Analysis of regional hemodynamic regulation in response to scald injury

5-HT2a receptor antagonism reduces burn-induced macromolecular efflux in rats

BACKGROUND

Major thermal injuries lead to a systemic inflammatory response with systemic capillary leakage and multiple organ dysfunction. This systemic inflammatory response is induced by a variety of immunmodulative molecules including TNFα and serotonin. Unspecific serotonin antagonism leads to reduced macromolecular efflux in rat mesenteries after burn plasma transfer. The aim of the present study was to evaluate the effect of specific 5-HT2a antagonism on early burn edema.

METHODS

Donor rats (DR) underwent thermal injury (100 °C water, 30% BSA, 12 s) for positive controls. For negative controls, DR underwent sham burn (37 °C water, 30% BSA, 12 s). DR plasma (harvested 4 h post-trauma) was transferred to healthy individuals for positive controls. Study rats received burn plasma (BP) and a Bolus injection of Ketanserin (Ket) (1 mg kg(-1) body weight). Negative controls underwent sham burn plasma infusion. Intravital microscopy was performed in mesenteric venules (0/60/120 min). Edema was assessed by FITC-albumin extravasation. Additionally, leukocyte rolling and sticking (cells mm(-2)) as well as microhemodynamic parameters were assessed.

RESULTS

Significant systemic capillary leakage was observed after BP transfer at 120 min and additional administration of Ket attenuated the postburn edema to sham burn levels. Ket also leads to significantly decreased leukocyte-endothelial interactions when compared to positive controls.

CONCLUSION

5-HT2a antagonism reduces plasma extravasation after burn plasma transfer in healthy individuals. The influence of leukocyte-endothelial interactions on postburn edema remains unclear.

Serotonin kinetics in patients with burn injuries: a comparison between the local and systemic responses measured by microdialysis-a pilot study

OBJECTIVES

To investigate serotonin (5HT) locally in burned and uninjured skin (intracutaneous) by microdialysis, and simultaneously record urinary and blood values in the same subjects. For comparison, serotonin values were also measured in skin of healthy controls.

DESIGN AND SETTING

An experimental study in burned patients with of more than 25% TBSA (total burn surface area) % in an 8-bed tertiary burns unit, serving about 3.5 million persons.

PATIENTS AND METHODS

Six subjects with a median TBSA% of 59% (range 33.5-90), and five healthy controls were examined by intracutaneous microdialysis of the skin.

RESULTS

5HT was increased in burned patients, compared with controls. This increase was tenfold in skin and was noted both in uninjured and burned skin. The highest values were recorded on day 1 (median 16.1nmol in uninjured and 9.5nmol in burned skin) and day 2 (15.6nmol in uninjured and 13.4nmol in burned skin). A rapid reduction was noted on day 3 (4.9nmol in uninjured and 3.8nmol in burned skin). The corresponding value for control subjects was 1.3nmol. The 5HT in blood was twice normal on day 2, and gradually reduced on days 3 and 4 (3189, 3035 and 2573nmol, respectively). Urinary 5HT concentrations were increased only on day 2 at 1755nmol and thereafter returned to the normal range on days 3 and 4 (1248 and 1344nmol, respectively).

CONCLUSIONS

We showed that microdialysis may be used in the critical care of burns, and local skin serotonin concentrations examined continuously for several days. The findings of significantly raised tissue serotonin concentrations, compared to that in blood and urine, suggests that serotonin may be important in local vascular control and formation of oedema.

Comparisons between electromagnetic and X-beam transit-time flow measurements for evaluating drug actions on cardiac output in the conscious dog

INTRODUCTION

Cardiac output remains an important preclinical measurement for evaluating the cardiovascular effects of drugs. We evaluated the performance of the Triton Active Redirection Transit-Time, ART(2), which represents a new class of X-beam flow systems and compared it in vivo and in vitro to an electromagnetic flow (EMF) system for measuring large vessel flow.

METHODS

In vivo, simultaneous aortic flow measurements were obtained during alpha- and beta-adrenergic receptor stimulation in 5 conscious dogs instrumented with both ART(2) and EMF probes on their ascending aortas. In vitro, simultaneous measurements of volume flow using the ART(2), EMF, and timed-volume collection were made using a novel benchtop flow apparatus that ensured probe alignment and precise timed-volume flow measurements. Accuracy and sensitivity of both systems were assessed by recording flow measurements while varying rates, temperature and hematocrit.

