Protein Phosphatase 5 Contributes to the Overexpression of Epigenetically Regulated T-Lymphocyte Genes in Patients with Lupus

OBJECTIVE

Lupus develops when genetically predisposed people encounter certain drugs or environmental agents causing oxidative stress such as infections and sun exposure, and then typically follows a chronic relapsing course with flares triggered by the exogenous stressors. Current evidence indicates that these environmental agents can trigger lupus flares by inhibiting the replication of DNA methylation patterns during mitosis in CD4⁺ T cells, altering the expression of genes suppressed by this mechanism that convert normal "helper" cells into auto reactive cells which promote lupus flares. How environmental stressors inhibit T cell DNA methylation though is incompletely understood. Protein phosphatase 5 (PP5) is a stress induced inhibitor of T cell ERK and JNK signaling in "senescent" CD4⁺CD28^- T cells, also characterized by DNA demethylation and altered expression of genes that promote atherosclerosis. We tested if PP5 is increased in CD4⁺CD28⁺ T cells by oxidative stress, if PP5 transfection causes overexpression of methylation sensitive genes in T cells, and if PP5 is overexpressed in lupus T cells.

RESULTS

PP5 was found to be overexpressed in CD4⁺CD28⁺ T cells treated with H₂O₂ and ONOO- and in T cells from lupus patients.

CONCLUSION

The results indicate that PP5 increases expression of methylation sensitive T cell genes, and may contribute to the aberrant gene expression in CD4⁺CD28⁺ T cells that characterize lupus flares as well as the aberrant gene expression in CD4⁺CD28^- T cells that promote atherosclerosis.

In vivo iron and zinc deficiency diminished T- and B-selective mitogen stimulation of murine lymphoid cells through protein kinase C-mediated mechanism

Zinc and iron are crucial mineral components of human diet, because their deficiency leads to several disorders, including alterations of the immune function. It has been demonstrated, in both humans and rodents, that a diminished number of lymphoid cells and a loss of lymphocyte activity accompany deprivation of these essential minerals. The aim of this work was to analyze if iron and/or zinc imbalances regulate lymphocyte activity and the intracellular signals involved in the effect. Mice from the BALB/c strain were fed with iron- and/or zinc-deficient or mineral-supplemented diets, according to the American Institute of Nutrition Rodent Diets. Levels of iron and zinc were assessed in blood, liver, or bone samples. Selective mitogen stimulation of T- and B-lymphocytes were performed. We found a diminished proliferative response in T- and B-lymphocytes from zinc- and/or iron-deficient animals with respect to controls. These effects were related to decreased mitogen-induced translocation of protein kinase C (PKC) activity to cell membranes on both cell types from all animals fed with deficient diets. Our results demonstrate that iron and zinc deficiencies affect both T- and B-lymphocyte function by PKC-dependent mechanisms.

Chronic stress influences the immune system through the thyroid axis

The aim of the present work was to analyze the effect of chronic stress on thyroid axis and its influence on the immune response. For this purpose a murine model of chronic stress was developed to evaluate and to correlate thyroid hormone levels with humoral alloimmune response. Results show a reduction in serum levels of thyroid hormones, specially a significant decrease in serum levels of triiodotyronine (T3) in stressed animals. On the other hand, alloimmunization was not able to induce an early increment in T3 and thyroxine (T4) levels as it was previously reported in normal animals. In addition, lower titers of alloantibodies were obtained in animals under stress conditions as compared to normal mice. The sustitutive T4 treatment in stressed animals increased significantly alloantibody production as well as the early increment in thyroid hormones after antigenic challenge. These findings suggest that chronic stress induces an alteration of the function of thyroid axis that alters the immune response.

Downregulation of beta adrenergic receptor expression on B cells by activation of early signals in alloantigen-induced immune response

Previously we described a decrease in beta-adrenergic receptor expression in B lymphocytes as a consequence of in vivo alloimmunization. This decrease correlates with the highest response of alloantibody production by B cells. In the present report we examined the participation of intracellular signals elicited after alloimmune stimulation. We showed that in vitro stimulation of B cells with mitomycin C-treated allogenic cells induced a reduction in the number of beta-adrenoceptors. This downregulation correlated to changes in basal and in isoproterenol-stimulated intracellular cAMP levels. We found that calcium mobilization and protein kinase C activation triggered after direct allogenic stimulation and/or by the action of T cell-soluble factors induced the reduction in beta-adrenoceptor sites. These findings could be of interest to understand the neuroendocrine mechanisms involved in the regulation of B cell activation.

