Increased PGE2 Synthesis Research Articles

The role of calcium in the stimulation of prostaglandin synthesis by vasopressin in rabbit renal-medullary interstitial cells in tissue culture.

The role of Ca2+ in the stimulation of prostaglandin (PG) biosynthesis by vasopressin was investigated in rabbit renal-medullary interstitial cells in tissue culture. A decrease in extracellular Ca2+ to less than 25 microM did not affect basal PGE2 production, but inhibited PGE2 synthesis stimulated by vasopressin, angiotensin and the Ca2+ ionophore A23187 by 55, 65 and 95% respectively. The study of vasopressin-stimulated PGE2 synthesis in the absence of extracellular Ca2+ demonstrated that: (a) hormone-sensitive phospholipase activity was inhibited as measured by [3H]arachidonic acid release; (b) the maximal rate of vasopressin-stimulated activity was decreased without a change in the vasopressin concentration that evoked half-maximal stimulation of PGE2 synthesis; and (c) the Ca2+-channel blocker verapamil and the Ca2+-calmodulin antagonist trifluoperazine mimicked the inhibitory effects of removing extracellular Ca2+. These agents had no effect in the absence of Ca2+. In contrast with their effects on vasopressin action, neither the removal of extracellular Ca2+ nor the addition of verapamil altered the ability of hyperosmotic mannitol to increase PGE2 synthesis. These data are consistent with the hypothesis that a component of vasopressin-stimulated PGE2 biosynthesis involves the influx of extracellular Ca2+, followed by the activation of Ca2+-calmodulin-stimulated phospholipase(s).

Effect of platelet-activating factor and serum-treated zymosan on prostaglandin E2 synthesis, arachidonic acid release, and contraction of cultured rat mesangial cells.

The interaction of inflammatory cells and glomerular prostaglandins (PG) may be important during glomerulonephritis. We therefore examined the influence of platelet-activating factor (PAF), (a mediator of inflammation released from leukocytes) and of phagocytosis of zymosan on arachidonic acid metabolism and on cell contractility in rat glomerular mesangial cells in culture. PAF increased PGE2 synthesis (determined by radioimmunoassay) within minutes (threshold: 10(-10)M; maximal effect: 10(-7)M). Serum-treated zymosan also stimulated PGE2, but with a slower onset. In cells prelabeled with [14C]arachidonic acid both PAF and serum-treated zymosan released 14C from phospholipids and increased free [14C]arachidonate. The ratio of 14C-release to PGE2 was, however, different with PAF and serum-treated zymosan, indicating different phospholipid pools. Under phase-contrast microscopy, PAF caused contraction of mesangial cells with a dose-response and time-course parallel to that for PGE2 synthesis. Serum-treated zymosan caused no contraction. The PAF-induced contraction was enhanced by PG synthesis inhibition and was attenuated by addition of PGE2, indicating a feedback mechanism. The mesangial contraction by PAF may be important in favoring deposition of immune complexes, while the PGE2 synthesis stimulated by PAF and by phagocytosis of zymosan may counteract the deleterious effects of PAF during induction of glomerulonephritis.

Prostaglandin synthesis by rat glomerular mesangial cells in culture. Effects of angiotensin II and arginine vasopressin.

Arginine vasopressin (AVP) and angiotensin II (ANG II) reduce the glomerular filtration rate and ultrafiltration coefficient. Vasodilatory prostaglandins (PG) antagonize these effects. AVP and ANG II also cause mesangial cell contraction. Therefore, possible PG stimulation by these peptides and two vasopressin analogues was studied in cultured rat glomerular mesangial cells. The effect of altered calcium availability on PG production was also studied. Glomeruli from 75-100-g Sprague-Dawley rats were cultured in supplemented nutrient media for 28 d and experiments were performed on the first passage. Mesangial cell morphology was confirmed by electron microscopy. Cells produced PGE2 much greater than PGF2 alpha greater than 6-keto-PGF1 alpha greater than thromboxane B2 when incubated with the divalent cation ionophore, A23187, or arachidonic acid (C20:4). ANG II and AVP selectively stimulated PGE2 at threshold concentrations of 10 nM ANG II and 100 pM of AVP. The effects of the antidiuretic analogue 1-desamino-8-D-arginine vasopressin (dDAVP) and the antipressor analogue [1-(beta-mercapto-beta beta-cyclopentamethylene propionic acid)-4-valine, 8-D-arginine]-vasopressin (d[CH2]5VDAVP), were studied. Neither compound stimulated PGE2 and preincubation with d(CH2)5VDAVP abolished, and dDAVP blunted, AVP-enhanced PGE2 production. Incubation in verapamil, nifedipine, or zero calcium media blocked peptide-stimulated PGE2 production. Increasing extracellular calcium or adding A23187 increased PGE2 synthesis. Selective stimulation of PGE2 by ANG II or AVP in mesangial cells suggests a hormone-sensitive phospholipase and a coupled cyclooxygenase capable of synthesizing only PGE2. Since neither vasopressin analogue stimulated PGE2, but both blocked AVP-enhanced PGE2 production, we conclude that these cells respond to the pressor activity of AVP. This is a calcium-dependent process. Selective stimulation of PGE2 by ANG II and AVP may modulate their contractile effects on the glomerulus.

