Early effects of Escherichia coli endotoxin infusion on vasopressin-stimulated breakdown and metabolism of inositol lipids in rat hepatocytes

Daily electroconvulsive shock treatment alters the inositol lipid system response in the rat hippocampus

The inositol lipid system (polyphosphoinositides and inositol phosphates) represents an important component of the cell signal transduction. Electroconvulsive shock (ECS) is known to activate cell signaling and lead to the release of second messengers. We tested the effects of daily ECS on the inositol lipid system and the generation of second messengers in vivo, by prelabeling the components of the system with [3H]myo inositol. The response to ECS was greater 30 sec after the sixth ECS, as compared to that obtained 30 sec after the first one. Also, rats killed 24h after the fifth ECS exhibited an increased PI labeling, as compared to rats handled for 6 days without receiving ECS. These results show that daily seizures (ECS-evoked) deeply modify the neuronal response to the stimulus, thus providing new information on the biochemical events involved in cell signal transduction during seizures.

LPS inhibits PI-phospholipase C but not PC-phospholipase D or phosphorylase activation by vasopressin and norepinephrine

Rats were infused with endotoxin (50 micrograms/100 g body wt) for 3 h, and the parenchymal cells of the liver were maintained in primary culture for 1-3 h. The effects of vasopressin, norepinephrine, and glucagon on the activation of phosphatidylinositol (PI)-phospholipase C, phosphatidylcholine (PC)-phospholipase D, and glycogen phosphorylase a were investigated. Activation of PI-phospholipase C was markedly reduced, particularly with norepinephrine. This confirms that one of the early metabolic impairments seen in acute endotoxin treatment is inhibition of PI-phospholipase C activity. However, the ability of vasopressin, norepinephrine, and glucagon to stimulate glycogen phosphorylase a and PC-phospholipase D was not affected by this endotoxin treatment. We conclude that activation of phosphorylase a by vasopressin and norepinephrine is not entirely dependent on the activation of PI-phospholipase C and inositol trisphosphate formation.

Light stimulates in vivo inositol lipid turnover in frog retinal pigment epithelial cells at the onset of shedding and phagocytosis of photoreceptor membranes

We have developed an experimental model to study in vivo inositol lipid metabolism in frog retinal pigment epithelial (RPE) cells, including the effect of light on phospholipase C-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate. RPE cells were rapidly isolated after either brief light or dark periods. Light and electron microscopy showed complete detachment of the retina from the RPE cells, and that the RPE cell suspensions were devoid of photoreceptor cell outer segments. Frog tissues were labeled in vivo for 20 hr by intravitreal injection of [3H]inositol (4 microCi, 4 microliters per eye) within a 24-hr constant illumination period. Following 1 hr of darkness (priming period), frogs were intravitreally injected with LiCl (0.5 M, 4 microliters per eye) 15 min before the onset of either 30-min light stimulation or an additional 30 min of darkness (controls). In order to preserve endogenous inositol phosphate pools present after dark and light exposure, the RPE cells were harvested in the shortest time possible, at low temperatures (18-20 degrees C), and in the presence of 10 mM LiCl. Total [3H]inositol-labeled water-soluble products (inositol plus inositol phosphates) were increased by 86% after 30 min of light. Inositol trisphosphate (IP3) showed the highest accumulation (a 5.5-fold increase), followed by inositol bisphosphate (1.9-fold increase) and inositol monophosphate (1.4-fold increase). Free [3H]inositol also accumulated (2.8-fold increase), reflecting only a partial inhibition of phosphomonoesterase by LiCl. These changes were paralleled by a 12% decrease in 3H-labeled phosphatidylinositol with no significant difference in the labeling of polyphosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of endotoxemia on concanavalin A induced alterations in cytoplasmic free calcium in rat spleen cells as determined with Fluo-3

