Humoral defence improvement and haematopoiesis stimulation in sows and offspring by oral supply of shark-liver oil to mothers during gestation and lactation

Shark-liver oil (SLO) contains two bioactive lipids: alkylglycerols andn-3 PUFA. Alkylglycerols have immunostimulating and haematopoietic properties, whilen-3 PUFA are essential for optimal neonatal development. We investigated the beneficial effects of dietary supplementation with 32g SLO/d to twelve pregnant and then lactating sows (from day 80 of pregnancy to weaning) on the growth and immune status of their offspring, compared with a control group. Sows were vaccinated against Aujeszky's disease 21d before term. Blood samples were collected from sows before treatment, on delivery and 14d later, and from five piglets per litter on days 2, 21 and 36 after birth; colostrum and milk samples were collected 12h, 14 and 28d postpartum. Compared with controls, supplemented sows had higher levels of both erythrocytes and Hb in their blood, and higher concentrations of IgG, alkylglycerols andn-3 PUFA in their mammary secretions. In piglets from supplemented sows, leucocytes and IgG were higher. Supplementation with SLO resulted in an increase in Aujeszky antibodies in both blood and colostrum of sows after vaccination, together with an increase in Aujeszky antibodies in piglet blood. Our findings demonstrate that improvement of both passive and active immune status in piglets is related to the consumption of alkylglycerols associated withn-3 PUFA in the sow diet. The overall improvement in offspring health status by SLO supplementation to the mother could be of interest for optimisation of the lipid diet during and after pregnancy.

1-O-alkylglycerols reduce the stimulating effects of bFGF on endothelial cell proliferation in vitro

1-O-alkylglycerols (alkyl-Gro) are natural etherlipids with multiple biological activities. We previously demonstrated that alkyl-Gro reduce endothelial permeability. Here we showed that alkyl-Gro reduced the basic Fibroblast Growth Factor (bFGF)-stimulated endothelial cell proliferation in a concentration-dependent manner. The effects of 0.5 and 5 ng/ml bFGF on growth were completely suppressed after 72 h-treatment by 50 microM alkyl-Gro. Since bFGF greatly increased (+56%+/-15) the production of 1-O-alkyl-2-acyl-sn-glycerophosphate in alkyl-Gro-treated endothelial cells, our data suggest that the observed effects of alkyl-Gro could be mediated through PLD activation. Inhibition of bFGF-stimulated endothelial proliferation could support anti-angiogenic activity of alkyl-Gro.

Natural 1-O-alkylglycerols reduce platelet-activating factor-induced release of [3H]-serotonin in rabbit platelets

Natural 1-O-alkylglycerols have multiple biological activities with distinct mechanisms. In THP-1 monocytes, they amplify platelet-activating factor production. In endothelial cells, they participate in the production of 1-O-alkyl-2-acyl-sn-glycerol, a PKC inhibitor. Since PAF as well as PKC may interfere with platelet functions, we studied the effect of natural alkylglycerols purified from shark liver oil on [3H]-serotonin release from rabbit platelets in vitro. [3H]-alkylglycerols (1 microM) were consistently incorporated into platelet lipids and after a 2-h incubation, they were metabolised into phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, which represented 53.5+/-1.7%, 36.3+/-1.8%, 5.3+/-0.5% of metabolised [3H]-alkylglycerols, respectively. Alkylglycerols (10 microM) had no effect on spontaneous [3H]-serotonin release. However, alkylglycerols partially inhibited PAF-induced [3H]-serotonin release while they did not modify thrombin-induced release. These data show that alkylglycerols inhibit partially and specifically PAF-induced platelet stimulation and suggest that this effect could result from interfering with PAF receptors.

