Evidence that endogenous vasopressin plays a protective role in circulatory shock. Role for reticuloendothelial system using Brattleboro rats

Effect of Low-Dose Supplementation of Arginine Vasopressin on Need for Blood Product Transfusions in Patients With Trauma and Hemorrhagic Shock: A Randomized Clinical Trial

Importance

Current therapies for traumatic blood loss focus on hemorrhage control and blood volume replacement. Severe hemorrhagic shock, however, is associated with a state of arginine vasopressin (AVP) deficiency, and supplementation of this hormone may decrease the need for blood products in resuscitation.

Objective

To determine whether low-dose supplementation of AVP in patients with trauma (hereinafter referred to as trauma patients) and with hemorrhagic shock decreases their need for transfused blood products during resuscitation.

Design, Setting, and Participants

This randomized, double-blind placebo-controlled clinical trial included adult trauma patients (aged 18-65 years) who received at least 6 U of any blood product within 12 hours of injury at a single urban level 1 trauma center from May 1, 2013, through May 31, 2017. Exclusion criteria consisted of prehospital cardiopulmonary resuscitation, emergency department thoracotomy, corticosteroid use, chronic renal insufficiency, coronary artery disease, traumatic brain injury requiring any neurosurgical intervention, pregnancy, prisoner status, or AVP administration before enrollment. Data were analyzed from May 1, 2013, through May 31, 2017, using intention to treat and per protocol.

Interventions

After administration of an AVP bolus (4 U) or placebo, participants received AVP (≤0.04 U/min) or placebo for 48 hours to maintain a mean arterial blood pressure of at least 65 mm Hg.

Main Outcomes

The primary outcome was total volume of blood product transfused. Secondary end points included total volume of crystalloid transfused, vasopressor requirements, secondary complications, and 30-day mortality.

Results

One hundred patients underwent randomization (49 to the AVP group and 51 to the placebo group). Patients were primarily young (median age, 27 years [interquartile range {IQR}, 22-25 years]) and male (n = 93) with penetrating trauma (n = 79). Cohort characteristics before randomization were well balanced. At 48 hours, patients who received AVP required significantly less blood products (median, 1.4 [IQR, 0.5-2.6] vs 2.9 [IQR, 1.1-4.8] L; P = .01) but did not differ in requirements for crystalloids (median, 9.9 [IQR, 7.9-13.0] vs 11.0 [8.9-15.0] L; P = .22) or vasopressors (median, 400 [IQR, 0-5900] vs 1400 [IQR, 200-7600] equivalent units; P = .22). Although the groups had similar rates of mortality (6 of 49 [12%] vs 6 of 51 [12%]; P = .94) and total complications (24 of 44 [55%] vs 30 of 47 [64%]; P = .37), the AVP group had less deep venous thrombosis (5 of 44 [11%] vs 16 of 47 [34%]; P = .02).

Conclusions and Relevance

Low-dose AVP during the resuscitation of trauma patients in hemorrhagic shock decreases blood product requirements. Additional research is necessary to determine whether including AVP improves morbidity or mortality.

Trial Registration

ClinicalTrials.gov identifier: NCT01611935.

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.

Vasopressin receptors in the area postrema differentially modulate baroreceptor responses in rats

This study examined the effects of microinjection of [Arg8]vasopressin (AVP) into the area postrema (AP) on baroreceptor reflex control of heart rate (HR) and sympathetic efferent discharge (SED) in anesthetized rats. Comparable increments in blood pressure evoked by systemic AVP, as opposed to phenylephrine, were associated with significantly greater reflex bradycardia. Similarly, AVP augmented the baroreflex-mediated sympathoinhibition; however, this effect was evident only with the lower increments in arterial pressure (< 45 mm Hg) i.e. following systemic administration of small doses of AVP. Beyond 45 mm Hg there was no further augmentation of baroreflex-mediated sympathoinhibition showing the non-linearity of the response compared to phenylephrine which was linear over a wide range of induced pressure increases. Microinjection of AVP into the AP produced a differential effect on HR and SED responses to baroreceptor activation by systemically administered phenylephrine, the baroreflex slope of HR response was attenuated whereas that of SED was enhanced. Microinjection of the V1 antagonist AVPX (d(CH2)5Tyr(Me)-AVP) into the AP abolished the inhibitory effect of AVP on the baroreceptor-HR response suggesting that V1 receptors are involved in this response. Further, AVPX inhibited the baroreceptor-SED response suggesting that V1 receptors in the AP are tonically involved in modulating the baroreceptor reflex control of SED. Qualitatively similar but smaller responses were obtained following microinjection of AVP into the nucleus tractus solitarii (NTS) suggesting involvement of neural input from the AP to the NTS in AVP-evoked responses in the AP. It is concluded that the AVP receptors in the AP differentially modulates the baroreceptor reflex control of HR and SED.

