Dieter Neuser

Endothelin stimulates release of atrial natriuretic peptides in vitro and in vivo

The effect of endothelin (END) on the release of atrial natriuretic peptides (ANP) was studied in isolated rat atria and in conscious rats. END stimulates the ANP release in vitro in a dose-dependent manner. An increase in ANP plasma levels and cyclic GMP plasma levels was also observed in conscious rats after injection of END. When a monoclonal antibody directed against ANP was injected together with END the increase in cyclic GMP was completely blocked. From this study it is concluded that END is a potent secretagogue for ANP both in vitro and in vivo.

Receptor binding, cGMP stimulation and receptor desensitization by atrial natriuretic peptides in cultured A 10 vascular smooth muscle cells

Receptor characteristics for atrial natriuretic peptides (ANP) were demonstrated in the permanent tissue culture system of vascular smooth muscle cell (VSMC) line. 125I‐ANP exhibited reversible and saturable binding to A10 rat VSMC, and the equilibrium dissociation constant, K d was 157 pM and maximal binding capacity, .B max amounted to 115 of protein. Binding of the 125I‐ligand was highly specific for certain potently displacing ANP analogues with inhibition constants (K i values) in the nano‐ or even subnanomolar concentration range. Pretreatment of VSMC with ANP yielded receptor desensitization to one half of the ANP receptor density, and supports the conclusion of receptor autoregulation by ANP in A10 VSMC. The receptor coupled intracellular cGMP system was stimulated, and thus demonstrates the application of A10 cells as a model for the study of ANP receptor interaction involved in vascular smooth muscle relaxation.

Different effects of ANP and nitroprusside on cyclic GMP extrusion of isolated aorta

Atrial natriuretic peptide (ANP) and sodium nitroprusside have potent vasodilator effects on the noradrenaline-precontracted isolated rabbit aorta. A distinct elevation of cyclic GMP in the aortic tissue was observed after both vasodilators. In contrast to sodium nitroprusside, ANP-(5-28) induced a dose-dependent cyclic GMP extrusion from the tissue into the medium. Thus, release of cyclic GMP appears to be specific for activation of particulate guanylate cyclase and provides a mechanism in addition to synthesis and degradation by which the cells can regulate their internal concentrations of cyclic GMP.

The use of a monoclonal antibody to measure plasma atriopeptins in rat

A monoclonal antibody with specificity for atrial natriuretic peptides (ANP) was produced, that can be used for the radioimmunological determination of ANP-immunoreactivity (ANP-IR) in rat plasma. The antibody recognizes atriopeptin I, II, III, as well as alpha-hANP and alpha-hANP fragment (7-28) and does not crossreact with ANP-fragments (13-28) and (18-28). Plasma levels of ANP-IR in conscious Wistar rats were determined before and after volume-loading. Basal plasma levels of ANP-IR were 108 +/- 12 pg/ml, and after volume-loading increased to 800 +/- 59 pg/ml.

Endothelin receptors in cultured renal epithelial cells

We demonstrated the presence of specific binding sites for endothelin in the renal epithelial cell lines. MDCK and LLC-PK1. Endothelin binding induced mobilisation of intracellular calcium, as shown by an increase in 45Ca2+ efflux. This suggests a direct effect of endothelin on renal reabsorption in addition to the effects on the renal vasculature.

125I-endothelin-1 and 125I-big endothelin-1 in rat tissues: autoradiographic localization and receptor binding

SummaryThe potent vasoconstrictor peptide, endothelin-1 (ET-1), which exhibits a characteristically long-acting activity in vitro and in vivo, is thought to be generated in endothelial cells from a less active intermediate, big endothelin-1 (big ET-1). In addition to ET-1, big ET-1 is also present in the circulation. The autoradiographic localization of 125I-big ET-1 and 125I-ET-1 has been studied after intravenous administration in rat tissues. Highest enrichment of radioactivity was found in the kidney cortex for both peptides. Compared to blood levels, enrichment of radioactivity is also detected, in the vascular wall of the aorta. Comparing the radioactivity pattern of ET-1 and big ET-1, a nearly identical tissue distribution is observed, with the exception of the relative enrichment in the lung and the zona glomerulosa after administration of ET-1.Both radioligands show a specific and saturable binding to lung and kidney membranes. In the case of lung tissue, Ki values are 10−10M for endothelin-1 and 10−8M for big endothelin-1. This difference in affinities may account for the lack of binding of big endothelin-1 to lung tissue.

The reduction of renin and aldosterone as a response to acute hypervolemia is blocked by a monoclonal antibody directed against atrial natriuretic peptides.

We have previously reported that the strong diuresis, natriuresis and urinary cyclic GMP excretion after acute volume loading in rats are caused by ANP and can be blocked by additionally given monoclonal antibodies directed against ANP. The present report describes that in contrast to the changes in ANP and cyclic GMP, the plasma renin activity and aldosterone concentration are decreased after volume loading. This decrease is completely blocked by simultaneous administration of the monoclonal antibodies. Plasma cyclic AMP levels are not affected. From this study it seems to be clear that the inhibition of the renin-aldosterone system is not a direct effect of volume expansion but is specially mediated by the released ANP.

Long-Term Efficacy and Tolerability of Acarbose Treatment in Patients with Type 2 Diabetes Mellitus

AbstractObjective:The aim of the study was to investigate the efficacy and tolerability of long-term acarbose therapy in type 2 diabetic patients.n Study design: In this double-blind, single-centre group comparison, patients were randomised to receive either acarbose or matching placebo, in addition to their regular antidiabetic therapy, over a period of 78 weeks. Eligibility for inclusion in the efficacy evaluation included a study duration of ≥510 days.n Methods: The primary efficacy parameter was the change in glycosylated haemoglobin (HbA1) from baseline to end of study. Secondary variables included changes in blood glucose and lipid parameters, as well as signs of retinopathy and nephropathy.n Patients: A total of 139 patients were assessed for safety and 88 patients (44 in each treatment group) were included in the efficacy analysis. Patients were generally overweight and the majority had previously been treated with sulphonylureas.n Results: Acarbose significantly improved fasting and 1-hour postprandial blood glucose levels compared with placebo (p = 0.039 and 0.009), and improvements in HbA1 with acarbose versus placebo fell just short of significance (p = 0.057). There were no differences between treatments in changes in microvascular complications, but blood pressure improved with acarbose treatment. Two patients in the acarbose group experienced elevated liver enzyme levels. Generally, acarbose had a good safety profile and was well tolerated.n Conclusion: Long-term treatment with acarbose was safe and efficacious in patients with type 2 diabetes mellitus that was insufficiently controlled by other oral antidiabetics.

Modulation of Anp Receptor-Mediated cGMP Accumulation by Atrial Natriuretic Peptides and Vasopressin in A10 Vascular Smooth Muscle Cells

ANP receptor binding and desensitization were demonstrated in the A10 vascular smooth muscle cell (VSMC) line. Concomitantly, the ANP receptor coupled guanylate cyclase activity was reduced by the receptor down-regulation with ANP. The ANP stimulated cGMP accumulation is modulated by arginine-vasopressin, while the arginine-vasopressin mediated cAMP system remained unaffected by ANP. Results suggest negative coupling of arginine-vasopressin receptors to the guanylate cyclase activity, and indicate that the vasorelaxant activity of ANP might be regulated in part by arginine-vasopressin via specific receptor sites.

α-h-ANP is the only form of circulating ANP in humans

It is therefore concluded that α‐h‐ANP is the only form of ANP circulating in human plasma.