bluuebunny/crossref_metadata_2025 huggingface dataset:
Decreased pressor reactivity to angiotensin II in cirrhotic rats. Evidence for a post-receptor defect in angiotensin action.
Authors: Murray B M , Paller M S
Published: June 2012

We used a model of cirrhosis in the rat, produced by inhalation of carbon tetrachloride for 6 weeks, to investigate the mechanism of resistance to the pressor effects of angiotensin II. The pressor response to angiotensin II was significantly lower in conscious cirrhotic animals than in controls. On the other hand, cirrhotic animals had normal pressor responses to norepinephrine, indicating that a generalized defect in vascular reactivity does not cause the decreased pressor response to angiotensin II. Enhanced baroreceptor activity was not the cause of the decreased pressor response to angiotensin II, since baroreflex control of heart rate after angiotensin II was similar in cirrhotics and controls. Pretreatment with either the converting enzyme inhibitor captopril to reduce circulating angiotensin II or the prostaglandin synthesis inhibitor meclofenamate failed to normalize the response to angiotensin II. Thus, neither prior occupancy of receptors with endogenous angiotensin II nor the production of vasodilatory prostaglandins was responsible for the decreased angiotensin II response. Studies of angiotensin II binding by mesenteric artery smooth muscle particles showed that, in cirrhotic animals, receptor affinity for angiotensin II, was significantly lower than in controls (kd: cirrhosis 1.11 +/- 0.09 nM, control 0.94 +/- 0.13 nM; P less than 0.02), whereas receptor number was significantly increased (cirrhosis 315 +/- 42 fmol/mg protein, control 277 +/- 43 fmol/mg protein, P less than 0.01). However, total binding of AII by vascular receptors from cirrhotics was no different than in controls, since the decrease in affinity negated the increase in receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)
Microneurographic studies of the mechanisms of sympathetic nerve responses to static exercise in humans.
Authors: Mark A L , Victor R G , Nerhed C , Wallin B G
Published: June 2012

The purpose of this study was to determine the contribution of muscle afferents and central command in regulating sympathetic nerve activity during static exercise in humans. In 20 healthy subjects, we recorded heart rate, arterial pressure, and efferent sympathetic nerve activity in the leg during arm exercise. Microelectrodes were inserted percutaneously into a fascicle of the peroneal nerve to measure sympathetic discharge to muscle. Measurements were obtained in nine subjects during sustained handgrip (30% maximal voluntary contraction) followed by relaxation or by arrested circulation of the forearm. Heart rate and arterial pressure increased during the first and second minutes of handgrip. Muscle sympathetic nerve activity increased from 261 +/- 46 to 504 +/- 97 units (mean +/- SE; units = burst frequency X amplitude; P less than 0.05) during the second minute of handgrip. During forearm ischemia following handgrip, heart rate returned promptly to control, whereas arterial pressure and muscle sympathetic nerve activity (631 +/- 115 units) remained elevated. In contrast, muscle sympathetic nerve activity returned toward control during relaxation without arrested circulation. These data indicate that muscle sympathetic nerve activity is increased by stimulation of chemically sensitive muscle afferents. To determine the influence of central command on muscle sympathetic nerve activity, we compared responses during an involuntary and a voluntary biceps contraction, each at 20% maximal voluntary contraction. Both maneuvers raised arterial pressure, but heart rate increased only during voluntary contraction. More importantly, muscle sympathetic nerve activity rose during involuntary contraction, but fell during voluntary effort.(ABSTRACT TRUNCATED AT 250 WORDS)
Atrial natriuretic factor inhibits the hypertension induced by chronic infusion of norepinephrine in conscious rats.
Authors: Yasujima M , Abe K , Kohzuki M , Tanno M , Kasai Y , Sato M , Omata K , Kudo K , Tsunoda K , Takeuchi K
Published: June 2012

To assess the physiological role of atrial natriuretic factors in the regulation of blood pressure and sodium-water excretion, we studied the chronic effects of continuous infusion of a synthetic atrial natriuretic factor of 25 amino acids for up to 3 days on systolic blood pressure, urine volume, and urinary excretion of sodium, prostaglandin E2 and kallikrein in conscious rats, and also evaluated the antihypertensive effect of this substance in rats with hypertension caused by chronic infusion of norepinephrine. Continuous infusion of atrial natriuretic factor (150 micrograms/kg per day) into the jugular vein via osmotic minipumps did not induce any changes in systolic blood pressure, urine volume, and urinary excretion of sodium, prostaglandin E2, and kallikrein for up to 3 days, compared with those in vehicle-infused rats. When the same dose of atrial natriuretic factor was administered simultaneously with 1.8 mg/kg per day of norepinephrine infused intraperitoneally by osmotic minipumps, the systolic blood pressure of conscious rats rose on day 1 to only 127.3 +/- 6.3 mm Hg compared with the rise to 146.3 +/- 1.6 mm Hg when norepinephrine alone was infused (P less than 0.05). The antihypertensive effect of atrial natriuretic factor was sustained for 3 days in rats infused with norepinephrine. The administration of atrial natriuretic factor to rats made hypertensive by 3 days of infusion with norepinephrine alone returned the blood pressure to control levels, and the antihypertensive effect was sustained throughout the experimental period lasting for 3 days.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of adenosine on ventricular overdrive suppression in isolated guinea pig hearts and Purkinje fibers.
Authors: Wesley R C , Belardinelli L
Published: June 2012

