The endocrine heart and natriuretic peptides: histochemistry, cell biology, and functional aspects of the renal urodilatin system

This review focuses on some selected aspects of the endocrine heart and natriuretic peptides. The endocrine heart is composed of specific myoendocrine cells of the cardiac atria. The myoendocrine cells synthesize and secrete the natriuretic peptide hormones which exhibit natriuretic, diuretic, and vasorelaxant properties. Immunohistochemical analyses show that natriuretic peptides of the A-type and B-type are localized not only in the specific granules of these myoendocrine cells but also in many other organs including the brain, adrenal medulla, and kidney. Also, their receptors are detected in many organs showing the multiple functions of these regulatory peptides. Of the members of the natriuretic peptide family, ANP (ANP for atrial natriuretic peptide; also denominated cardiodilatin, CDD), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and the A-type, including its renal form, urodilatin, are emphasized in this review. Urodilatin is localized in the kidney, differentially processed, and secreted into the urine. The intrarenal synthesis and secretion is the basis for a paracrine system regulating water and sodium reabsorption at the level of the collecting duct. CDD/ANP-1-126, cleaved from a precursor of 126 amino acids in the heart to a 28-amino acid-containing circulating molecular form (CDD/ANP-99-126), and urodilatin (CDD/ANP-95-126) share similar biochemical features and biological functions, but urodilatin may be more involved in the regulation of body fluid volume and water-electrolyte excretion, while circulating CDD/ANP-99-126 is responsible for blood pressure regulation. The physiological and pharmacological properties of these peptides have great clinical impact, and as a consequence urodilatin is involved in drug development for the treatment of acute renal failure, cardiomyopathia, and acute asthma.     

Mechanical Properties of Large Arteries in Mother and Fetus during Normal and Diabetic Pregnancy

Cardiodilatin (CDD)/atrial natriuretic peptide (ANP) is a 28-amino acid peptide hormone known to be synthesized in the heart of a large number of different vertebrates. It plays an important role in the regulation of blood pressure and natriuresis/diuresis. Since the cardiovascular system of the horse has to meet the highest requirements concerning its physiological performance, we intended to characterize the cardiodilatin/atrial natriuretic peptide system of this species. By means of immunohistochemistry and immunoelectron microscopy, we precisely identified auricular cardiocytes as the loci of CDD/ANP synthesis. Using aortic smooth muscle relaxation assay and CDD/ANP-ELISA, we succeeded in isolating the biologically active prohormone. We subsequently cloned the equine cDNA of the CDD/ANP precursor protein and deduced its primary sequence. The entire precursor protein is in good agreement with the CDD/ANP prohormones of other mammals. The deduced theoretical average Mr of equine CDD/ANP-1-126 is 13,764, corresponding to the molecular weight of purified peptide determined by ESI-MS. Our findings suggest that equine CDD/ANP is produced in auricular cardiocytes and the predominant storage form of CDD/ANP in the auricle is the prohormone CDD/ANP-1-126.     

Cannabinoid CB1 receptor and endothelium-dependent hyperpolarization in guinea-pig carotid, rat mesenteric and porcine coronary arteries