Effect of peripheral injection of arginine vasopressin and its receptor antagonist on burn shock in the rat

To investigate the effect of arginine vasopressin (AVP) in the peripheral circulation on burn shock in the rat, AVP and its nonselective V1/V2 receptor antagonist d(CH2)5Tyr (Et)VAVP were administered intravenously in burn shocked rats. Cardiovascular parameters were recorded including left ventricular systolic pressure (LVSP), +/- dP/dt max, total area of the cardiac force loop (Lo), mean arterial blood pressure (MAP), heart rate (HR) and electrocardiogram (ECG). Our results showed that AVP failed to increase MAP in burned rats whereas it elicited a greater fall in LVSP, +/- dP/dt max and Lo and MAP than seen in control burned rats and hastened the onset of the decompensatory phase of burn shock resulting in the early death of burn shocked animals. The receptor antagonist d(CH2)5Tyr(Et)VAVP elevated LVSP, +/- dp/dt max and Lo for the eight hour observation period, and allowed MAP to recover from the initial profound fall following burn injury. Furthermore, it prolonged the survival time of the burned rats. AVP treated rats also displayed earlier abnormal changes such as elevation of S-T segment, inversion of T wave and ventricular fibrillation in ECG. The onset of these changes was much delayed in antagonist treated rats.

Hypothalamic knife cuts alter vasopressin induced recovery of blood pressure following hemorrhage

Effects of knife cuts posterior to the paraventricular nucleus (PVN) alone or to both the PVN and the supraoptic nucleus (SON) on vasopressin dependent restoration and maintenance of blood pressure following hemorrhage were tested in the rat. Conscious, unrestrained animals were hemorrhaged a volume equivalent to 1.8% of body weight from a femoral arterial catheter. Blood pressure was monitored for 30 min with no treatment, 30 min following iv injection of a specific antagonist to the pressor action of vasopressin, and 15 min during iv infusion of the competitive blocker of angiotensin II, saralasin. Restoration of blood pressure and the decrease in blood pressure with vasopressin blockade in rats with knife cuts posterior to the PVN alone were similar to that of control-operated animals. However, if knife cuts extended to the level of the SON, blood pressure was not restored, and vasopressin blockade did not result in a reduction of blood pressure. Saralasin infusion produced a similar decrease in blood pressure in all groups of animals. These data show that when knife cuts are confined to the area posterior to the PVN, vasopressin contributes to the restoration of blood pressure following hemorrhage. However, when cuts extend into the ventral hypothalamus, the contribution of vasopressin is eliminated.

The cardiovascular effects of vasopressin after haemorrhage in anaesthetized rats

The cardiovascular effects of an acute haemorrhage (2% of the body weight) were studied over a 60 min period in three groups of rats: (a) Brattleboro rats with hereditary hypothalamic diabetes insipidus (b.d.i.) lacking circulating vasopressin, (b) control rats of the parent Long Evans (l.e.) strain, and (c) l.e. rats treated with an antagonist of the vascular action of vasopressin. Prior to the haemorrhage there were no significant differences between the three groups of rats with respect to mean arterial blood pressure, cardiac output, stroke volume or total peripheral resistance. Following the haemorrhage cardiac output and stroke volume were severely reduced in all three groups of rats. Total peripheral resistance was relatively unaffected in antagonist-treated l.e. rats and b.d.i. rats, but rose substantially in response to the loss of blood in the control l.e. group. Both total peripheral resistance and mean arterial blood pressure were markedly greater in the untreated l.e. control rats than in the other two groups of animals during the first 20 min after haemorrhage. The mean heart rate measured in Brattleboro rats was elevated compared with that of control l.e. rats throughout the experiment and, in addition, significantly greater than that of antagonist-treated l.e. rats during the first 40 min after the haemorrhage. Survival rate for the b.d.i. rats following the 2% haemorrhage was lower than that for l.e. control rats and antagonist-treated l.e. rats. The results indicate that the recovery of the blood pressure following an acute arterial haemorrhage is significantly influenced by vasopressin, particularly during the first 20 min, and that the predominant effect of the hormone is to increase the total peripheral resistance. The higher mortality associated with volume depletion in the b.d.i. rats is unlikely to be directly related to the absence of the vascular action of vasopressin, since administration of the vasopressin antagonist to normal l.e. rats does not reduce their survival rate.

