Synthesis of prostaglandins by cultured rat hearts myocytes and cardiac mesenchymal cells

Ischemia, trauma and hormonal stimulation elicit the release of prostaglandins (PGs) from the heart. Although PGI₂ is synthesized by coronary arteries, the capacities for PG synthesis of individual types of cells comprising the heart have not been elucidated. Accordingly, synthesis of prostaglandins by cultured rat cardiac myocytes and mesenchymal cells was evaluated by radiochromatography of products obtained by incubating cells with [1-¹⁴C]arachidonate, and verified by assessing the effects of cell incubation medium on platelet aggregation. Cultured mesenchymal cells synthesized PGs E₂, F_2α and 6-keto-F_1α, a metabolite of PGI₂ (2076 ± 183, 1284 ± 158 and 1194 ± 152 dpm/mg protein/30 min, respectively). Medium from mesenchymal cells inhibited platelet aggregation, an effect abolished by preincubating the cells with indomethacin, further indicating that these cells synthesized PGI₂. Cardiac myocytes synthesized PGE₂ and PGF_2α (952 ± 227 and 287 ± 104 dpm/mg protein/30 mins, respectively), but no PGI₂. Medium from myocytes did not inhibit platelet aggregation. Prostaglandins D₂, A₂ and thromboxane were not synthesized by either type of cell. Thus, PGI₂ is synthesized by cardiac mesenchymal cells and the hitherto uncharacterized sources of PGE₂ and PGF_2α found in coronary sinus effluent may include cardiac myocytes as well as mesenchymal cells.     

Prostaglandins of the one,two, and three series affect blood pressure in the American bullfrog, Rana catesbeiana

The effects of prostagandins (PGs), and three potential prostaglandin precursors, were studied on blood pressure and heart rate of the American bullfrog, Rana catesbeiana. Bullfrogs were chronically cannulated with a T cannula in the right sciatic artery. The mean systemic arterial blood pressure (SAP) prior to infusion was 20.4 ± 1.1 mm Hg. Mean preinfusion systolic and diastolic pressures were 23.9 ± 1.4 and 17.1 ± 0.9 mm Hg, respectively. Mean preinfusion heart rate was 41.1 ± 0.5 beats/min. Of the PGs tested, PGI₂ was a potent hypotensive agent, with effects at 0.03 μg/kg bw. PGE₂ was more potent than PGE₃, and PGE₁. PGA₁ and PGA₂ were the least potent, and were ineffective at doses below 100 μg/kg bw. PGF_2α was the most potent hypertensive agent tested, with thromboxane B₂ less potent. All compounds tested elevated heart rate, with PGE₂ the most effective. The prostaglandin precursors, eicosatrienoic acid, arachidonic acid, and eicosapentaenoic acid (2000 μg/kg bw) all decreased blood pressure by approximately 25%. The decrease was attenuated by indomethacin (4 mg/kg bw). These results indicate that the bullfrog utilizes all three hypotensive activity. The ability of the bullfrog to utilize several substrates makes it a good choice for comparative studies on prostaglandin synthesis.     

Age-related changes in arachidonic acid metabolism of normal,leukemic and autoimmune strain mice

Spleen synthesis of prostaglandins (PGs) and thromboxane (Tx) was examined as a function of age for autoimmune, leukemic and normal mouse strains. Prostaglandin and thromboxane production from ¹⁴C-arachidonic acid was assessed from 20 minute synthesis by tissue homogenates. Values for young animals, six to 10 weeks of age, were compared to those for eight-to 12-month-old mice, except in the cases of the early autoimmune strain BXSB male and MRL/Ipr mice which were examined at five to seven months of age. Total eicosanoid synthesis, as well as PGF_2α , PGE₂, and PGD₂ production showed, in general, a pattern of increase with age in nonautoimmune strain BALB/c, C57BI/6 and female BXSB mice. In contrast, PGE₂ and PGF_2α synthesis decreased in the autoimmune MRL/Ipr and male BXSB models and in the nonautoimmune, but lymphoma-developing AKR strain. The late autoimmune MRL/++ strain showed decreased PGE₂ but no change in PGF_2α with age. Age-related PGE₂ and PGF_2α changes were minimal in the nonautoimmune DBA/2 and in the late autoimmune PN strains. Thromboxane B₂ appeared to be conserved in all strains studied. The results suggest that diminished spleen PG production with age is linked to development of autoantibodies and lymphoproliferative disorders. Further studies are necessary to establish whether decreased synthesis of immunoregulatory PGs plays a causal role in disease development or arises as a consequence of disease.     

