Atriopeptins decrease resting and hormone-elevated cytosolic Ca in cultured mesangial cells

The purpose of this work was to investigate the effects of atrial peptides on the cytosolic Ca levels of cultured, adherent, mesangial cells. Resting Ca levels, measured by the use of fura-2, were dose-dependently decreased by up to 30%, by atriopeptin 23. The half-maximal effect was elicited by approximately 30 pM atriopeptin-23. Atriopeptin 21 also decreased resting Ca levels by up to 30%, but this peptide was approximately 30-fold less potent than atriopeptin 23. Atriopeptin 23 (100 nM) inhibited both the Ca transient and the peak Ca value elicited by 1 nM vasopressin, but the atrial peptide had no significant effect on the Ca transient elicited by higher vasopressin concentrations. At concentrations lower than 100 nM, atriopeptin 23 had no effect on the vasopressin-induced Ca transient. Atriopeptin 23 also decreased the Ca transient and the peak Ca value elicited by 100 nM angiotensin II. Similar to vasopressin, the angiotensin II-induced Ca transient was inhibited by 100 nM but not lower concentrations of atriopeptin 23. In contrast to the effect of atriopeptin 23, atriopeptin 21 (100 nM) had no effect on the Ca transient elicited by vasopressin. These results demonstrate that atriopeptins function as modulators of resting and, under certain conditions, of hormone-increased Ca levels in cultured mesangial cells.

Effects of bradykinin and angiotensin II on intracellular Ca2+ dynamics in endothelial cells

The purpose of this study was to investigate the effects of angiotensin II and bradykinin on intracellular Ca2+ dynamics in cultured endothelial cells. We used the "second-generation" fluorescent Ca2+ indicator fura-2, in conjunction with dual-wavelength fluorescence spectroscopy, in cultured adherent pulmonary arterial endothelial cells. Angiotensin II (up to 2 microM) had no consistent effect on intracellular Ca2+ levels. In contrast, bradykinin (10 nM) elicited a transient increase of cytosolic free Ca2+, from the resting value of 37 +/- 5 to 647 +/- 123 nM, followed by a decline to a steady-state value of 113 +/- 14 nM, which was significantly higher than the resting Ca2+ levels. Bradykinin's Ca-stimulatory effect was dose dependent, having a half-maximally effective concentration of approximately 1 nM and a maximally effective concentration of 10 nM. A B1-receptor agonist, Des-Arg9-bradykinin, was much less effective than bradykinin as modulator of cytosolic Ca2+. Moreover, a B1-receptor antagonist, Des-Arg9, [Leu8]-bradykinin, did not significantly affect the increase of cytosolic Ca2+ elicited by bradykinin. On the other hand, the bradykinin-elicited increase of Ca2+ was almost completely inhibited by a novel B2-receptor antagonist, D-Arg-[Hyp3, Thi5,8, D-Phe7]-bradykinin. Bradykinin increased cytosolic free Ca2+ levels in cells maintained in Ca2+-deficient extracellular medium, suggesting that the peptide mobilized Ca2+ from intracellular stores. However, the absence of extra-cellular Ca2+ resulted in an 80-90% attenuation of the transient Ca2+ response, whereas the posttransient steady-state response was completely absent. These findings are consistent with the notion that the bradykinin-elicited transient Ca2+ response is dependent on both extra- and intracellular Ca2+ and that the posttransient steady-state response is entirely dependent on extracellular Ca2+. Endothelial cells were responsive to a second dose of bradykinin after a 10-min interim period of incubation in the absence of the peptide hormone. The absence of extracellular Ca2+ during the interim period, or the pretreatment of cells with ionomycin in the absence of extracellular Ca2+, prevented the response of the cells to a second dose of bradykinin. Bradykinin- or ionomycin-desensitized cells could be resensitized by a brief incubation period in Ca2+-replete medium. The results are consistent with the notions that cellular resensitization requires the replenishment of intracellular Ca2+ and that bradykinin, but not angiotensin II, modulates intracellular Ca2+ dynamics in endothelial cells by interacting with a B2-type receptor.