1. The purpose of these experiments was to determine whether or not the endothelium-dependent hyperpolarizations of the vascular smooth muscle cells (observed in the presence of inhibitors of nitric oxide synthase and cyclo-oxygenase) can be attributed to the production of an endogenous cannabinoid. 2. Membrane potential was recorded in the guinea-pig carotid, rat mesenteric and porcine coronary arteries by intracellular microelectrodes. 3. In the rat mesenteric artery, the cannabinoid receptor antagonist, SR 141716 (1 microM), did not modify either the resting membrane potential of smooth muscle cells or the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (17.3 +/- 1.8 mV, n = 4 and 17.8 +/- 2.6 mV, n = 4, in control and presence of SR 141716, respectively). Anandamide (30 microM) induced a hyperpolarization of the smooth muscle cells (12.6 +/- 1.4 mV, n = 13 and 2.0 +/- 3.0 mV, n = 6 in vessels with and without endothelium, respectively) which could not be repeated in the same tissue, whereas acetylcholine was still able to hyperpolarize the preparation. The hyperpolarization induced by anandamide was not significantly influenced by SR 141716 (1 microM). HU-210 (30 microM), a synthetic CB1 receptor agonist, and palmitoylethanolamide (30 microM), a CB2 receptor agonist, did not influence the membrane potential of the vascular smooth muscle cells. 4. In the rat mesenteric artery, the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (19.0 +/- 1.7 mV, n = 6) was not altered by glibenclamide (1 microM; 17.7 +/- 2.3 mV, n = 3). However, the combination of charybdotoxin (0.1 microM) plus apamin (0.5 microM) abolished the acetylcholine-induced hyperpolarization and under these conditions, acetylcholine evoked a depolarization (7.7 +/- 2.7 mV, n = 3). The hyperpolarization induced by anandamide (30 microM) (12.6 +/- 1.4 mV, n = 13) was significantly inhibited by glibenclamide (4.0 +/- 0.4 mV, n = 4) but not significantly affected by the combination of charybdotoxin plus apamin (17.3 +/- 2.3 mV, n = 4). 5. In the guinea-pig carotid artery, acetylcholine (1 microM) evoked endothelium-dependent hyperpolarization (18.8 +/- 0.7 mV, n = 15). SR 141716 (10 nM to 10 microM), caused a direct, concentration-dependent hyperpolarization (up to 10 mV at 10 microM) and a significant inhibition of the acetylcholine-induced hyperpolarization. Anandamide (0.1 to 3 microM) did not influence the membrane potential. At a concentration of 30 microM, the cannabinoid agonist induced a non-reproducible hyperpolarization (5.6 +/- 1.3 mV, n = 10) with a slow onset. SR 141716 (1 microM) did not affect the hyperpolarization induced by 30 microM anandamide (5.3 +/- 1.5 mV, n = 3). 6. In the porcine coronary artery, anandamide up to 30 microM did not hyperpolarize or relax the smooth muscle cells. The endothelium-dependent hyperpolarization and relaxation induced by bradykinin were not influenced by SR 141716 (1 microM). 7. These results indicate that the endothelium-dependent hyperpolarizations, observed in the guinea-pig carotid, rat mesenteric and porcine coronary arteries, are not related to the activation of cannabinoid CB1 receptors.     

Understanding the interactions between physician assistants and their supervising physicians in the provision of patient care

Both contractile and relaxant responses to tetrapentylammonium ions (TPA+) were studied in rat isolated mesenteric artery. TPA+ (5-10 micromol/l) caused a sustained increase of muscle tension. The contractile effect of TPA+ (10 micromol/l) was dependent upon the presence of extracellular Ca2+ but independent of the presence of endothelium. TPA+ (10-50 micromol/l) induced biphasic contraction, and the amplitude of peak and sustained tension decreased with increasing TPA+ concentration. TPA+ (100-300 micromol/l) only produced monophasic contraction. TPA+ (50 micromol/l) abolished the transient contraction induced by caffeine (10 mmol/l) or phenylephrine (1 micromol/l) in the absence of extracellular Ca2+. Nifedipine and verapamil concentration-dependently reduced the TPA+-induced contraction with respective IC50 values of 1.34 +/- 0. 24 and 9.46 +/- 1.36 nmol/l, these values were similar to 1.35 +/- 0. 21 and 16.07 +/- 1.71 nmol/l, respectively, for the inhibitory effects of nifedipine and verapamil on the high K+ (60 mmol/l)-induced contraction. TPA+ (>10 micromol/l) concentration-dependently reduced the phenylephrine (1 micromol/l)-, U46619 (30 nmol/l)-, endothelin I (10 nmol/l)- and high K+ (60 mmol/l)-induced sustained tension with respective IC50 values of 53. 7 +/- 9.5, 31.9 +/- 5.3, 30.9 +/- 3.4 and 20.9 +/- 2.8 micromol/l. The present results indicate that TPA+ at low concentrations could contract the arterial smooth muscle probably through promoting Ca2+ influx. At higher concentrations (>20 micromol/l), TPA+ relaxes arterial smooth muscle probably through inhibition of both nifedipine-sensitive Ca+ channels and internal Ca2+ release. TPA+, unlike other quaternary ammonium ions, could therefore act at multiple sites in arterial smooth muscle.     

Effect of alkalinization of cytosolic pH by amines on intracellular Ca2+ activity in HT29 cells

