Stimulation of glycogenolysis and vasoconstriction in the perfused rat liver by the thromboxane A2 analogue U-46619

Normotensive placental extracellular vesicles provide long-term protection against hypertension and cardiovascular disease

BACKGROUND

Women with normotensive pregnancy are at a reduced risk of developing cardiovascular disease postpartum compared with those who experience hypertensive conditions during pregnancy. However, the underlying mechanisms remain poorly understood. During normotensive pregnancy, vast numbers of placental extracellular vesicles are released into the maternal circulation, which protect endothelial cells from activation and alter maternal vascular tone. We hypothesized that placental extracellular vesicles play a mechanistic role in lowering the risk of cardiovascular disease following normotensive pregnancy.

OBJECTIVE

This study aimed to investigate the long-term effects of placental extracellular vesicles derived from normotensive term placentae on the cardiovascular system and explore the mechanisms underlying their biological effects.

STUDY DESIGN

Spontaneously hypertensive rats were injected with placental extracellular vesicles from normotensive term pregnancies (2 mg/kg each time, n=8) or vehicle control (n=9) at 3 months of age. Blood pressure and cardiac function were regularly monitored from 3 months to 15 months of age. The response of mesenteric resistance arteries to vasoactive substances was investigated to evaluate vascular function. Cardiac remodeling, small artery remodeling, and renal function were investigated to comprehensively assess the impact of placental extracellular vesicles on cardiovascular and renal health.

RESULTS

Compared with vehicle-treated control animals, rats treated with normotensive placental extracellular vesicles exhibited a significantly lower increase in blood pressure and improved cardiac function. Furthermore, the vasodilator response to the endothelium-dependent agonist acetylcholine was significantly enhanced in the normotensive placental extracellular vesicle-treated spontaneously hypertensive rats compared with the control. Moreover, treatment with placental extracellular vesicles reduced wall thickening of small renal vessels and attenuated renal fibrosis.

CONCLUSION

Placental extracellular vesicles from normotensive term pregnancies have long-lasting protective effects reducing hypertension and mitigating cardiovascular damage in vivo.

Nonalcoholic Fatty Liver Disease and Endocrine Axes-A Scoping Review

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease. NAFLD often occurs associated with endocrinopathies. Evidence suggests that endocrine dysfunction may play an important role in NAFLD development, progression, and severity. Our work aimed to explore and summarize the crosstalk between the liver and different endocrine organs, their hormones, and dysfunctions. For instance, our results show that hyperprolactinemia, hypercortisolemia, and polycystic ovary syndrome seem to worsen NAFLD's pathway. Hypothyroidism and low growth hormone levels also may contribute to NAFLD's progression, and a bidirectional association between hypercortisolism and hypogonadism and the NAFLD pathway looks likely, given the current evidence. Therefore, we concluded that it appears likely that there is a link between several endocrine disorders and NAFLD other than the typically known type 2 diabetes mellitus and metabolic syndrome (MS). Nevertheless, there is controversial and insufficient evidence in this area of knowledge.

Peptides in the regulation of glucagon secretion

Glucose homeostasis is maintained by the glucoregulatory hormones, glucagon, insulin and somatostatin, secreted from the islets of Langerhans. Glucagon is the body's most important anti-hypoglycemic hormone, mobilizing glucose from glycogen stores in the liver in response to fasting, thus maintaining plasma glucose levels within healthy limits. Glucagon secretion is regulated by both circulating nutrients, hormones and neuronal inputs. Hormones that may regulate glucagon secretion include locally produced insulin and somatostatin, but also urocortin-3, amylin and pancreatic polypeptide, and from outside the pancreas glucagon-like peptide-1 and 2, peptide tyrosine tyrosine and oxyntomodulin, glucose-dependent insulinotropic polypeptide, neurotensin and ghrelin, as well as the hypothalamic hormones arginine-vasopressin and oxytocin, and calcitonin from the thyroid. Each of these hormones have distinct effects, ranging from regulating blood glucose, to regulating appetite, stomach emptying rate and intestinal motility, which makes them interesting targets for treating metabolic diseases. Awareness regarding the potential effects of the hormones on glucagon secretion is important since secretory abnormalities could manifest as hyperglycemia or even lethal hypoglycemia. Here, we review the effects of each individual hormone on glucagon secretion, their interplay, and how treatments aimed at modulating the plasma levels of these hormones may also influence glucagon secretion and glycemic control.

Pre-and postnatal exposition to fluorides induce changes in rats liver morphology by impairment of antioxidant defense mechanisms and COX induction

INTRODUCTION

Fluorides are common in the environment and are absorbed mostly in the stomach and gut, it can easily move through cell membranes and its accumulation can cause harmful effects in skeletal and soft tissues. One of the most important F- accumulation sites is the liver. The aim of this study was to determine whether F- can cause inflammation in rat liver by affecting the activity of antioxidant enzymes and changes in the synthesis of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2).

MATERIALS AND METHODS

An in vivo model of prenatal and postnatal exposure to sodium fluoride (NaF) was used to carry out the experiment. Animals from control group received tap water to drink, while animals exposed to F- received drinking water containing NaF, 50 mg/L. In serum and liver we analyzed F- concentration, in liver - antioxidant enzymes activity, PGE2 and TXB2 concentration and immunolocalization of COX1 and COX2 proteins were measured.

RESULTS

We observed significant changes in F- concentration only in liver. The results of this study showed that F- affects antioxidant enzymes activity, COX2 protein expression and PGE2 synthesis in liver. Also, in some regions of the liver of rats exposed to F-, the hepatocytes were diffusely altered, with changes resembling microvesicular steatosis.

CONCLUSION

Chronic exposure to F^- during development causes an accumulation of this element in the liver and changes in antioxidant enzymes activity and cyclooxygenase expression. Long term exposure to this element is toxic to the liver and can cause disturbances in its homeostasis.

Vasopressin and metabolic disorders: translation from experimental models to clinical use

Vasopressin has many physiological actions in addition to its well-defined role in the control of fluid homeostasis and urine concentration. An increasing body of evidence suggests that the vasopressin-hydration axis plays a role in glucose homeostasis. This review summarizes the knowledge accumulated over the last decades about the influence of vasopressin in the short-term regulation of glycaemia. It describes the possible role of this hormone through activation of V1a and V1b receptors on liver and pancreas functions and on the hypothalamic-pituitary-adrenal axis. Moreover, we report recent in vivo studies demonstrating the role of vasopressin in the long-term regulation of glycaemia. Indeed, V1a- or double-V1aV1b-receptor knockout mice display significant changes in the glucose and lipid metabolism. In rats, sustained high V1aR activation increases basal glycaemia and aggravates glucose intolerance in obese rats. Finally, the translation from animal findings to human was evidenced by epidemiological and genetic studies that showed that high vasopressin level is a risk factor for hyperglycaemia, metabolic disorders and diabetes.

