Deficient Collagen-Induced Activation in the Newborn Platelet

Abstract

ABSTRACT. We have investigated the impaired secretion response of neonatal platelets. We compared the response of washed neonatal and adult platelets to thrombin and collagen, and to specific activators of calcium flux (inositol trisphosphate) and protein kinase C activation (oleoylacetyl glycerol). Neonatal platelets show no impairment ofaggregation, secretion of ['4C]serotonin or phosphorylation of saecific intracellular rotei ins in resDonse to thrombin. inositol trisphosphate, o; oleoyl-acetyl glycerol. ow ever; neonatal platelets have a markedly decreased response to collagen. To further evaluate this deficient response, we examined specific aspects of the collagen activation pathway. Collagen-platelet interaction as measured by adhesion of platelets to collagen-coated dishes showed no difference in adhesion of neonatal platelets compared to adult controls (20.1 f 11.6 versus 18.6 2 9.3%). The presence of GPIa/ Ila, a Mgz+-dependent collagen receptor, was evaluated by flow cytometric analysis of binding of fluorescein-tagged monoclonal antibody, 6F1 (directed against GPIaJIIa). There was no difference either in the percent of platelets that bound antibody (80 versus 81%) or in the mean fluorescence intensity of the adult and neonatal samples. Phosphoinositide hydrolysis was decreased in neonatal platelets in response to collagen but normal in response to thrombin. Neonatal platelets released more arachidonic acid than adult platelets in response to thrombin (29.5 f 3.2 versus 19.6 + 1.8%) but less than adult platelets in response to 10 pg/mL collagen (3.2 2 1.1 versus 9.3 + 3.0%). Thromboxane B2 production was also decreased in response to collagen (52.7 f 12.6 versus 101.4 + 18.7 ng/mL). These results suggest that the deficient collagen response in neonatal platelets may lie in transduction of the collagen signal to phospholipases Az and C . (Pediatr Res 27: 337-343,1990) Abbreviations AA, arachidonic acid IP3, inositol-1,4,5-trisphosphate OAG, oleoyl-acetyl glycerol PIPZ, phosphatidylinositol-4,5-bisphosphate MLC, myosin light chain 47 K, 47000 dalton protein TxAZ, thromboxane A2 TxBz, thromboxane Bz HBSS, Hanks' balanced salt solution clinical importance to those caring for sick and premature infants. The differences in clotting factor activity and fibrinolytic enzymes between cord blood and that of adult controls are well established (1,2). The abnormalities of neonatal platelet function are less completely understood. In the mid-1970s, differences in the in vitro responses of cord and newborn platelets compared to those from older subjects were identified (3-6). These abnormalities include a decreased aggregation response to certain agonists including ADP, epinephrine and collagen (3, 4), and decreased secretion of dense granule contents (5, 6). Neonatal platelets were shown to have decreased endogenous stores of dense granule contents, ADP, and serotonin, although Whaun demonstrated that their uptake and storage of radiolabeled serotonin was as effective as that of adult platelets (6). In addition,...

Collagen/Endogenous Thrombin-Induced Platelet Aggregation in Cord versus Adult Whole Blood

“…There is an apparent contrast between results from conventional platelet aggregation assays that suggest an in vitro hypofunctional state of neonatal platelets [1][2][3] and the evidence of normal or even short in vivo bleeding times of the newborn [4] , which is a suitable test for assessing primary hemostasis [5] .…”

“…Herein, we present an in vitro model that might help to explain the clinically observed short bleeding times in neonates despite in vitro hypoaggregable platelets reported in various studies [1][2][3]19] . We found that aggregation of neonatal platelets in WB samples is as efficient as that of adult platelets when the physiological relevant activator collagen/endogenous thrombin is used.…”

Neonatal platelets: mediators of primary hemostasis in the developing hemostatic system

“…No difference was reported between neonatal platelet (derived from either cord or peripheral blood) and adult platelet delta granule release, as assessed by measurement of serotonin secretion, in response to stimulation with thrombin or the platelet agonists 1-oleolyl-2-acetyl-glycerol and inositol triphosphate (IP 3 ). However, serotonin secretion was markedly decreased in cord blood-derived neonatal platelets in response to collagen as compared to adult platelets (9). Further, as measured by mepacrine uptake, neonatal platelets (from cord blood) contained the same number of dense granules as adult platelets, but these same platelets had defective release of dense granules following thrombin stimulation (14).…”

Membrane-Activated Form of Glycoproteins IIb/IIIa Complex on Newborn Platelets

“…Some authors have found that platelets of healthy term newborns are hyporeactive [14,15] and demonstrated impaired capability of GPIIb/IIIa complex activation [16] , whereas others have revealed that they respond to agonists as well as in adults [17] . This controversy may result from different time of blood sample collecting.…”