Regulation of calcium signalling by 1-O-alkylglycerols in human Jurkat T lymphocytes

We studied the role of natural occurring 1-O-alkylglycerols on the calcium signalling in Jurkat T-cells. Alkylglycerols evoked an increase in free intracellular calcium concentration [Ca2+]i, in a dose-dependent manner. When the experiments were performed in calcium-free buffer, the alkylglycerol response on the rise of [Ca2+]i was wholly abolished compared with the one in calcium-containing buffer, suggesting that these etherlipids induce a calcium influx by the opening of Ca2+ channels. We further employed inhibitors of voltage-gated calcium channels. We observed that omega-conotoxin, a blocker of N-type voltage-activated Ca2+ channels, but not verapamil, a blocker of L-type voltage-activated Ca2+ channels, curtailed significantly the calcium rise evoked by the lipid agents. Alkylglycerols also induced plasma membrane depolarisation, known to be involved in the opening of the voltage-gated calcium channels. Our study shows that alkylglycerols increase [Ca2+]i influx in human Jurkat T-cells possibly by modulating the permeability of calcium channels.

Natural Alkylglycerols Restrain Growth and Metastasis of Grafted Tumors in Mice

Alkylglycerols are natural etherlipids abundant in shark liver oil (SLO) in a diacylated form. SLO is known to have antitumor properties and was recently described as an inhibitor of tumor neovascularization. However, most studies did not discriminate between the respective activities of alkylglycerols and of fatty acids, which both have potent biological properties. In this work, a mouse model was used to investigate the antitumor effects of SLO and of alkylglycerols purified from the same source, both administered orally. We demonstrated that either pure alkylglycerols or SLO reduced the tumor growth in a similar manner, suggesting that alkylglycerols were involved in this effect. In alkylglycerol-treated mice, metastasis dissemination was reduced by 64 +/- 8%, whereas SLO effect was 30 +/- 9% below control. Purified alkylglycerols also decreased significantly plasmalogen content in tumors, whereas SLO had no such effect. Finally, we demonstrated that a 5-day treatment with alkylglycerols curtailed the presence in tumors of von Willebrand factor, a marker of endothelial cells. This result suggested an anti-angiogenic effect of alkylglycerols. In summary, alkylglycerols were shown to decrease the growth, vascularization, and dissemination of Lewis lung carcinoma tumors in mice. These findings suggest that the antitumor activity of SLO is likely mediated by the presence of alkylglycerols.

Modulation of endothelial permeability by 1-O-alkylglycerols

Regulation of endothelial barrier function often occurs through signalling involving phospholipase C activation which produces diacylglycerol (DAG), a lipidic second messenger activator of protein kinase C (PKC). Therefore, modification of lipidic composition of endothelial cell membranes might modify DAG production and, as a result, alter regulation of endothelial permeability. We investigated the in vitro effects of natural 1-O-alkylglycerols on porcine aortic endothelial cell permeability to dye-labelled albumin. [3H]-1-O-alkylglycerols (10 microm) were substantially incorporated into phosphatidylcholine (6.6%) and phosphatidylethanolamine (4.4%). Stimulation of endothelial cell monolayer with phorbol-myristate-acetate or with the calcium ionophore A23187 resulted in a raise in permeability to albumin. Pre-treatment with 1-O-alkylglycerols (10 microm, 24 h) had no effect on basal albumin permeability but totally inhibited the effect of phorbol-myristate-acetate, and brought the permeability of A23187-stimulated endothelial cell monolayers below control. After incubation of cells with [3H]-1-O-alkylglycerols (10 microm, 24 h), we detected the production of the analogue of DAG, and PKC inhibitor, [3H]-1-O-alkyl-2-acyl-glycerol, in resting cells. This production was increased by 58% under A23187 stimulation while phorbol-myristate-acetate had no effect. Our data demonstrate that natural 1-O-alkylglycerols modify endothelial permeability, and suggest that this effect could be mediated through alteration of lipidic signalling.