Prostaglandin effects upon cyclic AMP levels, corticosterone output, and aldosterone output in the adrenal of the frog, Rana berlandieri forreri.

The mechanism of prostaglandin action in the adrenal of the frog (Rana berlandieri forreri) was evaluated in vitro. The prostaglandins evoked transient (PGA₂, PGB₁, PGE₂), continued (PGA₁, PGB₂, PGF_1α, PGF_2α), or no effects (PGE₁) upon cyclic AMP (cAMP) levels. Further, the cAMP levels were depressed (PGA₁, PGB₁, PGB₂), elevated (PGA₂, PGE₂, PGF_1α, PGF_2α), or unchanged (PGE₁) compared to the controls. Prostaglandins regulate cAMP levels in the frog adrenal. In addition, specific prostaglandins evoke specific effects in this regard. The frog adrenal corticosterone and aldosterone outputs are modulated by the prostaglandins. The modulations produced differ with the prostaglandins tested. The greatest adrenocortical sensitivity is to PGB₂ which evoked about a 13-fold increase in corticosterone output and a 5-fold increase in aldosterone output at 16 min. Only PGF_1α inhibited steroid output; the other prostaglandins stimulated steroid outputs to varying degrees. A close correlation of the prostaglandin-evoked corticosterone and aldosterone output responses with the cAMP changes was not present in the frog adrenal. The prostaglandins differentially affected cAMP levels and when compared to adrenocorticoid outputs, different prostaglandins produce different effects. The responses of the frog adrenal indicate that the mechanisms controlling adrenocortical function are more complex than originally visualized. In this regard, the site(s) of action (plasma membrane, mitochondrion, etc.) of a given factor must also be considered. Thus, the current concepts must be broadened to include a number of interacting factors among which are the cyclic nucleotides and the prostaglandins.     

Prostaglandin synthetase activity in bovine adrenocortical cells and subcellular preparations: Effect of ACTH

Prostaglandin (PGE₂, PGF_2α) production by bovine fasciculo-reticulata adrenocortical cell suspensions was examined using specific radioimmunoassay procedures. No detectable PGs (> 50 pg) could be measured in the extract from up to 2 × 10⁶ cell incubations after 1 h, with or without the presence of ACTH, although these cells expressed full steroidogenic capabilities under these conditions. The same preparations could produce PGs when supplemented with arachidonic acid but ACTH had no effect on this process. These negative findings could not be explained by analytical artifacts or metabolic transformation. However, an active PG synthetase system was characterized in bovine adrenocortical subcellular preparations. This system converted arachidonate and endogenous substrate(s) to PGE₂ as the major product. No thromboxane or prostacyclin pathways were detected even at high enzyme/substrate ratio. Although the microsornal adrenal cortex PG synthetase activity shares many features with those observed in other tissues (K_m = 8.3 × 10^?5 M, optimal pH at 8.0, stimulation of PGE₂ formation in the presence of glutathione and L-epinphrine), its specific activity was comparatively low (V_max = 2.5 ng PGE₂/min/mg microsornal proteins), which may explain our negative findings using cell suspensions. These findings do not provide evidence to support the hypothesis proposing a role of endogenous PGs in the mechanism of acute ACTH action in the case of bovine adrenal cortex.     

