A. Fortini

REDUCTION IN PROSTACYCLIN PLATELET RECEPTORS IN ACTIVE SPONTANEOUS ANGINA

The number and affinity of binding sites for tritiated prostacyclin (PGI2) in platelets were investigated in twenty-eight patients with spontaneous angina (fourteen in the active and fourteen in the inactive phase) and in nine healthy controls of similar age. Active-phase patients had significantly lower numbers of both classes of platelet PGI2 receptors (high affinity and low affinity) than controls or inactive-phase patients. In contrast, the affinity for PGI2 was not significantly different in the three groups. In six active-phase patients restudied in the inactive phase the previously low number of PGI2 receptors had returned to normal. These results suggest that the instability of angina is associated with functional changes not confined to the coronary vasculature.

Age related changes of platelet prostacyclin receptors in humans.

Abstract. Platelet receptors for PGI2 were investigated in eighteen healthy volunteers divided in two classes of age: nine were 18–40 years old and nine were 41–65 years old.

Acute reversible reduction of PGI2 platelet receptors after iloprost infusion in man

Platelet sensitivity to PGI2 and platelet PGI2 receptors were investigated in eight subjects with peripheral artery disease (stage IV according to Fontaine) treated for 14 consecutive days with six hour iv infusion of Iloprost (Schering, FRG) 2 ng/kg/min. Platelet studies were performed on the 1st, the 2nd, the 7th and the 14th day of therapy, immediately before infusion (between 8.00 and 9.00 a.m.), at the end and 6 and 18 hours (the following morning) after the end of the infusion. Platelet sensitivity to PGI2 was assessed by determining the PGI2 inhibitory dose 50(ID 50) on platelet aggregation induced by 5 microM ADP. PGI2 platelet receptors were investigated by a direct radioligand binding assay. PGI2 ID 50 after the infusion was significantly higher than that at baseline(p less than 0.01) and six hours later the baseline sensitivity was restored. After the six hour Iloprost iv infusion a significant reduction in the number of high affinity PGI2 platelet receptor (HAR) was observed (p less than 0.005) without any change in their affinity for the ligand. Six hours after the end of the infusion the number of the HAR was still significantly reduced (p less than 0.05). The following morning the receptor number of HAR was restored. The baseline values of PGI2 HAR, when reassessed after seven and fourteen days of treatment, were not significantly different from those recorded on the first day of therapy. These data indicate that the reduction of platelet PGI2 sensitivity following short-term Iloprost infusion is rapidly reversible and is related to a contemporary down-regulation of PGI2 platelet receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Human prostacyclin platelet receptors in diabetes mellitus

Conflicting data have been reported about the impaired sensitivity to the inhibitory effect of prostacyclin (PGI2) in platelets from patients with diabetes. In the present paper we investigated binding of and sensitivity to PGI2 of platelets from insulin dependent (IDDM) (n = 9), non insulin dependent (NIDDM) (n = 8) diabetics and two groups of ten healthy subjects of equivalent age in relation to platelet lipidic content. Platelet sensitivity to PGI2 (PGI2 IC50) was found not significantly changed in diabetics as compared to controls; similarly, no significant differences of the number of high affinity receptors for PGI2 in platelets from patients with IDDM and NIDDM were observed. Platelet sensitivity to PGI2 and PGI2 receptors were found to be significantly related to platelet cholesterol content (r = 0.89, p less than 0.001 and r = -0.80, p less than 0.001 respectively). In conclusion platelet PGI2 receptor changes are not detectable in diabetics in good metabolic control, but could take place when platelet lipid composition is altered.

Decreased number of PGD2 binding sites on platelets from patients with type IIa hyperlipoproteinemia

Platelets from patients with familial hypercholesterolemia (type IIa hyperlipoproteinemia), a condition associated with a high prevalence of atherosclerosis and its ischemic complications, are claimed to be hyperresponsive to aggregating stimuli. We investigated the platelet responsiveness to and the binding of PGD2, a potent endogenous inhibitor of platelet aggregation via stimulation of adenylate cyclase, in a group of 7 patients affected by IIa hyperlipoproteinemia (IIa HLP) and in a control group of 10 healthy subjects. Inhibition by PGD2 of ADP-induced platelet aggregation was significantly lower in IIa HLP patients than in controls. The number of binding sites for PGD2 of platelets from IIa HLP patients was significantly reduced in comparison with that from controls (93 +/- 19 and 232 +/- 23 receptors/platelet, respectively), whereas the affinity for PGD2 was comparable to that of controls (Kd = 68.8 +/- 19.8 nM in patients and 66.1 +/- 15.9 nM in controls). The reduced number of platelet PGD2 binding sites in IIa HLP patients may account for the impaired sensitivity to PGD2 shown in vitro by platelets and may contribute to the increased tendency to thrombotic manifestations observed in IIa HLP.

Binding of low-molecular-weight heparin to aortic endothelium in rabbits.

The ability of a low-molecular-weight heparin to bind in vivo to the aortic endothelium in rabbits, compared with that of unfractionated extractive sodium heparin (UHEP), was investigated. For this purpose a low-molecular-weight heparin (LMWHEP) fraction (CY 216 A, 4,000-5,000 daltons) and an extractive UHEP (average 17,000 daltons) were labeled with 99m Tc and injected (0.2, 0.6, and 1.2 mg/kg) intravenously in groups of 6 rabbits. The binding to endothelium was then measured by counting the radioactivity of samples of abdominal aorta. Both heparins bound to endothelium with a fast, saturable, and reversible binding. No significant difference in the total bound radioactivity was found between the two heparins, suggesting that the investigated LMWHEP retains the ability to bind to the endothelium, contributing to its athrombogenic properties.

