Vasopressin lowers pulmonary artery pressure in hypoxic rats by releasing atrial natriuretic peptide

Sepsis-Induced myocardial dysfunction: heterogeneity of functional effects and clinical significance

Sepsis is a life-threatening disease state characterized by organ dysfunction and a dysregulated response to infection. The heart is one of the many organs affected by sepsis, in an entity termed sepsis-induced cardiomyopathy. This was initially used to describe a reversible depression in ejection fraction with ventricular dilation but advances in echocardiography and introduction of new techniques such as speckle tracking have led to descriptions of other common abnormalities in cardiac function associated with sepsis. This includes not only depression of systolic function, but also supranormal ejection fraction, diastolic dysfunction, and right ventricular dysfunction. These reports have led to inconsistent definitions of sepsis-induced cardiomyopathy. Just as there is heterogeneity among patients with sepsis, there is heterogeneity in the cardiac response; thus resuscitating these patients with a single approach is likely suboptimal. Many factors affect the heart in sepsis including inflammatory mediators, catecholamine responsiveness, and pathogen related toxins. This review will discuss different functional effects characterized by echocardiographic changes in sepsis and their prognostic and management implications.

Effect of vasopressin on a porcine model of persistent pulmonary hypertension of the newborn

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is due to a failure of pulmonary vascular relaxation. Vasopressin, a systemic vasoconstrictor acting on smooth muscle AVPR1a receptors, is used in treatment of PPHN. We sought to determine acute effects of vasopressin infusion on pulmonary hemodynamics in a large animal model of hypoxic PPHN.

METHODS

PPHN was induced in 6 newborn piglets by 72 h normobaric hypoxia (FiO2 = 0.10); controls were 7 age-matched 3-day-old piglets. Animals were anesthetized and ventilated with central venous and arterial lines, and after stabilization, randomized using a crossover design to normoxic or hypoxic ventilation, then 30 min infusion of 0.0012 U/kg/min vasopressin, followed by 45 min vasopressin washout period. Echocardiographic parameters and oxygen consumption were measured before and after vasopressin. Relaxation to vasopressin was tested in isolated PPHN and control pulmonary arteries by isometric myography. Expression of AVPR1a receptor mRNA was quantified in arterial and myocardial tissues.

RESULTS

Vasopressin did not alleviate hypoxia-responsiveness of PPHN pulmonary circuit. There were no significant differences in pulmonary hypertension, cardiac function indices, or oxygenation indices after vasopressin infusion. Vasopressin did not dilate control or PPHN pulmonary arteries, and AVPR1 was minimally expressed.

CONCLUSIONS

Vasopressin does not have a direct pulmonary vasodilator effect in PPHN, within the timeframe studied.

Effects of vasopressin during a pulmonary hypertensive crisis induced by acute hypoxia in a rat model of pulmonary hypertension

BACKGROUND

A pulmonary hypertensive crisis (PHC) can be a life-threatening condition. We established a PHC model by exposing rats with monocrotaline (MCT)-induced pulmonary hypertension to acute hypoxia, and investigated the effects of vasopressin, phenylephrine, and norepinephrine on the PHC.

METHODS

Four weeks after MCT 60 mg kg^-1 administration i.v., right ventricular systolic pressure (RVSP), systolic BP (SBP), mean BP (MBP), cardiac index (CI), and pulmonary vascular resistance index (PVRI) were measured. PHC defined as an RVSP exceeding or equal to SBP was induced by changing the fraction of inspiratory oxygen to 0.1. Rats were subsequently treated by vasopressin, phenylephrine, or norepinephrine, followed by assessment of systemic haemodynamics, isometric tension of femoral and pulmonary arteries, cardiac function, blood gas composition, and survival.

RESULTS

PHC was associated with increased RV dilatation and paradoxical septal motion. Vasopressin increased MBP [mean (standard error)] from 52.6 (3.8) to 125.0 (8.9) mm Hg and CI from 25.4 (2.3) to 40.6 (1.8) ml min^-1 100 g^-1 while decreasing PVRI. Vasopressin also improved RV dilatation, oxygenation, and survival in PHC. In contrast, phenylephrine increased MBP from 54.8 (2.3) to 96.8 (3.2) mm Hg without improving cardiac pump function. Norepinephrine did not alter MBP. Vasopressin contracted femoral but not pulmonary arteries, whereas phenylephrine contracted both arterial beds. Hence, improvements with vasopressin in PHC might be associated with decreased PVRI and selective systemic vasoconstriction.