1-O-alkylglycerols improve boar sperm motility and fertility

1-O-alkylglycerols are naturally occurring ether lipids with potent biological activities. They may interfere with lipidic signaling, and they amplify platelet-activating factor (PAF) biosynthesis in a monocyte cell line. The PAF is produced by mammalian sperm and is an important activator of sperm motility. The aim of this study was to evaluate the effect of in vitro treatment of boar spermatozoa with natural 1-O-alkylglycerols (10 microM) on 1) boar sperm motility; 2) production of PAF and its metabolite, lyso-PAF, by spermatozoa; and 3) fertility in artificial inseminations of breeding sows. Using a computer-assisted spermatozoa analyzer, we found that 1-O-alkylglycerols increased percentage motility as well as velocity parameters after 24 h. These effects were partially or totally reversed by the PAF receptor-antagonist SR 27417. After [3H]-1-O-alkylglycerol incubation with boar spermatozoa, we identified [3H]lyso-PAF by high-performance liquid chromatography. Production of PAF and lyso-PAF was measured with a biological assay using [3H]serotonin release from rabbit platelets. 1-O-alkylglycerols significantly increased lyso-PAF production but had no effect on PAF production. The effect of 1-O-alkylglycerols on fertilization was also evaluated in industrial breedings: 1-O-alkylglycerol-treated or untreated semen dilutions were alternately used for artificial inseminations of sows on 12 farms. 1-O-alkylglycerol treatment increased the number of farrows but had no effect on the mean size of the litters. This study demonstrates that 1-O-alkylglycerol treatment of boar spermatozoa in vitro improves their motility and fertility, and it suggests that this effect is related to PAF metabolism and function in boar spermatozoa.

Eicosapentaenoic acid reduces thrombin-evoked release of endothelin-1 in cultured bovine endothelial cells

Endothelial cells were isolated from bovine thoracic aorta and cultured. Bovine aortic endothelial cells (BAEC) were incubated with radiolabeled arachidonic acid (3H-AA) or eicosapentaenoic acid (14C-EPA) (1 microM) for 3 hr. Both fatty acids were predominantly incorporated into phosphatidylcholine (57 +/- 2% and 62 +/- 2% respectively) and slightly into phosphatidylethanolamine (11 +/- 0.5% and 12 +/- 0.6% respectively). phosphatidylinositol (26 +/- 1.5% and 10 +/- 0.5% respectively) and neutral lipids (6 +/- 0.5% and 15 +/- 1% respectively). After BAEC incubation with 3H-AA for 24 hr with or without EPA (1 microM), the release of radioactive metabolites of AA induced by thrombin (5.5 U/ml) was strongly reduced by the preliminary treatment with EPA (72 +/- 5%). After BAEC incubation with AA, EPA or vehicle (control), endothelin-1 levels were measured by RIA in the culture medium and we observed that: 1) the basal production of endothelin-1 was not modified after either AA or EPA treatment, 2) the thrombin-evoked release of endothelin-1 was significantly reduced by EPA (5.8 +/- 0.82 and 3.8 +/- 0.50 pg/microg proteins in control and EPA-treated cells, respectively); 3) by contrast, AA had no significant effect on the thrombin-evoked release of endothelin-1. In conclusion, EPA reduces strongly the endothelin-1 release but AA is ineffective. This reduction of endothelin-1 release may account partly for some of the vascular effects of EPA.

Modulation of PAF production by incorporation of arachidonic acid and eicosapentaenoic acid in phospholipids of human leukemic monocyte-like cells THP-1

Stimulated leukocytes generate platelet-activating factor (PAF) from membrane 1-O-alkyl-2-acyl-sn-glycerophosphocholine through hydrolysis of fatty acid and subsequent acetylation at the sn2 position of glycerol. Since the enzymes involved in the hydrolysis step of PAF biosynthesis have relative selectivity for arachidonic acid (AA), the fatty acid composition of PAF precursors might modulate PAF production. We studied the effect of AA and eicosapentaenoic acid (EPA) incorporation on PAF biosynthesis, by measuring the incorporation of [(3)H]acetate, in Ca(2+) ionophore (A23187)-stimulated human leukemic monocyte-like cells, THP-1. Supplementation of THP-1 with AA (25 microM, 1 week) or EPA (25 microM, 1 week) led to their efficient incorporation, in comparable quantities and with similar distributions, into phosphatidylcholine and phosphatidylethanolamine, and to a lesser extent into phosphatidylinositol. THP-1 cells supplemented with AA or with EPA synthetized similar amounts of PAF and of acyl analog of PAF under resting condition. However, AA-supplemented cells responded to A23187 stimulation by important raises of PAF (+125.71%) and of acyl analog of PAF (+381.75%) productions, whereas the same stimulation had little effect or no effect at all in cells supplemented with EPA. These results show that both EPA and AA may influence PAF production through their incorporation into PAF precursors, indicating that PAF production might be modulated by the fatty acid composition of its precursors.

