Comparison between rat and rabbit anticyclic AMP antibodies--specificity toward acyl derivatives of cyclic AMP

Reduction by arachidonic acid of prostaglandin I2-induced cyclic AMP formation. Involvement of prostaglandins E2 and F2 alpha

Arachidonic acid reverses the increase in cyclic AMP levels of washed human platelets exposed to prostaglandin (PG)I2, under conditions where the PGH2 analogue U46619 is ineffective. This effect of arachidonic acid was inhibited by aspirin, a cyclooxygenase inhibitor, but not by the thromboxane (Tx) synthase inhibitor Ridogrel, which induces, by inhibiting the conversion of PGH2 into TxA2, an overproduction of PGE2, PGD2 and PGF2 alpha. Addition of PGE2 or PGF2 alpha, which share a receptor with PGI2, to washed human platelets also induced a decrease in cyclic AMP levels, but PGD2, which interacts with a different receptor, had no effect. Thus neither PGD2, PGG2, PGH2, TxA2 nor TxB2 formed from arachidonic acid via the cyclooxygenase pathway is involved in the decrease in cyclic AMP levels. These findings were confirmed using forskolin, a diterpene from the labdane family, which enhanced the formation of cyclic AMP synergistically with the PGs. Also, arachidonic acid, unlike U46619, is able to reverse the inhibition of platelet aggregation by PGI2 after a lag phase of about 4 min. Our data indicate that arachidonic acid decreased cyclic AMP levels through its cyclooxygenase metabolites PGE2 and PGF2 alpha probably interacting competitively with the receptor of PGI2. In addition, intracellular cyclic AMP levels and the degree of aggregation of platelets by arachidonic acid seem to be inversely correlated.

Guinea-pig treatment with pertussis toxin suppresses macrophage-dependent bronchoconstriction by fMLP and fails to inhibit the effects of PAF

1. Bronchoconstriction and thromboxane B2 (TxB2) release following the intra-tracheal administration of the secretagogue N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) to lungs from pertussis toxin-treated guinea-pigs in vivo and in vitro were inhibited as compared to saline-treated animals, under conditions where the responses to PAF were modified less effectively. 2. The cell target accounting for bronchoconstriction by fMLP and for inhibition by pertussis toxin is located in the airways and is probably the alveolar macrophage. Indeed (a) fMLP-induced superoxide anions and TxB2 formation by alveolar macrophages were inhibited by pertussis toxin given in vivo; (b) Gi proteins of membranes from alveolar macrophages were ADP-ribosylated in vivo by pertussis toxin and (c) bronchoconstriction and TxB2 release in response to the intra-tracheal administration of fMLP to lungs from pertussis toxin-treated animals were restored when alveolar macrophages from control guinea-pigs were transferred into the airways of pertussis toxin-treated animals before lung isolation. 3. Pertussis toxin administered to guinea-pigs in vivo, reduced the subsequent TxB2 formation and superoxide anion release by alveolar macrophages stimulated with PAF, but failed to inhibit PAF-induced bronchoconstriction. 4. Formation of TxB2 by alveolar macrophages following the intra-tracheal administration of fMLP accounts for bronchoconstriction and requires pertussis toxin-sensitive Gi proteins. PAF operates via a different mechanism, which is independent of Gi-like protein and involves mediators other than TxB2 and superoxide anions.

Alkaline phosphatase prevents platelet stimulation by thromboxane-mimetics

1. The effects of alkaline phosphatase on platelet aggregation, secretion and thromboxane B2 (TxB2) generation induced by the full dose-range of common platelet agonists were studied in human platelet-rich plasma and washed platelets. 2. Platelet aggregation and adenosine 5'-triphosphate (ATP) secretion induced by threshold and supramaximal concentrations of arachidonate and stable TxA2 and prostaglandin endoperoxide-mimetics (compounds U46619 and EP171) were abolished in the presence of alkaline phosphatase (0.5-1 u ml-1), even though the synthesis of TxB2 persisted. In contrast, platelet aggregation by PAF-acether and by supramaximal concentrations of thrombin as well as the primary wave of aggregation by adenosine diphosphate (ADP) and adrenaline were unaffected by alkaline phosphatase under conditions where the secondary wave of aggregation by ADP was blocked. 3. Alkaline phosphatase, unlike prostacyclin, failed to raise the adenosine 3':5'-cyclic monophosphate (cyclic AMP) content of the platelets. Also, the pretreatment of platelets by inorganic phosphate or by ATP plus creatine phosphate/creatine phosphokinase reversed the inhibitory effect of alkaline phosphatase. 4. Experiments performed in the guinea-pig in vivo showed that alkaline phosphatase was effective on thrombocytopenia induced by arachidonate. 5. Our results provide the first direct evidence for a specific inhibitory effect of alkaline phosphatase at a site sensitive to TxA2 and prostaglandin endoperoxides and suggest that its phosphorylation/dephosphorylation state may play an important role in modulating platelet activation. These results also suggest the presence of ecto-protein kinases on membrane platelets.

