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T N Tulenko

Publications and source records attributed to T N Tulenko.

At least 37 records · Page 2Linked to original sources
PubMed1994

Alterations in basal and serotonin-stimulated calcium permeability and vasoconstriction in atherosclerotic aorta.

Hypersensitivity to vasoactive stimuli, a common finding in atherosclerotic arteries, is thought to play an important role in the pathology of arterial and coronary vasospasm and may be a factor in myocardial ischemia and infarction. While this phenomenon is well documented, the underlying mechanism is unknown. The present study used isometric force measurements coupled with 45Ca2+ and Fura 2-AM techniques in aortic smooth muscle to probe transmembrane calcium movements and cytosolic calcium levels in an attempt to determine their relation to altered vasomotion in a rabbit model of dietary atherosclerosis. Following 10 weeks of cholesterol feeding (2%), basal (unstimulated) calcium influx was augmented 1.5-fold in atherosclerotic segments with no change in basal calcium efflux. Serotonin-stimulated calcium uptake was increased 1.9-fold in atherosclerotic segments and was accompanied by a fivefold increase in serotonin vasoconstrictor sensitivity and a 1.4-fold increase in serotonin-stimulated calcium efflux. Endothelial denudation did not alter either force generation or 45Ca2+ movements in serotonin-stimulated segments. In arterial smooth muscle cells dispersed from atherosclerotic vessels, basal and serotonin-stimulated cytosolic calcium levels were augmented approximately 2.3-fold and twofold, respectively. These findings contribute to our understanding of the cellular defects in calcium metabolism, which may ultimately explain the cellular basis of serotonin hypersensitivity in atherosclerotic arteries and certain arterial vasospastic syndromes in this disease state.

Animals↗
PubMed1994

The molecular basis for lacidipine's unique pharmacokinetics: optimal hydrophobicity results in membrane interactions that may facilitate the treatment of atherosclerosis.

Membrane-active drugs can be characterized by direct measurements of their membrane partition coefficients, washout rates from membranes, and washin rates into membranes. There appears to be a correlation between the duration of action of such membrane-active drugs and the membrane partition coefficient in conjunction with the washout rate. Lacidipine has a high membrane partition coefficient compared to other 1,4-dihydropyridine calcium-channel antagonists and a slow washout rate from membranes. Clinically, it also exhibits an extended duration of action. This control at the membrane molecular level may provide an optimal pharmacokinetic profile for lacidipine in the treatment of hypertension. In addition, these same properties may be important for lacidipine as an antiproliferative agent in the treatment of atherosclerosis.

Animals↗
PubMed1993

The order of dilator-constrictor administration affects stenotic hemodynamic responses.

This study tested the hypothesis that, due to intraluminal pressure changes, the order of constrictor-dilator administration alters stenotic hemodynamic responses. Canine carotid arteries were perfused with a physiologic salt solution under constant pressure (100 mm Hg). An intraluminal stenosis partially obstructed the arteries. Pressures proximal and distal to the artery and the flow were continually recorded as norepinephrine (10(-9)-10(-6) M) was added to the perfusate. Adding diltiazem (10(-7) M) before norepinephrine shifted the effective half maximum dose (ED50) of the norepinephrine flow curve from 7.35 +/- 0.66 X 10(-8) M to 6.39 +/- 0.72 X 10(-7) M (p < 0.05). More important, adding 10(-7) M diltiazem after norepinephrine-induced constriction did not reestablish stenotic pressure or flow: A 30-fold increase in diltiazem concentration (3.16 X 10(-6)M) was required to reestablish stenotic pressure (62.6 +/- 4.4 mm Hg) and flow (25.4 +/- 3.2 ml/min). Similarly, adding nitroglycerin (10(-7) M) before norepinephrine shifted the ED50 from 7.21 +/- 0.58 X 10(-8) to 5.94 +/- 0.78 X 10(-6) (p < 0.05). Adding 10(-7) M nitroglycerin after norepinephrine did not reestablish stenotic pressure or flow: 3.16 X 10(-6) M nitroglycerin was required to reestablish stenotic pressure (59.2 +/- 4.8 mm Hg) and flow (23.2 +/- 2.7 mL/min). This constrictor-dilation history did not occur in isolated arterial rings (norepinephrine + nitroglycerin = 38.1 +/- 13.9 g/cm2; nitroglycerin + norepinephrine = 42.2 +/- 9.4 g/cm2; p = not significant [NS]) or in normal arteries (norepinephrine + nitroglycerin = 4.89 +/- 0.14 mm [external diameter]; nitroglycerin + norepinephrine = 4.92 +/- 0.23 mm; p = NS). In stenotic arteries, intraluminal pressure influenced the order of constrictor-dilator administration on hemodynamic response, which was not observed in isolated arterial rings or in normal arteries. This pressure-dependent sensitivity affects vasomotor tone and may be important in the pathophysiology of ischemia.

