1,720,968 research outputs found
Lack of contribution of autonomic influences to vascular nitric oxide release? Studies in the unanesthetized rat.
No full textOBJECTIVE: To clarify the controversial issue of whether autonomic influences modulate vascular nitric oxide-mediated vasodilatation or even directly contribute to production of nitric oxide (NO) via nitroxidergic fibers. METHODS: Chronic venous and arterial catheters were implanted in Wistar-Kyoto rats (n = 65) for continuous blood pressure measurement, drug administration and blood sampling. Tonic NO-dependent vasodilatation in the conscious free-moving animal was evaluated as the pressor response to inhibition of NO synthesis by intravenous L-monomethylarginine (a 100 mg/kg intravenous bolus plus 0.5 mg/kg per min infusion for 30 min). Experiments were performed under control conditions, chemical sympathectomy by 6-hydroxy-dopamine, ganglionic blockade by hexamethonium, and surgical denervation of sino-aortic baroreceptors. RESULTS: Baseline mean arterial pressure was 100+/-4 mmHg (mean +/- SEM) in control rats and 73+/-3, 62+/-5, and 105+/-10 mmHg in sympathectomized, ganglion-blocked, and denervated rats, respectively. The peak increase in mean arterial pressure after administration of L-monomethylarginine was 38+/-3 mmHg in control rats and 51+/-3, 50+/-6, and 63+/-10 mmHg in sympathectomized, ganglion-blocked, and denervated rats, respectively. Epinephrine and norepinephrine levels in rats of separate groups of unanesthetized control, sympathectomized and ganglion-blocked animals were measured by high-performance liquid chromatography from an arterial blood sample, the results indicating drastic reductions in levels of both catecholamines in the ganglion-blocked (but not in the sympathectomized) rats compared with those in the control rats. CONCLUSIONS: Tonic NO-dependent vasodilatation can normally be maintained in the unanesthetized unrestrained rat irrespective of autonomic or humoral adrenergic influences
Sympathoadrenergic effects on low-frequency (LF) blood pressure oscillations in the unanesthetized free-moving normotensive rat
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Preservation of the baroreceptor heart rate reflex by chemical sympathectomy in experimental heart failure
No full textBACKGROUND: The mechanisms underlying impaired baroreflex sensitivity in congestive heart failure (CHF) are incompletely understood. The purpose of the present study was to test the hypothesis that this alteration depends on the marked degree of sympathetic overactivity known to characterize the CHF syndrome. METHODS AND RESULTS: Eight-week-old rats were subjected to induction of postmyocardial infarction CHF obtained by coronary ligation (Lig), chronic chemical sympathectomy by 6-hydroxydopamine (Sx), both interventions (Sx-Lig), or neither intervention (Veh-Sham, sham surgery, and vehicle administration). Four weeks after infarction, in conscious state, baroreflex sensitivity was assessed from the bradycardic responses to graded phenylephrine-induced elevations in blood pressure (BP). Left ventricular (LV) diameter was assessed by echocardiography, and plasma catecholamines were assayed to estimate sympathetic activity. Lungs were eventually excised and weighed (LW). CHF was associated with the following: (1) no changes in BP and heart rate; (2) sympathetic overactivity (norepinephrine, 320.2+/-53.8 pg/mL for Veh-Lig versus 173.4+/-20.5 pg/mL for Veh-Sham, P<0.01), prevented by Sx (181.2+/-35.5 pg/mL for Sx-Lig versus 159.8+/-33.1 pg/mL for Sx-Sham, P=NS); (3) LV enlargement (10.3+/-0.7 mm for Veh-Lig versus 6.8+/-0.6 mm for Veh-Sham, P<0.01), irrespective of Sx (9.7+/-0.7 mm for Sx-Lig versus 6.6+/-0.5 mm for Sx-Sham, P<0.01); (4) pulmonary congestion (LW, 7.55+/-0.40 mg per gram of body weight for Veh-Lig versus 5.21+/-0.44 mg per gram of body weight for Veh-Sham, P<0.01), marginally attenuated by Sx (6.54+/-0.28 mg per gram of body weight for Sx-Lig versus 4.98+/-0.22 mg per gram of body weight for Sx-Sham, P<0.05); (5) reduction in baroreflex sensitivity (0.443+/-0.032 ms/mm Hg for Veh-Lig versus 0.860+/-0.420 ms/mm Hg for Veh-Sham, P<0.01), entirely prevented by Sx (1.217+/-0.058 ms/mm Hg for Sx-Lig versus 1.345+/-0.093 ms/mm Hg for Sx-Sham, P=NS). CONCLUSIONS: In early post-MI CHF, sympathectomy only partially attenuated LV dysfunction and entirely prevented baroreflex sensitivity impairment that arises from enhanced sympathetic activity
Reproducibility of ultrasound assessment of common carotic and femoral artery compliance and distensibility in the anesthetized rat.
