Alessandro Pierucci

Effects of sulindac and ibuprofen in patients with chronic glomerular disease. Evidence for the dependence of renal function on prostacyclin.

We investigated whether the glomerular synthesis of prostacyclin modulates the renal blood flow and glomerular filtration rate in chronic glomerular disease. The urinary excretion of 6-keto-prostaglandin F1 alpha, a stable breakdown product of prostacyclin, was significantly (P less than 0.01) reduced in 20 women with chronic glomerular disease, as compared with 19 controls, whereas excretion of urinary prostaglandin E2 was unchanged. In 10 patients randomly assigned to one week of treatment with ibuprofen, excretion of urinary 6-keto-prostaglandin F1 alpha and prostaglandin E2 was reduced by 80 per cent, the level of serum creatinine was increased by 40 per cent, and creatinine and para-aminohippurate clearances were reduced by 28 and 35 per cent, respectively. The reduction of both clearances was inversely related (P less than 0.01) to the basal urinary excretion of 6-keto-prostaglandin F1 alpha but not of prostaglandin E2. No functional changes were detected in five healthy women, despite a similar suppression of renal prostacyclin synthesis by ibuprofen. In contrast, one week of treatment with sulindac did not affect renal prostacyclin synthesis or renal function in the other 10 patients, despite a marked inhibition of extrarenal cyclooxygenase activity. We conclude that in patients with mild impairment of renal function, the renal blood flow and glomerular filtration rate are critically dependent on prostacyclin production. In such patients sulindac may be a safe substitute for other nonsteroidal antiinflammatory drugs.

Estimated rate of thromboxane secretion into the circulation of normal humans.

We have measured the excretion of a major urinary metabolite of thromboxane B2 (TxB2), i.e., 2,3-dinor-TxB2, during the infusion of exogenous TxB2 over a 50-fold dose range to enable estimation of the rate entry of endogenous TxB2 into the bloodstream. Four healthy male volunteers received 6-h i.v. infusions of venhicle alone and TxB2 at 0.1, 1.0, and 5.0 ng/kg X min in random order. They were pretreated with aspirin at a dose of 325 mg/d in order to suppress endogenous TxB2 production. Urinary 2,3-dinor-TxB2 was measured before, during, and up to 24 h after the infusions and in aspirin-free periods, by means of radioimmunoassay. The nature of the extracted immunoreactivity was characterized by thin-layer chromatography and confirmed by negative ion-chemical ionization gas chromatography/mass spectrometry. Aspirin treatment suppressed urinary 2,3-dinor-TxB2 excretion by 80%. The fractional elimination of 2,3-dinor-TxB2 was independent of the rate of TxB2 infusion and averaged 5.3 +/- 0.8%. Interpolation of metabolite values obtained in aspirin-free periods onto the linear relationship between the quantities of infused TxB2 and the amount of metabolite excreted in excess of control values (y = 0.0066x, r = 0.975, P less than 0.001) permitted calculation of the mean rate of entry of endogenous TxB2 into the circulation as 0.11 ng/kg X min. The rate of disappearance of immunoreactive TxB2 from the circulation was monoexponential over the first 10 min with an apparent half-life of 7 min. This corresponded to a maximal estimate of the plasma concentration of endogenous TxB2 of 2.0 pg/ml. These results suggest that ex vivo platelet activation and/or analytical problems confound estimates of endogenous thromboxane release based on plasma TxB2 and provide a rationale for seeking longer-lived enzymatic metabolites of TxB2 in plasma.

