In vivo relevance for platelet glycoprotein Ib alpha residue Tyr276 in thrombus formation

Background: Platelet glycoprotein (GP) Ib-IX-V supports platelet adhesion on damaged vascular walls by binding to von Willebrand factor (VWF). For several decades it has been recognized that the alpha-subunit of GP (GPIb alpha) also binds thrombin but the physiological relevance, if any, of this interaction was unknown. Previous studies have shown that a sulfated tyrosine 276 (Tyr276) is essential for thrombin binding to GPIb alpha.Objectives: This study investigated the in vivo relevance of GPIb alpha residue Tyr276 in hemostasis and thrombosis.Methods: Transgenic mouse colonies expressing the normal human GPIb alpha subunit or a mutant human GPIb alpha containing a Phe substitution for Tyr276 (hTg(Y276F)) were generated. Both colonies were bred to mice devoid of murine GPIb alpha.Results: Surface-expressed GPIb alpha levels and platelet counts were similar in both colonies. hTg(Y276F) platelets were significantly impaired in binding alpha-thrombin but displayed normal binding to type I fibrillar collagen and human VWF in the presence of ristocetin. In vivo thrombus formation as a result of chemical damage (FeCl3) demonstrated that hTg(Y276F) mice have a delayed time to occlusion followed by unstable blood flow indicative of embolization. In models of laser-induced injury, thrombi developing in hTg(Y276F) animals were also less stable.Conclusions: The results demonstrate that GPIb alpha residue Tyr276 is physiologically important, supporting stable thrombus formation in vivo.

Differential roles of integrins alpha(2)beta(1), and alpha(IIb)beta(3) in collagen and CRP-induced platelet activation

Collagen and collagen-related peptide (CRP) activate platelets by interacting with glycoprotein (GP)VI. In addition, collagen binds to integrin alpha(2)beta(1) and possibly to other receptors. In this study, we have compared the role of integrins alpha(2)beta(1) and alpha(IIb)beta(3) in platelet activation induced by collagen and CRP. Inhibitors of ADP and thromboxane A(2) (TxA(2)) substantially attenuated collagen-induced platelet aggregation and dense granule release, whereas CRP-induced responses were only partially inhibited. Under these conditions, a proportion of platelets adhered to the collagen fibres resulting in dense granule release and alpha(IIb)beta(3) activation. This adhesion was substantially mediated by alpha(2)beta(1). The alpha(IIb)beta(3) antagonist lotrafiban potentiated CRP-induced dense granule release, suggesting that alpha(IIb)beta(3) outside-in signalling may attenuate GPVI signals. By contrast, lotrafiban inhibited collagen-induced dense granule release. These results emphasise the differential roles of alpha(2)beta(1) and alpha(IIb)beta(3) in platelet activation induced by collagen and CRP. Further, they show that although ADP and TxA(2) greatly facilitate collagen-induced platelet activation, collagen can induce full activation of those platelets to which it binds in the absence of these mediators, via a mechanism that is dependent on adhesion to alpha(2)beta(1).

GP views about a home from hospital service

This paper reports the results of an investigation, by postal questionnaire, of the views of 30 General Practitioners about a model of out of hospital care – the home from hospital (HFH) service, which mainly provides social care and rehabilitation for patients in their own home. The GPs, who all worked within one of the Health and Social Services Board areas in Northern Ireland during the time of the study (March-April 1998), indicated that the introduction of the HFH service, unlike other models of out of hospital care, did not increase their workload. Therefore, it is suggested that the HFH model of care should be given more attention in terms of research evaluation and service development.

Questionnaire Survey of Physical activITy in Genral Practictioners (PHIT GP Study)

Objectives: To assess the levels of physical activity and other health related behaviours of General Practitioners (GPs) and compare their reported levels of physical activity with those of the general population. Study Design: Cross sectional postal questionnaire survey. Methods: A questionnaire, which did not allow identification of individual respondents, was posted to all 1074 (GPs) in Northern Ireland. It included the validated International Physical Activity Questionnaire (IPAQ) and questions relating to smoking and alcohol consumption. A national survey of a representative sample of the general population of similar age (29-67 years; n = 3010) provided comparative data. Results: 735 GPs responded (68.4%). IPAQ data indicated that fewer GPs (43.4%) were “physically inactive” compared to the general population (56.2%) (p