Eduardo Villa

Effects of cicaprost and fosinopril on the progression of rat diabetic nephropathy.

We have studied the effects of chronic therapy with cicaprost (a PGI2 analog), fosinopril (a converting enzyme inhibitor), and the combination of both drugs on the progression of experimental diabetic nephropathy. Uninephrectomized streptozotocin-induced diabetic rats were maintained for 8 months with plasma glucose between 13.7 and 22.0 mmol/L to hasten renal damage. Systemic and renal parameters were measured periodically, and at sacrifice structural and morphometrical renal studies were performed to evaluate diabetic injury. Control rats exhibited characteristic features of this model, such as high blood pressure and plasma creatinine and urinary albumin excretion, together with prominent alterations in the kidney (renal and glomerular hypertrophies, mesangial matrix expansion, and tubular alterations). The three therapies attenuated equivalently the progression of diabetic renal injury, as estimated by lower urinary albumin excretion, renal and glomerular hypertrophies, and a better renal architectural preservation. No synergistic action was appreciated with the combined therapy. However, renal preservation achieved with cicaprost was not linked to reductions in systemic blood pressure, whereas in the groups treated with fosinopril the hypotensive effect of this drug could have contributed to the positive outcome of the therapy. Therefore, nephroprotection exerted by this PGI2 analog in this model seems more related to the derangement of renal local mechanisms than to systemic blood pressure control. Finally, the possibility that an impaired prostacyclin synthesis or bioavailability is involved in the pathogenesis of the diabetic nephropathy in this model underlies our results.

Salt sensitivity: Concept and pathogenesis

Almost two decades ago, the existence of a subset of essential hypertensive patients, who were sensitive (according to the increase in blood pressure levels) to the intake of a diet with a high salt content, was described. These patients are characterized by an increase in blood pressure and in body weight when switched from a low to a high sodium intake. The increase in body weight is due to the incapacity of the kidneys to excrete the whole intake of sodium until renal perfusion pressure (mean blood pressure) attains a level that is able to restore pressure-natriuresis relationship to values that enable the kidney to excrete the salt ingested or administered intravenously. Salt sensitivity does not seem to depend on the existence of an intrinsic renal defect to handle sodium, but on the existence of subtle abnormalities in the regulation of the sympathetic nervous system, the renin-angiotensin system or endothelial function. It is also relevant that organ damage secondary to arterial hypertension, has been shown in animal models and in hypertensive humans sensitive to a high salt intake to be significantly higher when compared with that of salt-resistant animals or humans. Interestingly, in humans, salt sensitivity has been shown to correlate with microalbuminuria, an important predictor of cardiovascular morbidity and mortality, which correlates with most of the cardiovascular risk factors commonly associated with arterial hypertension. One of these factors is insulin resistance, that usually accompanies high blood pressure in overweight and obese hypertensives. Insulin resistance and hyperinsulinism are present in a significant percentage of hypertensive patients developing cardiovascular symptoms or death. For these reasons, therapy of arterial hypertension must be directed, not only to facilitate the lowering of BP level, but also, to halt the mechanisms underlying the increase in BP, when salt intake is increased. Furthermore, therapy must preferably improve the diminished insulin sensitivity present in salt-sensitive subjects that contribute independently to increased cardiovascular risk.