Neuropeptide Y enhances the release of luteinizing hormone (LH) induced by LH-releasing hormone

Depending upon the steroid hormonal milieu, centrally administered neuropeptide Y (NPY) exerts differential effects on the release of LH. Ovarian hormones also effect the concentrations of NPY in hypothalamic nuclei, and some of the changes are similar to those caused by LHRH. The present studies tested whether NPY acts directly on the pituitary gland, either alone or in combination with LHRH, to modify LH secretion. Hemipituitary fragments obtained from ovariectomized rats were incubated in medium 199, and the in vitro effects on LH release of LHRH, NPY, or the two peptides together were assessed. As expected, LHRH (10(-9)-10(-7) M) produced a dose-dependent release of LH, whereas NPY alone had a lesser stimulatory effect at concentrations of 10(-7) or 10(-6) M. On the other hand, 10(-6) M NPY significantly enhanced LH release in response to 10(-9) M LHRH. A potentiation by NPY of the LHRH-induced LH response was observed in an anterior pituitary cell culture system. Cells from the pituitaries of ovariectomized rats were dispersed and cultured for 3 days in medium 199 with BSA, gentamicin, horse serum, and fetal calf serum. During a 3-h incubation, NPY alone (10(-9)-10(-7) M) failed to affect LH release, but significantly potentiated the release induced by 10(-9) or 10(-8) M LHRH. These findings are in accord with the hypothesis that hypothalamic NPY neurons may participate in the regulation of LH secretion in the rat and indicate that one of the mechanisms of its action may be to increase the pituitary LH response to LHRH.

Effects of vasoactive peptides on cytosolic calcium in cultured mesangial cells

We have used the "second generation" Ca indicator, fura-2, to measure cytosolic free Ca concentrations in superfused cultures of adherent primary renal mesangial cells. The basal cytosolic free Ca concentration in these cells was found to be 93 +/- 5 nM (n = 35). The Ca ionophore ionomycin (0.1 microM) increased cytosolic Ca levels to a peak value of fourfold above basal, followed by a decline to a steadily maintained concentration of twofold above basal. Two vasoactive peptide hormones, arginine vasopressin and angiotensin II, at maximally effective concentrations, transiently increased cytosolic free Ca levels to peak values of three- and sixfold, respectively, above basal levels. The angiotensin II-evoked increase declined to near basal values before rising again to a value of 1.5- to 2-fold above basal. Cells treated with vasopressin did not have a significant secondary increase of Ca above a small, time-dependent, spontaneous increase. Mesangial cells demonstrated tachyphylaxis to both peptides. However, cross-tachyphylaxis was not observed. Treatment of cells with angiotensin II in ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid-supplemented Ca-deficient medium, or with the Ca channel blockers nifedipine or verapamil, did not eliminate the transient phase of cytosolic Ca metabolism. In contrast, the Ca channel blockers completely inhibited the second sustained Ca response to angiotensin II. These results indicate that angiotensin II and vasopressin mobilize intracellular Ca in cultured adherent mesangial cells. Angiotensin II, but not vasopressin, also appears to increase cytosolic Ca by influx of extracellular Ca through specific channels.

Atriopeptin II decreases cytosolic free Ca in cultured vascular smooth muscle cells

We have examined the hypothesis that atriopeptin II decreases cytosolic free Ca concentrations in cultured aortic smooth muscle cells. Ca levels were measured, using the Ca indicator fura-2, by dual wavelength fluorescence spectroscopy, in superfused primary cultures of smooth muscle cells. Basal Ca values were between 40 and 100 nM. Angiotensin II (10 nM) elicited a transient threefold increase in Ca, followed by return to a sustained Ca level that was 30% higher than the original basal values. Atriopeptin II dose-dependently decreased basal Ca concentrations by 10-40%. Atriopeptin II did not have a significant effect on the transient Ca response elicited by 10 nM angiotensin II, but the atrial peptide dose-dependently decreased the sustained increase that followed the transient response. Atriopeptin II also decreased cytosolic Ca levels that were elevated by 50 mM KCl. These results support the hypothesis that atriopeptins relax vascular smooth muscle by decreasing basal and vasoconstrictor-elevated cytosolic free Ca levels and that these peptides may function as endogenous antagonists of Ca-mediated processes.

