摘要:

Adenosine, potassium ions and hydrogen ions are known to be vasoactive in the coronary circulation. Little is known, however, about the combined effects of these chemicals during reactive hyperemia, flow autoregulation or hypoxic hyperemia. Isolated, perfused guinea pig hearts were used to study the influence of simultaneously administered theophylline, ouabain and alkalosis on coronary flow responses (occlusive hyperemia, autoregulation, hypoxic hyperemia) thought to be contributed to by the above chemicals. Retrograde aortic inflow was monitored electromagnetically in the absence and presence of concurrently administered theophylline (5 × 10–5M), ouabain (1.4 X 10–7M), and alkalosis (perfusate pH 7.69). Upon release of a 30-sec inflow occlusion (in the presence of the above agents) mean peak coronary flow was modestly, but significantly, reduced. Volume flow rate and time for flow to return 50% towards control were reduced in the presence of the above agents, but failed to return to pre-experimental values upon removal of blockers. When perfusion pressure was increased from 65 to 95 cm H2O (antagonists present), coronary myogenic autoregulation was significantly enhanced. Upon decreasing pressure from 95 to 35 cm H2O, in the presence of blockers, calculated coronary resistance fell from 13 ± 0.6 to 9.5 ± 0.5 cm H2O/ml/min. The latter value was significantly higher than that seen in the absence of test agents. No difference in the maximum mean coronary flow achieved by hypoxia (20% O2–5% Co2-balance N2) was seen in the absence or presence of blockers. In conclusion, these experiments provide some indirect support for the involvement of the above metabolites in reactive hyperemia and as antagonists of myogenic blood flow autoregulation. Little evidence for their involvement in hypoxic hyperemia is available from th

ISSN:1018-1172    

DOI:10.1159/000158332

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The vessel wall tension is the product of pressure and internal radius divided by the vessel wall thickness. Hence, dilated vessels will be exposed to higher tension at a given intraluminal pressure. Provided the rise in cerebrovascular intraluminal pressure is sufficiently prominent, transient opening of the morphologic blood-brain barrier will occur. In the present study pressure increase, not sufficient in itself to cause barrier opening, was induced. However, at concomitant dilatation of the vessels – as induced by CO2 or papaverine – under otherwise identical pressure conditions a barrier opening was obtained. Hence, vasodilatation of cerebral vessels will increase their vulnerability to hypertens

ISSN:1018-1172    

DOI:10.1159/000158333

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The effects of N, N’-bis-(O-methoxybenzylaminohexyl)-cystamine tetrahydrochloride (BHC), 2-brom-d-lysergic acid diethylamide (BOL) and prazosin on 5-hydroxytryptamine (5-HT) dose-response curves in rabbit ear artery and thoracic aorta were determined. BHC, an irreversible alpha-adrenoceptor antagonist, and prazosin had no substantial effect while BOL shifted the 5-HT dose-response curve to the right in aorta. BHC shifted the curve to the right and reduced maximal response to 5-HT in ear artery. BOL shifted the curve to the right only above 10–6M 5-HT in control, but at all concentrations studied in BHC-pretreated ear arteries. In vitro denervation of the ear artery with 6-hydroxydopamine did not significantly alter the 5-HT dose-response curve, nor the effect of BHC on that curve. On the other hand, desipramine decreased the contractile response to high concentrations of 5-HT in non-denervated ear arteries. Prazosin increased the 5-HT threshold and slope of the curve in the ED50 region, but had no inhibitory effect on contractile responses above 3 × 10–7M 5-HT or on maximal response. It is concluded that 5-HT acts exclusively on 5-HT receptors in aorta, but on both alpha-adrenergic and 5-HT receptors in ear artery. 5-HT also possesses a small indirect sympathomimetic action at high concentrations in the ear artery. Prazosin has no effect on 5-HT receptors in either vessel and blocks the alpha-adrenoceptor stimulation by 5-HT in ear

ISSN:1018-1172    

DOI:10.1159/000158334

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Effects of antimycin A, oligomycin and KCN on tension responses to high K+ or NE and on related Ca++ movements were investigated in rabbit aortic smooth muscle. Selected concentrations of antimycin A(10–6 g/ml), oligomycin (10–6 g/ml) and KCN (1 mM) had little effect on the K+-induced contractile response even though all three agents abolished the increase in La+++-resistant low affinity Ca++ uptake elicited with high K+. Though the mitochondrial inhibitors had varied effects on the NE-induced contractile response, they had no effect on the NE-induced decrease in La+++-resistant high affinity Ca++. Oxygen consumption of the muscle tissue was decreased by antimycin A or oligomycin. These results suggest that the increase in low affinity Ca++ retention elicited with high K+ represents Ca++ uptake by mitochondria. Thus, the correlation between K+-induced uptake of Ca++ and an increased retention of La+++-resistant low affinity Ca++ after exposure to K+ are sequential events that can be dissociated by inhibitors of mitochondrial Ca++ upt

