Postnatal effects of intrauterine treatment of the growth-restricted ovine fetus with intra-amniotic insulin-like growth factor-1.

KEY POINTS: Fetal growth restriction increases the risk of fetal and neonatal mortality and morbidity, and contributes to increased risk of chronic disease later in life. Intra-amniotic insulin-like growth factor-1 (IGF1) treatment of the growth-restricted ovine fetus improves fetal growth, but postnatal effects are unknown. Here we report that intra-amniotic IGF1 treatment of the growth-restricted ovine fetus alters size at birth and mechanisms of early postnatal growth in a sex-specific manner. We also show that maternal plasma C-type natriuretic peptide (CNP) products are related to fetal oxygenation and size at birth, and hence may be useful for non-invasive monitoring of fetal growth restriction. Intrauterine IGF1 treatment in late gestation is a potentially clinically relevant intervention that may ameliorate the postnatal complications of fetal growth restriction. ABSTRACT: Placental insufficiency-mediated fetal growth restriction (FGR) is associated with altered postnatal growth and metabolism, which are, in turn, associated with increased risk of adult disease. Intra-amniotic insulin-like growth factor-1 (IGF1) treatment of ovine FGR increases growth rate in late gestation, but the effects on postnatal growth and metabolism are unknown. We investigated the effects of intra-amniotic IGF1 administration to ovine fetuses with uteroplacental embolisation-induced FGR on phenotypical and physiological characteristics in the 2  weeks after birth. We measured early postnatal growth velocity, amino-terminal propeptide of C-type natriuretic peptide (NTproCNP), body composition, tissue-specific mRNA expression, and milk intake in singleton lambs treated weekly with 360 µg intra-amniotic IGF1 (FGRI; n = 13 females, 19 males) or saline (FGRS; n = 18 females, 12 males) during gestation, and in controls (CON; n = 15 females, 22 males). There was a strong positive correlation between maternal NTproCNP and fetal oxygenation, and size at birth in FGR lambs. FGR lambs were ∼20% lighter at birth and demonstrated accelerated postnatal growth velocity. IGF1 treatment did not alter perinatal mortality, partially abrogated the reduction in newborn size in females, but not males, and reduced accelerated growth in both sexes. IGF1-mediated upregulation of somatotrophic genes in males during the early postnatal period could suggest that treatment effects are associated with delayed axis maturation, whilst treatment outcomes in females may rely on the reprogramming of nutrient-dependent mechanisms of growth. These data suggest that the growth-restricted fetus is responsive to intra-amniotic intervention with IGF1, and that sex-specific somatotrophic effects persist in the early postnatal period.

Effects of pre-eclampsia and fetal growth restriction on C-type natriuretic peptide.

OBJECTIVE: To determine changes in plasma C-type natriuretic peptide (CNP), a paracrine product of the vascular endothelium, in pregnancies with vascular disorders, and relate these to time of presentation and severity. DESIGN: Retrospective nested cases and controls. SETTING: Community study, Auckland New Zealand. POPULATION: Screening for Pregnancy Endpoints (SCOPE) data and bio-bank of maternal plasma. METHODS: Maternal plasma amino terminal proCNP (NTproCNP) was measured by radioimmunoassay in early (14-16 weeks of gestation, and again at 19-21 weeks of gestation) and late (34-36 weeks of gestation) pregnancy in three groups of women (20 per group): pre-eclampsia (pre-eclampsia); gestational hypertension (GHT) with small for gestational age (SGA); and uncomplicated pregnancy. MAIN OUTCOME MEASURES: Change in NTproCNP and associations with concurrent blood pressure, time of case presentation, severity, and infant birthweight. RESULTS: Plasma NTproCNP in early pregnancy in women with vascular disorders did not differ from those found in controls. In late pregnancy, levels in pre-eclampsia (28.8 ± 2.3 pM) and in GHT with SGA (28.6 ± 4.8 pM) were significantly increased (P = 0.01 and 0.027, respectively) compared with controls (21.3 ± 1 pM). In pre-eclampsia, levels were significantly higher (P < 0.03) at 14-16 weeks of gestation in women diagnosed prior to 34 weeks of gestation. Combining all three groups, associations of NTproCNP with concurrent diastolic and mean arterial pressure were found at 34-36 weeks of gestation (r = 0.46). No significant associations were identified with birthweight. CONCLUSIONS: CNP secretion during gestation is responsive to vascular stress. Plasma NTproCNP measurements may have clinical application in late pregnancy in defining the different phenotypes associated with pre-eclampsia.