CONCLUSIONS

In this rat model of a PHC, vasopressin, but not phenylephrine or norepinephrine, resulted in better haemodynamic and vascular recovery.

Treating Hypotension in Preterm Neonates With Vasoactive Medications

Preterm neonates often have hypotension which may be due to various etiologies. While it is controversial to define hypotension in preterm neonates, various vasoactive medications are commonly used to provide the cardiovascular support to improve the blood pressure, cardiac output, or to treat shock. However, the literature on the systemic and regional hemodynamic effects of these antihypotensive medications in neonates is deficient and incomplete, and cautious translation of findings from other clinical populations and animal studies is required. Based on a literature search on published reports, meta-analytic reviews, and selected abstracts, this review discusses the current available information on pharmacologic actions, clinical effects, and side effects of commonly used antihypotensive medications including dopamine, dobutamine, epinephrine, norepinephrine, vasopressin, and milrinone in preterm neonates.

Cardiovascular Supportive Therapies for Neonates With Asphyxia - A Literature Review of Pre-clinical and Clinical Studies

Asphyxiated neonates often have hypotension, shock, and poor tissue perfusion. Various "inotropic" medications are used to provide cardiovascular support to improve the blood pressure and to treat shock. However, there is incomplete literature on the examination of hemodynamic effects of these medications in asphyxiated neonates, especially in the realm of clinical studies (mostly in late preterm or term populations). Although the extrapolation of findings from animal studies and other clinical populations such as children and adults require caution, it seems appropriate that findings from carefully conducted pre-clinical studies are important in answering some of the fundamental knowledge gaps. Based on a literature search, this review discusses the current available information, from both clinical studies and animal models of neonatal asphyxia, on common medications used to provide hemodynamic support including dopamine, dobutamine, epinephrine, milrinone, norepinephrine, vasopressin, levosimendan, and hydrocortisone.

Vasopressors induce passive pulmonary hypertension by blood redistribution from systemic to pulmonary circulation

Vasopressors are widely used in resuscitation, ventricular failure, and sepsis, and often induce pulmonary hypertension with undefined mechanisms. We hypothesize that vasopressor-induced pulmonary hypertension is caused by increased pulmonary blood volume and tested this hypothesis in dogs under general anesthesia. In normal hearts (model 1), phenylephrine (2.5 μg/kg/min) transiently increased right but decreased left cardiac output, associated with increased pulmonary blood volume (63% ± 11.8, P = 0.007) and pressures in the left atrium, pulmonary capillary, and pulmonary artery. However, the trans-pulmonary gradient and pulmonary vascular resistance remained stable. These changes were absent after decreasing blood volume or during right cardiac dysfunction to reduce pulmonary blood volume (model 2). During double-ventricle bypass (model 3), phenylephrine (1, 2.5 and 10 μg/kg/min) only slightly induced pulmonary vasoconstriction. Vasopressin (1U and 2U) dose-dependently increased pulmonary artery pressure (52 ± 8.4 and 71 ± 10.3%), but did not cause pulmonary vasoconstriction in normally beating hearts (model 1). Pulmonary artery and left atrial pressures increased during left ventricle dysfunction (model 4), and further increased after phenylephrine injection by 31 ± 5.6 and 43 ± 7.5%, respectively. In conclusion, vasopressors increased blood volume in the lung with minimal pulmonary vasoconstriction. Thus, this pulmonary hypertension is similar to the hemodynamic pattern observed in left heart diseases and is passive, due to redistribution of blood from systemic to pulmonary circulation. Understanding the underlying mechanisms may improve clinical management of patients who are taking vasopressors, especially those with coexisting heart disease.