UP-REGULATED THROMBOXANE PRODUCTION IN THE RAT LIVER WITH BILIARY OBSTRUCTION DOES NOT CONTRIBUTE TO PROMOTE HEPATIC INJURY

This study sought to determine whether in vivo inhibition of thromboxane A2 (TXA2) action contribute to attenuate hepatic damage after bile duct ligation (BDL). Male Wistar rats were assigned to sham operation or BDL. At the time of operation, infusion pump with saline, ozagrel natrium (TXA2 synthase inhibitor), or SQ29548 (TXA2 receptor antagonists) was implanted in the abdominal cavity. Plasma alanine aminotransferase, aspartate aminotransferase, hyaluronic acid, and total bilirubin levels were measured at 4 days after the operation. The levels of plasma TXB2, a stable metabolite of TXA2, were significantly increased after BDL. Gene expression of TXA2 synthase was also significantly upregulated in the liver. Nonetheless, either an inhibition of TXA2 synthesis by ozagrel natrium or a blockade of TXA2 receptor by SQ29548 has no effect in every measured parameter related to hepatic function. These results indicated that despite a highly increased production in the liver, TXA2 is not directly related to the hepatic injury in BDL rats.

Effects of l-NAME on thromboxane A2-induced venoconstriction in isolated perfused livers from rat, guinea pig and mouse

Effects of L-NAME on U-46619 (a thromboxane A(2), analogue) -induced hepatic segmental venoconstriction were examined in mouse, rat and guinea pig isolated perfused livers. All livers were perfused portally and recirculatingly at a constant flow with diluted blood. U-46619 was administrated into the reservoir in a cumulative manner to gain the concentrations of 0.001-3 microM at 10 min after L-NAME or D-NAME (100 microM). The portal venous pressure, hepatic venous pressure and perfusate flow were monitored. In addition, the sinusoidal pressure was measured by the double occlusion pressure, and was used to determine the pre- (Rpre) and post-sinusoidal (Rpost) resistances. U-46619 concentration-dependently caused predominant presinusoidal constriction in all three species. The rat livers were the strongest while the mouse livers were the weakest in responsiveness and sensitivity to U-46619. L-NAME mainly augmented the U-46619-induced increases in Rpre, but not in Rpost, in rat and guinea pig. This augmentation was stronger in rat. However, L-NAME did not augment the response to U-46619 in mouse. In conclusion, in rat and guinea pig, NO may be released selectively from the presinusoids in response to U-46619, and then attenuate the U-46619-induced presinusoidal constriction. In mouse, U-46619-induced venoconstriction is weak and not modulated by NO.

LPS exacerbates endothelin-1 induced activation of cytosolic phospholipase A2 and thromboxane A2 production from Kupffer cells of the prefibrotic rat liver

BACKGROUND/AIMS

Thromboxane A2 (TXA2) has been suggested to play a significant role in the development of portal hypertension in fibrosis, and Kupffer cell (KC) derived TXA2 has been shown to mediate the hyperresponsiveness of the portal circulation to the vasoconstrictive actions of endothelin-1 (ET-1) during endotoxemia. The aim of this study was to determine whether the double stresses of prefibrotic changes and endotoxemia additively activate KC to increase release of TXA2 in response to ET-1, resulting in elevated portal resistance.

METHODS

One week Bile duct ligation (BDL) rats and sham-operated controls were subjected to isolated liver perfusions following LPS or saline for 6h. In a separate experiment, KC were isolated from BDL or sham rats and incubated with LPS or saline for 6h before the ET-1 treatment.

RESULTS

The double stresses of early fibrosis and LPS resulted in a greater sustained increase in portal pressure in response to ET-1 in BDL rats, and this increase correlated well with the much enhanced release of TXA2 in the perfusate. Media from the cultured KC showed significantly greater TXA2 release in response to ET-1 in BDL group than those in sham group, and LPS exacerbated this effect. Protein levels of cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2, and thromboxane synthase were also significantly elevated in KC from BDL rats. ET-1 produced a marked increase in cPLA2 activation as measured by the phosphorylation of cPLA2 in KC of both BDL and sham groups. LPS greatly exacerbated the activation of cPLA2.

CONCLUSIONS

The data suggest that the double stresses additively activate KC with an upregulation of the key enzymes in the TXA2 biosynthesis and release increased amount of TXA2 via the augmented activation of cPLA2 in response to ET-1, which leads to the increased portal resistance and ultimately hepatic microcirculatory dysfunction.

Effects of platelet-activating factor, thromboxane A2 and leukotriene D4 on isolated perfused rat liver

Vasoconstrictive lipid mediators, thromboxane A(2) (TxA(2)), platelet-activating factor (PAF) and leukotriene D(4) (LTD(4)) have been implicated as mediators of liver diseases. There are species differences in the primary site of hepatic vasoconstriction in response to these mediators. We determined the effects of a TxA(2) analogue (U-46619), PAF and LTD(4) on the vascular resistance distribution, weight and oxygen consumption of isolated rat livers portally perfused with blood. The sinusoidal pressure was measured by the double occlusion pressure (P(do)), and was used to determine the pre- (R(pre)) and post-sinusoidal (R(post)) resistances. All these three mediators increased the hepatic total vascular resistance (R(t)). The responsiveness to PAF was 100 times greater than that to U-46619 or LTD(4). Both of PAF and U-46619 predominantly increased R(pre) over R(post). At the comparable increased R(t) levels, U-46619 more preferentially increased R(pre) than PAF. In contrast, LTD(4) increased both the R(pre) and R(post) to similar extent. U-46619 caused liver weight loss, while high concentrations of either LTD(4) or PAF produced liver weight gain, which was caused by substantial post-sinusoidal constriction and increased P(do). PAF and U-46619 decreased hepatic oxygen consumption while LTD(4) induced biphasic change of an initial transient decrease followed by an increase. In conclusion, PAF is the most potent vasoconstrictor of rat hepatic vessels among these three mediators. Both TxA(2) and PAF constrict the pre-sinusoidal veins predominantly. TxA(2) more preferentially constricts the pre-sinusoids than PAF, resulting in liver weight loss. However LTD(4) constricts both the pre- and post-sinusoidal veins similarly. High concentrations of LTD(4) and PAF cause liver weight gain by substantial post-sinusoidal constriction. PAF and TxA(2) decrease hepatic oxygen consumption, whereas LTD(4) causes a biphasic change of it.

