Conversion of arachidonic acid to lipoxygenase products by human fetal tissues

[14C]Arachidonic acid was converted to several lipoxygenase products by homogenates of human fetal tissues as determined by thin-layer chromatography. The net conversions of [14C]arachidonic acid to radiolabeled lipoxygenase products were high (greater than or equal to 5%) in the case of fetal liver and brain, and low (less than or equal to 2%) in the case of fetal adrenal, heart, and kidney.

Stimulation of prostaglandin biosynthesis by urine of the human fetus may serve as a trigger for parturition

Urine of the human fetus stimulated prostaglandin biosynthesis in vitro by increasing the conversion of arachidonic acid into prostaglandins. The stimulatory activity in urine from fetuses delivered at term after labor of spontaneous onset was greater than that in urine from fetuses delivered by cesarean section at term before the onset of labor. Such stimulation of prostaglandin biosynthesis by the fetal membranes, by way of a substance released into the urine and thence into amniotic fluid, could serve as a signal for the initiation of parturition.

Lipoxygenase activity in human uterine and intrauterine tissues: new prospects for control of prostacyclin production in pre-eclampsia

The formation of lipoxygenase metabolites by human uterine and intrauterine tissues was evaluated using [1-14C]arachidonic acid (AA) as substrate. The major lipoxygenase product synthesized by human amnion, decidua vera and placenta was identified as 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE); smaller amounts of 5-HETE and 5-HETE (lactone form) were also formed. In chorion laeve only a trace amount of 12-HETE was detected. Human myometrium and cervical tissue converted [1-14C]AA to 5-HETE and 12-HETE in almost equal amounts. The formation of lipoxygenase products in all tissues was markedly inhibited by nordihydroguaiaretic acid (NDGA) an inhibitor of lipoxygenase activity and slightly stimulated or inhibited by indomethacin, an inhibitor of cyclooxygenase activity. These results are indicative that uterine and intrauterine tissues are probably potential sources of lipoxygenase products during pregnancy and parturition. Since 12-hydroperoxy-eicosatetraenoic acid (12-HPETE), the labile precursor of 12-HETE potently inhibits prostacyclin biosynthesis, our findings are suggestive of the possibility that aberrant lipoxygenase activities may contribute to the complications of pre-eclampsia.

Inhibiton of prostaglandin synthesis by human amniotic fluid: acute reduction in inhibitory activity of amniotic fluid obtained during labor

Human amniotic fluid contains an inhibitor of prostaglandin synthesis. The activity of the inhibitor was measured in amniotic fluid obtained in early pregnancy, and at term both before and after the onset of labor. The inhibitory activity was greater in amniotic fluid taken in early pregnancy than in fluid taken at term before the onset of labor (P less than 0.05). There was a further significant reduction in inhibitory activity (P less than 0.01) in amniotic fluid collected during labor. These results are suggestive that the onset of labor is associated with a local withdrawal of inhibition of prostaglandin biosynthesis.

Stimulants of prostaglandin biosynthesis in human fetal membranes, uterine decidua vera and placenta

Modulation of prostaglandin (PG) biosynthesis by cytosolic fractions derived from homogenates of human amnion, chorion laeve, decidua vera and placenta was examined. PGF2 alpha and 6-oxo-PGF1 alpha synthesis by bovine seminal vesicle (BSV) PG synthase was stimulated by the cytosolic fractions of each tissue in a dose-dependent manner. The cytosols from decidua vera and placenta were the most effective in stimulating synthesis and also stimulated PGE2 biosynthesis. Reduced glutathione (GSH) acted to increase the biosynthesis of PGE2 at the expense of other PGs both in the presence and absence of various cytosols. These data are indicative that the mode of action of cytosolic fractions on the stimulation of PG biosynthesis is unlike that of GSH. Indomethacin and aspirin, inhibitors of fatty acid cyclo-oxygenase activity, strongly inhibited the cytosol-induced stimulation of BSV PG synthase. The cytosolic factors that stimulated PG biosynthesis exhibited differential behavior towards boiling and dialysis. The stimulatory effect of all cytosolic fractions was sensitive to boiling except in the the chorion laeve effects toward 6-oxo-PGF1 alpha production. In dialysis studies we found that the cytosolic components that stimulated the production of PGF2 alpha were not removed by dialysis except in the case of cytosol of placenta whereas the stimulatory effects of various cytosols toward the biosynthesis of PGE2 and 6-oxo-PGF1 alpha were removed by dialysis. These results are indicative of the presence of endogenous factors in human intrauterine tissues that preferentially stimulate the biosynthesis of PGF2 alpha and 6-oxo-PGF1 alpha and are further suggestive that PG biosynthesis in intrauterine tissues is, at least in part, regulated by cytosolic factors.

