Imbalance of the autonomic nervous system at night in women with gestational diabetes

AIMS

Autonomic nervous system dysfunction is observed in Type 2 diabetes. As gestational diabetes is a potent risk factor of later Type 2 diabetes, we set out to determine whether autonomic nervous system imbalance could already be observed in women with this condition. Because activity of the sympathetic nervous system tends to be relatively stable in the nocturnal hours, we performed the study at night.

RESEARCH DESIGN AND METHODS

We studied 41 women with gestational diabetes, 22 healthy pregnant controls and 14 non-pregnant controls. We assayed plasma noradrenaline at 24.00, 04.00 and 07.00 h and performed an overnight Holter recording for heart rate variability analysis. In addition, we assayed plasma adrenomedullin, a cardiovascular protective hormone.

RESULTS

Compared with non-pregnant controls, plasma noradrenaline levels were increased at 04.00 and 07.00 h in the gestational diabetic (P = 0.003) and pregnant control (P = 0.002) groups, with no difference between them. Heart rate variability, very-low-frequency and low-frequency power were lower in pregnant groups compared to the non-pregnant controls. Heart rate variability remained unchanged between specified sampling times in the gestational diabetic group, in contrast to fluctuation seen in the control groups.

CONCLUSIONS

Gestational diabetes, compared with normal pregnancy, seems not to be a state of overall sympathetic nervous system activation. At the heart level, however, an inhibitory effect on autonomic nervous system modulation was seen. Plasma noradrenaline and heart rate variability correlated well, supporting the use of this function in future studies of overall sympathetic activity during pregnancy.

Plasma N terminal pro-brain natriuretic peptide levels and its determinants in a multi-ethnic population

This study documents the determinants and plasma levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) among hypertensive and normotensive subjects in a multi-ethnic population in the United Arab Emirates (UAE). We obtained demographic, anthropometric and clinical data, together with fasting NT-proBNP and biochemical indices from 128 hypertensive patients and 138 normotensive subjects matched for age, gender and ethnicity. Plasma NT-proBNP levels were significantly (P<0.001), and several-fold higher among hypertensives (median 5.92, inter quartile range (IQR): 1.79-18.48 pmol/l) than normotensives (median 1.78, IQR: 0.59-4.32 pmol/l) in the total study population, and the same was true for the ethnic groups separately. Similarly, plasma levels of glucose, blood urea nitrogen (BUN) and creatinine, but not insulin, were significantly (P<0.05) higher among hypertensives than normotensives. For all subjects combined, log NT-proBNP correlated positively and significantly with age (P<0.01), log glucose (P<0.05), systolic blood pressure (SBP, P<0.001), log BUN (P<0.001) and log creatinine (P<0.001). Multivariate regression analysis showed that NT-proBNP levels were independently and positively correlated with SBP, age, gender, log BUN, Emirati and South East Asian ethnic groups and inversely associated with current exercise. In conclusion, we found circulating levels of NT-proBNP to be significantly increased in hypertensive versus normotensive subjects in the UAE and independently related to SBP, age, gender, indices of renal function and possibly exercise. Our results further suggest a possible modulating effect of ethnicity on NT-proBNP levels.

Alendronate prevents bone loss in patients with acute spinal cord injury: a randomized, double-blind, placebo-controlled study

CONTEXT

Patients who sustain an acute spinal cord injury (SCI) experience rapid dramatic reductions in bone mineral density (BMD), especially marked in sublesional areas and sometimes leading to hypercalcemia and hypercalciuria, as well as increased fracture risk.

OBJECTIVE

In this prospective, double-blind, randomized, placebo-controlled study, we evaluated the hypothesis that oral alendronate administration would preserve BMD when administered soon after acute SCI.

PATIENTS AND INTERVENTION

Thirty-one patients with acute SCI were randomly allocated to receive oral alendronate 70 mg/wk or placebo, within 10 d of acute SCI, for 12 months.

MAIN OUTCOME MEASUREMENTS

At entry and at 3, 6, 12, and 18 months, total body bone density, lumbar and hip BMD, ultrasound of the calcaneus, 24-h urinary calcium, and serum C-telopeptide (betaCTX) were measured.

RESULTS

At study entry, patients in the two groups were well matched for age, gender, severity of neurological deficit, BMD, urinary calcium, and betaCTX. BMD indices declined steadily in the placebo group, and this effect was attenuated significantly by alendronate. After 12 months, there was a 5.3% difference (P<0.001) in total body BMD and a 17.6% difference (P<0.001) in the total hip BMD between the two groups. Alendronate compared with placebo induced significant (P<0.001) reductions in urinary calcium excretion and serum betaCTX. No treatment-related side effects were noted.

CONCLUSIONS

We conclude that alendronate therapy, 70 mg/wk, initiated soon after acute SCI, prevents bone loss and is not associated with side effects.

Short-term statin treatment improves endothelial function and neurohormonal imbalance in normocholesterolaemic patients with non-ischaemic heart failure

OBJECTIVES

To investigate the effect of short-term statin treatment on impaired endothelium-dependent vasodilatation and haemodynamic abnormalities typically occurring in chronic heart failure (CHF).