The present study was undertaken to demonstrate and characterize potentiation of ventricular overdrive suppression by adenosine. To substantiate that adenosine has an enhanced effect on overdrive suppression, it would be necessary to demonstrate that adenosine increases pause duration independent of slowing spontaneous pre-drive rate. In isolated perfused guinea pig hearts with surgically induced complete atrioventricular block, the effect of adenosine (2-20 microM) on pause duration was compared to two alternative means of slowing the pre-drive rate, i.e., hypothermia (28.0 degrees C to 34.0 degrees C) and cesium chloride (0.3-1.0 mM). The slope value of the linear regression line describing the relationship between pre-drive cycle length and pause duration for adenosine (15.8) was significantly greater than control (1.7), hypothermia (1.7), and cesium chloride (5.4). The competitive adenosine antagonist, aminophylline (60 microM), when infused at the initiation of overdrive during adenosine administration, significantly reduced the effect of adenosine on pause duration by 72.9 +/- 4.2% (mean +/- SEM). The reduction in pause duration by aminophylline was specific for adenosine and did not occur under control conditions or during cesium chloride administration. During hypoxia, aminophylline and adenosine deaminase, when infused at the initiation of overdrive, caused 72.3 +/- 5.6 and 63.3 +/- 6.1% reductions in pause duration, respectively. Endogenous adenosine levels rose significantly with hypoxia (1,687 +/- 202 vs. 36 +/- 4 pmol/min per g during normoxia) and increased significantly further during hypoxic overdrive (3,004 +/- 323 pmol/min per g). In isolated guinea pig Purkinje fibers (n = 4), adenosine (20 microM) increased pause duration by 73.6 +/- 9.9% while only minimally affecting the pre-drive cycle length (7.6 +/- 3.8%). These fibers, when stimulated at 1.5 Hz, also displayed an adenosine-induced reduction in action potential duration at 90% repolarization (16 +/- 2 msec). In addition, we demonstrated that adenosine had an enhanced effect on pause duration in the presence of ouabain (1 microM)-induced attenuation of overdrive suppression. Thus, in isolated Purkinje fibers, it is unlikely that the potentiating effect of adenosine on pause duration, which is independent of its chronotropic effect, is mediated via an enhancement of sodium potassium adenosine triphosphatase pump activity. The effect of adenosine is likely to be secondary to a direct action on outward potassium conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for a possible role of the brain kallikrein-kinin system in the modulation of the cerebral circulation.
Authors: Kamitani T , Little M H , Ellis E F
Published: June 2012

Experiments by others have shown that exogenous bradykinin dilates cerebral arterioles and that the brain contains kininogen and kallikrein, the latter being the enzyme which converts kininogen to bradykinin. The objective of these experiments was to determine if bradykinin produced from endogenous brain kininogen can affect the cerebral microcirculation. Rabbit pial arteriolar diameter was measured with a microscope using the closed cranial window technique. Topical application of bradykinin (10(-8)-10(-5) M) induced a dose-dependent vasodilation (8-46%) which was completely inhibited by the cyclooxygenase enzyme inhibitors indomethacin and meclofenamic acid. Topical application of 1 U of tissue kallikrein per milliliter of artificial cerebrospinal fluid induced 43% dilation, which could be prevented by local treatment with indomethacin or the proteinase inhibitor aprotinin. The action of aprotinin and indomethacin was specific, since aprotinin did not affect the dilation produced by bradykinin, and indomethacin did not affect dilation produced by adenosine. A second application of kallikrein had no effect on cerebral diameter, yet the arterioles still responded normally to exogenous bradykinin, indicating that the first application of kallikrein depleted brain kininogen. We suggest that activation of brain kallikrein and subsequent formation of kinin from brain kininogen may be important in modulation of cerebral blood flow or generation of cerebral edema.
Exposure to fatty acid increases human low density lipoprotein transfer across cultured endothelial monolayers.
Authors: Hennig B , Shasby D M , Spector A A
Published: June 2012

Human low density lipoproteins radiolabeled with 125I transfer across confluent monolayers of cultured porcine pulmonary artery endothelial cells. The amount transferred was dependent on the low density lipoprotein concentration and was not saturable at concentrations up to 300 micrograms protein per 0.5 ml medium. Gel filtration showed that more than 90% of the 125I which crossed the endothelial monolayer remained associated with low density lipoproteins, indicating that appreciable amounts of lipoprotein were not degraded during the transfer process. When the endothelial monolayer was exposed for 24 hours to culture media supplemented with 100-300 microM fatty acid complexed with 100 microM albumin, the amount of low density lipoprotein subsequently transferred increased by 65% to 150%. The extent of the increase was dependent on the type of fatty acid added and its concentration. At 200 microM, albumin-bound oleic and linoleic acids increased low density lipoprotein transfer, whereas palmitic, linolenic, arachidonic, and eicosapentaenoic acids did not. These results are consistent with the hypothesis that exposure of the endothelium to elevated concentrations of fatty acid may allow excessive amounts of cholesterol-rich lipoproteins to enter the arterial intima.
Volume regulation and plasma membrane injury in aerobic, anaerobic, and ischemic myocardium in vitro. Effects of osmotic cell swelling on plasma membrane integrity.
Authors: Steenbergen C , Hill M L , Jennings R B
Published: June 2012

