Plasma levels of atrial natriuretic peptide in severe burn injury

The endocrine response to severe burn trauma

The endocrine system is frequently altered after a major burn trauma. Besides the endocrine response to stress characterized by hypercortisolism, several hypothalamus-hypophysis-target gland axes are rapidly perturbed within a few days. These alterations can persist in the long term and deserve an appropriate treatment. Disturbances in water clearance and glucidic metabolism are also common and need to be diagnosed and corrected to decrease morbidity in such patients. Bone and mineral metabolism is deeply compromised and requires correction of mineral abnormalities in order to improve symptoms and prevent bone loss. No large prospective and/or intervention trials are available to date to elaborate age-related, evidence-based recommendations to monitor and treat burn-related endocrine alterations.

Opposite effects of ANP receptors in attenuation of LPS-induced endothelial permeability and lung injury

Atrial natriuretic peptide (ANP) has been recently identified as a modulator of acute lung injury (ALI) induced by pro-inflammatory agonists. While previous studies tested effects of exogenous ANP administration, the role of endogenous ANP in the course of ALI remains unexplored. This study examined regulation of ANP and its receptors NPR-A, NPR-B and NPR-C by LPS and involvement of ANP receptors in the modulation of LPS-induced lung injury. Primary cultures of human pulmonary endothelial cells (EC) were used in the in vitro tests. Expression of ANP and its receptors was determined by quantitative RT-PCR analysis. Agonist-induced cytoskeletal remodeling was evaluated by immunofluorescence staining, and EC barrier function was characterized by measurements of transendothelial electrical resistance. In the murine model of ALI, LPS-induced lung injury was assessed by measurements of protein concentration and cell count in bronchoalveolar lavage fluid (BAL). LPS stimulation significantly increased mRNA expression levels of ANP and NPR-A in pulmonary EC. Pharmacological inhibition of NPR-A augmented LPS-induced EC permeability and blocked barrier protective effects of exogenous ANP on LPS-induced intercellular gap formation. In contrast, pharmacological inhibition of ANP clearance receptor NPR-C significantly attenuated LPS-induced barrier disruptive effects. Administration of NPR-A inhibitor in vivo exacerbated LPS-induced lung injury, whereas inhibition of NPR-C suppressed LPS-induced increases in BAL cell count and protein content. These results demonstrate for the first time opposite effects of NPR-A and NPR-C in the modulation of ALI and suggest a compensatory protective mechanism of endogenous ANP in the maintenance of lung vascular permeability in ALI.

Atrial natriuretic peptide attenuates LPS-induced lung vascular leak: role of PAK1

Increased levels of atrial natriuretic peptide (ANP) in the models of sepsis, pulmonary edema, and acute respiratory distress syndrome (ARDS) suggest its potential role in the modulation of acute lung injury. We have recently described ANP-protective effects against thrombin-induced barrier dysfunction in pulmonary endothelial cells (EC). The current study examined involvement of the Rac effector p21-activated kinase (PAK1) in ANP-protective effects in the model of lung vascular permeability induced by bacterial wall LPS. C57BL/6J mice or ANP knockout mice (Nppa(-/-)) were treated with LPS (0.63 mg/kg intratracheal) with or without ANP (2 μg/kg iv). Lung injury was monitored by measurements of bronchoalveolar lavage protein content, cell count, Evans blue extravasation, and lung histology. Endothelial barrier properties were assessed by morphological analysis and measurements of transendothelial electrical resistance. ANP treatment stimulated Rac-dependent PAK1 phosphorylation, attenuated endothelial permeability caused by LPS, TNF-α, and IL-6, decreased LPS-induced cell and protein accumulation in bronchoalveolar lavage fluid, and suppressed Evans blue extravasation in the murine model of acute lung injury. More severe LPS-induced lung injury and vascular leak were observed in ANP knockout mice. In rescue experiments, ANP injection significantly reduced lung injury in Nppa(-/-) mice caused by LPS. Molecular inhibition of PAK1 suppressed the protective effects of ANP treatment against LPS-induced lung injury and endothelial barrier dysfunction. This study shows that the protective effects of ANP against LPS-induced vascular leak are mediated at least in part by PAK1-dependent signaling leading to EC barrier enhancement. Our data suggest a direct role for ANP in endothelial barrier regulation via modulation of small GTPase signaling.