Ecdysteroid-like compounds in the serum and urine of African patients infected with Loa loa and Mansonella perstans microfilariae

Ecdysteroids are compounds related to 20-hydroxyecdysone, the insect moulting hormone. Surprisingly, they have been found in serum and urine of patients infected with helminths. In these cases, the substances are assumed to be produced by the parasites and, therefore, might be used as a marker of parasitic infection. Thus, we need to know exactly which species, at which developmental stage, can release ecdysteroids in such large quantities that they could be detected in the biological fluids of the host. Large-scale investigations must, accordingly, be devoted to the major species of helminths. In the present study, we examined 100 African patients with Loa loa and/or Mansonella perstans microfilaraemia. About 70 of them had high levels of ecdysteroid-like materials in serum or urine. In contrast, uninfected patients and European controls had much lower concentrations. However, the ecdysteroid titres did not reflect the concentration of microfilariae actually present in the blood, and some heavily infected patients were even negative. Nevertheless, the most important point was that high ecdysteroid levels in man were always associated with a pathological condition. The precise significance of the phenomenon should be determined.

Interaction of 7-acetyltaxol with different tubulin assemblies

Equilibrium microdialysis of [3H]acetyltaxol against different tubulin assemblies showed that: (i) the binding capacity of tubulin does not depend on the temperature; (ii) two classes of 'polymers' exist, with respect to Ac-taxol binding. Some of them (plaques, complex cylinders induced with some polycations and spirals made with rhazinilam) bound Ac-taxol, as do normal microtubules. In contrast, spirals formed with vinblastine and griseofulvin, rings made with polycations and complex cylinders induced with spermine do not bind Ac-taxol as is the case with free tubulin.

Absence of 7-acetyl taxol binding to unassembled brain tubulin

The effect of taxol on microtubule proteins at 0 degrees C is controversial. In order to determine if taxol is unable to bind to unassembled tubulin, as has been hypothesized, the binding of [3H]acetyl taxol has been studied using equilibrium microdialysis. Ac-taxol bound to microtubules at 37 degrees C and the binding remained stable when the temperature was lowered to 0 degrees C. Ac-taxol bound also at 0 degrees C to microtubules stabilized with rhazinilam. In contrast, there was no binding of Ac-taxol to unassembled tubulin, either free tubulin at 0 degrees C or tubulin, complexed with several microtubule poisons, at 0 and 37 degrees C.

Modulation by cyclic AMP of arachidonic acid-induced platelet desensitization

We have previously demonstrated that arachidonic acid (AA) and the stable cyclic endoperoxide analogue (U46619) desensitize human platelets at a common site, which is sensitive to endoperoxides/thromboxane receptor antagonists. We now report on the influence of agents which evaluate intracellular levels of platelet adenosine 3',5'-cyclic monophosphate (cAMP) on AA- and U46619-induced platelet desensitization. Prostaglandin E1, prostacyclin, carbacyclin, forskolin or dibutyryl cAMP prevented platelet activation by and desensitization to AA and to U46619 under conditions where the formation of thromboxane B2 was not significantly modified. Inhibition of platelet activation (aggregation and secretion) required a lower increase of the cAMP content than was needed to inhibit desensitization, confirming previous findings that desensitization to and by AA or U46619 are independent from the platelet release reaction. Together, these results indicate that AA-induced desensitization can be modulated by the adenylate cyclase/cAMP system acting at a site distinct from the known mechanisms of Ca2+ sequestration. This site is shared by the AA metabolite responsible for desensitization and by U46619 and is related to their common platelet membrane receptor.

