Julian Donckier

Role of Endogenous Endothelin-1 in Experimental Renal Hypertension in Dogs

BACKGROUND Endothelin-1, a vasoconstrictive peptide released by endothelium, may be involved in the pathophysiology of hypertension. The goal of the present study was to evaluate the role of endogenous endothelin-1 in renal hypertension in dogs. The model of hypertension consisted of silk tissue wrapping of the left kidney, which produced hypertension associated with perinephritis after 6 to 8 weeks. METHODS AND RESULTS Thirty-two anesthetized open chest dogs were studied randomly: 8 dogs with perinephritic hypertension received the nonpeptidic ETA-ETB receptor antagonist bosentan (group 1); 8 other hypertensive dogs received the vehicle solution (group 2); 8 healthy dogs received bosentan (group 3); and 8 healthy dogs received the vehicle solution (group 4). Bosentan was injected as an intravenous bolus (3 mg/kg) followed by a 1-hour infusion at a rate of 7 mg.kg-1.h-1. In hypertensive dogs, bosentan produced a similar decrease (P = .0001) of both left ventricular systolic and mean aortic pressures, which averaged 38 mm Hg (-22% and -24%, respectively). These parameters remained unchanged with the vehicle solution. Left ventricular end-diastolic and left atrial pressures also declined significantly with bosentan (P = .0005 and P < .05, respectively). Left ventricular lengths tended to decrease. The other cardiovascular parameters (heart rate, peak [+]dP/dt, time constant of relaxation, and coronary vascular resistance) did not change significantly. In healthy dogs, bosentan decreased mean aortic pressure by 19 mm Hg (P = .004). Vehicle solution had no effect. Plasma endothelin-1 levels, similar under basal conditions in healthy and hypertensive dogs, increased 30-fold with bosentan (P = .0001). CONCLUSIONS Specific endothelin-1 receptor antagonism markedly lowers blood pressure in experimental hypertension but is less effective on blood pressure of healthy animals. This suggests that endothelin-1 plays a role in the pathophysiology of hypertension but contributes to a lesser extent to the maintenance of normal blood pressure. This role of endothelin-1 is unrelated to its plasma levels. The increase of plasma endothelin-1 with bosentan, due either to a displacement of endothelin-1 from its receptor or to a feedback mechanism, does not prevent this blood pressure reduction.

Additional Hypotensive Effect of Endothelin-1 Receptor Antagonism in Hypertensive Dogs Under Angiotensin-Converting Enzyme Inhibition

BACKGROUND Endothelin-1 (ET-1) may play a role in hypertension. ET-1 receptor antagonism by bosentan lowers blood pressure in hypertension. We evaluated whether the effect of bosentan is still observed under ACE inhibitors (ACEI). METHODS AND RESULTS Thirty anesthetized and 18 conscious hypertensive dogs were studied randomly. Anesthetized dogs were divided into 4 groups: group 1 received cumulative doses of bosentan (bolus+30-minute infusion: 0.1 mg/kg+/-0.23 mg/kg per hour to 3 mg/kg+/-7 mg/kg per hour); group 2, the same dose-responses after 1 mg/kg enalaprilat; group 3, the vehicle after enalaprilat; and group 4, the dose responses to bosentan followed by enalaprilat. The conscious dogs were divided into 3 groups: group 5 received 2 cumulative doses of bosentan; group 6, the vehicle; and group 7, enalaprilat alone. In groups 1 and 2, bosentan produced dose-related decreases (P=.0001) in left ventricular systolic pressure and mean aortic pressure (AOP). In group 1, bosentan decreased mean AOP by 22%. In group 2, enalaprilat decreased mean AOP by 25% (from 173+/-26 to 130+/-25 mm Hg; P<.005); an additional 18% decrease was obtained with bosentan, the mean AOP reaching 98+/-21 mm Hg (P<.01). In group 3, the effect of enalaprilat alone was a 22% decrease in mean AOP (P<.005). The additive effect of the bosentan-ACEI association was also observed in group 4. In group 5, bosentan reduced mean AOP by 20% (P<.005), whereas mean AOP remained unchanged in group 6. The effect of ACEI alone (group 7) was similar to that of bosentan. CONCLUSIONS Bosentan produces an additional hypotensive effect to that of ACEI, which opens new therapeutic perspectives.

Angiotensin II and endothelin-1 receptor antagonists have cumulative hypotensive effects in canine Page hypertension.