Cardiovascular effects of centrally administered vasopressin in conscious and anesthetized rats

Intracerebroventricular (ICV) injections of arginine vasopressin (AVP) in doses of 0.015 nmoles and 0.15 nmoles produced a fall in mean actual pressure heart rate and respiration in pentobarbital anesthetized rats. The changes in mean arterial pressure and respiration after the higher dose were significantly different from saline injection. In contrast, the same doses of AVP given to conscious animals increased both blood pressure and heart rate. Following the 0.15 nmole dose, there was a marked and significant rise in plasma norepinephrine and epinephrine, indicating that activation of the sympathetic nervous system was, at least in part, responsible for the rise in blood pressure. Plasma vasopressin increased by less than 10 pg/ml following injection. Similar doses of a vasopressin pressor antagonist had no significant effect on mean arterial pressure or heart rate. These results indicate that ICV injection of vasopressin has different effects on blood pressure, depending on the presence or absence of anesthesia: depressor responses in the anesthetized animal and pressor responses in the unanesthetized animal.

Absence of endotoxin-fever but not hyperthermia in Brattleboro rats

I.c.v. administration of bacterial endotoxin produced a fever in the Long-Evans rat but not in the Brattleboro rat. Similar administration of arachidonic acid, prostaglandin E2, prostacyclin, dibutyryl cAMP, norepinephrine, morphine and beta-endorphin caused hyperthermia in both Long-Evans and Brattleboro rats. Variable doses of exogenous arginine vasopressin (AVP) when centrally administered with endotoxin caused fever in the Brattleboro rat. It is suggested that AVP may play an important role in the production and release of endogenous pyrogen.

Central cardiovascular effects of mammalian neurohypophyseal peptides in conscious rats

To confirm and extend the results of previous studies which demonstrated central cardiovascular effects of vasopressin in anesthetized rats, we determined blood pressure and heart rate changes for 30 minutes after intracerebroventricular injections of arginine vasopressin, arginine vasotocin and oxytocin in conscious rats. As compared to sham injections, significantly greater increases in either systolic or diastolic blood pressure were noted over the 30 minutes which followed the injection of 0.15, 1.0 or 10.0 nM of either vasopressin or vasotocin. In animals given vasopressin, plasma levels of the peptide were determined. There was a substantial increase in plasma vasopressin only after the highest dose. Overall blood pressure responses to doses of oxytocin as high as 100 nM were not significantly different than sham injections. Heart rate following both vasopressin and vasotocin was increased at 0.15 nM, was initially decreased then increased at 1.0 nM and was substantially decreased after the 10.0 nM dose. There was a significant increase in heart rate at the 10.0 nM and 100 nM doses of oxytocin. Dose response curves for systolic blood pressure and heart rate 20 minutes after injection were similar for vasopressin and vasotocin. We conclude that arginine vasopressin has significant central pressor and tachycardic effects in conscious rats, and it is related, at least in part, to the tail structure of the peptide, which is shared with arginine vasotocin.

Vasopressin: a homeostatic effector in the febrile process

This review compares the physiological changes which accompany infection and fever with the effects of the peptide, arginine vasopressin (AVP). AVP may act as a neuromodulator, a releasing factor, or a hormone to induce responses which are opposite to those homeostatic changes accompanying fever. Since AVP is released into blood and brain during fever, it is hypothesized that AVP contributes to the maintenance of homeostasis in the infected organism.

Vasopressin: an essential pressor factor for blood pressure recovery following hemorrhage

Two experimental approaches were used to evaluate the importance of the pressor effects of vasopressin in blood pressure recovery following hypotensive hemorrhage. Experiments using homozygous Brattleboro rats demonstrated that the hemodynamic recovery of these animals was subnormal, even though the activation and efficacy of the sympathetic nervous and renin-angiotensin systems were intact. Experiments using an antipressor vasopressin analogue in normal rats during hypotensive hemorrhage demonstrated significantly blunted blood pressure recovery in the presence of the analogue. Thus, both experiments indicate that the pressor effects of circulating vasopressin play an essential role in blood pressure recovery following hypovolemic hypotension induced by hemorrhage.