Mechanisms of isoproterenol-induced atrial natriuretic peptide release from superfused rabbit atria

The mechanisms for isoproterenol-induced atrial natriuretic peptide (ANP) release were studied in superfused rabbit sliced right atria. Addition of 1 microM norepinephrine to this preparation induced a significant monophasic twofold rise in ANP release. This effect was abolished by 1 microM propranolol and mimicked by 1 microM isoproterenol. Furthermore, addition of 200 microM 3-isobutyl-1-methylxanthine (IBMX) to the superfusing medium potentiated isoproterenol effect 31%. In addition, superfusion of slices with 0.5 mM N6,2-O-dibutyryladenosine 3',5'-cyclic monophosphate [(Bu)-2cAMP] enhanced ANP release in the same manner as the beta-agonist. After isoproterenol stimulation, adenosine 3',5'-cyclic monophosphate (cAMP) concentration in effluents increased significantly. ANP secretory response to isoproterenol was unaffected by extracellular calcium concentration or 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). Finally, 10 microM indomethacin significantly reduced isoproterenol-stimulated ANP release. It is concluded that 1) norepinephrine-induced ANP release is mediated by its beta-agonist activity, 2) isoproterenol-stimulated release appears to be mediated by cAMP, 3) isoproterenol effect does not require extracellular calcium, and 4) prostaglandins may be involved in this beta-adrenergic effect.

Glomerular atrial natriuretic factor receptors in experimental congestive heart failure

Heart failure is usually characterized by a relative insensitivity to atrial natriuretic factor (ANF). Downregulation of ANF receptors has been reported but remains controversial. Renal response to ANF infusion, glomerular ANF receptors, and guanosine 3',5'-cyclic monophosphate (cGMP) production have been studied in rabbits with congestive heart failure (CHF) after traumatic aortic regurgitation and abdominal aortic stenosis. Diuresis and natriuresis induced by ANF infusions were significantly decreased in CHF animals. Plasma cGMP was higher in CHF rabbits before ANF administration than in controls (37.6 +/- 7.2 vs. 17.1 +/- 3.9 pmol/ml, P < 0.02) and increased to a same level after ANF in both groups (48.8 +/- 4.2 vs. 52.5 +/- 2.8 pmol/ml, NS). No difference was found in glomerular ANF receptor density (436 +/- 54 vs. 425 +/- 57 fmol/mg protein, NS) nor in affinity between the two groups (dissociation constant; 240 +/- 24 vs. 347 +/- 49 pM, NS). Moreover, in vitro glomerular cGMP production in response to exogenous ANF was preserved. In conclusion, despite a blunted renal response to ANF in vivo, glomerular ANF receptors were unchanged in this model, and no defect in cGMP production in response to ANF was found. This suggests the existence of an intracellular defect beyond the second messenger.

[Neurohormonal profile in aortic valve stenosis]

The authors studied the responses of the main systems of sympathetic and hormonal regulation in valvular aortic stenosis, a special model of dissociation between arterial pressure and left ventricular function. The series comprised 14 patients with an average age of 70 +/- 9 years without diuretic therapy presenting with pure calcific aortic stenosis without other valvular or coronary disease. All were in sinus rhythm; 5 were taking an angiotensin converting enzyme inhibitor. Plasma concentrations of endothelin 1, atrial natriuretic factor (ANF), arginine vasopressin (AVP), catecholamines, plasma renin activity (PRA), angiotensin II and aldosterone were measured in resting, fasting patients, by blood samplings from a peripheral vein immediately before cardiac catheterisation. The results were compared with the severity of the aortic stenosis (aortic valve area greater or less than 0.7 cm2), the ratio of left ventricular work/myocardial mass (greater or less than 0.6) and treatment (with or without ACE inhibitors). Catecholamine levels were much higher in severe aortic stenosis (noradrenaline: 579 +/- 66 pg/ml when valve surface area > 0.7 cm2 versus 900 +/- 92 pg/ml when valve surface area < 0.7 cm2; p < 0.01). Endothelin -1 and AVP concentrations were normal. Whereas PRA was normal, aldosterone levels were increased in patients without treatment by ACE inhibitors. This treatment did not, however, normalise the noradrenaline levels. The increase in ANF concentration was large when left ventricular work decreased with respect to myocardial mass (190.8 +/- 42.3 pg/ml if W/M was decreased versus 82.7 +/- 15.4 pg/ml when W/M was normal): this could be related to the degree of left ventricular hypertrophy.