Current Understanding of Gender Dimorphism in Hepatic Pathophysiology1

Studies have shown gender dimorphic response of the liver for various hepatic stresses including ischemia/reperfusion, hemorrhagic shock-resuscitation, hepatectomy, liver cirrhosis, endotoxemia, and chronic alcoholic consumption. The mechanisms responsible for the gender dimorphic response include differences in pro-inflammatory cytokine release, production of reactive oxygen species, and alteration in hepatic vasoregulatory action. These effects were shown to be modulated by circulating sex steroid levels. In this regard, modulation of sex steroid levels by agents/drugs has been proposed as a therapeutic option for preventing hepatic damage in various hepatic stress models. Further elucidation of precise mechanisms responsible for the gender-related differences in the hepatic pathophysiology is essential for the potential clinical application of sex hormone modulation therapy. In this article, current progress in our understanding the gender difference in the hepatic pathophysiology under the condition of hepatic stress is reviewed and discussed.

Effects of platelet-activating factor and thromboxane A2 on isolated perfused guinea pig liver

Lipid mediators, thromboxane A2 (TxA2) and platelet-activating factor (PAF), are potent vasoconstrictors, and have been implicated as mediators of liver diseases, such as ischemic-reperfusion injury. We determined the effects of a TxA2 analogue (U-46619) and PAF on the vascular resistance distribution and liver weight (wt) in isolated guinea pig livers perfused with blood via the portal vein. The sinusoidal pressure was measured by the double occlusion pressure (P(do)), and was used to determine the pre- (R(pre)) and post-sinusoidal (R(post)) resistances. U-46619 and PAF concentration-dependently increased the hepatic total vascular resistance (R(t)). The minimum concentration at which significant vasoconstriction occurs was 0.001 microM for PAF and 0.1 microM for U-46619. Moreover, the concentration of U-46619 required to increase R(t) to the same magnitude is 100 times higher than PAF. Thus, the responsiveness to PAF was greater than that to U-46619. Both agents increased predominantly R(pre) over R(post). U-46619 caused a sustained liver weight loss. In contrast, PAF also caused liver weight loss at lower concentrations, but it produced liver weight gain at higher concentrations (2.5 +/- 0.3 per 10g liver weight at 1 microM PAF), which was caused by substantial post-sinusoidal constriction and increased P(do). In conclusion, both TxA2 and PAF contract predominantly the pre-sinusoidal veins. TxA2 causes liver weight loss, while PAF at high concentrations increases liver weight due to substantial post-sinusoidal constriction in isolated guinea pig livers.

Thromboxane A2 from Kupffer cells contributes to the hyperresponsiveness of hepatic portal circulation to endothelin-1 in endotoxemic rats

We examined the role of thromboxane A2 (TXA2) in LPS-induced hyperresponsiveness of hepatic portal circulation to endothelins (ETs) and whether Kupffer cells are the primary source of TXA2 release in response to ET-1 in endotoxemia. After 6 h of LPS (1 mg/kg body wt ip) or saline (control), liver was isolated and perfused with recirculating Krebs-Henseleit bicarbonate buffer at a constant flow rate (100 ml.min(-1).kg body wt(-1)). ET-1 (10 pmol/min) was infused for 10 min. Portal pressure (PP) was continuously monitored during perfusion. Perfusate was sampled for enzyme immunoassay of thromboxane B2 (TXB2; the stable metabolite of TXA2) and lactate dehydrogenase (LDH) assay. ET-1 infusion resulted in a significantly greater increase of PP in the LPS group than in controls. Both TXA2 synthase inhibitor furegrelate (Fureg) and TXA2 receptor antagonist SQ-29548 (SQ) substantially blocked enhanced increase of PP in the LPS group (4.9 +/- 0.4 vs. 3.6 +/- 0.5 vs. 2.6 +/- 0.6 mmHg for LPS alone, LPS + Fureg, and LPS + SQ, respectively; P < 0.05) while having no significant effect on controls. GdCl3 for inhibition of Kupffer cells had similar effects (4.9 +/- 0.4 mmHg vs. 2.9 +/- 0.4 mmHg for LPS alone and GdCl3 + LPS, respectively; P < 0.05). In addition, the attenuated PP after ET-1 was found concomitantly with significantly decreased releases of TXB2 and LDH in LPS rats treated with Fureg, SQ, and GdCl3 (886.6 +/- 73.4 vs. 110.8 +/- 0.8 vs. 114.8 +/- 54.7 vs. 135.2 +/- 45.2 pg/ml, respectively; P < 0.05). After 6 h of LPS, Kupffer cells in isolated cell preparations released a significant amount of TXA2 in response to ET-1. These results clearly indicate that hyperresponsiveness of hepatic portal circulation to ET-1 in endotoxemia is mediated at least in part by TXA2-induced receptor activation, and Kupffer cells are likely the primary source of increased TXA2 release.

Role of thromboxane in producing portal hypertension following trauma-hemorrhage

Thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been proposed as the important vasoconstrictors that increase portal venous resistance in paracrine or autocrine fashion. We hypothesized that the hepatic damage following trauma-hemorrhage (T-H) is induced by the impaired hepatic circulation due to the increased production of vasoconstrictors such as ET-1 and TXA2 by the liver. To test this, male Sprague-Dawley rats (n = 6/group) were subjected to trauma (i.e., midline laparotomy) and hemorrhage (35-40 mmHg for 90 min followed by fluid resuscitation) or sham operation. At 2 or 5 h after the end of resuscitation, the liver was isolated and perfused and portal inflow pressure, bile flow, and release of ET-1 and thromboxane B2 (TXB2; a stable metabolite of TXA2) into the perfusate were measured. The level of portal pressure was higher at 5 h following T-H compared with 2 h after T-H and sham. The portal pressure was inversely correlated to the amount of bile production. Furthermore, the bile flow was significantly correlated to the hepatic damage as evidenced by release of lactate dehydrogenase into the perfusate. The level of ET-1 at 5 h following T-H in the perfusate after 30 min of recirculation did not show any difference from sham. However, the levels of TXB2 in the T-H group were significantly higher than those in sham at that interval. These results indicate that the increased release of TXA2 but not ET-1 following T-H might be responsible for producing the increased portal resistance, decreased bile production, and hepatic damage.

Inhibition of prostaglandin D2 clearance in rat hepatocytes by the thromboxane receptor antagonists daltroban and ifetroban and the thromboxane synthase inhibitor furegrelate

