An ovine model of acute myocardial infarction and chronic left ventricular dysfunction

In order to develop and validate an ovine model of myocardial infarction with subsequent impairement of left ventricular function, 15 instrumented sheep underwent selective microembolization of the left coronary arteries with 0.5 mL 90 microns polystyrene beads. Hemodynamics and plasma hormones were measured preembolization (baseline) and then at hours 2, 4, 6, and 12 and days 1, 2, 3, 5 and 7 postembolization. Of the 15 sheep studied, 2 (13%) died on the day of embolization from arrhythmias. In the remaining sheep, left ventricular systolic pressure and stroke work (both P < 0.001) were reduced promptly and remained below basal levels. Mean arterial pressure (P < 0.001) increased initially, then decreased to below basal levels by hour 6. Heart rate (P < 0.001) and left atrial pressure (P < 0.05) were increased while cardiac output was decreased (P < 0.05). Left ventricular ejection fraction at day 7 was reduced (38.8 +/- 3.5 vs 46.0 +/- 3.9% preembolization; P < 0.05). The cardiac enzymes creatine kinase (P < 0.001) and troponin-T (P < 0.001) were increased following microembolization and returned to basal levels by days 2 and 5 respectively. Plasma atrial and brain natriuretic peptides (both P < 0.001) and plasma renin activity (P < 0.005) were all increased following embolization. This ovine model mimics the hemodynamic and neurohumoral features of acute myocardial infarction, resulting in left ventricular dysfunction, and should prove suitable for the study of interventions in a number of these conditions.

Biceps rupture in a patient on long-term anticoagulation leading to compartment syndrome and nerve palsies

We report the case of a man on long term anticoagulation who presented with a rupture of the long head of the biceps resulting in a compartment syndrome and nerve palsies.

Hemodynamic, hormonal, and renal effects of adrenomedullin in conscious sheep

Adrenomedullin is a recently discovered peptide that has been shown to reduce arterial pressure and induce natriuresis. However, few studies have examined the biological actions of adrenomedullin in conscious animals in an integrative manner. Accordingly, we have examined the hemodynamic, renal, and endocrine actions of adrenomedullin infused intravenously at 10 and 100 ng.kg-1.min-1 (each 90 min) in a vehicle-controlled study in eight normal conscious sheep. Adrenomedullin reduced right atrial pressure (P < 0.05) and diastolic (15 mmHg, P < 0.01) and mean arterial pressure (10 mmHg, P < 0.05) and increased cardiac output (3 l/min, P < 0.001). Total peripheral resistance was reduced 40% (P < 0.001). Urinary sodium was reduced to 35% of control during the 90-min clearance period immediately postinfusion (P < 0.05). Adrenomedullin increased plasma adenosine 3',5'-cyclic monophosphate levels (P < 0.001). Plasma renin activity was elevated during adrenomedullin (P < 0.001) coincident with the peak hypotensive effect, whereas plasma aldosterone was not affected and plasma norepinephrine levels fell (P < 0.05). In conclusion, adrenomedullin had clear blood pressure-lowering effects with increased cardiac output and stimulation of renin but suppressed sympathetic activation in conscious sheep. The physiological implications of these findings require further study.

Adrenomedullin: a hypotensive hormone in man

1. Adrenomedullin, a recently discovered 52-amino-acid peptide hormone, circulates in plasma at low picomolar levels in man. Animal studies and studies in vitro indicate that it has diverse biological actions, including vasodilatation, natriuresis and diuresis, and positive inotropism as well as anti-proliferative effects. We investigated the bioactivity of two doses of adrenomedullin in healthy human subjects. 2. Human adrenomedullin was given intravenously to eight male subjects at 2 and 8 ng min-1 kg-1, and haemodynamic, hormonal, renal and biochemical responses were recorded in a placebo (vehicle)-controlled, randomized study. 3. Compared with vehicle, adrenomedullin reduced mean arterial pressure (P = 0.05 for duration of infusion, mean difference at end of infusion 7.7 mmHg), systolic arterial pressure (P = 0.04 for duration of infusion, mean difference at end of infusion 10.7 mmHg) and at the lower dose reduced diastolic arterial pressure (P = 0.05 for lower dose, mean difference at end of infusion 6.3 mmHg) in the absence of compensatory responses in sympathetic activity or renin release. Urine volume and electrolyte excretion were unaffected. 4. The threshold for biological activity of adrenomedullin in man is lower, for arterial pressure than for renal or hormonal responses, and is evident at plasma concentrations seen in disorders of the circulation. Adrenomedullin may be an important hormone under pathophysiological circumstances.

