Acute hemodynamic and renal effects of adrenomedullin in rats with aortocaval shunt

Roles of adrenomedullin 2 in regulating the cardiovascular and sympathetic nervous systems in conscious rats

Recently, a new member of the calcitonin gene-related peptide (CGRP) family, adrenomedullin 2 (AM2) or intermedin (IMD), was identified. AM2/IMD has been shown to have a vasodilator effect in mice and rats and an effect on urine formation in rats. In the present study, we investigated the effects of intravenously infused rat AM2 (rAM2) on blood pressure (BP), heart rate (HR), renal sympathetic nerve activity (RSNA), and renal blood flow (RBF) in conscious unrestrained rats relative to the effects of rat adrenomedullin (rAM) and proadrenomedullin NH2-terminal 20 peptide (rPAMP). Intravenous infusion of rAM2 (5 nmol/kg) significantly decreased BP and increased HR, RSNA, and RBF. These hypotensive and sympathoexcitatory effects diminished after 20 min, and HR returned to control levels 30 min after cessation of the infusion. In contrast, a significant increase in RBF was still evident 60 min after cessation of the peptide infusion. The duration of BP, HR, and RSNA responses was longer with rAM (5 nmol/kg) than with rAM2 infusion, whereas the increases in RBF induced by rAM2 and rAM were similar in their amplitude and duration. Infusion of rPAMP (200 nmol/kg) increased HR and RSNA but had no effect on RBF. Baroreceptor denervation suppressed, but did not diminish, the increases in HR and RSNA to rAM2. These findings indicate that the physiological roles of rAM2 and rAM are similar and that rAM2 also has a long-lasting vasodilator action on the renal vascular bed.

Renal effects of a new member of adrenomedullin family, adrenomedullin2, in rats

A new member of the adrenomedullin family, adrenomedullin2, was identified in mammals. The effects of adrenomedullin2 on renal hemodynamics and urine formation were examined in rats. Intrarenal arterial infusion of adrenomedullin2 at rates of 30, 100 and 300 pmol/kg/min decreased blood pressure and increased heart rate in a dose-dependent fashion. Adrenomedullin2 infusion at 100 pmol/kg/min significantly increased renal blood flow and urine flow. At the higher infusion rate (300 pmol/kg/min), adrenomedullin2 significantly decreased urine flow. Continuous intrarenal infusion of adrenomedullin2 at 100 pmol/kg/min significantly increased renal blood flow from 6.7+/-0.5 to 8.8+/-0.5 ml/min and decreased renal vascular resistance from 16+/-1 to 11+/-1 mm Hg min/ml. Urine flow was significantly increased from 21.5+/-4.9 to 36.2+/-8.5 microl/min and urinary excretion of sodium was increased from 2.3+/-0.9 to 4.9+/-1.4 microEq/min. Blood pressure, heart rate and glomerular filtration rate did not change. Infusion of a similar dose of adrenomedullin also increased renal blood flow (6.8+/-0.4-8.8+/-0.6 ml/min), urine flow (25.4+/-3.2-42.8+/-9.4 microl/min) and urinary excretion of sodium (2.8+/-0.6-6.5+/-1.2 microEq/min), decreased renal vascular resistance (15+/-1-11+/-1 mm Hg min/ml) and did not alter glomerular filtration rate. Thus, the renal actions induced by adrenomedullin2 were similar to those of adrenomedullin. These data suggest that adrenomedullin2 may play an important role in the regulation of renal hemodynamics and urine formation.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Attenuated natriuretic response to adrenomedullin in experimental heart failure

BACKGROUND

The recently discovered vasodilating and positive inotropic peptide, adrenomedullin (ADM), has strong natriuretic actions. ADM-induced natriuresis is caused by an increase in glomerular filtration rate and a decrease in distal tubular sodium reabsorption. Although ADM is activated in human and experimental heart failure, the role of ADM in the kidney in heart failure remains undefined.

METHODS AND RESULTS

The present study was performed to determine the renal hemodynamic and urinary excretory actions of exogenously administered ADM in a canine model of acute heart failure produced by rapid ventricular pacing. Experimental acute heart failure was characterized by a decrease in cardiac output and an increase in pulmonary capillary wedge pressure with an increase in plasma ADM concentration. Intrarenal infusion of ADM (1 and 25 ng/kg/min) induced an increase in urinary sodium excretion in the normal control dogs (change in urinary sodium excretion [Delta UNaV], +94.5 microEq/min during 1 ng/kg/min ADM infusion and +128.1 microEq/min during 25 ng/kg/min ADM infusion). In the acute heart failure dogs, intrarenal ADM infusion resulted in an attenuated increase in urinary sodium excretion (Delta UNaV, +44.8 microEq/min during 1 ng/kg/min ADM infusion and +51.8 microEq/min during 25 ng/kg/min ADM infusion). Both glomerular and tubular actions of ADM were attenuated in the acute heart failure group compared with responses in the normal control group.

CONCLUSION

The present study shows that the renal natriuretic responses to ADM are markedly attenuated in experimental acute heart failure. This study provides insight into humoral mechanisms that may promote sodium retention in heart failure via a renal hyporesponsiveness to natriuretic actions of ADM.

Neurohumoral blockade in CHF management

Is heart failure an endocrine disease? Historically, congestive heart failure (CHF) has often been regarded as a mechanical and haemodynamic condition. However, there is now strong evidence that the activation of neuroendocrine systems, like the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system, as well as the activation of natriuretic peptides, endothelin and vasopressin, play key roles in the progression of CHF. In this context, agents targeting neurohormones offer a highly rational approach to CHF management, with ACE inhibitors, aldosterone antagonists and beta-adrenergic blockade improving the prognosis for many patients. Although relevant improvements in clinical status and survival can be achieved with these drug classes, mortality rates for patients with CHF are still very high. Moreover, most patients do not receive these proven life-prolonging drugs, partially due to fear of adverse events, such as hypotension (with ACE inhibitors), gynaecomastia (with spironolactone) and fatigue (with beta-blockers). New agents that combine efficacy with better tolerability are therefore needed. The angiotensin II type 1 (AT(1))-receptor blockers have the potential to fulfil both these requirements, by blocking the deleterious cardiovascular and haemodynamic effects of angiotensin II while offering placebo-like tolerability. As shown with candesartan, AT(1)-receptor blockers also modulate the levels of other neurohormones, including aldosterone and atrial natriuretic peptide (ANP). Combined with its tight, long-lasting binding to AT(1)-receptors, this characteristic gives candesartan the potential for complete blockade of the RAAS-neurohormonal axis, along with the great potential to improve clinical outcomes.