Pharmacokinetics of pyrazinoyl-guanidine, 3-aminopyrazinoyl-guanidine and their corresponding pyrazinoic acid metabolites in humans and dogs.

Pyrazinoylguanidine (PZG), 3-aminopyrazinoylguanidine (NH2PZG) and their pyrazinoic acid metabolites were measured by a new reverse-phase HPLC method in the serum of dogs and humans after administration of PZG, NH2PZG or 2-pyrazinoic acid (PZA). Kinetic properties of PZG and its principal metabolite, PZA, were studied in normal humans and also in azotemic patients, since PZG acts on renal tubules of patients with kidney failure to increase urea elimination. In humans and dogs, PZG was rapidly hydrolyzed to PZA. The serum half-life (t1/2) of PZG was 1 h. In turn, PZA was metabolized to 5-hydroxy-PZA, but no evidence appeared for conjugation of PZA with glycine. The apparent volume of distribution of PZG and its 3-amino analog, NH2PZG, exceeded that of total body water. In the dog the serum t1/2 for NH2PZG was twice that of PZG. Compared to PZG, NH2PZG and its metabolite, 3-aminopyrazinoic acid, were much stabler in vitro in serum and water.     

Pyrazinoylguanidine: antihypertensive, hypocholesterolemic, and renin effects.

In a single-blind, placebo-controlled study of 12 subjects diagnosed as having mild to moderate hypertension and hypercholesterolemia, pyrazinoylguanidine (PZG) in a dose of 600 mg twice daily for 4 weeks reduced systolic blood pressure and heart rate. Pyrazinoylguanidine also reduced diastolic pressures, but to a lesser extent. Pyrazinoylguanidine reduced total serum cholesterol and low-density lipoprotein (LDL). Regression analysis indicated a dose-dependent reduction of both total cholesterol and LDL by PZG, i.e., the higher the presenting serum concentration, the greater the reduction by PZG. The extent of the reductions produced by PZG in elevated cholesterols and LDLs was highly correlated (r = .949). Normal high-density lipoprotein levels were unchanged by PZG. Pyrazinoylguanidine increased 24-hour urine volume and urinary excretion of sodium. Serum Na+, K+, or Cl- concentrations were unaltered. Means for plasma aldosterone and renin activities tended to decrease, but these trends did not attain statistical significance. Pyrazinoylguanidine was well tolerated. An activity profile that includes antihypertensive effects as well as reduction in hypercholesterolemia without major impact on serum renin or electrolyte balance makes PZG an attractive candidate for the management of hypertension.     

Studies on pyrazinoylguanidine: a novel antihypertensive, hypoglycemic and lipolytic drug intended for adjunctive use in hypertensive patients with type 2 diabetes mellitus

Herein are described the development and certain properties of a new drug, pyrazinoylguanidine (PZG), intended for use as an adjunct in the treatment of hypertensive patients with type 2 diabetes, formerly called noninsulin dependent diabetes mellitus. PZG is an analog of the potassium sparing diuretic, amiloride. However, in diabetic patients, amiloride exacerbates hyperglycemia and hyperlipidemia, whereas PZG reduces them. In several studies, PZG not only reduced elevated blood pressure in subjects with essential hypertension, but also downregulated the glucose fatty acid cycle in hypertensive patients with type 2 diabetes. PZG was well tolerated in all patients, as well as in normal subjects whose blood pressures and glucose metabolism were unaffected by PZG. However, in normal subjects made hyperglycemic by giving them hydrochlorothiazide, coadministration of PZG returned blood glucose concentrations to normal. Mechanisms for these effects of PZG in human subjects were investigated in both normal Sprague-Dawley rats and rats made diabetic with streptozotocin (STZ). In isolated rat adipocytes stimulated with theophylline, PZG downregulated both lipolysis and cyclic AMP concentrations. PZG, as well as insulin, increased adipose cyclic nucleotide phosphodiesterase activity, whereas theophylline reduced it. In perfused rat liver, PZG decreased gluconeogenesis and cyclic AMP concentrations. Collectively, these studies illustrate how the side effects (toxicity) of certain drugs, such as the tendency of thiazide diuretics to cause hyperglycemia and hyperlipidemia, can be modulated and even reversed by slight changes in the chemical structure of the molecule, specifically by removal of the 3,5-diamino and 6-chloro substituents on the benzene ring of amiloride to produce PZG.     