The relationship between cell swelling and plasma membrane disruption has been evaluated in thin myocardial slices incubated in oxygenated or anoxic Krebs-Ringer phosphate media. Electron microscopy and measurements of inulin-diffusible space were used to monitor plasma membrane integrity. Inulin is excluded from the intracellular space of intact cells; therefore, an increase in tissue inulin content is an excellent marker of loss of plasma membrane integrity. Cell volume was increased during exposure of aerobic slices to hypotonic media, but the inulin-diffusible space was not increased and electron micrographs showed no detectable plasma membrane alterations. Likewise, during prolonged anoxic isotonic incubation, no evidence of plasma membrane damage was observed. Incubation in anoxic hypotonic media for 60 minutes resulted in a larger increase in cell volume than under aerobic conditions, but plasma membrane integrity was maintained. Extended anoxic hypotonic incubation (300 minutes) produced no further change in tissue water, but the inulin-diffusible space was increased and electron micrographs revealed breaks in the plasma membranes primarily in association with large subsarcolemmal blebs. Likewise, myocardial slices incubated in isotonic anoxic media for 240 minutes and hypotonic anoxic media for 60 minutes had an increased inulin-diffusible space and the ultrastructural appearance was similar. This ultrastructural appearance is indistinguishable from that observed in myocytes lethally injured by ischemia. Measurements of tissue osmolarity during total ischemia showed that osmotically induced cell swelling could occur in ischemic myocardium prior to the onset of plasma membrane disruption. Our results indicate that cell swelling per se is incapable of rupturing plasma membranes; however, after prolonged periods of energy deficiency, the plasma membrane or its cytoskeletal scaffold become injured, which allows the membrane to rupture if the cell is swollen, as might occur during ischemia or reperfusion.
Active transendothelial transport of albumin. Interstitium to lumen.
Authors: Shasby D M , Shasby S S
Published: June 2012

Cultured porcine pulmonary artery endothelial monolayers actively transport albumin from interstitium to lumen. The active process favors interstitial to luminal transport by a factor of 10 even in the face of a 2:1 luminal:interstitial albumin gradient. The active process is abolished by treatment with 1 mM sodium cyanide. Dextran is not actively transported. This process could be important in determining transvascular fluid balance and transfer of macromolecules across the endothelium.
Association of clathrin with microsomes isolated from canine myocardium.
Authors: Caprette D R , Entman M L , Van Winkle W B
Published: June 2012

We and others have observed specialized regions of sarcoplasmic reticulum membranes that resemble coated vesicles, in the I-band region of myocardial cells. These structures have been named "corbular" sarcoplasmic reticulum, and are distinct in appearance from Golgi-associated coated vesicles, in that they are larger and contain a flocculent material that has been identified as calsequestrin. Whereas it has been suggested that these structures have a role in cardiac calcium metabolism, their function(s) and the molecular identity of the characteristic "bristle" coat remain unknown. Microsomes enriched in sarcoplasmic reticulum were prepared from canine ventricular muscle by Polytron homogenization in pH 6.5 buffer, followed by differential centrifugation. Protein was released by incubation in 50 mM Tris/HCl, pH 8, followed by centrifugation. We found these extracts to be enriched in a protein that was identical to brain clathrin in mobility on a Sepharose 4B gel filtration column, final position of the native protein following nondenaturing electrophoresis, relative mobility in denaturing (sodium dodecyl sulfate) electrophoresis on 6% and 7.5% gels, and antigenicity to anti-clathrin IgG. These findings confirmed the presence of clathrin triskelions in the cardiac microsome extract. On this basis, we suggest that clathrin may be a component of the electron dense "coat" of corbular sarcoplasmic reticulum.
Prevention of transcoronary macromolecular leakage after ischemia-reperfusion by the calcium entry blocker nisoldipine. Direct observations in isolated rat hearts.
Authors: McDonagh P F , Roberts D J
Published: June 2012

Coronary microvascular damage appears to play a role in reperfusion injury after myocardial ischemia. This study was designed to afford direct viewing of the effects of myocardial ischemia-reperfusion on the coronary microcirculation and to determine whether pretreatment with the calcium blocker nisoldipine would attenuate any microvascular damage during reperfusion. Four groups of isolated rat hearts were perfused with a solution that contained red cells and fluorescent albumin, but was essentially free of platelets and leukocytes. Group I served as a nonischemic control. Group II hearts were subjected to 30 minutes of no-flow ischemia followed by reperfusion. Group III hearts were pretreated with nisoldipine (1 microgram/min) for 5 minutes before ischemia, and group IV hearts were treated with nitroglycerin (93 micrograms/min) before and after ischemia to mimic the vasodilation caused by nisoldipine. Perfused coronary capillarity and transcoronary extravasation of plasma albumin were measured by direct visualization techniques before and after ischemia. For group I, there was no significant change in coronary resistance, perfused capillarity, or transcoronary extravasation with time. For both groups II and IV, ischemia-reperfusion caused no increase in coronary resistance, but a significant decrease in perfused capillarity and a marked increase in transcoronary extravasation of fluorescent albumin (P less than 0.05). The nisoldipine group (group III) demonstrated a similar decrease in perfused capillarity but no increase in protein extravasation during reperfusion. These results indicate that, in the heart, platelets and/or leukocytes are not absolutely necessary to induce either the no-reflow phenomenon or the permeability damage observed during reperfusion after ischemia. The protective effect of treatment with nisoldipine appeared to be independent of vasodilation. We speculate that this calcium blocker reduced endothelial uptake of calcium during reperfusion, preventing endothelial deformation and formation of interendothelial gaps.
Histochemical and fatigue characteristics of conditioned canine latissimus dorsi muscle.
Authors: Mannion J D , Bitto T , Hammond R L , Rubinstein N A , Stephenson L W
Published: June 2012

