San Antonio Vasopressin in Shock Symposium Report

Open Source Pharmacokinetic/Pharmacodynamic Framework: Tutorial on the BioGears Engine

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Effects of the Kv7 voltage-activated potassium channel inhibitor linopirdine in rat models of haemorrhagic shock

Recently, we demonstrated that Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements in short-term rat models of haemorrhagic shock. The aim of the present study was to further delineate the therapeutic potential and side effect profile of the Kv7 channel blocker linopirdine in various rat models of severe haemorrhagic shock over clinically relevant time periods. Intravenous administration of linopirdine, either before (1 or 3 mg/kg) or after (3 mg/kg) a 40% blood volume haemorrhage, did not affect blood pressure and survival in lethal haemorrhage models without fluid resuscitation. A single bolus of linopirdine (3 mg/kg) at the beginning of fluid resuscitation after haemorrhagic shock transiently reduced early fluid requirements in spontaneously breathing animals that were resuscitated for 3.5 hours. When mechanically ventilated rats were resuscitated after haemorrhagic shock with normal saline (NS) or with linopirdine-supplemented (10, 25 or 50 μg/mL) NS for 4.5 hours, linopirdine significantly and dose-dependently reduced fluid requirements by 14%, 45% and 55%, respectively. Lung and colon wet/dry weight ratios were reduced with linopirdine (25/50 μg/mL). There was no evidence for toxicity or adverse effects based on measurements of routine laboratory parameters and inflammation markers in plasma and tissue homogenates. Our findings support the concept that linopirdine-supplementation of resuscitation fluids is a safe and effective approach to reduce fluid requirements and tissue oedema formation during resuscitation from haemorrhagic shock.

Cardiovascular Responsiveness to Vasopressin and α1-Adrenergic Receptor Agonists After Burn Injury

The effects of burn injury on cardiovascular responsiveness to vasoactive agents are not well understood. The aims of this study were to determine whether burn injury alters cardiovascular reactivity to vasoactive drugs in vivo and intrinsic function of isolated mesenteric resistance arteries. Anesthetized Sprague-Dawley rats were subjected to sham procedure or 30% TBSA dorsal scald burn, followed by crystalloid resuscitation (Parkland Formula). At 24, 72, 96, and 168 hours post burn, rats were reanesthetized, and the mean arterial blood pressure (MAP) responses to various doses of the α1-adrenergic receptor agonist phenylephrine and arginine vasopressin were tested. Mesenteric arteries were harvested from uninjured animals and at 24 and 168 hours post burn. The responsiveness of arteries to phenylephrine and arginine vasopressin was tested by pressure myography. Dose response curves were generated and EC50 concentrations, Hill slopes, and maximal effects were compared. The potency of phenylephrine to increase MAP was reduced 2-fold 24 hours post burn (P < .05 vs sham) and gradually normalized at later time points. The reactivity of isolated arteries to phenylephrine was not significantly altered after burns. The potency of arginine vasopressin to increase MAP and to constrict isolated arteries was increased 2- to 3-fold at 24 hours post burn (P < .05) and normalized at later time points. Our findings suggest that burn injury differentially regulates vasopressor and blood pressure effects of α-adrenergic and vasopressin receptor agonists. Intrinsic vasopressin receptor reactivity of resistance arteries is sensitized early after burns. These findings will help to optimize resuscitation strategies and vasopressor use in difficult to resuscitate burn patients.

Supplemental arginine vasopressin during the resuscitation of severe hemorrhagic shock preserves renal mitochondrial function

Arginine vasopressin (AVP), a hormone secreted by the posterior pituitary, plays a vital role in maintaining vasomotor tone during acute blood loss. We hypothesized that decompensated hemorrhagic shock is associated with decreased AVP stores and supplementation during resuscitation would improve both blood pressure and renal function. Using a decompensated hemorrhagic shock model, male Long-Evans rats were bled to mean arterial blood pressure (MAP) of 40mmHg and maintained until the MAP could not be sustained without fluid. Once 40% of the shed volume was returned in lactated Ringer’s (Severe Shock), animals were resuscitated over 60 minutes with 4x the shed volume in lactated Ringer’s (LR) or the same fluids with AVP (0.5 units/kg+ 0.03 units/kg/min). Animals (n = 6-9/group) were sacrificed before hemorrhage (Sham), at Severe Shock, following resuscitation (60R, 60R with AVP) or 18 hours post-resuscitation (18hr, 18hr with AVP). Blood samples were taken to measure AVP levels and renal function. Pituitaries were harvested and assayed for AVP. Kidney samples were taken to assess mitochondrial function, histology, and oxidative damage. Baseline pituitary AVP stores (30,364 ± 5311 pg/mg) decreased with severe shock and were significantly depressed post-resuscitation (13,910 ± 3016 pg/ml. p<0.05) and at 18hr (15,592 ±1169 pg/ml, p<0.05). Resuscitation with LR+AVP led to higher serum AVP levels at 60R (31±8 vs 79±12; p<0.01) with an improved MAP both at 60R (125±3 vs 77±7mmHg; p<0.01) and 18hr (82±6 vs 69±5mmHg;p<0.05). AVP supplementation preserved complex I respiratory capacity at 60R and both complex I and II function at 18hr (p<0.05). AVP was also associated with decreased reactive oxygen species at 60R (856±67 vs 622±48F RFU) and significantly decreased oxidative damage as measured by mitochondrial lipid peroxidation (0.9±0.1 vs 1.7±0.1 fold change, p<0.01) and nitrosylation (0.9±0.1 vs 1.4±0.2 fold change, p<0.05). With AVP, renal damage was mitigated at 60R and histologic architecture was conserved at 18 hours. In conclusion, pituitary and serum AVP levels decrease during severe hemorrhage and may contribute to the development of decompensated hemorrhagic shock. Supplementing exogenous AVP during resuscitation improves blood pressure, preserves renal mitochondrial function, and mitigates acute kidney injury.