Management of Pulmonary Hypertension in the Operating Room

Pulmonary artery hypertension is defined as persistent elevation of mean pulmonary artery pressure > 25 mm Hg with pulmonary capillary wedge pressure < 15 mm Hg or elevation of exercise mean pulmonary artery pressure > 35 mm Hg. Although mild pulmonary hypertension rarely impacts anesthetic management, severe pulmonary hypertension and exacerbation of moderate hypertension can lead to acute right ventricular failure and cardiogenic shock. Knowledge of anesthetic drug effects on the pulmonary circulation is essential for anesthesiologists. Intraoperative management should include prevention of exacerbating factors such as hypoxemia, hypercarbia, acidosis, hypothermia, hypervolemia, and increased intrathoracic pressure; monitoring and optimizing right ventricular function; and treatment with selective pulmonary vasodilators. Recent advances in pharmacology provide anesthesiologists with a wide variety of options for selective pulmonary vasodilatation. Pulmonary hypertension is a major determinant of perioperative morbidity and mortality in special situations such as heart and lung transplantation, pneumonectomy, and ventricular assist device placement.

Protocol for a randomised controlled trial of VAsopressin versus Noradrenaline as Initial therapy in Septic sHock (VANISH)

INTRODUCTION

Vasopressin is an alternative vasopressor in the management of septic shock. It spares catecholamine use but whether it improves outcome remains uncertain. Current evidence suggests that it may be most effective if used early and possibly in conjunction with corticosteroids. This trial will compare vasopressin to noradrenaline as initial vasopressor in the management of adult septic shock and investigate whether there is an interaction of vasopressin with corticosteroids.

METHODS AND ANALYSIS

This is a multicentre, factorial (2×2), randomised, double-blind, placebo-controlled trial. 412 patients will be recruited from multiple UK intensive care units and randomised to receive vasopressin (0-0.06 U/min) or noradrenaline (0-12 µg/min) as a continuous intravenous infusion as initial vasopressor therapy. If maximum infusion rates of this first study drug are reached, the patient will be treated with either hydrocortisone (initially 50 mg intravenous bolus six-hourly) or placebo, before additional open-label catecholamine vasopressors are prescribed. The primary outcome of the trial will be the difference in renal failure-free days between treatment groups. Secondary outcomes include need for renal replacement therapy, survival rates, other organ failures and resource utilisation.

ETHICS AND DISSEMINATION

The trial protocol and information sheets have received a favourable opinion from the Oxford A Research Ethics Committee (12/SC/0014). There is an independent Data Monitoring and Ethics Committee and independent membership of the Trial Steering Committee including patient and public involvement. The trial results will be published in peer-reviewed journals and presented at national and international scientific meetings.

TRIAL REGISTRATION NUMBER

ISRCTN 20769191 and EudraCT 2011-005363-24.

Vasopressin improves survival compared with epinephrine in a neonatal piglet model of asphyxial cardiac arrest

BACKGROUND

Epinephrine is a component of all resuscitation algorithms. Vasopressin is a pulmonary vasodilator and systemic vasopressor. We investigated the effect of epinephrine vs. vasopressin on survival and hemodynamics after neonatal porcine cardiac arrest (CA).

METHODS

A 4-min asphyxial CA was induced, after which cardiopulmonary resuscitation (CPR) was commenced. Animals were randomized to low- (LDE: 0.01 mg/kg) or high-dose epinephrine (HDE: 0.03 mg/kg), low- (LDV: 0.2 U/kg) or high-dose vasopressin (HDV: 0.4 U/kg), or control (saline). Clinical and echocardiography indexes were monitored.

RESULTS

Sixty-nine animals were randomized. Survival was greater in HDV (n = 8 (89%); P < 0.05 ANOVA) vs. control (n = 7 (43%)) and LDE (n = 5 (36%)) but not vs. HDE (n = 7 (64%)) or LDV (n = 6 (75%)). Animals resuscitated with LDE required more shocks (2.5 (interquartile range: 2-6); P < 0.05) and higher doses of energy (15 J (interquartile range: 10-20); P < 0.05). Left ventricular output was comparable between groups, but a greater increase in superior vena caval flow was seen after HDV (P < 0.001 vs. control, LDE, and HDE). Plasma troponin was greatest in the HDE group (P < 0.05 vs. control and HDV).

CONCLUSION

Vasopressin results in improved survival, lower postresuscitation troponin, and less hemodynamic compromise after CA in newborn piglets. Vasopressin may be a candidate for testing in human neonates.

Vasopressin as a rescue therapy for refractory pulmonary hypertension in neonates: case series

OBJECTIVES

To determine the effect of vasopressin therapy on the efficacy of oxygenation and arterial pressure in infants with severe persistent pulmonary hypertension of the newborn.