To induce fatigue resistance in the latissimus dorsi muscle of the dog in preparation for possible myocardial assistance, eight adult male beagles underwent unilateral electrical stimulation of the thoracodorsal nerve at a frequency of 2 Hz (120 stimuli/min) and 10 Hz (600 stimuli/min) for a 6-week period. The conditioned muscles were compared with their unconditioned contralateral controls by fiber typing, pyrophosphate gel electrophoresis, isometric characteristics, and fatigue rates. At the end of the period of stimulation, the conditioned muscles had a greater percentage of slow-twitch, fatigue-resistant fibers on acid and alkaline stains (100 +/- 0.7% and 83 +/- 15.3%), respectively, than did their contralateral controls (45 +/- 7.6% and 43 +/- 7.0). Pyrophosphate gel electrophoresis revealed an increase in the slow myosin and a decrease in the fast myosin content in the conditioned muscles; the stimulated muscles also demonstrated a slower contraction time (87 +/- 20 msec vs. 57 +/- 17.9 msec), a lower initial tension (4.4 +/- 1.45 kg vs. 7.2 +/- 2.11 kg), and a slower fatigue rate during a 30-minute fatigue test than did their contralateral controls. The muscles stimulated at 2 Hz had fatigue rates similar to those stimulated at 10 Hz, but generally had less diminution in muscle fiber diameters and less interfiber connective tissue. Thus, it is possible to make canine latissimus dorsi muscles more fatigue resistant, and, theoretically, more capable of myocardial assistance by electrical stimulation of the thoracodorsal nerve at a frequency as low as 2 Hz--the natural canine heart rate.
Oxygen-dependent tension in vascular smooth muscle. Does the endothelium play a role?
Authors: Coburn R F , Eppinger R , Scott D P
Published: June 2012

We investigated a hypothesis that an oxygen sensor involved in hypoxia-induced relaxation of vascular smooth muscle may reside in endothelial cells. We also determined the oxygen dependence of hypoxia-induced decreases in cyclic guanosine 3',5'-monophosphate concentrations in vascular smooth muscle rings. Rings of canine femoral artery, rabbit thoracic aorta, and lamb ductus arteriosus, either with an intact endothelium or with damaged or absent endothelium, were studied using organ baths that allowed changes in PO2 without a change in pH. Hypoxia-induced relaxations of rabbit thoracic aorta, lamb ductus arteriosus, and canine femoral artery were not dependent on an intact endothelium. The magnitude of hypoxia-induced relaxations was unchanged in rings of canine femoral artery without intact endothelium compared to rings with endothelium. Quasi-steady state organ bath PO2-mechanical tension relationships were unchanged in rings of canine femoral artery without endothelium over an organ PO2 range of 200-20 mm Hg. With rabbit thoracic aorta, magnitudes of hypoxia-induced relaxations were significantly smaller in rings without endothelium. Quasi-steady state plots, where mechanical tension was given as percentage of maximal relaxation, were similar in rings either with or without intact endothelium. Cyclic guanosine 3',5'-monophosphate concentrations were shown to be oxygen-sensitive, decreasing during hypoxia-induced relaxations with a threshold PO2 of 80-100 mm Hg with canine femoral artery, and 60-80 mm Hg with rabbit thoracic aorta rings, but this finding seems unrelated to the mechanism of hypoxia-induced relaxation.
The energetics of myocardial stretch. Creatine kinase flux and oxygen consumption in the noncontracting rat heart.
Authors: Bittl J A , Ingwall J S
Published: June 2012

Previous studies have suggested that flux through the creatine kinase reaction is coupled to cardiac performance and to the rate of adenosine triphosphate synthesis in the intact, beating heart. To define the effect of passive myocardial stretch on creatine kinase kinetics, we measured the rate constants and chemical fluxes for both directions of the creatine kinase reaction with the 31P-nuclear magnetic resonance technique of magnetization transfer in isolated, arrested rat hearts at four levels of left ventricular pressure and volume. Adenosine triphosphate synthesis was estimated from oxygen consumption measurements. As left ventricular pressure rose from 0 to 24 mm Hg and oxygen consumption increased by 20%, we observed a twofold increase in the rate constants and fluxes (mean +/- SD, n = 4-7) for the creatine kinase reaction. The forward rate constant increased from 0.33 +/- 0.03 to 0.80 +/- 0.08, and the reverse rate increased from 0.34 +/- 0.11 to 0.74 +/- 0.32/sec. The forward and reverse fluxes for the creatine kinase reaction increased from 12.0 +/- 3.4 to 26.5 +/- 5.8 and from 9.1 +/- 3.4 to 19.1 +/- 3.4 mumol/g dry weight per sec, respectively. At each level of left ventricular pressure, the forward and reverse rate constants were the same. However, as left ventricular pressure increased, the ratio of the forward to the apparent reverse fluxes for the creatine kinase reaction increased. The relationships between the rate constant or flux through the creatine kinase reaction vs. left ventricular pressure were linear. In addition to providing further support for the coupling between creatine kinase and mitochondrial adenosine triphosphate synthesis, these results suggest that flux through the creatine kinase reaction and adenosine triphosphate synthesis increases with myocardial stretch in the intact, noncontracting heart.
Characterization of the human lymphocyte beta-adrenergic receptor by photoaffinity labeling. Alterations with desensitization.
Authors: Feldman R D , Lai C Y
Published: June 2012

