EFFECTS OF ISOMERIC CIS AND TRANS 18-CARBON MONOUNSATURATED FATTY-ACIDS ON PORCINE PLATELET-FUNCTION

The effects of different positional cis and tuans isomers (9, 11, 12 a nd 13) of C-18 monoenoic fatty acids on the response of porcine platel ets to collagen and thrombin stimulation were determined. Cis isomers inhibited aggregation in response to 2 mu g/ml or 5 mu g/ml collagen a nd 0.1 U/ml of thrombin with almost equal effectiveness, with the exce ption of the 9- and 11-isomers which gave reduced inhibition of aggreg ation with thrombin and collagen stimulation respectively. All cis iso mers inhibited TXA(2) formation (determined as TXB(2)) elicited by col lagen with almost equal effectiveness, Tuans isomers were less effecti ve than cis in inhibiting collagen induced aggregation particularly at the higher collagen concentrations. Inhibition of TXB(2) formation wa s less marked with trans isomers but a dear dissociation between the e xtent of inhibition of aggregation and TXB(2) formation was evident. C is isomers also inhibited aggregation in response to 0.1 U/ml thrombin whereas trans isomers augmented aggregation but still reduced TXB(2) formation, Isomers did not elicit their effects through incorporation into platelet membrane phospholipids. Aggregation studies were carried out using the impedance method which is more sensitive than the optic al method hitherto described, particularly for lipid studies.