METHODS

In a double-blind, crossover study endothelium-dependent vasodilatation was measured in conduit and resistance vessels of 23 patients with non-ischaemic CHF after 6 weeks of placebo and 40 mg atorvastatin. The haemodynamic impact was assessed by cardioendocrine hormones, echocardiography and clinical indicators of CHF.

RESULTS

Cholesterol concentrations were population average (low density lipoprotein 3.56 (SEM 0.16) mmol/l, triglycerides 1.70 (0.20) mmol/l and high density lipoprotein 1.17 (0.07) mmol/l). In resistance vessels, the area under the curve ratio during acetylcholine infusion increased from 9.2 (1.9) with placebo to 12.2 (2.1) with statin (p < 0.01). This improvement was reversed during co-infusion with the nitric oxide antagonist N(G)-monomethyl-L-arginine. In conduit arteries, flow-mediated dilatation increased from 5.64 (SEM 0.88)% with placebo to 6.83 (0.97)% with statin (p < 0.05). Endothelium-independent vasodilatation did not change (p = 0.68 for conduit and p = 0.45 for resistance vessels). Endothelin 1 and atrial natriuretic peptide (ANP) decreased from 1.57 (0.08) and 51.3 (1.0) with placebo to 1.42 (0.09) pg/ml (p < 0.05) and 42.1 (7.5) pmol/l (p < 0.05), respectively, with statin.

CONCLUSIONS

In patients with non-ischaemic CHF and population-average cholesterol concentrations, short-term statin treatment improves endothelial function in conduit and resistance vessels and lowers plasma endothelin 1 and ANP concentrations.

Natriuretic peptide and adrenomedullin levels in chronic renal failure and effects of peritoneal dialysis

Plasma levels of B-type natriuretic peptide (BNP) and its N-terminal propeptide (NT-BNP) are elevated in renal impairment and provide a robust prognostic index. The effect of peritoneal dialysis on plasma NT-BNP, however, is unknown. Furthermore, no information exists regarding levels of the N-terminal propeptide for C-type natriuretic peptide (NT-CNP) in renal failure and the effects of peritoneal dialysis. Accordingly, we documented venous levels of these peptides, and adrenomedullin, across peritoneal dialysis. We measured venous BNP, NT-BNP, NT-CNP, adrenomedullin, blood urea nitrogen (BUN) and creatinine before, during and after completion of overnight peritoneal dialysis in 11 patients, and identical sampling was carried out in eight patients (controls) but between peritoneal dialysis treatments. Peptide levels were measured using well-validated, published methods. Baseline levels of NT-CNP (212, 150-303 pmol/l, median and 25th and 75th percentiles) were much higher than recorded previously in healthy volunteers or in heart failure, and correlated with plasma creatinine (rs=0.53, P<0.05). Peritoneal dialysis had no effect on plasma NT-CNP, nor on NT-BNP, BNP or adrenomedullin (all elevated above normal), whereas both BUN and creatinine levels, as expected, declined (P<0.001). We conclude that plasma levels of NT-CNP are grossly elevated in chronic renal failure and correlated with plasma creatinine, but are not altered by peritoneal dialysis. Likewise, BNP, NT-BNP and adrenomedullin are elevated but are not altered by peritoneal dialysis. This information is needed if levels of these hormones are to be used as prognostic indicators or as a guide to the management of patients with chronic renal failure.

Adrenomedullin increases cardiac sympathetic nerve activity in normal conscious sheep

The sympathetic nervous system and adrenomedullin (AM) both participate in the regulation of cardiac and circulatory function but their interaction remains uncertain. We have examined the effects of AM on cardiac sympathetic nerve activity (CSNA) and hemodynamics and contrasted these effects with pressure-matched nitro-prusside (NP) administration in normal conscious sheep. Compared with vehicle control, arterial pressure fell similarly with AM (P=0.04) and NP (P<0.001). Heart rate rose in response to both AM (P<0.001) and NP (P=0.002) but the rise with AM was significantly greater than that induced by NP (P<0.001). Cardiac output increased in response to AM compared with both control and NP (both P<0.001). CSNA burst frequency (bursts/min) were increased in response to both AM (P<0.001) and NP (P=0.005) with the rise in burst frequency being greater with AM compared with NP (P<0.001). CSNA burst area/min was also raised by both AM (P=0.03) and NP (P=0.002) with a trend for burst area being greater with AM than NP (P=0.07). CSNA burst incidence (bursts/100 beats) showed no significant differences between any treatment day. In conclusion, we have demonstrated that AM is associated with a greater increase in CSNA and heart rate for a given change in arterial pressure than seen with the classic balanced vasodilator NP.

Hypertension--still an important cause of heart failure?

Hypertension has been the single most important risk factor for heart failure until the last few decades. Now, it is frequently claimed that atherosclerotic coronary artery disease dominates as the major underlying cause, and hypertension is of lesser importance. We here review evidence regarding the contribution of hypertension to heart failure in the recent decades. It is not possible, in our view, to be confident of the relative importance of hypertension and coronary artery disease since there are significant limitations in the available data. The often-questionable diagnostic criteria used in defining heart failure is one such limitation. The absence or inadequacy of blood pressure recordings over the years prior to a diagnosis of heart failure seriously hinders the reaching of firm conclusions in many reports. Extrapolations from aetiological observations in one racial group to those in other racial groups, and from highly selected study groups in tertiary referral centres to patients with heart failure in primary and secondary care, may not be justified. Finally, the situation of heart failure primarily due to impaired left ventricular diastolic function, where hypertension is a frequent precursor, is often ignored in discussions of aetiology. Our view is that hypertension remains and probably is the single most, important modifiable risk factor for cardiac failure in some races and countries, where the dominant cardiac abnormality is left ventricular diastolic dysfunction. The situation is less clear for patients with heart failure primarily due to left ventricular systolic dysfunction.