Cyclosporin reduces renal prostanoid excretion in type 1 diabetic patients

Prostacyclin and thromboxane A₂ are important regulators of kidney blood flow. To examine whether changes in their metabolism could be involved in the nephrotoxicity of cyclosporin, we determined urinary excretion of 6-keto PGF_1a and dinor-6-keto PGF_1a (prostacyclin metabolites) and dinor-TxB₂ (thromboxane metabolite) in five newly diagnosed type 1 diabetic patients during and after stopping cyclosporin therapy. In the resting state, cyclosporin had no effect on prostanoid excretion. In response to exercise, urinary excretion of 6-keto PGF_1a was reduced by 50% (P<0.02), dinor-6-keto PGF_1a by 15% (P<0.05) and dinor-TxB₂ by 45% (P<0.02), while albumin excretion increased 4.5-fold (P<0.05) during cyclosporin therapy. Simultaneously, there was a rise in serum creatinine concentration, and renal biopsy specimens obtained from three patients showed periglomerular and interstitial fibrosis and tubular atrophy. After the discontinuation of cyclosporin therapy, serum creatinine concentrations returned to normal, histological changes improved and there was an associated rise in urinary prostanoid excretion. These data suggest that a reduction in renal prostanoid synthesis by cyclosporin may diminish renal blood flow and function, and lead to histological changes in the kidney.     

Prostaglandins, Slow-reacting Substances (Leukotrienes) and the Lung

Abstract: Prostaglandins (PGs) are synthesised from arachidonic acid in human lung tissue and their effects on bronchial smooth muscle have suggested a possible role in the pathogenesis of airflow obstruction in asthmatic subjects, who are exquisitely sensitive to inhalation of PGF_2α. More recently it has become evident that the endoperoxides, which are unstable intermediates in the biosynthesis of PGs, may be converted to thromboxane A₂ which is more potent than PGF_2α in animal experimental models of airflow obstruction. Prostacyclin which is released by the lung into the circulation inhibits platelet aggregation but appears to have minimal effect on broncho-motor tone. Non-steroidal anti-inflammatory drugs such as aspirin and indomethacin prevent the formation of PGs and throm-boxanes by inhibiting the cyclooxygenase enzyme which converts arachidonic acid to the endoperoxides. The failure of indomethacin to prevent allergen-induced and exercise-induced asthma mitigates against a direct involvement of cyclooxygenase products. However experiments with human lung tissue in vitro have shown increased antigen-induced release of slow-reacting substance of anapbylaxis (SRS-A) in the presence of indomethacin. Since SRS-A is a potent broncho-constrictor it is possible that an enhanced release of SRS-A, in subjects pre-treated with indornethacin, was contributing to their continued bronchoconstriction following antigen or exercise challenge. A similar mechanism may be involved in aspirin-sensitive asthmatics. The recent discovery that SRS-A is a lipoxygenase product of arachidonic acid has emphasised the importance of this alternative pathway for the metabolism of arachidonic acid. The structure of SRS-A has been identified as leukotriene D and chemically pure leukotrienes have been synthesised to enable detailed studies of their role in the patho-pbysiology of asthma and other lung diseases. It should now be possible to develop leukotriene synthesis inhibitors and receptor antagonists for clinical use.     

Does of the local myocardial release of prostaglandin E2 or F2α contribute to the early consequences of acute myocardial ischaemia?

The possible role of prostaglandins in acute myocardial ischaemia was investigated in anaesthetized greyhounds which were subjected to either short (3 min) occlusions or permanent ligation of the left anterior descending coronary artery. Plasma PGE₂ and PGF_2α concentrations were measured by radioimmunoassay in blood from the aorta, the coronary sinus (draining the essentially normal myocardium) and from a local coronaryvein (draining the area rendered ischaemic by coronary artery ligation). In the permanent ligation studies PGE₂ and PGF_2α were measured before, and 2, 10 and 30 min post-ligation. At 2 and 10 min post ligation there were no significant changes in the concentrations of either prostaglandin in blood from the essentially normal myocardium or from the acutely ischaemic myocardium. After 30 min of coronary artery ligation there was a significant increase in PGE₂ in the local coronary vein. This release of PGE₂ from the ischaemic myocardium was not related to the occurrence of cardiac dysrhythmias but may reflect the onset of changes in cellular integrity in the developing area of infarction. Despite electrocardiographic and metabolic evidence of acute myocardial ischaemia there was no increase in PGE₂ or PGF_2α values in either the coronary sinus or the local coronary vein following the release of a 3-min coronary artery occlusion. Since neither PGE₂ nor PGF_2α is released from the acutely ischaemic myocardium during the first 10 min post-ligation or during reperfusion following 3-min occlusions, it is unlikely that either of these prostaglandins is involved in the early consequence of coronary artery ligation.     