DESIGN

Retrospective case study.

SETTING

Neonatal ICU, Hospital for Sick Children, Toronto, Canada.

SUBJECTS

Neonates with severe persistent pulmonary hypertension.

INTERVENTION

Intravenous infusion of vasopressin.

MEASUREMENTS AND MAIN RESULTS

Ten infants satisfied the inclusion criteria. Inhaled nitric oxide was used for median (interquartile range) duration of 15 hours (11-28 hr) prior to vasopressin commencement. Vasopressin was initiated at a mean dose of 0.0002 ± 0.0002 U/kg/min for a median (interquartile range) duration of 49 hours (13-95 hr). Administration of vasopressin was associated with an improvement in oxygenation index, peak effect 6 hours after drug initiation (p = 0.01), and a reduction in inhaled nitric oxide dose (p < 0.05). There was a concomitant improvement in blood pressure (p < 0.05) and urine output (p < 0.05), without drop in the serum sodium level or worsening in serum lactate level.

CONCLUSIONS

Although there is limited experience of vasopressin use in persistent pulmonary hypertension of the newborn infants, our case series suggests it to be a potential adjunctive therapy for improving the efficacy of oxygenation and systemic hypotension. A prospective randomized trial is needed to confirm its efficacy and safety in the management of severe persistent pulmonary hypertension of the newborn.

Terlipressin improves pulmonary pressures in cirrhotic patients with pulmonary hypertension and variceal bleeding or hepatorenal syndrome

Terlipressin has been shown to improve both pulmonary and systemic hemodynamics in stable cirrhotic patients with pulmonary hypertension, whereas other vasoconstrictors may cause pulmonary pressures to deteriorate. We investigated the pulmonary and systemic hemodynamic effects of the first terlipressin dose (2 mg) in 7 cirrhotic patients with PH presenting with variceal bleeding (n=4) or hepatorenal syndrome (n=3). Terlipressin decreased pulmonary vascular resistance (158.8+/-8.9 vs 186.5+/-13.9 dynes · sec · cm-5; P=0.003) together with an increase in systemic vascular resistance (2143+/-126 vs 1643+/-126 dynes · sec · cm-5; P<0.001). Terlipressin should be the vasoconstrictor treatment of choice when patients present with variceal bleeding or HRS.

Differential effects of terlipressin on pulmonary and systemic hemodynamics in patients with cirrhosis and pulmonary hypertension: an echo study

Terlipressin has been associated with pulmonary arterial vasodilation in patients with pulmonary hypertension (PH). We investigated the effects of terlipressin on pulmonary vascular resistance (PVR) in patients with cirrhosis without and with PH. Pulmonary vascular resistance and cardiac output (CO) by Doppler ultrasound, mean arterial pressure (MAP), and systemic vascular resistance (SVR) were evaluated in patients with cirrhosis with PVR -120 dyne s cm⁻⁵ (group 1, n = 20) and PVR >120 dyne s cm⁻⁵ (group 2, n = 10) before and 30 minutes after terlipressin infusion (2 mg). After terlipressin, PVR increased significantly in group 1 (96.1 ± 20.2 vs 85.1 ± 18 dyne s cm⁻⁵; P = .004) but decreased significantly in group 2 (170.4 ± 37.8 vs 157.8 ± 28.1 dyne s cm⁻⁵; P= .04). Pulmonary vascular resistance changes in group 2 correlated significantly with baseline PVR (r = -0.632; P = .04). Terlipressin induced a significant increase in MAP and SVR and a significant decrease in CO in both groups. Terlipressin significantly reduces pulmonary pressures in patients with cirrhosis having PH together with systemic hemodynamic improvement.

Significant improvement of portopulmonary hypertension after 1-week terlipressin treatment

Cirrhosis associated with moderate and severe portopulmonary hypertension carries a poor prognosis. Optimal management has not yet been defined. Current treatment options, such as prostacyclin analogues, endothelin antagonists, and phosphodiesterase-5 inhibitors, are characterized by slow onset of action and various adverse effects, particularly in patients with advanced cirrhosis. Here, we report the significant reduction of pulmonary arterial pressure after 1-week terlipressin treatment in a patient with concomitant hepato-renal syndrome. Terlipressin could be a novel and safe treatment for portopulmonary hypertension.