ISSN:1018-1172    

DOI:10.1159/000158335

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

In bicarbonate-buffered solution the Ba++-induced contraction of rat aorta was relaxed by an elevated extracellular K+ concentration. When the pH of the bicarbonate-buffered solution was lowered or the buffer system of the solution changed from bicarbonate to Tris or HEPES, the K+-induced relaxation was strongly inhibited. Raising the pH of the Tris-buffered solution restored the effect of K+. Addition of NH+4, which is known to cause a transient increase in intracellular pH, transiently inhibited and subsequently augmented the K+-induced vasodilation in all solutions. It is suggested that the K+-induced vasodilation results from membrane hyperpolarization following enhanced Na+, K+-ATPase activity and that this K+-induced vasodilation is affected by changes in the transmembrane pH gradient.

ISSN:1018-1172    

DOI:10.1159/000158336

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Effects of locally elevated shear stresses on thoracic aortic histamine formation and transmural albumin uptake have been examined under in vivo conditions in anesthetized male, mongrel dogs. Results indicate that if endothelium remains intact, significant linear relationships exist between the shear intensity and aortic histamine-forming capacity and aortic content of fluorescein-labeled bovine serum albumin following 20 h of circulation time. These data suggest that in vivo the aortic (and endothelial) histidine decarboxylase system is sensitive to local alterations in applied shear stress, and that de novo aortic histamine synthesis is involved in mediating shear-induced increases in aortic transmural permeability.

ISSN:1018-1172    

DOI:10.1159/000158337

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The relationship between contraction-induced arteriolar vasodilation, estimated blood flow (BF), and tissue oxygen tension (PtO2) in skeletal muscle of young rats was investigated. Arteriolar diameters, BF, and PtO2 were measured during cremaster muscle stimulation at 2, 4, and 8 Hz. At a suffusate PO2 (PsO2 30 µm diameter) did not significantly increase after 8 Hz stimulation. In contrast, with the same PsO2, third-order arterioles (3A, < 30 µm diameter) significantly dilated to 127 ± 9 (SE), 135 ± 12, and 160 ± 13% of control, respectively at 2, 4, and 8 Hz stimulation. Third-order arteriolar BFs at the end of the stimulation periods were: 119 ± 18, 176 ± 14, and 258 ± 43% of control, respectively. PtO2 remained essentially constant during and following 4 and 8 Hz stimulation if the systemic arterial blood pressure exceeded 80 mm Hg. When PsO2 was increased to 65–70 mm Hg, neither 3A diameters nor PtO2 during 8 Hz stimulation differed from paired comparisons of the response at low PsO2. These data indicate that dilation of small arterioles during increased muscle metabolic activity can occur without a mandatory change in PtO2. This circumstance is unaffected by a substantially increased supply of oxygen to

ISSN:1018-1172    

DOI:10.1159/000158338

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Perinephritic hypertension was induced in mongrel dogs by cellophane encapsulation of one kidney and simultaneous contralateral nephrectomy. Systolic blood pressure began to rise before diastolic blood pressure and both reached maximal values 3 weeks after surgery, their levels becoming stable thereafter up to the end of the study (20 weeks). Cardiac contractility, measured by the index dp/dt/P40 (rate of rise of isovolumic left intraventricular pressure at a developed left ventricular pressure of 40 mm Hg) was not altered during the evolution of hypertension; heart weight and left ventricular thickness were increased. Plasma renin activity markedly decreased in the chronic phase and plasma urea and creatinine levels rised initially in a moderate but significant way, thereafter remaining stable. The structure of the wrapped kidney remained normal 20 weeks after surgery, when microscopic arterial lesions were seen in other organs. The comparison of the evolution of this hypertensive model with other more commonly used renal experimental hypertension types allows us to conclude that cellophane perinephritic hypertension in the dog must be considered as an individual entity.

ISSN:1018-1172    

DOI:10.1159/000158339

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Active force (S) and rate of change of force (S) throughout the time of isometric contraction in electrically stimulated, circumferentially cut segments of dog anterior tibial artery were analyzed for dynamic indices of the contractile state. Previous works have determined indices that change with temperature but not with length (L) or calcium (Ca) and were designated indices of crossbridge dynamics. They assumed that changes in L and Ca change only the number of crossbridges between contractile filaments and temperature affects only the dynamics of individual crossbridges. We have shown: (1) specific ratios of S/S to be independent of L; (2) S/S at the same instant of time (V*CE) is related to an index from previous work which was defined as a velocity of internal shortening; (3) specific indices of S/S were decreased with lower temperature but increased with time in a Ca-free solution. Our results for a Ca-free solution do not agree with previous work but can be explained by changes of the smooth muscle cell membrane. This suggests that L-independent indices are useful for characterizing changes in the overall dynamic state of the tissue but are not necessarily representative of a change in crossbridge dynamics.

ISSN:1018-1172    

DOI:10.1159/000158340

出版商:S. Karger AG    

年代:1981

数据来源: Karger