The effect of secondary, tertiary and quaternary methyl- and ethylamines on intracellular pH (pHi) and intracellular Ca2+ activity ([Ca2+]i) of HT29 cells was investigated microspectrofluorimetrically using pH- and Ca2+- sensitive fluorescent indicators, [i.e. 2', 7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) and fura-2 respectively]. Membrane voltage (Vm) was studied by the patch-clamp technique. Secondary and tertiary amines led to a rapid and stable concentration-dependent alkalinization which was independent of their pKa value. Trimethylamine (20 mmol/l) increased pHi by 0.78 +/- 0.03 pH units (n = 9) and pH remained stable for the application time. Removal led to an undershoot of pHi and a slow and incomplete recovery: pHi stayed 0.26 +/- 0.06 pH units more acid than the resting value. The quaternary amines, tetramethyl- and tetraethylamine were without influence on pHi. All tested secondary and tertiary amines (dimethyl-, diethyl-, trimethyl-, and triethyl-amine) induced a [Ca2+]i transient which reached a peak value within 10-25 s and then slowly declined to a [Ca2+]i plateau. The initial Delta[Ca2+]i induced by trimethylamine (20 mmol/l) was 160 +/- 15 nmol/l (n = 17). The [Ca2+]i peak was independent of the Ca2+ activity in the bath solution, but the [Ca2+]i plateau was significantly lower under Ca2+-free conditions and could be immediately interrupted by application of CO2 (10%; n = 6), a manoeuvre to acidify pHi in HT29 cells. Emptying of the carbachol- or neurotensin-sensitive intracellular Ca2+ stores completely abolished this [Ca2+]i transient. Tetramethylamine led to higher [Ca2+]i changes than the other amines tested and only this transient could be completely blocked by atropine (10(-6) mol/l). Trimethylamine (20 mmol/l) hyperpolarized Vm by 22.5 +/- 3.7 mV (n = 16) and increased the whole-cell conductance by 2.3 +/- 0.5 nS (n = 16). We conclude that secondary and tertiary amines induce stable alkaline pHi changes, release Ca2+ from intracellular, inositol-1,4, 5-trisphosphate-sensitive Ca2+ stores and increase Ca2+ influx into HT29 cells. The latter may be related to both the store depletion and the hyperpolarization.     

Renal and vascular actions of equol in the rat

BACKGROUND: The urinary isoflavonoid equol inhibits membrane Na-K-Cl cotransporters at similar concentrations to those at which furosemide inhibits them, but the significance of this action is not known. OBJECTIVE: To investigate the potential salidiuretic and vascular actions of equol in the rat. METHODS: Renal functioning was assessed in vitro in the isolated perfused kidney and in vivo in conscious rats. The vascular contractility of isolated aorta was assessed. RESULTS: In the isolated perfused kidney equol was concentrated 50- to 70-fold in the urinary fluid, it was 3-4 times less potent than furosemide at increasing diuresis, natriuresis and kaliuresis (the difference was due to its higher protein-binding affinity), and it induced a modest but significant increase in glomerular filtration rate. In vivo, orally administered equol was a modest natriuretic agent, about 8-fold less potent than orally administered furosemide (in molar terms). In isolated aortic rings precontracted by administration of phenylephrine, administration of equol relaxed the contracted aorta at 10-fold lower concentrations (concentration for half-maximal activity 58.9 +/- 16 micromol/l, n = 3) than did furosemide (concentration for half-maximal activity 633 +/- 145 micromol/l, n = 3). CONCLUSIONS: Equol is a modest natriuretic and vasorelaxant agent in the rat. Further studies are required in order to investigate the potential natriuretic and perhaps hypotensive actions of dietary equol precursors (daidzein).     

Urinary and plasma urodilatin measured by a direct RIA using a highly specific antiserum

Urodilatin (95-126) (URO) appears to play a major physiologic role in fluid homeostasis and produces major changes when administered intravenously. Here we describe a monospecific, high-affinity antiserum against URO with no cross-reactivity (<0.01%) against the structural highly homologous atrial natriuretic peptide 99-126 (ANP-99-126), ANP analogs, and related peptides such as brain natriuretic peptide. A competitive RIA was developed, based on this antiserum. Urine samples with or without ethanol extraction and plasma samples without pretreatment were analyzed by the RIA, which had a detection limit of 10.5 ng/L, a linear measuring range between 10.5 and 1000 ng/L, and recoveries of 93-102% in urine and 90-104% in plasma. The intraassay CVs were 8.2% and 8.1% for urine samples with 269 and 669 ng/L URO; the interassay CV was 9.7% at 839 ng/L. Using this assay, we present URO data for urine from healthy volunteers receiving low and routine sodium diets and from clinical urine specimens; we also present pharmacokinetic data for URO in plasma from patients suffering from bronchial asthma and treated by URO infusion.     

Adrenomedullin, endothelin, neuropeptide Y, atrial, brain, and C-natriuretic prohormone peptides compared as early heart failure indicators

