Endothelium-derived nitric oxide is involved in the hypotensive and vasorelaxant effects induced by discretamine in rats.

The aim of this study was to investigate the pharmacological effects of discretamine, an isoquinoline alkaloid isolated from Duguetia magnolioidea Maas, on the cardiovascular system, using a combined in vivo and in vitro approach. Blood pressure and heart rate measurements, as well as changes in isometric tension in rat superior mesenteric arterial rings, elicited by discretamine were recorded. In normotensive non-anaesthetized rats (n = 6), discretamine (0.01; 0.05; 0.1; 0.5; 1, 5 and 10 mg/kg i.v., randomly) injections produced hypotension (-5.2 +/- 1.7; -5.1 +/- 2.1; -7.7 +/- 2; -8.9 +/- 1.7; -9.6 +/- 2.2; -16.8 +/- 2.8 and -13.4 +/- 1.3 mmHg, respectively) accompanied by tachycardia (24.2 +/- 6.1; 36.8 +/- 11.3; 44.2 +/- 7.7; 45.9 +/- 6.4; 48.2 +/- 9.1; 72.1 +/- 14.5 and 64 +/- 17 bpm, respectively). Hypotensive and tachycardic responses were significantly attenuated after L-NAME (20 mg/kg, i.v.) administration. In isolated rat mesenteric artery rings, with endothelium intact, discretamine (10(-12) - 10(-5) M) induced concentration-dependent relaxation of the contractions induced by phenylephrine (10 microM) [pD2 = 6.8 +/- 0.1]. The effect of the discretamine on phenylephrine induced contractions was significantly attenuated after removal of the vascular endothelium [pD2 = 5.8 +/- 0.04]. Similar results were obtained after pre-treatment with L-NAME 100 microM [pD2 = 5.8 +/- 0.04], L-NAME 300 microM [pD2 = 5.9 +/- 0.06], Hydroxocobalamin 30 microM [pD2 = 5.8 +/- 0.06] or ODQ 10 microM [pD2 = 5.8 +/- 0.04]. In addition, in rabbit aorta endothelial cell line, discretamine significantly increased NO3- levels. These results suggest that the hypotensive effect induced by discretamine is probably due to a peripheral vasodilatation, at least, in part, due to the release of NO from vascular endothelium and consequent activation of soluble guanylyl cyclase (GC) in the vascular smooth muscle cells.

Prevalence and risk factors for human toxoplasmosis in a rural community

Toxoplasma gondii infection may lead to important pathological questions, especially in rural areas, where several sources of infection exist. Therefore, it is important to determine risk factors in order to establish adequate prophylactic measures. The present study aimed to assess the prevalence and risk factors involved in human toxoplasmosis infection in a rural community, in Eldorado, Mato Grosso do Sul State, Brazil. This community was composed of 185 farms - with 671 inhabitants - from which 20 were randomly chosen. In these farms, blood samples were collected from rural workers, who also answered a risk factor questionnaire. Serum samples were analyzed by means of direct agglutination test for the detection of anti-Toxoplasma gondii antibodies. From 73 samples collected, 79.45% were positive. None of the studied variables was significantly associated with the prevalence of the infection. However, among the individuals who reported eyesight impairments, 94.4% had anti-T. gondii antibodies, compared with 74.0% who did not report eyesight changes (p = 0.0594). Moreover, most individuals in the study (68.20%) were older than 18 years and presented 84.44% positivity, compared with 66.67% of positive individuals younger than 18 years old. We were able to conclude that a high prevalence of antibodies did not imply significant associations with the risk factors studied.(AU)

Pharmacological profile of nitrergic nerve-, nitric oxide-, nitrosoglutathione- and hydroxylamine-induced relaxations of the rat duodenum.