Variations in plasma endothelin concentrations during coronary spasm

A provocation test using methylergometrine was carried out in patients with a normal coronary angiogram. Patients exhibiting spasm (Group 1, n = 6) were compared with non-spasm patients (Group II, n = 6). The endothelin concentration was determined in all cases at 0800, 1100, 1400, 1600, 1900, 2100, 2300 and 0100 h. The provocation test was carried out at 1700 h and an additional determination was made during spasm if the test was positive. The two groups had similar clinical characteristics and did not differ in terms of risk factors. Apart from the value recorded during spasm, the endothelin plasma level was significantly higher in Group I. A time x measurement interaction was noted in both groups, with a higher endothelin level in the morning. The endothelin level increased significantly during spasm in Group I patients. The plasma concentration of endothelin appeared to be higher in the basal state and during spasm in patients exhibiting spastic angina.

[Endothelin: the vasoconstrictor of the 1990's?]

Endothelin is a recently isolated 21 amino acid peptide with vasoconstrictor activity. It seems to be part of the "hormonal" production by the vascular endothelium and might play a key role in the regulation of vasomotricity. The principal property of endothelin is that it induces an intense and prolonged arterial and venous contraction. Endothelin is secreted by endothelial cells under the influence of various stimuli (thrombin, adrenaline, shearing stress, hypoxia, etc.), then binds to specific membrane receptors thereby increasing the intracellular free calcium concentration. Endothelin has many other vascular and extravascular properties: it has positive inotropic and chronotropic effects, increases renal vascular resistances and reduces the glomerular filtration rate, contracts bronchial and gastrointestinal smooth muscle, induces proliferation of the vascular smooth muscle cells as well as that of fibroblasts and glomerular mesangial cells. Compared with experimental data in animals, human data are still scantly. Plasma endothelin concentration rises in acute renal failure and in chronic renal failure treated by dialysis, diabetes mellitus, essential arterial hypertension, pre-eclampsia and asthma. The development of specific antagonists and endothelin in synthesis inhibitors should soon enable us to specify the modes of regulation of endothelin production before considering applications to therapy.

Plasma calcitonin gene-related peptide decreases in chronic congestive heart failure

To investigate the role of calcitonin gene-related peptide (CGRP) in cardiac failure, a sensitive and specific radioimmunoassay was developed to study plasma levels of CGRP in 37 normal subjects and 41 patients with heart failure (HF). The mean plasma levels of CGRP were 294.3 pg.ml-1 (SEM: 41.4) in normal subjects and 121.2 pg.ml-1 (SEM: 21.2) in HF patients. The significant decrease observed in HF patients suggests that CGRP is involved in the pathogenesis of heart failure via a direct effect or via modulation of sympathetic nervous activity.

[Atrial natriuretic factor in heart insufficiency]

The atrial natriuretic factor is a peptide with vasodilator and natriuretic properties which is synthesized and released by atrial myocytes. In patients with chronic heart failure the ventricles contribute to the synthesis of this peptide, so that its plasma concentration rises in proportion to the heart filling pressure. The atrial natriuretic factor, therefore, seems to be a good biological marker of functional and haemodynamic severity of heart failure. However, the weight of this factor in the neuro-hormonal balance has not yet been fully evaluated, owing to the usual attenuation of its biological effects. This, and the necessity of continuous parenteral administration limits, for the moment, its therapeutic applications. Inhibitors of the enzyme involved in its metabolism are being tested, but only preliminary results are available in humans.

[Atrial natriuretic factor and cardiac insufficiency]

The atrial natriuretic factor (ANF) is a vasodilating and natriuretic peptide. In experimental and human cardiac failure, plasma ANF concentrations are increased. The ANF is a good marker of functional and haemodynamic severity and of the prognosis of cardiac failure. In this syndrome, messenger RNA of ANF is expressed not only in the atria but also in the ventricles which also secrete the peptide. Attenuation of the natriuretic response is observed in cardiac failure. It may be related to an abnormality situated after the receptor and second messenger, cyclic GMP and/or the reduction of renal perfusion pressure which occurs in cardiac failure. The therapeutic perspectives of ANF in cardiac failure are limited by the necessity of continuous intravenous or parenteral administration. Inhibitors of the enzyme degrading the peptide, neutral endopeptidase, are under evaluation in clinical trials which are at a preliminary stage for the moment.

