Search results for "interactions."
showing 10 items of 1865 documents
Sexual differences in larval life history traits of acanthocephalan cystacanths
2006
Sexual differences in life history traits, such as size dimorphism, presumably arise via sexual selection and are most readily observed in adults. For complex life-cycle parasites, however, sexual selection may also have consequences for larval traits, e.g., growth in intermediate hosts. Two acanthocephalan species (Acanthocephalus lucii and Echinorhynchus borealis) were studied to determine, whether larval life histories differ between males and females. The size of female A. lucii cystacanths had a much stronger relationship with intermediate host size than males, suggesting females invest more in growth and are consequently more limited by resources. No relationship between host size and…
Benzodiazepine receptor binding: the interactions of some non-benzodiazepine drugs with specific [3H] diazepam binding to rat brain synaptosomal memb…
1978
The interaction of several non-benzodiazepine drugs with [3H] diazepam binding to benzodiazepine receptors in rat brain synaptosomal membranes was investigated. Baclofen, benzoctamine, hydroxyzine, chlorpromazine, haloperidol, imipramine, and amitriptyline displace specific [3H] diazepam binding, but the concentrations needed are too high to explain pharmacological effects of these drugs by an interaction with benzodiazepine receptors. The most potent non-benzodiazepine drug for inhibiting specific [3H] diazepam binding was methaqualone (IC50 value of 150 micrometer). It is suggested that interactions with benzodiazepine receptors may account for the anxiolytic and anticonvulsive side effec…
Modulation by nitric oxide of spontaneous mechanical activity in rat proximal colon.
1999
Summary 1 In order to examine the role of nitric oxide (NO) in the tonic neural inhibition in rat proximal colon, the effects of Nω-nitro- l-arginine methyl ester (L-NAME) were studied on the spontaneous contractions of circular muscle (monitored as intraluminal pressure changes) and of longitudinal muscle (detected as isometric tension changes). 2 L-NAME (3 × 10−−6–3 × 10−−4 m) caused a concentration-dependent increase in the amplitude of circular contractions, without affecting those of longitudinal muscle. This effect was prevented by l-arginine (1–5 × 10−−3 m), but not d-arginine. 3 In the presence of tetrodotoxin (10−−6 m), which per se induced increase of the pressure waves, L-NAME (1…
Modulation of adrenergic contraction of dog pulmonary arteries by nitric oxide and prostacyclin.
1999
Abstract The aim of this work was to investigate the influence of endothelium-derived nitric oxide and prostaglandins on the contractile responses of isolated dog pulmonary arteries to electrical field stimulation and noradrenaline. Electrical field stimulation (1–8 Hz, 20 v, 0.25 ms duration, for 30 s) produced frequency-dependent contractions that were abolished by tetrodotoxin, guanethidine and, prazosin (all at 10−6 M). Noradrenaline induced concentration-dependent contractions with an EC50 of 1.85 × 10−6 M. The increases in tension induced by electrical stimulation and noradrenaline were of greater magnitude in arteries denuded of endothelium. In segments with endothelium, NG-nitro- l …
Contribution of both ?- and ?-adrenoceptors to the inotropic effects of catecholamines in the rabbit heart
1992
The functional role of alpha-adrenoceptors was investigated in different parts of the rabbit heart. Phenylephrine (PE) caused a marked increase in force of contraction (Fc) and a prolongation of the action potential (AP) in preparations from the left atrium and the right ventricle. The response was less pronounced in the right atrium and in the left ventricle, whereas APs of spontaneously beating sinoatrial preparations remained completely unchanged. Phentolamine as well as the diesters phorbol 12,13 dibutyrate (PDBu) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) eliminated the effects of PE. The contribution of alpha-adrenoceptors to the effects of adrenaline (Adr) and noradrenaline (NA) …
The Oxidative Stress Concept of Nitrate Tolerance and the Antioxidant Properties of Hydralazine
2005
The hemodynamic and anti-ischemic effects of nitroglycerin (NTG) are rapidly blunted as a result of the development of nitrate tolerance. With initiation of NTG therapy, it is possible to detect neurohormonal activation and intravascular volume expansion. These so-called pseudotolerance mechanisms may compromise the vasodilatory effects of NTG. Long-term nitrate treatment also is associated with decreased vascular responsiveness caused by changes in intrinsic mechanisms of the tolerant vasculature itself. According to the oxidative stress concept, increased vascular superoxide (O 2 − ) production and an increased sensitivity to vasoconstrictors secondary to activation of protein kinase C co…
Disposition of acamprosate in the rat: Influence of probenecid
2002
The purpose of the present study was to investigate the disposition of acamprosate (calcium bis acetyl-homotaurine) in the rat. Initially, we studied the linearity of acamprosate disposition and the fraction of acamprosate excreted unchanged in the urine of the animals. Rats received 9.3, 36.6 or 73.3 mg/kg of the drug as an intravenous bolus. The statistical analysis of the pharmacokinetic parameters did not reveal any significant difference, indicating that acamprosate disposition was linear within the range of the doses assayed. On average, 95% of the administered dose was excreted unchanged in the urine of the animals in the 0-6 h post-administration period indicating that renal excreti…
The effects of phorbol 12,13-diacetate on responses of guinea-pig isolated trachea to methylxanthines, isoprenaline and ryanodine
1994
1. Using guinea-pig isolated trachea, we have studied how phorbol 12,13-diacetate (PDA) modulates mechanical responses of the tissue to methylxanthines, isoprenaline and ryanodine. 2. Caffeine (10 microM-5 mM), theophylline (10 microM-5 mM) and isoprenaline (1 nM-1 microM), each inhibited the spontaneous tone of the trachea. Pretreatment with PDA (0.1-10 microM) converted relaxant responses to high concentrations of the methylxanthines into contractions. PDA produced no equivalent effect against isoprenaline. Pretreatment with verapamil (1 or 10 microM), nifedipine (0.1 microM) or incubation with Ca(2+)-free, EGTA (0.1 mM)-containing physiological salt solution (PSS) suppressed the contract…
Cardiac effects of isoliquiritigenin
1997
The effects of isoliquiritigenin on force of contraction (Fc), L-type Ca2+ current (I(Ca)) and intracellular Ca2+ concentration ([Ca2+]i) were investigated in rat ventricular heart muscle. Isoliquiritigenin increased Fc and I(Ca) and, after longer exposure times, resting tension and [Ca2+]i. The effect of isoliquiritigenin (100 microM) on I(Ca) was diminished by Rp-cAMPS (30 microM). 1H-[1,2,4]oxa- diazolo[4,3-a]quinoxalin-1-one (50 microM) did not influence the effects of isoliquiritigenin on Fc and I(Ca). The positive inotropic effects of isoprenaline and forskolin, but not of 3-isobutyl-1-methylxanthine, were potentiated by isoliquiritigenin (100 microM). In the presence of milrinone (10…
Echinostoma caproni: kinetics of IgM, IgA and IgG subclasses in the serum and intestine of experimentally infected rats and mice.
2007
The kinetics of specific immunoglobulin M, A and IgG subclasses against Echinostoma caproni (Trematoda: Echinostomatidae) were analyzed in serum and intestinal fluid of two host species (Wistar rats and ICR mice) in which the course of the infection markedly differs. In rats, the worms were rapidly expelled, whereas E. caproni evokes in mice long-lasting infection. The pattern of antibody responses in both serum and intestinal samples was different in each host species. Serum responses in mice were characterized by significant increases of IgM, IgA, total IgG, IgG1 and IgG3, but not IgG2a. In contrast, serum responses in rats showed elevated levels of IgM, probably in relation to thymus-ind…