Objective To evaluate whether the cumulative hypotensive effect of the endothelin-1 receptor antagonist bosentan, previously demonstrated in the presence of an angiotensin converting enzyme inhibitor, persists under angiotensin II receptor blockade with losartan. Design The model of hypertension was canine renovascular hypertension (Page hypertension). Methods Ten conscious dogs, studied on two occasions, were administered losartan (a 0.1 mg/kg bolus plus 90 min infusion at 0.1 mg/kg per min) and then bosentan vehicle (experiment I) or losartan and then two cumulative doses of bosentan (a 0.3 mg/kg bolus plus 30 min infusion at 0.7 mg/kg per min; and a 3 mg/kg bolus plus 30 min infusion at 7 mg/kg per min; experiment II). Results At the end of the study, mean aortic pressure in dogs had decreased by 14% in experiment I (from 139 ± 4.7 to 119 ± 4.7 mmHg, P < 0.05), whereas a 28% reduction occurred in experiment II (from 145 ± 8.9 to 104 ± 5.0 mmHg, P < 0.005), corresponding to an additional 14% decrease after administration of bosentan (P < 0.005 between groups). This cumulative effect of bosentan was related to a decrease in systemic vascular resistance (from 1220 ± 119 to 847 ± 189 mmHg/ml per min per kg · 103, P < 0.05). Plasma angiotensin II level increased similarly in both experiments (in experiment I from 133 ± 43 to 622 ± 145 pg/ml, P = 0.01; in experiment II from 198 ± 63 to 771 ± 134 pg/ml, P < 0.005) whereas plasma endothelin-1 level increased only in experiment II (from 3.8 ± 0.4 to 32.7 ± 3.2 pg/ml, P < 0.001). Conclusion The cumulative hypotensive effect of bosentan suggests that, besides angiotensin II, endothelin-1 is independently involved in the pathophysiology of hypertension, which presents new therapeutic perspectives.

Carvedilol and Lacidipine Prevent Cardiac Hypertrophy and Endothelin-1 Gene Overexpression After Aortic Banding

Carvedilol and lacidipine have been shown to exert cardioprotective effects in rat models of chronic hypertension. We investigated their effects in an acute model of pressure overload produced by suprarenal aortic constriction, in which enhanced myocardial production of endothelin-1 could play a crucial role. In the absence of drug treatment, after 1 week, aortic banding provoked an increase in carotid pressure associated with left ventricular hypertrophy (29%; P<0.01). These changes were accompanied by increased myocardial expression of preproendothelin-1 (2.5 times; P<0.05) and skeletal alpha-actin (3.6 times; P<0.05), but the expression of cardiac alpha-actin was not modified. Oral administration of carvedilol at a dose of 30 mg. kg(-1). d(-1) to rats with aortic banding normalized carotid pressure and left ventricular weight as well as preproendothelin-1 and skeletal alpha-actin gene expression. Carvedilol at a lower dose (7.5 mg x kg(-1) x d(-1)) and lacidipine 1 mg x kg(-1) x d(-1) had only moderate and nonsignificant effects on carotid pressure but largely prevented left ventricular hypertrophy (P<0.01) and preproendothelin-1 overexpression (P<0.05). Labetalol (60 mg x kg(-1) x d(-1)) tended to exert similar effects but insignificantly. These results show that the antihypertrophic properties of carvedilol and lacidipine are partly independent of their antihypertensive effects and may be related to their ability to blunt myocardial preproendothelin-1 overexpression. Moreover, carvedilol at a dose of 7.5 mg x kg(-1) x d(-1) did not prevent myocardial overexpression of skeletal alpha-actin, which suggests that, in this model, reexpression of a fetal gene can be activated by pressure overload independently of cardiac hypertrophy.

Cardiovascular effects of beta 3-adrenoceptor stimulation in perinephritic hypertension.

Background A new beta 3‐adrenoceptor (β3‐AR) has been shown to mediate peripheral vasodilation. This study was conducted to evaluate effects of the β3‐AR agonist, SR58611 in normal and hypertensive dogs.

Increased expression of endothelin-1 and its mitogenic receptor ETA in human papillary thyroid carcinoma.

objective Since the isolation of endothelin‐1 (ET‐1) in 1988, there has been tremendous interest in the pathophysiological roles of ET‐1 as a vasoconstrictive and mitogenic peptide. Whereas ET‐1 is mainly released by vascular endothelial cells, it also proved to be produced by various tissues including the thyroid. Because of its mitogenic properties in malignancy and its role as an inflammatory modulator, ET‐1 could be involved in thyroid carcinogenesis and thyroiditis.

Interrelated overexpression of endothelial and inducible nitric oxide synthases, endothelin-1 and angiogenic factors in human papillary thyroid carcinoma

Objective  Nitric oxide (NO) and endothelin‐1 (ET‐1) are involved in carcinogenesis. Overexpression of the ET‐1 axis has been demonstrated in papillary thyroid carcinoma (PTC). This study investigated the expression of NO synthases (NOS) and their relationship with expression of ET‐1 and angiogenic markers in PTC.

Diastolic properties in canine hypertensive left ventricular hypertrophy: effects of angiotensin converting enzyme inhibition and angiotensin II type-1 receptor blockade.