OBJECTIVES:The present investigation was designed to determine the best endogenous plasma marker of early congestive heart failure (CHF). METHODS: Forty volunteers with mild CHF (New York Heart Association Class I, n = 12), moderate (Class II, n = 8), or severe (Class III and Class IV, each = n of 5) and 10 age-matched healthy individuals had the simultaneous evaluation of their respective plasma samples by the following radioimmunoassays: atrial natriuretic peptide, ANP; three N-terminal ANP prohormone assays, i.e., proANPs 1-30, 31-67, and 79-98 with the numbers referring to their amino acid (a.a.) sequences in their 126 a.a. prohormone; brain (BNP) and C-natriuretic peptides; N-terminal BNP prohormone; adrenomedullin; neuropeptide Y and endothelin. RESULTS: ProANPs 31-67, 1-30 and 79-98 had 100% (P = 0.01), 83% (P = 0.09) and 50% (P = 0.74) sensitivity in differentiating Class I CHF subjects from healthy subjects. The ANP, BNP, NT-proBNP, CNP, adrenomedullin, neuropeptide Y, and endothelin assays could not differentiate mild CHF subjects from healthy individuals. Logistic regression analysis revealed that only proANP 31-67 significantly (P = 0.0001) discriminated between early CHF (5226 +/- 377 pg/ml) and healthy individuals (1595 +/- 157 pg/ml). The positive and negative predicative values of proANP 31-67 were excellent (100% for each). The peptides measured in these assays were found to be independent markers of CHF with respect to left ventricular ejection fraction. CONCLUSIONS: ProANPs 31-67 is the most sensitive marker in discriminating NYHA Class I CHF subjects from healthy individuals. The ANP, BNP, NT-proBNP, CNP, adrenomedullin, neuropeptide Y and endothelin radioimmunoassays cannot discern mild CHF. These peptides are independent of left ventricular ejection fraction.     

Solid phase organic synthesis of polyamine derivatives and initial biological evaluation of their antitumoral activity

The hyperpolarization-activated inward current (If) has been discussed to contribute to arrhythmias in human atrial myocardium. If was found to be increased by beta-adrenergic stimulation. In the present study, we evaluate the modulation of If by carbachol, adenosine and by class Ic, III and IV antiarrhythmic drugs in isolated human atrial myocytes. The whole-cell patch-clamp technique was used to record If in isolated myocytes from 18 human right atrial appendages. A typical time- and voltage-dependent hyperpolarization-activated inward current could be recorded in all cells investigated (n=56). Mean current density recorded at -130 mV was -2.8+/-1.2 pApF(-1). Both adenosine and carbachol were found to directly inhibit If in human atrial myocytes by shifting the activation curves to more negative potentials. Adenosine 10(-5) mol/l shifted the potential of half-maximal activation by -5.9+/-0.4 mV from -99.4+/-0.6 mV to -105.3+/-0.4 mV (n=8; P<0.05), and carbachol 10(-5) mol/l by -5.7+/-0.5 mV from -99.2+/-0.5 mV to -104.9+/-0.6 mV (n=6; P<0.05). The concentration-response curve of adenosine calculated by a Hill function yielded a half-maximal effect of adenosine (EC50) at a concentration of 3.6+/-0.5 micromol/l, a maximal shift of -6.5+/-0.3 mV, and a Hill coefficient (h) of 2.40. We did not observe any effect of flecainide (10(-5) mol/l; n=8), sotalol (10(-5) mol/l; n=6), amiodarone (10(-5) mol/l; n=6) or verapamil (10(-5) mol/l; n=5) on If in human atrial myocytes. However, propafenone (10(-5) mol/l) was found to reversibly reduce If current size (9/13 cells) by shifting the activation curve by -5.2+/-0.4 mV (P<0.05). In human atria adenosine- and muscarinic receptor stimulation might function as endogenous protective mechanisms inhibiting the initiation of ectopic tachycardia by reducing If current size. Propafenone may be more effective in some patients with atrial tachycardias that do not respond to other class Ic, III and IV antiarrhythmic drugs. However, it has yet to be defined whether these agents suppress atrial tachycardias via an inhibition of If in vivo.     

Ca2+-independent phospholipase A2 contributes to the insulinotropic action of cholecystokinin-8 in rat islets: dissociation from the mechanism of carbachol