The effects of Escherichia coli heat-stable enterotoxin in renal sodium tubular transport.

To compare the function of sodium transport between intestine and renal tubule, we studied the effect of E. coli STa enterotoxin and 8-bromo cyclic GMP in perfused rat kidneys. Infusion of STa enterotoxin (0.017 and 0.1 micrograms/ml) caused a dose and time dependent decrease in total renal sodium tubular transport. The major site of STa effect was at the renal proximal tubule. Similar to Sta enterotoxin, 8-bromo cyclic GMP (10(-5) M) caused a significant decrease of fractional renal sodium proximal tubule transport. In contrast to STa enterotoxin, infusion of 8-bromo cyclic GMP resulted in a significant but short lasting (30 min.) increase in glomerular filtration rate. STa enterotoxin also decreased significantly the renal tissue potassium. This STa effect was related to a significant decrease in renal potassium tubular transport, resulting also in an increase of urinary potassium excretion. These studies demonstrate the specific functional effect of STa enterotoxin in promoting the decrease in renal proximal tubular sodium transport, similar to 8-bromo cyclic GMP. In perfused rat kidneys STa also decreased tissue potassium, mainly by a decrease in potassium transport and increase in urinary potassium excretion. These effects suggest the existence of an endogenous peptide resembling STa enterotoxin, that regulates the function of renal sodium tubular transport.     

The Effects of Escherichia coli Heat-Stable Enterotoxin in Renal Sodium Tubular Transport

Abstract: To compare the function of sodium transport between intestine and renal tubule, we studied the effect of E. coli STa enterotoxin and 8-bromo cyclic GMP in perfused rat kidneys. Infusion of STa enterotoxin (0.017 and 0.1 μg/ml) caused a dose and time dependent decrease in total renal sodium tubular transport. The major site of STa effect was at the renal proximal tubule. Similar to Sta enterotoxin, 8-bromo cyclic GMP (10^–5 M) caused a significant decrease of fractional renal sodium proximal tubule transport. In contrast to STa enterotoxin, infusion of 8-bromo cyclic GMP resulted in a significant but short lasting (30 min.) increase in glomerular filtration rate. STa enterotoxin also decreased significantly the renal tissue potassium. This STa effect was related to a significant decrease in renal potassium tubular transport, resulting also in an increase of urinary potassium excretion. These studies demonstrate the specific functional effect of STa enterotoxin in promoting the decrease in renal proximal tubular sodium transport, similar to 8-bromo cyclic GMP. In perfused rat kidneys STa also decreased tissue potassium, mainly by a decrease in potassium transport and increase in urinary potassium excretion. These effects suggest the existence of an endogenous peptide resembling STa enterotoxin, that regulates the function of renal sodium tubular transport.     

多枝雾水葛凝胶膏剂抗皮肤感染的药效学研究

目的：研究多枝雾水葛凝胶膏剂（Pouzolzia zeylanica var.microphylla gel，PZG）对皮肤感染性疾病的治疗作用。方法：建立金黄色葡萄球菌诱导的小鼠皮下脓肿模型和大鼠皮肤创伤性感染溃疡模型，通过检测体质量、皮肤脓肿体积或溃疡面积愈合率、皮肤细菌逆培养和局部皮肤病理形态、羟脯氨酸、肿瘤坏死因子-α（tumor necrosis factor-α，TNF-α）和白介素-10（interleukin-10，IL-10）含量等指标，考察PZG对感染性皮下脓肿和皮肤溃疡的治疗作用。结果：PZG能显著缩小皮下脓肿体积，提高皮肤溃疡面积愈合率，且有一定的量效关系；PZG可抑制皮肤感染部位的细菌生长，改善局部皮肤病理形态；PZG可降低溃疡部位TNF-α和IL-10水平，增加组织中羟脯氨酸的含量，促进溃疡愈合。结论：中药有效部位制剂PZG具有良好的抗皮肤感染作用，机制可能与其综合的抗菌、抗炎作用有密切关系。     