Comparative Effect of PGE2 and PGI2 on Renal Function

Rapid degradation of prostacyclin (PGI2) inherent to its molecular structure has long been a major limitation in assessing the natriuretic effect of this prostaglandin. The recent availability of the stable PGI2 analogue iloprost now allows for a comparative study with prostaglandin E2 (PGE2). In the present study conducted in six anesthetized dogs, the intrarenal effects of two consecutive doses (1 and 4 ng x kg(-1) x min(-1)) of PGE2 on renal blood flow, glomerular filtration rate, and urinary sodium excretion were compared with the effects of two identical doses of iloprost. The selected doses of PGE2 were those producing a maximal natriuretic and vasodilator response without affecting mean arterial pressure. A washout period was allowed between administration of PGE2 and iloprost. PGE2 infusion significantly increased fractional sodium excretion from 0.69+/-0.1 to 2.79+/-1.1% and 4.27+/-1.2%% (P<.05), respectively. These changes in fractional sodium excretion induced by PGE2 were associated with significant increases in renal blood flow from 151.1+/-62 to 185+/-64.3 and 185.6+/-64.3 mL/min (P<.05), respectively; however, no significant alterations were seen in glomerular filtration rate, from 29.5+/-9.4 to 35.2+/-12.2 and 32.7+/-7.8 mL/min (NS), and mean arterial pressure, from 117.6+/-26 to 113.9+/-24.1 and 112.3+/-24.1 mm Hg (NS) during control and PGE2 infusion. At identical doses, sequential infusion of PGI2 had no effect on renal blood floww and glomerular filtration rate, producing natriuresis only at the highest dose, a fractional sodium excretion from 0.69+/-0.1 to 0.8+/-0.28 mm Hg (NS) and 1.05+/-0.34% (P<.05), respectively. In conclusion, the present study confirms that PGE2 exerts a natriuretic effect during increases in renal blood flow. In contrast, PGI2 had no hemodynamic effect, and the natriuresis was markedly blunted.

Effects of UP269-6, a New Angiotensin II Receptor Antagonist, and Captopril on the Progression of Rat Diabetic Nephropathy

To estimate the effects of UP269-6, a nonpeptide angiotensin II receptor antagonist, and captopril, a converting enzyme inhibitor, on the progression of nephropathy, 77 uninephrectomized diabetic rats were maintained for 8 months with plasma glucose levels from 300 to 500 mg/dL. Systemic and renal parameters were periodically measured, and, at the time of death, a histological evaluation of renal damage was performed. Control rats (no additional treatment but insulin) showed increased blood pressure and urinary albumin levels, together with prominent alterations in the kidney (renal and glomerular hypertrophies, tubular atrophy, and 19% of sclerotic glomeruli). Captopril (50 mg/kg/day) and UP269-6 (10 mg/kg/day) reduced blood pressure and albumin excretion levels, and improved histological renal preservation (lower renal and glomerular hypertrophies, tubular atrophy, and percentage of sclerotic glomeruli: 5% and 7%, respectively). Finally, a low dose of UP269-6 (1 mg/kg/day), which induced an intermediate level of blood pressure between control and the other treated groups, produced an equivalent degree of nephroprotection. Our data demonstrate the efficacy of this new angiotensin II receptor antagonist on the progression of diabetic renal damage. These results also reinforce the role attributed to angiotensin II in the development of renal derangement in this model, as UP269-6 is devoid of agonistic effect on the kinin system.

Effects of chronic combined treatment with captopril and pravastatin on the progression of insulin resistance and cardiovascular alterations in an experimental model of obesity in dogs

Obesity is a metabolic disorder in which multiple clinical and biochemical alterations coexist. However, the progression of these alterations in relation to weight gain has not been investigated in detail. Therefore, we studied the evolution of insulin resistance and associated risk factors in a model of experimental obesity in dogs. We also studied whether chronic exposure to these pathogenic factors could induce cardiac and vascular alterations. Twenty male age- and body weight-matched beagle dogs were divided into four groups (n = 5), according to diet and pharmacologic therapy received, and followed for 2 years. Control animals were maintained with a regular diet, while the 15 remaining animals were fed a high-fat diet. The Obese group of dogs received no therapy, whereas the Capto group received 25 mg/12 h captopril, and the Prava+Capto was treated with 10 mg/24 h pravastatin plus the same dose of captopril throughout the study. Periodical determinations of clinical and biochemical parameters were made, and the degree of insulin resistance was also estimated. After the 2-year follow-up, the dogs were killed and vascular thickening in the aorta and the coronary arteries was evaluated. In addition, cardiac hypertrophy was estimated by heart weight and free-wall left ventricular width. Chronic pravastatin plus captopril treatment, together with decreasing weight gain rate, ameliorated the progression of insulin resistance and associated risk factors (hyperinsulinemia, hypercholesterolemia) related to this severe model. In addition, this combined therapy showed cardioprotective action, as cardiac and vascular hypertrophy observed in the Obese group was prevented. These positive results seems to emerge from the synergistic effects of both drugs, as captopril as monotherapy induced only a slight benefit on these parameters.

