Cell volume signalling, osmolytes and liver function

Preventing cardiac arrest during hemorrhagic shock with vasopressin

The optimal strategy of stabilizing hemodynamic function in uncontrolled traumatic hemorrhagic shock states is unclear. Although fluid replacement is established in controlled hemorrhagic shock, its use in uncontrolled hemorrhagic shock is controversial, because it may worsen bleeding. In the refractory phase of severe hemorrhagic shock, arginine vasopressin has been shown to be beneficial in selected cases due to an increase in arterial blood pressure, shift of blood away from a subdiaphragmatic bleeding site toward the heart and brain, and decrease in fluid-resuscitation requirements. Especially in patients with severe traumatic brain injury, rapid stabilization of cardiocirculatory function is essential to ensure adequate brain perfusion, thus, to prevent neurologic damage and to improve outcome. In addition, despite wide distribution of highly developed and professional emergency medical systems in western industrialized countries, survival chances of patients with uncontrolled traumatic hemorrhagic shock in the preclinical setting are still poor.

Spontaneous apoptosis and proliferation in human pancreatic cancer

Several studies have documented the role of programmed cell death in the development and/or progression of cancer. The aims of this study were to analyze (a) the spontaneous apoptosis in human pancreatic duct carcinoma by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labeling (TUNEL); (b) its correlation with the proliferation rate of the tumor (determined by immunohistochemistry by using monoclonal antibody MIB-1); and (c) the association of apoptotic and mitotic index with the histologic features of the tumor and the outcome of patients. In pancreatic cancer, the apoptotic index (AI) was 4.9 +/- 4.8, and the mitotic index (MI) was 1.3 +/- 1.0 (mean +/- SD). AI was higher in small (<4 cm) than in large (>4 cm) size primary tumors (p = 0.02) and in undifferentiated as compared with differentiated cancers (p = 0.05). Significantly higher values of MI were detected in advanced as compared with early-stage carcinomas (p = 0.03) and when perineural invasion was present (p = 0.03). No correlation was found between AI and MI. Patients with AI > 2.3 survived significantly less than those with lower AI values (p = 0.03). Mitotic index >0.5 was associated with a worse survival (p = 0.006). These results suggest that in pancreatic cancer, spontaneous apoptosis is present and is more evident in small and undifferentiated tumors. Proliferation is increased in the advanced stage of cancer and seems to be independent of apoptosis. Higher levels of apoptosis and proliferation are negative prognostic indexes.

Regulation of bile salt export pump mRNA levels by dexamethasone and osmolarity in cultured rat hepatocytes

The major canalicular bile salt export pump (Bsep) of mammalian liver is downregulated by endotoxin. This study reports on the effects of dexamethasone and osmolarity on Bsep mRNA expression in cultured rat hepatocytes and its functional relevance in rat liver. Expression of Bsep mRNA in rat hepatocytes 24 and 48 h after isolation was dependent on the presence of dexamethasone (100 nM) in the culture medium. Bsep was functionally active at the pseudocanalicular membrane in cells cultured for 4 days in medium containing dexamethasone. Hypoosmolarity (205 mosmol/l) led to an induction of Bsep mRNA levels, whereas expression was decreased by hyperosmolarity (405 mosmol/l). Also the decay of Bsep mRNA following dexamethasone withdrawal was osmosensitive. In rat liver, dexamethasone counteracted the lipopolysaccharide (LPS)-induced down-regulation of Bsep mRNA levels after 12 hours and abolished the LPS-induced inhibition of taurocholate excretion. These results indicate that glucocorticoids are strong inducers of Bsep in liver. Furthermore, Bsep mRNA levels are osmosensitively regulated. The data suggest a longterm control of Bsep mRNA by osmolarity in addition to the short-term effects on canalicular bile acid excretion, which were reported recently.

Adaptive hepatic changes in mild stenosis of the common bile duct in the rat

Adaptive hepatic changes were investigated in rats with mild stenosis of the common bile duct and in sham-operated controls. The studies were performed 24 h and 7-12 days postoperatively. A continuous intravenous infusion of taurocholic acid at stepwise-increasing rates was performed to explore the responses to bile acid effects. During the infusion, bile flow and the outputs of bile acids, phospholipids, cholesterol, alkaline phosphatase and gamma glutamyl transpeptidase were studied. At the end of the infusion, hepatic morphometric measurements were performed. In other experimental sets, biliary excretions of horseradish peroxidase, a marker of microtubule-dependent vesicular transport in the hepatocyte, and sulphobromophthalein, a well-known organic anion model, were studied. In other rats, bile acid pool size and composition were determined by depletion of bile. The results in rats with mild stenosis maintained for 24 h showed a greater susceptibility to the toxicity of taurocholic acid, as revealed by the abrupt decrement in bile flow at high rates of infusion, and increased outputs of phospholipids and canalicular enzymes. Conversely, rats with mild stenosis maintained for 7-12 days showed decreased bile acid maximum secretory rate and biliary outputs of phospholipids and canalicular enzymes, as well as hepatocyte hypertrophy. These findings may explain the limited hepatic and systemic repercussion of experimental mild stenosis of the common bile duct and help us to understand the early stages of constriction of the common bile duct in man.

Release of osmolytes from perfused rat liver on perivascular nerve stimulation: alpha-adrenergic control of osmolyte efflux from parenchymal and nonparenchymal liver cells

The effects of perivascular nerve stimulation and phenylephrine on osmolyte release were studied in the intact perfused rat liver and isolated liver parenchymal cells (PC) and nonparenchymal cells. In the perfused liver, electrical stimulation of perivascular nerves (20 Hz/2 ms/20 V) led to a phentolamine-sensitive increase of cell hydration by 6.5% +/- 1.2% (n = 3) and a transient phentolamine-sensitive stimulation of taurine and inositol, but not betaine, release. These nerve effects were mimicked by phenylephrine, but not prostaglandin F2alpha, and were not affected by sodium nitroprusside (SNP) or ibuprofen. Nerve stimulation-induced taurine, but not inositol, release was inhibited by 4, 4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS) (50 micromol/L). Single-cell fluorescence studies with isolated liver PC, Kupffer cells (KC), sinusoidal endothelial cells (SEC), and hepatic stellate cells (HSC) revealed that phenylephrine induced an increase in cytosolic free Ca2+ only in PC and HSC, but not in KC and SEC, whereas extracellular uridine triphosphate (UTP) produced Ca2+ transients/oscillations in all liver cell types studied. Phenylephrine had no effect on osmolyte release from isolated KC and SEC, but increased taurine (but not inositol) release from PC and inositol (but not taurine) efflux from HSC. The data suggest that: 1) liver cell hydration and-consecutively-osmolyte content are modulated by hepatic nerves via an alpha-adrenergic mechanism, which does not involve eicosanoids or hemodynamic changes; 2) that PC and HSC are the primary targets for nerve-dependent alpha-adrenergic activation, whereas 3) KC and SEC probably do not express alpha-adrenoceptors coupled to Ca2+ mobilization or osmolyte efflux.