945 resultados para Induced Response


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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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This paper presents an investigation into some practical issues that may be present in a real experiment, when trying to validate the theoretical frequency response curve of a two degree-of-freedom nonlinear system consisting of coupled linear and nonlinear oscillators. Some specific features, such as detached resonance curves, have been theoretically predicted in multi degree-of-freedom nonlinear oscillators, when subject to harmonic excitation, and the system parameters have been shown to be fundamental in achieving such features. When based on a simplified model, approximate analytical expression for the frequency response curves may be derived, which may be validated by the numerical solutions. In a real experiment, however, the practical achievability of such features was previously shown to be greatly affected by small disturbances induced by gravity and inertia, which led to some solutions becoming unstable which had been predicted to be stable. In this work a practical system configuration is proposed where such effects are reduced so that the previous limitations are overcome. A virtual experiment is carried out where a detailed multi-body model of the oscillator is assembled and the effects on the system response are investigated.

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The aim of this study was to determine the relationship between blood lactate and glucose during an incremental test after exercise induced lactic acidosis, under normal and acute β-adrenergic blockade. Eight fit males (cyclists or triathletes) performed a protocol to determine the intensity corresponding to the individual equilibrium point between lactate entry and removal from the blood (incremental test after exercise induced lactic acidosis), determined from the blood lactate (Lacmin) and glucose (Glucmin) response. This protocol was performed twice in a double-blind randomized order by ingesting either propranolol (80 mg) or a placebo (dextrose), 120 min prior to the test. The blood lactate and glucose concentration obtained 7 minutes after anaerobic exercise (Wingate test) was significantly lower (p<0.01) with the acute β-adrenergic blockade (9.1±1.5 mM; 3.9±0.1 mM), respectively than in the placebo condition (12.4±1.8 mM; 5.0±0.1 mM). There was no difference (p>0.05) between the exercise intensity determined by Lacmin (212.1±17.4 W) and Glucmin (218.2±22.1 W) during exercise performed without acute β-adrenergic blockade. The exercise intensity at Lacmin was lowered (p<0.05) from 212.1±17.4 to 181.0±15.6 W and heart rate at Lacmin was reduced (p<0.01) from 161.2±8.4 to 129.3±6.2 beats min-1 as a result of the blockade. It was not possible to determine the exercise intensity corresponding to Glucmin with β-adrenergic blockade, since the blood glucose concentration presented a continuous decrease during the incremental test. We concluded that the similar pattern response of blood lactate and glucose during an incremental test after exercise induced lactic acidosis, is not present during β-adrenergic blockade suggesting that, at least in part, this behavior depends upon adrenergic stimulation.

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Progesterone (P-4), 17 beta- estradiol (E2) and androstenedione (A4) plasma concentrations were correlated with palpated corpora lutea (CL), recovered embryos and viable embryos in 13 Nelore cows induced to superovulate with FSH, starting on Day 10 of the estrous cycle. Administration of FSH increased the number of ovulations and recovered embryos. Plasma P4, E2 and A4 levels on Day O and of P4 on Days 10 and 11 of the cycle were not correlated with the superovulatory response. Determination of CL by palpation per rectum was used to estimate the number of recovered embryos. Plasma P4 levels higher than 1 ng/ml on the induced estrus day (Day 14) had an adverse effect on the embryo viability rate. Plasma E2 concentrations on Day 14 were positively correlated with the number of viable embryos collected, a correlation that has not been previously reported. The present data indicate that plasma P4 and E2 concentrations in FSH-PGF2 alpha-treated Nelore cows are useful for the identification of 2 different populations of Nelore donors and are correlated with superovulatory response and, particularly, with the number of viable embryos.

