No abstract

SummaryAnalysis of platelet membrane proteins and glycoproteins by SDS Polyacrylamide gel electrophoresis was carried out before and after treatment with thrombin. Extended incubation with thrombin (in the presence of EDTA or adenosine, which inhibit aggregation) produced extensive changes in the bands observed. With incubation times of a few minutes however, the changes were restricted to a glycopeptide, GP IV (approx. 90,000 Daltons) and one or two polypeptides of low molecular weight, in particular polypeptide 16 (approx. 23,000 Daltons). At 0–3° C only polypeptide 16 was still hydrolyzed.Chymotrypsin, which does not activate platelets, attacked glycopeptides I, II, III but no changes were apparent in GP IV and polypeptide 16. When chymotrypsin-treated platelets were further incubated with thrombin, only GP IV and one to two low molecular weight polypeptides, especially polypeptide 16, were affected. As polypeptide 16 appears to be an integral membrane component it is possible that it, either by itself or in combination with GP IV, represents the primary thrombin substrate involved in platelet activation.Aggregated IgG, which also activates platelets, does not modify the membrane glycoproteins but does change the low molecular weight region in particular band 16.

No abstract

The correlations between the levels of various plasma proteins and lipids and platelet function on glass and platelet factor 3 (PF 3)-availability in children of different age-groups were investigated. Several statistically significant positive and some significant negative correlations were found. Although conclusions based solely on such correlations should be considered with reservation, in our opinion the following factors should stimulate platelet function: prealbumin (adhesion and PF 3-availability in all age-groups, aggregation--specifically for children in puberty); alpha 1-antitrypsin (PF 3-availability); alpha 2-macroglobulin (platelet spreading capacity, PF 3-availability); plasminogen (platelet adhesion and aggregation--specifically for boys in puberty); caeruloplasmin (number of "free adhering platelets" spreading capacity); lysolecithin and lecithin (time-dependent increase of spontaneous platelet adhesion and aggregation, PF 3-availability); and free fatty acids (FFA) (PF 3-availability). Plasminogen and complement component C'3 show a negative relationship to the time-dependent increase of spontaneous platelet adhesiveness and aggregability in platelet-rich plasma.

Platelet counts, adhesiveness, aggregation and spreading capacity, as well as the thrombopoiesis index, thrombelastogram and fibrinogen were examined in 74 healthy children aged from 2 to 14 years. Sex-linked differences were only found in the thrombopoiesis index. Age-linked differences showed in practically all the parameters, especially in the platelet counts, fibrinogen and thrombelastograms.