Sustained elevation of norepinephrine depresses hepatocellular function.

The sympathetic-adrenal system is rapidly activated in response to sepsis or hemorrhagic shock, resulting in an increase in circulating levels of catecholamines. Although it has been shown that the occurrence of hepatocellular dysfunction under such conditions is associated with an early and sustained increase in plasma norepinephrine (NE), it remains unknown whether the increased NE per se plays any role in producing hepatocellular dysfunction. To study this, exogenous NE was administered, by implantation of a peritoneal mini-osmotic pump (consistently releasing NE), to produce a plasma level of NE similar to that observed after sepsis or hemorrhage. At 24 h after the pump implantation, cardiac output was determined by dye dilution technique and hepatocellular function [i.e., the maximal velocity (V(max)) and the efficiency of the transport (K(m)) of in vivo indocyanine green clearance) was assessed without blood sampling. In addition, tissue perfusion in various organs was determined using laser Doppler flowmetry. Plasma levels of interleukin-6 were measured by bioassay and liver enzymes were assayed enzymatically. The results indicate that sustained (24 h) elevation of plasma levels of NE caused a decrease in cardiac output and microvascular blood flow in the liver, spleen, and small intestine. In addition, the increase in plasma NE produced significant depression in hepatocellular function as evidenced by reduced V(max) and K(m). This was associated with elevated plasma levels of liver enzymes, indicating hepatocyte injury. In addition, plasma levels of interleukin-6 increased significantly. These findings suggest that sustained elevated levels of NE, observed after sepsis or hemorrhagic shock, may play an important role in producing hepatocellular dysfunction and altered hepatocyte integrity.

Tumor necrosis factor-alpha administration increases Kupffer cell cyclic adenosine monophosphate levels.

Although studies have indicated that both Kupffer cell cyclic adenosine monophosphate (cAMP) and circulating TNF levels increase following trauma-hemorrhage and resuscitation, it remains unknown whether the elevated TNF levels are responsible for the increased Kupffer cell cAMP levels. To determine this, recombinant murine TNF-alpha (1.2 x 10(7) U/mg) was infused intravenously (.25 mg/kg body wt) over 30 min in normal rats. At 1 h after TNF-alpha or vehicle infusion, Kupffer cells and hepatocytes were isolated and cAMP levels were determined by radioimmunoassay. The levels of cAMP in the spleen and kidney were also measured. In addition, the maximal binding capacity and affinity of beta-adrenergic receptors were determined in Kupffer cells and hepatocytes by using [125I]iodopindolol. To determine whether there is any correlation between Kupffer cell cAMP and prostaglandin E2 (PGE2) or epinephrine, plasma levels of catecholamines and PGE2 were measured. The results indicated that TNF-alpha infusion significantly increased Kupffer cell cAMP levels while hepatocyte cAMP levels were not altered. Moreover, cAMP levels also increased in the macrophage/lymphocyte-rich spleen but were not altered in the kidney. Kupffer cell beta-receptor binding characteristics were not significantly affected by TNF-alpha infusion. In contrast, TNF-alpha administration markedly increased plasma levels of PGE2 and epinephrine. Thus, the elevated Kupffer cell cAMP levels induced by TNF-alpha are not due to upregulation of beta-adrenergic receptors, but may be associated with the elevated levels of circulating PGE2 and/or epinephrine.

Sustained elevation in circulating catecholamine levels during polymicrobial sepsis.

Although studies have indicated that the levels of catecholamines increase during sepsis, it remains unknown whether the elevated levels of epinephrine, norepinephrine, and dopamine observed in early sepsis are sustained during late, hypodynamic stages of sepsis. In this study, rats were subjected to sepsis by cecal ligation and puncture (CLP, i.e., polymicrobial sepsis). Immediately after CLP or sham operation, animals received 3 mL/100 g body weight normal saline subcutaneously. At .5, 2, 10 (i.e., early sepsis), or 20 h (late sepsis) after CLP, blood samples were drawn and the plasma was separated. Plasma levels of epinephrine, norepinephrine, and dopamine were determined using a [3H]-radioenzymatic assay. The results indicate that plasma levels of epinephrine, norepinephrine, and dopamine increased significantly as early as .5 h after CLP. The increase in catecholamine levels persisted throughout the study periods. Thus, circulating levels of catecholamines were elevated in both early and late stages of polymicrobial sepsis. These results suggest that the increased catecholamine levels at .5-10 h after CLP may contribute to the hypermetabolic conditions that occur during early, hyperdynamic sepsis. However, there is a lack of an association between the elevated plasma catecholamine levels and hypometabolic/hypodynamic state in late sepsis.

Pentoxifylline restores cardiac output and tissue perfusion after trauma-hemorrhage and decreases susceptibility to sepsis.