The effects of acute (3 h) and chronic (30 h) in vivo infusions of Escherichia coli endotoxin on the Ca2+ homeostasis of rat spleen cells was investigated. Conditions were established for obtaining reliable estimates of [Ca2+]i in these cells using the newly-developed Ca2+ indicator Fluo-3. The resting [Ca2+]i of splenocytes and T lymphocyte-enriched preparations were 119 +/- 35 and 102 +/- 31 nM, respectively. Treatment of the cells with concanavalin A (Con A) resulted in a rapid increase in [Ca2+]i. The magnitude of the increase was positively correlated with the concentration of Con A, whereas the time required to reach the maximum [Ca2+]i was inversely related to the amount of Con A. The peak [Ca2+]i was attained more rapidly in splenocytes (i.e. less than or equal to 30 s) than in the T cell-enriched fraction (i.e. 1.5-2.0 min). Both the resting [Ca2+]i and the Con A-induced increase in [Ca2+]i were similar to values previously reported for other lymphocyte cell types using different Ca2+ indicators, thereby supporting the values obtained with Fluo-3. Infusions of saline or endotoxin prior to the isolation of the cells did not result in significant alterations of either resting [Ca2+]i or the cells' response to Con A. Since chronic infusions of endotoxin have previously been shown to cause a reduction in blastogenic responsiveness of splenocytes to Con A, these data suggest that the endotoxin-induced lesion occurs distal to the mobilization of intracellular Ca2+.

Continuous infusion of Escherichia coli endotoxin in vivo primes in vitro superoxide anion release in rat polymorphonuclear leukocytes and Kupffer cells in a time-dependent manner

Continuous infusion of a nonlethal dose of Escherichia coli lipopolysaccharide (LPS) (0.5 mg/kg) induced early (3 h) accumulation of polymorphonuclear leukocytes (PMNL) in rat liver followed by later (30 h) greater extravasation of mononuclear phagocytes (MNP) (E. B. Rodriguez de Turco and J. A. Spitzer, J. Leukocyte Biol. 48:488-494, 1990). Nonparenchymal liver cells from rats treated for 3 and 30 h with LPS were recovered by centrifugal elutriation, yielding a 23-ml/min fraction (endothelial cells) and a 45-ml/min fraction (PMNL, Kupffer cells, and MNP), and compared for their capacity for basal and agonist-stimulated superoxide (O2-) production. Stimulation with phorbol myristate acetate and opsonized zymosan caused a dose-dependent release of O2- from the 45-ml/min fraction derived from rats treated for 3 h with saline, but not from the 23-ml/min fraction. Further purification of the 45-ml/min fraction by discontinuous density gradient centrifugation into a Kupffer and a PMNL fraction revealed that most of the agonist-induced O2- release was generated by infiltrating PMNL at this early time point of LPS infusion. By 30 h of LPS infusion, although enhancement of the phorbol-12-myristate-13-acetate- and opsonized zymosan-stimulated release of O2- was observed in the 45-ml/min fraction, but not in the 23-ml/min fraction, the maximum release of O2- was smaller than that observed in the rats treated for 3 h. Our results support the following conclusions: (i) after a 3-h LPS infusion, PMNL found in the liver in increased numbers are also highly primed for agonist-stimulated release of O2-, while Kupffer cell priming is of a lesser extent; (ii) after a 30-h infusion of LPS, infiltrating MNP found in the liver in increased numbers are primed for agonist-induced O2- release, while priming of PMNL has diminished; (iii) at both 3 and 30 h of LPS infusion, liver endothelial cells are not significantly primed for agonist-stimulated O2- release; and (iv) in vivo priming by LPS infusion at both 3 and 30 h was not reversed by the experimental method used for cell recovery (ca. 3 h), thus suggesting that in vivo LPS priming of O2- release may ultimately lead to severe impairment of liver function and metabolism observed during endotoxemia and sepsis if not therapeutically blocked at an early time point.

Hepatic phosphatidylinositol kinase activity in continuously endotoxemic rats

The activity of phosphatidylinositol (PI) kinase and the content and fatty acid composition of inositol phospholipids (IPLs) were analyzed in the livers of rats that had been continuously infused with Escherichia coli endotoxin (ET) or saline for 30 h. Maximal enzymatic activity in total liver membrane fractions was observed in the presence of 1 mM ATP, 20 mM MgCl2, exogenously added 0.3 mM PI and Triton X-100 (0.25%). The activity of PI kinase for endogenous and exogenous PI was 43 and 79% higher respectively, in ET- as compared with saline-infused rats. The Km of the enzyme for ATP was not altered (0.175 mM), while the apparent Vmax was higher for ET- as compared with saline-infused rats (0.48 and 0.38 nmol of phosphatidylinositol 4-phosphate formed/mg protein per min, respectively). The ET-induced higher activity of PI kinase was paralleled by a 68-78% increase in the content of polyphosphoinositides (PPI), while PI content was unchanged. All IPLs from livers of endotoxemic rats had a lower content of arachidonic acid. We demonstrate for the first time that ET can directly and/or indirectly stimulate the net synthesis of PPI in liver cells. This effect could serve to modulate the PPI derived signals by increasing the availability of the substrate phosphatidylinositol 4,5-bisphosphate.

