ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A plasma membrane preparation purified from guinea pig ventricles without the use of high concentrations of detergents or structure-disrupting salts was used to compare the mechanisms controlling sodium, potassium-activated adenosinetriphosphatase (Na, K-ATPase) and adenylate cyclase activities. The basal ATPase activity of 4–6 μmoles Pi/hour mg−1protein, measured in 120 mM NaCl or KC1, was approximately doubled in 100 mM NaCl plus 20 mM KC1. This increment, the Na, K-ATPase, was abolished by 10−5M ouabain, the KIfor ouabain being approximately 3 × 10−7M.l-Epinephrine had no effect on Na, K-ATPase, but NaF was inhibitory. Adenylate cyclase, which had a basal activity of approximately 200 pmoles cyclic AMP/min mg−1protein, was increased approximately 50% by NaCl or KC1 alone at concentrations up to 0.2M. There was no additional stimulation of adenylate cyclase activity when Na+and K+were included together. Bothl-epinephrine and NaF caused significant stimulation of adenylate cyclase, but neither basal nor activated cyclic AMP production was influenced by ouabain. Half-maximal stimulation was seen at approximately 5 × 10-υMl-epinephrine. Both the catecholamine and NaF increased the Vmaxof cardiac plasma membrane adenylate cyclase without significantly influencing3 Km. Increasing Ca2+in the range between 10−7and 10−3M inhibited basal,l-epinephrine-stimulated, and NaF-stimulated activities. Basal rates of cyclic AMP production were more sensitive to Ca than wasl-epinephrine-stimulated adenylate cyclase activity, so that Z-epinephrine stimulation was increased from approximately 60% in 0.5 mM EGTA to approximately 150% in 10−7M Ca and 400% in 10−5M Ca2+. The inhibitory effect of Ca2+on adenylate cyclase activity may represent2+ a negative feedback mechanism by which elevation of intracellular Ca concentration lowers cellular levels of cyclic AMP and thus reduces Ca2+influx into the myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A comparison of regional cerebral blood flow measurements made with beta-and gamma-emitting isotopes revealed good correspondence in areas of normal perfusion and reactive hyperemia but poor correspondence in areas of focal ischemia. After middle cerebral artery occlusion at normocapnia, there was a 65% reduction in regional cerebral blood flow from 1.40 ± 0.27 ml/g min−1to 0.49 ± 0.10 ml/g min−1in monkeys studied with85Kr but only a 27% reduction in regional cerebral blood flow from 0.84 ± 0.09 ml/g min−1to 0.61 ± 0.08 ml/g min−1in monkeys studied with133Xe. The lack of correlation within areas of focal, incomplete ischemia was attributed to an impairment of isotope delivery to the area of ischemia coupled with the inherent lack of spatial resolution of determinations made with133Xe. This finding may partly explain the numerous discrepancies in experimental and clinical studies of the effects of alterations in the arterial partial pressure of CO2on regional cerebral blood flow in areas of ischemia; it may also explain the failure of such studies to reflect the true severity of focal ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The influence of osmolality of the external medium on the calcium (Ca) dependency of contractility of isolated electrically excited cat papillary muscle was examined. Maximum unloaded velocity of shortening was directly measured by load clamping the muscle from the preload (at the length, Lmax, at which maximum active tension was developed) to zero load (zero load clamp). Peak velocity of shortening at the Lmaxpreload, peak total force, peak rate of force development, time to peak force, and time to half relaxation were also recorded. The performance-Ca response curves (Ca concentration between 1.25 nM and 10 nM) for maximum unloaded velocity of shortening, peak shortening velocity at Lmaxpreload, total force, and peak rate of force development were shifted to the left when osmolality was increased (from 290 mosmoles to 410 mosmoles) with sucrose, and to the right when osmolality was increased with NaCl. The sensitivity for Ca, as determined from the slopes of these response curves, appeared essentially unaltered by either sucrose or NaCl, except for the high Ca concentrations (above 5 mM) at the higher osmolalities (above 370 mosmoles) especially with sucrose.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

We investigated the relationship between prostaglandin release and the coronary vasodilatation evoked by anoxia. Isolated rabbit hearts were perfused via the aorta with Krebs-Ringer's solution. The coronary effluent was bioassayed continuously in terms of prostaglandin E2for prostaglandinlike substance which was present (at < 1 ng/ml) in 60 of 66 hearts. This basal release was abolished by the prostaglandin synthetase inhibitor, indomethacin (1–2 μg/ml), a result which adds further to the identity of the prostaglandinlike substance as a prostaglandin. Anoxia increased coronary flow sometimes by 100% and evoked prostaglandin release shortly thereafter. Abolition of prostaglandin synthesis by indomethacin pretreatment did not affect nor did infusion of exogenous prostaglandin mimic the anoxia-induced flow increment; thus, we conclude that prostaglandin release cannot account for the anoxia-induced vasodilator response. Furthermore, the failure of indomethacin to alter resting coronary blood flow suggests that a local prostaglandin release is not responsible for either the maintenance or the modulation of coronary flow in this preparation.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Phasic variations in the size, position, and geometry of the tricuspid valve annulus during the cardiac cycle were studied in five normal anesthetized dogs 2–6 weeks after 8–11 lead beads had been sutured on the endocardial surface of the valve ring during cardiopulmonary bypass. Field-by-field measurements from biplane videoangiograms were used to assess changes in valve ring size and shape during control hemodynamic conditions and during increased heart rates. In addition, the percutaneous production of a complete atrioventricular block in two dogs enabled us to observe the effect of isolated atrial contractions on the valve annulus. During normal sinus rhythm, progressive narrowing of the annulus during atrial and ventricular contractions reduced its area by 20–39% of the maximal valve circumference during diastole; approximately two-thirds of the total ring narrowing was associated with atrial systole. These findings suggest that one of the functions of atrial contraction is the reduction in size of the atrioventricular valve orifices prior to the onset of ventricular systole.