Anti-5-hydroxytryptamine antibodies: studies on their cross-reactivity in vitro and their immunohistochemical specificity

Antibodies to 5-hydroxytryptamine (5-HT) were obtained from 4 rabbits after injections of 5-HT coupled to bovine serum albumin by means of paraformaldehyde (PF). Two methods were used to monitor the development of antibodies (AB): the one based on the "in vitro" competitive binding properties of the antibodies with 3(H)5-HT, the other, on their "in situ" binding properties to endogenous 5-HT, using the peroxidase-anti-peroxidase immunohistochemical technique, applied to paraffin embedded sections of cat brainstem. No pharmacological processing, detergents or proteolytic enzymes were used. The specificity of the antiserum was tested by competitive procedures with 20 analogs using the "in vitro" and "in situ" techniques. "In vitro" studies were performed with 5-HT free analogs and with analogs previously coupled with PF to lysine. Radioimmunological tests showed that the antibodies recognize mainly the ethylamine (CH2-CH2-NH2)-chain of the free analogs and that the best specificity was obtained with the 5-HT conjugate (5-HT-lysine-PF). The results suggest that the hapten is coupled through the phenolic positions C4 or C5. The "in situ" immunohistochemical extinction assays also revealed a distinct specificity for 5-HT. Possible optical and ultrastructural applications are illustrated in the raphé nuclei of the cat. These results confirm the reliability of radioimmunological tests for studying the specificity of AB directed against haptens, provided that haptens and analogs tested were first chemically transformed to resemble the immunogen (herewith lysine-PF coupling) with regard to its antigenic structure.

Immunorecognition of anti-serotonin antibodies by using a radiolabelled ligand

Specificity of anti-serotonin antibodies to be assayed for immunocytochemical studies was tested in vitro by using a radiolabelled ligand mimicking the hapten structure. A good immunorecognition was found after coupling [3H]HT to a lysine with formaldehyde. Competition experiments by equilibrium dialysis were then carried out between [3H]HT-F-ALM and both conjugated and unconjugated indoles. The cross-reactivity ratios showed that the antibody recognition, though less specific than expected, was found suitable for immunocytochemical applications.

Antibodies against gamma-aminobutyric acid: specificity studies and immunocytochemical results

Antibodies against gamma-aminobutyric acid (GABA)-glutaraldehyde-lysine were obtained by using a procedure based upon (i) a high yield of coupling of GABA to protein carriers, (ii) the reduction of the resulting immunoreactive double bonds, and (iii) a protocol of alternative immunizations using different immunogens having in common only the GABA-glutaraldehyde-lysine segment. This strategy led to the use of the resulting GABA antiserum without further purification. Specificity controls have been carried out with a radiolabeled ligand, [3H]GABA-glutaraldehyde- prolylphenylalanyl -lysine , which mimicked the structure of the immunogen and the fixed hapten in the tissue. Displacement curves showed that the nearest coupled analogs, beta-alanine and glycine, cross-react poorly with GABA, requiring 175-fold or 795-fold higher concentrations, respectively. Immunocytochemical results indicated that the localization obtained with this GABA antiserum largely corresponds with that reported after glutamate decarboxylase immunocytochemistry. The approach may have general applicability to other small molecules such as amino acids.

Antibodies to dopamine: radioimmunological study of specificity in relation to immunocytochemistry

Two classes of anti-3,4- dihydroxyphenylethylamine (dopamine) antibodies were raised in rabbits using dopamine conjugated to albumin either via formaldehyde or via glutaraldehyde. Each was usable for immunohistochemical detection of dopamine neurons provided that the tissue was fixed by the homologous cross-linking agent. However, anti-dopamine-glutaraldehyde antibodies turned out to be of more general use because of the better fixative properties of glutaraldehyde which fixed dopamine in rat and in teleost, whereas formaldehyde only worked in lower vertebrates (such as goldfish) and not in rat brain. The specificity of anti-dopamine-glutaraldehyde antibodies was firmly established by competition experiments in equilibrium dialysis, using an immunoreactive tritiated derivative synthesized by coupling dopamine to N-alpha-acetyl-L-lysine N-methylamide via glutaraldehyde. Specificity studies in vitro and immunohistological results demonstrating the specific staining of dopaminergic neurons were found to correlate well.

