Laura Zingaro

Relationship of fibrinogen levels and hemostatic abnormalities with organ damage in hypertension.

Elevated plasma levels of fibrinogen and activated coagulation pathways are risk factors of cardiovascular disease in the general population. In a cross-sectional study of a case series, we investigated the relationship between fibrinogen and hemostatic markers with target-organ damage (TOD) in patients with arterial hypertension. Prothrombin time, partial thromboplastin time, fibrinogen, fibrin D-dimer, prothrombin fragment 1+2 (F1+2), and antithrombin III were measured in 352 untreated patients with mild to moderate essential hypertension and 92 normotensive controls. Staging of TOD was assessed according to W.H.O. guidelines by clinical evaluation and laboratory tests including measurements of creatinine clearance, proteinuria, ophthalmoscopy, electrocardiography, echocardiography, and ultrasound examination of major arteries. F1+2 concentrations were significantly greater in hypertensive patients than normotensive controls and were positively correlated with blood pressure. Age, blood pressure levels, duration of hypertension, smoking, HDL-cholesterol, triglycerides, and plasma fibrinogen, fibrin D-dimer, and F1+2 levels were significantly related to the presence and severity of TOD in univariate analysis. Plasma fibrinogen and D-dimer levels were related to organ damage independent of age, blood pressure, duration of hypertension, and smoking status. Separate analysis indicated significant association of fibrinogen and D-dimer levels with cardiac, cerebrovascular, peripheral vascular, and renal damage. In conclusion, elevated plasma levels of fibrinogen and a prothrombotic state are associated with the presence and severity of TOD in patients with essential hypertension and may contribute to the development of atherosclerotic disease in these patients.

Abnormalities of coagulation in hypertensive patients with reduced creatinine clearance

PURPOSE The prothrombotic state that occurs in uremic patients may increase their cardiovascular risk. We studied hypertensive patients with mild-to-moderate impairment of renal function to determine if they had evidence of abnormalities in the coagulation system. SUBJECTS AND METHODS Renal function was assessed in 382 patients with essential hypertension, in whom 24-hour creatinine clearance, urinary protein excretion, and microalbuminuria were measured. We evaluated the function of the coagulation system by measurement of platelet counts, prothrombin time, partial thromboplastin time, and plasma antithrombin III, fibrinogen, D-dimer, and prothrombin fragment 1 + 2 levels. RESULTS Impaired renal function, defined as a creatinine clearance of 30 to 89 mL per minute per 1.73 m(2) of body surface area, was found in 168 (44%) of the patients. Age, blood pressure, duration of hypertension, and plasma levels of fibrinogen, D-dimer, prothrombin fragment 1 + 2, and lipoprotein(a) were significantly greater in these patients than in those with normal renal function; these differences persisted after adjustment for potential confounders. Creatinine clearance was significantly and inversely correlated with levels of plasma fibrinogen (Spearmans rho = -0.26, P <0.001), D-dimer (rho = -0.33, P <0.001), and prothrombin fragment 1 + 2 (rho = -0.20, P <0.001). Levels of plasma fibrinogen (P = 0.009) and D-dimer (P = 0.003) were correlated with renal function independent of age, blood pressure, duration of hypertension, triglyceride level, urinary protein excretion, and erythrocyte sedimentation rate. Lipoprotein(a) levels were correlated with fibrinogen (rho = 0.16, P = 0.003) and D-dimer (rho = 0.26, P <0.001) levels. CONCLUSIONS Increased plasma levels of fibrinogen, D-dimer, and prothrombin fragment 1 + 2 are present in hypertensive patients with mildly decreased creatinine clearance, suggesting that the coagulation system is activated in these patients.