Insulin secretion induced by cholecystokinin-8 (CCK-8) was recently suggested to involve phospholipase A2 (PLA2) activation. In this study, we examined whether CCK-8 stimulates the Ca2+-independent form of PLA2 in isolated rat islets, in comparison with stimulation by the PLA2-activating cholinergic agonist carbachol. We found that CCK-8 (100 nmol/l; 5.6 mmol/l glucose) induces lysophosphatidylcholine accumulation from [3H]palmitate-prelabeled islets (170 +/- 39%; P = 0.003) as well as arachidonic acid (AA) efflux from [3H]AA-prelabeled islets (190 +/- 13%; P < 0.001), and that p-amylcinnamoylantranilic acid (ACA) (50 micromol/l)-mediated PLA2 inhibition reduces CCK-8-induced AA efflux (52 +/- 11%; P = 0.001) and insulin secretion (67 +/- 16%; P < 0.001). Neither the Ca2+ channel antagonist verapamil (100 micromol/l) nor the Ca2+ATPase inhibitor thapsigargin (1 micromol/l) affected CCK-8-induced AA efflux and insulin secretion. Furthermore, despite removal of extracellular Ca2+, CCK-8 still increased AA efflux (48 +/- 14%; P = 0.006) and insulin secretion (105 +/- 46%; P = 0.025). In contrast, carbachol (100 micromol/l)-stimulated AA efflux was reduced by verapamil by 36 +/- 6% (P < 0.001) and abolished by removal of extracellular Ca2+. Overnight protein kinase C (PKC) downregulation by 12-O-tetradecanoyl phorbol-13-acetate (TPA) (500 nmol/l) reduced CCK-8-induced AA efflux (45 +/- 12%; P = 0.003) and insulin secretion (40 +/- 16%; P = 0.020). No additive action regarding either AA formation or insulin secretion was seen by combining TPA overnight and ACA, which implies the involvement of an additional PLA2- and PKC-independent signaling mechanism. The results show that CCK-8, in contrast to carbachol, activates Ca2+-independent PLA2 in islets and that the PLA2-activating capacity of CCK-8 is partly PKC dependent. Hence, Ca2+-independent PLA2 seems important for the insulinotropic effect of CCK-8, but not for that of carbachol.     

Umbilical venous guanosine 3',5'-cyclic phosphate (cGMP) concentration increases in asphyxiated newborns

Guanosine 3',5'-cyclic phosphate (cGMP) is known to be the second messenger of natriuretic peptides and nitric oxide (NO). To investigate the involvement of natriuretic peptides in the regulation of the feto-placental circulation, specific radioimmunoassays were used to measure the concentrations of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and cGMP in the umbilical venous plasma of normal and asphyxiated newborns. The plasma concentrations of ANP, BNP and cGMP in asphyxiated newborns were 48.3 +/- 12.9 pm, 24.5 +/- 9.4 pm and 4.4 +/- 1.6 nM (mean +/- s.e.m., n = 10), respectively. These values were significantly higher than those in the normal newborns (17.4 +/- 1.9 pm, 4.7 +/- 1.0 pm, and 0.78 +/- 0.14 nM, respectively). Moreover, the expression of both ANP-A and ANP-B receptor, biologically active receptors for natriuretic peptides, was detected in term human placenta by Northern bolt analysis. The expression of natriuretic peptide receptors was further confirmed by binding assay using [125I]-labelled ANP and solubilized crude membrane preparations of placental tissue. These findings suggest that cGMP is produced in the placenta, at least partly, by the action of ANP and BNP secreted from fetal heart, in pathophysiological conditions such as fetal hypoxia.     

Cyclic guanosine monophosphate responses to atrial natriuretic factor, brain natriuretic peptide, but not C-type natriuretic peptide, and the characterization of their receptors in rat medullary thick ascending limb

The effects of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) on renal medullary thick ascending limb (mTAL) have not been fully understood. The aim of this study is to examine the second-messenger responses of rat mTAL to ANF, BNP, and CNP. Characterizations of the ANF, BNP, and CNP receptors in mTAL were also performed by radioligand studies. Results showed that ANF and BNP were both capable of eliciting cyclic guanosine monophosphate (cGMP) responses in mTAL. Conversely, no cGMP response was observed upon stimulation by CNP in mTAL. The presence of ANF receptors was demonstrated by radioligand studies. One receptor site was found, and the Kd and maximum binding capacity were 4.0 +/- 0.45 nmol/L and 277.8 +/- 47.7 fmol/mg protein, respectively. BNP receptors were also found in mTAL, and ANF and BNP were sharing the same receptor. On the contrary, no CNP receptor could be shown by radioligand studies. These results suggest that guanylyl cyclase-coupled receptors (atrial natriuretic peptide receptor-A [ANPR-A]) specific for ANF and BNP are present in rat mTAL, while those for CNP (ANPR-B) are absent. ANF and BNP but not CNP act on mTAL to control water excretion.     