Desensitization of the leukocyte beta-receptor system has been associated with a functional uncoupling of the components of the beta-receptor complex. In order to determine whether desensitization and uncoupling of the leukocyte beta-receptor is associated with any structural alterations in the beta-receptor, we studied labeling of lymphocytes using the photoactive beta-adrenergic antagonist p-azido-m-[125I]iodobenzylcarazolol. Labeled peptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detected using autoradiographic techniques. In broken cell preparations, specific labeling was demonstrated in two major peptide bands: mol wt approximately equal to 68,000 and mol wt approximately equal to 55,000. Inhibition of photolabeling was stereospecific and demonstrated an order of potency for agonists consistent with labeling of a beta 2-receptor. Preincubation of cells with the beta-agonist, isoproterenol, resulted in a reduction in beta-adrenergic-mediated adenylate cyclase activity to 60% of control, but no change in total binding sites as determined by [125I]iodocyanopindolol binding. In photolabeling studies, desensitization was associated with a reduction in proportional labeling of the 55,000 mol wt band as compared to the 68,000 mol wt band to 58 +/- 3% of control and a reduction in mobility of the upper band. These studies suggest that structural alterations in the human lymphocyte beta-receptors occur with desensitization, analogous to changes in several other beta-receptor model systems. Also, since the techniques described can identify alterations in human beta-receptor structure, these methods may be exploited to determine whether structural alterations in lymphocyte beta-receptors may occur in human disease states.
Decreased number and affinity of rat atrial natriuretic peptide (6-33) binding sites in the subfornical organ of spontaneously hypertensive rats.
Authors: Saavedra J M , Israel A , Kurihara M , Fuchs E
Published: June 2012

Binding sites for rat atrial natriuretic peptide (6-33) were quantified by incubation of brain sections with (3-[125I]iodotyrosyl28) rat atrial natriuretic peptide (6-33), followed by autoradiography with computerized microdensitometry. Spontaneously hypertensive rats present lower numbers and lower affinity of binding sites than normotensive controls, Wistar-Kyoto rats, in the subfornical organ (binding capacity 61.7 +/- 8.9 and 124.3 +/- 10.7 fmol/mg protein; affinity constant 4.25 +/- 0.55 and 11.10 +/- 1.67 X 10(9) M-1, respectively). In the choroid plexus, hypertensive rats have lower numbers of sites than normotensive rats (binding capacity 72.7 +/- 10.5 and 173.6 +/- 22.8 fmol/mg protein, respectively), but there was no difference in the binding affinity (affinity constant 6.28 +/- 0.82 and 7.60 +/- 2.06 X 10(9) M-1, respectively). Our results suggest that discretely localized brain binding sites for rat atrial natriuretic peptide (6-33) may have a physiological function in genetically hypertensive rats.
Phorbol diester modulates alpha-adrenergic receptor-coupled calcium efflux and alpha-adrenergic receptor number in cultured vascular smooth muscle cells.
Authors: Colucci W S , Gimbrone M A , Alexander R W
Published: June 2012

The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate was used to probe the role of protein kinase-C in the modulation of alpha-adrenergic receptor-coupled calcium efflux in cultured vascular smooth muscle cells derived from rabbit aorta. Exposure of cells to 12-O-tetradecanoyl phorbol-13-acetate for 6 minutes caused a concentration-related (maximum effect at greater than or equal to 10 nM) increase in calcium-45 efflux from preloaded cells. Maximum calcium-45 efflux stimulated by 12-O-tetradecanoyl phorbol-13-acetate was equivalent to maximum norepinephrine-stimulated calcium-45 efflux, and maximally effective concentrations of 12-O-tetradecanoyl phorbol-13-acetate and norepinephrine together were no more potent than either drug alone. Exposure of cells to 12-O-tetradecanoyl phorbol-13-acetate for periods of 1-24 hours resulted in complete loss of norepinephrine-stimulated calcium-45 efflux and a much slower, concentration-related reduction in alpha-adrenergic receptor number, with a maximum reduction of 50-60% at 12-O-tetradecanoyl phorbol-13-acetate concentrations greater than or equal to 10 nM. Twenty-four hours of exposure to 12-O-tetradecanoyl phorbol-13-acetate (10 nM) and norepinephrine (10 microM) together caused no greater reduction in [3H]prazosin binding than did norepinephrine alone. 12-O-tetradecanoyl phorbol-13-acetate had no effect on [3H]prazosin-binding affinity. These data suggest an important role for protein kinase-C in both the acute excitation-contraction coupling of vascular smooth muscle alpha-adrenergic receptors, and in the long-term modulation of vascular alpha-adrenergic receptor responsiveness.
Myocardial biochemical, contractile, and electrical performance after imposition of hypertension in young and old rats.
Authors: Capasso J M , Malhotra A , Scheuer J , Sonnenblick E H
Published: June 2012