Hypoxia-induced change in prostanoids production and coronary flow in isolated rat heart

The contribution of prostanoids to the change in coronary flow induced by hypoxia was examined in Langendorff-perfused rat heart. In the coronary effluent, 5 prostanoids, i.e., prostaglandins (PGs) D2, E2, and F2 alpha, 6-keto PGF1 alpha and thromboxane (TX) B2, were quantified by GC/MS, whereas PGA2, B2, and E1 were not detected under any conditions. During hypoxia, coronary flow initially increased to 189.5 +/- 17.8% of the control, and at the same time release of all PGs, except for TXB2, increased significantly (6-keto PGF1 alpha: from 3.57 +/- 0.98 to 5.54 +/- 1.25 pmol/min.g, D2: from 1.47 +/- 0.26 to 2.22 +/- 0.26 pmol/min.g, E2: from 0.27 +/- 0.08 to 0.96 +/- 0.21 pmol/min.g, F2 alpha: from 0.23 +/- 0.09 to 0.48 +/- 0.13 pmol/min.g, TXB2: from 0.61 +/- 0.10 to 0.58 +/- 0.15 pmol/min.g). During the later phase (10-20 min) of hypoxia, coronary flow decreased without concomitant decrease in the release of PGs. The administration of indomethacin (10 microM) and aspirin (1 mM) did not affect the normoxic coronary flow. However, during the early phase of hypoxia, they significantly suppressed the increase in coronary flow. Administration of arachidonic acid (1 mg/l) increased PG release 6.4-12.5-fold and increased coronary flow to 176.1 +/- 6.5% of the control level. In the presence of arachidonic acid, there was a good correlation between the coronary flow and the amount of released vasodilative PGs (PGE2 and 6-keto PGF1 alpha), suggesting the contribution of these PGs to coronary vasoregulation. On the other hand, when hearts were made hypoxic in the presence of arachidonic acid, percentage increase in PG release was much reduced, and similarly, coronary flow was not elevated. These results indicate that the increase in coronary flow during the early phase of hypoxia is mediated, at least in part, by the increased release of vasodilative PGs.     

An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation

This study explored the potential for ovarian-derived prostaglandins (PGs) to be involved in the regulation of oocyte maturation and ovulation in zebrafish. It was demonstrated that cultured vitellogenic follicles have the capacity to produce prostaglandin E₂ (PGE₂) and PGF_2α in response to arachidonic acid (AA) in a concentration-dependent manner, and that AA stimulates the in vitro production of 17β-estradiol (E₂). The production of AA-stimulated PGF_2α was significantly reduced by treatment with the non-selective cyclooxygenase (COX) inhibitor, indomethacin (INDO). Treatment of full-grown follicles with AA did not induce oocyte maturation as assessed by germinal vesicle breakdown, but INDO significantly decreased the rate of spontaneous maturation. Using Real-Time PCR, it was shown that follicles of different developmental size classes (primary growth and pre-vitellogenic, early-vitellogenic, and mid- to full-grown vitellogenic) express enzymes that release (cytosolic phospholipase A₂ (cPLA₂); phospholipase Cγ1) or metabolize (COX-1, COX-2, and prostaglandin synthase-2) AA to PG metabolites. The expression of cPLA₂ was found to be significantly greater in full-grown follicles compared to follicles of the pre- and early-vitellogenic stages. In vivo studies demonstrated that breeding groups of zebrafish exposed to 100 μg/L INDO exhibited reduced spawning rates and clutch sizes compared with control and 1 μg/L INDO exposed fish. In other studies, it was shown that naturally spawning groups of females exhibit increased ovarian levels of PGF_2α, E₂, and 17α,20β-dihydroxy-4-pregnen-3-one (a maturation-inducing hormone in zebrafish) near the time of ovulation compared with non-breeding females. Collectively, these experiments indicate that the AA pathway in zebrafish ovaries is involved in the regulation of oocyte maturation and ovulation and a non-selective inhibitor of COX disrupts these processes.     