Formation of arachidonate lipoxygenase metabolites by human fetal membranes, uterine decidua vera and placenta

Homogenates (1000 x g supernatant fraction) of human amnion, chorion laeve, decidua vera and placenta were incubated with [1(-14)C] arachidonic acid in the presence or absence of indomethacin, an inhibitor of cyclooxygenase activity and nordihydroguairetic acid (NDGA), an inhibitor of lipoxygenase activity. After incubation, the products were extracted with ethyl acetate and identified by thin layer chromatography and high performance liquid chromatography. The major lipoxygenase products formed by human amnion, decidua vera and placenta were 12-L-hydroxy-5,8,10,14-eicosatretetraenoic acid (12-HETE) and smaller amounts of 5-HETE. Chorion laeve produced only a trace amount of 12-HETE. The formation of these products was abolished by NDGA and slightly stimulated by indomethacin. These findings demonstrate the existence of lipoxygenase activity in human intra-uterine tissues and suggest that products of lipoxygenase activity in these tissues may regulate the recruitment of leukocytes and/or macrophages during pregnancy and parturition.

Inhibition of prostaglandin biosynthesis by human low-density and high-density lipoproteins

The ability of human low-density lipoprotein (LDL) and high-density lipoprotein (HDL) to inhibit the biosynthesis of prostaglandin (PG) E2, F2 alpha prostacyclin from arachidonic acid by bull seminal vesicle (BSV) PG synthase was studied. Both LDL an HDL inhibited the PG synthase activity in BSV microsomes. The greatest inhibitory effect was observed against th biosynthesis of PGE2. These results show an higher to unrecognised property of human lipoproteins that may mediate some of the biological actions of these substances.

Endogenous peptides that inhibit brain cyclic AMP phosphodiesterase

Peptide extracts of rat brain powerfully inhibited the cyclic AMP phosphodiesterase activity of rat brain homogenate. Similar extracts of ox brain showed comparable although less potent activity. Preliminary investigation of the physicochemical properties of brain extracts indicated that the rat brain extract contained an active peptide of low molecular weight (about 1400), whereas ox brain contained two such peptides (about 1400 and 900). These studies indicate that endogenous oligopeptides that inhibit cyclic AMP phosphodiesterase are present in brain. Experiments on several pure peptides known to be present in brain. Experiments on several pure peptides known to be present in the CNS showed that the majority were inactive against brain phosphodiesterase, but ACTH(1-24), somatostatin, substance P and Lys8-vasopressin, in descending order of potency, were active. To help distinguish the peptides found in rat and ox brain extracts from known peptides, preliminary analyses of amino acid composition were performed. These suggested that the peptides found in brain extracts were distinct from known peptides having the ability to inhibit cyclic AMP phosphodiesterase.

Comparisons between the abilities of various human and ovine plasmas to inhibit prostaglandin synthesis

The ability of various human and ovine blood plasmas to inhibit prostaglandin synthesis in vitro has been tested. Human plasmas were significantly more potent in their ability to inhibit prostaglandin synthesis than their counterpart ovine plasmas. In general, female plasma had greater inhibitory activities than male plasmas and adult plasmas were more active than fetal plasmas. There was no simple correlation between the activity of plasmas as inhibitors of prostaglandin synthesis and their respective albumin or haptoglobin contents.

Prostaglandin synthesis inhibition by maternal and fetal sheep plasma and its relation to haptoglobin and albumin levels

Mammalian plasmas and sera have been reported to contain endogenous inhibitors of prostaglandin synthesis (EIPS), but the identity and role of these suggested inhibitors is as yet undetermined. Albumin and haptoglobin have been proposed as possible inhibitors, and it has been suggested that EPIS may have a part to play in the control of PG production during pregnancy and in the neonatal period. As part of a series of studies aimed at elucidating the identity and role of EIPS, maternal and fetal blood samples were collected from chronically catheterized pregnant ewes, and plasma levels of albumin, haptoglobin and EIPS activity determined. Pregnant ewe plasma possessed high EIPS activity and fetal lamb plasma little or no EIPS activity. Levels of albumin and/or haptoglobin did not consistently parallel that of EIPS activity. A post-operative rise (4 sheep studied) and a pre-parturition nadir (1 sheep studied) in maternal plasma EIPS activity were also noted. The possible physiological significance of these results is discussed.