Chemical composition and diuretic, natriuretic and kaliuretic effects of extracts of Mimosa bimucronata (DC.) Kuntze leaves and its majority constituent methyl gallate in rats.

OBJECTIVES: Some species of the genus Mimosa showed promising results in previous investigations, which include diuretic effect; however, no chemical analyses or animal model has been conducted so far to evaluate the biological properties of M. bimucronata. METHODS: Male Wistar rats received the oral treatment with vehicle; hydrochlorothiazide; methanolic extract from M. bimucronata (MEMB), dichloromethane (DCM) and ethyl acetate (EA) fractions or methyl gallate (MG). The cumulative urine volume, electrolytes excretion, pH and osmolality were determined at the end of the experiment. KEY FINDINGS: The chemical studies demonstrated that the phenolic compounds are the majorities in the plant, with the MG being the main substance identified. We showed that MEMB and EA fraction, but not DCM, exhibited diuretic and saluretic effects. Similarly, the MG also revealed diuretic, natriuretic and kaliuretic properties to both normotensive and spontaneously hypertensive rats. Atropine, a muscarinic receptor antagonist, fully prevented MG-induced diuresis and saluresis. In addition, MG did not alter the viability of A7r5 and L929 cell lines and neither stimulated nitric oxide generation. CONCLUSIONS: These findings suggest that M. bimucronata extracts and its majority compound MG present diuretic, natriuretic and kaliuretic properties, which was dependent on the activation of muscarinic acetylcholine receptor.

Diuretic, natriuretic and potassium-sparing effect of nothofagin isolated from Leandra dasytricha (A. Gray) Cogn. leaves in normotensive and hypertensive rats.

Active constituents from natural origin have long been used for the treatment of patients suffering from cardiovascular and renal diseases. This study therefore aimed to investigate the diuretic and natriuretic properties of nothofagin, a dihydrochalcone isolated from Leandra dasytricha (A. Gray) Cogn. leaves in normotensive and hypertensive rats. Male Wistar normotensive rats were orally treated with vehicle (1 ml/kg); hydrochlorothiazide (HCTZ; 25 mg/kg); ethyl acetate fraction from L. dasytricha (EALD; 3-30 mg/kg) and nothofagin (NOT; 0.3-3 mg/kg). Spontaneously hypertensive rats (SHR) received NOT (1 mg/kg), HCTZ (25 mg/kg) or vehicle. The cumulative diuretic index, urinary electrolytes excretion (Na+ and K+), pH, density and conductivity were measured at the end of the experiment (after 8 h). A7r5 and L929 cell lines were used to measure cell viability after exposure to NOT. Nitric oxide generation was quantified in A7r5 cell supernatant, and DPPH assay was used for evaluating the antioxidant properties of NOT. The urinary volume of normotensive rats were increased after the treatment with EALD, without any changes in Na+ or K+ excretion. NOT was able to induce diuresis and natriuresis, but not kaliuresis, in both normotensive and hypertensive rats. The reduction in prostanoids generation through cyclooxygenase inhibition, as well as the muscarinic receptor antagonism, fully avoided NOT-induced increases in diuretic index. NOT, which did not interfere with L929 or A7r5 cell viability, was able to stimulate nitric oxide generation in A7r5 cell, besides showing an antioxidant effect in scavenging the free-radical DPPH. Taken together, our study shows, for the first time, the diuretic, natriuretic and potassium-sparing effect of nothofagin in rats, which was associated with prostanoids generation, muscarinic receptor activation and antioxidant properties.

Atrial natriuretic hormone, vessel dilator, long-acting natriuretic hormone, and kaliuretic hormone decrease the circulating concentrations of CRH, corticotropin, and cortisol.

The present investigation was designed to determine whether atrial natriuretic peptides consisting of amino acids 1-30 (i.e. long-acting natriuretic hormone), 31-67 (vessel dilator), 79-98 (kaliuretic hormone), and 99-126 (atrial natriuretic hormone) of the 126 amino acid atrial natriuretic hormone prohormone decrease CRH, ACTH, and/or cortisol in healthy humans (n = 30). Vessel dilator, kaliuretic hormone, long-acting natriuretic hormone, and atrial natriuretic hormone decreased the circulating concentration of CRH 84%, 74%, 67%, and 62% (P < 0.001 for each), respectively, when infused at 100 ng/kg body weight.min for 60 min. Vessel dilator, kaliuretic hormone, long-acting natriuretic hormone, and atrial natriuretic hormone decreased circulating ACTH concentrations 58%, 80%, 81%, and 70% (P < 0.001) and the circulating concentration of cortisol 73%, 72%, 73%, and 67% (P < 0.001), respectively. The decreases in CRH, ACTH, and cortisol lasted 11/2 to 3 h after cessation of the respective atrial natriuretic peptide infusions. These data, along with the knowledge that cortisol upregulates atrial natriuretic peptides' gene expression and CRH and ACTH stimulate atrial natriuretic peptides' release, suggest that these four atrial natriuretic peptides may be part of an intricate feedback system to help regulate cortisol concentrations via their ability to decrease the circulating concentration of CRH which, in turn, results in a decrease in ACTH and cortisol.