Increased cardiac sympathetic nerve activity following acute myocardial infarction in a sheep model

The time course of cardiac sympathetic nerve activity (CSNA) following acute myocardial infarction (MI) is unknown. We therefore undertook serial direct recordings of CSNA, arterial blood pressure (MAP) and heart rate (HR) in 11 conscious sheep before and after MI, and compared them with 10 controls. Conscious CSNA recordings were taken daily from electrodes glued into the thoracic cardiac nerves. Infarction was induced under pethidine and diazepam analgesia by applying tension to a coronary suture. MI size was assessed by left ventricular planimetry (%) at postmortem, peak troponin T and brain natriuretic peptide levels (BNP). Baroreflex slopes were assessed daily using phenylephrine-nitroprusside ramps. The mean infarcted area was 14.4 +/- 2.9%, troponin T 1.88 +/- 0.39 microg l(-1) and BNP 8.4 +/- 1.3 pmol l(-1). There were no differences in haemodynamic parameters or CSNA between groups at baseline. MAP and HR remained constant following MI. CSNA burst frequency increased from baseline levels of 55.8 +/- 7.1 bursts min(-1) to levels of 77.5 +/- 8.7 bursts min(-1) at 2 h post-MI, and remained elevated for 2 days (P < 0.001). CSNA burst area also increased and was sustained for 7 days following MI (P= 0.016). Baroreflex slopes for pulse interval and CSNA did not change. CSNA increases within 1 h of the onset of MI and is sustained for at least 7 days. The duration of this response may be longer because the recording fields decrease with time. This result is consistent with a sustained cardiac excitatory sympathetic reflex.

Adrenomedullin in heart failure: potential therapeutic implications

Adrenomedullin (AM) may play a role in the pathophysiology of heart failure. Plasma levels of AM are raised in cardiovascular disease in proportion to severity of cardiac dysfunction, and plasma AM levels measured in acute myocardial infarction and heart failure are a useful prognostic indicator of outcome. AM administration in both experimental and human heart failure induces a beneficial spectrum of biological action including reduced arterial and atrial pressures, improved cardiac output, inhibition of plasma aldosterone and preservation or augmentation of urinary sodium excretion. Combining AM administration with either angiotensin-converting enzyme inhibition or neutral endopeptidase inhibition results in augmentation of the hemodynamic and renal effects of the individual treatments. Manipulating the AM system may prove beneficial as an adjunctive therapeutic strategy in cardiac disease.

Hemodynamic and hormonal actions of adrenomedullin

Adrenomedullin, a 52-amino acid residue peptide, has numerous biological actions which are of potential importance to cardiovascular homeostasis, growth and development of cardiovascular tissues and bone, prevention of infection, and regulation of body fluid and electrolyte balance. Studies in man using intravenous infusion of the peptide have demonstrated that, at plasma levels detected after myocardial infarction or in heart failure, adrenomedullin reduces arterial pressure, increases heart rate and cardiac output, and activates the sympathetic and renin-angiotensin systems but suppresses aldosterone. The thresholds for these responses differ, being lower under some experimental circumstances for arterial pressure than for the other biological effects. Adrenomedullin administration inhibits the pressor and aldosterone-stimulating action of angiotensin II in man. By contrast, the pressor effect of norepinephrine is little altered by concomitant adrenomedullin administration. Although in the absence of a safe, specific antagonist of the actions of endogenous adrenomedullin it is difficult to be certain about the physiological and pathophysiological importance of this peptide in man, current evidence suggests that it serves to protect against cardiovascular overload and injury. Hope has been expressed that adrenomedullin or an agonist specific for adrenomedullin receptors might find a place in the treatment of cardiovascular disorders.

Effect of changes in body posture on vasoactive hormones in pre-eclamptic women

The aim of this study was to determine the normality or otherwise of neurohormone indices, particularly the sympathetic nervous system, in pre-eclamptic patients and document whether changes in body posture magnify any differences between pre-eclamptic and normal women. We studied 11 women with pre-eclampsia and compared them with 17 matched normotensive pregnant women and eight nonpregnant women. Measurements of arterial pressure, heart rate and neurohormones were carried out with subjects in the left lateral position, then supine, left lateral, with upright posture and finally with assumption of the left lateral position again. Main outcome measures were arterial pressure, heart rate and hormones (plasma norepinephrine, renin activity, natriuretic peptides and endothelin-1). We observed that plasma norepinephrine levels were higher in pre-eclamptic than normotensive pregnant women and this was most obvious in the upright position. Plasma renin activity was likewise higher in pre-eclamptic than normotensive pregnant women, again most obvious with upright posture. Plasma natriuretic peptides and endothelin-1 levels were similar in pre-eclamptics and normotensive pregnant women. These data strengthen the premise that pre-eclampsia is associated with sympathetic overactivity as reflected by plasma norepinephrine levels, most obviously observed in the upright position.