Increase of cyclic AMP concentrations in cultured vascular smooth muscle cells by vasoactive peptide hormones. Role of endogenous prostaglandins

We have evaluated the hypothesis that vasoactive hormones increase cellular cyclic AMP (cAMP) levels in cultured vascular smooth muscle cells from rat mesenteric arteries by stimulating endogenous prostaglandin (PG) synthesis. Vasopressin and angiotensin II, which were shown previously to provoke the synthesis of PGs in cultured vascular smooth muscle cells, increased cellular cAMP concentrations by about 2-fold, whereas a peptide analog of vasopressin, 1-desamino-8-D-arginine vasopressin, mostly lacking vasopressin's ability to elicit PG synthesis, was ineffective. Two other chemically dissimilar effectors that provoked the synthesis of PGs in cultured vascular smooth muscle cells, namely arachidonate and ionophore A23187, also increased cellular cAMP levels. The increase of cAMP by vasopressin and angiotensin II was transient, reaching a maximum at 1 to 2 min of incubation, followed by a decline to basal levels. Acetylsalicylic acid, a specific inhibitor of PG synthesis, completely prevented vasopressin- and arachidonate-evoked increases of cAMP but did not affect basal cAMP concentrations. Exogenous prostacyclin and prostaglandin E2 dose-dependently increased cAMP concentrations although prostacyclin was more effective than prostaglandin E2. The ability of exogenous prostacyclin to evoke cAMP increases was not inhibited by acetylsalicylic acid. The results support the hypothesis that the stimulation of endogenous PG synthesis by vasoactive hormones in turn modulates cellular cAMP levels in cultured vascular smooth muscle cells from rat mesenteric arteries.

Treatment with dexamethasone increases glomerular prostaglandin synthesis in rats

To determine whether chronic glucocorticoid excess influences the metabolism of arachidonic acid to prostaglandins (PGs) in the renal cortex, the authors investigated the effects of dexamethasone treatment (2.5 mg/kg/week) on the metabolism of arachidonic acid by renal cortex homogenates and microsomes and by isolated glomeruli, and on the release of immunoreactive prostanoids from isolated glomeruli incubated for 30 min in buffered salt solution at 37 degrees C. Glomeruli from dexamethasone-treated rats released, during basal incubation conditions, about twice (P less than .01) as much PGE2 and PGF2 alpha as did glomeruli from vehicle-treated rats. During incubation with arachidonic acid (33 microM) or calcium ionophore, A23187 (2.0 micrograms/ml), the release of PGE2 and PGF2 alpha from glomeruli of rats receiving dexamethasone also exceeded (P less than .01) the release from glomeruli of control rats. The rate of conversion of [1-14C]arachidonic acid to PGE2 and PGF2 alpha and to less polar metabolites having the chromatographic mobility of 5-hydroxyeicosatetraenoic acid and 12-hydroxyeicosatetraenoic acid, by isolated glomeruli and by renal cortex homogenates and microsomes from dexamethasone-treated rats, was higher (P less than .01) than the conversion by glomeruli and renal cortex homogenates and microsomes from control rats. The metabolism of arachidonic acid to the nonpolar metabolite(s) was not inhibited by indomethacin (10 microM), suggesting that it is not catalyzed by cyclooxygenase. The authors conclude that chronic dexamethasone treatment increases the release of glomerular PGE2 and PGF2 alpha and the metabolic transformation of arachidonic acid by glomeruli and by renal cortex homogenates and microsomes via both cyclooxygenase and noncyclooxygenase pathways.