Endothelin in chronic renal failure

The aims of the present study were to determine plasma endothelin (ET) in chronically uraemic patients, the renal clearance of endogenous ET in normal dog and man, and the effect of acute volaemic expansion on ET. The mean plasma ET concentration in haemodialysis patients was 57.5 +/- 5 pg/ml before haemodialysis and remained unchanged at 52.5 +/- 5 pg/ml after haemodialysis. They were thus significantly elevated both before and after haemodialysis (P less than 0.01) compared with plasma ET in normal subjects of 20.8 +/- 0.8 pg/ml. There was no evidence of ET clearance across the cuprophane membrane of the dialyser. Resting plasma ET values in the 15 non-dialysed uraemic patients ranged between 20 and 52.5 pg/ml (mean 38.2 +/- 2.3 pg/ml), significantly greater than those observed in controls (P less than 0.01). In CAPD patients, plasma ET was also significantly (P less than 0.01), elevated (63 +/- 10 pg/ml) when compared to controls, and similar to those observed in patients before haemodialysis. In dogs, mean ET did not diminish between the aorta and the renal vein (28.1 +/- 1 versus 28.4 +/- 2 pg/ml). In man mean ET did not significantly decline between the renal artery and the renal vein (17 +/- 3 to 13 +/- 0.8 pg/ml). In the seven healthy subjects who received 2000 ml of isotonic saline intravenously ET remained unchanged (24 +/- 2; 23 +/- 1 and 23 +/- 2 pg/ml before and 1 and 2 h after starting hydration respectively). We have thus shown that plasma ET is elevated in patients with chronic renal failure especially those on dialysis and CAPD.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of arginine vasopressin and extracellular osmolarity on atrial natriuretic peptide release by superfused rat atria

This study investigated the characteristics of atrial natriuretic peptide (ANP) release from superfused sliced atria and ventricles of rats. Right atria spontaneously released more immunoreactive ANP (Ir-ANP: pg/min per mg tissue) (32 +/- 3) than did left atria (11 +/- 2) or right ventricles (1.5 +/- 0.5). Addition of 10(-9) to 10(-5) M of arginine vasopressin (AVP) to the superfusing fluid or increasing its osmolarity (290 to 490 mOsM) resulted in a significant increase of the Ir-ANP outflow from right atria. The effect of AVP was prevented by a specific V1 receptor antagonist, ([d(ch2)5Tyr(Me)]AVP). Superfusion with indomethacin (10(-5) M) did not alter spontaneous release but inhibited the peak levels of Ir-ANP induced by AVP (10(-5) M). Moreover, DDAVP, a specific V2 receptor agonist, did not induce Ir-ANP release. Ca(2+)-free medium alone or plus 1 mM EGTA induced a significant increase in basal Ir-ANP outflow. The Ir-ANP released chromatographed similarly to the standard alpha-rANP. These results suggest a specific stimulatory effect of AVP and osmolarity and a negative influence of extracellular Ca2+ on atrial spontaneous Ir-ANP release. It appears that the effect of AVP could be mediated by prostaglandin synthesis.

Alterations in the levels of iron, ferritin and other trace metals in Parkinson's disease and other neurodegenerative diseases affecting the basal ganglia