Renal disease profoundly alters cortical interstitial cell function

Interstitial cells were cultured from explants of the unilaterally hydronephrotic, contralateral, and normal kidneys. Two types of cells were identified in culture, macrophages, and cells which were tentatively identified as fibroblasts. Cells grew at a significantly faster rate in hydronephrotic compared to contralateral or normal kidneys. Cells from the hydronephrotic kidney increased prostaglandin (PG)E2 production in response to bradykinin. Cells from contralateral and normal renal cortex did not increase PGE2 production in response to bradykinin. These results indicate hydronephrosis induces functional changes in interstitial cells cultured from the cortex of hydronephrotic compared to contralateral and normal kidneys. The induction of increased PGE2 synthesis and bradykinin responsiveness in hydronephrotic cortex could be related to the exaggerated prostaglandin synthesis known to occur in hydronephrotic cortex. In hydronephrosis, cortical interstitial cells elaborate increased amounts of substances such as prostaglandins which have the capacity to modulate important parameters of renal function.

Renin release selectively stimulated by prostaglandin I2 in isolated rat glomeruli

Renal glomeruli were isolated from rat kidneys using a passive mechanical sieving technique. Glomerular microsomal fraction, glomerular homogenate, or intact glomeruli were incubated with [1-14C]arachidonic acid, and the profile of prostaglandin (PG) synthesis was determined by thin-layer chromatography. The three incubation systems produced 15.3, 20.8, and 40.4% 6-keto-PGF1 alpha; 19.1, 23.5, and 15.3 PGF2 alpha; 5.7, 9.1, and 3.9% thromboxane (TX) B2; 36.0, 35.1, and 37.0% PGE2; and 23.9, 11.3, and 3.4% PGD2, respectively. Glomeruli were placed in suspension within glass chambers and superfused with Krebs solution. Superfusion with 1.6 x 10(-4) M arachidonic acid stimulated a significant release of renin from glomeruli, whereas 2.7 x 10(-6) M PGE1, PGE2, PGF2 alpha, TXB2, PGD2, or a stable analog of PGH2 had no effect on renin. When the rapid breakdown of PGI2 was counteracted by either increasing the concentration to 1.7 x 10(-4) M or stabilizing in Krebs at pH 9.4, it stimulated a significant increase in renin release. Reducing the arachidonic acid concentration to 1.6 x 10(-5) M eliminated both renin release and PGI2 synthesis, while increased PGE2 synthesis persisted. Finally, using an inhibitor of PGI2 synthesis, azo analog 1 (2.8 x 10(-6) M), 6-keto-PGF1 alpha produced in response to arachidonic acid was eliminated, as was the concurrent release of renin, but PGE2 synthesis was not affected. These results suggest that the mechanism of direct interaction between renal PG and renin in isolated glomeruli is selectively due to the action of PGI2.

Mononuclear cell modulation of fibroblast procoagulant activity.

The release of procoagulant material by connective tissue cells as a sequel to cell injury can initiate blood coagulation and may thus play a role in he pathogenesis of inflammatory lesions. Human foreskin fibroblasts were shown to synthesize high levels of the procoagulant TF in vitro. Generation of TF by fibroblasts was inhibited by addition of supernatants of PHA-stimulated human mononuclear cells to fibroblast cultures. The inhibition was independent of supernatant effects on cellular proliferation and was accompanied by up to a 20-fold increases in PGE2 synthesis in the fibroblast cultures. The inhibition of TF generation by MC-SNs was reversed by adding indomethacin to the fibroblast cultures, suggesting that mononuclear cells suppress fibroblast TF generation by stimulation of endogenous fibroblast synthesis of prostaglandin. Regulation of fibroblast PCA by products of immune cells may be important in the pathogenesis of inflammatory lesions.

Changes in maternal serum aldosterone, potassium and prolactin levels during beta-receptor agonist treatment in third trimester pregnancies.