Renal sodium handling for body fluid maintenance and blood pressure regulation

Renal sodium handling is an essential physiologic function in mammal for body fluid maintenance and blood pressure regulation. Recent advances in molecular biology have led to the identification of kidney-specific sodium transporters in the renal tubule, thereby supplying vast information for renal physiology as well as systemic physiology. Renal urinary concentration for body fluid maintenance is accomplished by counter current multiplication in the distal tubule. Sodium transport in the thick ascending limb of Henle (TAL) is the initial process of this system. We have demonstrated that renal urinary concentration is regulated in part by the expression of the Na(+)-K(+)-2Cl(-) co-transporter (BSC1) in TAL, by showing two mechanisms of BSC1 expression: pitressin vasopressin (AVP)-dependent and AVP-independent mechanisms. Two additional findings, namely, a lack of the ability to increase BSC1 expression leads to urinary concentrating defect and an enhanced BSC1 expression underlies the edema-forming condition, confirm the close association between sodium handling in TAL and body fluid accumulation. The lines of evidence from our genetic studies of the general Japanese population suggest the importance of mendelian hypertension genes in the genetic investigation of essential hypertension. Because those genes directly or indirectly regulate sodium transport by the Na-Cl co-transporter or the epithelial sodium channel in the distal convoluted tubule to the collecting duct (distal tubular segments after TAL), sodium handling in this part of the renal tubule may be, at least in part, involved in blood pressure regulation. The unveiling of such physiologic roles of sodium handling based on the sodium transporters or on the tubular segments may lead to a better understanding of systemic physiology as well as to the development of novel therapy for body fluid or blood pressure disorders.     

Renal epidermal growth factor receptor: its role in sodium and water homeostasis in diabetic nephropathy

1. Volume expansion is observed in animal and human models of diabetic nephropathy, which is in a large part a result of disordered renal tubular cell sodium and water transport. 2. Sodium transport in the proximal tubule is increased in diabetes mellitus as a result of enhanced activity of the sodium-hydrogen exchanger-3 (NHE3), the key transporter for transcellular reabsorption of sodium. Transactivation of the epidermal growth factor receptor (EGFR) by factors inherent in the milieu of diabetes mellitus increases serum glucocorticoid regulated kinase-1 (Sgk1), a key regulator of NHE3. 3. Enhanced sodium and water reabsorption, occurring as a consequence of endogenous or pharmacological stimulation of the peroxisome proliferator-activated receptor gamma is Sgk1 mediated. 4. EGFR inhibitors, which are currently used clinically to treat malignancies, might have potential in attenuating the cellular mechanisms responsible for thiazolidinedione (TZD)-mediated sodium and water transport in diabetes. 5. In the present review, the authors focus on the importance of the EGFR in sodium and water uptake in the proximal tubule in the environment of pathophysiological and pharmacological influences.     

Acute effects of gentamicin on thick ascending limb function in the rat

It is well established that the aminoglycoside antibiotics can adversely affect proximal tubule function. Predominantly indirect evidence suggests that aminoglycosides may also affect function of more distal nephron segments. The present study utilized whole kidney clearance, in vivo micropuncture and in vitro microperfusion to directly determine whether acute gentamicin treatment affects sodium chloride transport in the thick ascending limb of the loop of Henle. Gentamicin (25 mg/kg) significantly increased urine flow, as well as sodium, potassium and chloride excretion within 15 min of intravenous injection. Glomerular filtration rate and proximal tubule fluid reabsorption were not altered by acute gentamicin treatment. In contrast, both fractional and absolute loop chloride transport was significantly decreased. In the in vitro microperfused medullary thick ascending limb, luminal but not basolateral administration of gentamicin (1 mM) significantly decreased chloride reabsorption when compared to time controls. These data suggest that the increased urine and electrolyte excretion associated with acute gentamicin treatment is, at least in part, a consequence of decreased transport in the thick ascending limb of Henle's loop.     