Substitution of 15(S)hydroxyeicosatetraenoic acid in phosphatidylinositol alters the growth of liver epithelial cells

We investigated the substitution of 15(S)-hydroxyeicosatetraenoic acid (15(S)HETE) in phospholipid signaling pathways and its consequences on the growth of non-transformed (NT-) and spontaneously transformed (T-) rat liver epithelia cells (RLEC). 15(S)HETE was selectively incorporated into the sn-2 position of phosphatidylinositol (PI) and at a higher rate into T-RLEC. RLEC rapidly mobilized the resulting 15(S)HETE-containing PI (15(S)HETE-PI) and produced 1-acyl,2-[1(S)HETE]-glycerol. Although total diacylglycerol levels were similar in both cell types, the ratio 1-acyl,2-[15(S)HETE]-glycerol / 15(S)HETE-PI was higher in NT-RLEC, suggesting a lower mobilization of 15(S)HETE-PI in T-RLEC. Using rat brain protein kinase C, 1-stearoyl,2-[15(S)HETE]-glycerol was as potent an in vitro protein kinase C activator as 1-stearoyl,2-arachidonoyl-glycerol. Finally, selective substitution of 15(S)HETE in PI altered DNA synthesis in T-RLEC: whereas low concentrations of 15(S)HETE (1 nM and 10 nM) in these cells were mitogenic, higher concentrations resulted in a 30% inhibition of DNA synthesis.

Stimulation of Rb+ influx by bradykinin through Na+/K+/Cl- cotransport and Na+/K(+)-ATPase in NIH-3T3 fibroblasts

Bradykinin receptor stimulation results in G-protein-coupled phospholipase activation, initiating protein kinase C (PKC) stimulation and cytosolic free Ca2+ concentration ([Ca2+]i) rises as signalling pathways. Using Rb+ as a tracer for K+, we have studied the mechanisms involved in bradykinin-stimulated Rb+ influx in NIH-3T3 fibroblasts. The furosemide-sensitive Na+/K+/Cl- cotransport and the ouabain-sensitive Na+/K(+)-ATPase were both involved in Rb+ influx under resting conditions with a ratio Na+/K+/Cl- cotransport/Na+/K(+)-ATPase (r) = 0.73. Bradykinin stimulated Rb+ influx (+82.6%) through both systems without changing their ratio (r = 0.72). PKC stimulation by a 15-min-treatment with phorbol 12-myristate 13-acetate (PMA) (2x10(-7) M) increased Rb+ influx in resting cells by 75.7% without affecting r (0.75). PKC inhibition by H-7, and PKC down-regulation by 24-h PMA (10(-6) M) treatment decreased the bradykinin-induced stimulation of Rb+ influx (+31% and +14.9% above control, respectively). Both down-regulation and inhibition of PKC dramatically reduced the furosemide-sensitive Na+/K+/Cl- cotransport, as r fell to 0.239 and 0.032 in bradykinin-stimulated cells after H-7 and 24-h PMA treatments, respectively. BAPTA/AM pretreatment (10(-4) M, 60 min), which complexed with [Ca2+]i, not only prevented the bradykinin-induced [Ca2+]i raise, but also partially inhibited bradykinin-induced Rb+ influx stimulation (+39% above control), without modifying r (0.76). We conclude that stimulation of PKC is a major pathway involved in bradykinin stimulation of Rb+ influx in NIH-3T3 fibroblasts, and that rises in [Ca2+]i participate in bradykinin signalling, possibly through PKC activation. Our data also suggest that active PKC is required for basal and bradykinin-stimulated Na+/K+/Cl- cotransport activity in these cells.