Relationship between cellular calcium and prostaglandin synthesis in cultured vascular smooth muscle cells

We have investigated the effects of extracellular and intracellular Ca deficits and of pharmacologic agents thought to inhibit Ca influx or intracellular Ca mobilization on vasopressin-evoked changes of cytosolic Ca2+ levels and PG synthesis in cultured rat mesenteric arterial vascular smooth muscle cells. Vasopressin rapidly increased cytosolic Ca2+ as well as PG synthesis. The increase of cytosolic Ca2+ and the rate of PG synthesis were both maximal within the first minute of incubation. An extracellular Ca deficit of short duration partially inhibited both vasopressin-evoked PG synthesis and the increase of cytosolic Ca2+ by 40 to 60%. Two procedures which deplete cells of some of their intracellular Ca, namely a 30 min incubation in EGTA-supplemented, Ca-lacking media, or a 1 min incubation with ionophore A23187 in Ca-deficient media, decreased PG synthesis by 65% to 100%. The addition of extracellular Ca to Ca-depleted cells restored the ability of vasopressin to stimulate PG synthesis. Two Ca channel antagonists, nifedipine or cinnarizine, had no effect on either vasopressin-evoked PG synthesis or increased cytosolic Ca2+, whereas TMB-8 (10 microM), a putative inhibitor of intracellular Ca mobilization, decreased PG synthesis by 75% by inhibiting acylhydrolase as well as cyclo-oxygenase activities, but had no effect on basal or vasopressin-evoked increase of cytosolic Ca2+, documenting that its inhibitory effect was not a consequence of decreased cytosolic Ca2+. These results demonstrate that decreased cellular Ca levels are associated with decreased cytosolic Ca2+ levels and PG synthesis, and support the hypothesis of a link between, on the one hand, cellular Ca and/or cytosolic Ca2+ and on the other hand, PG synthesis.

Bradykinin-evoked modulation of cytosolic Ca2+ concentrations in cultured renal epithelial (MDCK) cells

We have investigated the effect of bradykinin on cytosolic Ca2+ concentrations of renal MDCK cells cultured as monolayers. Bradykinin rapidly (within 5 to 20 s) increased cytosolic Ca2+ concentrations, measured by using the fluorescent indicator quin-2, from the basal value of 103 nM to a maximal value of 578 nM at about 10(-8) M bradykinin. The increase of Ca2+ was transient, returning to baseline within 1.5 to 2 min. The transient response appeared to be due to cell desensitization rather than peptide degradation. Previously desensitized cells could be resensitized after a 10 min incubation in the absence of bradykinin. The removal of extracellular Ca2+ or the addition of verapamil did not have a major effect on the maximal bradykinin-evoked changes of Ca2+, suggesting that Ca2+ released from intracellular stores plays a pivotal role in this process. Bradykinin-evoked Ca2+ metabolism may play an important role as modulator of the cellular functions of MDCK cells.

Stimulation of prostacyclin synthesis by thromboxane A2-like prostaglandin endoperoxide analogues in cultured vascular smooth muscle cells

