Tumor necrosis factor (TNF) and interleukin 6 (IL-6) are purported to be important mediators of inflammatory responses. It is not known whether the plasma levels of these cytokines are altered after trauma and hemorrhage. Our objectives were to determine whether there is any elevation of plasma TNF or IL-6 after trauma and hemorrhage and to what extent these changes are due to tissue trauma vs. simple hemorrhage. Trauma was induced in Sprague-Dawley rats under light ether anesthesia by performing a 5-cm midline laparotomy. On closure, animals were catheterized, awakened, hemorrhaged to a mean blood pressure of 40 mmHg, and maintained at that pressure until 40% of maximum shed blood volume was returned in the form of Ringer lactate (RL). Animals were then resuscitated with RL equivalent to four times shed blood volume. Blood samples (0.5 ml) were taken before inducing hemorrhage, at maximal bleed out (45 min), and at 4 and 6 h posthemorrhage to obtain plasma. IL-6 and TNF levels were measured using cytokine-dependent cellular assays. TNF levels were significantly elevated at 45 min into hemorrhage and remained so up to 4 h after hemorrhage. IL-6 levels were also elevated 45 min into hemorrhage and remained so up to 6 h posthemorrhage. IL-6, unlike TNF, was already significantly increased after midline laparotomy and before initiation of hemorrhage compared with unmanipulated animals. Thus induction of IL-6 by trauma may be partially independent of those mechanisms in hemorrhage that are involved in the release of TNF.

Although depressed endothelium-dependent relaxation occurs during early sepsis, the precise mechanism responsible for this remains unknown. Because the elevated levels of plasma tumor necrosis factor (TNF) play a major role in the pathophysiology of sepsis, we investigated whether TNF-alpha administration alters endothelium-dependent relaxation. To study this, recombinant TNF-alpha (1.2 x 10(7) U/mg) was infused intravenously (0.25 mg/kg body wt) for 0.5 h in normal rats, and mean arterial pressure was monitored. At 1 h after the completion of TNF-alpha or vehicle infusion, the aorta and a pulmonary artery were isolated, cut into 2.5-mm rings, and placed in organ chambers. Norepinephrine (2 x 10(-7) M) was applied to achieve near-maximal contraction, and dose responses for an endothelium-dependent vasodilator, acetylcholine, and an endothelium-independent vasodilator, nitroglycerine, were determined. In additional studies, aortic rings from normal animals were incubated with TNF-alpha for 2 h in vitro, and vascular reactivity was determined. The results indicate that TNF-alpha administration significantly reduced acetylcholine-induced vascular relaxation both in vivo and in vitro. Such a reduction was sustained at least 80 min after the completion of 2-h incubation with TNF-alpha. In contrast, TNF did not alter nitroglycerine-induced vascular relaxation. Thus TNF-alpha depresses endothelium-dependent relaxation in vitro as well as in vivo. Because TNF-alpha infusion increases plasma TNF levels without decreasing mean arterial pressure, the depressed endothelium-dependent relaxation observed during early sepsis may be due to the elevated circulating levels of TNF.

Although the cytokines tumor necrosis factor (TNF), interleukin-1 (IL-1), and interleukin-6 (IL-6) are important mediators of hemodynamic, metabolic, and immunologic alterations in the host during sepsis, it is not known whether there is any association between the release of these cytokines and prostanoids during sepsis. Sepsis induced by cecal ligation and puncture in rats led to a persistent elevation (p less than 0.05) of plasma TNF until 10 hours, steadily increasing (p less than 0.05) IL-1 plasma levels, and enhanced (p less than 0.05) IL-6 plasma levels at all time points compared to the sham group. Prostaglandin E2 plasma levels were elevated (p less than 0.05) at 5 hours (153 +/- 29 pg/mL; control: 47 +/- 11 pg/mL) and 10 hours (96 +/- 16 pg/mL; control: 21 +/- 5 pg/mL). Prostaglandin E2 production by splenic macrophages (sM phi) from septic animals was increased (p less than 0.05) at 5 hours (9.1 +/- 2.2 ng/mL) and 10 hours (5.6 +/- 1.5 ng/mL) compared to controls (3.3 +/- 0.3 ng/mL at 5 hours; 1.3 +/- 1.3 ng/mL at 10 hours). Incubation of sM phi from septic animals with ibuprofen enhanced (p less than 0.05) IL-1 and TNF synthesis, while IL-6 production was reduced (p less than 0.05). These results indicate that the alterations in prostanoid release and elevated plasma prostanoids may regulate the release and consequently the circulating levels of cytokines during sepsis.

Because the liver experienced the most severe reduction in VO2 associated with an unchanged oxygen extraction capacity, this organ appears to be more vulnerable to hypoxic insult after hemorrhagic shock.

