和脂肪酸不影响肌醇- 1,4,5-三磷酸（IP_3）的产生，这被认为是触发细胞内池释放Ca^<2+>。这些不饱和脂肪酸通过抑制花生四烯酸酯代谢抑制血小板功能的可能性也被否认。腺苷酸环化酶，负责环AMP的合成，被认为是由膜的脂质环境调节。用二苯己三烯及其三甲胺衍生物进行的荧光分析表明，多不饱和脂肪酸在增加环AMP浓度和抑制血小板聚集的浓度范围内，通常会增加膜宽深度的流动性。由此得出结论，多不饱和脂肪酸抑制血小板聚集是由于刺激腺苷酸环化酶，而腺苷酸环化酶是通过膜扰动介导的。

cis-Polyunsaturated fatty acids such as linoleic acid and alpha-linolenic acid inhibit platelet aggregation induced by ADP and other agonists. They inhibited the aggregation due to the inhibition of agonist-induced increase in cytoplasmic Ca^<2+>. Therefore, we then observed the effects of the fatty acids on the levels of intracellular cyclic AMP which is known to be one of the substances to regulate intracellular Ca^<2+>. According to radioimmunoassay study, addition of these fatty acids increased cyclic AMP contents in the presence of theophylline corresponded with their inhibitory effects on aggregation. These fatty acids induced a 1.6 % - 1.8 times increase over basal concentration of cyclic AMP in the concentration ranges that fully inhibited aggregation. On the other hand, saturated fatty acid, stearic acid, affected neither aggregation nor cyclic AMP levels. cis-Polyunsaturated fatty acids did not affect the production of inositol- 1,4,5-trisphosphate (IP_3) which is suggested to trigger Ca^<2+> release from intracellular pools. The possibility was also denied that these unsaturated fatty acids inhibit platelet functions by inhibiting arachidonate metabolism. Adenylate cyclase, which is responsible for the synthesis of cyclic AMP, is believed to be modulated by the lipid environment of the membrane. Fluorescence analysis with diphenylhexatriene and its trimethylammonium derivative showed that polyunsaturated fatty acids commonly increased membrane fluidity in wide depths of the membrane in the concentration ranges in which these fatty acids increased cyclic AMP concentration and inhibited platelet aggregation. From these results it is concluded that polyunsaturated: fatty acids inhibit platelet aggregatio due to stimulation of adenylate cyclase which is mediated by membrane betturbation.