The effects of renovascular hypertension on the biochemical, contractile, and electrical performance of myocardial tissue from rats of various ages has been examined. Male Fischer rats, 2, 7, 12, and 17 months old, were made hypertensive by constriction of the left renal artery. Ten weeks after the onset of hypertension, left ventricular papillary muscles were isolated from those four groups when 5, 10, 15, and 20 months old, respectively. Mechanical performance and transmembrane electrical events were recorded simultaneously. Contractile protein enzyme activity was determined in the same hearts from which papillary muscles were used for acquisition of mechanical and electrical information. There was a slight increase in blood pressure in control groups as a function of age while blood pressure maintained a range of approximately 179-188 mm Hg for all hypertensive groups. Heart weight of control animals increased significantly from 5 months to 20 months of age from 539 +/- 26 to 1088 +/- 56 mg, representing an increase of 101%. In hypertensive animals, heart weight increased 50% in 5-month-, 15% in 10-month-, 50% in 15-month-, and 11.7% in 20-month-old animals. Although control groups revealed alterations in mechanical, electrical, and biochemical parameters that increased as a function of age, the magnitude of the biochemical, contractile, and electrical response to hypertension varied monotonically with the extent of myocardial hypertrophy, rather than age per se. Adaptation to the stress of hypertension was observed in each age group, and was revealed as prolongation of mechanical and electrical timing parameters, depression of the load-velocity relation, and contractile protein enzyme activity. Thus, the stress of hypertension, which was tolerated by the 10- and 20-month-old animals with lesser relative hypertrophy and lesser changes in measured parameters, may represent a differential adaptation to the stress of hypertension.
Endothelial cells express a spectrin-like cytoskeletal protein.
Authors: Heltianu C , Bogdan I , Constantinescu E , Simionescu M
Published: June 2012

Vascular endothelium was investigated by indirect immunofluorescence and immunoautoradiography for the possible presence of spectrin-like molecules. Antibodies were raised against electrophoretically purified rat, rabbit, and bovine red blood cell spectrin and against rabbit brain fodrin. Antibody specificity was assessed by immunoblotting and double-diffusion technique. Homogenates of endothelial cells freshly isolated from heart microvasculature or aorta, as well as cultured aortic endothelial cells, were analyzed by gel electrophoresis. Immunoautoradiograms of gels incubated with spectrin specific antibody, followed by radio-labeled protein A, revealed two bands of electrophoretic mobility similar to that of the alpha- and beta-subunits of spectrin. Indirect immunofluorescence of endothelial cells, both in situ and in vitro, showed the existence of a protein which cross-reacted with the antibodies against spectrin and fodrin. Controls, in which endothelial cells were exposed to spectrin antibody absorbed with pure spectrin or preimmune serum, were negative. These findings indicate that endothelial cells express a protein antigenically related to the spectrin family; both spectrin- and fodrin-like molecules, in various proportions, may coexist. In the endothelial cell, these proteins may play an important role in modulation of the cytoskeleton in response to various stimuli, and in maintaining the biochemically differentiated microdomains of plasmalemma.
Trophic interactions between rat nerves and blood vessels in denervated peripheral arteries and in anterior eye chamber transplants.
Authors: Todd M E
Published: June 2012

This investigation was undertaken to examine trophic interrelationships between nerves and arteries in male Wistar rats. Two approaches were used. (1) Surgical denervation of two peripheral muscular arteries in the thigh (the superficial epigastric and saphenous) was carried out on young animals (5-20 days old). (2) Arteries from young adults, either with a high density of innervation in situ (the tail artery), or virtually uninnervated (the femoral artery), were transplanted into intact or sympathectomized anterior eye chambers of adult rat hosts. In the denervation experiments, the maximum length of time before reinnervation occurred was 15 days postoperatively. The only evidence of morphological change in the vessel wall was in the external elastic lamina that became irregular and laminated. Reinnervation followed the typical developmental sequence, and was accelerated in the younger animals and by a double lesion. Translocating the proximal part of the nerve carrying the vasomotor innervation indicated that sprouting was directional toward the muscular arteries, bypassing an artery with very sparse innervation. The transplant experiments into the anterior eye chamber showed that only an artery densely innervated in situ (the tail artery) could induce reinnervation by iridean nerve sprouting. The tail artery, in the chamber lacking adrenergic innervation of the iris, became reinnervated by terminals with small agranular vesicles. These vesicles were part of Schwann cell complexes, at a similar relative density, occupying the same position in the vessel wall, as the ingrowing nerves in the fully innervated iris. The latter also had a proportion of terminals with the small clear vesicles. A small population of large granular vesicles could also be found in both types of terminals. Therefore, tissue normally having only sympathetic innervation cannot be assumed to be completely noninnervated when transplanted into a sympathectomized anterior eye chamber. The denervation and transplant experiments described here demonstrated the presence of trophic interactions between nerves and arteries, but also revealed a heterogeneity of response between vessels with very high and extremely low levels of innervation in situ.
Ryanodine inhibits the release of calcium from intracellular stores in guinea pig aortic smooth muscle.
Authors: Ito K , Takakura S , Sato K , Sutko J L
Published: June 2012