Enhanced brain natriuretic peptide response to peak exercise in heart transplant recipients

We investigated the atrial (ANP) and brain natriuretic peptides (BNP), catecholamines, heart rate, and blood pressure responses to graded upright maximal cycling exercise of eight matched healthy subjects and cardiac-denervated heart transplant recipients (HTR). Baseline heart rate and diastolic blood pressure, together with ANP (15.2 +/- 3.7 vs. 4.4 +/- 0.8 pmol/l; P < 0.01) and BNP (14.3 +/- 2. 6 vs. 7.4 +/- 0.6 pmol/l; P < 0.01), were elevated in HTR, but catecholamine levels were similar in both groups. Peak exercise O2 uptake and heart rate were lower in HTR. Exercise-induced maximal ANP increase was similar in both groups (167 +/- 34 vs. 216 +/- 47%). Enhanced BNP increase was significant only in HTR (37 +/- 8 vs. 16 +/- 8%; P < 0.05). Similar norepinephrine but lower peak epinephrine levels were observed in HTR. ANP and heart rate changes from rest to 75% peak exercise were negatively correlated (r = -0.76, P < 0.05), and BNP increase was correlated with left ventricular mass index (r = 0.83, P < 0.01) after heart transplantation. Although ANP increase was not exaggerated, these data support the idea that the chronotropic limitation secondary to sinus node denervation might stimulate ANP release during early exercise in HTR. Furthermore, the BNP response to maximal exercise, which is related to the left ventricular mass index of HTR, is enhanced after heart transplantation.     

Superiority of brain natriuretic peptide as a hormonal marker of ventricular systolic and diastolic dysfunction and ventricular hypertrophy

Atrial and brain natriuretic peptides (ANP and BNP) are produced by the heart, and their plasma concentrations are increased in human chronic congestive heart failure. Although separate studies have suggested that circulating levels of the biologically active C-terminal ANP, the biologically inactive N-terminal ANP, and BNP may have diagnostic utility in the detection of left ventricular systolic dysfunction or left ventricular hypertrophy, no studies have directly assessed the relative value of these peptides prospectively. We therefore designed this study to compare the relative ability of the different natriuretic peptides to detect abnormal left ventricular systolic and diastolic function and left ventricular hypertrophy. Using a prospective study design, we investigated 94 patients referred for cardiac catheterization and 15 age-matched normal subjects. The diagnostic abilities of elevated plasma C-terminal ANP, N-terminal ANP-(1-30), and BNP concentrations to identify systolic dysfunction (ejection fraction < 45%), diastolic dysfunction (time constant of left ventricular relaxation > 55 milliseconds, left ventricular end-diastolic pressure > 18 mm Hg), and left ventricular hypertrophy (left ventricular mass index > 120 g/m2) were objectively compared by receiver operating characteristic analysis. The areas under the receiver operating characteristic curve of BNP for detecting each of these abnormalities ranged from 0.715 to 0.908 and were significantly greater than those of C-terminal ANP or N-terminal ANP-(1-30). The sensitivity and specificity of an elevated plasma BNP, which we defined as greater than the mean + 3 SD of the 15 age-matched normal subjects, were 0.83 and 0.77, respectively, for detecting ejection fraction less than 45%, 0.85 and 0.70 for detecting the time constant of left ventricular relaxation greater than 55 milliseconds, 0.63 and 0.76 for detecting left ventricular end-diastolic pressure greater than 18 mm Hg, and 0.81 and 0.85 for detecting left ventricular mass index greater than 120 g/m2. The use of BNP and one other peptide increased sensitivity (0.90 to 0.96), albeit with lower specificity (0.56 to 0.71). An elevated plasma BNP was a more powerful marker of left ventricular systolic dysfunction, left ventricular diastolic dysfunction, and left ventricular hypertrophy than C-terminal ANP or N-terminal ANP-(1-30) in this population of patients with suspected cardiac disease. Measurement of BNP alone or in combination with C-terminal ANP or N-terminal ANP-(1-30) has potential utility for the detection of altered left ventricular structure and function in a patient population at risk for cardiovascular disease.     

Regulation of hepatic lecithin:retinol acyltransferase activity by retinoic acid receptor-selective retinoids

In the present study the electrophysiological characteristics and the proarrhythmic potential of cisapride and a structurally related drug, mosapride, were compared. In the anesthetized guinea pig, cisapride and d-sotalol (0.01-10 micromol/kg i.v., n = 6) dose-dependently prolonged the duration of the monophasic action potential recorded from the left ventricle. The maximal lengthening was 18 +/- 3.2% at 1.0 micromol/kg (mean +/- S.E.M., P < .01 vs. base line) and 19 +/- 2.5% at 10 micromol/kg (P < .001) for cisapride and d-sotalol, respectively. In contrast, mosapride did not increase this variable. In a rabbit model of the acquired long QT syndrome, infusion of cisapride (0.3 micromol/kg/min for 10 min maximum, n = 6), but not mosapride or vehicle, was associated with a significant lengthening of the QTU interval (43 +/- 3.8 ms, P < .01). Furthermore, torsades de pointes appeared in two of the six rabbits given cisapride. In isolated rabbit Purkinje fibers (PF), cisapride increased the action potential duration (48 +/- 5.6% at 0.1 micromol/l, P < .01 vs. control, n = 4). Mosapride did not significantly influence the action potential duration (3 +/- 2.0% increase at 1.0 micromol/l, n = 6). However, after mosapride was washed out, the addition of cisapride (0.1 micromol/l) caused a 46 +/- 3.2% lengthening of the action potential duration (P < .01 vs. 1.0 micromol/l mosapride). Early afterdepolarizations and triggered activity appeared in four of eight cisapride-superfused PF stimulated at a very low frequency (0.1 Hz). In isolated rabbit cardiomyocytes, cisapride concentration-dependently blocked (IC50 = 9 nmol/l) the rapid component of the delayed rectifying K+ current (I(Kr)). Mosapride was approximately 1000-fold less potent in blocking I(Kr) (IC50 = 4 micromol/l). It is concluded that the electrophysiological characteristics of cisapride may explain the recently reported propensity to prolong the QT interval and to induce torsades de pointes in susceptible patients, although a structurally related benzamide, mosapride, did not appear to have electrophysiological features of relevance for induction of torsades de pointes in common with cisapride.     