Summary of studies of changes in vascular reactivity caused by natriuretic hormones.

Endogenous Na, K pump inhibitors may contribute to the pathogenesis of hypertension, and could do so by causing direct vasoconstriction and/or enhancing sensitivity to other vasoconstrictor agents. These effects of the Na, K pump inhibitors are likely due to inhibition of Na-K-ATPase. In turn, cells become depolarized, internal sodium concentration increases and internal calcium is increased by exchange for sodium via the sodium/calcium exchange carrier. This extra calcium is sequestered, increasing the size of the releasable intracellular calcium pool. Both depolarization and the increase in cytosolic calcium can cause vasoconstriction. Both depolarization and the increased size the intracellular calcium pool can sensitize the blood vessel to other vasoconstrictor agents. Endogenous pump inhibitors may also stimulate the release of catecholamines from the intramural sympathetic nerve terminals. Studies of a variety of candidate endogenous Na, K pump inhibitors are reviewed. These include presently unidentified substances extracted from human urine, from peritoneal dialysate of hypertensives with renal failure, and from bovine and rat hypothalamus. Additional candidate compounds include ouabain, selected pregnanes and marinobufagenin, a steroid originally identified in the venom of the frog, Bufo marinus.

A new endogenous natriuretic factor: LLU-alpha.

For over three decades, renal physiology has sought a putative natriuretic hormone (third factor) that might control the body's pool of extracellular fluid, an important determinant in hypertension, congestive heart failure, and cirrhosis. In our search for this hormone, we have isolated several pure natriuretic factors from human uremic urine that would appear, alone or in combination, to mark a cluster of phenomena previously presumed to be that of a single "natriuretic hormone." This paper reports the purification, chemical structure, and total synthesis of the first of these compounds, LLU-alpha, which proved to be 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman, presumably a metabolite of gamma-tocopherol. Both natural LLU-alpha and synthetic material are identical (except for optical activity) with respect to structure and biological activity. It appears that the natriuretic activity of LLU-alpha is mediated by inhibition of the 70 pS K+ channel in the apical membrane of the thick ascending limb of the kidney.

Endogenous natriuretic factors 3: isolation and characterization of human natriuretic factors LLU-alpha, LLU-beta 1, and LLU-gamma.

A low molecular weight endogenous substance believed to be responsible for extracellular fluid homeostasis in mammals has been sought for many years. Our goal is to isolate and structurally characterize this putative "natriuretic hormone." We have developed an assay using the conscious rat to measure prolonged natriuresis (Benaksas et al (1993) Life Sciences, 52, 1045-1054), the activity originally described for this putative substance. Using this assay we have identified a number of natriuretic compounds isolated from human uremic urine. The collected urine is processed by ultrafiltration (< or = 3 kDa), gel filtration chromatography (G-25) and extraction with isopropanol and diethyl ether. The organic soluble material is then subjected to sequential high-performance liquid chromatography. We report here the initial characterization of two pure isolates (LLU-alpha and LLU-gamma) obtained by this method, and the structural elucidation of a third pure compound, LLU-beta 1, a natriuretic and previously unreported metabolite of the drug diltiazem.

Characterization of a low molecular weight Na-K-ATPase inhibitor of urinary origin.

It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an "endogenous ouabain."

Biologic and physical characteristics of the non-peptidic, non-digitalis-like natriuretic hormone.

At least three independent groups of natriuretic hormones have been isolated over the past ten years. Two, atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP), are proteins and the third is made up of digitalis-like substances (DLS). The present report concerns the isolation, substantial purification and biologic actions of an entirely different natriuretic hormone (NH) which appears to be steroidal in nature and an isomer of cortisone. The source of NH was uremic urine. Purification involved successive chromatographic steps including gel filtration and multiple HPLC runs through C-18 resins. A translucent crystal ultimately was obtained. The product was examined using mass spectroscopy with trimethylsilyl derivatization. Only one compound was identifiable. The characteristics of the molecule include: a molecular weight, 360.4; a molecular formula, C21H28O5; a steroidal nucleus; UV absorption at 220 and 290 nm; and intrinsic fluorescence. The onset of action occurs within minutes both in the rat and, as previously shown, in several in vitro systems including the frog skin, toad bladder, fibroblasts and renal tubular epithelial cells grown in culture and isolated perfused cortical collecting tubules. In contrast to DLS, NH has been previously shown not to cross react with digoxin antibodies. Moreover, when given to intact rats, it produces a profound natriuresis but little or no kaliuresis. In contrast to ANF and BNP the compound is active orally as well as intravenously. It is clearly different from cortisone, based both on its biologic and mass spectroscopic characteristics.

An intestinal natriuretic factor.