We have examined the effects of ryanodine, an inhibitor of the release of sarcoplasmic reticulum calcium in cardiac muscle, on contractile tension and calcium-45 movement in aortic smooth muscle of guinea pigs to learn whether this agent also modifies the release of stored calcium in vascular smooth muscle. Ryanodine (3-100 microM) suppressed the phasic contractions induced by caffeine and norepinephrine in calcium-free medium and prevented the stimulation of calcium-45 efflux by these agonists. Ryanodine did not significantly alter either the contractile response or the increased cellular influx of calcium-45 caused by high potassium in more than 1 mM calcium, suggesting that this agent does not affect depolarization-induced calcium entry into the cells. In a calcium-free, high potassium solution, the addition of calcium at concentrations of 1 mM and less resulted in a contraction which appeared to depend largely on the release of calcium from intracellular stores. This contraction was blocked by ryanodine. These data are consistent with the hypothesis that ryanodine causes a diminished release of calcium from the intracellular store in vascular smooth muscle, as it does in cardiac muscle. Moreover, our results indicate that a calcium-induced calcium release may exist in smooth muscle, and that this release is antagonized by ryanodine.
Myoplasmic calcium, myosin phosphorylation, and regulation of the crossbridge cycle in swine arterial smooth muscle.
Authors: Rembold C M , Murphy R A
Published: June 2012

Our objective was to test the hypothesis that changes in crossbridge phosphorylation in the swine carotid media are due to changes in the myoplasmic calcium concentration. The photoprotein aequorin was loaded intracellularly by incubation in a series of calcium-free solutions. This loading procedure did not affect subsequent stress development, myosin light chain phosphorylation, or ultrastructure. The time course of light production, myosin light chain phosphorylation, shortening velocity at zero load, and active stress were measured in three stimulus protocols: depolarization with 109 mM potassium chloride at 22 degrees C, 37 degrees C, and 37 degrees C, followed by a reduction in potassium chloride to 20 mM to induce stress maintenance with basal phosphorylation (latch). Light-predicted intracellular calcium concentration was found to correlate with myosin phosphorylation and unloaded shortening velocity. The calcium concentration required for half-maximal myosin phosphorylation was approximately twice that for stress maintenance. These estimates depend on many assumptions, but they compared favorably with the half-maximal myosin phosphorylation values obtained for the calcium-dependence of stress maintenance and phosphorylation in Triton X-100 skinned carotid media preparations. This supports the hypothesis that myoplasmic calcium is the determinant of myosin phosphorylation and mean crossbridge cycling rates in intact smooth muscle depolarized by potassium chloride.
Myosin transitions in the bovine and human heart. A developmental and anatomical study of heavy and light chain subunits in the atrium and ventricle.
Authors: Cummins P , Lambert S J
Published: June 2012

Transitions in cardiac myosin isotypes occur in response to a variety of stimuli. These are well documented in small, but less so in larger, mammals where data on quantitative isotype composition of normal atria and ventricles are scarce. In this study, heavy and light chain isotypes were examined in fetal, neonatal, and adult bovine and human hearts. Defined anatomical areas of chambers were studied, and detailed mapping of isotypes was conducted on bovine atria. Heavy chain isotype quantification was carried out electrophoretically either after peptide mapping or by a new technique for separating whole cardiac alpha- and beta-heavy chains capable of detecting 5% of either isotope. Atrial and ventricular light chains were resolved electrophoretically, and all isotypes were quantified densitometrically. Beta-Heavy chain was almost exclusively expressed (greater than 95%) in the ventricles at all ages except in the bovine neonate. Ventricular light chains predominated in the adult ventricle, but atrial light chain 1 was present at mid-gestation. This was replaced by ventricular light chain 1 in the neonate with no transitions in light chain 2 isotypes. Transitions were more marked in the atria. Only alpha-heavy chains were detected at mid-gestation, but beta-heavy chain increased toward birth. After a decline in the neonatal period, beta-heavy chain levels usually increased in the adult. Atrial light chains were the main isotypes in the atria, but ventricular light chain 2 was the major adult bovine atrial isotype. Transitions in isotypes were significant at birth as in smaller mammals. No close relationship existed between heavy and light chain transitions. Significant anatomical variation in bovine atrial isotype expression was present, and may reflect functional demand in each area.
Resolution of intracellular calcium metabolism in intact segments of rabbit aorta.
Authors: Phair R D , Hai C M
Published: June 2012