Incorporation of 12(S)-hydroxyeicosatetraenoic acid into the phosphatidylcholine signaling pathway

The incorporation of 12-lipoxygenase metabolites into phospholipids (PLs) could modify second messengers such as diacylglycerols (DAG) and phosphatidic acids. Incubation of [(14)C]12(S)-HETE (1 microM) with bovine pulmonary artery endothelial cells (BPAEC), resulted in its incorporation in PLs with concentration-dependent kinetics. After a 4 h incubation, the proportion of radioactive phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) + phosphatidylinositol (PI) isolated by TLC, was 77.9%, 16.4% and 5.7%, respectively. In PC, [(14)C]12(S)-HETE was incorporated at the position 2 of the glycerol. Three major peaks of radioactive PC were isolated on RP-HPLC which were hydrolysed by phospholipase C (PLC). The resulting diacylglycerols were derivatized and identified by GC/MS as 1-oleyl-, 1-stearoyl- and 1-palmitoyl-2-[12-HETE] PC. BPAEC were incubated with [(14)C]12(S)-HETE (1 microM) before stimulation with bradykinin (1 microM). (A) 1-acyl-2-[12-HETE] diacylglycerols were isolated, derivatized and analysed by MS. We identified a major ion with m/z = 926 that corresponds to the molecular ion of authentic 1-stearoyl-2-12(S)-HETE DAG, and 2 other ions with m/z = 924 and 898 that correspond to the molecular ions of 1-oleyl- and 1-palmitoyl-2-12(S)-HETE DAG, respectively. (B) Radioactive PA was isolated and hydrolysed by alkaline phosphatase. The MS of resulting diacylglycerols identified 1-stearoyl-, 1-oleyl-, and 1-palmitoyl-2-12(S)-HETE phosphatidic acids. The quantities of 12-HETE PA and the 3 major 12-HETE diacylglycerols were shown to increase following bradykinin stimulation. Thus, the incorporation of 12(S)-HETE into PLs results in the production of altered phosphatidic acids and diacylglycerols. The time-course of increases in 1-acyl-2-(12-HETE) phosphatidic acids and 1-acyl-2-(12-HETE) diacylglycerols showed maximal concentrations 1 and 2 min after bradykinin stimulation, respectively, followed by the decrease of both compounds. Propranolol, an inhibitor of PA phosphohydrolase, totally abolished the bradykinin-induced increase in 12-HETE DAG while increasing the magnitude and duration of 12-HETE PA release. The inhibiting effect of propranolol on bradykinin-induced increase of 12-HETE DAG demonstrates that 12-HETE PA is the principal precursor for 12-HETE DAG. This affords a novel method for confirming the major role of phospholipase D in PC metabolic pathways triggered during cell signaling.

Incorporation of 12(S)-hydroxyeicosatetraenoic acid into phospholipids and active diacylglycerols in rat liver epithelial cells: effects on DNA synthesis

12(S)-Hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase-derived metabolite of arachidonic acid, was incorporated into membrane phospholipids (PL) in various cells. PL are precursors of diacylglycerol (DAG), a protein kinase C (PKC) activator involved in cell-growth signaling. We studied 12-HETE incorporation into PL in non-transformed (NT-) and spontaneously transformed (T-) rat liver epithelial cells (RLEC), and its consequence on DNA synthesis. NT- and T-RLEC incorporated 12-HETE predominantly into phosphatidylcholine (PC). 12-HETE was incorporated at a greater rate, and with a higher phosphatidylethanolamine (PE)/PC ratio in T-cells. Preincubation of RLEC with 12-HETE at > or = 0.5 microM partially inhibited basal DNA synthesis in NT- and T-RLEC. Preincubation of NT-RLEC with 12-HETE (2.5 microM) also decreased bradykinin-stimulated DNA synthesis. Unstimulated RLEC produced 1-acyl-2-(12-HETE)DAG which was increased in NT-RLEC by bradykinin stimulation. Finally, 1-stearoyl-2-(12-HETE)DAG was as potent an in vitro PKC activator as 1-stearoyl-2-arachidonyl-DAG. These data demonstrate that 12-HETE incorporation into PL resulted in the production of active 12-HETE-containing DAG, together with reduced DNA synthesis.