C-type natriuretic peptide in Parkinson's disease: reduced secretion and response to deprenyl.

C-type natriuretic peptide (CNP) is a neurotrophic factor widely expressed in the central nervous system including the basal ganglia, limbic system and hypothalamus. Nothing is known of CNP's role in the human brain but in rodents CNP promotes axon growth and branching, and interacts with dopaminergic function in models of addiction. Because preliminary evidence showed reduced levels in Parkinson's disease (PD), we examined concentrations of CNP peptides in cerebrospinal fluid (CSF) in 146 PD patients from the DATATOP study to determine changes over time in relation to medication status and cognitive function. CNP and an aminoterminal product of proCNP (NTproCNP) were measured in extracts from stored CSF by radioimmunoassay. CSF samples were obtained twice-at enrolment and at the study's endpoint (requirement for levodopa treatment) after treatment with placebo or deprenyl. At enrolment, median baseline concentration of CSF NTproCNP (776 pmol/L, n = 146) was significantly lower than that in a reference group without neurological disorder (1,010 pmol/L, p < 0.001). Concentrations declined significantly during placebo (p = 0.02) and lower values at enrolment were associated with more rapid functional decline (p < 0.01). In contrast, deprenyl-a treatment which delayed the need for levodopa-nullified the time-dependent decline in CSF NTproCNP. In conclusion subnormal CSF NTproCNP which declines with time and associates with increasing functional disability implicates CNP in PD. Concordant clinical and peptide responses to deprenyl suggest that some of the benefits of monoamine oxidase inhibitors in PD are mediated by preserving tissue CNP activity.

Impact of age, phenotype and cardio-renal function on plasma C-type and B-type natriuretic peptide forms in an adult population.

CONTEXT: In contrast to the cardiac hormones, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), variations in plasma concentrations of C-type natriuretic peptide (CNP) in healthy adults are ill-defined, limiting their clinical application. OBJECTIVE: Our objective was to define the effect of age, phenotype (gender, height, BMI), and cardiac and renal function on plasma CNPs in an adults population without renal or cardiovascular disease. DESIGN AND SETTING: This was a prospective cross-sectional observational study of adult volunteers, aged 21-80 years, randomly selected from the electoral roll. SUBJECTS AND METHODS: Plasma CNP and its associated aminoterminal propeptide (NTproCNP) were measured in 258 subjects and related to age, gender, height and plasma creatinine. Subgroup analyses seeking associations with cardiac function (plasma BNP and NTproBNP) and bone turnover bone-specific alkaline phosphatase (bALP) were also determined. RESULTS: Plasma concentrations of CNPs in men continued to decline from adolescent values to reach a nadir in the 5th decade after which values increased. Similar but less marked changes occurred in women. In both sexes, NTproCNP was inversely and independently correlated with height. In contrast to B-type natriuretic peptides (BNPs), NTproCNP was higher in men, significantly related to creatinine and positively related to bALP. CONCLUSIONS: Gender- and age-specific changes affect CNPs in adults. Inverse associations of NTproCNP with adult height, positive correlation with creatinine - and in contrast to CNP - no association with BNP are further unique findings distinguishing NTproCNP, which need to be considered in future studies.

Caloric restriction, but not caloric loading, affects circulating fetal and maternal C-type natriuretic peptide concentrations in late ovine gestation.