Prostanoids, i.e. prostaglandins and thromboxane, regulate liver-specific functions both in homeostasis and during defense reactions. For example, prostanoids are released from Kupffer cells, the resident liver macrophages, in response to the inflammatory mediator anaphylatoxin C5a, and mediate an enhanced glucose output from hepatocytes as energy supply. In perfused rat livers, the thromboxane receptor antagonist daltroban enhanced C5a-induced prostanoid overflow and reduced glucose output. It was the aim of this study to elucidate whether daltroban interfered with prostanoid release from Kupffer cells or prostanoid clearance by hepatocytes, and/or whether it directly influenced prostanoid-dependent glucose metabolism in these cells. In perfused rat livers, daltroban enhanced prostaglandin (PG)D(2) overflow not only after infusion of C5a (15-fold), but also after PGD(2) (10-fold). Neither daltroban nor another receptor antagonist, ifetroban, or the thromboxane synthase inhibitor furegrelate enhanced prostanoid release from Kupffer cells. In contrast, all inhibitors reduced clearance, i.e. uptake and degradation, of PGD(2) by hepatocytes: within 5 min uptake of 1 nmol/L PGD(2) was reduced from 43+/-5 fmol (controls) to 22+/-6 fmol (daltroban), 24+/-6 fmol (ifetroban) and 21+/-6 fmol (furegrelate). PGD(2) in the medium was reduced to 39+/-7% in the controls, but remained at 93+/-9%, 93+/-11% and 60+/-3% in the presence of the inhibitors. PGD(2)-dependent glucose output in the perfused liver or activation of glycogen phosphorylase in isolated hepatocytes remained unaffected by daltroban. These data clearly demonstrate that the thromboxane-inhibitors reduced PGD(2) clearance by hepatocytes, presumably by inhibition of prostanoid transport into the cells. In contrast, they did not interfere with PGD(2)-dependent glucose metabolism, suggesting an independent mechanism for the inhibition of glucose output from the liver.

Role of thromboxane A2 in early BDL-induced portal hypertension

Although the mechanisms of cirrhosis-induced portal hypertension have been studied extensively, the role of thromboxane A(2) (TXA(2)) in the development of portal hypertension has never been explicitly explored. In the present study, we sought to determine the role of TXA(2) in bile duct ligation (BDL)-induced portal hypertension in Sprague-Dawley rats. After 1 wk of BDL or sham operation, the liver was isolated and perfused with Krebs-Henseleit bicarbonate buffer at a constant flow rate. After 30 min of nonrecirculating perfusion, the buffer was recirculated in a total volume of 100 ml. The perfusate was sampled for the enzyme immunoassay of thromboxane B(2) (TXB(2)), the stable metabolite of TXA(2). Although recirculation of the buffer caused no significant change in sham-operated rats, it resulted in a marked increase in portal pressure in BDL rats. The increase in portal pressure was found concomitantly with a significant increase of TXB(2) in the perfusate (sham vs. BDL after 30 min of recirculating perfusion: 1,420 +/- 803 vs. 10,210 +/- 2,950 pg/ml; P < 0.05). Perfusion with a buffer containing indomethacin or gadolinium chloride for inhibition of cyclooxygenase (COX) or Kupffer cells, respectively, substantially blocked the recirculation-induced increases in both portal pressure and TXB(2) release in BDL group. Hepatic detection of COX gene expression by RT-PCR revealed that COX-2 but not COX-1 was upregulated following BDL, and this upregulation was confirmed at the protein level by Western blot analysis. In conclusion, these results clearly demonstrate that increased hepatic TXA(2) release into the portal circulation contributes to the increased portal resistance in BDL-induced liver injury, suggesting a role of TXA(2) in liver fibrosis-induced portal hypertension. Furthermore, the Kupffer cell is likely the source of increased TXA(2), which is associated with upregulation of the COX-2 enzyme.

Functions of anaphylatoxin C5a in rat liver: direct and indirect actions on nonparenchymal and parenchymal cells

Growing evidence obtained in recent years indicates that anaphylatoxin C5a receptors (C5aR) are not restricted to myeloid cells but are also expressed on nonmyeloid cells in different tissues such as brain, lung, skin and liver. In contrast to its well-defined systemic functions, the actions of anaphylatoxins in these organs are poorly characterized. The liver can be a primary target organ for the C5a anaphylatoxin since the liver is directly connected to the gut, via the mesenteric veins and portal vein which is a main source of complement activating lipopolysaccharides (LPS). In the normal rat liver, the C5aR is only expressed by nonparenchymal cells, i.e. strongly by Kupffer cells (KC) and hepatic stellate cells (HSC) and weakly by sinusoidal endothelial cells (SEC), but not expressed by the parenchymal hepatocytes (HC). Accordingly, direct effects of C5a were only found in the C5aR-expressing KC and HSC: C5a induced the release of prostanoids from KC and HSC and enhanced the LPS-dependent release of interleukin-6 from KC. These soluble mediators indirectly influenced effector functions of the C5aR-free HC. C5a enhanced the glycogen phosphorylase activity and thus the glucose output from HC indirectly via prostanoids released from KC and HSC. Glucose can serve as an energy substrate as well as an electron donor for the synthesis of reactive oxygen intermediates by KC. Moreover, C5a also enhanced transcription of the gene for the type-2 acute phase protein alpha 2-macroglobulin in HC indirectly by increasing LPS-dependent IL-6 release from KC. Under pathological conditions, C5aR was found to be upregulated in various organs including the liver. Simulation of inflammatory conditions by treatment of rats with IL-6, a main inflammatory mediator in the liver, caused a de novo expression of functional C5aR in HC. In livers of IL-6-treated rats, C5a initiated glucose output from HC and perhaps other HC-specific defense reactions directly without the intervention of soluble mediators from nonparenchymal cells.

Increase by anaphylatoxin C5a of glucose output in perfused rat liver via prostanoids derived from nonparenchymal cells: direct action of prostaglandins and indirect action of thromboxane A(2) on hepatocytes

In the perfused rat liver the anaphylatoxin C5a enhanced glucose output, reduced flow, and elevated prostanoid overflow. Because hepatocytes (HCs) do not express C5a receptors, the metabolic C5a actions must be indirect, mediated by e.g. prostanoids from Kupffer cells (KCs) and hepatic stellate cells (HSCs), which possess C5a receptors. Surprisingly, the metabolic C5a effects were not only impaired by the prostanoid synthesis inhibitor, indomethacin, but also by the thromboxane A(2) (TXA(2)) receptor antagonist, daltroban, even though HCs do not express TXA(2) receptors. TXA(2) did not induce prostaglandin (PG) or an unknown factor release from KCs or sinusoidal endothelial cells (SECs), which express TXA(2) receptors, because (1) daltroban did neither influence the C5a-induced release of prostanoids from cultured KCs nor the C5a-dependent activation of glycogen phosphorylase in KC/HC cocultures and because (2) the TXA(2) analog, U46619, failed to stimulate prostanoid release from cultured KCs or SECs or to activate glycogen phosphorylase in KC/HC or SEC/HC cocultures. In the perfused liver, Ca(2+)-deprivation inhibited not only flow reduction but also glucose output elicited by C5a to similar extents as daltroban. Similarly, in the absence of extracellular Ca(2+), flow reduction and glucose output induced by U46619 were almost completely prevented, whereas glucose output induced by the directly acting PGF(2alpha) was only slightly lowered. Thus, in the perfused rat liver PGs released after C5a-stimulation from KCs and HSCs directly activated glycogen phosphorylase in HCs, and TXA(2) enhanced glucose output indirectly mainly by causing hypoxia as a result of flow reduction.

