Biomedical subjects

A Hassid

Publications and source records attributed to A Hassid.

At least 37 records · Page 2Linked to original sources

PubMed1989

Modulation of Ca by agents affecting voltage-sensitive Ca channels in mesangial cells.

The purpose of this study was to investigate the effects of depolarizing media and of Ca-channel activators and blockers on cytosolic free Ca in cultured rat mesangial cells. Membrane depolarizing media, containing 10-100 mM K+, dose dependently increased cytosolic Ca, and this effect was sustained and reversible. Nifedipine and lanthanum ion inhibited this increase, whereas verapamil was ineffective. A Ca-channel activator, BAY K 8644, dose dependently increased resting Ca levels, and nifedipine inhibited this effect. Moreover, the increase of Ca induced by maximally effective high K+ and BAY K 8644 was additive, suggesting differential mechanisms of action for the two channel activators. Nifedipine and verapamil decreased resting Ca levels by up to 35-40%. The results support the idea that mesangial cells have spontaneously active Ca channels that can be further activated by membrane depolarization or by the Ca-channel activator, BAY K 8644, and inhibited by the Ca-channel blockers, nifedipine or verapamil. Voltage-sensitive Ca channels in mesangial cells may play a role in the regulation of the glomerular filtration rate.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

Nitric oxide-generating vasodilators and 8-bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells.

Endothelium-derived relaxing factor has been recently identified as nitric oxide. The purpose of this study was to determine if vasodilator drugs that generate nitric oxide inhibit vascular smooth muscle mitogenesis and proliferation in culture. Three chemically dissimilar vasodilators, sodium nitroprusside, S-nitroso-N-acetylpenicillamine and isosorbide dinitrate, dose-dependently inhibited serum-induced thymidine incorporation by rat aortic smooth muscle cells. Moreover, 8-bromo-cGMP mimicked the antimitogenic effect of the nitric oxide-generating drugs. The antimitogenic effect of S-nitroso-N-acetylpenicillamine was inhibited by hemoglobin and potentiated by superoxide dismutase, supporting the view that nitric oxide was the ultimate effector. Sodium nitroprusside and S-nitroso-N-acetylpenicillamine significantly decreased the proliferation of vascular smooth muscle cells. Moreover, the inhibition of mitogenesis and proliferation was shown to be independent of cell damage, as documented by several criteria of cell viability. These results suggest that endogenous nitric oxide may function as a modulator of vascular smooth muscle cell mitogenesis and proliferation, by a cGMP-mediated mechanism.

Animals↗

PubMed1989

Mechanism of atriopeptin-induced decrease of cytosolic free Ca in rat vascular smooth muscle cells: evidence for an intracellular locus of action.

The purpose of this study was to investigate the subcellular mechanism of action of atriopeptins in relation to intracellular Ca dynamics. Atriopeptin 23, an analogue of the circulating hormone, decreased cytosolic free Ca in cultured adherent aortic smooth muscle cells, both in the presence and absence of extracellular Ca. Moreover, the atrial peptide did not alter Ca efflux. Atriopeptin 23 decreased the Ca transient induced by angiotensin II (Ang II), but only at low concentrations of the vasoconstrictor peptide. Similar to atriopeptin 23, S-nitroso-N-acetylpenicillamine, an organic nitrovasodilator that increases cGMP levels in vascular tissues, decreased resting Ca in adherent cells, supporting the notion that cGMP is a mediator of atriopeptin action. The results support the concept that atriopeptin decreases intracellular Ca by enhancing intracellular Ca sequestration and/or inhibiting intracellular Ca release.

Animals↗

PubMed1988

A novel biological effect of atrial natriuretic hormone: inhibition of mesangial cell mitogenesis.

We have investigated the effect of atrial natriuretic hormone on serum-induced mitogenesis in cultured rat mesangial cells. Synthetic peptides, atriopeptin 28 and atriopeptin 24, dose-dependently decreased thymidine incorporation, with a half-maximal effect at approximately 1 nM and a maximal inhibition of approximately 60%. Moreover, atriopeptin 28 significantly decreased the clonal proliferation of mesangial cells. Atriopeptin 28 also decreased resting cytosolic Ca but had no effect on the increase induced by serum, relative to the lower baseline established by atriopeptin 28. Nevertheless, the overall effect of atriopeptin 28 on Ca was to attenuate the serum-induced increase, relative to the original resting level. These results therefore provide evidence for a novel biological effect of atrial natriuretic hormone and suggest that the antimitogenic effect may be mediated by atriopeptin-induced alterations of intracellular Ca dynamics. We speculate that atrial natriuretic hormone may be a modulator of mesangial cell mitogenesis in vivo.

Animals↗

PubMed1988

Mediation of augmented monocyte adhesiveness by thromboxane.

We examined the potential contribution of thromboxanes in human monocyte adherence to plastic. Monocyte adherence to plastic could be augmented by various stimuli including lipopolysaccharide, chemotactic peptide, and supernates of antigen-stimulated lymphocytes. Increments in monocyte adhesiveness were suppressed by inhibition of cyclooxygenase, thromboxane synthetase, or by antiserum to thromboxane B2. Neither prostaglandin E2 or F2 alpha significantly affected baseline or lipopolysaccharide-stimulated monocyte adherence. Additional experiments confirmed incremental production of thromboxane B2 by monocytes after incubation with lipopolysaccharide. Thromboxane B2 itself did not stimulate monocyte adhesiveness. These data demonstrate that monocytes release thromboxane A2 following stimulation and suggest that thromboxane A2 may play a significant role in monocyte-substrate attachment.

Carbazoles↗

PubMed1987

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.

Angiotensin II↗

PubMed1987

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.

Angiotensin II↗

PubMed1987

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.

Animals↗

PubMed1986

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.

Animals↗

PubMed1986

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.

Angiotensin II↗

PubMed1986

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.

Angiotensin II↗

PubMed1986

Functional properties of glomerular cells in culture.

With the development of techniques to isolate and propagate homogeneous cultures of glomerular cell types, numerous investigations have been initiated to study the functional characteristics of cultured glomerular cells. Since much of the work to date has been performed on glomerular mesangial cells, a good deal of this discussion will be about this cell type. Glomerular mesangial cells together with the surrounding matrix material form the glomerular mesangium. These cells contain contractile microfilaments as well as receptors for vasoconstrictor substances such as angiotensin II. Therefore, one proposed function of this cell type is the regulation of glomerular perfusion and filtration by contraction. Cultured mesangial cells contract in response to angiotensin II and arginine vasopressin and, in addition, produce prostaglandins which may function to regulate contraction. In this article, we will review the evidence that has accumulated concerning the contractile nature of mesangial cells. Since prostaglandins may influence mesangial cell contraction, the prostaglandin synthetic capabilities of glomerular epithelial and mesangial cells will be discussed. We will conclude by discussing how glomerular cell culture can be used to study the pathobiology of certain glomerular diseases.

Angiotensin II↗

PubMed1986

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.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1986

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.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1985

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.

Aminoquinolines↗

PubMed1984

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.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1983

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.

Animals↗

PubMed1983

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.

1-Methyl-3-isobutylxanthine↗