Alterations in cardiac beta-adrenergic receptors in chagasic mice and their association with circulating beta-adrenoceptor-related autoantibodies

OBJECTIVE

Cardiac tissue from chagasic mice was studied to evaluate the expression and biological activity of beta-adrenoceptors in association with circulating beta-adrenoceptor-related autoantibodies.

METHODS

BALB/c inbred mice that were either treated or not treated with atenolol (2.5 mg/kg) and infected or not infected with 1 x 10(4) trypomastigotes (CA-1 strain) were sacrificed weekly up to week nine. Morphological, binding and contractility studies were performed on the four different groups of animals. The effect of their serum antibodies was also assayed in binding and contractility studies on normal heart preparations.

RESULTS

Hearts from chagasic myocarditis mice showed a beta-adrenoceptor-related dysfunction, with a decrease in heart contractility, impaired response to exogenous beta-adrenoceptor agonist and a significant reduction in beta-adrenergic binding sites. Those effects were maximum at eight-nine weeks post-infection and were improved by treating infected mice with atenolol. In addition, serum or IgG from chagasic myocarditis mice was capable of interacting with cardiac beta-adrenoceptors, reducing the number of binding sites and inhibiting the contractile response to exogenous norepinephrine. IgG effects that were observed in normal myocardium, were highest in sera from mice eight-nine weeks post-infection and correlate with the degree of myocarditis. Moreover, chagasic autoantibodies from infected mice recognized a peptide corresponding to the sequence of the second extracellular loop of the human beta 1-adrenoceptor.

CONCLUSIONS

(1) The development of alterations in beta-adrenergic receptors, related to cardiac dysfunction, may be associated with the presence of circulating antibodies against these receptors and (2) it is possible that the chronic deposits of these autoantibodies in cardiac beta-adrenoceptors could lead to a progressive blockade with sympathetic denervation, a phenomenon that has been described in the course of chagasic myocarditis.

Trypanosoma cruzi antigens down-regulate T lymphocyte proliferation by muscarinic cholinergic receptor-dependent release of PGE2

Here we demonstrate that T. cruzi antigen molecule SAPA (shed acute phase antigen) with neuraminidase-trans sialidase activity triggers down-regulation of T lymphocyte proliferation by interacting with T lymphocyte muscarinic acetylcholine receptors (mAChR). SAPA attachment to mAChR from Lyt 2.2+ T cells resulted in synthesis of cyclic GMP (cGMP) and secretion of PGE2, an immunoregulator effector substance. These T suppressor cell signals were blunted by atropine and by indomethacin. Cell sorter analysis showed that the interaction of SAPA with purified T cells, affected the ratio of L3T4+/Lyt 2.2+ T cells increasing the percentage of Lyt 2.2+ T cells, effect that was inhibited by the mAChR antagonist, atropine. The interaction between SAPA and mAChR from Lyt 2.2+ T cells may result, therefore, in the down-regulation of the host immune response as consequence of T suppressor/cytotoxic cells activation and PGE2 release as they were observed. These results support the theory of an immunosuppressive state that contribute to the chronic course of Chagas' disease.

Angiotensin 1-7 induces bradykinin-mediated relaxation in porcine coronary artery

Angiotensin 1-7 (Ang 1-7) has been reported to induce relaxation which is partially blocked by a kinin receptor antagonist. We investigated the relationship between kinins and angiotensin peptides with use of preconstricted isolated pig coronary arteries. Ang 1-7 alone (up to 10(-5) M) had no relaxant effect. Bradykinin (BK) (10(-10)-10(-7) M) induced transient relaxation, returning to basal tone, although BK remained in the bath. In these BK-stimulated rings, Ang 1-7 but not BK (both 5 x 10(-6) M) again relaxed the rings by approximately 50%. This relaxation was blocked by a BK B2 antagonist, a kininase, and a nitric oxide synthase inhibitor. Ang 1-7 inhibited purified angiotensin-converting enzyme (ACE) by 30 +/- 3.5% (n = 4) at 10(-6) M. However, in BK-pretreated rings, the ACE inhibitor ramiprilat did not induce relaxation, nor did it affect the relaxant response to Ang 1-7, which suggests that the effect of Ang 1-7 was not caused by ACE inhibition. Ang 1-7-induced vasodilation was reduced by 69.9 +/- 6.2% by an AT2 receptor blocker, PD-123319, and 29.3 +/- 7.3% by an AT1 antagonist, losartan. Neither the nonselective AT1/AT2 receptor antagonist sarthran nor saralasin inhibited the response to Ang 1-7. Ang II did not elicit relaxation either alone or in the presence of losartan, which suggests that activation of AT2 receptors does not cause relaxation. Thus, in the presence of bradykinin, Ang 1-7 relaxes pig coronary arteries via a PD-123319-sensitive mechanism involving nitric oxide, kinins and the BK B2 receptor. The kallikrein-kinin and renin-angiotensin systems may be linked through the interaction of Ang 1-7 and BK.

