IN VIVO INTERACTION BETWEEN HUMAN PLATELET FACTOR 4 (PF4) AND PROTAMINE SULPHATE (PS) IN THE PRESENCE OF DIFFERENT GLYCOSAMI-NOGLYCANS (GAGs)

Anti-heparin substances, like PF4 or PS, have been studied largely in reference to their ability to neutralize the anticoagulant activity of heparin. On the other hand, few data are available concerning the relationship between GAGs and anti-heparin proteins clearance. We studied the action of PS on human PF4 kinetics in anesthetized rabbits pre-treated with heparin (H, 1000 I.U.), heparan sulphate (HS, 30 mg) and derma tan sulphate (DS, 30 mg). PF4 (given at a dose of 45 μgAg) disappearance reflected its different affinity for the GAGs, with the following half lives (min): control 2.09±0.28, H 14.80±1.47, HS 10.90±1.91, DS 6.87±0.68. Moreover, circulating PF4 (ng/ml) at 1 min was as follows: control 109±8, H 873±134, HS 751±34 and DS 473±15. In another group of H pre-treated rabbits, a bolus injection of PS (10 or 20 mg) caused an immediate disappearance in th.e circulating plasma PF4, from 900±23 ng/ml (1 min after PF4) to 75±11 ng/ml (1 min after 10 mg PS). However, a subsequent H injection 10 min after PS induced a peak release of PF4 (520±21 ng/ml). In a further group of animals pre-treated with HS, the interaction between PS and PF4 was similar to that observed after H treatment. In the last group, pre-treated with DS, the interaction between PF4 and PS was also similar, however, unexpectedly, when 20 mg of PS were given a subsequent bolus of H did not produce any increase of circulating PF4We suggest that PS displaces PF4 from its binding sites on H or HS, thus allowing its uptake by the storage sites in the body, from where it can be harvested again after the subsequent H administration. In the presence of DS again PS is able to displace PF4, however the remaining excess of PS could neutralize the subsequent H injection, thus rendering it unable to induce PF4 release.