1,720,966 research outputs found
The interference by nicardipine and diltiazem on alpha-adrenergic receptor-mediated vasoconstriction in isolated human subcutaneous arterioles
No full textThe effects of nicardipine and diltiazem on alpha-adrenergic receptor-mediated vasoconstriction in isolated human subcutaneous arterioles was studied. Arterioles were mounted in a myograph and stimulated at 50% of maximal contraction with norepinephrine. The vasoconstrictor responses to an unrelated agonist, endothelin, was used for comparison. The percentage of decrement in tension produced by nicardipine or diltiazem was the parameter evaluated. Both calcium channel blockers caused an equipotent and dose-dependent relaxation of the vasoconstrictor responses to norepinephrine and endothelin I. The equipotent alpha-adrenolytic effect exerted by nicardipine and diltiazem in subcutaneous arterioles contrasts with the preferential antagonism by local nicardipine in the forearm. This suggests that the interaction between alpha-adrenergic receptor activation and structurally unrelated calcium channel blockers is affected by the regional and functional characteristics of the vessels under stud
Reactive hyperemia during short-term blood flow and pressure changes in the hypertensive forearm.
No full textThe aim of the present study was to further validate our method for the determination of minimal forearm vascular resistance after ischemia (13 min arterial occlusion and 1 min hand exercise) in patients with hypertension. This parameter, calculated as the ratio of mean blood pressure (intra-arterial recordings on the experimental side) to forearm blood flow (strain-gauge venous plethysmography), was measured basally and after either increasing (through unrelated vasodilators such as sodium nitroprusside or the calcium antagonist nicardipine in six mild-to-moderate uncomplicated hypertensives) or decreasing (norepinephrine, n = 4) flow without changes in systemic pressure. In spite of the divergent starting flow values, minimal postischemic forearm vascular resistance was unchanged, indicating a lack of relationship with functional arteriolar tone and the achievement of maximal dilatation. In two additional groups of patients, systemic arterial pressure was decreased by approximately equipotent oral doses of either nifedipine, a calcium antagonist (n = 6), or captopril, an angiotension converting enzyme inhibitor (n = 5). Under these conditions, minimal forearm vascular resistance was unchanged from pretreatment values, suggesting that local autoregulatory mechanisms were overridden during the reactive hyperemia, and that the vessel lumen was dependent on the distending pressure. Overall, the data show that our experimental conditions are suitable for measuring minimal forearm vascular resistance as a functional correlate of the morphological status of systemic arterioles in arterial hypertension
Calcium entry blockade and agonist-mediated forearm vasoconstriction in hypertensive patients. Difference between nicardipine and verapamil.
No full textThe interference by nicardipine and verapamil with the response to vasoactive stimuli, such as lower body negative pressure and angiotensin II, has been evaluated in the forearm of hypertensive patients. Forearm blood flow was monitored during the intraarterial infusion of either drug at rates equieffective on basal flow. Nicardipine blunted the peak forearm vasoconstrictor action of lower body negative pressure and a comparable result was obtained when angiotensin II was administered intraarterially. In spite of a comparable increase in forearm flow, nicardipine was more potent than verapamil in inhibiting vasoconstriction following both stimuli. Thus, nicardipine suppressed regional vascular reactivity, probably by blockade of the influx of extracellular calcium, in response to receptor activation, since both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. However, the results of the comparison with an unrelated calcium entry blocker, such as verapamil, may suggest that nicardipine, and possibly other dihydropiridine derivatives, preferentially antagonize agonist-mediated vasoconstriction in the human forearm
Maximal postischemic forearm vasodilation in human hypertension: a reassessment of the method
No full textCalcium entry blockade and agonist-mediated vasoconstriction in hypertensive patients.
No full textThe effects of two chemically unrelated calcium channel blockers--nicardipine and verapamil--on vascular responses to exogenous norepinephrine were evaluated in uncomplicated hypertensive patients. Each drug was infused into the brachial artery at rates that did not affect systemic blood pressure or heart rate, and forearm blood flow was measured using strain gauge venous plethysmography. Nicardipine 1 microgram/100 ml forearm tissue/min dilated the forearm arterioles and antagonized the vasoconstrictor effect of norepinephrine, whereas verapamil 1 microgram/100 ml tissue/min was ineffective, even though both drugs relaxed basal tone to the same extent. The difference between nicardipine and verapamil was also evident when reflex forearm vasoconstriction was elicited by the application of a lower body negative pressure and the drugs were infused intra-arterially at 1 and 3 micrograms/100 ml tissue/min, respectively. To evaluate whether a comparable behavior might also hold for nonsympathomimetic agents, increasing doses of angiotensin II were administered to the forearm vascular bed after pretreatment with either nicardipine or verapamil. Both drugs increased forearm blood flow, but only nicardipine antagonized the effect of angiotensin II in the forearm, showing that the impairment of vasoconstrictor mechanisms was not dependent on a specific receptor. Important differences seem to exist between nicardipine and verapamil with regard to agonist-mediated vasoconstriction in hypertensive patients, which is consistent with the heterogeneity of calcium channel blockers as a pharmacological class. Preferential antagonism of a series of vasoconstrictor stimuli may characterize the vasodilatory and, possibly, the antihypertensive effect of nicardipin
Going 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
Atrial natriuretic factor as a vasodilator agent in hypertensive patients.
No full textTo investigate the role of Atrial Natriuretic Factor (ANF) in modulating arteriolar tone in hypertension, a synthetic 25 AA human ANF-analogue (anaritide) was infused intraarterially in the forearm vascular bed of five patients with mild hypertension. A dose-dependent increase in blood flow (plethysmographic technique) was seen at rates covering a thousand-fold range (0.008, 0.08, 0.8, 8.0 micrograms/dl tissue/min x 15 minutes each). At the lowest infusion rate, the forearm blood flow increment was associated with changes in local venous ANF concentrations comparable with those reported during biological stimuli in hypertensive man and consistent with an ANF physiologic role in forearm arterioles of hypertensive patients. However, at local venous concentrations greater than 1000 pg/ml, ANF did not relax forearm vessels by more than about one-fourth of the total forearm vasodilator capacity (as assessed through a maximally active ischemic stimulus). These data confirm the low potency of ANF as an endogenous vasodilator, although vasodilator potency is not a necessary requirement for physiologic systems involved in the regulation of muscular vascular tone. Systemic arterial pressure, heart rate, and contralateral flow did not change during the study in spite of the markedly increased peripheral ANF levels recirculating from the local forearm administration. This behavior indicates that arteriolar vasodilation is apparently not the main mechanism of action of ANF on systemic hemodynamics in hypertensive patients
- …