Angiotensin-(1-7) induces bradykinin-mediated hypotensive responses in anesthetized rats

Angiotensin-(1-7) [Ang-(1-7)] reportedly potentiates hypotensive responses to bradykinin. We studied whether increases in circulating bradykinin would alter responses to Ang-(1-7). In rats anesthetized with thiobutabarbital, bradykinin infusion (5 microg/kg per minute I.A.) resulted in a rapid decrease in mean arterial pressure (MAP) of about 20 mm Hg (P<.01, n=9), although MAP slowly increased by 10 mm Hg after 15 minutes. When Ang-(1-7) (20, 80, and 380 nmol per rat I.A.) was given during bradykinin infusion, it elicited hypotension at 80 and 380 nmol (deltaMAP: -15+/-2.7 and -21+/-3.3 mmHg, respectively; P<.001); this hypotension was not affected by the angiotensin type 1 antagonist L-158,809 (200 microg/kg I.A.), the angiotensin type 2 antagonist PD 123319 (10 mg/kg I.A.), saralasin, or sarthran (10 microg/kg per minute). The bradykinin type 2 receptor antagonist icatibant (30 microg per rat) eliminated the hypotensive responses to Ang-(1-7), which now increased MAP at all doses tested (P<.005). Thus in the presence of bradykinin, Ang-(1-7) induces hypotensive responses that are blocked by icatibant and unaffected by angiotensin receptor antagonists. Ang-(1-7) given to saline-infused rats elicited hypertensive responses at all doses (deltaMAP: 6.4+/-1.5, 12+/-1.6, and 16.3+/-2.7 mmHg, respectively; P<.01); these responses were abolished by L-158,809 and sarthran. In rats pretreated with saralasin, Ang-(1-7) induced hypotension at 80 and 380 nmol (deltaMAP: -7.7+/-2.3 and -9.5+/-2.7, respectively; P<.05), whereas icatibant abolished this response. Thus in the rat, Ang-(1-7) can decrease blood pressure by a mechanism involving the bradykinin type 2 receptor and participates with bradykinin in a vasodepressor pathway that may serve a counterregulatory role, modulating the vasoconstrictor effects of Ang II.

Lymphocyte muscarinic cholinergic activity and PGE2 involvement in experimental Trypanosoma cruzi infection

In this paper, we demonstrated that the production of PGE2 by CD8+ T lymphocytes through muscarinic cholinergic receptor (mAChR) activation of lymphocytes from mice acutely infected with nonlethal Trypanosoma cruzi CA-1 strain could enhance resistance to infection. Treatment in vivo with either atropine or cyclooxygenase inhibitors enhanced mortality rates and parasitemia of mice infected with T. cruzi CA-1 strain. The mechanism by which CD8+ T lymphocytes released PGE2 appears to involve the activation of the cells by circulating IgG present in mice infected with T. cruzi CA-1 strain. Binding of these antibodies to mAChR on CD8+ T lymphocytes triggered the release of large amounts of PGE2. The results point to a role of serum antibodies against mAChR in the protection of T. cruzi infection. The prostanoid acting as an immunomodulator contributed to the maintenance of the chronic course of experimental Chagas disease.

Modulation of cardiac physiology by an anti-Trypanosoma cruzi monoclonal antibody after interaction with myocardium