A novel SGLT is expressed in the human kidney

Selective inhibitors of sodium-glucose cotransporter 2 (SGLT2)-mediated reabsorption of glucose in the proximal tubule of the kidney are being developed for the treatment of diabetes. SGLT2 shares high degree of homology with SGLT3; however, very little is known about the expression and functional role of SGLT3 in the human kidney. Indeed, the SGLT2 inhibitors that are currently in clinical trials might affect the expression and/or the activity of SGLT3. Therefore, the present study examined the expression of SGLT3 mRNA and protein in human kidney and in a human proximal tubule HK-2 cell line. The results indicated that human SGLT3 (hSGLT3) message and protein are expressed both in vivo and in vitro. We also studied the activity of hSGLT3 protein following its over-expression in mammalian kidney-derived COS-7 cells and in HK-2 cells treated with the imino sugar deoxynojirimycin (DNJ), a potent agonist of hSGLT3. Over-expression of hSGLT3 in COS-7 cells increased intracellular sodium concentration by 3-fold without affecting glucose transport. Activation of hSGLT3 with DNJ (50μM) increased sodium uptake in HK-2 cells by 5.5 fold and this effect could be completely blocked with SGLT inhibitor phlorizin (50μM). These results suggest that SGLT3 is expressed in human proximal tubular cells where it serves as a novel sodium transporter. Up-regulation of the expression of SGLT3 in the proximal tubule in diabetic patients may contribute to the elevated sodium transport in this segment of the nephron that has been postulated to promote hyperfiltration and renal injury.     

新型痛风治疗药物lesinuard sodium

lesinuard sodium是一种新型的痛风治疗药物,于2008年由Ardea Biosciences公司研发。该药物主要通过抑制尿酸盐转运蛋白1（URAT1）增加尿酸的排泄来治疗痛风。URAT1被认为是存在于肾脏中用于转运尿酸盐的主要蛋白,能够将尿酸从管腔转入近曲小管上皮细胞并转化为单羧酸盐。临床研究显示,lesinuard sodium可被良好耐受,且能剂量相关性地降低血浆中的尿酸水平。主要介绍lesinuard sodium的药物概况、相关背景、合成路线、药理作用、临床前及临床试验的研究、安全性评价等方面。     

Regulation of renal tubular sodium transport by angiotensin II and atrial natriuretic factor

1. The effects of angiotensin II (AngII) on water and electrolyte transport are biphasic and dose-dependent, such that low concentrations (10(-12) to 10(-9) mol/L) stimulate reabsorption and high concentrations (10(-7) to 10(-6) mol/L) inhibit reabsorption. Similar dose-response relationships have been obtained for luminal and peritubular addition of AngII. 2. The cellular responses to AngII are mediated via AT(1) receptors coupled via G-regulatory proteins to several possible signal transduction pathways. These include the inhibition of adenylyl cyclase, activation of phospholipases A(2), C or D and Ca(2+) release in response to inositol-1,4,5,-triphosphate or following Ca(2+) channel opening induced by the arachidonic acid metabolite 5,6,-epoxy-eicosatrienoic acid. In the brush border membrane, transduction of the AngII signal involves phospholipase A(2), but does not require second messengers. 3. Angiotensin II affects transepithelial sodium transport by modulation of Na(+) /H(+) exchange at the luminal membrane and Na(+)/HCO(3) cotransport, Na(+)/K(+)-ATPase activity and K(+) conductance at the basolateral membrane. 4. Atrial natriuretic factor (ANF) does not appear to affect proximal tubular sodium transport directly, but acts via specific receptors on the basolateral and brush border membranes to raise intracellular cGMP levels and inhibit AngII-stimulated transport. 5. It is concluded that there is a receptor-mediated action of ANF on proximal tubule reabsorption acting via elevation of cGMP to inhibit AngII-stimulated sodium transport. This effect is exerted by peptides delivered at both luminal and peritubular sides of the epithelium and provides a basis for the modulation by ANF of proximal glomerulotubular balance. The evidence reviewed supports the concept that in the proximal tubule, AngII and ANF act antagonistically in their roles as regulators of extracellular fluid volume.     

硒对顺铂肾毒性的防护作用

大鼠亚硒酸钠2mg·kg~1·d~1 ip,连续2d,d 2给药后4 h ip顺铂5 mg/kg,能明显降低由ip顺铂引起的尿量、尿NAG活性及血尿素氮和血浆肌酐的升高,使尿渗透浓度维持正常水平,并使顺铂引起的大鼠肾脏近曲小管上皮细胞变性坏死明显减轻。亚硒酸钠在减少顺铂肾毒性的同时并不影响其抗癌效应。     

Correlation of the in vivo and in vitro renal toxicity of S-(1,2-dichlorovinyl)-L-cysteine