RESULTS

In vivo aortic flow measurements between ART(2) and EMF were closely correlated (linear regression r(2) values ranged from 0.84 to 0.99), with the ART(2) system recording lower flow values than the EMF. In vitro ART(2) flow rates were in excellent agreement with timed-volume flow, while EMF flow rates were lower (p<0.05) and exhibited more variation and dependency upon temperature or hematocrit than the ART(2). Saline flows measured by ART(2) and EMF averaged 97+/-2% and 91+/-5% accuracy, respectively, over the temperature range 32 degrees C to 42 degrees C. For blood hematocrit values between 35% and 45%, ART(2) accuracy averaged 98+/-2%, compared to 89+/-5% accuracy with the EMF.

DISCUSSION

The ART(2) flow measurements in conscious dogs correlated closely to concurrent measurements obtained with the EMF over a wide range of flow rates, even though the absolute aortic flow values differed. Since it accurately measured flow in vitro, the ART(2) system is an appropriate alternative for evaluating cardiovascular effects of disease progression or drug administration in experimental animals.

Nitric oxide, inflammation and acute burn injury

Nitric oxide (NOz.rad;) is a diatomic mediator liberated on oxidation of L-arginine by the nitric oxide synthase (NOS) family of enzymes. It has complex and wide ranging functions in vivo and has been implicated in the development of the profound inflammatory response that occurs as a result of cutaneous burn injury. In addition, dysregulation of NOS activity has been associated with multiple organ failure in human burn patients and may therefore represent a novel therapeutic target in such circumstances. This review focuses on the role of NOz.rad; in inflammation, with particular emphasis on the acute post-burn inflammatory response. Specific areas of discussion include the maintenance of microvascular haemostasis, leukocyte recruitment and remote organ dysfunction following thermal injury.

Microvascular changes in large flame burn wound in sheep

Advances in local wound management with early excisional therapy have decreased morbidity and mortality of massive third-degree burn patients. Although blood redistribution within burned tissue is of clinical interest, few studies have longitudinally determined the regional blood flow of various layers of the burn wound. We used a conscious ovine model in which animals were subjected to 40% third degree burn. Burned tissue was divided into the four layers (i.e. skin, panniculus carnosus, adipose tissue, and skeletal muscle), and regional blood flow was determined separately, with fluorescent microspheres, while measuring systemic hemodynamics and total burned tissue microvascular fluid flux. The subburn adipose tissue exhibited a remarkable biphasic alteration in regional blood flow, whereas the skin layer showed only decreased blood flow during the whole experimental period. The increase in blood flow to the adipose tissue seems to be related to a sustained fluid filtrate in the postresuscitation period, resulting in edema formation mainly located in the adipose tissue at the endpoint.

Methysergide reduces nonnutritive blood flow in normal and scalded skin

Methysergide is a serotonin antagonist and has been demonstrated to reduce wound blood flow and edema formation. We have determined the effect of methysergide on protein kinetics in normal and scalded skin of anesthetized rabbits. L-[ring-(13)C(6)]- or L-[ring-(2)H(5)]phenylalanine was used to reflect skin protein kinetics by use of an ear model, and L-[1-(13)C]leucine was used to reflect whole body protein kinetics. The results were that infusion of methysergide (2-3 mg. kg(-1). h(-1)) reduced the blood flow rate in normal skin by 50% without changing skin or whole body protein kinetics. After scald injury on the ear, administration of methysergide for 48 h reduced the weight of scalded ears (43 +/- 4 vs. 30 +/- 5 g, P < 0.01) and ear blood flow rate (42.6 +/- 4.9 vs. 5.8 +/- 1.0 ml. 100 g(-1). min(-1), P < 0.0001) and did not change wound protein kinetics. Methysergide reduced arteriovenous shunting and maintained inward phenylalanine transport from the blood to the skin pool. Using the microsphere technique, we found that the infusion of methysergide decreased blood perfusion by 33-36% in both normal and scalded ear skin. We conclude that methysergide administration reduces nonnutritive, as opposed to nutritive, blood flow in normal and scalded skin.