A neural mechanism for sudden death after myocardial infarction

By monitoring efferent cardiac sympathetic nerve activity (CSNA) directly in a conscious animal we observed, for the first time, that ventricular fibrillation (VF) following myocardial infarction (MI) was preceded by a paroxysm of CSNA which was not baroreflexmodulated. This observation has potential therapeutic implications.

Effects of endothelin-1 on release of adrenomedullin and C-type natriuretic peptide from individual human vascular endothelial cells

Regulation of cardiovascular system activity involves complex interactions amongst numerous factors. Three of these vasoactive factors are adrenomedullin, C-type natriuretic peptide (CNP) and endothelin-1 (ET-1), each of which is claimed to have important local effects. To investigate paracrine/autocrine regulation of the secretion of these peptides we used a cell immunoblot method. We postulated that basal release of adrenomedullin and CNP by endothelial cells is modulated by ET-1. Dispersed human aortic endothelial cells were attached to a protein binding membrane and incubated for 1 or 4 h with control medium or with ET-1, endothelin receptor antagonists or antibody to ET-1, and then submitted to immunohistochemical staining. Peptides (adrenomedullin, CNP and ET-1) within individual cells were stained, as was peptide secreted and adjacent to the cell. It was demonstrated that adrenomedullin, CNP and ET-1 can be contained within the same cell. In addition, we observed that individual endothelial cells can secrete all three peptides. The endothelin ET-A/ET-B receptor antagonist, bosentan, the ET-B receptor antagonist, BQ-788, and anti-ET-1 serum decreased the percentage of endothelial cells that secreted adrenomedullin and CNP relative to control. Conversely, the addition of ET-1 induced an increase in the number of endothelial cells that secreted adrenomedullin and CNP. These results provide strong evidence that endogenous ET-1, from human vascular endothelial cells, acts in a paracrine/autocrine manner to modulate the basal release of adrenomedullin and CNP. Our observations of this modulation suggest that vascular endothelial cells of humans constitute an important component of a self-responsive vasoregulatory system.

Adrenomedullin modulates the neurohumoral response to acute volume loading in normal conscious sheep

The physiological role of adrenomedullin (ADM) in volume and pressure homeostasis remains unclear. Accordingly, we assessed possible modulatory actions of ADM infusions on the neurohumoral response to acute volume loading with dextran in normal conscious sheep. Dextran (15 ml/kg), given with concurrent ADM (5.5 pmol/kg per min--raising plasma ADM from below detection to approximately 10 pmol/l) or vehicle control infusions, induced matched significant (P<0.001 by ANOVA) falls in hematocrit (27-30%) during both ADM and control and similar increases in right atrial pressure (approximately 10 mmHg). Compared with control, both systemic (P=0.033) and pulmonary (P=0.005) arterial pressure and peripheral resistance (P=0.004) were reduced during ADM but were raised post-infusion. The dextran-induced increase in cardiac output was augmented by ADM (P=0.048). Dextran-induced increases in plasma atrial natriuretic peptide (ANP; P=0.008), brain natriuretic peptide (BNP; P=NS) and cyclic guanosine monophosphate (cGMP; P=0.003) were augmented post-ADM infusions. The dextran-induced fall in plasma renin activity (PRA) was attenuated by ADM (P=0.039) whereas plasma aldosterone levels were unaltered. ADM augmented the increase in urinary volume during the second 2-h clearance period post-dextran. Our data indicate that ADM modifies the hemodynamic and hormonal response to an acute volume challenge, enhances natriuretic peptide secretion and reduces systemic vascular resistance. These results provide further evidence that ADM plays a physiological role in volume and pressure homeostasis.

Comparative actions of adrenomedullin and nitroprusside: interactions with ANG II and norepinephrine

The role of adrenomedullin (ADM) in volume and pressure homeostasis remains undefined. Accordingly, we compared the biological responses to infusions of ADM and nitroprusside (NP; matched for reduction of arterial pressure) and assessed their effects on responses to ANG II and norepinephrine in eight conscious sheep. During matched falls in arterial pressure (8-10 mmHg, both P < 0.001) ADM and NP induced similar increases in heart rate. ADM increased cardiac output (P < 0.001), and the fall in calculated peripheral resistance was greater with ADM than NP (P = 0.013). ADM infusions raised plasma ADM levels (P < 0.001), plasma renin activity (P = 0.001), and ANG II (P < 0.001) but tended to blunt any concurrent rise in aldosterone compared with NP (P = 0.056). ADM maintained both urine flow (P < 0.001) and sodium excretion (P = 0.01) compared with falls observed with NP. ADM attenuated the vasopressor actions of exogenous ANG II (P = 0.006) but not norepinephrine. In addition, ADM antagonized the ANG II-induced rise in plasma aldosterone (P < 0.001). In conclusion, ADM induces a different spectrum of hemodynamic, renal, and endocrine actions to NP. These results clarify mechanisms by which ADM might contribute to volume and pressure homeostasis.