Effects of oestrogen on progesterone synthesis and arachidonic acid metabolism in human luteal cells

OBJECTIVE Locally produced oestrogens and prostaglandins (PGs) are implicated in the regulation of luteal lifespan in the human ovary. This study (1) assesses direct effects of these factors on progesterone synthesis in isolated luteal cells, and (2) explores interactions between luteal age and treatment with gonadotrophin or oestrogen on the metabolism of arachidonic acid (prostaglandin precursor) by steroidogenic luteal cells in vitro. DESIGN Primary monolayer cultures of human luteal cells obtained at different stages of the luteal phase were used to investigate the effect of oestradiol, catechol oestrogens (2- and 4-hydroxyoestradiol), diethylstilboestrol, PGE₂ and PGF_2x on basal and human chorionic gonadotrophin (hCG) stimulated progesterone production in vitro. The role of PGs as modulators of luteal cell function was further investigated by studying the metabolic fate of radioactively labelled arachidonic acid in hormone treated (oestradiol and hCG) and control cultures, assessed by high performance liquid chromatography. ATIENTS Corpora lutea were enucleated from nine women with regular ovulatory cycles undergoing microsurgical reversal of tubal sterilization. Granulosa cell aspirates were obtained from three patients undergoing in-vitro fertilization treatment. RESULTS PGE₂ and PGF_2α, at various concentrations did not have a consistent effect, whereas oestradiol, diethylstilboestrol (and 2-hydroxyoestradiol in early luteal cell cultures) significantly inhibited basal and hCG stimulated progesterone biosynthesis. Evidence for direct inhibition of 3β-hydroxysteroid dehydrogenase enzymic activity by oestradiol was obtained. Both major metabolic pathways of arachidonic acid (lipoxygenase and cyclo-oxygenase) were operative in steroidogenic luteal cells recovered throughout the luteal phase. The ratio of PGE₂ to PGF₂ synthesis in vitro by human luteal cells from endogenously incorporated arachidonic acid did not change significantly with corpus luteum age, with PGE₂ tending to predominate. Oestradiol treatment shifted arachidonic acid metabolism from the lipoxygenase towards the cyclo-oxygenase pathway in cells isolated from ageing corpora lutea. CONCLUSIONS Oestradiol, at relatively high concentrations, is a potent inhibitor of basal and hCG induced luteal cell steroidogenesis in vitro. No support is provided for the concept that luteolysis is mediated by local production of PGF_2α. The putative luteolytic effect of oestradiol may entail reduced metabolism of arachidonic acid to lipoxygenase derived products by luteal cells rather than direct stimulation of prostaglandin production by itself.     

Importance of gastric motility in the pathogenesis of indomethacin-induced gastric lesions in rats

Effects of indomethacin on gastric motility and secretion, and levels of endogenous prostaglandins (PGs) were investigated in rats, in attempts to elucidate the factors involved in the pathogenesis of indomethacin-induced macroscopic gastric lesions. Subcutaneous administration of indomethacin had no effect on the gastric mucosa at doses of 1 and 5 mg/kg, but induced visible lesions dose dependently at over 10 mg/kg within 4 hr. At 25 mg/kg, there were apparent nonhemorrhagic lesions within 1 hr, and these lesions became hemorrhagic with time. Acid secretion was not affected by this agent at either dose level, but pepsin or acid-induced HCO₃ ^– secretion was significantly increased or decreased, respectively, at a dose less than 5 mg/kg, which did not induce any lesion. Gastric motility, however, was dose dependently increased after administration of indomethacin, and its effect was significant at 10 mg/kg or greater. Time-course changes in the motility were in parallel with those of the lesion formation. PGE₂ and 6-keto PGF₁ levels in the corpus mucosa were reduced around 80–90% for more than 4 hr from 30 min after administration of 5 mg/kg or more of indomethacin. When all the above changes caused by indomethacin were plotted for the various doses, a significant correlation (r=0.958, P<0.01) was found between the lesion index and the changes in motility, but not in other factors, including PG levels. These results indicate that gastric motility may be an important factor in the pathogenetic mechanism of indomethacin-induced gastric lesions in rats. A deficiency of endogenous PGs may be a prerequisite for later extension of the lesions.     