BACKGROUND: Although pentoxifylline produces various beneficial effects in a preheparinized model of hemorrhagic shock, it was unknown whether this agent restores the depressed cardiac output (CO) and tissue perfusion in a nonheparinized model of trauma-hemorrhage and resuscitation and, if so, whether it decreases the susceptibility to sepsis after hemorrhage. METHODS: After laparotomy (i.e., induction of trauma), rats were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of Ringer's lactate. The animals were then resuscitated with Ringer's lactate, four times the volume of shed blood. Pentoxifylline (50 mg/kg body weight) or normal saline solution was infused intravenously more than 95 minutes during and after resuscitation. At 1.5 and 4 hours after resuscitation, CO, tissue perfusion, and plasma liver enzyme levels were determined. Sepsis was induced by cecal ligation and puncture at 20 hours after hemorrhage, and the necrotic cecum was excised 10 hours thereafter. RESULTS: CO and tissue perfusion in the liver, kidney, spleen, and small intestine decreased significantly after hemorrhage and resuscitation. Pentoxifylline treatment, however, restored the depressed CO and tissue perfusion. The elevated liver enzyme levels were also significantly reduced by pentoxifylline treatment. Moreover, pentoxifylline prevented the increased mortality of posthemorrhaged rats subjected to sepsis. CONCLUSIONS: Because pentoxifylline restored the depressed CO and tissue perfusion and decreased the susceptibility to sepsis, this agent appears to be a useful adjunct to crystalloid resuscitation after trauma and hemorrhage, even in the absence of blood resuscitation.

Downregulation of hepatic beta-adrenergic receptors after trauma and hemorrhagic shock.

Although it is well known that sympathoadrenal activity increases under various adverse circulatory conditions, it is not known whether there are any alterations in hepatic plasma membrane beta-adrenergic receptors after trauma-hemorrhage and crystalloid 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 the maximal bleedout (MB) volume was returned in the form of Ringer lactate. The animals were then resuscitated with four times the volume of MB in the form of Ringer lactate over 60 min. Hepatic plasma membranes were isolated using discontinuous Percoll gradient centrifugation. The maximal binding capacity and dissociation constant (i.e., 1/affinity) of [125I]iodopindolol binding to beta-adrenergic receptors were determined using a membrane filtration assay and Scatchard analysis. The results indicate that there was a significant decrease in the maximal binding capacity at the time of MB, which persisted despite crystalloid resuscitation after hemorrhage. However, there were no significant changes in the dissociation constant at any time point during this study. The downregulation of beta-adrenergic receptor binding capacity may be responsible for metabolic abnormalities observed after hemorrhagic shock.

ATP-MgCl2 administration normalizes macrophage cAMP and beta-adrenergic receptors after hemorrhage and resuscitation.

Although ATP-MgCl2 attenuates the release of inflammatory cytokines and restores the defective macrophage (M phi) antigen presentation function after hemorrhage and resuscitation, it is not known whether administration of this agent after hemorrhage affects M phi adenosine 3',5'-cyclic monophosphate (cAMP) levels and beta-adrenergic receptors. To determine this, rats underwent a midline laparotomy (i.e., induction of trauma) and were then bled to and maintained at a mean arterial pressure of 40 mmHg until 40% of maximum bleedout volume was returned in the form of Ringer lactate (RL). Animals were resuscitated with four times the volume of shed blood with RL, during and after which ATP-MgCl2 (50 mumol/kg) or saline was administered over 95 min. At 1.5 h postresuscitation (i.e., 10 min after completion of ATP-MgCl2 infusion), peritoneal M phi and Kupffer cells were isolated, and cAMP levels were measured by radioimmunoassay. beta-Receptor binding characteristics were also determined in isolated Kupffer cells. The results indicate that cAMP levels increased significantly in both peritoneal M phi and Kupffer cells after hemorrhage and resuscitation. Maximum binding capacity (Bmax) of beta-receptors increased in Kupffer cells, suggesting that the elevated cAMP may be due to the increased beta-receptor Bmax under such conditions. ATP-MgCl2 treatment, however, markedly decreased beta-receptor Bmax in Kupffer cells and cAMP in both peritoneal M phi and Kupffer cells, and the values were similar to shams. Thus normalization of M phi cAMP levels and beta-receptor binding capacity by ATP-MgCl2 may contribute to the immunoenhancing effects of this agent observed after trauma-hemorrhage and fluid resuscitation.

Alterations in circulating blood volume during polymicrobial sepsis.

Although a great deal is known concerning the pathophysiology of sepsis, it is not clear whether circulating blood volume (CBV) is altered under such conditions. To study, this, rats were subjected to sepsis by cecal ligation and puncture (CLP). Immediately after CLP or sham operation, the animals received 3 ml/100 g body weight normal saline subcutaneously. CBV was determined by using in vivo indocyanine green (ICG) clearance at 2, 5, 10, or 20 hr after CLP or sham operation. This technique does not require any blood sampling. Serum glutamic pyruvic transaminase (SGPT) and glutamic oxaloacetic transaminase (SGOT) were assayed enzymatically as indicators of hepatocyte damage. Hepatic microcirculation was assessed at a selected time point (10 hr post-CLP) by using laser Doppler flowmetry and colloidal carbon infusion techniques. The results indicate that CBV, as determined by ICG clearance, remained unchanged up to 10 hr following the onset of sepsis (i.e., early sepsis) but decreased significantly at 20 hr after CLP (late sepsis). However, systemic hematocrit increased significantly at 5, 10, and 20 hr after CLP, indicating that plasma volume decreased at those time points. This suggests that there may be limitations in accurately assessing CBV at 5 and 10 hr after CLP, i.e., during the hyperdynamic circulatory state of sepsis, using the ICG clearance method. Moreover, SGPT and SGOT levels increased significantly at 10 hr, and the levels increased further at 20 hr post-CLP. In contrast, microvascular blood flow and carbon-perfused areas in the liver were significantly increased at 10 hr post-CLP.