The factors regulating the greatly elevated concentrations of maternal plasma C-type natriuretic peptide (CNP) forms in ruminant pregnancy are largely unknown, but nutrient status is likely to be important. Previous work has shown that increases in maternal plasma CNP, sourced from the placenta, occur in response to caloric restriction in late gestation. Whether oversupply of nutrients also regulates CNP secretion in pregnancy has not been studied. Hypothesising that CNP in fetal and maternal tissues will be responsive to both deficiency and excess, we studied changes in CNP and a cosecreted fragment, namely N-terminal pro-CNP (NTproCNP), during short-term periods of caloric restriction (CR) and loading (CL). Twin-bearing ewes received CR (fasted Days 121-124), CL (Days 110-124) or control maintenance diets. During CR, fetal plasma CNP forms, insulin-like growth factor (IGF)-1 and liveweight all fell, and maternal plasma NTproCNP increased. During CL, fetal IGF-1 increased, whereas CNP forms and liveweight were unchanged, as were maternal concentrations of CNP forms. The high abundance of CNP peptides in placental tissues was unaffected by these short-term changes in nutrient supply. We conclude that CNP in the fetal-maternal unit is acutely responsive to undernutrition, but is unaffected by oversupply in late gestation.

Pharmacodynamic responses of plasma and tissue C-type natriuretic peptide to GH: correlation with linear growth in GH-deficient rats.

Studies from genetic modification and spontaneous mutations show that C-type natriuretic peptide (CNP) signalling plays an essential part in postnatal endochondral growth, but measurement of CNP proteins and changes in their abundance in tissues and plasma during normal growth has not been reported. Using rodent pups with GH deficiency, we now describe the pharmacodynamic response of CNP and rat amino-terminal proCNP (NTproCNP) in plasma and tissues, and relate these to changes in linear growth (nose-tail length, tibial length and tibial growth plate width) during the course of 1 week of GH or saline (control) administration. Compared with saline, significant increases in plasma and tissue CNP forms were observed after 24 h in GH-treated pups and before any detectable change in linear growth. Whereas CNP abundance was increased in most tissues (muscle, heart and liver) by GH, enrichment was the greatest in extracts from growth plates and kidney. Plasma and tissue concentrations in GH-treated pups were sustained or further increased at 1 week when strong positive associations were found between plasma NTproCNP and linear growth or tissue concentrations. High content of NTproCNP in kidney tissue strongly correlated with plasma concentrations, which is consistent with previous data showing renal extraction of the peptide. In showing a prompt and significant increase in CNP in tissues driving normal endochondral growth, these findings provide further rationale for CNP agonists in the treatment of growth disorders resistant to current therapies and support the use of CNP concentrations as biomarkers of linear growth.

Plasma C-type natriuretic peptide forms and thyroid status in prepubertal children with acquired thyroid disease.

OBJECTIVE: C-type natriuretic peptide (CNP) and thyroid hormone (TH) are essential for normal skeletal growth. Plasma CNP peptides correlate with growth velocity, but the relationship between thyroid status and CNP production is unknown. This study examined the impact of restoring normal TH levels on CNP and height velocity (HV) in children with acquired hypo- and hyperthyroidism. DESIGN: We performed a prospective, observational study in prepubertal children with acquired hypothyroidism (n = 15) and hyperthyroidism (n = 12). MEASUREMENTS: Blood levels of CNP, amino-terminal proCNP (NTproCNP), bone-specific alkaline phosphatase (BSAP), IGF-I and TH levels were measured before and during the first 6 months of standard treatment for hypo- and hyperthyroidism, and correlations were determined. RESULTS: At baseline, HV, CNP, NTproCNP and BSAP were significantly higher in hyper- than in hypothyroid subjects. Changes in TH after treatment were closely coupled to change in CNP and NTproCNP in hyperthyroid, but not in hypothyroid, children. In addition, a positive association of HV with CNP peptides was found during treatment of hyperthyroidism. Normalizing TH did not correlate with changes in BSAP or IGF-I in either group. CONCLUSIONS: Plasma CNP peptides are higher in children with hyperthyroidism than in those with hypothyroidism at diagnosis and, in hyperthyroid children, change concordantly with TH and HV during treatment. Differential responses of CNP in the two groups suggest CNP production is dependent on growth plate activity and not a direct effect of TH on CNP gene expression. Our findings suggest novel mechanisms underlying changes in skeletal response during treatment in children with acquired thyroid disease.