Increased cardiovascular responses to prostaglandin F2alpha in spontaneously hypertensive rats: evidence for neural mediation.

Earlier studies have shown that autonomic nerve system integrity is necessary for the spontaneously hypertensive rat (SHR) to demonstrate increased vasodepressor responses to depressor prostaglandins (PG). We compared normotensive rat (NR) and SHR microvascular and blood pressure responses to PGF_2α before and after ganglionic or α-adrenergic blockade to determine whether autonomic nerve integrity is necessary for SHRs to react with increased responses to the pressor prostaglandin F_2α. Before neural blockade, PGF_2α caused mean arterial pressure, pulse pressure, and cremaster muscle arterioles (?75 μm) of young (90–130 g), prehypertensive SHRs to react statistically significantly more than matched NR. PGF_2α had no effect on NR or SHR cremaster venule diameter. After ganglionic or α-adrenergic blockade of NRs and SHRs, PGF_2α increased SHR mean arterial pressure and pulse pressure only to NR levels and increased NR arteriole constriction to the same levels observed in SHRs. This study presents further evidence of altered prostaglandin-autonomic nervous system interaction in SHRs.     

Role of prostaglandins and histamine in hyperemic response to superficial and deep gastric mucosal injury and H+ back-diffusion in cats

This study was undertaken to examine the role of prostaglandins and histamine in the hyperemic response to gastric mucosal damage followed by H⁺ back-diffusion. Cat stomachs were exposed to 2 mol/liter NaCl for 10 min followed by luminal perfusion at pH 1. Hypertonic saline caused extensive (microscopic) damage to the surface epithelium, increased gastric mucosal blood flow, and increased release of histamine, PGE₂, and 6-keto PGF_1α (prostacyclin) into portal venous blood. The effect of indomethacin and histamine blockers (H₁+H₂) on the hyperemic response to acid back-diffusion was related to the depth of the mucosal injury and the region of the stomach. In the corpus, indomethacin enhanced mucosal injury. In areas with superficial damage, the hyperemia was inhibited by indomethacin and antihistamines and eliminated by the combination of both. In corpus areas with indomethacin-induced deep lesions, the blood flow was very high, and this hyperemia was partly inhibited by antihistamines. In the antrum the hyperemic response was reduced by antihistamines. Indomethacin increased the release of histamine into the portal venous blood (baseline recordings) and reduced basal gastric mucosal blood flow.     

Comparisons of prostaglandin vasoactive effects and interactions in the in vivo microcirculation of the rat urinary bladder

A combination of techniques for in vivo transillumination, topical application of vasoactive agents, and direct microscopic observation of microcirculatory responses was utilized to evaluate the vasomotor actions of prostaglandins (PGs) E₁, E₂, F_1α, F_2α, A₁, and A₂ on rat urinary bladder arterioles and venules. The effects of PGE₁ and histamine (HIS) on arteriolar responsiveness to norepinephrine (NE), serotonin (5-HT), and PGF_2α were measured. Histochemical studies were completed to determine the primary site of prostaglandin (PG) metabolic deactivation in the urinary bladder. Arteriolar dilatation occurred with HIS, PGE₁, PGE₂, PGA₁, PGA₂, and PGF_1α, all of which (with the exception of HIS) demonstrated significant dose-related responses. Overall, PGE₁ and PGE₂ were of greatest potency. Significant dose-related arteriolar constriction occurred with NE > PGF_2α > 5-HT (in order of decreasing potency). HIS, PGE₁, PGE₂, and PGA₁ produced significant venular dilatation; PGE₁ and HIS were dose related. Only NE resulted in significant venoconstriction. Arteriolar responsiveness to NE and PGF_2α decreased after pretreatment with PGE₁ but was unchanged by HIS pretreatment, whereas application of 5-HT following pretreatment with PGE₁ or HIS produced equivalent levels of arteriolar constriction. The primary site of deactivation of PGE₁ was histochemically localized to bundles of smooth muscle fibers in the muscular coat of the rat urinary bladder wall.     