Clinical review: Vasopressin and terlipressin in septic shock patients

Vasopressin (antidiuretic hormone) is emerging as a potentially major advance in the treatment of septic shock. Terlipressin (tricyl-lysine-vasopressin) is the synthetic, long-acting analogue of vasopressin, and has comparable pharmacodynamic but different pharmacokinetic properties. Vasopressin mediates vasoconstriction via V₁ receptor activation on vascular smooth muscle. Septic shock first causes a transient early increase in blood vasopressin concentrations; these concentrations subsequently decrease to very low levels as compared with those observed with other causes of hypotension. Infusions of 0.01–0.04 U/min vasopressin in septic shock patients increase plasma vasopressin concentrations. This increase is associated with reduced need for other vasopressors. Vasopressin has been shown to result in greater blood flow diversion from nonvital to vital organ beds compared with adrenaline (epinephrine). Of concern is a constant decrease in cardiac output and oxygen delivery, the consequences of which in terms of development of multiple organ failure are not yet known. Terlipressin (one or two boluses of 1 mg) has similar effects, but this drug has been used in far fewer patients. Large randomized clinical trials should be conducted to establish the utility of these drugs as therapeutic agents in patients with septic shock.

[Indications of vasopressin in the management of septic shock]

OBJECTIVE

Vasopressin (antidiuretic hormone) is emerging as a potentially major advancement in the treatment of septic shock. Vasopressin is both a vasopressor and an antidiuretic hormone. It also has haemostatic, gastrointestinal, and thermoregulatory effects. This article reviews the physiology of vasopressin and all the relevant clinical literature on its use in the treatment of septic shock.

DATA SOURCES AND EXTRACTION

Extraction from Pubmed database of French and English articles on the physiology and clinical use of vasopressin. The following key words were selected: vasodilatory shock, vasopressin, septic shock, catecholamines, norepinephrine, renal function, diuresis, mesenteric haemodynamic. The collected articles were reviewed and selected according to their quality and originality.

DATA SYNTHESIS

Vasopressin mediates vasoconstriction via V1-receptor activation on vascular smooth muscle. Septic shock causes first a transient early increase in blood vasopressin concentrations that decreases later to very low concentrations compared to other causes of hypotension. Vasopressin infusion of 0.01-0.04 U min(-1) in septic shock patients increases plasma vasopressin concentrations. This increase is associated with a lesser need for other vasopressors. Vasopressin has been shown to produce greater blood flow diversion from non-vital to vital organ beds than does adrenaline. A large randomized clinical trial should be performed to assess its place as a therapeutic agent of septic shock patient.

Physiology of vasopressin relevant to management of septic shock

Vasopressin is emerging as a rational therapy for the hemodynamic support of septic shock and vasodilatory shock due to systemic inflammatory response syndrome. The goal of this review is to understand the physiology of vasopressin relevant to septic shock in order to maximize its safety and efficacy in clinical trials and in subsequent therapeutic use. Vasopressin is both a vasopressor and an antidiuretic hormone. It also has hemostatic, GI, and thermoregulatory effects, and is an adrenocorticotropic hormone secretagogue. Vasopressin is released from the axonal terminals of magnocellular neurons in the hypothalamus. Vasopressin mediates vasoconstriction via V1-receptor activation on vascular smooth muscle and mediates its antidiuretic effect via V2-receptor activation in the renal collecting duct system. In addition, vasopressin, at low plasma concentrations, mediates vasodilation in coronary, cerebral, and pulmonary arterial circulations. Septic shock causes first a transient early increase in blood vasopressin concentrations that decrease later in septic shock to very low levels compared to other causes of hypotension. Vasopressin infusion of 0.01 to 0.04 U/min in patients with septic shock increases plasma vasopressin levels to those observed in patients with hypotension from other causes, such as cardiogenic shock. Increased vasopressin levels are associated with a lesser need for other vasopressors. Urinary output may increase, and pulmonary vascular resistance may decrease. Infusions of > 0.04 U/min may lead to adverse, likely vasoconstriction-mediated events. Because clinical studies have been relatively small, focused on physiologic end points, and because of potential adverse effects of vasopressin, clinical use of vasopressin should await a randomized controlled trial of its effects on clinical outcomes such as organ failure and mortality.