Animals↗
PubMed1993

Acute exposure to cholesterol increases arterial nitroprusside- and endothelium-mediated relaxation.

The effect of cholesterol enrichment on arterial relaxation was studied by evaluating sodium nitroprusside (SNP)- and endothelium-mediated relaxation of isolated rabbit carotid artery. Arterial segments were perfused in vitro (4 h) with cholesterol-rich liposomes consisting of free cholesterol (FC) and phospholipid (PL) in a 2:1 molar ratio. Ring segments from arteries exposed to cholesterol-rich liposomes exhibited a 60% increase (P < 0.01) in FC content without affecting PL content. Cholesterol-enrichment was associated with a twofold increase (r = 0.92, P < 0.05) in acetylcholine- and A23187-induced endothelium-mediated relaxation. Bioassay of endothelium-derived relaxing factor(s) (EDRF) after cholesterol exposure indicated that EDRF half-life and/or release increased (P < 0.05) threefold. A trend (P = 0.07) toward increased smooth muscle cell sensitivity to EDRF after cholesterol enrichment was also observed. Cholesterol enrichment increased (P < 0.05) sensitivity to SNP 12-fold, and this difference was further augmented (P < 0.01) twofold with endothelium removal. Cholesterol enrichment had no effect on relaxation to N2,2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate. These data indicate that acute cholesterol enrichment increases EDRF activity from arterial endothelium and increases smooth muscle responses to both EDRF and SNP.

Animals↗
PubMed1992

Platelet amplification of vasospasm.

Platelets may accentuate vasoconstriction in stenotic arteries capable of vasomotion. We examined the interaction of platelets, stenosis, and arterial vasoconstriction in normal and stenotic arteries with intact endothelium. Beagle carotid arteries (n = 38) were isolated, removed, and placed in an in vitro perfusion system. Platelet-rich plasma (PRP) or platelet-poor plasma (PPP) were perfused through the arteries under constant pressure (100 mmHg) and a fixed distal resistance. In intact arteries without a stenosis, angiotensin II (ANG II) decreased luminal diameter without altering flow during PRP perfusion. After creating an intraluminal stenosis, vasoconstriction produced by ANG II resulted in near total cessation of flow. During PRP perfusion, this effect was amplified, demonstrating suppression of flow at significantly (P less than 0.05) lower concentrations of ANG II (PRP, ED50 = 0.03 +/- 0.01 x 10(-8) M) compared with arteries perfused with PPP (PPP, ED50 = 2.7 +/- 0.8 x 10(-8) M). This accentuated vasoconstrictor response in the presence of platelets was not blocked by SKF 96148 (a thromboxane A2 antagonist) but was abolished by ketanserin (a 5-HT2-serotonergic blocker). This increased sensitivity to vasoconstriction was not due to significant platelet plugging inasmuch as no cyclic flow reductions were observed, aspirin (acetylsalicylic acid) did not prevent this accentuated vasoconstrictor response, and adventitial administration of nitroglycerin restored flow to baseline levels. These studies illustrate that 1) platelets amplify the effect of vasoconstrictors in stenotic arteries, 2) this amplification of vasoconstriction is primarily due to platelet release of serotonin, and 3) the amplification occurs in the absence of significant platelet plugging and endothelial damage.

Animals↗
PubMed1991

Importance of endothelial function in stenotic haemodynamic responses.