Rapid assay of plasma brain natriuretic peptide in the assessment of acute dyspnoea

AIM

Recognition of heart failure may be difficult in patients presenting with acute dyspnoea, particularly in the presence of chronic airways obstruction or obesity. In a previous study of patients with acute dyspnoea, we showed that the measurement of plasma brain natriuretic peptide (BNP)-a hormone secreted in increased amounts by the failing heart-accurately distinguishes heart failure from primary lung disorder. The aim of the present study was to develop a rapid assay for BNP and evaluate its diagnostic use in patients acutely hospitalised for increasing dyspnoea of any cause.

METHODS

A rapid assay for plasma BNP, providing results within 24 h of blood collection, was developed without loss of precision. The results of the rapid and previously established BNP assays were highly correlated (r = 0.9). To determine the diagnostic value of the rapid assay, measurements were undertaken on the day of admission in 123 breathless patients (mean age 68.3, range 23 to 90 years) and related to conventional diagnostic assessments and final outcome.

RESULTS

In patients diagnosed and treated urgently for clinical heart failure, plasma BNP was significantly higher (115 (SE 13) pmol/L, n = 39) than in those without clinical heart failure (33 (5) pmol/L, n = 84, p < 0.001). Using a cut-off of 50 pmol/L for the presence of heart failure, there was discordance between BNP level and clinical diagnosis in 21 of 123 cases. Reassessment after independent analysis of discordant cases increased the difference in BNP level in the presence (123 (13) pmol/L, n = 43) or absence (24 (1.5) pmol/L, n = 80) of heart failure. Using two way analysis of variance, no further improvement in discrimination was found when chest radiographs were used together with the BNP data.

CONCLUSION

Rapid BNP assays are practicable and provide accurate information on cardiac status-superior to chest radiographs in many cases-early in the course of the patient's presentation with acute dyspnoea.

Low-dose brain natriuretic peptide infusion in normal men and the influence of endopeptidase inhibition

1. To assess the threshold dose for bioactivity of brain natriuretic peptide and the role of endopeptidase 24.11 in metabolism of brain natriuretic peptide at physiological plasma levels, we studied eight normal men receiving 2 h infusions of low-dose brain natriuretic peptide [0.25 and 0.5 pmol min-1 kg-1 with and without pretreatment with an endopeptidase inhibitor (SCH 32615, 250 mg intravenously)] in placebo-controlled studies. 2. Plasma brain natriuretic peptide increased 2-fold during the infusion of 0.25 pmol min-1 kg-1 (mean increment above control 3.9 pmol/l, P < 0.001), and tripled (P < 0.001) with 0.5 pmol min-1 kg-1. Plasma renin activity was inhibited by both doses (14.8%, P < 0.01, and 20%, P < 0.001, respectively). A significant natriuresis (56% increase in urine sodium/creatinine ratio, P < 0.02) occurred with the higher dose. Blood pressure, haematocrit, plasma cGMP, atrial natriuretic peptide and aldosterone were unaffected by either dose. 3. Compared with brain natriuretic peptide (0.5 pmol min-1 kg-1) alone, SCH 32615 pretreatment increased peak plasma brain natriuretic peptide (13.4 +/- 0.78 versus 12.4 +/- 0.86 pmol/l, P < 0.05), ANP (7.5 +/- 0.96 versus 5.9 +/- 0.4 pmol/l, P < 0.01) and cGMP (4.8 +/- 1.7 versus 3.9 +/- 1.4 nmol/l, P < 0.001). Plasma renin activity was further suppressed with SCH 32615 pretreatment (29% compared with 20%, P < 0.001). 4. Small acute increments in plasma brain natriuretic peptide (4 pmol/l) have significant biological effects in normal men without altering plasma atrial natriuretic peptide or cGMP.

Hypothalamo-pituitary-adrenal axis response to coronary artery embolization: an ovine model of acute myocardial infarction

Although previous studies have described the hypothalamo-pituitary-adrenal (HPA) response to the stress of acute myocardial infarction, it is not possible to study the hormone changes immediately after infarction in humans. Accordingly, we have examined the HPA response to microembolization of coronary arteries in 13 sheep compared with 5 sham control sheep. Plasma vasopressin (AVP; P < 0.001), ACTH (P = 0.005) and cortisol (P = 0.005) were all increased 2 h (first sample time) after embolization. Plasma ACTH and cortisol levels returned to baseline levels by 6 h but plasma AVP levels did not return to baseline levels until more than 12 h after embolization. Plasma corticotrophin-releasing hormone (CRH) showed no significant change in response to embolization. In a subset of six animals which were sampled more frequently, the peak responses for plasma AVP, ACTH and cortisol occurred at 40 min after embolization. The maximum responses in any individual sheep observed at this time point were 744 pmol/l for AVP, 144 pmol/l for ACTH and 492 nmol/l for cortisol. CRH levels tended to increase across the first hour but these changes were not statistically significant. In conclusion, the stress hormone responses to microembolization of the coronary arteries have been defined in an ovine model of myocardial infarction. This model is suitable for studying the effects of novel treatments to reduce the stress of myocardial infarction.