OBJECTIVE Angiotensin II has been suggested to be involved in the pathogenesis of diastolic dysfunction in left ventricular hypertrophy (LVH). The purpose of this study was to asses the effects of enalaprilat and L-158,809, an angiotensin II type-1 receptor antagonist, on LV diastolic function in 16 normal control dogs and 20 LVH dogs with perinephritic hypertension. METHODS LV hemodynamics was studied before and after intravenous injection of enalaprilat (0.25 mg/kg) or L-158,809 (0.3 mg/kg). The hemodynamic data were analyzed in relation to the changes in myocardial blood flow (measured by radioactive microspheres) and in the circulating angiotensin II and norepinephrine levels. RESULTS AND CONCLUSIONS At baseline, significant increases were observed for LV/body weight ratio as well as LV systolic and end-diastolic pressure in the LVH dogs (all P < 0.01 vs. the control group). In addition, LV relaxation time constant was prolonged and the chamber and myocardial stiffness constants were increased (P < 0.01) in the LVH dogs, suggesting an impairment of LV diastolic function. Administration of enalaprilat or L-158,809 improved LV stiffness constants in the LVH dogs (P < 0.05). The diastolic LV pressure-diameter relation shifted downwards in the LVH dogs whereas diastolic distensibility was not altered in the control dogs. Although the circulating angiotensin II levels were significantly decreased by enalaprilat in the LVH dogs, they did not correlate with the changes in the stiffness constants. Furthermore, the alterations of LV diastolic properties in the LVH group could not be attributed to myocardial perfusion, which was rather decreased by administration of enalaprilat and L-158,809. These results suggest that angiotensin II, particularly at the local level, is involved in the pathogenesis of diastolic dysfunction in pressure-overload LVH. The data also support the concept that ACE inhibitors and angiotensin II receptor blockers are potentially beneficial in the treatment of the hypertrophied heart.

MINOR ALTERATIONS IN THYROID – FUNCTION TESTS ASSOCIATED WITH DIABETES MELLITUS AND OBESITY IN OUTPATIENTS WITHOUT KNOWN THYROID ILLNESS

Abstract Thyroid function tests might be affected by diabetes and obesity. To evaluate the influence of these parameters in routine conditions, 72 diabetic and 53 non-diabetic outpatients without known thyroid diseases or severe chronic illness were recruited over a 7 – month period. For each patient, dosages of thyrotropin (TSH), total and free thyroxine (TT4 and FT4, respectively), total and free triiodothyronine (TT3 and FT3) and T3 resin uptake (T3RU) were performed by radioimmunoassays. The simultaneous influence of various parameters known to affect thyroid-function tests was evaluated by multivariate linear regression. The studied variables included gender, age, glucosteroids, estrogens, tobacco habits, iodine contacts, body mass index (BMI) and diabetes mellitus. Tobacco habits and iodine contacts did not influence any tests. As expected, estrogens induced an increase in TT4 and TT3 values (p<0.001 and 0.020, respectively) associated with a decrease in T3RU (p<0.001). Consequently, females had lower T3RU than males (p<0.0001). Corticotherapy was associated with decreased TSH values (p=0.022). TT3 and FT3 decreased with age (p<0.001), whereas T3RU and FT4 increased (p=0.020 and 0.004, respectively). In contrast to an increase in TSH (p=0.006), TT4 and FT4 decreased at higher BMI levels (p=0.018 and 0.004, respectively), which is consistent with subclinical hypothyroidism. In diabetic patients, TSH was lower than in non-diabetic subjects (p=0.039). Thus, the present study indicates that besides known parameters such as age and drugs, thyroid-function tests can also be altered by diabetes mellitus and obesity.

Phaeochromocytoma : state-of-the-art.

Abstract Phaeochromocytomas are catecholamine-secreting tumours that arise from chromaffin cells of the adrenal medulla and extra-adrenal sites. Extra-adrenal phaeochromocytomas are called paragangliomas. A diagnosis of phaeochromocytoma is suspected by typical paroxysmal symptoms, unusual or refractory hypertension, discovery of an adrenal incidentaloma or a family history of phaeochromocytoma or paraganglioma, possibly associated with other genetic syndromes (multiple endocrine neoplasia type 2 A or B, neurofibromatosis type 1 and von Hippel-Lindau disease). It can be confirmed by measurements of urinary or plasma fractionated catecholamines and metanephrines. The best diagnostic performances are achieved by metanephrines. Twenty-four hour urine fractionated metanephrines are still recommended as a screening test but some experts prefer plasma measurements in high-risk patients. Increased serum chromogranin-A levels, combined with high catecholamine or metanephrine in a patient with normal renal function is also a tool, virtually diagnostic of phaeochromocytoma. Recent studies have suggested that 25% of patients with phaeochromocytoma have germline mutations of several genes (NF1, VHL, SDHD, SDHB and RET). Thus, genetic testing should be carried out according to an algorithm of risk factors and specific characteristics. Once a biochemical diagnosis of phaeochromocytoma is made, a CT scan or MRI of the abdomen and pelvis should be performed first. If these investigations remain negative, the chest and neck should be explored. After anatomical imaging, functional imaging by 123I-MIBG should be considered. If the MIBG scan is negative, other imaging modalities have recently proven to be useful (PET, Octreoscan). After localization, the treatment of phaeochromocytoma is a surgical resection, which may be laparoscopic. Preoperative preparation with a-and ß-adrenergic blockade and/or calcium channel blockers associated with volume expansion is essential. Malignant phaeochromocytoma is rare and its treatment still unsatisfying. Phaeochromocytoma during pregnancy is also rare and its diagnosis easily missed because of its clinical resemblance to pre-eclampsia.