Heparin does not interfere with prostacyclin and prostaglandin D2 binding to platelets

Heparin has been reported to antagonize the platelet antiaggregating activity of prostacyclin (PGI2) and prostaglandin D2 (PGD2). To investigate whether heparin interferes with PGI2 and/or PGD2 binding to the specific membrane platelet receptors, the number and the affinity of binding sites for tritiated PGI2 and PGD2 were determined in 8 healthy subjects (aged 25-32; 4 for PGI2 and 4 for PGD2 studies) in the absence and in the presence of heparin. Preliminary aggregation tests indicated that the heparin concentration tested (2 I.U./ml) reduced the antiaggregating activity of PGI2 and PGD2. Heparin, when preincubated with platelet suspension, did not induce any significant change in the number/platelet (bs/plt) and affinity (Kd) of PGI2 and PGD2 binding sites (bs) in comparison to control values (PGI2 high affinity bs: bs/plt = 106 +/- 12 vs 107 +/- 17 - Kd = 9.7 +/- 3.1 vs 10.0 +/- 2.3 nM; PGI2 low affinity bs: bs/plt = 3551 +/- 233 vs 3670 +/- 465 - Kd = 877 +/- 125 +/- 125 vs 833 +/- 104 nM; PGD2 bs: bs/plt = 228 +/- 14 vs 234 +/- 24 - Kd = 68 +/- 10 vs 73 +/- 7 nM; p greater than 0.4 for all the differences). No significant binding modification was also observed when heparin was preincubated with 3H-PGI2 and 3H-PGD2. The present demonstration that heparin does not interfere with PGI2 and PGD2 binding to platelets is consistent with the hypothesis that heparin reduces the antiaggregating effects of PGI2 and PGD2 by directly potentiating platelet aggregation.

Role of Prostacyclin and Thromboxane A2 in Ischaemic Heart Disease

Many investigations have shown that cardiac tissue is able to produce prostaglandins (PGs) of D, E, F series and over all prostacyclin (1–3) both in animals and in humans. Much evidence indicates that the primary site of PGs synthesis is the coronary vasculature and not the cardiac myocytes (3,4).

The predictive role of the Bova risk score in acute normotensive pulmonary embolism: A retrospective analysis on a real life cohort

Accurate prognostic stratification is of utmost importance for the optimal management of acute pulmonary embolism (PE). It has been shown that the combination of history, clinical parameters, echocardiographic and computer tomography pulmonary angiography patterns and cardiac biomarkers permits to stratify short-term PE prognosis [1]. Although many prognostic models have been proposed, it is still to be determined which one is to be preferred [2]. The Bova score is a new proposed risk assessment model aimed to stratify 30-day prognosis in normotensive patients suffering for acute PE [3]. Briefly, Bova risk score is composed of four variables, i.e. systolic blood pressure (SBP) 90–100 mm Hg (2 points), heart rate (HR) ≥ 110 beats per minute (bpm) (1 point), troponin elevation (2 points) and echocardiographic or computer tomographypulmonary angiography right heart dysfunction (RHD)(2 points). Therefore Bova score ranges from zero points (all variables absent) to seven points (all variables present). The Bova score categorizes three risk classes at low (≤2 points), intermediate (3–4 points) and high (≥5 points) risk of PE-related complications, defined as death from PE, hemodynamic collapse, or recurrent nonfatal PE [3]. The score was retrospectively evaluated in a large patient cohort from Spain, in which the increasing risk on PE-related adverse events among patients classified in the 3 risk classes was confirmed [4]. Patients with Bova risk score ≤ 2 (class I) had in-hospital 3.7% and 30-day 4%,, patients with Bova risk score 3–4 (class II) had in-hospital 15% and 30-day 18% and patients with Bova risk score ≥ 5 (class III) had in-hospital 37% and 30-day 42% of PE-related complications, respectively [4]. Morever inhospital and 30-day PE-related mortality were 2.5% and 3.1% in class I, 6.2% and 6.8% in class II and 8.8% and 10.5% in class III, respectively. The Area under receiver operating characteristics (ROC) curves (AUC) of the Bova score for the main endpoint in the validation cohort was 0.74 (95% CI: 0.68–0.80), whereas it was 0.60 (95% CI: 0.52–0.69) for in-hospital PE-related mortality [4]. The Bova score requires further evaluation and especially in real life cohorts before it may be recommended for use on clinical practice. Therefore we retrospectively calculated the Bova risk score and tested its predictive ability as prognosticator for all cause and PE-related inhospital mortality in normotensive PE patients admitted in twenty-

Low-Dose Heparin as an Antithrombotic Agent

Heparin, after subcutaneous administration, has been found to be able to bind to endothelial receptors both in rabbits and in humans. N-sulphonate 35S-heparin remains bound in rabbits for at least 24 h and is able to enhance the inactivation process of thrombin and factor Xa. Heparin subcutaneously (200 U/kg) injected for 2 weeks resulted in an enhanced inactivation of thrombin and factor Xa by the endothelium. The antithrombin-enhancing activity persists longer than the anti-Xa activity. In man, daily subcutaneous administration of heparin (12,500 U/day) for 2 weeks significantly reduces the increased fibrinopeptide A plasma levels and normalizes the increased 125I-fibrinogen turnover. The present work indicates that heparin administration at a low dose represents a treatment able to remarkably enhance the antithrombotic properties of the vessel wall, independently of the presence of detectable heparin levels in the circulating blood.