Evidence for a Direct Stimulatory Effect of Prostacyclin on Renin Release in Man

THE OBJECTIVES OF THIS INVESTIGATION WERE: (a) to characterize the time and dose dependence of the effects of prostacyclin (PGI(2)) on renin release in healthy men; (b) to define whether PGI(2)-induced renin release is secondary to hemodynamic changes; (c) to determine the plasma and urine concentrations of 6-keto-PGF(1alpha) (the stable breakdown product of PGI(2)) associated with renin release induced by exogenous or pharmacologically enhanced endogenous PGI(2). Intravenous PGI(2) or 6-keto-PGF(1alpha) infusions at nominal rates of 2.5, 5.0, 10.0, and 20.0 ng/kg per min were performed in each of six normal human subjects; in three of them, PGI(2) infusion was repeated after beta-adrenergic blockade and cyclooxygenase inhibition. PGI(2), but not 6-keto-PGF(1alpha), caused a time- and dose-dependent increase of plasma renin activity, which reached statistical significance at 5.0 ng/kg per min and was still significantly elevated 30 min after discontinuing the infusion. Although combined propranolol and indomethacin treatment significantly enhanced the hypotensive effects of infused PGI(2), it did not modify the dose-related pattern of PGI(2)-induced renin release. Plasma 6-keto-PGF(1alpha) levels rose from undetectable levels (<7.5 pg/ml) in a stepwise fashion during increasingly higher infusion rates of PGI(2) or 6-keto-PGF(1alpha). The threshold concentration of plasma 6-keto-PGF(1alpha) associated with a statistically significant stimulation of renin release was approximately 200 pg/ml. Upon discontinuing PGI(2) or 6-keto-PGF(1alpha) infusion, the disappearance of 6-keto-PGF(1alpha) from blood showed an identical biphasic behavior, the initial phase having an apparent t((1/2)) of 3.2 min. The intravenous infusion of furosemide, which is known to stimulate renin release via a cyclooxygenase-dependent mechanism, caused a three-to fourfold increase of urinary 6-keto-PGF(1alpha) excretion rate, concomitant with the elevation of plasma renin activity levels, in six healthy women. 6-Keto-PGF(1alpha) remained undetectable in peripheral venous plasma throughout the study. WE CONCLUDE THAT IN HUMAN SUBJECTS: (a) PGI(2)-induced renin release occurs with a dose and time dependence similar to its reported platelet effects; (b) PGI(2)-induced renin release is not mediated by adrenergic stimuli or cyclooxygenase-dependent mechanisms secondary to hemodynamic changes; (c) furosemide-induced renin release is associated with increased renal PGI(2) formation; and (d) PGI(2) appears to act as a local modulator rather than a circulating hormone in controlling juxtaglomerular function.

Improvement of Renal Function with Selective Thromboxane Antagonism in Lupus Nephritis

To test the hypothesis that the vasoconstrictor thromboxane A2 may affect renal hemodynamics in lupus nephritis, we examined the short-term effects of a selective thromboxane-receptor antagonist, BM 13,177, and of low-dose aspirin. In a randomized, double-blind, crossover study, 10 patients with biopsy-proved lupus nephritis were given a 48-hour continuous infusion of BM 13,177 or placebo. At base line, seven patients had markedly elevated urinary levels of thromboxane B2, the breakdown product of thromboxane A2. During the infusion of BM 13,177, the inulin clearance rate, which was 68 ml per minute per 1.73 m2 of body-surface area at base line, increased by an average of 24 percent (range, 12 to 47 percent; P less than 0.01). Para-aminohippurate clearance was increased to the same extent, with no change in the filtration fraction. The bleeding time doubled, indicating an occupancy of platelet thromboxane receptors of more than 95 percent. The hemodynamic changes were associated with a significant increase in sodium excretion from 76 to 118 mmol per day (P less than 0.01) but with no change in arterial blood pressure. In another study, 10 additional patients with lupus nephritis were randomly assigned to receive either placebo or 20 mg of aspirin twice daily for four weeks. The aspirin regimen produced a selective, cumulative inhibition of platelet cyclooxygenase activity and a doubling of bleeding time. However, there was no change in the inulin clearance rate and no change in urinary levels of thromboxane B2 or 6-keto-prostaglandin F1 alpha, which are indicators of renal synthesis of thromboxane A2 and prostacyclin, respectively. We conclude that in lupus nephritis, impairment of renal function is at least in part mediated hemodynamically and is reversible with a thromboxane antagonist. Platelets, however, are not a major source of thromboxane A2 synthesis and action within the kidney.