The trophoblast binucleate cell is the source of maternal circulating C-type natriuretic peptide during ovine pregnancy.

Maternal plasma concentrations of C-type natriuretic peptide (CNP) and a co-secreted bioinactive amino-terminal fragment (NTproCNP) are elevated during ovine pregnancy. Although the uteroplacental unit has been implicated as a likely source of CNP, the relative contributions of specific uterine and placental tissues, and identity of the cellular site/s of production remain unknown. Therefore, we measured CNP and NTproCNP in intercaruncular uterine tissue and maternal (caruncle) and fetal (cotyledon) placental tissues throughout gestation. Concentrations of CNP forms in placental tissues greatly exceeded those in intercaruncular uterine tissue throughout pregnancy (P < 0.05). Mean caruncular concentrations (CNP 32 ± 4, NTproCNP 56 ± 6 pmol g(-1)) peaked at day 60 whereas in the cotyledon there was a progressive increase in CNP forms to peak values (CNP 66 ± 6, NTproCNP 134 ± 9 pmol g(-1)) at day 100-135 followed by a sharp decline just prior to term (day 143). At term CNP gene expression was 6-fold greater in placental tissue compared with intercaruncular uterine tissue. Changes in maternal plasma concentration of CNP forms closely followed those in cotyledonary tissue whereas fetal plasma levels fell progressively throughout gestation. Immunohistochemistry revealed staining in binucleate cells (BNC) and around placental blood vessels. CNP's localization to the BNC suggests a novel endocrine role during pregnancy, in addition to its paracrine actions within the placental vasculature. The function of CNP in maternal circulation remains to be determined, but as proposed for other BNC products, may involve manipulation of maternal physiology and placental function to favour fetal growth.

Predicting surgically remedial primary aldosteronism: role of adrenal scanning, posture testing, and adrenal vein sampling.

Distinguishing surgically remedial forms from other causes of primary aldosteronism (PA) may be difficult, and it is made more challenging by the earlier detection of milder disease. The technical demands of bilateral adrenal vein sampling (AVS)-increasingly advocated for localizing a unilateral autonomous lesion (UAL)- and lack of agreed criteria for establishing unilateral autonomy, add further to the diagnostic challenge. This retrospective review of 49 hypokalemic patients with unequivocal PA (41 with surgically proven and remedial UAL, eight patients with bilateral adrenal hyperplasia) analyzes the value of computerized tomography adrenal scanning (n = 32), 4 h erect posture testing (n = 42), and AVS (n = 27) in predicting and lateralizing a surgically remedial lesion. A fall in plasma aldosterone during 4 h erect posture (positive test) occurred in 63% of patients with UAL and in none with bilateral adrenal hyperplasia. A positive posture test or computerized tomography adrenal scan (single focal macroadenoma) both had high positive predictive value (100% and 89% respectively), but low sensitivity for diagnosis of UAL. AVS, undertaken during low dose ACTH stimulation, localized the UAL in all cases (positive predictive value 100%) where the aldosterone/cortisol ratio of blood drawn from the uninvolved gland was less than that of peripheral blood (contralateral ratio <1). Biochemical severity, reflected by overnight supine plasma aldosterone, was strongly correlated with the degree of contralateral gland suppression (n = 16, r = 0.79, P < 0.001). Importantly, the AVS findings show that when bilateral access is not possible, UAL can be successfully lateralized when only one adrenal vein (the contralateral) is accessed, or the ipsilateral vein is sampled in subjects whose posture test was positive. In this series of patients with overt (hypokalemic) PA, preoperative testing successfully identified a surgically remedial lesion in 39 of 41 cases. Confirmation of the recommended diagnostic approach must now await larger prospective studies.

An unusual cause of hyperinsulinaemic hypoglycaemia syndrome.