Beta-receptor agonist (terbutalin or isoxsuprin) administration to pregnant women either because of premature labor (therapy group; T; n = 8) or as prophylactic treatment (prophylaxis group; p; n = 8) resulted in a marked drop in serum potassium (p less than 0.001) during the first two hours of infusion in all patients. In five diabetic women in the P group the prolactin was significantly decreased (P less than 0.01) as was serum aldosterone levels (p less than 0.01). These changes were not observed in the T group. The two groups of pregnant women responded with a significant increase in free fatty acids (FFA) and glucose but the magnitude and the time coarse differed. Thus in T women, FFA reached a peak after 30-60 minutes into treatment and then returned to baseline levels. A closer analysis revealed that this pattern was only obtained in patients receiving terbutalin. Among women given prophylactic treatment with terbutalin, a continuous increase in FFA was noted over the initial two hours (p less than 0.001). The increase in serum glucose was continuous in the two patient groups (p less than 0.001). It is suggested that beta-receptor agonists in diabetic women induces a dopaminergic type of response since serum prolactin levels but not TSH concentrations were affected. The possibility that an increased PGE2 synthesis at the expense of PGF2 alpha might mediate this effect of beta-receptor agonists in discussed. It is also suggested that an increased prostaglandin synthesis might interfere with aldosterone secretion. The possibility that falling serum potassium levels may activate dopaminergic systems via PGE2 synthesis is also emphasized.

Regional aortic differences in atherosclerosis susceptibility. Relationship to lipid concentration and prostaglandin biosynthesis.

In spontaneously atherosclerosis-susceptible White Carneau pigeons intimal cushions are noted consistently at the coeliac branch of aorta at birth. While these cushions do not progress into atherosclerotic lesions, the area across from the cushion (so called "lesion area") develop a classic atherosclerotic plaque by three years of age. In order to explain this regional aortic susceptibility to atherosclerosis, cholesterol and cholesteryl ester concentrations and prostaglandin biosynthesis in the two aortic regions were examined. It was found that the concentration of free and esterified cholesterol was higher in the intimal cushion area. Examination of the formation of various prostaglandins from C14-arachidonic acid indicates a striking increase in PGE2 synthesis in the lesion area with no difference in the formation of 6-keto PGF1 alpha (stable product of PGI2). These studies suggest that one of the earliest changes noted in the "lesion area" that differs from the intimal cushion is the enhanced formation of PGE2.

Interaction of vasopressin and prostaglandins in the toad urinary bladder.

Prostaglandins are important modulators of the action of vasopressin. Others researchers have proposed that vasopressin stimulates prostaglandin synthesis, completing a negative feedback loop and thereby limiting vasopressin's antidiuretic effect. We have re-examined this question, using specific radioimmunoassay and thin-layer radiochromatography to determine prostaglandin synthesis by the toad bladder. Under control conditions, the bladder synthesizes prostaglandin (PG)E2 and thromboxane (TX)B2. There was no evidence for synthesis of PGE1 or PGF2 alpha by radioimmunoassay, or of other prostaglandins by radiochromatography. Furthermore, there was no evidence for metabolism of PGE2 by the bladder. Using a variety of protocols, in isolated epithelial cells as well as intact bladders, we were unable to detect any significant increase in PGE2 or TXB2 synthesis after stimulation with arginine vasopressin (AVP) or deamino-8-D-arginine vasopressin (DDAVP). Arachidonic acid, the specific precursor of prostaglandin synthesis, increased PGE2 synthesis twofold, and significantly inhibited AVP- and DDAVP-stimulated water flow by 60 and 75%, respectively. Naproxen and acetaminophen inhibited prostaglandin synthesis and enhanced water flow in response to AVP and DDAVP (44-54%). Our findings indicate that the toad bladder produces tow prostaglandins, PGE2 and TXB2, and that vasopressin does not alter their rate of synthesis. Because agents such as acetaminophen and naproxen inhibit prostaglandin synthesis and enhance vasopressin- and DDAVP-stimulated water flow, we suggest that it is the inhibitory effect of these agents on the hormone-independent rate of prostaglandin synthesis that is responsible for their enhancement of water flow. Furthermore, because AVP appears to increase prostaglandin synthesis by the intact kidney, we suggest that cells other than those of the collecting tubule are responsible for the increased prostaglandin production.

The metabolism of dihomo‐γ‐linolenic acid in man

Orally administered dihomo-gamma-linolenic acid (DHLA) is well absorbed in man; it appears in blood after ca. 4 hr first as triglyceride ester and later as phospholipid. After sustained-dosing, DHLA penetrated membrane pools and all phospholipid components but, depending on the dosage, reached a metabolic equilibrium in 4-16 days. Intact platelets do not accumulate arachidonate following DHLA administration, and species differences occur in the capacity of animals to metabolize DHLA to arachidonic acid (AA). The rat appears to be unusual in having a very active hepatic delta5-desaturase enzyme system. Potentially antithrombotic changes in platelet function which followed the administration of DHLA to man were accompanied by a significant increase in the capacity of platelets to synthesize PGE1. Concomitant increases in PGE2 synthesis do not apparently result from an increased production of AA and suggest that DHLA, or a DHLA metabolite, interferes with the metabolism of AA. Effects on thromboxane and prostacyclin synthesis are being studied.