Alteration of hepatic microcirculation by oxethazaine and some vasoconstrictors in the perfused rat liver

We previously reported that, in isolated perfused rat livers in a constant flow system, oxethazaine (OXZ) rapidly increased portal pressure (PP) accompanied by inhibition of oxygen uptake and the subsequent metabolic effects. In this study, hemodynamic changes were studied by using an indicator dilution technique and by microscopic observation of post-fixed liver samples stained with acridine orange or trapped fluorescence microspheres (FMSs). During the increase in PP induced by OXZ, the mean transit times of both red blood cells and azoalbumin were shortened markedly, and the vascular and extravascular albumin spaces decreased to 55 and 18% of the controls, respectively. With acridine orange, in the control livers, all the dye infused was taken up and the periportal zones were uniformly stained over all the liver sections, whereas in the OXZ-treated livers, about 30% of the dye drained out, and extensive staining was observed in the central portion of the liver mass, but the peripheral portions of the liver were much less stained. The staining was often localized around large portal vein branches and spread toward the hepatic veins. These changes were recoverable in the absence of OXZ. Distributions of 1-microm and 15-microm FMSs were likewise altered by OXZ. Thus, uneven perfusion may be the primary cause of decreased tissue spaces and also of the metabolic effects produced by OXZ. Endothelin 1 also produced OXZ-like changes, while U-46619 had lesser effects. The methodology used in this study may help delineate the hepatic perfusion disturbance caused by various vasoconstrictors.

Thromboxane A2 analogue contracts predominantly the hepatic veins in isolated canine liver

Thromboxane A2 (TxA2) is a potent vasoconstrictor and has been implicated as a mediator of liver diseases such as ischemic-reperfusion injury. We determined the effects of TxA2 and the well-known hepatic venoconstrictor histamine, on the vascular resistance distribution and liver weight in isolated canine livers perfused with blood via the portal vein. The stable TxA2 (STA2; 20 micrograms, n = 5) and histamine (5 micrograms, n = 6) similarly increased the hepatic total vascular resistance, 2.5- and 2.4-fold, respectively. The increase in the hepatic venous resistance was significantly greater than that of the portal resistance (threefold vs. 1.9-fold for STA2; threefold vs. 1.8-fold for histamine). Predominant hepatic venoconstriction induced by both agents was confirmed in livers perfused in a reverse direction from the hepatic vein to the portal vein, as shown by marked precapillary vasoconstriction. STA2 transiently increased liver weight loss (-3.6 g/100 g liver weight), followed by a gradual weight gain (9.0 g/100 g). Histamine caused a progressive weight gain (9.1 g/100 g). In conclusion, similar to histamine, TxA2 constricts predominantly the hepatic vein in isolated canine livers.

The metabolic and hemodynamic effects of oxethazaine in the perfused rat liver

Alteration of hepatic microcirculation and its effects on hepatic metabolism were examined using oxethazaine (OXZ). The infusion of OXZ into isolated perfused livers rapidly increased the portal perfusion pressure (PP) and inhibited oxygen (O2) uptake, which was followed by a decrease in tissue ATP content and an increase in lactate, pyruvate and glucose release into the perfusate. P-450-dependent reductive drug metabolism was enhanced by OXZ, whereas oxidative drug metabolism was suppressed, and this was accompanied by a decrease in substrate uptake. During OXZ infusion, a time delay between the inhibition of O2 uptake and the release of cellular and xenobiotic metabolites was observed. The actions of OXZ required Ca2+. It is unlikely that the inhibition of O2 uptake is due to the inhibition of cellular respiration. The PP increase induced by OXZ was inhibited by papaverine, but not by prazosin, sodium nitroprusside and verapamil, whereas all of these vasodilators were effective against norepinephrine. Under retrograde perfusion, the PP increase by OXZ was abolished, but norepinephrine, uridine 5'-triphosphate, angiotensin II and endothelin 1 were still effective. The extrahepatic portal vein preparation contracted at high concentrations of OXZ. The results suggest that OXZ acts differently from other known vasoconstrictors and possibly narrows hepatic sinusoids to reduce the rate of substance exchange between the sinusoids and hepatocytes, including a reduction in O2 extraction.

Inhibition by the protein kinase C activator 4 beta-phorbol 12-myristate 13-acetate of the prostaglandin F2 alpha-mediated and noradrenaline-mediated but not glucagon-mediated activation of glycogenolysis in rat liver

In perfused rat livers, infusion of prostaglandin F2 alpha (PGF2 alpha) or noradrenaline increased glucose and lactate output and reduced flow. Glucagon increased glucose output and decreased lactate output without influence on flow. Infusion of phorbol 13-myristate 14-acetate (PMA) for 20 min prior to these stimuli strongly inhibited the metabolic and hemodynamic effects of noradrenaline, reduced the metabolic actions of PGF2 alpha but did not alter the effects of glucagon. In isolated rat hepatocytes PGF2 alpha, noradrenaline and glucagon activated glycogen phosphorylase but only PGF2 alpha and noradrenaline increased intracellular inositol 1,4,5-trisphosphate (InsP3). The noradrenaline- or PGF2 alpha-elicited activation of glycogen phosphorylase and increase in InsP3 were largely reduced after preincubation of the cells for 10 min with PMA, whereas the glucagon-mediated enzyme activation was not affected. In contrast to PMA, the phorbol ester 4 alpha-phorbol 13,14-didecanoate, which does not activate protein kinase C, did not attenuate the PGF2 alpha- and noradrenaline-elicited stimulation of glucose output, glycogen phosphorylase and InsP3 formation. Stimulation of InsP3 formation by AlF4-, which activates phospholipase C independently of the receptor, was not attenuated by prior incubation with PMA. Plasma membranes purified from isolated hepatocytes had both a high-capacity, low-affinity and a low-capacity, high-affinity binding site for PGF2 alpha. The Kd of the high-capacity, low-affinity binding site was close to the concentration of PGF2 alpha that increased glycogen phosphorylase activity half-maximally. Binding to the high-capacity, low-affinity binding site was enhanced by guanosine 5'-O-(3-thio)triphosphate (GTP[S]). This high-capacity, low-affinity site might thus represent the receptor. The Bmax and Kd of the high-capacity site, as well as the enhancement by GTP[S] of PGF2 alpha binding to this site, remained unaffected by PMA treatment. It is concluded that, in hepatocytes, activation of protein kinase C by PMA interrupted the InsP3-mediated signal pathway from PGF2 alpha via a PGF2 alpha receptor and phospholipase C to glycogen phosphorylase at a point distal of the receptor prior to phospholipase C.