Effect of intravenous atrial natriuretic peptide on pulmonary dysfunction and renal function following burn shock

BACKGROUND

The typical response to burn stress causes burn shock, followed by a diuretic phase; however, fluid management remains crucial in this phase in the treatment of the elderly, patients with preexisting cardiac or renal diseases, and patients developing acute renal failure. We studied the effects of human atrial natriuretic peptide (hANP), which is a renal vasodilator, natriuretic, and inhibitor of renin secretion, on renal function in these patients with burn injuries.

METHODS

Thirty-three severely burned patients (44.8% +/- 20.6% total burn surface area) with prolonged cardiovascular overload and pulmonary edema after burn shock receiving a continuous infusion of hANP (0.025 microg/kg/min and 0.05 microg/kg/min, hANP group) were compared with control (no-hANP group, n = 25). Vital signs, urine output (UO) and blood gas analysis before and 72 hour after the start of hANP were recorded. Creatinine clearance, free water clearance, and fractional excretion of sodium were also calculated.

RESULTS

Sixteen (48%) patients were elderly, over 80 years old. Twenty (60%) had preexisting cardiovascular disease, renal insufficiency, or diabetes. hANP infusion increased UO in 25 (66%) cases and improved oxygenation in 31 (82%) cases. Treatment with hANP increased creatinine clearance, fractional excretion of sodium, and UO, except in four cases that had already progressed to complete renal failure before the infusion of hANP.

CONCLUSIONS

Intravenous hANP seems to be effective for postresuscitative pulmonary dysfunction and renal function after burn shock in the vulnerable elderly, or patients with preexisting disease, suggesting that it could be valuable in facilitating fluid management in the acute phase in severely burned patients.

Atrial natriuretic peptide release associated with smoke inhalation and physiological responses to thermal injury in sheep

Markedly elevated levels of plasma atrial natriuretic peptide (ANP), which exhibit potent diuretic and vasoactive properties, has been well documented in patients with acute lung injury. We examined the physiological effects of additional smoke inhalation on plasma ANP concentrations in an ovine burn model. Seventeen sheep were instrumented to receive fluid and have physiological measurements taken. The burn group (n=8) received 40% body surface area third degree burn and the burn+smoke group (n=9) received the same burn plus 48 breaths of cotton smoke insufflation. The animals were resuscitated according to the Parkland formula with Ringer's lactate in the following 72 h period. Hemodynamic, oxygenation, fluid balance, and plasma ANP levels were serially determined. The effects of smoke inhalation manifested as deteriorated oxygenation, and increased fluid accumulation after a sustained initial shock period of more than 12 h. Plasma ANP levels in the burn+smoke group showed a biphasic elevation, whereas the burn group showed no appreciable changes throughout the whole experimental period. The initial increase in plasma ANP concentrations occurred immediately after injury (from 96+/-10 at baseline to 136+/-17 pg/mL at 3h after injury); thereafter, it decreased towards baseline value, followed by a second increase in the post resuscitation period (183+/-43 pg/mL at 72 h after injury). Decreased urine output and accentuated pulmonary vascular resistance in the combined injury group was observed between the two ANP level peaks, indicating that ANP release modified physiological responses to the burn+smoke injury.

Myocardial function and haemodynamics in extensive burn trauma: evaluation by clinical signs, invasive monitoring, echocardiography and cytokine concentrations. A prospective clinical study

BACKGROUND

The objectives of this study were to (1). describe the haemodynamic profile of patients with extensive burns during the early fluid resuscitation phase, (2). evaluate myocardial performance by invasive monitoring and echocardiography and (3). analyze the relations between serum cytokine (IL-6, IL-8, TNF) and natriuretic peptide (ANP, BNP) concentrations and myocardial function in these patients.

METHODS

Prospective, clinical study in a tertiary care burn centre. Invasive haemodynamic measurements including a pulmonary artery catheter, echocardiography, blood samples for cytokine and atriopeptide analyses. The follow-up time was up to 72 h postinjury.