Fractional conversion of thromboxane B2 to urinary 11-dehydrothromboxane B2 in man

Thromboxane (TX) B2, the chemically stable hydration product of pro-aggregatory TXA2, undergoes two major pathways of metabolism in man, resulting in the formation of 2.3-dinor-TXB2 and 11-dehydro-TXB2, respectively. We have measured the excretion of the latter during the infusion of exogenous TXB2 over a 50-fold dose range in order to examine the fractional conversion of TXB2 to urinary 11-dehydro-TXB2 and to re-assess the rate of entry of endogenous TXB2 into the circulation. Four healthy male volunteers received 6-h intravenous infusions of the vehicle alone and TXB2 at 0.1, 1.0 and 5.0 ng.kg-1.min-1 in random order. They were pretreated with aspirin 325 mg/d in order to suppress endogenous TXB2 production. Urinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured before, during and up to 24 h after the infusions and in aspirin-free periods, by means of NICI-GC/MS-validated radioimmunoassays. Aspirin treatment suppressed urinary 11-dehydro-TXB2 by 91%. The fractional elimination of 11-dehydro-TXB2 was independent of the rate of TXB2 infusion and averaged 6.8 +/- 0.7%, as compared to 6.4 +/- 0.9% for 2,3-dinor-TXB2. Interpolation of 11-dehydro-TXB2 values obtained in aspirin-free periods onto the linear relationship between the quantities of infused TXB2 and the amount of metabolite excreted in excess of control values (y = 0.0058x, r = 0.94, P less than 0.001) permitted calculation of the mean rate of entry of endogenous TXB2 into the circulation as 0.12 ng.kg-1.min-1. We conclude that: (a) urinary 11-dehydro-TXB2 is at least as abundant a conversion product of exogenously infused TXB2 as 2,3-dinor-TXB2; (b) its excretion increases linearly as a function of the rate of entry of TXB2 into the circulation up to approx. 40-fold the calculated rate of secretion of endogenous TXB2; (c) the latter is consistent with previous estimates based on monitoring of the beta-oxidation pathway of TXB2 metabolism.

Characterization of furosemide-induced activation of the renal prostaglandin system

A detailed time course of changes in plasma renin activity (PRA), urinary prostaglandin (PG) E2, PGF2 alpha, thromboxane (TX) B2 and sodium excretion rates following furosemide was obtained in 7 women. PRA increased within the first 15 min and remained elevated all through the experiment. PGE2, PGF2 alpha, TXB2 and sodium increased simultaneously, reached a peak between 15 and 45 min after furosemide and declined thereafter. It is concluded that furosemide induces a generalized activation of the renal PG system temporally related to the increase of renin release and natriuresis.

Regional citrate anticoagulation in cardiac surgery patients at high risk of bleeding: a continuous veno-venous hemofiltration protocol with a low concentration citrate solution.

IntroductionRegional citrate anticoagulation (RCA) is a valid option in patients at high risk of bleeding who are undergoing continuous renal replacement therapy (CRRT). The aim of this study was to evaluate, in critically ill patients with severe acute kidney injury following cardiac surgery, the efficacy and safety of RCA-continuous veno-venous hemofiltration (CVVH) using a low concentration citrate solution.MethodsIn high bleeding-risk cardiac surgery patients, we adopted, as an alternative to heparin or no anticoagulation, RCA-CVVH using a 12 mmol/l citrate solution. For RCA-CVVH settings, we developed a mathematical model to roughly estimate citrate load and calcium loss. In order to minimize calcium chloride supplementation, a calcium-containing solution was used as post-dilution replacement fluid.Statistical analysis was performed using the Student t-test or analysis of variance (ANOVA) with post-hoc tests, Wilcoxon or Kruskal-Wallis tests for non-parametric analysis, and Kaplan-Meier survival analysis with Log Rank test.ResultsThirty-three patients (age 70.8 ± 9.5, Sequential Organ Failure Assessment (SOFA) score 13.9 ± 2.5) were switched to RCA-CVVH from no anticoagulation CRRT. Among them, 16 patients had been previously switched from heparin to no anticoagulation because of bleeding or heparin-related complications. RCA-CVVH filter life (49.8 ± 35.4 hours, median 41, 152 circuits) was significantly longer (P < 0.0001) when compared with heparin (30.6 ± 24.3 hours, median 22, 73 circuits) or no anticoagulation (25.7 ± 21.2 hours, median 20, 77 circuits). Target circuit and systemic Ca++ were easily maintained (0.37 ± 0.09 and 1.18 ± 0.13 mmol/l), while the persistence of a mild metabolic acidosis required bicarbonate supplementation (5.8 ± 5.9 mmol/hours) in 27 patients. The probability of circuit running at 24, 48, 72 hours was higher during RCA-CVVH (P < 0.0001), with a lower discrepancy between delivered and prescribed CRRT dose (P < 0.0001). RCA was associated with a lower transfusion rate (P < 0.02). Platelet count (P = 0.012) and antithrombin III activity (P = 0.004) increased throughout RCA-CVVH, reducing the need for supplementation.ConclusionsRCA safely prolonged filter life while decreasing CRRT downtime, transfusion rates and supplementation needs for antithrombin III and platelets. In cardiac surgery patients with severe multiple organ dysfunction syndrome, the adoption of a 12 mmol/l citrate solution may provide a suboptimal buffers supply, easily overwhelmed by bicarbonate supplementation.