Although hemorrhage produces alterations in hemodynamics and cellular functions, it remains unknown if endothelial cell function is depressed in a nonheparinized model of trauma-hemorrhage and resuscitation. To study this, rats underwent a 5-cm midline laparotomy (i.e., trauma induced) and were bled to and maintained at a mean arterial pressure of 40 mmHg until 40% of maximal bleed-out volume was returned in the form of Ringer lactate (RL). They were then resuscitated with four times the volume of the shed blood with RL over 60 min. At the time of maximal bleed out (approximately 50 min from the onset of hemorrhage), 1.5, and 4 h after the completion of resuscitation, aortic rings (approximately 2.5 mm in length) were isolated and mounted in organ chambers. Dose responses for an endothelium-dependent vasodilator (acetylcholine) and endothelium-independent vasodilator (nitroglycerin) were determined. The results indicate that endothelium-dependent relaxation was depressed at the time of maximal bleed out and persisted even after resuscitation. However, there was no significant difference in nitroglycerin-induced relaxation at any point during the study period. In addition, hypoxia-induced contraction, a process mediated by endothelium-derived contracting factor, decreased significantly following hemorrhage and resuscitation. Thus endothelial cell dysfunction (i.e., reduced release of endothelium-derived relaxing and contracting factors) occurs very early after trauma-hemorrhage and persists despite fluid resuscitation.

No abstract

Background: Initial cardiovascular responses during sepsis are characterized by hyperdynamic circulation. Although studies have shown that a novel potent vasodilatory peptide, adrenomedullin (ADM), is up-regulated under such conditions, it remains unknown whether ADM is responsible for initiating the hyperdynamic response. Objective: To determine whether increased ADM release during early sepsis plays any major role in producing hyperdynamic circulation. Design, Intervention, and Main Outcome Measure: Synthetic rat ADM (8.5 µg/kg of body weight) was infused intravenously in normal rats for 15 minutes at a constant rate.Cardiacoutput,strokevolume,andmicrovascularblood flow in various organs were determined immediately as well as 30 minutes after ADM infusion. At 30 minutes after infusion, plasma ADM level was also measured. In additional groups, rats were subjected to sepsis by cecal ligation and puncture. At 1.5 hours after cecal ligation and puncture, specific anti-rat ADM antibodies were infused, which completely neutralized the circulating ADM. Various hemodynamic variables were measured 5 hours after cecal ligation and puncture (ie, the early stage of sepsis). Results: Cardiac output, stroke volume, and microvascular blood flow in the liver, small intestine, kidney, and spleen increased, and total peripheral resistance decreased 0 and 30 minutes after ADM infusion. In addition, plasma levels of ADM increased from the preinfusion level of 92.7 ± 5.3 to 691.1 ± 28.2 pg/mL 30 minutes after ADM infusion, which was similar to ADM levels observed during early sepsis. Moreover, 5 hours after the onset of sepsis, cardiac output, stroke volume, and microvascular blood flow in various organs increased and total peripheral resistance decreased. Administration of anti-ADM antibodies, however, prevented the occurrence of the hyperdynamic response. Conclusions: The results suggest that increased ADM production and/or release plays a major role in producing hyperdynamic responses during early sepsis. Since our previous studies have shown that vascular responsiveness to ADM decreases in late sepsis, maintenance of ADM vascular responsiveness by pharmacological agents during the course of sepsis may prevent transition from the hyperdynamic to the hypodynamic state.

Although mice are widely used for the study of immune consequences of hemorrhage, the changes of cardiac output (CO) and blood flow (BF) in response to trauma and hemorrhage in this species have not been well defined. To study this, nonheparinized C3H/HeN mice (n = 6 per group) underwent laparotomy (i.e., trauma induced), were bled to a mean arterial pressure of 35 mmHg, and maintained for 90 min by withdrawing more blood or returning Ringer lactate. The animals were then resuscitated with four times the volume of maximal bleedout in the form of Ringer lactate over 60 min. Sham-operated mice underwent the same procedure but were neither bled nor resuscitated. At the end of hemorrhage, 60 min postresuscitation, or corresponding time after sham operation, CO and BF were determined by radioactive microspheres. Results indicate that CO and BF decreased significantly at the end of hemorrhage. Resuscitation, however, restored CO and BF in various organs except the brain and skeletal muscle. Despite this, 9 of 16 mice died within 6 days postresuscitation, whereas none of sham mice died (n = 16 per group in this additional study). Therefore, we have developed a nonheparinized model of trauma-hemorrhage and resuscitation in mice that is associated with late mortality. Furthermore, the microsphere technique provides a reliable method for assessing CO and BF in mice. Thus it may be possible to study the correlation between cardiovascular and immunologic alterations under such conditions.