Down-regulation of inducible nitric-oxide synthase (NOS-2) during parasite-induced gut inflammation: a path to identify a selective NOS-2 inhibitor

Nitric oxide (NO) possesses potent anti-inflammatory properties; however, an over-production of NO will promote inflammation and induce cell and tissue dysfunction. Thus, the ability to precisely regulate NO production could prove beneficial in controlling damage. In this study, advantage was taken of the well characterized inflammatory response caused by an intestinal parasite, Trichinella spiralis, to study the relationship between intestinal inflammation and the regulation of nitric oxide synthase-type 2 (NOS-2) expression. Our study revealed that a specific gut inflammatory reaction results in inhibition of NOS-2 expression. Characteristics of this inhibition are: 1) local jejunal inflammation induced by T. spiralis systemically inhibits NOS-2 gene transcription, protein expression, and enzyme activity; 2) the inhibition blunts endotoxin-stimulated NOS-2 expression; 3) the inhibition does not extend to the expression of other isoforms of NOS, to paxillin, a housekeeper protein, or to cyclooxygenase-2, another protein induced by proinflammatory cytokines; 4) the inhibition is unlikely related to the formation of specific anti-parasite antibodies; and 5) the inhibition may involve substances other than stress-induced corticosteroids. Elucidation of such potent endogenous NOS-2 down-regulatory mechanisms could lead to the development of new strategies for the therapy of inflammatory conditions characterized by the overproduction of NO.

Does the binding of cyclosporine to calmodulin result in immunosuppression?

The cyclosporines are a family of cyclic endecapeptides that cause a profound suppression of primary immune stimulation both in vitro and in vivo. Recently, the regulatory protein calmodulin (CaM) has been implicated as a target for cyclosporin A (CsA) binding. This study utilized two less-active isomers of CsA to evaluate the specificity and biological significance of CaM binding. The three cyclosporines exhibited equivalent in vitro binding to CaM, regardless of immunosuppressive activity. Furthermore, CaM-dependent enzyme systems were inhibited equally by active and inactive cyclosporines, but only at concentrations 100 times those necessary to block lymphocyte activation. Thus the exquisite immunosuppressive stereospecificity displayed by cyclosporine isomers is not reflected in the binding to and inhibition of CaM, suggesting that inhibition of CaM-dependent processes is not sufficient to explain the immunosuppressive activity of CsA.

Does interferon exert its actions through opiate receptors

It had been reported that alpha interferon (alpha-IFN) induces endorphin-like effects such as analgesia and catatonia. These effects, reversed and prevented by naloxone, suggest that the alpha-IFN effect is mediated via opiate receptors. In order to examine this hypothesis, the present study was initiated. Extracellular cortical cell recording and microiontophoretic application of alpha-IFN, morphine, and naloxone, as well as the application of these three drugs on the coaxially stimulated guinea-pig ileum preparation were used. alpha-IFN application induced excitation in cortical cells and on the guinea-pig ileum. In contrast, the main effect elicited by morphine was a decrease in both preparations. Naloxone was able to reverse and/or prevent the morphine effects in both preparations, but failed to alter the effects induced by alpha-IFN. The present observations using the guinea-pig ileum preparation and cortical neurons recording failed to support the hypothesis that alpha-IFN effects are mediated via opiate receptors.

Effect of dopamine on esophageal motor function

Intravenous administration of dopamine produced a dose-dependent decrease in lower esophageal sphincter pressure and a dose dependent increase in contractile activity of the body of the esophagus. The threshold dose of dopamine was 0.25 mug/kg, and the effect reached a plateau at about 6 mug/kg. A dose of 6 mug/kg of dopamine produced 83%+/-3 (SE) reduction in the lower esophageal sphincter pressure and 12+/-1 (SE) contractions in the body of the esophagus within 5 min of the bolus injection. Atropine, phentolamine, propranolol, and bilateral cervical vagotomy did not modify the effect of dopamine. Both haloperidol and bulbocapnine potently antagonized the effect of dopamine. The amplitude of esophageal contraction in the lower esophagus in response to pharyngeal stimulation and esiogageal distention was significantly increased after administration of haloperidol. It is concluded that intravenous administration of dopamine has potent effects on the motor function of the lower esophageal sphincter and the body of the esophagus. The effect of dopamine is not mediated via the vagal centers in the brain or cholinergic muscarinic and adrenergic receptors. The response of the smooth muscle segment of opossum esophagus to intravenous dopamine is mediated via specific dopamine receptors. The inhibitory dopamine receptors may play a physiological role in controlling the amplitude of esophageal contractions.