Hemodynamic and metabolic effects of low-dose vasopressin infusions in vasodilatory septic shock

OBJECTIVE

To investigate the physiologic effects of exogenous vasopressin as a potential alternative to traditional high-dose catecholamine therapy for septic patients with vascular hyporeactivity to catecholamines.

DESIGN

Prospective, case-controlled study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Vasopressin was infused in 16 critically ill septic patients who remained persistently hypotensive despite infusions of pharmacologic doses of catecholamines.

INTERVENTION

Continuous intravenous infusion of vasopressin at 0.04 units/min for 16 hrs, in place of escalating the amount of catecholamines being infused.

MEASUREMENTS AND MAIN RESULTS

After administration of vasopressin, systemic vascular resistance and mean arterial pressure were immediately and significantly increased in comparison with the values obtained just before vasopressin. When the vasopressin infusions were discontinued, mean arterial pressure decreased immediately and dramatically. We did not detect any obvious adverse cardiac effects during the vasopressin infusions. Vasopressin had no effect on other hemodynamic parameters or any of the metabolic parameters studied, including measures of oxygenation, plasma glucose, or electrolytes. Urine output increased significantly during the administration of vasopressin, although this effect may be nonspecific. Lactate concentrations decreased, particularly in the survival group, but the decreases were not significant. Overall survival was 56%.

CONCLUSIONS

Low-dose vasopressin infusions increased mean arterial pressure, systemic vascular resistance, and urine output in patients with vasodilatory septic shock and hyporesponsiveness to catecholamines. The data indicate that low-dose vasopressin infusions may be useful in treating hypotension in these patients.

Regulation of natriuretic peptide secretion by the heart

Secreted by the heart, more specifically by atrial cardiomyocytes under normal conditions but also by ventricular myocytes during cardiac hypertrophy, natriuretic peptides are now considered important hormones in the control of blood pressure and salt and water excretion. Studies on natriuretic peptide secretagogues and their mechanisms of action have been complicated by hemodynamic changes and contractions to which the atria are constantly subjected. It now appears that atrial stretch through mechano-sensitive ion channels, adrenergic stimulation via alpha 1A-adrenergic receptors, and endothelin via its ETA receptor subtype are major triggering agents of natriuretic peptide release. With several other stimuli, such as angiotensin II and beta-adrenergic agents, modulation of natriuretic peptide release appears to be linked to local generation of prostaglandins. In all cases, intracellular calcium homeostasis, controlled by several ion channels, is considered a key element in the regulation of natriuretic peptide secretion.

Hypoxia stimulates atrial natriuretic peptide gene expression in cultured atrial cardiocytes

The current study tested the hypothesis that hypoxia stimulates atrial natriuretic peptide (ANP) gene expression and secretion in cultured atrial myocytes (AT-1 cells). AT-1 cells were obtained from a transplantable mouse atrial cardiomyocyte tumor lineage. Confluent AT-1 cells were exposed to hypoxia (1% oxygen) or normoxia (21% oxygen) as controls for 6 hours to 7 days. Medium ANP levels were measured by radioimmunoassay, and intracellular ANP gene transcripts were quantified by Northern and slot blot analyses. Exposure to hypoxia resulted in a significant increase in cellular ANP mRNA levels within 36 hours, which peaked (3.6-fold increase) at 2 days after hypoxic exposure, and produced a time-dependent increase in the release of ANP from AT-1 cells for 2 to 7 days. Transfection studies with recombinant DNA constructs that contained fragments of the -3003/+62 sequence of the ANP promoter and the luciferase reporter gene revealed that the regulatory sequences that mediate the hypoxia-induced increase in transcription are located within a region that extends from -638 to -518 bp to the transcriptional start site of the ANP gene. Gel mobility shift assays demonstrated that hypoxia-inducible nuclear proteins that bound to the 120-bp putative hypoxia-responsive elements of the ANP gene were produced during hypoxic exposure. We have thus defined a 120-bp region within the ANP gene promoter that contains hypoxia-responsive elements that might be responsible for the enhancement of ANP gene expression in atrial myocytes during hypoxic exposure.

Vasopressin and oxytocin release during prolonged environmental hypoxia in the rat

BACKGROUND

The mechanism causing peripheral oedema in hypoxaemic chronic obstructive pulmonary disease has not been established. Vasopressin, a powerful antidiuretic hormone involved in salt and water homeostasis, is released in response to acute hypoxia. However, the effect of prolonged hypoxaemia on hypothalamic and pituitary release of the magnocellular hypothalamic hormones, vasopressin and oxytocin, has not previously been studied.