Thromboxane A2 mimetic U46619 stimulates ciliary motility of rabbit tracheal epithelial cells

To elucidate whether thromboxane A2 (TxA2), one of the important arachidonic acid metabolites that may play a role in the development of airway inflammation, affects respiratory ciliary motility and, if so, what the mechanism of action is, we measured ciliary beat frequency (CBF) of rabbit cultured tracheal epithelium in response to U46619, a TxA2 mimetic agonist, by a photoelectric method. Addition of U46619 (10(-5) M) increased CBF from 17.7 +/- 0.7 to 22.8 +/- 1.4 Hz (mean +/- SE, p less than 0.01) within 5 min, which was followed by a decline to the baseline value by 10 min. This effect was concentration-dependent, the maximal increase from the baseline value and the drug concentration required to produce a half-maximal effect (EC50) being 26.9 +/- 4.6% (p less than 0.01) and 3 x 10(-7) M, respectively. The U46619-induced increase in CBF was abolished by SQ29548, and TxA2 receptor antagonist, and inhibited by verapamil, a Ca(2+)-entry blocker, and H-7, a protein kinase C inhibitor. These results suggest that TxA2 stimulates ciliary motility through the activation of airway epithelial TxA2 receptors, and that this effect may be exerted from Ca(2+)-influx and protein kinase C.

Eicosanoid-mediated increase in glucose and lactate output as well as decrease and redistribution of flow by complement-activated rat serum in perfused rat liver

Rat serum, in which the complement system had been activated by incubation with zymosan, increased the glucose and lactate output, and reduced and redistributed the flow in isolated perfused rat liver clearly more than the control serum. Heat inactivation of the rat serum prior to zymosan incubation abolished this difference. Metabolic and hemodynamic alterations caused by the activated serum were dose dependent. They were almost completely inhibited by the cyclooxygenase inhibitor indomethacin and by the thromboxane antagonist 4-[2-(4-chlorobenzesulfonamide)-ethyl]-benzene-acetic acid (BM 13505), but clearly less efficiently by the 5'-lipoxygenase inhibitor nordihydroguaiaretic acid and the leukotriene antagonist N-(3-[3-(4-acetyl-3-hydroxy-2-propyl-phenoxy)-propoxy]-4-chlorine-6-meth yl- phenyl)-1H-tetrazole-5-carboxamide sodium salt (CGP 35949 B). Control serum and to a much larger extent complement-activated serum, caused an overflow of thromboxane B2 and prostaglandin F2 alpha into the hepatic vein. It is concluded that the activated complement system of rat serum can influence liver metabolism and hemodynamics via release from nonparenchymal liver cells of thromboxane and prostaglandins, the latter of which can in turn act on the parenchymal cells.

Prostanoid release of cultured liver sinusoidal endothelial cells in response to endotoxin and tumor necrosis factor. Comparison with umbilical vein endothelial cells

Vascular endothelial cells release prostanoids, especially prostacyclin, when properly stimulated. In addition to short acting stimuli like thrombin and histamine an increased prostanoid release occurs in the presence of endotoxin, interleukin 1 or tumor necrosis factor (TNF). The response of sinusoidal endothelial liver cells to such stimuli - probably important in hepatic inflammatory disease - is unknown. Sinusoidal endothelial liver cells from the guinea pig were isolated by centrifugal elutriation and investigated as confluent monolayers. Their prostanoid release in response to endotoxin and human recombinant TNF was determined by radioimmunoassays and compared to that obtained with cultured human umbilical vein endothelial cells. A pronounced time- and dose-dependent release of prostanoids was found with both cell types in response to endotoxin. In contrast to umbilical vein cells, liver endothelial cells produced not only large amounts of 6-keto-PGF1 alpha and some PGE2 but also thromboxane B2. Only umbilical vein endothelial cells responded to TNF with an increased 6-keto-PGF1 alpha release, emphasising the metabolic differences between both cell types.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.

[Regulation of liver functions by autonomic hepatic nerves]

The liver is the glucose reservoir of the organism and moreover an important blood reservoir, which takes up or releases glucose and blood depending on demand. Activation of the sympathetic nerves increases glucose release, shifts lactate uptake to output and reduces a.o. oxygen uptake. Moreover, it elicits a reduction of blood flow, and, by closing of sinusoids, an intrahepatic redistribution as well as a mobilization of blood. Activation of parasympathetic nerves enhances glucose utilization and causes a re-opening of closed sinusoids. The actions of sympathetic nerves can be modulated by hormones. Extracellular calcium as well as the mediators noradrenaline and probably also prostaglandins are involved in the signal chain. Intracellularly the signal chain is propagated by an increase of cytosolic calcium.

Mechanism of action of cysteinyl leukotrienes on glucose and lactate balance and on flow in perfused rat liver. Comparison with the effects of sympathetic nerve stimulation and noradrenaline

Rat livers were perfused at constant pressure via the portal vein with media containing 5 mM glucose, 2 mM lactate and 0.2 mM pyruvate. 1. Leukotrienes C4 and D4 enhanced glucose and lactate output and reduced perfusion flow to the same extent and with essentially identical kinetics. They both caused half-maximal alterations (area under the curve) of carbohydrate metabolism at a concentration of about 1 nM and of flow at about 5 nM. The leukotriene-C4/D4 antagonist CGP 35949 B inhibited the metabolic and hemodynamic effects of 5 nM leukotrienes C4 and D4 with the same efficiency, causing 50% inhibition at about 0.1 microM. 2. Leukotriene C4 elicited the same metabolic and hemodynamic alterations with the same kinetics as leukotriene D4 in livers from rats pretreated with the gamma-glutamyltransferase inhibitor, acivicin. 3. The calcium antagonist, nifedipine, at a concentration of 50 microM did not affect the metabolic and hemodynamic changes caused by 5 nM leukotriene D4. The smooth-muscle relaxant, nitroprussiate, at a concentration of 10 microM reduced flow changes, without significantly affecting the metabolic alterations. 4. Leukotriene D4 not only reduced flow; it also caused an intrahepatic redistribution of flow, restricting some areas from perfusion. Thus, leukotrienes increased glucose and lactate output directly in the accessible parenchyma and, in addition, indirectly by washout from restricted areas during their reopening upon termination of application. 5. The phospholipase A2 inhibitor, bromophenacyl bromide, but not the cyclooxygenase inhibitor, indomethacin, at a concentration of 20 microM reduced the metabolic and hemodynamic effects of 5 mM leukotriene D4. 6. Stimulation of the sympathetic hepatic nerves with 2-ms rectangular pulses at 20 Hz and infusion of 1 microM noradrenaline increased glucose and lactate output and decreased flow, similar to 10 nM leukotrienes C4 and D4. The kinetics of the metabolic and hemodynamic changes caused by the leukotrienes differed, however, from those due to nerve stimulation and noradrenaline. 7. The leukotriene-C4/D4 antagonist, CGP 35949 B, even at very high concentrations (20 microM) inhibited the metabolic and hemodynamic alterations caused by nerve stimulation or noradrenaline infusion only slightly and unspecifically.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of thromboxane release by extracellular UTP and ATP from perfused rat liver. Role of icosanoids in mediating the nucleotide responses