Diagnosis of Insulin Resistance

SummarySoon after the discovery of insulin, the importance of insulin sensitivity assessment was recognised. Recently, the role of insulin resistance in cardiovascular morbidity and mortality has been widely accepted and many methods for in vivo assessment of insulin resistance have been developed. They may be classified as ‘closed-loop’ techniques (in which insulin and glucose concentrations are allowed to interact freely), ‘open-loop’ techniques (in which insulin and/or glucose levels are fixed) and ‘model methods’ (which use a mathematical model to analyse the interactions between insulin secretion patterns and glucose disposal). Although there is no ideal method available to date, open-loop techniques avoid many of the difficulties involved in the interpretation of closed-loop or model methods, and are preferred by most investigators. The glucose clamp technique is recognised as the ‘gold standard’ for assessment of insulin sensitivity; however, the insulin suppression test is adequate in most circumstances and is much simpler to perform.

Prostacyclin: its pathogenic role in essential hypertension and the class effect of ACE inhibitors on prostaglandin metabolism.

Angiotensin-converting enzyme inhibitors (ACEI) block degradation of bradykinin, and bradykinin stimulates prostacyclin synthesis. Therefore, we set out to determine whether the effects of ACE inhibitors on prostaglandin production in essential hypertensive patients are class effects or are dependent on ACE inhibitor structure. In addition, we studied whether hypertensives show an impaired capacity to synthesize vasodilator prostaglandins. To address these questions, we compared the effects of captopril (sulfhydryl-containing inhibitor), enalapril and ramipril (carboxyl-containing inhibitors) and fosinopril (phosphoryl-containing inhibitor) on blood pressure and urinary excretion of 6-keto-prostaglandin (PG) F1-alpha (the breakdown product of prostacyclin) in 44 mild-to-moderate essential hypertensive subjects before and 8 weeks after administration of an ACEI. We also studied prostacyclin excretion in 15 normotensive healthy controls. Levels of urinary 6-keto-PGF1-alpha (pg/ml) were measured by specific radioimmunoassay. Hypertensive subjects showed a lower excretion of 6-keto-PGF1-alpha than normotensive controls (212+/-147 vs 353+/-98 pg/ml, p < 0.001). All ACEI induced a significant decrease in MAP and increased the rate of excretion of the prostacyclin metabolite: C, 211+/-200 to 338+/-250 pg/ml, p < 0.05; E, 202+/-133 to 296+/-207 pg/ml, p < 0.05; R, 205+/-127 to 342+/-211 pg/ml, p < 0.05; F, 235+/-128 to 347+/-241 pg/ml, p < 0.05. In hypertensives (n = 44) the decrease in blood pressure correlated negatively with the rise in 6-keto-PGF1-alpha excretion (r = -0.51, p < 0.001). These data suggest that impaired prostacyclin biosynthesis in hypertensive patients could account for haemodynamic changes leading to the hypertensive state. Moreover, the hypotensive mechanisms of ACEI may be mediated by an increase in prostacyclin production; this effect seems to be class-dependent.