Levels of iron, copper, zinc and manganese were measured by inductively coupled plasma spectroscopy in frozen postmortem brain tissue from patients with Parkinson's disease (PD), progressive supranuclear palsy (PSP), multiple system atrophy with strionigral degeneration (MSA), and Huntington's disease (HD) compared with control subjects. Total iron levels were found to be elevated in the areas of basal ganglia showing pathological change in these disorders. In particular, total iron content was increased in substantia nigra in PD, PSP and MSA, but not in HD. Total iron levels in the striatum (putamen and/or caudate nucleus) were increased in PSP, MSA and HD but not in PD. Total iron levels were decreased in the globus pallidus in PD. There were no consistent alterations of manganese levels in basal ganglia structures in any of the diseases studied. Copper levels were decreased in the substantia nigra in PD, and in the cerebellum in PSP, and were elevated in the putamen and possibly substantia nigra in HD. Zinc levels were only increased in PD, in substantia nigra and in caudate nucleus and lateral putamen. Levels of the iron binding protein ferritin were measured in the same patient groups using a radio-immunoassay technique. Increased iron levels in basal ganglia were generally associated with normal or elevated levels of ferritin immunoreactivity, for example, the substantia nigra in PSP and possibly MSA, and in putamen in MSA. The exception was PD where there was a generalized reduction in brain ferritin immunoreactivity, even in the substantia nigra. An increase in total iron content appears to be a response to neurodegeneration in affected basal ganglia regions in a number of movement disorders. However, only in PD was there an increased total iron level, decreased ferritin content, decreased copper content, and an increased zinc concentration in substantia nigra. These findings suggest an alteration of iron handling in the substantia nigra in PD. Depending on the form in which the excess iron load exists in nigra in PD, it may contribute to the neurodegenerative process.

Low molecular weight hydroxyethyl starch 6% compared to albumin 4% during intentional hemodilution

Intentional normovolemic hemodilution was chosen as the model to compare a 6% low molecular weight hydroxyethyl starch (LMW HES) to 4% albumin. The study ran over the plasma exchange period for 24 h. Nine patients, scheduled for abdominal aortic surgery, were included in each group. After basal measurements, blood was withdrawn and simultaneously replaced by either 4% albumin (Group 1) or 6% LMW HES (Group 2) to achieve a final hematocrit of approximately 30%. Hemodynamic blood oxygen gas and hormonal plasma levels were determined before hemodilution then at 30 min, 1, 2, 3, and 24 h after the end of hemodilution. Basal value for total blood volume was 4377 +/- 162 ml in group 1 and 4138 +/- 315 ml in group 2. As in both groups the decrease in blood cell volume was exactly compensated by the increase in plasma volume, no significant change in total blood volume (respectively 4432 +/- 159 and 4305 +/- 267 ml) was observed. Throughout the study, in both groups, no significant change in mean arterial and right atrial pressures was observed. In group 2 (LMW HES), a significant increase of pulmonary capillary wedge pressure was noted 120 min after hemodilution. After hemodilution, despite a significant decrease in arterial oxygen O2 content, systemic oxygen transport did not significantly vary until 24 h in relation to the increased cardiac index. An increase in O2 extraction was observed after the exchange but no further increase was observed until the 24 h. No significant changes either in global O2 consumption or in lactate concentration were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

[From the circulating renin-angiotensin system to the intratissular renin-angiotensin systems. A complex relationship stage]

Since renin angiotensin (RA) system discovery during 1930 decade, its physiopathological importance was only recently demonstrated with the dramatic therapeutic value of angiotensin converting enzyme (ACE) inhibitors. The tissular localisation of some of its compounds progressively lead to the concept of a tissular RA system. However non consensus can be established concerning either its existence or its physiological role. The distribution of the classical components of the RA system in the cardiac and other tissues is not homogenous enough to demonstrate the existence of such a functional and coherent system. Numerous technical problems concerning dosage methodologies are encountered especially with angiotensin II determination and must rend cautious when interpreting data. Non specific actions of ACE inhibitors can explain discrepancies between their effects and the level of RA system activation. Indeed they interfere with other systems such as prostaglandins, leucotriens, bradykinins, free radicals. Different tissues such as those of the cardiovascular system directly interfere with angiotensin II production. However, mechanisms and enzymatic reactions that are involved in such a production are multiple and their respective roles remain to be determined.

Regional distribution of calcitonin gene-related peptide-, substance P-, cholecystokinin-, Met5-enkephalin-, and dynorphin A (1-8)-like materials in the spinal cord and dorsal root ganglia of adult rats: effects of dorsal rhizotomy and neonatal capsaicin