1. In isolated perfused rat liver, infusion of UTP (20 microM) led to a transient, about sevenfold stimulation of thromboxane release (determined as thromboxane B2), which did not parallel the time course of the UTP-induced stimulation of glucose release. An increased thromboxane release was also observed after infusion of ATP (20 microM). Although the maximal increase of portal pressure following ATP was much smaller than with UTP (4.2 vs 11.5 cm H2O), the peak thromboxane release was similar with both nucleotides. 2. Indomethacin (10 microM) inhibited the UTP-induced stimulation of thromboxane release and decreased the UTP-induced maximal increase of glucose output and of portal pressure by about 30%. The thromboxane A2 receptor antagonist BM 13.177 (20 microM) completely blocked the pressure and glucose response to the thromboxane A2 analogue U-46619 (200 nM) and decreased the ATP- and UTP-induced stimulation of glucose output by about 25%, whereas the maximal increase of portal pressure was inhibited by about 50% and 30%, respectively. BM 13.177 and indomethacin inhibited the initial nucleotide-induced overshoot of portal pressure increase, but had no effect on the steady-state pressure increase which is obtained about 5 min after addition of ATP or UTP. 3. The leukotriene D4/E4 receptor antagonist LY 171883 (50 microM) inhibited not only the glucose and pressure response of perfused rat liver to leukotriene D4, but also to leukotriene C4 by about 90%. This suggests that leukotriene D4 (not C4) is the active metabolite in perfused liver and the effects of leukotriene C4 are probably due to its rapid conversion to leukotriene D4. LY 171883 also inhibited the response to the thromboxane A2 analogue U-46619 by 75-80%, whereas the response of perfused liver to leukotriene C4 was not affected by the thromboxane receptor antagonist BM 13.177 (20 microM). The glucose and pressure responses of the liver to extracellular UTP were inhibited by LY 171883 and by BM 13.177 by about 30%. This suggests that the inhibitory action of LY 171883 was due to a thromboxane receptor antagonistic side-effect and that peptide leukotrienes do not play a major role in mediating the UTP response. 4. In isolated rat hepatocytes extracellular UTP (20 microM), ATP (20 microM), cyclic AMP (50 microM) and prostaglandin F2 alpha (3 microM) increased glycogen phosphorylase a activity by more than 100%.(ABSTRACT TRUNCATED AT 400 WORDS)

Output and effects of thromboxane produced by the liver perfused with phorbol myristate acetate

The capacity of the perfused rat liver to produce thromboxane after stimulation by phorbol myristate acetate was examined. A total of 109 +/- 20 and 155 +/- 28 pmol/g liver were found in the perfusate and in the bile, respectively, after 40 min. The amount of thromboxane recovered in the perfusate and in the bile accounted for 12.6% of the production calculated from the same number of Kupffer cells in primary cultures, indicating that a major part of thromboxane was taken up and inactivated by hepatocytes. The effect of endogenously synthesized thromboxane on the liver was assessed by using CGS 13080, a thromboxane synthase inhibitor, or BM 13.177, a thromboxane receptor antagonist. 20 nM CGS 13080 in the perfusate inhibited the synthesis of thromboxane and at the same time the elevation of portal pressure and glycogenolysis following administration of phorbol 12-myristate 13-acetate (PMA). The thromboxane receptor antagonist BM 13.177 did not inhibit the synthesis of thromboxane, but reduced the PMA-related elevation of portal pressure and glycogenolysis to the same extent (greater than 60%) as CGS 13080. Sodium nitroprusside, a vasodilator, inhibited the rise in portal pressure caused by PMA to the same extent as CGS 13080 or BM 13.177 but reduced the increase in glycogenolysis only by 25%. These results indicate that thromboxane released by stimulated Kupffer cells of the liver elevates portal pressure and glycogenolysis in the perfused rat liver, although by different mechanisms.

Hepatocyte heterogeneity in response to icosanoids. The perivenous scavenger cell hypothesis

1. The metabolic and hemodynamic effects of prostaglandin F2 alpha, leukotriene C4 and the thromboxane A2 analogue U-46619 were studied during physiologically antegrade (portal to hepatic vein) and retrograde (hepatic to portal vein) perfusion and in a system of two rat livers perfused in sequence. 2. The stimulatory effects of prostaglandin F2 alpha (3 microM) on hepatic glucose release, perfusion pressure and net Ca2+ release were diminished by 77%, 95% and 64%, respectively, during retrograde perfusion when compared to the antegrade direction, whereas the stimulation of 14CO2 production from [1-14C]glutamate by prostaglandin F2 alpha (which largely reflects the metabolism of perivenous hepatocytes) was lowered by only 20%. Ca2+ mobilization and glucose release from the liver comparable to that seen during antegrade perfusion could also be observed in retrograde perfusions; however, higher concentrations of the prostaglandin were required. 3. The glucose, Ca2+ and pressure response to leukotriene C4 (20 nM) or the thromboxane A2 analogue U-46619 (200 nM) of livers perfused in the antegrade direction were diminished by about 90% during retrograde perfusion. Sodium nitroprusside (20 microM) decreased the pressure response to leukotriene C4 (20 nM) and U-46619 (200 nM) by about 40% and 20% in antegrade perfusions, respectively, but did not affect the maximal increase of glucose output. 4. When two livers were perfused antegradely in series, such that the perfusate leaving the first liver (liver I) entered a second liver (liver II), infusion of U-46619 at concentrations below 200 nM to the influent perfusate of liver I increased the portal pressure of liver I, but not of liver II. At higher concentrations of U-46619 there was also an increase of the portal pressure of liver II and with concentrations above 800 nM the pressure responses of both livers were near-maximal [19.6 +/- 0.8 (n = 7) cm H2O and 16.5 +/- 1.1 (n = 8) cm H2O for livers I and II, respectively]. There was a similar behaviour of glucose release from livers I and II in response to U-46619 infusion. When liver I was perfused in the retrograde direction, a significant pressure or glucose response of liver II (antegrade perfusion) could not be observed even with U-46619 concentrations up to 1000 nM. 5. Similarly, the perfusion pressure increase and glucose release induced by leukotriene C4 (10 nM) observed with liver II was only about 20% of that seen with liver I.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential role for prostaglandin F2 alpha, D2, E2 and thromboxane A2 in mediating the metabolic and hemodynamic actions of sympathetic nerves in perfused rat liver