RESULTS

According to echocardiography, patients were hypovolaemic despite aggressive (median 7,9 ml kg(-1) h(-1), range 3.3-11.7) fluid resuscitation and adequate urine output (median 0.9 ml kg(-1) h(-1), range 0.46-1.35) during the first day postinjury. There were no consistent findings of hyperlactatemia, metabolic acidosis or low mixed venous oxygen saturations. Daily highest and lowest values of cardiac index and stroke volume index increased and the lowest and highest values of systemic vascular resistance decreased. Cardiac performance (stroke volume index) improved during the study period even though there were no initial signs of myocardial depression in echocardiography. Three patients received a dobutamine infusion based on clinical judgement. There was no consistent association between haemodynamic changes and plasma cytokine concentrations.

CONCLUSION

Persisting hypovolaemia is evident in the resuscitation phase of extensive burns despite aggressive fluid therapy and the lack of classic signs of hypoperfusion. Cardiac performance improves during the first days after extensive burn injury without association with plasma cytokine profile.

Plasma levels of N-terminal peptide of pro-atrial natriuretic peptides in myoskeletal injuries

To determine whether concentrations of the N-terminal peptide of pro-atrial natriuretic peptide (proANP) and of alpha atrial natriuretic peptide 1-28 (aANP) releases are affected by myoskeletal injuries, samples from 24 patients with muscle injuries were therefore collected within 48 h of injury. The mean age of patients was 65; range: 17-90 years. These were compared with 18 non-injured subjects with a mean age of 40; range: 17-80 years. A specific enzyme immunoassay (EIA) method suitable for the determination of proANP and aANP was used. aANP required plasma extraction and no extraction was needed for proANP determination.ProANP level was significantly higher in patients on admission and this level was maintained 24 h after admission (p < 0.05) compared to controls. However, aANP 1-28 level remained statistically unchanged in the patients samples. The level of proANP was over 10 times greater than the levels obtained with aANP. N-terminal peptide of proANP may be a supplementary tool in the study of early phase of myoskeletal injuries in human.

Neuropeptide variability in man

BACKGROUND

Previous studies have established short-term variability in the circulating plasma levels of cardiac peptides such as atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). Our aim was to investigate whether such variable patterns could be observed in other vasoactive peptides.

METHODS

We measured the immunoreactivity of vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), endothelin-1 (ET-1) and calcitonin gene-related peptide (CGRP) in peripheral venous plasma collected at 2-min intervals over a 20-min period from patients with chronic cardiac failure (CCF) and from control subjects. In a second study, blood samples were obtained at 2-min intervals from the pulmonary artery, femoral artery and antecubital vein from patients with normal cardiac function while right atrial pressure and heart rate were constant.

RESULTS

Peripheral blood VIP, NPY and ET-1 had peaks and troughs (levels > 2SD from the mean) in both patients and controls, with approximate intervals of 10 min. Levels of CGRP showed little variation. The overall levels [median (range); pmol L-1] of VIP [patients 27 (2.1-85.5); controls 9.8 (0-34)] and NPY [patients 20 (0-110); controls 12 (5-19)] were higher in patients (P < 0.05). Circulating plasma levels of ET-1 and CGRP were about the same in both groups [ET-1: patients 18 (2-84); controls 18 (0-48); CGRP: patients 4 (1-18.5), controls 5.5 (1-15); P = NS]. Levels of CGRP, VIP and ET-1 were similar in the pulmonary and femoral arteries, whereas systemic arterial levels of NPY were higher than in the pulmonary artery.

CONCLUSIONS

The data demonstrate marked variability in circulating levels of the neuropeptides studied. In addition, peaks and troughs were observed every 10-15 min from all three vascular beds. If these peptides are secreted in a pulsatile pattern, then interpretations of single measurements should be guarded. Furthermore, this study raises interesting questions about the physiology of hormone secretion in man.

Plasma-circulating levels of natriuretic peptides in patients with bone and soft tissue injuries

To evaluate the release and possible role of N-terminal end of atrial natriuretic factor (ANF) prohormone (proANF-1-30) and C-terminal end of ANF prohormone (aANP-1-28) in patients with soft tissue and bone injuries, 20 patients with soft tissue injuries, 18 bone-fractured patients, and 21 healthy controls were examined. Samples were collected from patients within 24 h after injury. Plasma level of proANF-1-30 and aANP-1-28 were higher in orthopedic patients than the soft tissue injury patients compared to controls (P < 0.005, P<0.05, respectively). proANF-1-30 was over 15-fold greater than aANP-1-28 in the healthy control samples. These data hypothesized that the concentration of proANF-1-30 may be related to tissue damages in man.