Regulation and possible physiological role of the Ca(2+)-dependent K+ channel of cortical collecting ducts of the rat

In the luminal membrane of rat cortical collecting duct (CCD) a big Ca(2+)-dependent and a small Ca(2+)-independent K+ channel have been described. Whereas the latter most likely is responsible for the K+ secretion in this nephron segment, the function of the large-conductance K+ channel is unknown. The regulation of this channel and its possible physiological role were examined with the conventional cell-free and the cell-attached nystatin patch-clamp techniques. Patch-clamp recordings were obtained from the luminal membrane of isolated perfused CCD segments and from freshly isolated CCD cells. Intracellular calcium was measured using the calcium-sensitive dye fura-2. The large-conductance K+ channel was strongly voltage- and calcium-dependent. At 3 mumol/l cytosolic Ca2+ activity it was half-maximally activated. At 1 mmol/l it was neither regulated by cytosolic pH nor by ATP. At 1 mumol/l Ca2+ activity the open probability (Po) of this channel was pH-dependent. At pH 7.0 Po was decreased to 4 +/- 2% (n = 9) and at pH 8.5 it was increased to 425 +/- 52% (n = 9) of the control. At this low Ca2+ activity the Po of the channel was reduced by 1 mmol/l ATP to 8 +/- 4% (n = 6). Cell swelling activated the large-conductance K+ channel (n = 14) and hyperpolarized the membrane potential of the cells by 9 +/- 1 mV (n = 23). Intracellular Ca2+ activity increased after hypotonic stress. This increase depended on the extracellular Ca2+ activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ischaemic myelopathy following aortic surgery or traumatic laceration of the aorta

Microcirculatory derangement, energy depletion and lipid peroxidation have been related to development of ischemia-reperfusion injury in the liver. This study investigates the effects of hyperbaric oxygen (HBO) on hepatic ischemia-reperfusion injury. Adult, male Sprague-Dawley rats were used. Three groups were evaluated: 1) sham-operated control (laparotomy only, no ischemia, no HBO), n=8; 2) ischemia control (1-h ischemia, 2-h reperfusion, no HBO), n=8; and 3) HBO pretreatment (100%, oxygen, 2.5 atm absolute, 90 min) plus ischemia (1-h ischemia, 2-h reperfusion), n=8. An in vivo microscope was used to investigate hepatic microcirculation. Tissue malondialdehyde (MDA) and adenosine triphosphate (ATP) were determined. In comparison with the ischemia control group, HBO significantly improved harmful insults following ischemia-reperfusion. HBO lessened adherent leukocyte count (6.00+/-1.31 cells/200 microm vs 11.38+/-2.88 cells/200 microm), and improved flow velocity (1.72+/-0.26 mm/s vs 0.83+/-0.19 mm/s) in post-sinusoidal venules. HBO also reduced MDA (1.04+/-0.24 nmol/mg protein vs 2.24+/-0.49 micromol/g protein), and increased ATP (2.03+/-0.17 micromol/g wet wt vs 0.73+/-0.11 micromol/g wet wt) levels. This study demonstrates that HBO before ischemia may ameliorate the ischemia-reperfusion injury of the liver in the rat model.     

