Involvement Of Eicosanoids Research Articles

Possible involvement of eicosanoids in the actions of sympathetic hepatic nerves on carbohydrate metabolism and hemodynamics in perfused rat liver

In isolated rat liver perfused at constant pressure with Krebs-Henseleit buffer containing 5 mM glucose, 2 mM lactate, 0.2 mM pyruvate and 0.1% bovine serum albumin, perivascular nerve stimulation (20 V, 20 Hz, 2 ms) and infusion of ATP (100 μM), noradrenaline (1 μM) or arachidonic acid (100 μM) caused an increase in glucose and lactate output and a reduction of perfusion flow. The metabolic effects of nerve stimulation but not those of ATP and noradrenaline were inhibited strongly by the phospholipase A 2 inhibitor bromophenacyl bromide (BPB, 20 μM) and the cyclooxygenase inhibitor indomethacin (Indo, 20 μM) and only slightly by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 20 μM). In contrast, the hemodynamic effects not only of nerve stimulation but also of ATP and noradrenaline were inhibited strongly by BPB and Indo and slightly by NDGA. The metabolic and hemodynamic actions of arachidonate were inhibited specifically by Indo. These results suggest that the effects of nerve stimulation were at least partially mediated or modulated by eicosanoids, especially by prostanoids.

Possible involvement of eicosanoids in the zymosan and arachidonic-acid-induced oxygen uptake, glycogenolysis and Ca2+ mobilization in the perfused rat liver.

Exposure of perfused rat livers to zymosan, arachidonic acid and phenylephrine, but not to latex particles, induces pronounced oxygen uptake, glycogenolysis and Ca2+ mobilization. The oxygen uptake induced by arachidonic acid and by zymosan remains elevated even after the agents have been removed. NaN3 was found to be much more effective in inhibiting the oxygen uptake induced by phenylephrine than that induced by zymosan or arachidonic acid. Glucose release induced by zymosan and by arachidonic acid reaches a maximum after about 2 min and then declines very rapidly even while the agents are still being infused. In contrast, glucose release induced by phenylephrine remains elevated for the duration of the infusion. Ca2+ fluxes induced by arachidonic acid are similar to those induced by phenylephrine in that efflux occurs when the agent is administered and influx occurs only when the agent is removed. This contrasts to the Ca2+ flux changes induced by zymosan where both Ca2+ efflux and Ca2+ influx occur even while zymosan is still being infused. Glucose release induced by zymosan is inhibited by bromophenacylbromide and nordihydroguaiaretic acid, but not by indomethacin. Indomethacin, however inhibits the arachidonic-acid-induced glucose release which is also inhibited by nordihydroguaiaretic acid but not by bromophenacylbromide. Indomethacin inhibits also the arachidonic-acid-induced Ca2+ flux changes whereas the zymosan- and the phenylephrine-induced Ca2+ flux changes are not inhibited by the cyclooxygenase inhibitor. The data presented in this paper suggest that in the perfused rat liver the zymosan-induced glycogenolysis, as well as the Ca2+ flux changes and glycogenolysis induced by arachidonic acid, are mediated by eicosanoids.

Arachidonic acid metabolism in human granulosa cells: evidence for cyclooxygenase and lipoxygenase activity in vitro

In view of the studies demonstrating the involvement of eicosanoids (prostaglandins and hydroxyperoxides, including leukotrienes) in ovulation in several mammalian species, we have examined the activity of the two enzyme systems, lipoxygenase and cyclooxygenase in human granulosa cells obtained from women undergoing in-vitro fertilization--embryo transfer. The activity of cyclooxygenase was assessed by radioimmunoassay of prostaglandin E and of 6-keto-prostaglandin F1 alpha, the conversion product of prostacyclin, accumulated in the culture medium of granulosa cells. Lipoxygenase activity was detected by the conversion of [14C]arachidonic acid into its products (hydroxyperoxides and leukotrienes) separated by reversed phase high-performance liquid chromatography. The results confirmed the activity of cyclooxygenase in human granulosa cells, production in vitro of prostaglandin E and prostacyclin and demonstrated the presence of active lipoxygenase enzymes. These results support the possible involvement of eicosanoids in ovulation of the human.

Involvement of eicosanoids in release of oxytocin and vasopressin from the neural lobe of the rat pituitary.

Arachidonic acid (AA) is oxidized via three pathways which result in several series of distinct metabolites. Cyclooxygenase produces prostaglandins (PGs), prostacyclins, and thromboxanes. Lipoxygenase produces hydroperoxy/hydroxyeicosatetraenoic acids (HPETE/HETEs) and leukotrienes. Epoxygenase, a recently uncovered pathway, results in epoxyeicosatrienoic acids (EETs). Based on reverse phase HPLC product analysis, this study establishes that all three pathways of AA metabolism are present in microsomal incubates of the neural lobe of the pituitary gland. Addition of PGE2 to incubated fragments of neural lobes of the rat pituitary stimulates secretion of both arginine vasopressin (AVP) and oxytocin in vitro. Inclusion of 5-HETE and 12-HETE in the incubation medium stimulates marginal release of AVP and oxytocin by 12-HETE only. The magnitude of AVP and oxytocin secretion stimulated by the epoxygenase metabolites 8,9-, 11,12-, and 14,15-EET is equal to that caused by PGE2. Maximal stimulation of secretion (3- to 4-fold) requires an EET concentration 10-15 times greater than that of PGE2. In contrast, 5,6-EET is inactive. These data suggest that oxygenated products of AA play a role in AVP and oxytocin secretion. Although PGs appear to be the dominant arachidonate metabolites involved in the release of AVP and oxytocin, the EETs probably have a contributing role.