Kv7 voltage-activated potassium channel inhibitors reduce fluid resuscitation requirements after hemorrhagic shock in rats

Background

Recent evidence suggests that drugs targeting Kv7 channels could be used to modulate vascular function and blood pressure. Here, we studied whether Kv7 channel inhibitors can be utilized to stabilize hemodynamics and reduce resuscitation fluid requirements after hemorrhagic shock.

Methods

Anesthetized male Sprague-Dawley rats were instrumented with arterial and venous catheters for blood pressure monitoring, hemorrhage and fluid resuscitation. Series 1: Linopirdine (Kv7 channel blocker, 0.1–6 mg/kg) or retigabine (Kv7 channel activator, 0.1–12 mg/kg) were administered to normal animals. Series 2: Animals were hemorrhaged to a MAP of 25 mmHg for 30 min, followed by fluid resuscitation with normal saline (NS) to a MAP of 70 mmHg until t = 75 min. Animals were treated with single bolus injections of vehicle, linopirdine (1–6 mg/kg), XE-991 (structural analogue of linopirdine with higher potency for channel blockade, 1 mg/kg) prior to fluid resuscitation. Series 3: Animals were resuscitated with NS alone or NS supplemented with linopirdine (1.25–200 μg/mL). Data were analyzed with 2-way ANOVA/Bonferroni post-hoc testing.

Results

Series 1: Linopirdine transiently (10–15 min) and dose-dependently increased MAP by up to 15%. Retigabine dose-dependently reduced MAP by up to 60%, which could be reverted with linopirdine. Series 2: Fluid requirements to maintain MAP at 70 mmHg were 65 ± 34 mL/kg with vehicle, and 57 ± 13 mL/kg, 22 ± 8 mL/kg and 22 ± 11 mL/kg with intravenous bolus injection of 1, 3 and 6 mg/kg linopirdine, respectively. XE-991 (1 mg/kg), reduced resuscitation requirements comparable to 3 mg/kg linopirdine.

Series 3: When resuscitation was performed with linopirdine-supplemented normal saline (NS), fluid requirements to stabilize MAP were 73 ± 12 mL/kg with NS alone and 72 ± 24, 61 ± 20, 36 ± 9 and 31 ± 9 mL/kg with NS supplemented with 1.25, 6.25, 12.5 and 200 μg/mL linopirdine, respectively.

Conclusions

Our data suggest that Kv7 channel blockers could be used to stabilize blood pressure and reduce fluid resuscitation requirements after hemorrhagic shock.

Pharmacological targeting of chemokine (C-X-C motif) receptor 4 in porcine polytrauma and hemorrhage models

BACKGROUND

Recent evidence suggests that chemokine receptor CXCR4 regulates vascular α1-adrenergic receptor function and that the noncognate CXCR4 agonist ubiquitin has therapeutic potential after trauma/hemorrhage. Pharmacologic properties of ubiquitin in large animal trauma models, however, are poorly characterized. Thus, the aims of the present study were to determine the effects of CXCR4 modulation on resuscitation requirements after polytrauma, to assess whether ubiquitin influences survival times after lethal polytrauma-hemorrhage, and to characterize its dose-effect profile in porcine models.

METHODS

Anesthetized pigs underwent polytrauma (PT, femur fractures/lung contusion) alone (Series 1) or PT/hemorrhage (PT/H) to a mean arterial blood pressure of 30 mmHg with subsequent fluid resuscitation (Series 2 and 3) or 40% blood volume hemorrhage within 15 minutes followed by 2.5% blood volume hemorrhage every 15 minutes without fluid resuscitation (Series 4). In Series 1, ubiquitin (175 and 350 nmol/kg), AMD3100 (CXCR4 antagonist, 350 nmol/kg), or vehicle treatment 60 minutes after PT was performed. In Series 2, ubiquitin (175, 875, and 1,750 nmol/kg) or vehicle treatment 60 minutes after PT/H was performed. In Series 3, ubiquitin (175 and 875 nmol/kg) or vehicle treatment at 60 and 180 minutes after PT/H was performed. In Series 4, ubiquitin (875 nmol/kg) or vehicle treatment 30 minutes after hemorrhage was performed.