The major site at which vinyl cysteine conjugates exert nephrotoxicity is the proximal tubule. Since this is the site of all active anion and cation transport, tubule transport integrity was used to assess nephrotoxicity. Tubules were isolated from young rabbits to study the in vivo and in vitro nephrotoxicity of the conjugate, dichlorovinyl cysteine (DCVC). In vivo exposure to DCVC caused necrosis in the pars recta region of the proximal tubules (20-100 mg/kg ip) and a dose-dependent decrease in tubular active transport. Addition of DCVC to the perfused kidney and tubule suspensions resulted in similar decreases in tubular organic ion transport. At 0.01 mM DCVC, transport was similar to controls while 1 mM DCVC completely inhibited active accumulation of the organic ions. Thus kidney tubule active transport is similarly inhibited in vivo and in vitro by DCVC indicating that bioactivation of DCVC and inhibition of active transport occur directly in the renal tubule.     

Effect of 1,4-dimorpholino-7-(4-hydroxyphenyl)pyrido[3,4-d]) pyridazine [DS-511(4'-OH)] on the transepithelial transport of sodium and water and the permeability to urea in the toad urinary bladder.

To elucidate the mechanism of the inhibitory action of 1,4-dimorpholino-7-phenylpyrido[3,4-d]pyridazine (DS-511) on water and sodium reabsorption at the renal tubules, the effect of DS-511 (4'-OH), which is similar in diuretic effect to but more water-soluble than DS-511, on the transepithelial transport of sodium and water and permeability to urea was studied in isolated toad urinary bladder. Application of DS-511(4'-OH) at concentrations above 2 x 10(-4) mol/l to the serosal side of the bladder depressed the transepithelial potential difference, short circuit current (SCC), and membrane conductance as well as the increased response of the SCC to arginine vasopressin (AVP) and cyclic AMP. The effect of DS-511 (4'-OH) applied to the mucosal side was delayed in onset and less pronounced. Neither serosal nor mucosal 10(-3) mol/l DS-511(4'-OH) depressed the increased response of the SCC to amphotericin B. 2 x 10(-4) mol/l DS-511 (4'-OH) applied to the serosal side did not affect osmotic water flow, but potentiated the increase in water flow caused by AVP. Basal urea permeability as well as the increase in urea permeability caused by AVP were depressed by serosal 10(-3) mol/l DS-511 (4'-OH). The results show that DS-511(4'-OH) has two actions, the depression of the transepithelial transport of sodium and urea, and the potentiation of the increased water permeability caused by AVP.     

The sites of action of bumetanide in man

Some pharmacological effects of bumetanide were investigated in 8 healthy volunteers. It was a very potent diuretic, as judged by the fact that, at peak effects during water diuresis, 20% of filtered sodium was excreted in the urine. During water diuresis it reduced free water clearance by approximately 25% and during hydropoenia it reduced the reabsorption of solute free water to a similar extent, indicating a major site of action on the ascending limb of the loop of Henle. A significant phosphaturia was induced during the period of maximum diuresis suggesting an additional action on the proximal tubule. The excretion of urinary titratable acid and ammonium as well as potassium were increased, indicating that the drug did not have a significant effect on sodium transport in the distal tubule. Glomerular filtration rate was not affected but the drug caused a decrease in the renal clearance of uric acid.     

Pharmacologic probing of amphotericin B-induced renal dysfunction in the neonatal rat

Acetazolamide, furosemide, chlorothiazide, and amiloride are pharmacologic agents that act primarily in the proximal tubule, loop of Henle, early distal tubule and late distal tubule and collecting duct, respectively. In order to investigate the renal pathophysiology induced by amphotericin B, these diuretic agents were used as probes of discrete segments of the nephron in the neonatal rat. Six-day-old rats were treated with amphotericin B (20 mg/kg, sc) or the vehicle. Twenty-four hours later, when evidence of amphotericin B-induced renal pathophysiology is detectable, the responses to the diuretic agents were assessed in a 2-hr clearance test, during which creatinine clearance (CCr) and the fractional excretion (FE) of water and various components of the filtrate were determined. Amphotericin B induced alterations in basal function including azotemia, hypostenuria, increases FE water and electrolytes, and a decreased FE urea (although CCr was normal). The diuretic responses to furosemide, chlorothiazide, and amiloride were not altered, indicating that the functional viability of the respective tubular segments was not affected by amphotericin B treatment. Although the maximal response to acetazolamide also remained unchanged in amphotericin B-treated pups, there was an attenuation in the half-maximal response, reflecting an apparent shift in the sensitivity to acetazolamide. All of the diuretic agents elicited an increase in urea excretion in amphotericin B-treated pups such that FE urea approached control values. Additionally, the magnitude of this increase was proportional to the magnitude of the increase in water excretion induced by each diuretic agent. These results indicate a disruption of urea recycling in the nephron and support the hypothesis that amphotericin B acts to increase the permeability of the distal tubule to urea. Thus, results from this study demonstrate the usefulness of pharmacologic agents as functional probes in the characterization of specific components of renal pathophysiology.     