Bioactivity of adrenomedullin and proadrenomedullin N-terminal 20 peptide in man

Although the biological effects of adrenomedullin (AM) and PAMP have been reported extensively in animal studies and from in-vitro experiments, relatively little information is available on responses to the hormone administered to man. This review summarizes data from the few studies carried out in man. In healthy volunteers, i.v. infusion of AM reduces arterial pressure, probably at a lower rate of administration than is required to elicit other responses. AM stimulates heart rate, cardiac output, plasma levels of cAMP, prolactin, norepinephrine and renin whilst inhibiting any concomitant response in plasma aldosterone. Little or no increase in urine volume or sodium excretion has been observed. Patients with essential hypertension differ only in showing a greater fall in arterial pressure and in the development of facial flushing and headache. In patients with heart failure or chronic renal failure, i.v. AM has similar effects to those seen in normal subjects but also induces a diuresis and natriuresis, depending on the dose administered. Infusion of AM into the brachial artery results in a dose-related increase in forearm and skin blood flow, more prominent and more dependent on endogenous nitric oxide in healthy volunteers than in patients with cardiac failure. When infused into a dorsal hand vein, AM partially reversed the venoconstrictor action of norepinephrine. Although much more information is required to clarify the role of AM under physiological and pathophysiological circumstances, it is clear that it has prominent hemodynamic and neurohormonal effects, though generally lesser urinary effects when administered short-term in doses sufficient to raise its levels in plasma to those seen in a number of clinical disorders. The only study of PAMP in man showed that its skeletal muscle vasodilator potency, when infused into the brachial artery of healthy volunteers, was less than one hundredth that of AM, and it was without effect on skin blood flow.

Adrenomedullin augments the neurohumoral response to haemorrhage in non-pregnant but not in pregnant sheep

Adrenomedullin (ADM) is a novel peptide with actions which include reduction of arterial pressure and interaction with a number of hormone systems. In order to assess possible interactions with the renin-angiotensin system (RAS) and the hypothalamo-pituitary-adrenal (HPA) axis, we have examined neurohumoral responses to hypotensive haemorrhage (15 ml/kg over 15 min) with or without co-infusions of ADM (5.5 pmol/kg per min) in six non-pregnant and eight pregnant conscious sheep. Haemorrhage induced a greater decrease in arterial pressure, but a blunted increase in heart rate in pregnant sheep. There was no significant effect of ADM on haemodynamic responses to haemorrhage in either group. In non-pregnant sheep, haemorrhage-induced activation of both RAS and HPA was significantly augmented by ADM, as indicated by greater increases in plasma renin activity (P<0.01), angiotensin II (P<0.05) and arginine vasopressin (P<0.01). In contrast, ADM did not augment these responses to haemorrhage in pregnant sheep. Rather, plasma concentrations of aldosterone (P=0.039) and adrenocorticotrophic hormone (P=0.012) were decreased by ADM. In conclusion, ADM-induced augmentation of the RAS and HPA responses to hypotensive haemorrhage is abolished in the pregnant state.

Brain natriuretic peptide-guided therapy for heart failure

The drug treatment of heart failure, once simple, has become complex. Apart from a loop diuretic and digoxin, most patients should now be receiving an angiotensin-converting enzyme inhibitor (or angiotensin II receptor blocker), a beta-blocker and spironolactone. Newer drugs, such as endothelin-receptor antagonists and combined blockers of converting-enzyme and neutral endopeptidase, might soon become available. When to introduce these drugs and what dose is optimal for any individual, are questions that currently vex clinicians. We proposed that plasma levels of the cardiac hormone brain natriuretic peptide (BNP, or better, its 1-76 amino-acid N-terminal fragment, N-BNP), would provide an objective index for guiding drug treatment in patients with established, stable cardiac failure. In a pilot study, 69 patients were randomized to drug treatment based on clinical criteria, or based on plasma levels of N-BNP. After a median follow-up of 9.6 months, those in the N-BNP group had fewer clinical end-points than those in the group managed by clinical criteria alone (19 vs 54; P= 0.02). These preliminary data encourage the concept that the increasingly complex pharmacotherapy for heart failure, both chronic (as in this trial) and acute, might best be guided by an objective measure such as plasma levels of BNP or N-BNP.

Identification of amino-terminal pro-C-type natriuretic peptide in human plasma

We report the first identification of a circulating peptide from the amino-terminal end of proCNP. A specific radioimmunoassay was established based on antisera to the synthetic peptide proCNP(1-15). Extracts of plasma, drawn from patients with congestive heart failure or from sheep with experimental heart failure, were subjected to size exclusion and reverse-phase high-pressure liquid chromatography (HPLC) coupled to radioimmunoassay (RIA). These studies revealed the presence of an immunoreactive peptide with a molecular weight (M(r) approximately 5 kDa) similar to that expected for NT-proCNP(1-50), a potential fragment released during processing of pro(CNP). The same material was isolated from extracts of homogenized ovine pituitary, a tissue known to be a relatively enriched source of CNP. Plasma NT-proCNP levels in 22 patients with congestive heart failure (9.7 +/- 0.5 pmol/L, mean +/- SEM, range 5.4-13.7 pmol/L) were raised (P = 0.003) compared to those in 16 healthy volunteers (7.4 +/- 0.3 pmol/L, range 5.7-10.7 pmol/L) and were higher than levels reported for CNP in similar subjects. This first identification of circulating NT-proCNP opens the possibility of studying the factors regulating CNP production and metabolism in vivo.