In isolated rat liver perfused at constant pressure perivascular nerve stimulation caused an increase of glucose and lactate output and a reduction of perfusion flow. The metabolic and hemodynamic nerve effects could be inhibited by inhibitors of prostanoid synthesis, which led to the suggestion that the effects of nerve stimulation were, at least partially, mediated by prostanoids [Iwai, M. & Jungermann, K. (1987) FEBS Lett. 221, 155-160]. This suggestion is corroborated by the present study. 1. Prostaglandin D2, E2 and F2 alpha as well as the thromboxane A2 analogue U46619 enhanced glucose and lactate release and lowered perfusion flow similar to nerve stimulation. 2. The extents, the kinetics and the concentration dependencies of the metabolic and hemodynamic actions of the various prostanoids were different. Prostaglandin F2 alpha and D2 caused relatively stronger changes of metabolism, while prostaglandin E2 and U46619 had stronger effects on hemodynamics. Prostaglandin F2 alpha elicited greater maximal alterations than D2 with similar half-maximally effective concentrations. Prostaglandin F2 alpha mimicked the nerve actions on both metabolism and hemodynamics best with respect to the relative extents and the kinetics of the alterations. 3. The hemodynamic effects of prostaglandin F2 alpha could be prevented completely by the calcium antagonist nifedipine without impairing the metabolic actions of the prostanoid. Apparently, prostaglandin F2 alpha influenced metabolism directly rather than indirectly via hemodynamic changes. The present results, together with the previously described effects of prostanoid synthesis inhibitors, suggest that prostanoids, probably prostaglandin F2 alpha and/or D2, could be involved in the actions of sympathetic hepatic nerves on liver carbohydrate metabolism. Since prostanoids are synthesized only in non-parenchymal cells, nervous control of metabolism appears to depend on complex intra-organ cell-cell interactions between the nerve, non-parenchymal and parenchymal cells.

Net prostaglandin release by perfused rat liver after stimulation with phorbol 12-myristate 13-acetate

Phorbol myristate acetate, which was shown previously to elicit eicosanoid synthesis in primary cultures of Kupffer cells, led to a net release of prostaglandins (PG) D2 and E2 from the perfused rat liver. While a substantial amount of PGD2 (the major prostaglandin of Kupffer cells) left the liver, very little PGE2 was found in the effluent. Considerable amounts of immunologically reactive PGD2 and E2 were secreted with the bile. PGE2 rather than PGD2 was able to stimulate glycogenolysis and to increase perfusion pressure. These effects were, however, strongly dependent on the direction of the flow. If the liver was perfused in a retrograde fashion, i.e., from the vena cava to the portal vein, phorbol myristate acetate or PGE2 exerted only minor effects. These observations suggest a topological heterogeneity of producer and responder cells, respectively, in the liver sinusoid.

Leukotrienes increase glucose and lactate output and decrease flow in perfused rat liver

In isolated perfused rat liver leukotriene C4 and D4 but not B4 and E4 enhanced glucose and lactate output and lowered perfusion flow similar to the thromboxane A2 analogue U46619, extracellular ATP and prostaglandin F2 alpha. The kinetics of the metabolic changes caused by leukotriene C4 and D4 resembled those effected by U46619 and ATP but not those elicited by prostaglandin F2 alpha; the kinetics of the hemodynamic changes were similar only to those caused by U46619. The results show that leukotrienes could be important modulators of hepatic metabolism and hemodynamics and point to a complex intra-organ cell-cell communication between non-parenchymal and parenchymal cells.

Effects of leukotrienes and the thromboxane A2 analogue U-46619 in isolated perfused rat liver. Metabolic, hemodynamic and ion-flux responses

1) Addition of leukotriene C4 to isolated perfused rat liver led to a stimulation of hepatic glucose output, a slight decrease of 14CO2 production from [1-14C] glutamate, an increase of portal pressure and an inhibition of hepatic oxygen uptake. Withdrawal of leukotriene C4 caused a transient further stimulation of hepatic glucose output. 2) These effects were accompanied by a slow net Ca2+ release from the liver, which was not completed within 8 min. Following leukotriene withdrawal there was a further Ca2+ release for about 1 min superimposing a slow reuptake of Ca2+ of about 10 min duration. 3) Leukotriene C4 induced a characteristic biphasic K+ release from the liver. Withdrawal of the leukotriene resulted in a further net K+ release for about 4 min, being followed by a K+ reuptake over more than 10 min. 4) Effects comparable to those induced with leukotriene C4 (20nM) were obtained with leukotriene D4 (20nM), were as leukotriene B4 and E4 (20nM each) were much less effective. 5) The thromboxane A2 analogue U-46619 produced ionic, metabolic and hemodynamic responses similar to leukotriene C4; however, when given at concentration yielding a comparable glucose release, the thromboxane analogue was much more vasoactive than leukotriene C4. The thromboxane A2 receptor antagonist BM-13.177 (20 microM) blocked the metabolic, hemodynamic and ion flux responses to U-46619 almost completely, but had no effect on the response to leukotriene C4. 6) Each, leukotrienes, U-46619 and UTP led to an inhibition of hepatic oxygen uptake. The extent of inhibition of oxygen uptake induced by these compounds was not exclusively explained by their effects on hepatic circulation: a 30% inhibition of oxygen uptake by leukotriene C4, U-46619 or UTP was accompanied by increases of the portal pressure of 4.9 +/- 0.4 (481 +/- 39 Pa) (n = 7), 16.0 +/- 1.9 (1570 +/- 186 Pa) (n = 7) or 11.4 +/- 0.4 (1118 +/- 39 Pa) (n = 13) cm H2O, respectively. 7) The data show that leukotrienes and possibly also thromboxanes are potent regulators of hepatic metabolism and hemodynamics, probably acting by a Ca2+ mobilizing mechanism and involving different receptor systems. The response of perfused liver to these compounds is qualitatively similar to that obtained with extracellular UTP, but different to that with prostaglandins, extracellular ATP or phenylephrine. The data further support the view that eicosanoids are important modulators of hepatic metabolism and point to a complex regulatory interaction between hepatic parenchymal and non-parenchymal cells.

Potentiation of the glycogenolytic and haemodynamic actions of adenosine in the perfused rat liver by verapamil

The effects of calcium channel blockers on the glycogenolytic and haemodynamic responses to adenosine were determined in perfused rat liver. Verapamil, 5-25 microM, potentiated the increased glucose output and vasoconstriction observed in response to adenosine. In the absence of perfusate calcium, adenosine responses were inhibited and verapamil was without effect. Verapamil did not potentiate the elevation of hepatic cAMP observed in response to a sub-maximal adenosine concentration (15 microM). In contrast to verapamil, nifedipine, 5 microM, was without effect on hepatic responses to adenosine. It is concluded that the potentiating effects of verapamil on hepatic responses to adenosine may be unrelated to the calcium-channel blocking activity of the compound

Activation of hepatic glycogenolysis by phagocytic stimulation

Infusion of latex beads into isolated perfused rat livers transiently increased glucose output, perfusate lactate/pyruvate ratio and portal vein pressure, mimicking hepatic effects of heat-aggregated IgG (HAG). Indomethacin attenuated hepatic responses to latex beads, and extracellular calcium was required for full expression of hepatic responses. Prior infusion of HAG inhibited the glycogenolytic response to latex beads, supporting a common mechanism of action for the two agents.