METHODS

Male Wistar rats were randomly allocated to either normobaric, hypoxic (10% O2) or control (21% O2) environmental chambers. An initial series of experiments examined plasma vasopressin concentration, osmolality, sodium concentration, packed cell volume (PCV), and weight gain at weekly intervals (n = 4-6) for six weeks. The maximum increase in plasma vasopressin concentration and PCV occurred after five weeks. In a second experiment vasopressin and oxytocin concentrations in the hypothalamus, pituitary gland, and plasma were measured in eight control and eight hypoxic rats after five weeks in the environmental chambers.

RESULTS

In rats exposed to environmental hypoxia PCV increased (p < 0.001) and weight gain decreased (p < 0.05) compared with controls. The plasma vasopressin concentration increased progressively from a baseline of 1.36 (0.2) pmol/l (n = 6) to a maximum of 4.38 (0.8) pmol/l (n = 6; p < 0.01) during the first five weeks of environmental hypoxia (difference 3.02 (95% CI 1.18 to 4.86)). Plasma osmolality and sodium concentration were unchanged in hypoxic rats compared with controls during the six week period. The hypothalamic vasopressin concentration was increased (p < 0.001) after five weeks of environmental hypoxia (91.6 (4.8) pmol/ hypothalamus) compared with controls (57.4 (5.1) pmol/hypothalamus), the difference being 34.2 pmol/hypothalamus (95% CI 21.6 to 46.5). The pituitary vasopressin concentration was unchanged. In hypoxic rats hypothalamic oxytocin (59.6 (3.2) pmol/hypothalamus) was greater (p < 0.01) than in controls (42 (3.8) pmol/hypothalamus), a difference of 17.6 pmol/ hypothalamus (95% CI 8.7 to 26.5). Similarly, the plasma oxytocin concentration was increased (p < 0.05) in hypoxic rats (6.78 (1.2) pmol/l) compared with controls (3.3 (0.8) pmol/l), a difference of 3.48 pmol/l (95% CI 0.89 to 6.07). The pituitary oxytocin concentration was unchanged in the two groups.

CONCLUSIONS

These results demonstrate an increase in hypothalamic production of vasopressin and oxytocin in rats during prolonged hypoxaemia. Increased plasma concentrations of neurohypophysial hormones would be expected to impair sodium and water homeostasis in patients with hypoxaemia. However, the absence of change in the plasma osmolality and sodium concentrations in this study and previous clinical investigations suggests that compensatory mechanisms modulate the actions of both vasopressin and oxytocin. A reduction in renal blood flow or decreased renal responsiveness to the neurohypophyseal hormones may be involved.

Circulating concentrations and physiologic role of atrial natriuretic peptide during endotoxic shock in the rat

OBJECTIVES

To determine if there are changes in circulating concentrations of endogenous atrial natriuretic peptide and the physiologic role of this peptide in endotoxic shock.

DESIGN

A prospective, randomized, controlled animal trial.

SETTING

University research laboratory.

SUBJECTS

Anesthetized male Wistar rats, weighing 250 to 350 g.

INTERVENTIONS

Six rats received 1.5 mg/kg body weight of lipopolysaccharide alone. Five rats received 1.5 mg/kg of lipopolysaccharide and 200 microL/100 g body weight of rabbit anti-atrial natriuretic peptide serum. Another five rats received 1.5 mg/kg of lipopolysaccharide and normal rabbit serum in the same volume as the antiserum.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of atrial natriuretic peptide, arginine vasopressin, and aldosterone were measured, and changes in hemodynamic parameters and renal function were monitored in rats with endotoxic shock after catheterization of the right jugular vein. Urine volume, urine sodium excretion, urinary potassium excretion, and urine 3', 5'-cyclic guanosine monophosphate (cGMP) excretion were measured at 12-hr intervals. The plasma atrial natriuretic peptide concentration was slightly but significantly lower 30 mins after the lipopolysaccharide injection (114.8 +/- 9.0 pg/mL at 0 hr, 75.6 +/- 6.2 pg/mL at 30 mins, p < .01) and then began to increase, peaking at 6 hrs (752.8 +/- 104.5 pg/mL, p < .01 vs. 0 time) and remaining at higher concentrations than before the preinjection value, up to 24 hrs. In contrast, acute spike-like increases of arginine vasopressin and aldosterone concentrations were observed 30 mins after the lipopolysaccharide injection, preceding the increase of the plasma atrial natriuretic peptide concentration. Measurements of urine volume and urine sodium excretion showed oliguria during the initial 12 hrs after the lipopolysaccharide injection, followed by diuresis and natriuresis during the subsequent 12 hrs. In addition, injection with anti-atrial natriuretic peptide serum in the diuretic phase 12 hrs after the lipopolysaccharide injection significantly inhibited the diuresis, natriuresis, and urine cGMP excretion in this model. Furthermore, the plasma aldosterone concentration 24 hrs after the lipopolysaccharide injection was significantly increased by the administration of the antisera.