Circulating antibodies from human and murine chagasic sera are able to interact with myocardium, activating neurotransmitter receptors. Here, we studied the effects of a monoclonal antibody (MAb CAK20.12), which recognizes a 150 kilodalton antigen of Trypanosoma cruzi and reacts with normal human and murine striated muscles and with cardiac tissue. The MAb CAK20.12 binds to purified cardiac membranes and interferes with the binding of beta-adrenergic receptor radioligand ([125I]CYP) and muscarinic cholinergic receptor (mAChR) radioligand ([3H]QNB) in a noncompetitive way. As a consequence of this interaction, beta-adrenergic receptor and mAChR were activated, leading to increased intracellular levels of cyclic AMP as a result of beta-adrenergic receptor-coupled adenylate cyclase triggering. When its sympathetic action was abrogated, it also induced an mAChR-mediated increase in cyclic GMP. Furthermore, cardiac physiology was modified by MAb CAK20.12, as it was able to increase cardiac contractility through beta-adrenoceptor activation and to decrease atrial frequency as a result of mAChR activation. The fact that this MAb modulates and modifies the mechanical and biochemical activity of normal murine heart established an important basis for future research and understanding of how the host's humoral immune response acts on the course and development of the chronic chagasic myocardiopathy.

Down-regulation of beta-adrenergic receptors induced by mitogen activation of intracellular signaling events in lymphocytes

The expression of beta-adrenergic receptors on murine lymphocytes stimulated with concanavalin A was studied. A decrease in beta-adrenoceptor number on T lymphocytes and a diminished response to specific agonist stimulation at the peak of proliferation was found. The blockade of cell proliferation by tyrosine kinases or protein kinase C inhibitors reversed the decrease in beta-adrenoceptor number. PMA plus ionophore or interleukin-2 but not PMA alone were able to induce beta-adrenoceptor down-regulation accompanying cellular proliferation. These results showed that the intracellular signals triggered during lymphocyte activation are involved in beta-adrenoceptor down-regulation and it would represent the loss of a mechanism that exerts negative neuroimmune control of cellular proliferation.

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE2 involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE2 serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE2 release per cell by CD8+; values of PGE2 release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE2 (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE2 could play a role in resistance in mice infected with K98.

Antilaminin IgG triggers the murine atria phosphoinositide hydrolysis through muscarinic receptor stimulation

Induction of polyphosphoinositide hydrolysis in cardiac tissue by specific recognition of laminin by antilaminin IgG was assayed. BALB/c mice atria were labelled with the myo-[3H]-inositol precursor and inositol phosphate production was measured in the presence and absence of antilaminin and normal IgG. Antilaminin IgG but not normal IgG specifically increased phosphoinositide (PI) turnover. This increment was blocked by the muscarinic cholinergic antagonist atropine and mimicked by the cholinergic agonist carbachol. The phospholipase C inhibitor diphenylcarbamate (NCDC) also antagonized the stimulatory action of antilaminin IgG on PI turnover. By using an immunofluorescence technique, antilaminin IgG reacted with myocardial cell basement membranes. This antibody fixation was not blocked by atropine. These data suggest that antilaminin IgG specifically recognized myocardial laminin molecules and activated PI turnover through cholinergic stimulation. Even though laminin and cholinergic receptors are different, they probably share common signal transduction systems.

Prostanoids synthesis in lymphocyte subpopulations by adrenergic and cholinergic receptor stimulation

The release of eicosanoids (PGE2 and TXB2) as a consequence of specific neurotransmitter receptor agonist stimulation is described herein. The differential expression of beta adrenergic and muscarinic cholinergic receptors on sets and subsets of lymphocytes was first identified. Saturation assays with a specific radioligand for beta adrenergic receptors (3H-DHA) showed that B-, T-, T-helper (Th) and T-suppressor/cytotoxic (Ts/c) lymphocyte enriched populations all displayed beta adrenergic receptors. In contrast, when a specific radioligand for muscarinic cholinergic receptors (3H-QNB) was used, B-lymphocytes showed a lack of high-affinity muscarinic cholinergic receptors, while T-lymphocytes expressed them. Ts/c murine lymphocytes had more muscarinic cholinergic receptors than did Th cells. Specific receptor stimulation by the agonist caused a release of different eicosanoids depending on the cell type. Isoproterenol, triggered the release of TXB2 by B and Th-cells, but had no effect on Ts/c-cells. On the other hand, the muscarinic cholinergic agonist, carbachol only induced the release of PGE2 by Ts/c-cells. These results suggest differences in the expression and function of neurotransmitter receptors in sets and subsets of murine lymphocytes regarding the release of eicosanoids.