Antisera against catecholamines: specificity studies and physicochemical data for anti-dopamine and anti-p-tyramine antibodies

Antibodies against dopamine and p-tyramine were raised in rabbits. The two catecholamines were conjugated to albumin by glutaraldehyde. The specificity of the antibodies was established by equilibrium dialysis competition experiments using an immunoreactive tritiated derivative synthesized by coupling dopamine or p-tyramine to N-alpha-acetyl-L-lysine N-methylamide with glutaraldehyde. Hence, these radiolabelled ligands mimicked the antigenic determinant of conjugated immunogens. A comparison of the data obtained showed the high specificity of each antiserum for its hapten coupled by glutaraldehyde. The anti-dopamine antibodies recognized dopamine-glutaraldehyde but not p-tyramine-glutaraldehyde. The opposite occurred for the anti-p-tyramine antibodies. A slight modification of the molecular structure provided the opportunity for a specific response against that molecule. But this difference was more important when related to the hapten region where the antibody affinity was maximal. The cross-reactivity was observed to be more important dopamine and p-tyramine than between dopamine and noradrenaline on the one hand and between p-tyramine and dopamine than p-tyramine and octopamine on the other hand.

Further evidence for lack of specific receptors for PGE2 in the rat ovary

Prostaglandin E2 (PGE2) seems to stimulate cAMP accumulation in ovaries of all mammals. While it acts through specific receptors in some species, our earlier observations (1) suggest absence of PGE2 receptors in the rat ovary. In order to further substantiate this assumption we digested ovarian membranes from the bovine and the rat with various enzymes and measured cAMP after stimulation with PGE2, NaF, and hCG. Pronase, trypsin, and phospholipase C abolished cAMP accumulation completely. Neuraminidase, beta-galactosidase and phospholipase D did not interfere with cAMP formation. After treatment with phospholipase A2, PGE2-mediated cAMP accumulation was abolished in the bovine but not in the rat ovary. Formation of cAMP disappeared after hCG but not after NaF in both species. Furthermore specific binding of PGE2 could not be demonstrated in phospholipase A2-treated bovine ovaries. These findings are consistent with presence of specific PGE2 receptors in the bovine and their absence in the rat ovary.

Ovarian-adrenal interactions in regulation of endocrine pancreatic function in the rat

The interference of adrenal hormones with the oestradiol-induced modifications of endocrine pancreatic function remains controversial. For this reason, we compared sham-operated, ovariectomized and adrenalectomized-ovariectomized female rats. In each group, control and 17-beta-oestradiol-treated rats (0.1 mg/day for 14 days) were studied, the latter group being compared with similar rats treated with corticosterone (0.4 mg/day). Oestradiol treatment induced hypoglycaemia and hyperinsulinism in basal and glucose-stimulated states, and hypoglucagonaemia. The presence of adrenal glands was necessary for the full expression of oestradiol effects on pancreatic islet B cells: in adrenalectomized-ovariectomized rats, oestradiol treatment induced an unexpected decrease in insulin response to intravenous glucose, and in pancreatic insulin content. Corticosterone treatment partly restored the oestradiol-induced rise of plasma insulin, and restored the B cell response to intravenous glucose. A permissive action of glucocorticoids may be a prerequisite for the effect of oestrogens on B cells. Since oestrogens by themselves augment the plasma corticosterone level, the insulinotropic effect of oestrogens may be partly mediated by the increase in endogenous corticosteroids. In contrast, oestradiol seems to suppress islet A cell function.

Ecdysone and 20 hydroxyecdysone: new hormones for the human parasite schistosoma mansoni

The insect moulting hormones, ecdysone and 20 hydroxyecdysone, were detected by the combined use of radioimmunoassay and high performance liquid chromatography in the human parasite Schistosoma mansoni. On day 11 after infection only the ecdysone form is present, but, on day 40 after infection the ratio between ecdysone and 20 hydroxyecdysone changes with anatomic localization of the adult worms in mammalian host. In the eggs, the ratio of these two hormones is identical to the ratio found in sexually mature worms located in mesenteric veins. These data demonstrate for the first time that S. mansoni synthesizes the steroid hormones ecdysone and 20 OH ecdysone which are potent molecules in stimulating growth and vitello-genesis of this gonochoric trematode.