Endogenous hyperinsulinism as a cause for hypoglycaemia can be attributed to a number of different causes including insulinoma, sulphonylurea drugs and the newly described disorder non-insulinoma pancreatogenous hypoglycaemia (NIPH). The calcium stimulation test is increasingly used as a method for not only localizing insulinoma but also for distinguishing the above entities. We describe a case in which felonious sulphonylurea administration was used to mimic either an insulinoma or NIPH. Importantly, this case demonstrates that, contrary to previous reports, the insulin response to calcium stimulation in such cases may be uniformly positive and should alert the physician to possible surreptitious sulphonylurea ingestion.

Outcome from surgical management of secretory pituitary adenomas in Christchurch, New Zealand.

BACKGROUND: Recent evidence has highlighted the importance of the neurosurgeon in the management of secretory pituitary tumours, but most reports are from major centres. AIMS: To audit the surgical outcome of patients with acromegaly and Cushing's disease treated in a small centre (Christchurch, New Zealand) by a dedicated neurosurgeon with an interest in pituitary disease, and follow-up through an outpatient Department of Endocrinology. METHODS: All cases of acromegaly and Cushing's disease admitted for surgery in Christchurch Hospital between 1984 and 2000 were audited. Data concerning preoperative findings, surgical remission rate, complications and follow-up were obtained from 44 patients (28 acromegaly, 16 Cushing's disease). RESULTS: Of the 28 acromegalic patients, 14 patients (50%) had a mean growth hormone level <2.5 micro g/L within the first postoperative week. Of the 15 Cushing's disease patients in whom the pituitary fossa was explored, 13 patients (87%) entered a postoperative remission, defined as an 08.00 h cortisol <200 nmol/L (normal range 250-800 nmol/L). No perioperative deaths occurred. Two of the 43 patients (4.7%) developed permanent diabetes insipidus, while eight of the 28 patients who were operated on for acromegaly (29%) eventually required some replacement treatment for hypopituitarism during follow-up (one presented with apoplexy and seven were treated with postoperative radiotherapy). CONCLUSION: In a small centre with a dedicated pituitary surgeon, operative remission rates approach those obtained in larger, more specialized centres. However, given New Zealand's small, but geographically spread population, consideration should be given to establishing one or two units for the surgical management of secretory pituitary adenomas.

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.

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.

C-type natriuretic peptide expression in olfactory regions of rat brain is modulated by acute water deprivation, salt loading and central angiotensin II.

To elucidate the central role of c-type natriuretic peptide (CNP), levels of CNP mRNA in control rat brain were compared with levels following acute water deprivation, salt loading and central administration of angiotensin II (AII), using Northern blot and in situ hybridisation. Rats with water deprivation (WD) had no access to water for 48 h, rats with salt loading (SL) had access to 2% saline for 48 h, and control rats had free access to water. Both WD and SL significantly raised plasma sodium (Na). Levels of CNP mRNA in olfactory regions were significantly decreased in WD and increased in SL. In the medulla, WD and SL both increased CNP mRNA, but levels of CNP mRNA elsewhere in the brain were not significantly altered. Intracerebroventricular AII (500 ng) increased water intake, and induced a significant increase in CNP expression at 4 h in olfactory regions, but not in other brain sites. In summary, CNP expression is regulated in olfactory regions of the rat brain in response to acute challenges to water and salt balance and by central AII.

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.

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.

Delayed metabolism of human brain natriuretic peptide reflects resistance to neutral endopeptidase.

Metabolism of natriuretic peptides is regulated by two degradative pathways: uptake by the clearance receptor (natriuretic peptide receptor C--NPR-C) and hydrolysis by neutral endopeptidase (NEP). Affinity studies favour a dominant role of NPR-C in hormone degradation in several species but do not account for the efficacy of NEP inhibitors in vivo, nor the uniquely prolonged half life (t((1/2))) of human brain natriuretic peptide (hBNP). Postulating that (1) delayed metabolism of hBNP reflects resistance to NEP and (2) interactions between NPR-C and NEP increase enzyme activity, we have used purified ovine and human NEP, plus ovine lung plasma membranes to study the relative importance of receptor and enzyme pathways. We have also related the findings to hormone metabolism in vivo. Binding affinities of atrial natriuretic peptide (ANP), hBNP and ovine BNP (oBNP) to oNPR-C were similar (K(d)=8-16 pM). In contrast, unlike ANP and oBNP, hBNP was not significantly degraded by purified oNEP or plasma membranes. Despite similar (and high) affinity of oNPR-C for oBNP and hBNP, the t((1/2)) of hBNP (12.7 min) was more than fourfold that of oBNP (2.6 min). Although we found no evidence for receptor-enzyme interaction, our results show that the delayed metabolism of hBNP reflects resistance to NEP. These findings have important implications for future treatment strategies in human disease.