Chagasic IgG stimulates phosphoinositide hydrolysis via neurotransmitter receptor activation: role of calcium

Induction of polyphosphoinositide hydrolysis in cardiac tissue by IgG from chagasic mice was assayed. BALB/c mice auricles were labelled with myo-[3H]inositol precursor and inositol phosphate production in the presence or absence of chagasic IgG and the corresponding F(ab')2 was measured. Both chagasic IgG and F(ab')2 but not the normal forms specifically increased phosphoinositide turnover. This increment was blocked by muscarinic cholinergic antagonists and to an even greater extent by the phospholipase C inhibitor NCDC. Moreover, calcium channel blocking agents such as diltiazem, verapamil and D-600 also exerted an inhibitory action. A muscarinic cholinergic agonist, carbachol, and the ionophore A-23187, mimicked the action of the chagasic IgG upon phosphoinositide turnover. It is concluded that murine chagasic IgG and its F(ab')2 fragments result in stimulation of phospholipase C-mediated phosphoinositide hydrolysis through the interaction with muscarinic cholinergic receptors requiring the cytosolic calcium concentration to be raised.

Modification of G regulatory protein mediated actions by the interaction of histocompatibility antigens with cardiac muscarinic cholinergic receptors

In this work we characterized the interaction of class I histocompatibility (HC) antigens (Ag) with cardiac cholinergic receptors by means of specific radioligand binding and by production of cholinergic-mediated cellular transmembrane signals. Alloimmune as well as anti-class I but not anti-class II antibodies were able to inhibit in an allosteric manner the binding of [3H]quinuclidinyl benzilate to cardiac membrane. Moreover, alloantibody could modify all of the muscarinic cholinergic effects mediated by a G regulatory protein, i.e. decrement of atria contractility, inhibition of cAMP stimulation, and activation of the turnover of phosphoinositides via phospholipase C. The cGMP production was not altered by the alloantibody. The data indirectly indicated that HC-Ag-muscarinic cholinergic interactions trigger all the cholinergic functions related to G proteins. The induction of intracellular second messengers by class I antigens and hormone-receptor interactions is discussed.

T lymphocytes from T. cruzi-infected mice alter heart contractility: participation of arachidonic acid metabolites

T lymphocytes from T. cruzi infected mice susceptible to the development of myocarditis altered the contractility of normal mouse atria in vitro. While lymphocytes obtained from normal mice had no effect, lymphocytes from T. cruzi-infected mice cultured with normal atria induced negative or positive inotropic effects depending upon the post-infection period; negative inotropism was induced by lymphocytes obtained from animals at 1 to 4 weeks post-infection, and positive inotropism was induced by lymphocytes taken at 7 to 14 weeks post-infection. These effects were mediated by soluble factors as evidenced by the ability of lymphocyte culture supernatants to alter contractility. Cell enrichment experiments indicated that T lymphocytes rather than B lymphocytes were responsible for these inotropic effects. Lyt(2+)-enriched T lymphocytes were found to be responsible for triggering the negative inotropic effect at 3 weeks post-infection when myocarditis was less intense, whereas Lyt1(+)-enriched T lymphocytes induced the positive inotropic effect at 8 weeks after T. cruzi infection when myocarditis was severe. Furthermore, inhibitors of the cyclooxygenase pathway of arachidonic acid metabolism blunted the negative inotropic effect while inhibitors of lipoxygenase pathway inhibited the positive inotropic effect. PGE2 was found to be spontaneously released by Lyt(2+)-enriched T cells obtained at 3 weeks post-infection while LTC4 was released by atria cultured in the presence of Lyt 1+ T cells obtained at 8 weeks post-infection. In conclusion, these findings suggest that infiltrating T lymphocytes may contribute to myocardial dysfunction during T. cruzi infection by releasing or inducing the release of harmful arachidonic acid metabolites such as PGE2 and LTC4 which alter normal cardiac function.

Chagasic IgG binding with cardiac muscarinic cholinergic receptors modifies cholinergic-mediated cellular transmembrane signals

The interaction of the IgG from Trypanosoma cruzi-infected mice (chagasic IgG) with cardiac cholinergic receptors by means of specific radioligand binding and by production of cholinergic-mediated cellular transmembrane signals was characterized. Chagasic IgG inhibited, in a noncompetitive manner, the binding of [3H]quinuclidinyl benzilate to the cardiac membrane. Moreover, chagasic IgG could modify all of the muscarinic cholinergic effects mediated by a G regulatory protein, i.e., decrement of atria contractility, inhibition of cAMP, or activation of the turnover of phosphoinositides via phospholipase C. The cGMP production was also increased by the antibody. The data demonstrated that chagasic IgG interacting with cardiac muscarinic cholinergic receptor triggers the biological effects associated with cholinergic-mediated cellular transmembrane signals. The implications of the results in the pathogenesis of Chagas' myocarditis are discussed.