Differing thresholds for modulatory effects of adrenomedullin infusion on haemodynamic and hormone responses to angiotensin II and adrenocorticotrophic hormone in healthy volunteers

Experimental data indicate that adrenomedullin (AM) interacts at various levels with the renin-angiotensin-aldosterone system and the hypothalamic-pituitary-adrenal axis, but data from humans are scant. We examined the effects of intermediate-dose, short-term AM infusion on angiotensin II- and adrenocorticotrophic hormone (ACTH)-mediated hormone and haemodynamic responses in healthy subjects. Seven normal volunteers (age 18-25 years) completed a placebo-controlled crossover study. Each subject was studied on day 4 of two periods of a low-salt diet (40 mmol of sodium and 80 mmol of potassium daily), receiving incremental infusions of angiotensin II in the morning and ACTH in the afternoon of each study day, on a background infusion of AM (4 pmol.min(-1).kg(-1)) or vehicle (hemaccel). Achieved plasma AM levels (23+/-6 pmol/l) and peak angiotensin II levels (160 pmol/l) were similar on the two experimental days. While the pressor action of angiotensin II was attenuated by AM (P<0.01) and noradrenaline levels rose (P<0.05), the aldosterone response was unaltered. During ACTH infusion, AM increased heart rate (P<0.01), plasma adrenaline (P<0.01) and plasma noradrenaline (P<0.05), and augmented the cortisol response (P<0.01), but was without effect on aldosterone levels and blood pressure. We conclude that the threshold for the effects of AM on aldosterone secretion in humans is set higher than for other biological responses to this hormone, namely blood pressure, heart rate, sympathetic activity and cortisol secretion, under these experimental conditions.

A Comparative Study of Blood Pressure Control with Short In-Center versus Long Home Hemodialysis

We conducted a randomized crossover trial to establish, within patients, whether long-slow hemodialysis (HD) was associated with better blood pressure (BP) control than standard HD. Nine home HD patients, not on antihypertensive drugs, were dialyzed to the same eKt/V(urea) and target weights for 6-8 h (LD) at home and for 3.5-4.5 h (SD) in the dialysis center 3 times weekly in randomized sequence, with each phase lasting 8 weeks. Ambulatory BP, bioimpedance, neurohormones and autonomic function were measured in each phase. Pre- and postdialysis systolic, ambulatory systolic and diastolic BP were all higher with SD than with LD and intradialysis hypotension was more common. Weight, ECF volume and neurohormones did not differ between treatments. Muscle sympathetic activity was increased in both phases and cardiac sympathetic activity tended higher during SD. These findings suggest that additional factors to ECF volume may contribute to the superior BP control produced by long-slow HD.

Plasma N-terminal pro-brain natriuretic peptide and adrenomedullin: prognostic utility and prediction of benefit from carvedilol in chronic ischemic left ventricular dysfunction. Australia-New Zealand Heart Failure Group

OBJECTIVES

We sought to assess plasma concentrations of the amino (N)-terminal portion of pro-brain natriuretic peptide (N-BNP) and adrenomedullin for prediction of adverse outcomes and responses to treatment in 297 patients with ischemic left ventricular (LV) dysfunction who were randomly assigned to receive carvedilol or placebo.

BACKGROUND

Although neurohormonal status has known prognostic significance in heart failure, the predictive power of either N-BNP or adrenomedullin in chronic ischemic LV dysfunction has not been previously reported.

METHODS

Plasma N-BNP and adrenomedullin were measured in 297 patients with chronic ischemic (LV) dysfunction before randomization to carvedilol or placebo, added to established treatment with a converting enzyme inhibitor and loop diuretic (with or without digoxin). The patients' clinical outcomes, induding mortality and heart failure events, were recorded for 18 months.

RESULTS

Above-median N-BNP and adrenomedullin levels conferred increased risks (all p < 0.001) of mortality (risk ratios [95% confidence intervals]: 4.67 [2-10.9] and 3.92 [1.76-8.7], respectively) and hospital admission with heart failure (4.7 [2.2-10.3] and 2.4 [1.3-4.5], respectively). Both of these predicted death or heart failure independent of age, New York Heart Association functional class, LV ejection fraction, previous myocardial infarction or previous admission with heart failure. Carvedilol reduced the risk of death or heart failure in patients with above-median levels of N-BNP or adrenomedullin, or both, to rates not significantly different from those observed in patients with levels below the median value.

CONCLUSIONS

In patients with established ischemic LV dysfunction, plasma N-BNP and adrenomedullin are independent predictors of mortality and heart failure. Carvedilol reduced mortality and heart failure in patients with higher pre-treatment plasma N-BNP and adrenomedullin.

