Infection with Helicobacter pylori is responsible for gastritis and gastroduodenal ulcers but is also a high risk factor for the development of gastric adenocarcinoma and lymphoma. The most pathogenic H. pylori strains (i.e., the so-called type I strains) associate the CagA virulence protein with an active VacA cytotoxin but the rationale for this association is unknown. CagA, directly injected by the bacterium into colonized epithelium via a type IV secretion system, leads to cellular morphological, anti-apoptotic and proinflammatory effects responsible in the long-term (years or decades) for ulcer and cancer. VacA, via pinocytosis and intracellular trafficking, induces epithelial cell apoptosis and vacuolation. Using human gastric epithelial cells in culture transfected with cDNA encoding for either the wild-type 38 kDa C-terminal signaling domain of CagA or its non-tyrosine-phosphorylatable mutant form, we found that, depending on tyrosine-phosphorylation by host kinases, CagA inhibited VacA-induced apoptosis by two complementary mechanisms. Tyrosine-phosphorylated CagA prevented pinocytosed VacA to reach its target intracellular compartments. Unphosphorylated CagA triggered an anti-apoptotic activity blocking VacA-induced apoptosis at the mitochondrial level without affecting the intracellular trafficking of the toxin. Assaying the level of apoptosis of gastric epithelial cells infected with wild-type CagA+/VacA+ H. pylori or isogenic mutants lacking of either CagA or VacA, we confirmed the results obtained in cells transfected with the CagA C-ter constructions showing that CagA antagonizes VacA-induced apoptosis. VacA toxin plays a role during H. pylori stomach colonization. However, once bacteria have colonized the gastric niche, the apoptotic action of VacA might be detrimental for the survival of H. pylori adherent to the mucosa. CagA association with VacA is thus a novel, highly ingenious microbial strategy to locally protect its ecological niche against a bacterial virulence factor, with however detrimental consequences for the human host.

In the aged rat, the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis was found to be increased. In fact, the plasma corticosterone concentrations in the aged (25 months) Sprague-Dawley rat were higher than in the young (3 months) Sprague-Dawley rat. To determine which component of the HPA axis principally contributes to this hyperactivity, an in vitro approach was applied. Neither the adrenal nor the pituitary revealed any age-induced modification in their basal or hormone-stimulated in vitro activity. Moreover, the ability of corticosterone to inhibit the in vitro stimulated pituitary adrenocorticotropic hormone release was preserved in aged rats. On the contrary, the in vitro hypothalamic activity was altered in aged rats. The basal and stimulated release of bioactive corticotropin-releasing factor were increased in aged rats. The results obtained in this study indicate that the hypercorticosteronemia of the aged Sprague-Dawley rat is associated with hypothalamic hyperactivity and with normal in vitro activity and reactivity of the adrenal and pituitary.

As shown by an increase in plasma corticosterone concentrations, adenosine administration stimulated pituitary-adrenocortical activity. This effect was prevented by dexamethasone (2 mg/kg i.p.). Added in vitro, adenosine reduced both adrenal basal and adrenocorticotropic hormone (ACTH)-stimulated corticosterone release, while it stimulated pituitary ACTH release. This ACTH response was blocked by dexamethasone but not by Tyr-somatostatin. Restraint stress increased adenosine content in the anterior pituitary, suggesting its possible involvement in hormonal stress response. Because the effect of adenosine on plasma corticosterone was still present in rats with a pharmacological block of the endogenous corticotropin-releasing factor release, we propose that adenosine is involved in the regulation of adrenocortical secretion at the level of the anterior pituitary and that this role is exerted through an interaction with a stimulatory adenosine receptor.

SummaryCysteinyl leukotrienes (i.e. LTC4, LTD4), produced by activated leukocytes or by transcellular metabolism may act at different levels on vascular smooth muscle cells (VSMC) during inflammatory processes or atherosclerosis. We studied the effect of LTC4, LTD4, and LTE4 on the in vitro proliferation of rat VSMC, measured by [3H]-thymidine incorporation and cell count. LTD4 had a stronger stimulatory effect on [3H]-thymidine incorporation than LTC4, whereas LTE4 was inactive. The effect of LTD4 on [3H]-thymidine incorporation was dose-dependent, with the maximal activity at 10−6 M. The stimulatory activity of LTD4 was inhibited in a dose-dependent manner by MK-571, a specific LTD4 receptor antagonist. In addition, MK-571 (1 mg/kg/day) given for at least 1 day after injury in a model of balloon catheter injury of rat carotid artery, provided effective inhibition of myointimal VSMC proliferation, with a 58% reduction of 5-bromo-2’-deoxyuridine (BrdU) uptake in the neointima and 69% reduction of neointimal thickening. Our data support the importance of inflammatory mechanisms in the pathogenesis of atherosclerosis and suggest a possible role for cysteinyl leukotrienes, specifically LTD4, in the control of VSMC proliferation.

Although the role of serotonin (5HT) in the regulation of anterior pituitary hormone secretion is well documented, the involvement of specific 5HT receptor subtypes in this action is not yet fully elucidated. In the present work we attempted to determine the neuroendocrine role of the 5HT1A receptor subtype. This was chosen mainly because highly selective pharmacological tools are available for that subtype. 8-Hydroxy-2-(di-n-propylamino)tetralin (8OHDPAT) and ipsapirone were injected iv in conscious, freely moving male rats cannulated in the jugular vein. For the sake of comparison, a 5HT receptor agonist with preference for the 5HT1B and 5HT1C receptor subtypes 1-(m-trifluoromethyl-phenyl)piperazine (TFMPP) was also administered. Plasma PRL, ACTH, and beta-endorphin levels increased in a dose-dependent manner after 8-OHDPAT (0.01-1 mg/kg) or ipsapirone (0.5-7.5 mg/kg) injection. Maximal effects were obtained between 7-15 min. Only the highest dose of 1-(m-trifluoromethyl-phenyl)piperazine (5 mg/kg) resulted in the same response. In contrast, none of the drugs used affected plasma GH, TSH, or LH levels at any dose tested. The results indicate that 5HT1A receptors are involved in the regulation of PRL as well as ACTH and beta-endorphin secretion. 8OHDPAT was almost 40 times more potent than ipsapirone. The maximal effects of the two drugs on PRL release were comparable. In contrast, ipsapirone behaved as a partial agonist only on ACTH and beta-endorphin secretion, thus suggesting that different neuronal targets are involved in the stimulation of the three hormones by 5HT.