Trypanosoma cruzi attachment to lymphocyte muscarinic cholinergic and beta adrenergic receptors modulates intracellular signal transduction

Plasma membrane vesicles of Trypanosoma cruzi (PMVs) formed saturation binding isotherms with naive murine T lymphocytes. Parasite membrane attachment to the muscarinic cholinergic receptors of Lyt 2.2+T cells (suppressor cells) resulted in the synthesis of cGMP, attenuation of cAMP levels and in the secretion of prostaglandin E2, an immunoregulator effector substance. These T suppressor cell signals were blunted by atropine and by monospecific antibody against T. cruzi surface epitopes. The interaction of T. cruzi PMVs with the beta adrenergic receptors of Lyt L3T4+T cells (helper cells) resulted in the synthesis of cAMP and in the attenuation of cGMP levels. T helper cells did not secrete prostaglandin E2 when T. cruzi PMVs were added to this system. These T helper cell signals were blunted by propranolol and by monospecific antibody against T. cruzi surface epitopes. The interaction of T. cruzi with T lymphocytes may result, therefore, in the down-regulation of the immune response induced by prostaglandin E2 T suppressor cell secretion and by cAMP inhibition of proliferation of T helper cells.

Antibodies bind and activate beta adrenergic and cholinergic lymphocyte receptors in Chagas' disease

It is demonstrated that murine chagasic IgG and the corresponding F(ab')2 fragments interfere with beta adrenergic and muscarinic cholinergic specific ligand occupancy on T cell-enriched population. From the interaction between chagasic IgG or F(ab')2 with Lyt-1+ cells, an increase in cAMP levels occurs as a consequence of beta adrenergic receptor activation. On the contrary, chagasic IgG or F(ab')2 interactions with Lyt-2+ cells induce an activation of muscarinic cholinergic receptor, leading to an increment in cGMP. Muscarinic cholinergic and beta adrenergic stimulation trigger the release of PGE2 and TXB2, respectively. Lyt-2+ cells treated with chagasic IgG or F(ab')2 are able to decrease the contractility of mouse atria. The same negative inotropic effect is elicited with Lyt-2+ cells from Trypanosoma cruzi-infected mice susceptible to developed myocarditis. The implications of these results in the pathogenesis of Chagas' myocarditis are discussed.

Human chagasic IgG interacting with lymphocyte neurotransmitter receptors triggers intracellular signal transduction

It is demonstrated that human IgG in Chagas' disease and the corresponding F(ab)'2 fragment attach to lymphoid cells by specific interaction with beta-adrenergic and muscarinic cholinergic receptors. This interaction resulted in the transduction of signals that increased intracellular levels of cAMP in enriched T helper cell preparations and cGMP in enriched T suppressor cell preparations. The stimulation of Ts cell muscarinic cholinergic receptors by Chagas IgG or the corresponding F(ab)'2 fraction triggers the release of the immunomodulatory substance PGE2. These results are unified in a theory of immunoregulation and could contribute to the chronic course of Chagas' disease.

Dual effects of alpha-adrenoceptor agonist on contractility of mice isolated atria

Contractility responses of mice atria to alpha-adrenergic agonists (methoxamine and clonidine) were studied. The alpha-adrenergic agonists increased the rate of force development (dF/dt) and decreased contractile frequency. The positive inotropic effect was mediated through cardiac alpha-adrenoceptors, while the negative chronotropic effect involved parasympathetic activation. Blockers of phospholipase C inhibited both the positive inotropic and the negative chronotropic effects of the alpha-adrenergic agonists. Inhibitors of phospholipase A2 and cyclooxygenase activity attenuated the positive inotropic effect of the agonists without modifying the negative chronotropic effect.

Diabetes alters the reactivity of myocardium to a thromboxane analogue

Atrial contractile response to U-46619 was studied in auricles from normal and acutely diabetic rats. U-46619 induced an increment of dF/dt in diabetic atria, whereas nondiabetic auricles elicited a negative contractile effect. Blockers of arachidonic acid metabolism via cyclooxygenase inhibited the stimulatory action of U-46619. The stimulant action of the thromboxane A2 mimetic was attenuated when diabetic auricles were incubated with lipoxygenase(s) blocking agents. Results suggest that in diabetic atria, the abnormal inotropic effect induced by U-46619 may be associated with thromboxane formation and with lipoxygenase(s) metabolites.