A single radioimmunological assay for serotonin, N-acetylserotonin, 5-methoxytryptamine, and melatonin

A radioimmunoassay of melatonin using a new iodinated derivative has been developed. Simple chemical treatments have then been designed to convert serotonin, N-acetylserotonin, and 5-methoxytryptamine to melatonin. Thus these four molecules, belonging to the same metabolic pathway, were separately assayed in the same radioimmunological system at the same sensitivity level (0.01 pmol). Some biological results on the circadian variations of melatonin and serotonin in blood, pineal, and miscellaneous brain structures are presented.

Radioimmunoassay of insect juvenile hormones and of their diol derivatives

We have developed a radioimmunoassay for insect juvenile hormones. The C18 hormone (JH I) was first converted into diol by opening the 10, 11-epoxy ring. Diol was then succinylated and coupled to human serum albumin to make it immunogenic. High titer antisera were obtained from immunized rabbits. Succinyl juvenile hormone was also coupled to the peptide glycyltyrosine and iodinated so as to form a water-soluble 125I-labelled analogue well recognized by antibodies (60% bound by the 1/2000 000 dilution of antiserum routinely used in radioimmunoassay). Standards and biological samples were treated with acidic dioxane in order to convert each hormone into its corresponding diol. In this way, the sensitivity threshold of the radioimmunoassay was under 0.015 pmol. All three diols were equally recognized by the antibodies. Hormones JH I, JH II and JH III could be assayed separately as diols after thin-layer chromatography or high-pressure liquid chromatography purification of the biological samples. This method was used to determine physiological levels of juvenile hormones in the haemolymph of several insects at different development stages including embryos and in corpora allata cultures.

A radioimmunoassay for cyclic AMP (cAMP) obtained by acetylation of both unlabeled and labeled (3H-cAMP) ligand, or of unlabeled ligand only

A sensitive radioimmunoassay (limit of detection 7 +/- 1 fmol per tube) for cyclic AMP (cAMP) based on acetylation of both 3H-cAMP and unlabeled ligand was developed. Rabbit anti-cAMP antibodies had an apparent Ka for the acetylated ligand of 2 x 10(10) l/mol. When the unlabeled ligand only was acetylated an increased sensitivity was obtained without loss of specificity.

Heterogeneity of antibodies to adenosine 5'-monophosphate

Antibodies to adenosine 5'-monophosphate were produced in rabbits by injecting a conjugate of the nucleotide (oxidized with periodate) with bovine serum albumin. AMP-specific antibodies were isolated by affinity chromatography. The antiserum was first applied on oligoadenylic acids-agarose column and then the unbound proteins on a morpholine derivative of AMP-agarose column. The antibodies purified on these two columns interact differently with AMP derivatives as shown by immunodiffusion. These results are confirmed by the values of the binding constants of the complexes Fab fragments- AMP and AMP derivatives. The study of Fab fragments -- C(8)-substituted AMP derivatives complexes suggest a syn conformation for the bound nucleotide. Thermodynamic parameters for the Fab fragments-AMP complexes have been determined (deltaHdegrees = --13 kcal/mol and deltaSdegrees = --15 cal - degree-1 - mol-1).

Interactions of colipase with bile salt micelles. 2. Study by dialysis and spectrophotometry

The finding reported in the preceding paper that colipase is able to bind one sodium taurodeoxycholate micelle per molecule was confirmed by dialysis and spectrophotometry. Dialysis in the presence of labelled sodium taurodeoxycholate provided a direct qualitative proof of taurodeoxycholate binding to colipase. This binding was found to occur only above the critical micelle concentration. But, dialysis did not give any information about the composition of the associations, because equilibrium was not attained at the end of the assays. Addition of sodium taurodeoxycholate above the critical micelle concentration was also observed to induce a strong perturbation of the ultraviolet spectrum of one or several of the three tyrosines of colipase. The variation of the perturbation as a function of sodium taurodeoxycholate concentration was consistent with the binding of a single micelle to colipase. The dissociation constant calculated in "micelle molarity" was approximately 1 X 10(-4) M. The colipase-bile salt micelle association can fix one molecule of lipase to form a ternary complex which represents an interesting model of a protein-protein interaction mediated by an organized lipid structure. The ternary complex is probably also a model for lipase-substrate interactions in the presence of an amphipath.