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Shortening of the anterior papillary muscle of the left ventricle was demonstrated in six intact, tranquilized dogs. Two small metal markers that had been surgically implanted 3–50 months earlier were cineradiographically photographed during approximately ten sequential cardiac cycles in each of two orthogonal positions. Distances between markers were plotted for successive frames. The resulting curves were used to obtain maximum velocities of papillary muscle shortening and lengthening: 1.08 ± 0.29 muscle lengths/sec and 1.39 ± 0.48 muscle lengths/sec, respectively. From the two orthogonal planes, the average maximum spatial distance and the average minimum spatial distance between the markers were calculated. The mean percent shortening of 22.8 ± 6.5% was surprisingly large: it approximated the distance from the foot to the peak of the ascending limb of the myocardial length-tension curve derived from isolated muscle studies. Mechanical studies on isolated papillary muscle have consistently shown reduced shortening with increasing loads. Since the in vivo dog papillary muscle has been reported to be under considerable tension during systole, there appears to be some contradiction between the degree of shortening found in the present study and the shortening observed in isolated papillary muscle studies.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The present study was undertaken to determine the mechanism of neointima formation in rabbit arteries subjected to extensive endothelial desquamation. Endothelial cells were selectively removed from the abdominal aorta by passing an inflated balloon catheter through the vessel. The healing response was then studied serially for up to a week, when neointima formation had provided a virtually complete cover. In en face preparations, the early neointimal cells appeared in random locations; they did not develop in apposition to residual, healthy endothelium. The possibility of blood cell colonization was explored by inserting killed aortic homografts. Since these homografts showed neointima formation only close to the site of junction with the normal aorta and as a direct extension of healthy endothelium, the likelihood of significant blood cell colonization was deemed small. Histologic and electron microscopic sections provided evidence that the early neointimal cells in the healing aorta were derived from medial smooth muscle cells. Healing of the injured arterial intima was accompanied by thickening instead of prompt restoration to normal, and the thickened intima resembled an arteriosclerotic plaque. The present study thus supports the concept that arteriosclerosis is a disease involving proliferation of medial smooth muscle cells.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

We evaluated the effects of hemodilution, expansion of intravascular volume, and expansion of interstitial volume on the distribution of cortical renal blood flow, utilizing the microsphere technique. Hemodilution without volume expansion (saline exchange) produced an increase in fractional blood flow in zone 1 (outermost zone) of the cortex from 34 ± 1% to 43 ± 2% and a decrease in fractional blood flow in zone 4 (innermost zone) from 16 ± 2% to 13 ± 2%. Hemodilution without volume expansion or a decrease in plasma protein concentration (isoncotic exchange) produced a similar redistribution in blood flow in zone 1 from 34 ± 2% to 41 ± 2% and in zone 4 from 14 ± 2% to 10 ± 1%. Hemodilution with intravascular volume expansion (hyperoncotic albumin infusion) also produced a superficial shift; blood flow in zone 1 increased from 27 ± 1% to 30 ± 1% and that in zone 4 decreased from 19 ± 2% to 15 ± 1%. Previous studies have demonstrated a redistribution to the juxtamedullary area after saline expansion. Our data demonstrate that hemodilution causes flow to redistribute to the superficial rather than the deep cortex. This superficial shift appears to be secondary to decreased hematocrit rather than to dilution of plasma proteins or expansion of intravascular volume. The deep shift in cortical blood flow which occurs during saline loading is presumably a consequence of expansion of interstitial volume.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effects of static and dynamic passive stretch and shortening on electrical activity and active force were analyzed in the isolated rat portal vein. Static stretch by 40% of muscle length evoked moderate excitatory effects with enhanced mechanical activity and an average increase in spike discharge of 12% above the control value of 55 ± 2.6 spikes/min. The dynamic responses studied at various rates of length change (dL/dt) over the range between −12 and +12 mm/min, i.e., −3 and +3% muscle length/sec, were much more pronounced. Active force and spike activity showed graded increases with increasing rates of stretch. The electrical activity reached a value of 180 spikes/min (≈ 325% of control) at 5 mm/min; this frequency was then maintained for stretch rates up to 12 mm/min. Mechanical activity during stretch was further reinforced by the shift along the length-tension diagram. Passive shortening at rates from −1 to −12 mm/min caused graded decreases in mechanical and electrical activity below the control levels, complete inhibition being observed at the latter dL/dt. Blockade of a and β receptors indicated that the responses were myogenic in nature. The findings seem to provide direct support for the myogenic hypothesis of vascular tone and responses to stretch of the vascular wall, but they indicate that emphasis should be placed on the dynamic characteristics of the stimulus rather than its static nature. This emphasis constitutes a new concept in the myogenic control of the peripheral circulation.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID