ISSN:1018-1172    

DOI:10.1159/000159071

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Forearm plethysmography coupled with brachial artery drug administration and the Aellig technique in hand veins coupled with local venous drug administration are both extremely powerful tools, now widely available to the clinical pharmacologist. These techniques allow precise assessment of drug effects on vascular smooth muscle in vivo, without the confounding influences of drug effects on other organs or activation of neurohumoral reflexes. These local techniques allow the direct study of human vascular physiology, pharmacology, and pathophysiology in vivo in humans. In addition, they can form an important part of the early clinical development programme for new cardiovascular drugs, including drugs affecting the renin-angiotensin system and the sympathetic nervous system, as well as the novel agents arising from research on the vascular endothelium. Given the power of these techniques, it is important to consider where studies in patient volunteers might answer particular questions better than experiments in animal models of disease.

ISSN:1018-1172    

DOI:10.1159/000159072

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

These studies examine the possibility that alterations in the expression of G protein α subunits occur during desensitization of adrenergic responses in the cardiovascular system. To desensitize adrenergic receptors, rats were infused with norepinephrine (NE) subcutaneously (0.1 mg/kg/h) for 3 or 6 days using osmotic minipumps. G protein α subunits and their mRNAs were then measured in the aorta and heart using selective antibodies and cDNA probes. Infusion of NE for 6 days significantly decreases the levels of Gsα, Giα and Goα in the aorta. The mRNAs for the α subunits are not altered in the aorta after NE infusion for 3 or 6 days indicating that reduced mRNA expression does not account for the decreased proteins. In the atrium and ventricle the levels of Gsα decrease after NE infusion for 3 days but then return to control levels by day 6. The levels of atrial and ventricular Giα are unaltered after NE infusion for 3 days but increase significantly by day 6. Goα levels do not change in the atrium or ventricle on either day. The level of Gi2α mRNA increases after NE infusion for 6 days and may account for the increased αi protein. The levels of the other Gα mRNAs do not change in the atrium or ventricle. These results demonstrate that expression of G protein α subunits is altered during cardiovascular desensitization, raising the possibility that modulation of the α subunits may contribute to reduced adrenergic r

ISSN:1018-1172    

DOI:10.1159/000159073

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Objectives: Magnetization exchange experiments and force analysis were performed on porcine carotid arteries with varied phosphocreatine (PCr) levels. The aim of these experiments was to determine the creatine kinase (CK) kinetics and the role in hypoxic relaxation. Methods: The magnetization exchange techniques used were multisite saturation transfer (MST) and conventional saturation transfer (CST). The two techniques were used because CST assumes a two-site exchange while MST allows one to assume a three-site exchange. Mechanical parameters of tension generation and relaxation were measured to determine the energetic effects on contractility of carotid strips. Results: Measurements of molecular exchange between ATP and PCr found the pseudo first-order rate constant (kf) of 0.17 ± 0.04 s–1 (PCr → ATP) and kr = 0.12 ± 0.03 s-1 (ATP → PCr) in unstimulated porcine carotid artery. In the carotids, despite increased PCr and K+ stimulation, no magnetization exchange is observable with MST. This result indicates that the ATPase was less than 0.04 µmol/g/s (below the NMR resolution) while CK was 0.11 µmol/g/s. Creatine-loaded carotids showed no significant differences in force measurements: maximal force, resting tension, and the rate of hypoxia were all unchanged. Conclusions: The flux ratio (flux forward over flux reverse) was 0.94 ± 0.13 which was considered to be indicative of CK being at equilibrium in the resting porcine carotid artery. The rate of the CK reaction is rapid enough to assume a two-site kinetic exchange not limiting energetic supply during hypoxia-induced

ISSN:1018-1172    

DOI:10.1159/000159074

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Endothelial cells (EC) are fastidious in their growth requirements in vitro and will not survive extensive passages. We have partially characterized a continuous cell line (>40 passages) established in culture from New Zealand White rabbit vena cava endothelium (REVC). REVC cells resemble typical EC, but remain hardy when grown on uncoated plastic in DMEM/F12 + 10% FBS. REVC cells have typical cobblestone appearance, are contact-inhibited in monolayers and express factor VIII-related antigen. Weibel-Palade bodies were not seen by electron microscopy. REVC cells grown in 2% FBS on plastic demonstrate dose-dependent increases in [3H]thymidine uptake in response to acidic FGF (10-100 ng/ml), basic FGF (3–100 ng/ml), EGF (10–50 ng/ml), and ECGS (10–100 µg/ml). Heparin (5–100 µg/ml) potentiates proliferation induced by aFGF and lowered the ED50 for aFGF. REVC cells did not show an increased proliferative rate in response to vascular endothelial growth factor. Transforming growth factor β1 and β2 profoundly inhibited thymidine uptake at doses as low as 100 pg/ml. When grown on a collagen I substratum, REVC cells became larger, more polygonal and assumed a sheet-like appearance upon reaching confluence. REVC cells plated on fibronectin, laminin or poly-L-lysine demonstrated increases in pericellular granularity and pronounced spreading, especially on fibronectin. Phorbol myristate acetate produced profound morphological changes characterized by swirling whorls of bipolar cells surrounding patches of polygonal cells and multilayered overgrowth. When plated on EHS (Engelbreth-Holm-Swarm) tumor extracellular matrix (Matrigel), REVC cells became quiescent and underwent morphological changes reminiscent of differentiation with elongated cytoplasmic extensions. Chromosomal examination of REVC cells revealed a normal diploid karyotype (2n = 44). This continuous cell line is undergoing further characterization and may be quite useful in investigating many aspects of endothelial cell biolo

ISSN:1018-1172    

DOI:10.1159/000159075

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Intraluminal flow can cause both dilation or constriction of small arteries, depending on the level of tone. Both responses are specifically modulated in the same way by small changes in extracellular Na+ ([Na+]e). We have investigated the effect of changes in [Na+]e on the level of contraction induced by a standard flow of physiological salt solution in ring of segments of the rabbit facial vein and on the associated 45Ca2+ influx and net uptake. Decreasing [Na+]e by 20% reduced the response to flow by 58%, and increasing it by 20% augmented the flow response by the same extent. There is a linear relationship between the level of the flow-induced contraction and [Na+]e over the range 120-180 mM. An alteration in [Na+]e of 10 mM corresponds to a 20% change in flow-induced contraction. This relationship is quantitatively the same as that previously reported for the rabbit ear resistance artery [10]. Histamine (1 µM) induced tone was not affected by changes in [Na+]e within the range 75-180 mM. 45Ca2+ influx and net uptake per unit force developed in response to flow were unaffected by these changes in [Na+]e. The flow-induced contraction of the vein was selectively, in comparison to that due to histamine, attenuated by amiloride, methyl-isobutyl-amiloride and monensin. It is argued that the observation that flow-induced contraction, caused by small alterations in extracellular sodium concentration, is not associated with changes in calcium uptake per unit force is consistent with an extracellular flow sensor. The similarities of the effects of sodium concentration change and amiloride, methyl-isobutyl-amiloride and monensin in the rabbit facial vein to what has been previously found in the resistance branch of the rabbit ear artery suggest that the flow-sensitive mechanism may be similar in the two vessels

ISSN:1018-1172    

DOI:10.1159/000159076

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

In segments of rabbit basilar artery (BA) platelet-activating factor (PAF) initiated a concentration-dependent transitory contraction which was unaffected by indomethacin or nordihydroguaiaretic acid (NDGA). Nω-nitro-L-arginine (NLA) did not change the magnitude of PAF-induced contraction, but in the presence of NLA the contraction tended to be more prolonged. In precontracted BA segments, PAF caused a concentration-dependent relaxation which was unaffected by NDGA. Indomethacin and NLA decreased PAF-induced relaxation by 10-30 and 70-90%, respectively; in combination these agents totally eliminated PAF-induced vessel reactions. Treatment of BA segments by rabbit peritoneal polymorphonuclear leukocytes (PMNLs) activated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) for 20 min led to PMNL adhesion to the vascular endothelium and a significant decrease (60-100%) in acetylcholine-induced endothelium-dependent vessel relaxation. After the treatment of BA segments, PAF induced strong, slow, tonic contraction of either non-precontracted or precontracted vessels which was unaffected by indomethacin or NLA. NDGA decreased this contraction by 30-60%. These results indicate that PAF is an endothelium-dependent vasodilator that can also produce an insignificant constrictor effect. However, when the vessels are affected by activated PMNLs, PAF is transformed to a strong vasoconstrictor, presumably due to the generation of as yet unknown vasoconstrictor stimuli resulting from PMNL-endothelium interactions. Under these conditions the PAF-induced contraction is partly mediated by 5-lipoxygenase metabolites