Heterotopic ossification after severe burns: a report of three cases and review of the literature

Heterotopic ossification (HO) is a rare complication of head and spinal injuries, polio, orthopaedic surgery and burns. Three patients are reported, who developed severe HO following major, life-threatening burn injury. The aetiology, diagnosis and treatment of this condition are discussed. Particular attention is given to measures which may help reduce morbidity.

Comparative bioactivity of atrial and brain natriuretic peptides in an ovine model of heart failure

1. Whereas many studies have detailed the effects of exogenous atrial natriuretic peptide (ANP) infusions in heart failure, and a limited number have examined the effects of brain natriuretic peptide (BNP), none have directly compared the bioactivity of similar doses of ANP and BNP under standard conditions of impaired cardiac function. We compared the hormonal, haemodynamic and renal effects of 3 h infusions of ANP, BNP and a vehicle control in eight sheep with pacing-induced heart failure (225 beats/min for 8-12 days). 2. Infusion of ANP and BNP increased plasma ANP (P < 0.001) (276 +/- 27 versus control 142 +/- 26 pmol/l) and BNP (P < 0.001) (257 +/- 34 versus control 45 +/- 5 pmol/l) respectively, in association with increased cyclic 3',5'-guanosine monophosphate [control, 40 +/- 6; ANP, 53 +/- 6 (P < 0.05); BNP, 57 +/- 7 nmol/l (P < 0.001)]. Metabolic clearance rate and half-life were similar for both peptides. Infusion of ANP and BNP similarly reduced mean arterial pressure [control, 73.0 +/- 1.6; ANP, 67.6 +/- 1.2 (P < 0.01); BNP, 65.7 +/- 1.7 mmHg (P < 0.001)], left atrial pressure (both P < 0.05) (control, 22.0 +/- 0.7; ANP, 19.9 +/- 1.0; BNP, 19.8 +/- 0.9 mmHg) and peripheral resistance [control, 50.3 +/- 4.1 mmHg l-1 min-1; ANP, 46.0 +/- 2.8 (P < 0.05); BNP, 43.8 +/- 4.5 (P < 0.01)], and increased urine volume (2-3-fold, both P < 0.05), sodium excretion (> 10-fold, both P < 0.01) and haematocrit levels relative to control (both P < 0.05). Infused BNP tended to raise plasma ANP levels (by 28 pmol/l), while ANP increased plasma BNP (by 18 pmol/l). Plasma aldosterone was reduced by approximately 40% by both peptides (both P < 0.05). 3. In conclusion, ANP and BNP are both powerfully, natriuretic, similarly suppress aldosterone and appear equipotent in reducing preload and afterload in this model of pacing-induced heart failure.

The role of the circulation in processing pro-brain natriuretic peptide (proBNP) to amino-terminal BNP and BNP-32

Human proBNP (purified from cardiac tissue) was incubated at 37 degrees C in whole blood, serum and plasma and the products analyzed by size exclusion high pressure liquid chromatography and radioimmunoassay (RIA). In addition to RIAs for BNP-32 and NT-proBNP(1-13), a newly developed RIA for proBNP(62-76) was also used to identify the peptides. Incubation with serum resulted in the formation of a 9 kDa and a 3 kDa peptide, consistent with the N-terminal and the C-terminal peptides of the propeptide. Minimal processing of proBNP was seen in blood or plasma, suggesting that the circulation does not play a major role in the activation of proBNP. Analysis of degradation products of human proBNP using site directed specific antisera indicates that removal of N-terminal amino acids from proBNP occurs in serum. These findings support the view that the "high molecular weight BNP-32" previously identified in human plasma comprises amino-terminal deleted forms, and is unlikely to be intact proBNP(1-108).