No full textOBJECTIVE: To validate ultrasound assessment of common carotid and femoral artery compliance and distensibility in the anesthetized rat. MATERIALS AND METHODS: A reproducibility study was performed by taking measurements twice on two different days in anesthetized Wistar-Kyoto (WKY) rats. The common carotid or femoral arterial diameter on one side and the contralateral arterial blood pressure were measured using a 10-MHz probe echo-Doppler device and an arterial catheter, respectively. The pressure and diameter data were stored in a computer programmed to calculate the arterial compliance and distensibility coefficients (Reneman formulas) and compliance and distensibility indices (arctangent model of Langewouters). A second experimental session was repeated 1 day later, and mean values, day-to-day mean differences and repeatability coefficients were calculated for each parameter. RESULTS: For both the common carotid and the femoral artery, the mean values for heart rate, mean arterial pressure, arterial diameter, arterial compliance and arterial distensibility were similar on the first and second days; mean day-to-day differences were small and repeatability coefficients were in the range 5-10% of the mean value for diameter and mean arterial pressure and 10-20% of the mean value for compliance and distensibility. CONCLUSIONS: In the anesthetized rat, ultrasound evaluation of the mechanical properties of the common carotid and femoral arteries is a reliable and reproducible technique
Interplay of nitric oxide and sympathetic activin in the control of blood pressure and its variability in unanesthetized unrestrained rats
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Enhanced vascular reactivity in the sympathectomized rat: studies in vivo and in small isolated resistance arteries.
Full text linkOBJECTIVE: In the conscious rat, sympathectomy (6-hydroxydopamine pretreatment, 100 mg/kg intraperitoneally, twice in the previous 5-6 days) induces, among various homeostatic modifications, the frequent occurrence of sudden and wide oscillations of blood pressure. Since one of the mechanisms underlying this, as yet unexplained, phenomenon may be an enhanced vascular reactivity, we tested the hypothesis that sympathectomized rats exhibit such a hyper-reactivity. We examined the response to a variety of vasoactive agents both in vivo (chronically instrumented conscious animals) and in vitro (small isolated resistance arteries). DESIGN AND METHODS: Wistar-Kyoto sympathectomized rats (6-hydroxydopamine pretreatment, n = 19) and control rats (vehicle pretreatment, n = 23) were studied. In conscious animals, concentration-blood pressure response curves to intra-venous bolus injections of vasopressin, phenylephrine and angiotensin II were obtained. In isolated vessels, concentration-wall tension response curves were obtained for norepinephrine, phenylephrine, vasopressin, serotonin and potassium. Vasodilator responses to acetylcholine (with or without L-NAME), bradykinin and sodium nitroprusside were also evaluated after precontraction with norepinephrine (mesenteric arteries) or vasopressin (cerebral arteries). RESULTS: In sympathectomized rats in vivo the pressor responses to vasopressin, phenylephrine and angiotensin II were significantly larger than in control rats, the difference amounting to 46.5, 40.2 and 57.1%, respectively (all P < 0.05). In vitro, the vascular reactivity of isolated cerebral arteries was similar in sympathectomized and control rats. In contrast, the mesenteric arteries showed significantly increased contractions in sympathectomized compared to control rats in response to norepinephrine, phenylephrine and vasopressin but not to serotonin and potassium, whereas the vasodilator responses to acetylcholine and sodium nitroprusside (but not to bradykinin and acetylcholine+L-NAME) were reduced. CONCLUSIONS: In conclusion, we showed that sympathectomy produces complex alterations of vascular reactivity both in vivo and in isolated vessels, which shift the balance of the sensitivity of the vessel between vasoconstrictor and vasodilating agents towards an increased constriction. These results are unlikely to simply reflect denervation supersensitivity; their underlying receptor, post-receptor and/or contractile mechanisms are yet to be identified
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