RESULTS

In Series 1, resuscitation fluid requirements were significantly reduced by 40% with 350-nmol/kg ubiquitin and increased by 25% with AMD3100. In Series 2, median survival time was 190 minutes with vehicle, 260 minutes with 175-nmol/kg ubiquitin, and longer than 420 minutes with 875-nmol/kg and 1,750-nmol/kg ubiquitin (p < 0.05 vs. vehicle). In Series 3, median survival time was 288 minutes with vehicle and 336 minutes and longer than 420 minutes (p < 0.05 vs. vehicle) with 175-nmol/kg and 875-nmol/kg ubiquitin, respectively. In Series 4, median survival time was 147.5 minutes and 150 minutes with vehicle and ubiquitin, respectively (p > 0.05).

CONCLUSION

These findings further suggest CXCR4 as a drug target after PT/H. Ubiquitin treatment reduces resuscitation fluid requirements and provides survival benefits after PT/H. The pharmacological effects of ubiquitin treatment occur dose dependently.

Terlipressin with limited fluid resuscitation in a swine model of hemorrhage

BACKGROUND

Principles of damage control resuscitation include minimizing intravenous fluid (IVF) administration while correcting perfusion pressure as quickly as possible. Recent studies have identified a potential advantage of vasopressin over catecholamines in traumatic shock. Terlipressin (TP) is a vasopressin analogue used to reverse certain shock etiologies in some European countries.

STUDY OBJECTIVE

We evaluated three dosages of TP when combined with a limited colloid resuscitation strategy on mean arterial pressure (MAP) and lactatemia in a swine model of isolated hemorrhage.

METHODS

Sixty anesthetized swine underwent intubation and severe hemorrhage. Subjects were randomized to one of four resuscitation groups: 4 mL/kg Hextend(®) (Hospira Inc, Lake Forest, IL) only, 3.75 μg/kg TP + Hextend, 7.5 μg/kg TP + Hextend, or 15 μg/kg TP + Hextend. MAP and heart rate were recorded every 5 min. Baseline and serial lactate values at 30-min intervals were recorded and compared.

RESULTS

Subjects receiving 7.5 μg/kg TP had significantly higher MAPs at times t15 (p = 0.012), t20 (p = 0.004), t25 (p = 0.018), t30 (p = 0.032), t35 (p = 0.030), and t40 (p = 0.021). No statistically significant differences in lactate values between TP groups and controls were observed.

CONCLUSION

Subjects receiving 7.5 μg/kg of TP demonstrated improved MAP within 10 min of administration. When combined with minimal IVF resuscitation, TP doses between 3.75 and 15 μg/kg do not elevate lactate levels in hemorrhaged swine.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

Arginine vasopressin: the future of pressure-support resuscitation in hemorrhagic shock

BACKGROUND

Arginine vasopressin (AVP) is a key player in maintaining the intravascular volume and pressure during hemorrhagic shock. During the past 2 decades, animal studies, case reports, and reviews have documented the minimized blood loss and improved perfusion pressures in those receiving pressure support with AVP.

MATERIALS AND METHODS

A PubMed search of studies was conducted with the terms: "AVP," "arginine vasopressin," "antidiuretic hormone," "hemorrhagic shock," "hemorrhage," "circulatory shock," "fluid resuscitation," "trauma," "massive transfusion protocol," "physiology," "cerebral," "renal," "cardiac," "perfusion," "dose," and "hypotension." The studies were located by a search of a combination of these terms. Also, within-PubMed citations relating to the studies gathered from the initial search were explored. Reports discussing vasopressin in hemorrhagic states were considered. No predetermined limit was used to choose or exclude articles.

RESULTS

AVP is an important hormone in osmoregulation and blood pressure. During stress, such as hemorrhage, the levels have been shown to rapidly decrease. Furthermore numerous animal studies and limited human studies have shown that circulatory support with AVP is linked to improved outcomes. No large human prospective studies are available to guide its use at present, but some of its effectiveness seems to lie in its ability to increase calcium sensitivity in acidotic environs, thereby allowing for more effective maintenance of vascular tone than catecholamines. It also redirects blood from the periphery, creating a steal syndrome, and increases the oxygen supply to vital organs, minimizing blood loss, and allowing additional time for surgical repair.

CONCLUSIONS

With these encouraging data, there is hope that "pressure support" will be the "resuscitation" considered necessary for a patient's optimum survival.