Biochemical mapping of five different peptide-like materials--calcitonin gene-related peptide (CGRP), substance P (SP), Met5-enkephalin (ME), cholecystokinin (CCK), and dynorphin A (1-8) (DYN)--was conducted in the dorsal and ventral zones of the spinal cord at the cervical, thoracic, and lumbar levels in 3-month-old rats 10 days after unilateral dorsal rhizotomy at the cervical level (C4-T2) or after neonatal administration of capsaicin (50 mg/kg s.c.). In control rats, all peptide-like materials were more abundant in the dorsal than in the ventral zone all along the spinal cord. However, in both zones, absolute concentrations of CGRP, SP, ME, and CCK were significantly higher at the lumbar than at the cervical level. Rhizotomy-induced CGRP depletion (-85%) within the ipsilateral dorsal zone of the cervical cord was more pronounced than that due to neonatal capsaicin (-60%), a finding suggesting that this peptide is contained in both capsaicin-sensitive (mostly unmyelinated) and -insensitive (myelinated) primary afferent fibers. In contrast, similar depletions of SP (-50%) were observed after dorsal rhizotomy and neonatal capsaicin treatment, as expected from the presence of SP only in the capsaicin-sensitive small-diameter primary afferent fibers. Although the other three peptides remained unaffected all along the cord by either intervention, evidence for the existence of capsaicin-insensitive CCKergic primary afferent fibers could be inferred from the increased accumulation of CCK (together with SP and CGRP) in dorsal root ganglia ipsilateral to dorsal root sections.

Decreased ferritin levels in brain in Parkinson's disease

Ferritin levels were measured in postmortem brain tissue from patients dying with Parkinson's disease [treated with L-3,4-dihydroxyphenylalanine (L-DOPA)] and from control patients. Ferritin levels were decreased in the substantia nigra, caudate-putamen, globus pallidus, cerebral cortex, and cerebellum when compared with age-matched control tissues. However, in CSF from L-DOPA-treated patients and in serum from L-DOPA-treated and untreated parkinsonian patients, ferritin levels were normal. Previous studies have suggested an increased total iron content in substantia nigra of parkinsonian brain. The failure of substantia nigra ferritin formation to be stimulated by increased iron levels suggests some defect in iron handling in this critical brain region in Parkinson's disease. The reason for decreased ferritin levels throughout the parkinsonian brain is not clear but does not seem to reflect a general system deficit in ferritin.

Characteristics of atrial natriuretic hormone receptors in human pheochromocytomas

The presence of functional receptors for human atrial natriuretic hormone in human pheochromocytomas was recently reported. The present study reports the binding of hANH as measured by Scatchard analysis in 4 human adrenal glands and in 5 human pheochromocytomas. Binding assays using [3H]ANH revealed a single class of high-affinity binding sites for hANH in both tissues. Human pheochromocytomas present a lower number of binding sites than normal human adrenal gland (Bmax of 7.1 +/- 2.1 vs 33.6 +/- 6.9 fmol/mg protein, respectively). However, the decreased number of ANH receptors was not paralleled by modifications of tissular cyclic GMP (cGMP). Moreover, plasma hANH concentrations in 7 patients with pheochromocytomas (20.2 +/- 2.7 pmol/l) were statistically higher than those obtained in 25 normal control humans (8.1 +/- 0.6 pmol/l, p less than 0.001). We also demonstrated the presence of immunoreactive ANH in the tumour itself.

Beta-adrenoceptor blockade potentiates exercise-induced release of atrial natriuretic peptide

The effect of a non selective and a cardio-selective beta-blocker on basal and exercise-stimulated plasma atrial natriuretic peptide concentrations in healthy volunteers has been studied. Nine healthy volunteers received single oral doses of 5 mg tertatolol, 100 mg atenolol or placebo, at one week intervals, in a double blind cross over trial. At rest plasma atrial natriuretic peptide, aldosterone, antidiuretic hormone and cyclic GMP concentrations and plasma renin activity were not modified by the treatments. During exercise plasma atrial natriuretic peptide concentrations were significantly increased by each treatment, the increment being significantly greater on beta-blockers than on placebo. The rise in atrial natriuretic peptide was 72% after placebo (from 24 to 42 pg/ml), 184% after atenolol (from 30 to 86 pg/ml), and 183% after tertatolol (from 34 to 95 pg/ml), respectively. Thus, the study has shown that in healthy subjects the plasma natriuretic peptide concentration is increased by exercise and that the increase is considerably and equally potentiated by selective and non selective beta-adrenoceptor blockade. The effect may be mainly due to a reduction in ventricular contractility with an increase in atrial pressure. The beta-blockers did not influence the resting plasma atrial natriuretic peptide levels, which suggests that in healthy subjects basal atrial natriuretic peptide secretion is not controlled via beta-receptors.