Degradation of human adrenomedullin(1-52) by plasma membrane enzymes and identification of metabolites

Very little is known about degradation or metabolism of adrenomedullin. To this end, we incubated adrenomedullin with ovine adrenal, kidney and lung plasma membrane preparations and showed the major degradation products were ADM(2-52) and ADM(8-52). Smaller amounts of ADM(26-52), (27-52), (28-52) and (33-52) were also produced. Degradation was inhibited by EDTA and 1,10 phenanthroline but not by phosphoramidon, leupeptin and pepstatin. The above data are consistent with initial hydrolysis adjacent to hydrophobic residues by a metalloprotease, generating ADM(8-52), (26-52) and (33-52), followed by an aminopeptidase action to produce ADM(2-52), (27-52) and (28-52). Improved understanding of the metabolism of ADM may have therapeutic implications, for example in the treatment of heart failure.

Differing biological effects of equimolar atrial and brain natriuretic peptide infusions in normal man

Atrial natriuretic peptide (ANP) and Brain natriuretic peptide (BNP) are cardiac hormones with similar actions and potency in humans yet with distinctly different effects on plasma cyclic guanosine monophosphate (cGMP). Because most biological actions of natriuretic peptides are thought to be mediated by the guanylate cyclase (G-C) receptors via cGMP, we have compared the biological and G-C-stimulating effects of equimolar infusions of ANP and BNP (2 pmol/kg.min), or vehicle control, on renal, hormonal and hemodynamic function in 8 normal subjects. In addition, the modulating effects of ANP and BNP on the biological actions of infused angiotension II (AngII) were studied. During ANP infusions, plasma ANP concentration increased from 8.8 +/- 0.7 pmol/L to 34 +/- 3 pmol/L at 120 min. Similar increments in plasma BNP occurred during BNP infusions (7.3 +/- 0.6 pmol/L preinfusion, 37 +/- 1 pmol/L at 120 min). Increase in plasma cGMP during ANP infusions was 4-fold that observed during BNP infusions yet natriuresis, contraction in plasma volume, and inhibition of plasma aldosterone were comparable. By contrast, ANP (but not BNP) significantly inhibited the plasma aldosterone response to AngII (P < 0.001). The pressor response to AngII was unaltered by ANP or BNP. Thus, at plasma ANP/BNP levels observed in mild heart failure, ANP is more potent than BNP in inhibiting the aldosterone response to AngII. Comparable natriuresis and inhibition of basal aldosterone is seen, despite much less stimulation of plasma cGMP by BNP, suggesting a different mechanism of hormone action-possibly via non-G-C receptor pathways.

Natriuretic peptides in sheep with pressure overload left ventricular hypertrophy

To examine tissue and plasma atrial (ANP) and brain natriuretic peptide (BNP) responses to left ventricular hypertrophy (LVH) 7 sheep underwent suprarenal aortic banding (20 mmHg initial pressure differential). Median survival time was 15 days. Proximal mean aortic pressure (MAP) increased from 65.1 +/- 5.0 mmHg (baseline) to 111.6 +/- 7.5 mmHg (day 7, p < 0.0001). Distal systolic aortic pressure fell from 85.5 +/- 8.7 mmHg (baseline) to 55.6 +/- 6.4 mmHg (day 7, p = 0.0002). Maximal plasma ANP (26.9 +/- 3.6 vs 10.1 +/- 1.2 pmol/L, p = 0.005) and BNP (15.3 +/- 3.6 vs. 3.5 +/- 1.0 pmol/L, p = 0.006) were recorded at 15 +/- 4.0 days. Coarctation induced rapid increases in PRA and plasma aldosterone and a fall in urinary sodium. Post-mortem examination of hearts confirmed LVH. Compared with controls, tissue ANP concentration was reduced in left atrium (p = 0.04) and LV (p = 0.04). BNP concentration was reduced in left atrium (p = 0.02) but tended to be higher in LV. In conclusion, suprarenal aortic coarctation leads to progressive hypertension resulting in LVH, progressive increases in plasma ANP and BNP and, in most cases, death from heart failure.

Neutral endopeptidase inhibition: augmented atrial and brain natriuretic peptide, haemodynamic and natriuretic responses in ovine heart failure