Correlation of the in vivo and in vitro Renal Toxicity of S-(1,2-Dichlorovinyl)-L-Cysteine

ABSTRACT

The major site at which vinyl cysteine conjugates exert nephrotoxicity is the proximal tubule. Since this is the site of all active anion and cation transport, tubule transport integrity was used to assess nephrotoxicity. Tubules were isolated from young rabbits to study the in vivo and in vitro nephrotoxicity of the conjugate, dichlorovinyl cysteine (DCVC). In vivo exposure to DCVC caused necrosis in the pars recta region of the proximal tubules (20–100 mg/kg ip) and a dose-dependent decrease in tubular active transport. Addition of DCVC to the perfused kidney and tubule suspensions resulted in similar decreases in tubular organic ion transport. At 0.01 mM DCVC, transport was similar to controls while 1 mM DCVC completely inhibited active accumulation of the organic ions. Thus kidney tubule active transport is similarly inhibited in vivo and in vitro by DCVC indicating that bioactivation of DCVC and inhibition of active transport occur directly in the renal tubule.     

Role of cytochrome P450 metabolites of arachidonic acid in hypertension

Considerable evidence has accumulated over the last decade implicating a role of cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA) in the pathogenesis of hypertension. Indeed, 20-hydroxyeicosatetraenoic acid (20-HETE) is produced by vascular smooth muscle (VSM) cells and is a potent vasoconstrictor that depolarizes VSM by blocking large conductance Ca+-activated K2+ channels. In contrast, epoxyeicosatrienoic acids (EETs) are synthesized by the vascular endothelium and have opposite effects on VSM (hyperpolarization and vasodilatation). Inhibition of the synthesis of 20-HETE attenuates myogenic tone and autoregulation of blood flow and modulates vascular responses to vasodilators (NO and CO) and vasoconstrictors (angiotensin II, endothelin). In the kidney, 20-HETE inhibits sodium transport in the proximal tubule by blocking Na+-K+-ATPase activity. In the thick ascending limb of the loop of Henle, 20-HETE inhibits Na+-K+-2Cl- transport, in part, by blocking a 70 pS apical K+ channel. EETs are produced in the proximal tubule where they inhibit Na+-H+ exchange and in the collecting duct where they inhibit sodium and water transport. Numerous studies have established that the formation of EETs and 20-HETE and the expression of CYP enzymes are altered in the kidney in many genetic and experimental animal models of hypertension and in some forms of human hypertension. However, the functional significance of these changes remains to be determined. Given the importance of this pathway in the control of renal function and vascular tone, it is likely that alterations in the renal formation of CYP-dependent metabolites of AA will be shown to participate in the development of hypertension in many of these models.     

Modulation by locally produced luminal angiotensin II of proximal tubular sodium reabsorption via an AT1 receptor.

The concentration of angiotensin II reported in proximal tubular fluid in anaesthetized rats is considerably higher than in plasma, indicating secretion of this peptide into the tubular lumen. Shrinking split-drop micropuncture was used to examine the effect of endogenous angiotensin on sodium and water absorption in the proximal convoluted tubule. Addition of losartan, a nonpeptide AT1 receptor blocker, to intratubular fluid increased fluid uptake by 15.7 +/- 3.9% (10(-5) M) and 24.7 +/- 9.4% (10(-4) M) whereas the AT2 inhibitor, PD123319 had no effect. We conclude that angiotensin II is secreted into proximal tubular fluid and, in the anaesthetized rat, is maintained at a concentration that inhibits sodium and water transport via AT1 receptors.