Abnormalities of Insulin Receptors in Spontaneously Hypertensive Rats

Insulin resistance is present in some strains of rats with genetic hypertension. To determine whether this abnormality is present at the level of the insulin receptor, we compared insulin sensitivity, insulin receptor binding, and mRNA levels in tissues of 10-week-old spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WKY) controls. Because we have previously demonstrated an inverse relationship between dietary sodium intake and renal insulin receptor density and mRNA levels in normal Sprague-Dawley rats, the two rat strains in the current experiment were fed either low salt (0.07% NaCl) or high salt (7.5% NaCl) chow until the SHR became hypertensive. Fasting plasma glucose and plasma insulin levels did not differ between SHR and WKY and were not affected by salt intake. When the rats were maintained on the low salt diet, the rate of glucose infusion required to main euglycemia during a hyperinsulinemic clamp was significantly lower in SHR than WKY. High salt diet decreased the rate of glucose utilization during the hyperinsulinemic clamp in WKY but not SHR. During the low salt diet, insulin infusion decreased sodium excretion in both WKY and SHR. When the rats were maintained on the high salt diet, the antinatriuretic response to insulin was blunted in WKY but not SHR. Both the density and mRNA levels of insulin receptor were comparable in the kidney of WKY and SHR, but only WKY had the previously demonstrated decrease in receptor number and mRNA levels when fed the high salt chow. Hepatic insulin receptor mRNA levels were significantly lower in SHR than WKY fed the low salt diet. High salt diet decreased significantly insulin receptor mRNA levels in the liver of WKY but not of SHR. Thus, SHR appear to have lost the feedback mechanism that normally limits insulin-induced sodium retention when extracellular volume is expanded. A decreased expression of insulin receptor in the liver of SHR provides a possible explanation for the insulin resistance and decreased insulin clearance present in this strain.

Glucose metabolism and insulin receptor binding and mRNA levels in tissues of Dahl hypertensive rats

Increased insulinemic response to an oral glucose load has been demonstrated in Dahl salt-sensitive hypertensive rats. To determine whether this abnormality is mediated at the level of the insulin receptor, we compared insulin receptor binding and mRNA levels in tissues of Dahl salt-sensitive rats (DS) and in their normotensive controls, Dahl salt-resistant rats (DR). To evaluate possible influences of dietary sodium intake, rats were fed either low (0.07% NaCl) or high salt (7.5% NaCl) chow until the DS became hypertensive, and then were killed by decapitation. Fasting plasma glucose and plasma insulin levels did not differ between DR and DS rats and were not affected by salt intake. In response to an oral glucose load, plasma glucose had a similar increase in DR and DS rats, but the increase in plasma insulin was significantly greater in DS rats. Scatchard analysis of binding was obtained from in situ autoradiographic studies performed in frozen skeletal muscle and kidney sections, and insulin receptor mRNA levels were measured by slot-blot hybridization. Number and affinity of insulin receptors were comparable in skeletal muscle and kidney of DR and DS rats and, in both groups, binding parameters were not affected by dietary sodium chloride. Hepatic and renal insulin receptor mRNA levels were also comparable in DR and DS rats fed either low or high salt chow. Thus, increased plasma insulin response to oral glucose load is associated with normal insulin receptor binding and gene expression in peripheral tissues in rats with Dahl hypertension. A postreceptor defect is likely responsible for the decreased sensitivity to insulin in this model of genetic hypertension.

Hypertension and Abnormalities of Carbohydrate Metabolism Possible Role of the Sympathetic Nervous System

To investigate the relationships between the sympathetic nervous system (SNS) and parameters of glucose metabolism in arterial hypertension, daily urinary excretion of catecholamines and plasma glucose, insulin, and C-peptide response to an oral glucose load (OGL) have been evaluated in 77 untreated patients with mild-to-moderate essential hypertension and in 31 normotensive controls. Urinary excretion of norepinephrine (UNE) was positively correlated with body mass index and with plasma glucose levels both at fast and after OGL. No correlations were found between urinary excretion of catecholamines and plasma insulin and C-peptide levels both at fast and in response to OGL. Because the frequency distribution of UNE was bimodal, hypertensive subjects were separated into two subgroups using an arbitrary cutoff, and the parameters of glucose metabolism were compared. Subjects with UNE > 205 microg/day had greater levels of fasting glucose and greater glycemic response to OGL than subjects with UNE < 205 microg/day, whereas no significant differences between the groups were found in fasting and stimulated plasma insulin and C-peptide. Thus, activation of SNS is related to glucose tolerance but not hyperinsulinemia and insulin hypersecretion in essential hypertension. Plasma glucose levels, independent of insulin, may contribute to the relationship between SNS activity and blood pressure in essential hypertension.