Describing and interpreting 24-hour blood pressure patterns in physiologic pregnancy

The time course of blood pressure in clinically healthy (pregnant and nonpregnant) women was followed by automatic ambulatory monitoring. Chronobiologic methods revealed the time course of dynamic rhythm characteristics as a function of gestational age. Differences were found between nonpregnant and pregnant women with an overall lowering during pregnancy of the rhythm-adjusted midline estimating statistic of rhythm (mesor).

Effects of sulindac on renal and extrarenal eicosanoid synthesis

We measured the renal and extrarenal synthesis of prostacyclin and thromboxane A2, as reflected by the urinary excretion of the stable hydration products 6‐keto‐prostaglandin F1α and thromboxane B2 and the corresponding 2,3‐dinor‐derivatives, during chronic administration of sulindac (200, 400, 600, and 800 mg/day, each dose given for 7 days in successive weeks) in seven healthy subjects. Urinary eicosanoids were measured by negative ion, chemical ionization–GC/MS–validated RIA techniques. Both 2,3‐dinor‐thromboxane B2 and 2,3‐dinor‐6‐keto‐prostaglandin F1α showed a dose‐dependent reduction, ranging between 45% and 85%. In contrast, the urinary excretion of 6‐keto‐prostaglandin F1α and thromboxane B2 did not change significantly throughout the study. These results extend previous observations of a selective sparing of renal cyclooxygenase activity by sulindac in humans and demonstrate that this selectivity is not related to an overall weaker enzyme inhibition.

Renal effects of nonsteroidal anti-inflammatory drugs in chronic glomerular disease

In contrast to a variety of clinical conditions characterized by ineffective circulatory volume, chronic glomerular disease is not usually associated with increased circulating levels of vasoconstrictor hormones. However, a reduction in glomerular prostacyclin production can possibly account for the prostaglandin dependence of renal function in these patients by virtue of the enhanced constrictor effects of angiotensin II on glomerular arterioles and mesangium. The reduction of renal function induced by a nonselective cyclo-oxygenase inhibitor is inversely related to the basal prostacyclin production. Increased renal synthesis of vasoconstrictor thromboxane A2, as noted in patients with systemic lupus erythematosus, might contribute to the cyclo-oxygenase dependence of renal function. Aspirin as well as a variety of structurally unrelated nonsteroidal anti-inflammatory drugs reduce renal function in systemic lupus erythematosus patients. However, the functional consequences of renal cyclo-oxygenase inhibition are partially attenuated in patients with lupus nephritis vis-à-vis other forms of chronic glomerular disease because of concomitant suppression of enhanced glomerular thromboxane A2 production. Animal data consistent with a prevailing functional significance of vasodilator prostaglandins have also been reported. Short-term administration of sulindac at the recommended dosage is relatively safe in patients with chronic glomerular disease because of selective sparing of glomerular cyclo-oxygenase activity. The long-term consequences of selective versus nonselective cyclo-oxygenase inhibition remain to be established in humans. The beneficial effects of a combination of aspirin and dipyridamole in slowing the deterioration of renal function in patients with membranoproliferative glomerulonephritis does provide a rationale for exploring the effects of low-dose aspirin (i.e., 0.5 to 1.0 mg/kg per day), which most effectively suppresses platelet thromboxane A2 production without interfering with renal prostacyclin synthesis.