Incorporation of arachidonic and eicosapentaenoic acids into phospholipids of non-transformed and spontaneously-transformed rat liver epithelial cells: effects on DNA-synthesis

We compared the incorporation of arachidonic acid (AA) and eicosapentaneoic acid (EPA) into phospholipids of non-transformed (NT-) and spontaneously-transformed (T-) rat liver epithelial cells (RLEC), and their consequences on DNA-synthesis. In NT-cells, both radioactive fatty acids were preferentially incorporated into phosphatidylcholine (PC). In T-cells, in contrast, AA was predominantly incorporated into phosphatidylethanolamine (PE), whereas EPA remained preferentially incorporated into PC. After pulse labelling, we observed in both cell types a progressive decrease in AA- and EPA-labelled PC associated with an increase in AA- and EPA-labelled PE. Preincubation of NT-cells with increasing concentrations of AA or EPA (0.1 microM to 20 microM) resulted in a concentration-dependent DNA-synthesis stimulation with a stronger effect of AA compared with EPA. In T-cells, the same treatment had no effect on DNA-synthesis.

Substitution of 15-hydroxyeicosatetraenoic acid in the phosphoinositide signaling pathway

Consideration of how 15-hydroxyeicosatetraenoic acid (15-HETE) might exert its biological actions led us to investigate the consequences of its incorporation into bovine pulmonary arterial endothelial cell (BPAEC) phospholipids [3H]15(S)-HETE was incorporated mainly (89%) into phosphatidylinositols, predominantly as 1-stearoyl-2-(15-HETE) phosphatidylinositol. By contrast 5(S)- and 12(S)-HETE are incorporated largely into phosphatidylcholine. 15-HETE had a long persistence in the phosphatidylinositols of BPAEC with a half-life of 12 h; its uptake was concentration-dependent, and it accumulated so that 2-(15-HETE) phosphatidylinositol accounted for 10.9% of total phosphatidylinositol after four sequential 1-h incubations of cells with 1 microM 15(S)-HETE. After incubating BPAEC with 15(S)-HETE, stimulation of the cells with bradykinin led to an increase in the levels of 15-HETE. Following addition of bradykinin to cells exposed to [3H]15(S)-HETE, a radiolabeled diacylglycerol was isolated. A mass spectrum of its pentafluorobenzoyl (PFBO) trimethylsilyl (Me3Si) derivative obtained with direct electron capture negative ion chemical ionization mass spectrometry (DNICI/MS) revealed a molecular anion and fragment ions that were identical with those observed with the PFBO/Me3Si derivative of authentic 1-stearoyl-2-(15-HETE) diacylglycerol. There was a lesser quantity of 1-oleoyl-2-(15-HETE) diacylglycerol. An increase in the quantity of 1-stearoyl-2-(15-HETE) diacylglycerol from 6 +/- 1.4 pmol/10(7) cells in the basal state to 12.7 +/- 3.5 after bradykinin was measured by DNICI/MS utilizing a deuterium-labeled analog as an internal standard. Thus, incorporation of 15(S)-HETE into the phosphatidylinositol of these cells led to the release of altered second messengers.