The effects of human burn injury on urinary nitrate excretion

Different studies have demonstrated both an increase and a decrease in the biosynthesis of nitric oxide (NO) during the first 2 days following experimental and human burn trauma. This study investigated changes in urinary nitrate excretion in humans following thermal injury in order to determine the temporal relationship between NO release and the initial injury. Urinary nitrate was measured in daily 24-h urine collections taken on days 1-7 following burn injury from 15 patients. The control group consisted of 11 healthy, age- and sex-matched patients who kept a nitrate-restricted diet for five days prior to collection of a single 24-h urine sample. The burns group had a mean age of 41.9 +/- 19.4 (mean +/- S.D.) years and a mean total burn surface area (TBSA) of 30.2 +/- 24.9% (mean +/- S.D.). In the burn injured patients, urinary nitrate levels peaked at day 4 and a 2-fold increase relative to day 1 was observed. Urinary nitrate levels were significantly higher in the burns group than the control group on days 4 and 5 only (p < 0.05 for both days). There was no correlation between TBSA and the measured urinary nitrate levels. This study confirms that the biosynthesis of NO is increased during the first week following burn trauma and establishes that the renal elimination of the by-products of NO metabolism is not increased during the first three days after injury. Notwithstanding the potential effects of burns on nitrate distribution, our findings may reflect a delay in the release of NO following the initial insult.

Serotonin receptors regulate canine regional vasodilator responses to burn

OBJECTIVE

To determine which serotoninergic receptor subtype(s) mediates the regional vasodilator response to scald injury.

DESIGN

Prospective, randomized trial.

SETTING

Microcirculation research laboratory.

SUBJECTS

Anesthetized dogs.

INTERVENTIONS

Mechanically ventilated dogs underwent cannulation of a brachial artery and placement of an ultrasonic flow probe around one femoral artery. All animals received a 2% to 3% body surface area partial thickness scald injury by immersing the paw ipsilateral to the instrumented femoral artery into 100 degrees C water for 5 secs. In one group of dogs, BMY 7378 (a serotoninergic1A receptor antagonist) was given by the peripheral intravenous route before burn. These results were compared with those findings obtained from a group of animals that received a burn only, and groups of animals given a peripheral intravenous injection of methysergide (a serotoninergic receptor antagonist) or ritanserin (a serotoninergic2 receptor blocking agent) before burn. Experiments were conducted for two postburn hours.

MEASUREMENTS AND MAIN RESULTS

Burn injury caused a marked and persistent increase in regional (e.g., femoral artery) blood flow, an effect that was significantly blunted by preburn administration of the serotoninergic receptor antagonist, methysergide. Preburn administration of BMY 7378 increased baseline femoral blood flow by 13%, reflecting its known serotonin agonist properties. However, when compared with the mean postscald increases in femoral blood flow over baseline seen in scald only dogs and in animals given the serotoninergic2 receptor blocking agent, ritanserin (before scald), the BMY 7378-treated group demonstrated a significant (p < .001 by analysis of variance) 2-hr-postscald blunting of this femoral vasodilator response.

CONCLUSION

These data suggest that serotoninergic1A-like receptors play an integral, albeit not an exclusive, role in blood flow regulation to the site of burn injury.

Autonomic control of the regional hemodynamic response to scald

Ultrasonic flow probes were placed around the ascending aorta and each femoral artery of dogs to record cardiac index and femoral blood flow, respectively. Intravenous hexamethonium (n = 5) produced 30% decreases in systemic mean arterial pressure and in cardiac index, and a 14% increase in femoral blood flow, effects that waned over time, consistent with the half-life of the agent. Without hexamethonium, hind paw scalding with boiling water for 5 sec (n = 5) caused a marked increase in ipsilateral femoral artery blood flow (70.7 +/- 8.9 ml/min pre-burn vs 243.7 +/- 23.7 ml/min 5 min post-burn) that persisted for the 3 hr observation period. Contralateral femoral blood flow, systemic mean arterial pressure, and cardiac index were unchanged. Compared to burn only dogs, pre-burn treatment with hexamethonium (n = 6) blunted the femoral vasodilator response to burn (78.8 +/- 9.7 ml/min pre-burn vs 116.5 +/- 7.5 ml/min 5 min post-burn). These data suggest that postganglionic autonomic nerves are at least partially responsible for mediation of the regional vasodilator response to thermal injury.