ISSN:1018-1172    

DOI:10.1159/000159077

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The respective effects of hyperosmolarity caused by impermeant solutes, such as mannitol and sucrose, on the endothelium and smooth muscles cell responses were investigated in the rat tail artery. The vessels, with or without endothelium, were infused and superfused with an isosmolar saline solution, and were repeatedly stimulated with phenylephrine. Superfusing with hyperosmolar fluid (390–420 mosm/l) produced a transient increase in the arterial basal perfusion pressure which peaked after approximately 5 min and then declined within 15 min to a stable nonsignificant value above control values in subsequent experiments. In arteries with functional endothelium, the effect of phenylephrine was about 1.9-fold larger in hyperosmotic medium compared to that in isosmotic medium. In hyperosmotic media the response was still more than twofold enhanced in endothelium-denuded vessels compared to those with endothelium. In the latter, indomethacin (10 µM) had no effect, but Nω-nitro-L-arginine methylester (L-NAME; 30 µmol/l), an inhibitor of NO production, enhanced the response to phenylephrine to reach the same magnitude of response as seen in endothelium-denuded arteries. This effect of L-NAME was antagonized by L-arginine. Relaxation induced by the NO donor SIN-1 was unchanged by hyperosmolarity, indicating that the effect of NO was not impaired. It is concluded that, in the rat tail artery, the enhancement in phenylephrine-induced contractions produced in a hyperosmolar solution is due to both an endothelium-independent increase in smooth muscle responses and a moderate decrease in the production of NO, or an NO-like factor, by the endothelium. In spite of this reduction, endothelium-derived NO still plays a major role in attenuating phenylephrine-induced contractions in hyperosmolar me

ISSN:1018-1172    

DOI:10.1159/000159078

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

This cross-sectional study examined responses of the isolated cystic artery to 3 α-adrenoceptor agonists and the effects of 2 antagonists in relation to subjects’ blood pressures. Potency of the 3 amines studied was: α-methylnorepinephrine > norepinephrine > phenylephrine. Responses to clonidine were trivial (<5% of maximum) and remained <25% of maximum in the presence of sub-threshold concentrations of angiotensin II. A weak trend for increased potency of α-methylnorepinephrine was noted in arteries of subjects with higher blood pressures (r = 0.268, p = 0.027). There was no relationship between blood pressure and pA2 for yohimbine. The pA2 for prazosin could not be calculated because of a decline in maximal responses but prazosin was clearly more potent than yohimbine. The decline in maximal responses to norepinephrine and phenylephrine after prazosin treatment was related to subjects’ diastolic blood pressures (r = –0.400, p = 0.003). There were no significant relationships between these measurements of vascular responsiveness and a family history of hypertension. There were also no significant relationships betwen these measurements of vascular responsiveness and plasma norepinephrine levels, α2-adrenoceptor binding or platelets of β2-adrenoceptor binding of lymphocytes. The major postjunctional α-adrenoceptors in this artery are of the α1 type. The data suggest that differences in potency of α-adrenoceptor agonists in relation to blood pressure may be due to differences in the α2-adrenoceptor but are not likely due to a difference in binding to the receptor itself. The explanation for the effect of prazosin on maximal responses to α-adrenoceptor agonists in relationship to blood pressure in the present study requires further study. If the results in blood cell adrenoceptors are parallel to those in cystic artery, increased potency of α2-adrenoceptor agonists in the artery in subjects with higher blood pressure is not due to an increased number of adrenoceptors and therefore is most likely due to differences in postreceptor excitation-contraction coupling. Future experiments should utilize preparations such as subcutaneous resistance vessels where α2-adrenoceptors are

ISSN:1018-1172    

DOI:10.1159/000159079

出版商:S. Karger AG    

年代:1995

数据来源: Karger