Effects of sodium chloride and relative humidity on growth and sporulation of moulds isolated from cured fish

1. The aim of this study was to determine plasma levels of N-terminal atrial natriuretic peptide and atrial natriuretic peptide in normal subjects and in patients with essential hypertension, cardiac transplant and chronic renal failure, using radioimmunoassays directed towards the mid-portion pro-atrial natriuretic peptide (31-67) and pro-atrial natriuretic peptide (1-30) of the N-terminal atrial natriuretic peptide and atrial natriuretic peptide (99-126). The circulating form(s) of the immunoreactive N-terminal atrial natriuretic peptide in plasma extracts has been investigated using all three radioimmunoassays by means of gel filtration chromatography to further clarify the major immunoreactive molecular circulating form(s) of N-terminal atrial natriuretic peptide in man. 2. The plasma level (mean +/- SEM) of N-terminal pro-atrial natriuretic peptide (31-67) in the normal subjects was 547.2 +/- 32.7 pg/ml (n = 36) and was significantly elevated in patients with essential hypertension (730.2 +/- 72.3 pg/ml, P < 0.025, n = 39), in cardiac transplant recipients (3214.0 +/- 432.2 pg/ml, P < 0.001, n = 9) and in patients with chronic renal failure (3571.8 +/- 474.1 pg/ml, P < 0.001, n = 11). Plasma levels of N-terminal pro-atrial natriuretic peptide (1-30) and atrial natriuretic peptide were similarly elevated in the same patient groups when compared with the mean plasma values in the normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recommended restrictions after 131I therapy: measured doses in family members

Previous studies have shown that levels of plasma brain natriuretic peptide (BNP) increase in an early phase of acute myocardial infarction. However, the relations between plasma BNP levels and left ventricular remodelling, which occurs long after acute myocardial infarction, are not fully understood. Venous plasma BNP levels were measured 2, 7, 14, 30, 90 and 180 days after the onset of acute myocardial infarction in 21 patients. Left ventricular end-diastolic volume index (EDVI, ml/m2) in acute (5 days) and chronic (6 months) phases were assessed by electron-beam computed tomography using Simpson's method. The remodelling group (n=9) was defined by an increase in EDVI >/=5 ml/m2 relative to the baseline value. Plasma BNP levels on days 2, 7, 14, 30 and 90 were significantly higher in the remodelling group than in the non-remodelling group (n=12, P<0.05). Sustained elevation of plasma BNP levels was noted from day 2 (61+/-12 pmol/l) to day 90 (55+/-12 pmol/l) and significantly decreased on day 180 (24+/-3 pmol/l) in the remodelling group. In contrast, plasma BNP levels significantly decreased from day 2 (25+/-4 pmol/l) to day 90 (9+/-1 pmol/l) and reached a steady level thereafter in the non-remodelling group. Plasma BNP levels on day 7 correlated positively with an increase in EDVI (r=0.70, P<0.001) from the acute to chronic phase. More importantly, the sustained elevation of plasma BNP (percentage decrease smaller than 25%) from day 30 to day 90 identified patients in the remodelling group with a sensitivity of 100% and a specificity of 83%. In conclusion, not only the high levels of plasma BNP in an acute phase, but also the sustained elevation of plasma BNP in a chronic phase, may be associated with progressive ventricular remodelling occurring long after acute myocardial infarction.     

Isolated perfused rabbit colon crypts: stimulation of Cl- secretion by forskolin

The aim of this study was to characterize ion conductances and carrier mechanisms of isolated in vitro perfused rabbit colonic crypts. Crypts were isolated from rabbit colon mucosa and mounted on a pipette system which allowed controlled perfusion of the lumen. In non-stimulated conditions basolateral membrane voltage (Vbl) was -65 +/- 1 mV (n = 240). Bath Ba2+ (1 mmol/l) and verapamil (0.1 mmol/l) depolarized Vbl by 21 +/- 2 mV (n = 7) and 31 +/- 1 (n = 4), respectively. Lowering of bath Cl- concentration hyperpolarized Vbl from -69 +/- 3 to -75 +/- 3 mV (n = 9). Lowering of luminal Cl- concentration did not change Vbl. Basolateral application of loop diuretics (furosemide, piretanide, bumetanide) had no influence on Vbl in non-stimulated crypts. Forskolin (10(-6) mol/l) in the bath depolarized Vbl by 29 +/- 2 mV (n = 54) and decreased luminal membrane resistance. In one-third of the experiments a spontaneous partial repolarization of Vbl was seen in the presence of forskolin. During forskolin-induced depolarization basolateral application of loop diuretics hyperpolarized Vbl significantly and concentration dependently with a potency sequence of bumetanide > piretanide > or = furosemide. Lowering bath Cl- concentration hyperpolarized Vbl. Lowering of luminal Cl- concentration from 120 to 32 mmol/l during forskolin-induced depolarization led to a further depolarization of Vbl by 7 +/- 2 mV (n = 10). We conclude that Vbl of rabbit colonic crypt cells is dominated by a K+ conductance. Stimulation of the cells by forskolin opens a luminal Cl- conductance. Basolateral uptake of Cl- occurs via a basolateral Na+:2Cl-:K+ cotransport system.