In 1975, reports were published that suggested that the gastrointestinal tract can "taste" the intake of sodium and in some unknown way influence the kidneys to increase sodium excretion. To test whether the intestine contained a natriuretic factor, intestinal tissue from cats was homogenized and fractionated by ultrafiltration to a molecular range of approximately 500-10,000 Da and separated by gel chromatography (Sephadex G25). The fractions were pooled into four large fractions that were assayed for "natriuretic" activity on anesthetized rats. The fraction containing the material with an apparent molecular mass of 500-1,000 Da augmented renal excretion of sodium and water, whereas the other pooled fractions did not exhibit any consistent natriuretic effect. The "natriuretic" fractions from gel filtration were further purified by ion exchange chromatography using a cation exchanger. The natriuretic activity was eluted from the ion exchange chromatography column at a NaCl concentration of 250 mM. Preliminary experiments on Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) suggest that the intestinal influence on renal sodium excretion is more pronounced in SHR than in WKY rats.

Endogenous natriuretic factors. 2: Characterization of natriuretic and vasopressive substances from human uremic urine.

It is our intention to isolate, purify, and characterize the putative low-molecular-weight "natriuretic hormone" responsible for extracellular fluid (ECF) homeostasis. Toward this end, we are purifying from human uremic urine, and identifying endogenous vasopressor and natriuretic compounds. Bioactive components from large volumes of pooled urine were purified by ultrafiltration (< or = 3 kDa), gel filtration chromatography, and sequential reverse-phase and normal-phase high-performance liquid chromatography (HPLC). After each HPLC step, the fractions were evaluated in vivo, were assayed for inhibition of Na+/K(+)-ATPase-mediated 86Rb+ uptake, and were checked for cross-reactivity with an anti-ouabain antibody. Fractions assayed in vivo were identified that induced natriuresis, altered mean arterial pressure, or increased plasma cyclic-GMP. Also, many fractions inhibited Na+/K(+)-ATPase and/or cross-reacted with anti-ouabain antibody. None of the in vitro assays correlates with natriuretic or pressor effects. This plethora of bioactivities, revealed only with increased sample purity, may account for much of the confusion and multiplicity of crude isolates claimed to be the putative hormone. Presently we are attempting to purify and identify these natriuretic materials. One of these, a 3-substituted indole, has been partially characterized.

[Effect of a natriuretic factor of hepatic origin on the indices of water-salt metabolism and blood circulation]. / Vliianie natriureticheskogo faktora pechenochnogo proiskhozhdeniia na pokazateli vodno-solevogo obmena i krovoobrashcheniia.

The influence of natriuretic factor inhibiting the Na--K--ATPase, on the volume-regulating function of kidneys and the hemodynamics was studied in dogs. A single administration of natriuretic factor in a dose increasing the renal excretion of water, sodium and osmotically active substances, affected the hemodynamics. The changes of both the central hemodynamics and of the renal blood circulation were of a shorter duration compared with the changes in renal functions. The activation of water and electrolyte-excreting activity of the kidneys seems to be due to a reduced tubular reabsorption but not to the glomerular filtration.

Partial purification of a sodium pump inhibitor from bovine adenohypophysis. Its comparison with the natriuretic factor isolated from hypothalamus.

Adenohypophysis and hypothalamic bovine tissues were homogenized, lipid extracted, salt removed and loaded onto 2 successive mu Bondapak HPLC columns, semipreparative and analytic, respectively. In vitro sodium-pump inhibitory activity, recovered from each tissue, showed similar chromatographic patterns, but hypothalamus seems to contain a major hydrophobic material which appears at the end of the run, when acetonitrile gradient raised 40% approximately. Digitalis-like activity disappears along the purification procedure, and this fact suggests a clear dissociation between (Na/K)ATPase inhibition and digoxin-like activity, measured as crossing with digoxin antibodies.

Preliminary isolation of mosquito natriuretic factor.

A natriuretic factor that triggers diuresis in isolated Malpighian tubules of the mosquito was isolated from the head of the yellow-fever mosquito Aedes aegypti by passing a saline extract of mosquito heads through low-pressure and then high-pressure liquid chromatography (HPLC) columns. Three fractions with biologic activity eluted during a reverse-phase HPLC linear acetonitrile gradient run. Fraction I depolarized the transepithelial voltage (Vt) of isolated perfused Malpighian tubules but did not not stimulate fluid secretion in the Ramsay assay (J. A. Ramsay, J. Exp. Biol. 31: 104-113, 1954). Fraction II depolarized and fraction III hyperpolarized Vt, and both stimulated fluid secretion three- to fourfold. Even though the effects of fractions II and III on Vt differed, both stimulated fluid secretion by increasing the rate of NaCl secretion without affecting K secretion. The selective stimulation of active secretory Na transport by fraction III is mimicked by cyclic AMP (cAMP), suggesting the second messenger role of cAMP in the effects of fraction III. Because fraction III stimulates a NaCl-rich, as opposed to KCl-rich, fluid, the term mosquito natriuretic factor is proposed for this active fraction.