Hypotensive and Natriuretic Actions of Adrenomedullin in Subjects With Chronic Renal Impairment

Abstract —Plasma levels of adrenomedullin are increased in chronic renal failure. The significance of this finding is uncertain, because the biological effects of adrenomedullin in renal impairment are unknown. Therefore, we studied the effects of adrenomedullin infusion in subjects with chronic renal impairment. Eight males with IgA nephropathy and plasma creatinine of 0.19±0.03 mmol/L (mean±SEM) were studied in a vehicle-controlled crossover design. Each subject was studied twice; subjects were administered either adrenomedullin at a low dose and then a high dose (2.9 and 5.8 pmol/kg per minute, respectively, for 2 hours each) or a 4-hour vehicle control (Hemaccel), in random order, on day 4 of controlled metabolic diets. Adrenomedullin infusion achieved plasma adrenomedullin concentrations in the pathophysiological range after the low (31.2±5.1 pmol/L) and high (47.4±4.3 pmol/L) dose, and plasma cAMP was increased. Compared with vehicle control, high-dose adrenomedullin increased peak heart rate (+21.7±3.3 bpm, P <0.01) and cardiac output (+2.9±0.2 L/min, P <0.01) and lowered both systolic and diastolic blood pressures by >10 mm Hg ( P <0.05). Plasma renin activity, angiotensin II, and norepinephrine increased by up to 50% above baseline levels ( P <0.05 for all), whereas aldosterone and epinephrine were unchanged. Urinary volume and sodium excretion increased significantly ( P <0.05) with low-dose adrenomedullin, whereas creatinine clearance was stable, and proteinuria tended to decrease. In subjects with chronic renal impairment due to IgA nephropathy, adrenomedullin infusion lowered blood pressure, stimulated sympathetic activity and renin release, and caused diuresis and natriuresis. Adrenomedullin may have a role in modulating blood pressure and kidney function in renal disease.

Atrial (ANP) and brain natriuretic peptide (BNP) expression after myocardial infarction in sheep: ANP is synthesized by fibroblasts infiltrating the infarct

Cardiac gene expression of atrial natriuretic peptide (ANP) and that of brain natriuretic peptide (BNP) are markedly elevated after myocardial infarction. The cellular distribution and temporal responses of ANP and BNP messenger RNA (mRNA) expression were compared by in situ hybridization for 5 weeks after left coronary artery ligation in sheep. Ligation resulted in highly reproducible, transmural, left ventricular infarcts. Within the infarct, ANP mRNA appeared from 7 days after ligation, whereas BNP expression was undetectable in the infarct at any time. The cells synthesizing ANP were shown by in situ hybridization and immunocytochemistry to be fibroblasts invading the infarct. The appearance of ANP expression coincided with the transition of these cells to the myofibroblast phenotype. Treatment of cultured cardiac fibroblasts with transforming growth factor-beta (10 ng/ml) induced the expression of alpha-smooth muscle actin, characteristic of the transformation to myofibroblasts, and raised ANP concentrations in the medium. In the surviving myocardium of the left ventricle, ANP and BNP expression increased in response to ligation, BNP mRNA was particularly strong at the lateral margins of the infarct. In both left and right atria, levels of BNP mRNA increased markedly over the first 18 h, whereas levels of atrial ANP mRNA decreased over 3 days after infarction. This is the first report of ANP expression and synthesis by cardiac fibroblasts invading the fibrotic scar, suggesting that ANP may be involved in regulating fibroblast proliferation during reparative fibrosis.

Adrenomedullin attenuates pressor response to angiotensin II in conscious sheep

Biologic actions attributed to adrenomedullin include reduction of arterial pressure and suppression of aldosterone secretion. To assess possible in vivo antiangiotensin II actions of adrenomedullin, we examined hemodynamic and adrenal responses to stepped angiotensin II infusions with or without co-infusions of adrenomedullin (33 ng/kg/min) in conscious sheep under controlled conditions of a low sodium intake. Plasma adrenomedullin levels rose during peptide infusions (p < 0.001) to plateau at approximately 15-18 pM. The dose-dependent pressor response (15-20 mm Hg) of angiotensin II was both delayed and markedly attenuated (p = 0.017) by adrenomedullin, which also stimulated heart rate (p < 0.001) and cardiac output (p < 0.001). Adrenomedullin prevented the angiotensin II-induced increase in peripheral resistance (p < 0.001). Plasma aldosterone responses to angiotensin II were variable and were not significantly altered by concomitant adrenomedullin infusion. In conclusion, low-dose infusion of adrenomedullin administered to conscious sheep on a low-salt diet clearly antagonized the vasopressor actions of administered angiotensin II while stimulating cardiac output and heart rate. The data suggest a possible role for adrenomedullin in cardiovascular homeostasis in part through antagonism of the vasopressor action of angiotensin II.

Beneficial renal and hemodynamic effects of omapatrilat in mild and severe heart failure

Omapatrilat is a member of the new drug class of vasopeptidase inhibitors that may offer benefit in the treatment of heart failure (HF) through simultaneous inhibition of angiotensin-converting enzyme and neutral endopeptidase. We examined the effects of omapatrilat in a placebo-controlled crossover study using a pacing model of HF. Seven sheep were paced sequentially at 180 bpm (mild HF) and then 225 bpm (severe HF) for 7 days each. Omapatrilat (0.005 mg/kg) or vehicle was administered by intravenous bolus on days 4 to 7 of each paced period. Omapatrilat lowered mean arterial and left atrial pressure and increased cardiac output acutely and chronically in both mild and severe HF (P<0.01 for all). Plasma atrial and brain natriuretic peptide and cGMP levels were stable acutely (P=NS), while brain natriuretic peptide increased after repeated dosing in severe HF (P<0.05). Plasma renin activity rose, whereas angiotensin II and aldosterone levels fell after acute and repeated dosing in both states (P<0.01 for all). Omapatrilat increased urinary sodium excretion by day 7 in both mild and severe HF (P<0.05). Effective renal plasma flow and glomerular filtration rate increased or were stable after omapatrilat in mild and severe HF after both acute and repeated dosing. Omapatrilat exhibited pronounced acute and sustained beneficial hemodynamic and renal effects in both mild and severe heart failure.