Effects of adenosine and analogs on adenylate cyclase activity in cultured bovine aortic endothelial cells

We studied the effects of adenosine and analogs on adenylate cyclase (AC) activity in membranes from long-term cultured bovine aortic endothelial cells, using [alpha-32]ATP as substrate and chromatographic separation of [32P]cAMP. Compared to our previous findings in cultured bovine pulmonary arterial endothelial cells (Legrand et al., Biochem Pharmacol 38: 423-430, 1989), the present results were qualitatively and quantitatively comparable between the two cell types. In aortic cells, AC activity was stimulated in a concentration-dependent manner by isoproterenol, forskolin and 5'-guanylylimidodiphosphate (Gpp(NH)p), by 2.6-, 5.2- and 4.8-fold respectively. The A2 adenosine agonist 5'-(N-ethyl)-carboxamidoadenosine induced a smaller (60%) increase of AC activity. Adenosine (10(-3) M) partially inhibited (30%) the Gpp(NH)p-stimulated AC activity. Similarly, adenosine partially reversed, but 2',5'-dideoxyadenosine (DDA) totally blocked (IC50: 540 microM), the forskolin-induced stimulation of AC activity. DDA and 2'-deoxyadenosine-3'-monophosphate (2'-deoxy-3'-AMP) also inhibited the isoproterenol-induced stimulation of AC activity (IC50: 350 and 23 microM respectively). Adenosine-induced inhibition of stimulated AC activity does not appear to involve adenosine A1 receptors since the specific A1 agonist cyclohexyladenosine did not reverse forskolin stimulation of AC activity. Instead, it suggests a direct action of adenosine on the catalytic subunit of the adenylate cyclase (P site). We conclude that membranes from long-term cultured bovine aortic endothelial cells, express beta-adrenergic and adenosine A2 receptors coupled to adenylate cyclase activation. The two P site agonists, DDA and 2'-deoxy-3'-AMP, and, with a weaker effect, adenosine itself, inhibited the activated cyclase at the P site. The natural nucleotide 2'-deoxy-3'-AMP was a strong inhibitor in aortic cell types (as in pulmonary arterial endothelial cells) and may possibly act as a modulator of adenylate cyclase in these cells.

Modulation of adenylate cyclase activity in cultured bovine pulmonary arterial endothelial cells. Effects of adenosine and derivatives

We studied the effects of adenosine and adenosine derivatives on adenylate cyclase activity in cultured endothelial cells from bovine pulmonary artery. Basal and stimulated enzyme activities were measured in membrane preparations using [alpha-32P]ATP as the substrate and chromatographic isolation of formed [32P]cAMP. Basal cyclase activity was 11 +/- 1 (mean +/- SEM) pmol/mg protein/min. Forskolin, 5'-guanylylimidodiphosphate (Gpp(NH)p) and (-)isoproterenol stimulated adenylate cyclase in a concentration-dependent manner, producing maximal stimulations of three, seven and four times the basal activity respectively. In the presence of adenosine deaminase, cyclohexyladenosine, an A1 agonist, had no effect on basal and forskolin- or Gpp(NH)p-stimulated activities, whereas 5'-(N-ethyl)-carboxamidoadenosine (NECA), an A2 agonist, had a small stimulatory effect (52% increase over basal). In the presence of IBMX, adenosine and two P-site agonists, 2',5'-dideoxyadenosine (DDA) and 2'-deoxyadenosine-3'-monophosphate (2'-deoxy-3'-AMP), inhibited forskolin (30 microM)-stimulated adenylate cyclase activity with an order of potency of 2'-deoxy-3'-AMP greater than DDA greater than adenosine. DDA and 2'-deoxy-3'-AMP were also able to inhibit cyclase activity stimulated by Gpp(NH)p (10(-5)M) or isoproterenol (10(-6)M) with the same order of potency. Only 2'-deoxy-3'-AMP inhibited the stimulated adenylate cyclase activity by more than 50% (IC50 = 19-32 microM). These findings indicate that (1) long-term cultured endothelial cells from bovine pulmonary artery express A2 and beta-adrenergic receptors which stimulate adenylate cyclase activity through Gs transducer proteins, and (2) the natural compound and P-site agonist, 2'-deoxy-3'-AMP, is a potent inhibitor, and possibly a natural regulator, of adenylate cyclase activity in this tissue.