A new method, based on computer-assisted kinetic analysis of 45Ca efflux data, was used to measure calcium contents and fluxes for extracellular and intracellular compartments in intact segments of rabbit aorta. After a 1-hour loading period, efflux data were collected for 8 hours using a flow-through tissue chamber. These long-term effluxes were necessary because information on intracellular calcium metabolism was concentrated in the slow components of the efflux curves while earlier components appeared to be dominated by washout of extracellular calcium. Intracellular compartments were identified as those whose calcium contents were altered by 10 microM phenylephrine. This method complements previous approaches by providing simultaneous estimates of compartmental calcium contents and fluxes without requiring the assumption of isotopic equilibrium and without recourse to standard wash techniques for removal of extracellular calcium. In normal, calcium-containing, bicarbonate-buffered physiological salt solution these compartments contained a total of approximately 300 nmol Ca/g wet aorta. Of this total, 55 nmol/g were associated with the slowest resolvable compartment whose turnover time was 170 minutes and whose exchange flux was 0.32 nmol min-1g-1. Two other intracellular compartments had turnover times of 30 minutes. One of these was phenylephrine releasable and contained 145 nmol/g; it exchanged calcium at 4.9 nmol min-1g-1. In normal physiological salt solution the plasma membrane was, surprisingly, not rate limiting for Ca efflux; and in 10 microM phenylephrine the membrane Ca flux was even greater, increasing 3.5-fold compared to control.
The role of high-energy phosphate in norepinephrine-induced acute renal failure in the dog.
Authors: Sinsteden T D , O'Neil T J , Hill S , Lifschitz M D , Stein J H
Published: June 2012

Previous studies have demonstrated that pretreatment with mannitol, furosemide, or bradykinin can attenuate the severity of norepinephrine-induced renal functional impairment. The present studies were designed to evaluate the possibility that these agents are protective, in part, by preserving cellular metabolic integrity. The renal cortex was repetitively biopsied during the course of this study, and high-pressure liquid chromatography was used to analyze the tissue content of adenine nucleotides (expressed in nanomoles per gram of wet tissue). The adenine nucleotide charge ratio (CR) and total adenine nucleotide (TAN) content were calculated as indices of cellular metabolic integrity. In addition to the above-established protective agents, phenoxybenzamine was used to evaluate a direct toxic effect of norepinephrine on renal tissue. Inulin clearance at 3 hours post infusion (expressed as a percent of control) was 7% with norepinephrine alone and, in the protected groups, 36% with bradykinin, 61% with furosemide, 51% with mannitol, and 100% with phenoxybenzamine. There was no change in CR or TAN with phenoxybenzamine. In contrast, during norepinephrine administration CR fell significantly in all other groups. Three hours after stopping norepinephrine, CR had returned toward control values and the level of CR was significantly better in all protected groups when compared with norepinephrine alone. Similarly, the levels of TAN were significantly diminished in the norepinephrine-alone group when compared to all protected groups, and there was significantly more tubular necrosis as well. The maintenance of higher levels of TAN and the preserved ability to regenerate adenosine triphosphate in the protected groups, when compared to the norepinephrine-alone group, support the contention that these agents offer protection, at least in part, by preserving cellular metabolic integrity.
Absence of functioning alpha-adrenergic receptors in mature canine coronary collaterals.
Authors: Harrison D G , Chilian W M , Marcus M L
Published: June 2012

To determine if mature coronary collateral vascular smooth muscle contains functioning alpha-adrenergic receptors, we studied 13 dogs, 6-10 months after circumflex ameroid occlusion. Regional myocardial blood flow was measured with radioactive microspheres in a blood-perfused heart preparation at constant aortic pressure (80 mm Hg). Normal zone resistance was calculated as aortic pressure divided by normal zone flow, and transcollateral resistance was calculated as aortic pressure minus circumflex pressure distal to the ameroid constrictor divided by coronary collateral flow. Flow and resistance were measured during adenosine vasodilation before and during graded doses of a constant infusion of the alpha-adrenergic agonist methoxamine (n = 6) or the alpha 2-adrenergic agonist clonidine (n = 7). In the hearts that received methoxamine, normal zone resistance increased from a control of 0.29 +/- 0.06 to 0.39 +/- 0.06 mm Hg X min/ml per 100 g (resistance units) during infusion of 10(-5)M methoxamine (p less than 0.05). In contrast transcollateral resistance averaged 0.24 +/- 0.02 resistance units under control conditions and did not change during methoxamine infusion. In the hearts that received clonidine, normal zone resistance averaged 0.24 +/- 0.03 resistance units and increased to 0.39 +/- 0.07 resistance units (p less than 0.05) with the highest dose of clonidine administered (10(-5) M). Transcollateral resistance averaged 0.17 +/- 0.03 resistance units during control conditions and did not change with clonidine infusion. In separate studies isometric tension development by the left anterior descending and coronary collateral vessels was examined in organ baths. The left anterior descending coronary artery demonstrated dose-dependent constriction to phenylephrine (peak response 22 +/- 5% of the response to 100 mM KCl). Clonidine produced weak constrictor responses in the left anterior descending coronary artery (5 +/- 2.5% maximal KCl response). In contrast, neither phenylephrine nor clonidine produced responses in mature collaterals. We also examined responses of mature collateral vessels to nonadrenergic agonists. In the vascular ring preparation the mature collaterals developed tension in the presence of KCl (2.3 +/- 0.9 g), prostaglandin F2 alpha (16 +/- 18% of the KCl responses), and vasopressin (90 +/- 30% of the KCl response). In adenosine-vasodilated hearts, pharmacologic doses of vasopressin caused a two-fold increase in transcollateral resistance. Thus, these studies performed on intact hearts and isolated vascular rings demonstrate that mature coronary collaterals do not contain functioning alpha-adrenergic receptors.(ABSTRACT TRUNCATED AT 400 WORDS)