CONCLUSIONS

These findings suggest that endogenous atrial natriuretic peptide increases in the acute phase of endotoxic shock and plays an important role in water and electrolyte balance by regulating diuresis.

The antidiuretic effect of pneumadin requires a functional arginine vasopressin system

Pneumadin is an antidiuretic decapeptide, recently isolated from rat and human lung. Bolus intravenous injection of 5 nmol of pneumadin into water-loaded rats caused a rapid and significant antidiuresis and a reduction in Na+ and Cl- excretion. Pneumadin administration did not alter mean arterial pressure, right atrial pressure, heart rate or haematocrit. Bolus intravenous injection of 20 nmol of pneumadin into non-water-loaded rats caused a significant increase in arginine vasopressin (AVP) within 10 min. Pneumadin administration also increased circulating atrial natriuretic peptide (ANP) but did not alter aldosterone or plasma renin activity levels. Injection of pneumadin into water-loaded Brattleboro rats, which genetically lack circulating AVP, did not change urine flow, confirming that the pneumadin induced antidiuresis is AVP dependent. Radioactive pneumadin was cleared from the circulation with a t1/2 beta of 480.3 s. Radioactive pneumadin, isolated from plasma, eluted at an altered position on reverse phase HPLC, which indicated that the peptide was modified in vivo. This modification was also observed when synthetic pneumadin was incubated in rat plasma in vitro. Purification and sequencing of the modified synthetic peptide indicated that the modification is not a proteolytic cleavage. These results indicate that pneumadin injected into the rat caused an antidiuresis by altering circulating AVP levels.

Dynamic aspects of regulatory lung peptides in chronic hypoxic pulmonary hypertension

Male Sprague-Dawley rats were placed in hypobaric hypoxia for 17-21 d (FIO2 10%) to establish pulmonary hypertension (PH) and control rats were kept in normobaric room air. Right mean atrial and ventricular pressures (PRA, PRV) were recorded, left ventricular (LV) blood was collected, and lungs were perfused with heparinized saline. Hearts were removed to evaluate right ventricular (RV) hypertrophy (RV/(LV+septum)%). Peptides were quantitated with radioimmunoassay in lung tissue extracts and plasma. Wet lung weight, PRA, PRV, and RV/(LV+S)% were higher and body weight was lower in hypoxia rats, and lung morphometry revealed increased arterial medial thickness (MT/OD%) and elastification of arterioles and capillaries. Lung tissue CGRP, PYY, gamma 2-MSH, and SOM were higher in PH rats and ANP was unchanged. Blood AVP, CGRP, PYY, VIP, and SOM were reduced in PH rats and ANP was unchanged. Lung levels of PYY and SOM correlated significantly with the time in hypoxia and with all parameters examined and CGRP and gamma 2-MSH correlated with all but medial thickness. PYY had the highest correlation of the peptides with body weight, PRV, and RV/(LV+S)%, and SOM the highest with time in hypoxia, wet lung weight, PRA, MT/OD%, and elastification of arterioles and capillaries. Blood peptides correlated inversely with these parameters. ANP had the overall weakest correlations and CGRP, PYY, and SOM had the highest. SOM correlated the highest with arterial medial hypertrophy, PRV, RV hypertrophy, and elastification of peripheral capillaries. VIP correlated the highest of the blood peptides with body weight and wet lung weight. Statistically significant correlations do not necessarily imply causal relationships. The putative roles of these peptides in pulmonary function are discussed.