In this study, the ability of two chemically stable thromboxane A2-like PG endoperoxide analogues, 15S-hydroxy-9 alpha,11 alpha-(epoxymethano)-prosta-5Z,13E-dienoic acid and 15S-hydroxy-11 alpha,9 alpha-(epoxymethano)-prosta-5Z,13E-dienoic acid, to stimulate PGI2 synthesis by cultured vascular smooth muscle cells isolated from rat superior mesenteric arteries was evaluated. The aforementioned analogues, at concentrations of 0.1 to 10 micrograms/ml, stimulated PGI2 synthesis by 1.5 to 3 fold over basal synthesis. Evoked PGI2 synthesis was essentially over within 2 to 3 min of incubation, similar to previous findings made in vascular smooth muscle cells incubated with peptide hormones, vasopressin and angiotensin II. The PG-stimulatory activity of 15S-hydroxy-9 alpha,11 alpha-(epoxymethano)-prosta-5Z-13E-dienoic acid appeared to be receptor-mediated inasmuch as it was completely inhibited by (+/-)5-endo-(6'-carboxyhex-2'Z-enyl)-6-exo-[1''-[N- (phenylthiocarbamoyl)-hydrazono]-ethyl]-bicyclo[2,2,1] heptane, a novel antagonist of PG endoperoxide analogue-provoked smooth muscle contraction and platelet aggregation. The results suggest that thromboxane A2 and/or PG endoperoxide may stimulate PGI2 synthesis in vascular smooth muscle by a direct, receptor-mediated, interaction.

Vasoconstrictor-evoked prostaglandin synthesis in cultured vascular smooth muscle

We investigated the hypothesis that vasopressin, angiotensin II, and norepinephrine stimulate the synthesis of vasodilatory prostaglandins in cultured vascular smooth muscle cells from rat mesenteric arteries. The major prostaglandin synthesized by subcultured vascular smooth muscle cells was PGI2 (measured as its stable metabolite 6-keto-PGF1 alpha) followed by 1/20th to 1/40th as much PGF2 alpha and PGE2. Vasopressin and angiotensin II dose dependently increased prostaglandin synthesis with a half-maximal stimulatory concentration of the order of 1 X 10(-8) M for both peptides. However, vasopressin could provoke the synthesis of two to three times as much PGI2 as angiotensin II, at maximally effective concentrations. Vasopressin's ability to provoke prostaglandin synthesis depended on its pressor activity as demonstrated by the ability of a potent antipressor analogue of vasopressin, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine] arginine vasopressin, to completely inhibit vasopressin-provoked prostaglandin synthesis. Moreover, 1-desamino-8-D-arginine vasopressin, an analogue having full antidiuretic but no pressor activity was much less effective than vasopressin as a prostaglandin-stimulatory agent. Unlike peptide vasoconstrictors, norepinephrine (10(-9) to 10(-5) M) had no ability to stimulate prostaglandin synthesis in vascular smooth muscle cells. We conclude that the potent vasodilator PGI2, released from vascular smooth muscle cells, may buffer the peptide-induced vasoconstriction.

Modulation of cyclic 3'5'-adenosine monophosphate in cultured renal (MDCK) cells by endogenous prostaglandins

Cyclic AMP plays an important regulatory role in transport activity and proliferation of renal MDCK cells. This observation and the ability of MDCK cells to synthesize prostaglandins provided the impetus to assess the hypothesis that endogenous prostaglandins modulate cyclic AMP concentrations in MDCK cells. Three dissimilar cyclo-oxygenase inhibitors: acetylsalicylate, 5, 8, 11, 14-eicosatetraynoate, and meclofenamate significantly decreased cellular cyclic AMP levels and inhibited basal prostaglandin E2 synthesis. On the other hand, three dissimilar stimulators of prostaglandin synthesis: bradykinin, Ca2+-ionophore A23187 and arachidonate, increased cellular cyclic AMP levels, and stimulated prostaglandin E2 synthesis. Acetylsalicylate inhibited the bradykinin- and A23187-evoked increases of cyclic AMP as well as that of prostaglandin E2 synthesis. Prostaglandin E2, the major prostaglandin synthesized by MDCK cells, dose-dependently increased cAMP levels when added exogenously. Acetylsalicylate did not significantly affect increases of cyclic AMP evoked by exogenous prostaglandin E2, documenting that acetylsalicylate inhibited cellular cyclic AMP levels by decreasing endogenous prostaglandin synthesis, rather than by a direct effect on cyclic AMP metabolism. Other prostaglandins synthesized by MDCK cells, i.e., prostaglandins I2, 6-keto-F1 alpha, and F2 alpha added exogenously did not significantly affect MDCK cyclic AMP levels, suggesting that they were probably ineffective as endogenous modulators of cyclic AMP. Moreover, endogenous prostaglandin E2 appeared four- to eightfold more potent as a stimulator of cyclic AMP levels than exogenous prostaglandin E2. The results support the concept that prostaglandin E2 is an endogenous cellular mediator that acts between an extracellular effector such as bradykinin and a second endogenous mediator of hormone action: cyclic AMP.