Activation of inhibitory nonadrenergic noncholinergic (NANC) nerves in the rat duodenum cause relaxations, which are reduced by nitric oxide synthase (NOS) inhibitors indicating that this response involves a nitrergic neurotransmission. The precise nature of the nitrergic neurotransmitter is still controversial since nitric oxide (NO) scavengers and superoxide generators, even in the presence of superoxide dismutase inhibitors, failed to inhibit nitrergic neurotransmission mediated relaxations. In order to understand the role of NOS in nitrergic neurotransmission and considering that N-OH-arginine (OH-L-Arg), L-citrulline, NO, S-nitrosoglutathione (GSNO) and hydroxylamine (NH2OH) can be formed in cells during the N(G)-oxidation of L-arginine catalyzed by NOS we explored whether any of these products could exhibit biological properties comparable to those of the nitrergic neurotransmitter. After establishing which of them was able to relax the rat duodenum, the pharmacological profile of such effect was determined employing oxyhemoglobin (OxyHb), pyrogallol (PYR), hydroquinone (HQ), hydroxocobalamin (HC) or carboxy-PTIO (C-PTIO) and compared with that of nerve mediated relaxations. NO, GSNO and NH2OH, but not OH-L-ARG and L-citrulline, caused concentration-dependent relaxations that were not affected by tetrodotoxin or L-NOARG. OxyHb almost abolished NO-induced relaxations but decreased only marginally the magnitude of nerve-, NH2OH- and SNG-induced relaxations. PYR, HQ and C-PTIO reduced significantly GSNO- and NO- induced relaxations but did not affect those induced by NH2OH or nerve activation. In contrast, HC abolished NO-induced relaxations while it did not affect those induced by GSNO, NH2OH and nerve activation. The catalase inhibitor 1,2,4 aminotriazole failed to affect nerve and NH2OH induced relaxations. These findings indicate that among the products that can be formed during NOS catalyzed L-arginine N(G)-oxidation, only NH2OH caused relaxations that exhibited a pharmacological profile similar to those induced by the nitrergic neurotransmitter. Furthermore, if NH2OH is the actual neurotransmitter it appears to be acting either directly or by a catalase independent release of NO.

Effect of hydroquinone, hydroxocobalamin and carboxy-PTIO on non-adrenergic non-cholinergic nerve mediated relaxations of the rat duodenum.

Relaxation induced by NANC-nerve stimulation is reduced by nitric oxide synthase (NOS) inhibitors but not by superoxide generators or NO scavengers, casting doubts on the precise nature of the neurotransmitter being released by these nerves. The lack of effect of superoxide anion generators to inhibit nitrergic nerve-mediated relaxations has been attributed to the protective action of high tissue levels of superoxide dismutase (SOD). The effects of hydroquinone, hydroxocobalamin and carboxy-PTIO, three NO inactivators which do not depend on superoxide anion generation, upon nitrergic nerve-mediated relaxations of the rat proximal duodenum were determined in order to elucidate whether they are mediated by free NO. GABA and nicotine caused relaxations of isolated segments of the rat proximal duodenum in a concentration-dependent manner that were abolished by tetrodotoxin (TTX). Similarly, transmural electrical stimulation (TES) caused frequency-dependent relaxations that were also abolished by TTX. The NOS inhibitors L-NAME and L-NOARG reduced in a concentration-dependent manner nerve-mediated relaxations elicited by TES, nicotine and GABA. The effect of NOS inhibitors was prevented by L-arginine but not D-arginine. NO caused concentration-dependent relaxations that were not affected by TTX or L-NOARG but were abolished by hydroquinone, hydroxocobalamin and carboxy-PTIO. In contrast, these compounds failed to affect TES-, nicotine- and GABA-induced relaxations. The lack of effect of hydroquinone, hydroxocobalamin and carboxy-PTIO upon nerve-mediated relaxations was unaltered by pretreatment with the SOD irreversible inhibitor DETCA. The present findings show that nitrergic nerve-mediated relaxations of the rat duodenum are unaffected by NO inactivators that do not generate superoxide anion. It is suggested that either a NO-containing molecule that is unreactive with the inactivators tested is the inhibitory neurotransmitter released by nitrergic nerves or that NOS activity fulfills another role in nitrergic nerves which could be related to the release of an still unidentified transmitter.