摘要:

Preliminary experiments in our laboratory have shown that the distensibility characteristics of the capillary compartment in the bat wing depended upon its location in the vascular tree. The capillaries were then divided into arteriolar, middle and venular segments (according to their proximity to precapillary sphincters or nonmuscular venules). The bat was enclosed in an airtight box, one wing protruding through a slit and extended over a glass plate for microscopic observations. Continuous recordings of the diameter of the capillary segments were obtained; after 5 min of control recordings, the box pressure was raised in steps of 25 mm Hg to a maximum of 100 mm Hg and then returned to control level. The duration of each step was 4 min. Each increase of the pressure led to the dilatation of the capillary, but its arteriolar segment appeared to be more distensible than the middle and venous ones. After shifting the box pressure, the diameter increase was gradual and capillary distensibility decreased with increasing pressure (the venular segment showed the most prominent reduction in distensibility). These findings suggest the existence of a longitudinal gradient of distensibility in the capillary compartment.

ISSN:1018-1172    

DOI:10.1159/000158783

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The isothiocyanate analog (IBI) of tolazoline produced contraction of the rat aortic strip, with an ED50 value of 1.63 × 10–5 M. The maximum contraction of the analog was nearly equal to that of tolazoline or phenylephrine. At 27 °C the tissue reactivity of phenylephrine and IBI was similar. When compared at equiactive concentrations, the total duration of contraction of IBI was three times longer than that of tolazoline. Thus, the longer duration of action of IBI may be attributed to the S=C=N group substitution of the molecule. IBI at 10-6 M shifted the dose-response curve of phenylephrine to the right with reduction in maxima. Phentolamine and other α1or α2 adrenoceptor blockers failed to block the responses of IBI in aorta, whereas verapamil or nifedipine blocked the response significantly. It appears that IBI is acting through calcium-channel-sensitive or calcium-receptor-related mechanism(s). In aspirin-treated platelets from human plasma, a distinct phase of aggregation induced by epinephrine can be blocked by IBI with KB of 2 × 10–5 M. This indicates a small but selective α2 related action of IBI. The aggregation induced by ADP or second component of aggregation induced by epinephrine were also blocked by IBI at concentrations comparable to that of the 012-adrenoceptor-mediated response. This indicates a lack of specificity of IBI in differentiating various phases of aggregation. Therefore, as compared to tolazoline, IBI presents an interesting paradox in its interaction with various receptors or mechanisms in the vascular tissue and

ISSN:1018-1172    

DOI:10.1159/000158784

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

The interaction between cooling and vasoactive substances, e.g. 5-hydroxytryptamine (5-HT), plays an important role in the pathophysiology of cold-induced vasospasm. Our objective was to study the effect of cooling on the 5-HT vascular response, classify the involved 5-HT receptors, and to analyze the role of the endothelium. Ring segments from the rat jugular vein, a preparation without α-adrenergic receptors, were suspended in organ baths to record the circular motor activity. The temperature was initially 37 °C and was thereafter either continuously lowered to 10 °C or kept constant at different temperatures within this range. 5-HT at low concentrations (10–11 to 3 × 10–8 M) induced relaxation at 37 °C in segments precontracted by prostaglandin F2α– The relaxation was recognized to be mediated via an endothelium-dependent 5-HT1-like receptor mechanism presumably involving the release of endothelium-derived relaxing factor (EDRF). Cooling to 29 and 20 °C diminished the relaxation, probably due to an attenuated release of EDRF. 5-HT at concentrations of more than 10–8M induced a contraction in all vessels at 37 °C mediated via a 5-HT2 receptor. An increased 5-HT-induced contraction was seen at temperatures below 37 °C in vessels with an intact endothelium. Endothelial denudation diminished the cold-induced enhancement of the contraction to 5-HT. These studies suggest that endothelial mechanisms contribute to a cold-induced augmented

ISSN:1018-1172    

DOI:10.1159/000158785

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

Contradictory results concerning the effects of oxygen and flow on blood vessel dimensions have been published. The aim of this study was to investigate the diameter changes in isolated, cannulated femoral arteries (n = 5) of the rabbit in a preconstricted state (two norepinephrine levels) during high and low pO2 (both inside and outside) at different flow levels. In this way the interaction between oxygen and flow is also investigated. Results were normalized to relative diameters, where the diameter at zero flow, during high pO2 and low norepinephrine concentration was considered as a control diameter (100%). We found three effects in this study: (1) going from high to low oxygen, there was a global vasoconstriction (repeated measures, analysis of variance, p = 0.016 with low norepinephrine and p = 0.015 with high norepinephrine); (2) when flow was increased from 1 to 100 ml/h, we found a significant (p < 0.001) flow-dependent constriction under all four conditions, and (3) there is an interaction between flow and oxygen, for example at low norepinephrine the constriction due to low oxygen is 16 % at zero flow and 1 % at a flow of 1 ml/h, at high norepinephrine these numbers are 22 and 10%, respectively.

ISSN:1018-1172    

DOI:10.1159/000158786

出版商:S. Karger AG    

年代:1989

数据来源: Karger

摘要:

We studied the role of the endothelium in diameter changes as a function of flow of the isolated femoral artery of the rabbit (n = 15) perfused and superfused with a physiological salt solution (37 °C). In 10 vessels, diameters were studied before and after exposure to gossypol, an agent that impairs the endothelial function pharmacologically. In 5 of these 10 vessels we added albumin (1.5%) to the perfusion solution. The mean external diameter (±SEM) after equilibration for 60 min at a transmural pressure of 50 cm H2O (n = 10) was: 1,426 ± 34 µM Vessels were then constricted with norepinephrine (1.0–1.5 µM in the supervision solution) to 70% of the resting diameter, acetylcholine was used to check endothelial function. All vessels constricted as flow was increased (p < 0.001), irrespective of the impairment of the endothelial function by gossypol or the presence of albumin. It is therefore unlikely that the flow-induced constriction results from a ‘wash away’ effect of endothelium-derived relaxing factor (EDRF). To test whether EDRF could still play a role after gossypol, we used hemoglobin (n = 5) to bind EDRF. Flow-dependent constriction was still observed, although the mean diameter was decreased. We conclude that flow-dependent constriction is either mediated via the endothelial cells, but not via EDRF, or that the endothelial cells are no

ISSN:1018-1172    

DOI:10.1159/000158787

出版商:S. Karger AG    

年代:1989

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158788

出版商:S. Karger AG    

年代:1989

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158789

出版商:S. Karger AG    

年代:1989

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158790

出版商:S. Karger AG    

年代:1989

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158782

出版商:S. Karger AG    

年代:1989

数据来源: Karger