1. Atrial and brain natriuretic peptide are both circulating hormones subject to degradation by neutral endopeptidase 24.11. Whereas endogenous levels of atrial natriuretic peptide are increased by neutral endopeptidase inhibition in most pathophysiological states, the effect on brain natriuretic peptide and the influence of cardiac status is less clear. To further evaluate the role of neutral endopeptidase 24.11, we directly compared the responses of atrial and brain natriuretic peptide, together with the effects on other vasoactive hormones, haemodynamics and renal indices, to a neutral endopeptidase inhibitor, SCH32615, and a vehicle control in eight conscious sheep before and during pacing-induced heart failure. 2. In normal animals, SCH32615 significantly increased concentrations of plasma atrial natriuretic peptide (22 +/- 5 pmol/l compared with 14 +/- 2 pmol/l in control, 1.6-fold increase) and brain natriuretic peptide (6.5 +/- 1.2 pmol/l compared with 4.1 +/- 0.7 pmol/l in control, 1.6-fold increase), whereas in heart failure, plasma levels of atrial natriuretic peptide (306 +/- 38 pmol/l compared with 187 +/- 25 pmol/l in control, 1.6-fold increase) and brain natriuretic peptide (93 +/- 11 pmol/l compared with 55 +/- 9 pmol/l in control, 1.7-fold increase) were elevated to a significantly greater absolute, but proportionately similar, extent. In both normal and heart-failed animals, SCH32615 induced reductions in mean arterial pressure and left atrial pressure and increases in haematocrit, plasma cGMP and endogenous creatinine clearance. However, only in heart failure did neutral endopeptidase inhibition induce a significant and marked natriuresis (> 10-fold increase) and diuresis (4-fold increase), together with suppression of renin activity and haemodynamic effects including decreased peripheral resistance and raised cardiac output. 3. In conclusion, neutral endopeptidase inhibition increases plasma concentrations of atrial and brain natriuretic peptide to a proportionately similar extent in both normal and heart-failed sheep. The striking natriuresis and diuresis and additional haemodynamic effects demonstrated in sheep with heart failure, where natriuretic peptide levels are elevated compared with normal sheep, supports the concept that neutral endopeptidase inhibition augments endogenous atrial and brain natriuretic peptide.

Clearance receptors and endopeptidase 24.11: equal role in natriuretic peptide metabolism in conscious sheep

Although many studies have examined the effects of administering natriuretic peptide receptor C (NPR-C) ligands and endopeptidase 24.11 (EP 24.11) inhibitors on clearance and bioactivity of atrial natriuretic peptide (ANP), none have systematically compared their effects on the endogenous levels of both ANP and brain natriuretic peptide (BNP) under physiological conditions. Accordingly, we examined the hemodynamic, hormonal, and renal actions of an EP 24.11 inhibitor, SCH-32615, and an NPR-C ligand, C-ANP-(4-23), both alone and in combination in eight normal conscious sheep. NPR-C blockade and EP 24.11 inhibition induce similar rises in plasma ANP, BNP, and guanosine 3',5'-cyclic monophosphate (cGMP). Synergistic increments in plasma ANP, BNP, and cGMP observed during combined administration are likely to be due to the reduced clearance of C-ANP-(4-23) in the setting of EP 24.11 inhibition, leading to increased inhibition of the receptor pathway. Combined administration was also associated with enhanced hemodynamic actions and diuretic and natriuretic effects. Our findings show that both enzymatic and receptor clearance pathways contribute equally to natriuretic peptide clearance and induce potentially important hemodynamic and renal effects in normal conscious sheep.

The emerging syndrome of envenoming by the New Guinea small-eyed snake Micropechis ikaheka

The New Guinea small-eyed or ikaheka snake, Micropechis ikaheka, which occurs throughout New Guinea and some adjacent islands, is feared by the indigenes. The first proven human fatality was in the 1950s and this species has since been implicated in many other cases of severe and fatal envenoming. Reliable attribution of envenoming to this species in victims unable to capture or kill the snake recently became possible by the use of enzyme immunoassay. Eleven cases of proven envenoming by M. ikaheka, with two fatalities, were identified in Papua New Guinea and Irian Jaya. Five patients showed no clinical signs of envenoming. The other six patients showed symptoms typical of envenoming by other Australasian elapids: mild local swelling, local lymphadenopathy, neurotoxicity, generalized myalgia, spontaneous systemic bleeding, incoagulable blood and passage of dark urine (haemoglobinuria or myoglobinuria). Two patients developed hypotension and two died of respiratory paralysis 19 and 38 h after being bitten. In vitro studies indicate that the venom is rich in phospholipase A2, is indirectly haemolytic, anticoagulant and inhibits platelets, but is not procoagulant or fibrinolytic. It shows predominantly post-synaptic neurotoxic and myotoxic activity. Anecdotally, Commonwealth Serum Laboratories' (CSL) death adder antivenom has proved ineffective whereas CSL polyvalent antivenom may be beneficial. Anticholinesterase drugs might prove effective in improving neuromuscular transmission and should be tested in patients with neurotoxic envenoming.