RESUMEN
The effects of different positional cis and trans isomers (9, 11, 12 and 13) of C(18) monoenoic fatty acids on the response of porcine platelets to collagen and thrombin stimulation were determined. Cis isomers inhibited aggregation in response to 2 microgram/ml or 5 microgram/ml collagen and 0.1 U/ml of thrombin with almost equal effectiveness, with the exception of the 9- and 11-isomers which gave reduced inhibition of aggregation with thrombin and collagen stimulation respectively. All cis isomers inhibited TXA(2) formation (determined as TXB(2)) elicited by collagen with almost equal effectiveness. Trans isomers were less effective than cis in inhibiting collagen induced aggregation particularly at the higher collagen concentrations. Inhibition of TXB(2) formation was less marked with trans isomers but a clear dissociation between the extent of inhibition of aggregation and TXB(2) formation was evident. Cis 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 optical method hitherto described, particularly for lipid studies.