Inhibition of prostaglandin biosynthesis in renal (MDCK) cells by cAMP

Page C369: A. Hassid. “Inhibition of prostaglandin biosynthesis in renal (MDCK) cells by cAMP.” Page C369: in the abstract, the first sentence should read: Cultured renal tubular cells (MDCK) have many of the biological properties of cortical medullary tubular epithelial cells, including the ability to synthesize prostaglandin E2 (PGE2) as the major arachidonate metabolite. Page C373: Table 3 should read as follows:

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Inhibition of prostaglandin biosynthesis in renal (MDCK) cells by cAMP

Cultured renal tubular cells (MDCK) have many of the biological properties of renal medullary tubular epithelial cells, including the ability to synthesize prostaglandin E2 (PGE2) as the major arachidonate metabolite. The hypothesis that adenosine 3',5'-cyclic monophosphate (cAMP) regulates prostaglandin synthesis in these cells was investigated by using cAMP, two degradation-resistant cAMP analogues [8-bromo-cAMP (8-BrcAMP) and N6,O2'-dibutyryl cAMP (DBcAMP)], and a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). These agents inhibited basal-, calcium ionophore (A23187)-, or bradykinin-stimulated PGE2 biosynthesis by MDCK cells. The observed inhibition was dose- and time-dependent and could be reversed after 30 min of incubation in the absence of inhibitor. IBMX dose-dependently increased intracellular and extracellular cAMP levels by severalfold, suggesting that it was inhibiting prostaglandin biosynthesis by increasing cellular cAMP levels. Vasopressin, which stimulated cAMP levels by less than two-fold, did not inhibit prostaglandin synthesis. 8-BrcAMP and N6,O2'-DBcAMP inhibited A23187- or bradykinin-stimulated release of [3H]arachidonate from prelabeled cells, suggesting that cAMP inhibited acylhydrolase activity. Moreover, 8-BrcAMP also inhibited the conversion of exogenous arachidonate to PGE2 in intact cells and in a subcellular fraction containing prostaglandin synthetase activity, suggesting that cAMP inhibited cyclooxygenase and/or PGE2 isomerase activity. cAMP thus appears to regulate prostaglandin biosynthesis in MDCK cells by modulating the activity of two or more of the enzymes involved in the biosynthetic process.

Prostacyclin substitution for heparin in long-term hemodialysis

We studied prostacyclin as a substitute for heparin in 12 patients who underwent maintenance hemodialysis. All subjects underwent initial hemodialysis with prostacyclin as the sole anticoagulant; 10 of the 12 were restudied during heparin hemodialysis. Few adverse reactions occurred during prostacyclin hemodialysis in the 10 patients in whom dialysis was performed against a bicarbonate-containing dialysate; however, significant hypotension developed in two subjects when an acetate bath was used. Platelet aggregation progressively decreased during prostacyclin hemodialysis (p less than 0.02), but not during heparin hemodialysis, and returned toward control values after hemodialysis. Platelet thromboxane release decreased during both prostacyclin and heparin hemodialysis. Intradialytic percent decrements in serum urea nitrogen and creatinine were greater during prostacyclin than heparin administration (42 +/- 2.9 percent versus 36 +/- 2.6 percent [p less than 0.05] and 33 +/- 2.6 percent versus 29 +/- 2.1 percent [0.05 less than p less than 0.1], respectively). The plasma concentrations of 6-keto-prostaglandin-F1 alpha, a prostacyclin metabolite, reached peak levels by 120 minutes of hemodialysis and declined biexponentially toward predialysis concentrations during 120 minutes after hemodialysis, thereby providing an index of cumulative prostacyclin dosage. We conclude that prostacyclin is not only a safe alternative to heparin anticoagulation during hemodialysis, but that prostacyclin might also increase the efficiency of hemodialysis.