Urinary Excretion of Prostaglandin F2α and 6-Keto-Prostaglandin F1αa during Volume Expansion in Patients with Glomerulonephritis

ABSTRACT. Thirteen patients with active IgA glomerulonephritis (IgA GN), ten patients with a history of Henoch-Schönlein glomerulonephritis (HS GN) and nine healthy controls were studied during hydropenia (HP) and 3% volume expansion (VE) with isotonic saline. Clearance of inulin and para-aminohippurate, urinary excretion of Na, immunoreactive prostaglandin F_2α (PGF_2α) and 6-keto-prostaglandin F_1α (6-keto-PGF_1α) were determined. The patients with a history of HS GN had normal blood pressure and renal function. As in the controls, the urinary excretion of PGF_2α decreased and the excretion of 6-keto-PGF_1α increased during VE. In the patients with IgA GN the glomerular filtration rate (GFR) was normal, markedly reduced and supernormal. Five patients had hypertension and an increased N A excretion in relation to the GFR during VE. As a group, the patients with IgA GN increased their urinary excretion of 6-keto-PGF_1α during VE, while the excretion of PGF_2α did not change. In relation to the GFR, the urinary excretion of PGF_2α, and 6-keto-PGF_1α was markedly increased in two patients with low GFR, which implies that these substances play a role in advanced renal disease. VE had little effect on PG excretion in these patients. In the hypertensive patients the urinary excretion of PGF_2α and 6-keto-PGF_1α was the same as in those with normal blood pressure. PGs are therefore not likely to mediate the increased natriuretic response to VE in hypertension.     

Effect of the ultrashort-acting β-blocker Brevibloc on free-radical-mediated injuries during the early reperfusion state

Summary The left descending coronary artery (LAD) was ligated for 45 min or 90 min followed by 1-h reperfusion. During experiments the animals in Group I (15 dogs) received saline infusion, in Group II (20 dogs) they received the ultrashort-acting -blocker Brevibloc (esmolol HCl). The marker of lipid peroxidation the malondialdehyde (MDH) as well as endogen scavengers, the glutathione (GSH), and superoxide dismutase (SOD) were measured in the heart tissue homogenates. In blood and heart tissue samples the 6-keto-prostaglandin F1 . (PGF1 ) and thromboxane B2 (TXB2) were determined. Biochemical measurements revealed that esmolol HCl has beneficial effect on the free-radical-meduated-damage reducing the MDA content in the ischemic area. In Group I the value of MDA after 90 min of LAD ligature was 138 ± 5.6 %, in Group II the elevation was only 107.4 ± 3.2 %. After treatment with Brevibloc the GSH content of ischemic-reperfused areas decreased slightly (81.75 ± 3.5 % of the normal value), moreover, in Group I the depletion of GSH was considerable (64.5 ± 4.2 %). Coronary reperfusion caused the release of eicosanoids in both groups, mainly in the first 10 min. The highest value of thromboxane in blood samples could be measured in Group I after 90 min of LAD ligature (24.8 ± 3.6 pmol/ml; the normal value 8–12 pmol/ml). In Group II during the same period of experiments the TXB2 in the blood was 14 ± 3.7 pmol/ml. In heart tissue samples the amount of endoperoxides increased in ischemic and non-ischemic areas of Group I and II. Nevertheless, the calculated ratio of PGF1 and TXB2 was near to the normal after Brevibloc treatment (0.85–0.9; the normal values were 1–1.2). These results indicate that esmolol HCl can modulate both the free-radical-mediated reaction and arachidonic acid metabolism.     