Assessment of cardiotoxicity during haemopoietic stem cell transplantation with plasma brain natriuretic peptide.

Cardiac failure is a known complication of haemopoietic stem cell transplantation (HSCT) and is often difficult to diagnose as patients may have multiple medical problems. Since brain natriuretic peptide (BNP) is largely a hormone of cardiac ventricular origin and is released early in the course of ventricular dysfunction, we have examined the value of serial plasma BNP levels for detecting cardiac failure in patients undergoing cytotoxic conditioning for HSCT. Fifteen patients undergoing HSCT were evaluated (10 undergoing autologous HSCT; five undergoing allogeneic HSCT). BNP was measured by radioimmunoassay prior to therapy and weekly for 5 weeks. Seven patients had a significant rise in BNP level (above a previously established threshold of 43 pmol/l associated with cardiac failure), occurring 1-4 weeks post commencement of conditioning. In three of these patients, cardiac failure was subsequently diagnosed clinically 3, 9 and 23 days after a BNP level of 43 pmol/l had been detected. These three patients had the highest peak BNP levels for the group and in each case elevation in BNP level occurred for a period exceeding 1 week. Although numbers were relatively small, a BNP >43 pmol/l was significantly associated with the inclusion of high-dose cyclophosphamide in the preparative regimen (P = 0.02). BNP levels showed no relationship to febrile episodes. In conclusion, these results show that plasma BNP may be used as a marker for early detection of cardiac dysfunction in patients undergoing HSCT, particularly if levels are increased for periods exceeding 1 week. Measurement of BNP during HSCT may be helpful in patients at risk of cardiac failure, in complex clinical situations and in monitoring the cardiotoxicity of preparative regimens.

Deconvolution analysis of cardiac natriuretic peptides during acute volume overload.

Cardiac natriuretic peptides, especially amino terminal pro-Brain Natriuretic Peptide (NT-proBNP), are emerging as powerful circulating markers of cardiac function. However, the in vivo secretion and elimination (t1/2) of these peptides during acute volume overload have not been studied. We present the first report of the secretion and elimination of cardiac natriuretic peptides, based on deconvolution analysis of endogenous ovine plasma levels measured by specific radioimmunoassay. Four normal, conscious sheep underwent rapid right ventricular pacing (225 bpm) for 1 hour to stimulate acute cardiac natriuretic peptide release. Plasma samples and right atrial pressure measurements were taken at regular intervals 30 minutes before, during, and 4 hours after pacing. Baseline right atrial pressure significantly increased (P:=0.02) during the 1 hour of pacing in association with a prompt increase in plasma BNP (P:=0.03), atrial natriuretic peptide (P:=0.01), and NT-proBNP (P:=0.02). Deconvolution analysis showed that the t1/2 of NT-proBNP (69.6+/-10.8 minutes) was 15-fold longer than BNP (4.8+/-1. 0 minutes). Despite sustained increases in atrial pressure, cardiac secretion of natriuretic peptides (particularly atrial natriuretic peptide) fell during the pacing period, suggesting a finite source of peptide for secretion. Size-exclusion high-performance liquid chromatography revealed NT-proBNP to be a single immunoreactive peak, whereas BNP comprised at least 2 immunoreactive forms. These findings, especially the prompt secretion of BNP and the prolonged t1/2 of NT-proBNP, clarify the metabolism of BNP forms and help to explain the diagnostic value of NT-proBNP measurement as a sensitive marker of ventricular function.