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The present experiments were conducted to investigate the role of the α1- and α2-adrenergic receptors of the lateral hypothalamus (LH) on the drinking response elicited by intracerebroventricular (i.c.v) injections of carbachol and angiotensin II (AII) in rats. Clonidine (an α2-adrenergic agonist) injected into the LH produced a dose-dependent reduction of the drinking responses elicited by i.c.v. administration of carbachol and AII. The α1-adrenergic agonist phenylephrine injected into the LH reduced the dipsogenic response to i.c.v. AII, but not to carbachol. Injection of yohimbine (an α2-adrenergic antagonist) and prazosin (an α1-adrenergic antagonist) into the LH also reduced the water intake produced by i.c.v. injection of AII. Previous injection of α1- or α2-adrenergic antagonists into the LH increased the antidipsogenic effect of clonidine or phenylephrine injected into the same area on the water intake induced by i.c.v. AII. These results show that the α1- and α2-adrenergic receptors of the LH are involved in the control of drinking responses elicited by i.c.v. injection of AII in rats. They also show that clonidine, but not phenylephrine, suppresses the drinking induced by i.c.v. carbachol. The data suggest that the discharge of central α-adrenergic receptors has a dual (inhibitory and excitatory) effect on water intake induced by central AII. © 1991.

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We explored the role of angiotensin II and vasopressin in the maintenance of blood pressure during the nephrotic syndrome of adriamycin-induced nephropathy in rats. All 91 rats treated with adriamycin developed chronic renal failure with nephrotic syndrome, which was more pronounced in the normotensive rats than the 35% who became hypertensive. Angiotensin II blockade with DuP 753 produced a significantly greater hypotensive response in both the adriamycin-hypertensive (-16 +/- 3 mm Hg) and adriamycin-normotensive (-14 +/- 5 mm Hg) groups than the saline-treated controls (-5 +/- 1 mm Hg, P < .05). Vasopressin blockade with either a V1V2 inhibitor or a selective V1 inhibitor produced a hypotensive response in adriamycin-hypertensive rats only (by -16 +/- 4 and -17 +/- 2 mm Hg, respectively, P < .01), although the nonselective vasopressin inhibitor produced similar fluid loss and body weight reduction in all three groups. The data suggest that in adriamycin-induced nephropathy with nephrotic syndrome, angiotensin II contributes to blood pressure maintenance in both hypertensive and normotensive animals, whereas the pressor action of vasopressin contributes to elevated blood pressure in hypertensive animals only.

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Cardiac or ventricular remodeling is characterized by molecular, cellular, and interstitial alterations that lead to changes in heart size, mass, geometry and function in response to a given insult. Currently, tobacco smoke exposure is recognized as one of these insults. Indeed, tobacco smoke exposure induces the enlargement of the left-sided cardiac chambers, myocardial hypertrophy, and ventricular dysfunction. Potential mechanisms for these alterations include hemodynamic and neurohormonal changes, oxidative stress, inflammation, nitric oxide bioavailability, matrix metalloproteinases and mitogen-activated protein kinase activation. This review will focus on the concepts, relevance, and potential mechanisms of cardiac remodeling induced by tobacco smoke.

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In the aquatic environment, biotransformation enzymes are established biomarkers for assessing PAH exposure in fish, but little is known about the effect of 17β-estradiol (E2) on these enzymes during exposure to benzo(a)pyrene (BaP). In this study, Nile tilapia (Oreochromis niloticus) were exposed for 3, 5, and 10 days to BaP (300 μg L(-1)) and E2 (5 μg L(-1)). These substances were applied isolated or mixed. In the mixture experiment, fish were analyzed pre- and postexposure in order to better understand whether preexposure to the hormone masks the responses activated by PAH or vice versa. Phase I enzymes ethoxyresorufin-O-deethylase (EROD), pentoxyresorufin-O-depenthylase (PROD), and benzyloxyresorufin-O-debenzylase (BROD) activities as well as the phase II enzyme glutathione S-transferase (GST) were analyzed. Isolated E2 treatment decreased EROD activity after 3 days, but this enzyme activity returned to control values after 5 and 10 days of exposure. Isolated BaP treatment significantly induced EROD activity after 3 and 5 days, and the activity returned to control levels after ten exposure days. Combined treatment (E2 + Bap) significantly increased EROD activity, both in the pre- and postexposure. This increase was even higher than in the isolated BaP treatment, suggesting a synergism between these two compounds. When E2 and BaP were used singly, they did not change BROD and PROD activities. However, combined treatment (E2 + Bap) significantly increased PROD activity. Isolated BaP treatment increased GST activity after 10 days. However, this response was not observed in the mixture treatment, suggesting that E2 suppressed the GST induction modulated by BaP. The results put together indicated that E2 altered the biotransformation pathway regarding enzymes activated by BaP in Nile tilapia.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)