Lipoxygenase activity in rat kidney glomeruli, glomerular epithelial cells, and cortical tubules

We examined the possibility that renal glomerular and cortical tubular tissue has lipoxygenase activity in addition to the well established cyclo-oxygenase pathway of arachidonic acid metabolism. Homogenized rat kidney glomeruli, in the presence of meclofenamate (33 microM) and divalent cation ionophore A23187 (3 microM), metabolized octatritiated arachidonic acid to 12-hydroxyeicosatetraenoic acid and lesser amounts of 80 and/or 9-hydroxyeicosatetraenoic acid. These products were identified by thin layer chromatography, high performance liquid chromatography, and gas chromatography-mass spectroscopy. In order to rule out the synthesis of hydroxylated fatty acids by platelets and leukocytes entrapped in the glomeruli, we studied lipoxygenase products in glomerular epithelial cells after 9 days in cell culture. Homogenized glomerular epithelial cells converted octatritiated arachidonic acid to 12-hydroxyeicosatetraenoic acid solely. The lipoxygenase activity in cortical tubules was substantially less than in glomeruli and only 12-hydroxyeicosatetraenoic acid was synthesized. The production of hydroxyeicosatetraenoic acid by lipoxygenase inhibitors, nordihydroguaiaretic acid, 5,-homogenized glomeruli, glomerular epithelial cells, and cortical tubules was inhibited by three 8,11,14-eicosatetraynoic acid, and 1-phenyl-3-pyrazolidone. These data demonstrate that there is lipoxygenase activity in rat kidney glomeruli, glomerular epithelial cells and to a lesser extent cortical tubules, and may imply a role of the lipoxygenase products in the regulation of normal glomerular function and inflammatory disease of the kidney.

Prostaglandin biosynthesis by lapine articular chondrocytes in culture

Secondary monolayer and spinner cultures of rabbit articular chondrocytes released into the culture medium prostaglandins the synthesis of which was inhibited by sodium meclofenamate. The prostaglandins measured by radioimmunoassay were, in order of decreasing abundance, prostaglandin E2, 6-oxo-prostaglandin F1 alpha (the stable metabolite of prostacyclin) and prostaglandin F2 alpha. Several lines of evidence indicated that chondrocytes synthesize little if any thromboxane B2 (the stable metabolite of thromboxane A2). The presence of prostaglandins was confirmed by radiometric thin-layer chromatography of extracts of culture media incubated with [3H]arachidonic acid-labeled cells. In monolayer culture, chondrocytes synthesized immunoreactive prostaglandins in serum-free as well as serum-containing medium. Monolayer chondrocytes produced higher levels of prostaglandin E2 relative to 6-oxo-prostaglandin F1 alpha than did spinner cells, but the latter synthesized more total prostaglandins. The identity of endogenous prostaglandins as well as those synthesized in short-term culture by rabbit cartilage slices was compared to those produced by chondrocytes in long-term culture. Chondrocytes synthesized all of the prostaglandins found in articular cartilage. Minimal quantities of thromboxane B2 were detected in cartilage. A higher percentage of 6-oxo-prostaglandin F1 alpha relative to other prostaglandins was found in cartilage than in either monolayer or spinner chondrocyte cultures. These results demonstrate that articular chondrocytes synthesize prostaglandins and prostacyclin. These prostaglandins may exert significant physiological effects on cartilage, since exogenous prostaglandins depress chondrocyte sulfated-proteoglycan synthesis and may even promote proteoglycan degradation.