Lipoprotein (a), haemostatic variables and cardiovascular damage in hypertensive patients

Objective Lipoproteins and coagulation factors are independent predictors of atherothrombotic events in the general population and their interaction may contribute to the development of cardiovascular damage. This study was designed to assess relationships between lipoproteins, haemostatic variables, and atherosclerotic complications in hypertensive patients. Methods In 389 untreated essential hypertensive patients recruited at a hypertension clinic, we measured plasma lipids, apolipoproteins, lipoprotein (a), apolipoprotein (a) isoforms, fibrinogen, and parameters that directly reflect the coagulation activation. Hypertensive patients were compared to 92 normotensive controls. Results Univariate analysis showed log lipoprotein (a) concentrations to be significantly correlated with age (P <0.02), apolipoprotein B (P <0.02), plasma fibrinogen (P <0.001), and fibrin D-dimer (P <0.001) levels, but not with body mass index, blood pressure, dietary fat intake, cholesterol, triglycerides, apolipoprotein AI, prothrombin fragment 1 + 2, and antithrombin III. The relationship of lipoprotein (a) with fibrinogen and D-dimer was present in both sexes, whereas the relationship of lipoprotein (a) with age and apolipoprotein B was found only in males. Multiple regression analysis showed that both fibrinogen and D-dimer were independently related with lipoprotein (a). Elevated fibrinogen, D-dimer, and lipoprotein (a) levels were significantly and independently associated with clinical evidence of atherosclerotic disease. To investigate whether the relationships of lipoprotein (a) with coagulation parameters are genetically determined, we analysed apolipoprotein (a) phenotypes in a subset of 188 hypertensive patients. While lipoprotein (a) levels were inversely correlated with apolipoprotein (a) isoform protein size, both fibrinogen and D-dimer concentrations were comparable in patients with apolipoprotein (a) isoforms of different size. Conclusions This study demonstrates a relationship between lipoprotein (a) and clotting variables in hypertensive patients that may contribute to atherosclerotic damage in these patients. There is no evidence of a genetic background for this relationship.

Effects of angiotensin II on insulin receptor binding and mRNA levels in normal and diabetic rats

Summary Both the density and level of mRNA encoding insulin receptors in the kidney are inversely related to the dietary sodium content, suggesting a feedback mechanism that limits the insulin-induced sodium retention when extracellular fluid volume is expanded. Because angiotensin II affects tissue sensitivity to insulin in humans, we investigated whether angiotensin II affects insulin receptor binding and mRNA levels in the kidney, liver, and renal arteries of normal rats and rats with streptozotocin-induced diabetes mellitus. Non-diabetic and diabetic rats were infused for 7 days with either vehicle or angiotensin II at a rate of 200 ng · kg−1· min−1. In a separate experiment, normal rats were treated with an angiotensin converting enzyme inhibitor (captopril, 100 mg/dl in the drinking water) or vehicle for 7 days. Regional analysis of insulin receptor binding in the kidney and renal arteries was performed by an in situ technique using computerized microdensitometry and emulsion autoradiography. Insulin receptor mRNA levels were determined in renal and hepatic tissue by Northern blot hybridization and normalized with 28S rRNA. No differences in blood pressure were observed among diabetic and non-diabetic rats infused with either vehicle or angiotensin II, whereas captopril-treated rats had significantly lower blood pressure levels than their respective controls. Angiotensin II significantly decreased plasma renin concentration in both non-diabetic and diabetic rats. Insulin receptor number was significantly greater in the renal cortex of diabetic rats than in non-diabetics, whereas no significant differences were found in the outer medulla, inner medulla, or renal arteries. Angiotensin II infusion did not affect either the number or affinity of insulin receptors in any of the renal regions studied. Insulin receptor mRNA levels were significantly greater in the kidney and liver of diabetic rats than in non-diabetics and were not affected by angiotensin II infusion. Similar to angiotensin II infusion, captopril treatment did not affect either renal insulin receptor binding or mRNA levels. Thus, diabetic rats have increased insulin receptor binding and mRNA levels in comparison to non-diabetic rats. Angiotensin II infusion and captopril treatment do not affect insulin receptor binding and mRNA levels in the kidney, arguing against a role for this peptide in the modulation of renal sensitivity to insulin. [Diabetologia (1997) 40: 770–777]