Eicosanoid synthesis in children with cholestatic disease

Summary The possibility of malabsorption of triglycerides contained in the diets of children with cholestasis suggests a deficiency of essential fatty acids and, therefore, probable effects on eicosanoid metabolism. Children with either biliary atresia (BA) or syndromatic paucity of interlobular bile ducts (PILBD) were evaluated as to plasma and platelet total lipid fatty acid composition and synthesis of prostaglandins (PG) E₁, PGE₂, PGI₂, PGF₂, and thromboxane (TXB₂) by whole blood incubated at 37°C for 10 min. In both diseases linoleate deficiency was present as shown by low 18:2 fatty acids in plasma lipids. The children with BA had lower plasma arachidonate than controls but normal eicosanoid synthesis except for excess PGI₂. Those with PILBD had low platelet arachidonate and were severely deficient in TXB₂ synthesis (<10% of controls). Three children with PILBD were fed a supplement of structured triglyceride (Captex 810) intended to provide as much as 10% of energy as linoleate for 2–3 months. Results for these three cases suggested that insufficient linoleate was absorbed to increase plasma linoleate and differences in eicosanoids could not be attributed to linoleate supplementation.Journal Paper No. J-12248 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project Number 2728.     

Proposed signaling role of arachidonic acid in human myometrium

The objective of this study was to test the hypothesis that, in human myometrial cells (HMC), PGF_2α and oxytocin promote the release of arachidonic acid (AA) which, in turn, acts to mobilize intracellular Ca²⁺. Primary monolayer cultures of HMC were labeled with [³H]arachidonic acid ([³H]AA) to isotopic equilibrium before exposure to PGF_2α or oxytocin. Radiolabeled phospholipids were separated on thin layer chromatography and quantitated by scintillation counting. Prostanoids were analyzed by high performance liquid chromatography. Calcium release was quantitated in digitonin-permeabilized myocytes preloaded with ⁴⁵Ca, in the presence of ATP and ruthenium red. PGF_2α (10⁻⁷ M) caused a rapid (peaking at 2 min), and significant (P < 0.01) increase in [³H]AA release that was derived selectively from phosphatidylethanolamine (PE), indicative of phospholipase A₂ activation. Oxytocin caused a rapid (30 s) and significant increase in diacylglycerol, concomitant with a drop in phosphoinositides, as well as an increase in [³H]AA and a fall in PE and phosphatidylcholine. Exogenous AA caused a rapid and dose-related efflux of⁴⁵Ca²⁺, which was not inhibited by blockers of AA metabolism, or by heparin that abolished inositol 1,4,5-trisphosphate-induced ⁴⁵Ca²⁺ release. It is concluded that PGF_2α and oxytocin promote, by different mechanisms, the release of AA, which in turn may amplify their action by enhancing Ca²⁺ mobilization from the sarcoplasmic reticulum, thereby fulfilling the role of intracellular signaling molecule in human myometrium.     

The mechanism of action of leukotrienes A4, C4 and D4 on human lung parenchymain vitro

Indomethacin (20μg.ml⁻¹), a cyclooxygenase inhibitor, and OKY-1581 (50 ug.ml⁻¹), a thromboxane synthetase inhibitor, did not affect contractions of the superfused human lung parenchymal strips induced by histamine, leukotriene C₄ (LTC₄) and leukotriene D₄ (LTD₄). Indomethacin but not OKY-1581 reduced by 50% the myotropic activity of leukotriene A₄ (LTA₄) on the human lung strips. Injections of LTD₄ (100 ng; 0.2 n mole) in the circulation of perfused specimens of human lung did not stimulate the release of prostaglandins (PGs) and thromboxanes (TXs) whereas they produced a large release of these icosanoids from perfused guinea-pig lungs. Perfused human lung specimens almost completely inactivated intraarterial injections of PGE₂ (50 ng) and released PGs and TXs upon mechanical stimulation. It is concluded that the actions of leukotrienes C₄ and D₄ in human lung (parenchymal strips and perfused specimens) are not mediated by the release of PGs and TXs.