The effect of arginine vasopressin and its analogs on the synthesis of prostaglandin E2 by rat renal medullary interstitial cells in culture

Arginine vasopressin (AVP) stimulates renal prostaglandin (PG) production which is thought to inhibit vasopressins' antidiuretic action. Using rat renal medullary cells in culture (RMIC), we compared the ability of the following peptides which possess different biological activities to stimulate prostaglandin biosynthesis: AVP (high antidiuretic and pressor activities); 1-desamino-8-D-arginine vasopressin (a synthetic peptide with high antidiuretic and no pressor activity); and oxytocin (intermediate pressor, low antidiuretic activity). Radiometric thin-layer chromatography of supernatant media from cells incubated with octatritiated or [14C]arachidonic acid revealed only one radiolabeled peak which co-migrated with PGE2. Radioimmunoassay confirmed that PGE2 was the only prostaglandin synthesized by RMIC. Incubation of cells with AVP (1 nM to 3 microM) increased PGE2 synthesis measured by radioimmunoassay in a concentration-dependent fashion up to 2 1/2-fold over control; 1-desamino-8-D-arginine did not increase PGE2 synthesis. Oxytocin stimulated PGE2 synthesis, but was less potent than AVP. Preincubation of RMIC with [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid)-4-valine, 8-D-arginine]vasopressin, a synthetic nonpressor, nonantidiuretic antagonists of AVP's pressor activity, completely blocked the ability of AVP to stimulate PGE2 synthesis. We conclude that the ability of AVP to stimulate PGE2 synthesis in RMIC is related to its pressor, not its antidiuretic, activity.

Thromboxane A2 mediates augmented polymorphonuclear leukocyte adhesiveness

We examined the role of prostaglandins and thromboxanes as mediators of plasma-dependent increased polymorphonuclear leukocyte adhesiveness induced by Escherichia coli lipopolysaccharide. The cyclo-oxygenase inhibitors-indomethacin and d,l-6-chloro-alpha-methyl-carbozole-2-acetic acid (R020-5720)-reduced lipopolysaccharide-induced adherence of polymorphonuclear leukocytes by 74 and 62%, respectively. In addition, inhibitors of thromboxane synthetase-imidazole, 9,11-azoprosta-5,13-dienoic acid, and 1-benzylimidazole-suppressed the stimulation of adherence by 31, 66, and 83%, respectively. Exogenous prostaglandins E(1), E(2), and F(2)alpha did not increase polymorphonuclear leukocyte adherence, nor were they detected in significant quantities in supernates of polymorphonuclear leukocytes exposed to lipopolysaccharide. However, inhibitors of both cyclo-oxygenase and thromboxane synthetase reduced increases in adherence induced by arachidonic acid (10 mug/ml), suggesting that lipopolysaccharide-mediated increases in adherence were due to an arachidonic acid product other than prostaglandin E(2) or F(2)alpha. 8,11,14-Eicosatrienoic acid, a precursor of monoenoic prostaglandins, did not enhance polymorphonuclear leukocyte adhesiveness. We next demonstrated lipopolysaccharide-stimulated generation, by polymorphonuclear leukocytes, of a labile, low molecular weight, dialyzable substance capable of enhancing the adherence of unstimulated leukocytes. In parallel experiments, a 10-fold increase in immunoreactive thromboxane B(2) over basal levels was detected after exposure of leukocytes to lipopolysaccharide. The inhibition of lipopolysaccharide enhancement of adherence by specific rabbit antibodies to thromboxane B(2) strongly supported a primary role for thromboxane A(2) as the mediator of the observed increases in adherence. Lipopolysaccharide-stimulated purified platelets did not increase leukocyte adherence, whereas thrombin-stimulated platelets did increase adherence. These studies suggest that lipopolysaccharide stimulates polymorphonuclear leukocytes to produce thromboxane A(2), which enhances their adhesiveness to nylon.