Effects of l-Arginine Infusion on Renal Hemodynamics and Sodium Excretion During Hypo-, Normo-, and Hyperinsulinemia, as Studied in Dogs

The response of renal hemodynamics and sodium excretion (NaU) to an infusion of L-arginine, in the presence (experiment I) or absence (experiment II) of endogenous insulin secretion and during a sustained hyperinsulinemic euglycemic state (experiment III), was studied in 10 age-matched beagle dogs. The experiments were preceded by a standard oral glucose tolerance test (OGTT), performed 1 week before experiment I. One week resting periods were allowed between experiments I, II, and III. No differences in renal hemodynamics and NaU were observed between basal (experiment I) and insulin secretion suppressed states (experiment II). L-Arginine infusion increased renal plasma flow (RPF), glomerular filtration rate (GFR), and NaU to a similar extent in both experiments. The hyperinsulinemic-euglycemic state (experiment III) induced a decrease in renal hemodynamics and NaU. In this situation, the infusion of L-arginine increased NaU, but was unable to increase RPF and GFR. Our data suggest that a sustained hyperinsulinemic state can interact with the physiological vasoactive mechanisms involved in the regulation of renal vasculature. These results may be pertinent to human disease, especially in pathological conditions in which insulin resistance is present.

Comparison of the effects of four ACE inhibitors on sympathetic reactivity to cold pressor test in essential hypertensive patients

Background. We compared the effects of four different structural angiotensin-converting enzyme (ACE) inhibitors on the hemodynamic profile and catecholamine response to the cold pressor test (CPT) in hypertensive patients. Methods. We studied 44 patients with mild to moderate essential hypertension. The patients were divided into four groups according to the ACE inhibitor [enalapril (E), fosinopril (F), captopril (C), or ramipril (R)]. They were given for 8 weeks. Sympathetic reactivity was evaluated by a CPT at baseline and at the end of therapy. Blood pressure (BP), heart rate (HR), and plasma norepinephrine (NE, pg ml−1) were measured at the times 0, 2, 4, 6, 8, 10, and 15 min. The delta (subtracting the basal values from the min 2 values) and the area under the curve (AUC) of the response during the CPT were studied. Results. The rise in diastolic blood pressure (DBP) (AUC) during the cold stimulus was significantly attenuated by all inhibitors studied (P<0.01): E, 17±22 to 0±20; F, 23±41 to −4±40; C, 34±33 to 7±28; R, 32±28 to −1±25. Drug therapy also blunted the response of HR to cold stress (delta HR, bpm): E, 2±2 to 0±2, P<0.05; F, 2±2 to 0±2, P<0.05; C, 3±3 to −1±3, P<0.01; R, 2±4 to −2±3, P<0.05. The rise in plasma NE (AUC) during CPT was decreased by all ACE inhibitors: E, 198±405 to 24±148, P<0.05; F, 353±436 to 51±412, P<0.05; C, 315±318 to 124±516, P<0.05; R, 677±398 to 251±307, P<0.01. Conclusions. The results in our study suggest that the blunting effects of ACE inhibitors on adrenergic tone seem to be class-dependent.

Natriuretic effects of dopamine agonist drugs in models of reduced renal mass.

In addition to recognized neurotransmitter properties in the central nervous system, dopamine (DA) plays a role in the physiological activity of the kidney through its hemodynamic and natriuretic effects. On the basis of these data, some pharmacological interventions have focused their attention on the use of DA-related drugs to improve renal sodium handling. We summarize the data obtained from two studies using two DA agonist drugs, lisuride (LIS) and fenoldopam (FEN), in two situations of reduced renal mass. During an intravenous sodium load performed on 10 uninephrectomized dogs, LIS induced a significant blockade of the concomitant pressor response, estimated by lower blood pressure and norepinephrine levels. Under these same conditions, FEN significantly decreased blood pressure and elevated the natriuretic response. In a second study, when FEN was administered at nonhypotensive doses to chronic renal failure patients, it evoked an enhancement of diuresis, natriuresis, and creatinine clearance. These data seem to confirm the involvement of DA in the regulation of cardiovascular homeostasis and its role in renal sodium handling. Furthermore, these beneficial effects support the use of DA-related drugs in the field of hypertension.