Hemodynamic, hormone, and urinary effects of adrenomedullin infusion in essential hypertension

We examined the effects of the vasodilator peptide adrenomedullin (AM) infused intravenously into subjects with essential hypertension. Eight men 39 to 58 years old with uncomplicated hypertension (147/96+/-5/3 mm Hg at baseline) were studied in a placebo-controlled, crossover design. Each subject received intravenous AM in a low and a high dose (2.9 and 5.8 pmol. kg(-1). min(-1) for 2 hours each) or vehicle-control (Hemaccel) infusion in a random order on day 4 of a controlled metabolic diet (80 mmol/d Na(+), 100 mmol/d K(+)). Plasma AM reached pathophysiological levels during infusion (18+/-4 pmol/L in low dose, 34+/-9 pmol/L in high dose) with a concurrent rise in plasma cAMP (+8.4+/-1.2 pmol/L, P:<0. 05 compared with control). Compared with control, high-dose AM increased peak heart rate (+17.8+/-2.3 bpm, P<0.01), lowered systolic (-24.6+/-0.9 mm Hg; P<0.01) and diastolic (-21.9+/-1.4 mm Hg; P<0.01) blood pressure, and increased cardiac output (+1.0+/-0. 1 L/min in low dose, +2.9+/-0.2 L/min in high dose; P<0.01 for both). Despite a rise in plasma renin activity during high dose (P<0.05), aldosterone levels did not alter. Plasma norepinephrine levels increased 1295+/-222 pmol/L (P<0.001) and epinephrine increased 74+/-15 pmol/L (P<0.05) with high-dose AM compared with control. AM had no significant effect on urine volume and sodium excretion. In subjects with essential hypertension, the intravenous infusion of AM to achieve pathophysiological levels produced significant falls in arterial pressure, increased heart rate and cardiac output, and stimulated the sympathetic system and renin release without concurrent increase in aldosterone. Urinary parameters were unaltered. Although AM has potent hemodynamic and neurohumoral effects in subjects with essential hypertension, the threshold for urinary actions is set higher.

The clinical, cardiac, renal, arterial and neurohormonal effects of omapatrilat, a vasopeptidase inhibitor, in patients with chronic heart failure

OBJECTIVES

We sought to examine the effects of long-term vasopeptidase inhibition in patients with heart failure.

BACKGROUND

The long-term effects of omapatrilat, an agent that inhibits both neutral endopeptidase and angiotensin-converting enzyme, on clinical status, neurohormonal indexes and left ventricular function in patients with chronic heart failure (CHF) have not been previously documented.

METHODS

Forty-eight patients in New York Heart Association functional class II or III, with left ventricular ejection fraction (LVEF)< or =40% and in sinus rhythm were randomized to a dose-ranging pilot study of omapatrilat for 12 weeks. Measurements were performed at baseline and 12 weeks.

RESULTS

There was an improvement in functional status, as reported by the patient (p<0.001) and physician (p<0.001) at 12 weeks. Dose-dependent improvements in LVEF (p<0.001) and LV end-systolic wall stress (sigma) (p<0.05) were seen, together with a reduction in systolic blood pressure (p<0.05). There was evidence of a natriuretic effect (p<0.001), and total blood volume decreased (p<0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (p<0.01) in the high dose groups, with a reduction in predose plasma brain natriuretic peptide (p<0.001) and epinephrine (p<0.01) levels after 12 weeks of therapy. Omapatrilat was well tolerated.

CONCLUSIONS

The sustained hemodynamic, neurohumoral and renal effects of omapatrilat, together with improved functional status, suggest that vasopeptidase inhibition has potential as a new therapeutic modality for the treatment of CHF.

Impact of NO on ET-1- and AM-induced inotropic responses: potentiation by combined administration

We characterize herein the impact of myocardial nitric oxide (NO) synthesis on the inotropic response to two cardioactive peptides, endothelin-1 (ET-1) and adrenomedullin (AM). In the isolated perfused rat heart preparation, intracoronary infusion of AM (0.03 and 1 nmol/l) and ET-1 (0.08 and 1 nmol/l) for 30 min induced a dose-dependent, gradual increase in developed tension, the maximal responses being equal. Inhibition of myocardial NO synthase (NOS) by N(omega)-nitro-L-arginine methyl ester (L-NAME; 300 micromol/l) enhanced the inotropic response to ET-1 at a concentration of 1 nmol/l; meanwhile, the effect of AM was not augmented significantly. The inotropic response to simultaneous administration of low, equipotent doses of AM (0.03 nmol/l) and ET-1 (0.08 nmol/l) was significantly smaller than that of either peptide alone. This depressed response was more than overcome by concomitant administration of L-NAME. In conclusion, this study reveals that the maximal inotropic response to ET-1 can be augmented by inhibition of myocardial NOS, whereas it has only a minor impact on the effect of AM. The inotropic response to combined administration of low doses of AM and ET-1 is substantially suppressed by endogenous NO, whereas the individual effects of the peptides at these doses are not the subject of secondary modulation by NO.