Interrelationship between hepatic ureagenesis and gluconeogenesis in early sepsis

This study was performed to investigate the interrelationship between gluconeogenesis and ureagenesis during sepsis. In isolated perfused livers, gluconeogenesis was assessed using either lactate or a combination of lactate, glutamine, and alanine as substrate. Ureagenesis was assessed using either NH4Cl or glutamine plus alanine as substrate. NH4Cl stimulated urea production in livers from both septic and sham-operated control rats. Urea release was approximately 1.2 and 2.0 mg urea nitrogen.g-1.h-1 for 1 and 5 mM NH4Cl, respectively, and was equal for both groups. With amino acids as substrate, urea production was significantly greater in livers from septic animals compared with controls. Phenylephrine stimulated urea production in the sham-operated group by about twofold, whereas in the septic group urea release was slightly inhibited. Gluconeogenesis from lactate was inhibited by NH4Cl (1 and 5 mM) in both groups, with no difference between groups. In contrast to enhanced ureagenesis from amino acids in septic rats, gluconeogenesis was decreased by approximately 24% (P less than 0.5). Similarly, phenylephrine (1 microM) stimulated gluconeogenesis by 13 +/- 1 mumol.g-1.h-1 in sham-operated rats but only by 9 +/- 1 mumol.g-1.h-1 in septic rats (P less than 0.02). These results suggest that hepatic gluconeogenic and ureagenic pathways are intact in sepsis but that altered substrate preference and hormone sensitivity may result in decreased gluconeogenesis in the presence of elevated amino acid levels.

Participation of calcium ion on depletion mechanism of liver glycogen by purified glucocorticoid antagonizing factor released in blood during endotoxemia

The present study was conducted by the use of purified glucocorticoid antagonizing factor (GAF) released in blood of endotoxemic mice to determine whether or not the factor (GAF and Ca2+) may play a possible role of mediator in depletion mechanism of liver glycogen in endotoxemia. The liver glycogen level in 2 hr after injection with GAF plus cortisone-treated mice was markedly lower than that in cortisone alone-treated mice. However, the administration of trifluoperazine or verapamil markedly increased glycogen levels in liver of GAF plus cortisone-injected mice. On the other hand, when the mice fed a calcium-free diet were injected with GAF plus cortisone, there was merely a significant difference in liver glycogen level as compared to cortisone alone-treated mice. The level of Ca2+ in liver cytosol fraction in cortisone-treated mice was higher 2 hr after GAF injection than that in the cortisone alone-treated one. The phosphorylase a activity in liver 2 hr after injection of GAF plus cortisone did not show a significant difference as compared to that in mice treated with cortisone alone. However, the activity ratio of glycogen synthase enzyme (synthase I synthase I + D) was decreased in GAF plus cortisone-treated mice as compared to that in cortisone alone-treated mice. These findings suggest that there are participations of Ca2+ and mediator GAF released from reticuloendothelial system (RES macrophages in glucoregulation of endotoxemia. Thus, it may be speculated that intracellular Ca2+ may mediate glycogenesis rather than glycogenolysis in the depletion mechanism of liver glycogen during GAF-poisoning.

Inositol lipid metabolism in vasopressin stimulated hepatocytes from rats infused with tumor necrosis factor

We studied the effect of i.v. infusion of human recombinant tumor necrosis factor alpha (rHuTNF alpha, Cetus, 15 micrograms/100 g bw over 3 h) on vasopressin (VP)-stimulated 32P-inositol lipid turnover and the release of 3H-inositol phosphates in isolated rat hepatocytes. The early VP-induced decrease (within 30 s) in 32P-phosphatidylinositol 4-phosphate and 32P-phosphatidylinositol 4,5-bisphosphate labeling was significantly reduced (-40%) and at the same time the uptake of 32P into phosphatidic acid was 50% lower than in saline-infused (matched control) rats. Within 5 min of VP-stimulation, lower 32P phosphatidylinositol (-40%) and higher 32P-phosphatidic acid (+30%) labeling were observed in rHuTNF alpha-infused rats. Infusion of rHuTNF alpha also affected the VP-induced release of 3H-inositol phosphates. The accumulation of 3H-inositol-labeled water soluble products was decreased by 25% and 17% at 30 s and 10 min, respectively. These data show that rHuTNF alpha mimics early perturbations induced by Escherichia coli endotoxin infusion in VP-stimulated inositol lipid metabolism in rat hepatocytes.