STUDY OBJECTIVE: The aim was to examine endothelium mediated flow dependence in a dynamic stenosis. DESIGN: The coronary circulation was modelled as a proximal compliant stenosis and a fixed distal resistance. Pressures and flow were calculated using standard haemodynamic equations. Within the stenosis, the vessel wall was composed of normal and rigid sections, and the normal section dilated proportionally with flow. From this theoretical analysis, three perfusion pressures (150, 100, and 75 mm Hg) and two distal resistances (high and low) were examined. MAIN RESULTS: In a stenotic artery (93% area reduction) with high flow dependence, decreasing distal resistance increased flow substantially. At 75 mm Hg perfusion pressure, flow increased from 40.8 to 81.6 ml.min-1. With moderate flow dependence, flow increases were attenuated. Without flow dependence, flow increases were smaller, and at low perfusion pressure, flow paradoxically decreased (39.0 to 0.0 ml.min-1) when distal resistance decreased. Vasoconstriction responses with and without flow dependence were analysed. In a stenotic artery, vasoconstrictors caused a concentration dependent decrease in flow. Without flow dependence, the flow dose-response curve was shifted to the left: a lower level of arterial vasoconstriction resulted in a greater flow decrease. CONCLUSIONS: The theoretical analysis shows significantly different flow responses to decreasing distal resistance and to vasoconstriction depending on endothelial function. Endothelial dysfunction may be important in the pathophysiology of angina pectoris.

Arterial Occlusive Diseases↗
PubMed1991

Excess membrane cholesterol alters calcium movements, cytosolic calcium levels, and membrane fluidity in arterial smooth muscle cells.

The relations between membrane cholesterol content, basal (unstimulated) transmembrane 45Ca2+ movements, cytosolic calcium levels, and membrane fluidity were investigated in cultured rabbit aortic smooth muscle cells (SMCs) and isolated SMC plasma membrane microsomes. SMCs were enriched with unesterified (free) cholesterol (FC) for 18-24 hours with medium containing human low density lipoprotein and FC-rich phospholipid (PL) liposomes. This procedure increased cholesterol mass without affecting PL mass, resulting in an increase in the FC/PL molar ratio compared with controls in cells (67% FC increase, p less than 0.001; 43% FC/PL ratio increase, p less than 0.01) and in SMC microsomes (52% FC increase, p less than 0.05; 43% FC/PL ratio increase, p less than 0.05). Cholesterol enrichment also increased unstimulated 45Ca2+ influx (p less than 0.001) and efflux (p less than 0.05). Cellular cholesterol content correlated in a linear fashion with these changes (influx: r = 0.722, p less than 0.01; efflux: r = 0.951, p less than 0.05). In addition, cytosolic calcium levels increased approximately 34% (p less than 0.01) with cholesterol enrichment. The cholesterol-induced increase in 45Ca2+ influx was reversible with time and demonstrated sensitivity to the channel blockers. Fluorescence anisotropy measured from 5 degrees C to 40 degrees C using the fluorophore diphenylhexatriene showed decreased membrane fluidity in microsomal membranes obtained from cholesterol-enriched SMCs compared with controls (p less than 0.02). These results suggest that the SMC plasma membrane is very sensitive to cholesterol enrichment with liposomes or human low density lipoprotein and that increases in membrane cholesterol content increase cytosolic calcium levels in SMCs, are associated with a decrease in membrane fluidity, and unmask a new, or otherwise silent, dihydropyridine-sensitive calcium channel that may be involved in altered arterial wall properties with serum hypercholesterolemia.

Animals↗
PubMed1991

Cholesterol enrichment increases basal and agonist-stimulated calcium influx in rat vascular smooth muscle cells.

The effect of cholesterol enrichment on vascular smooth muscle cell (VSMC) calcium homeostasis was studied by evaluating calcium uptake, efflux, and intracellular content in cultured VSMC derived from the rat pulmonary artery. Incubation of VSMC with liposomes consisting of free cholesterol (FC) and phospholipid (2:1 molar ratio, 1 mg FC/ml medium) for 24 h resulted in a 69 +/- 19% increase (P less than 0.01; n = 10) in FC which was associated with a 73 +/- 11% increase (P less than 0.005; n = 10) in intracellular calcium content as assessed by isotopic equilibrium with 45Ca2+ and a 65 +/- 11% increase (P less than 0.024; n = 3) as assessed by atomic absorption spectroscopy. Cholesterol enrichment caused a marked increase in the unidirectional calcium uptake rate from 0.026 +/- 0.03 to 0.158 +/- 0.022 nmol calcium/s per mg protein (P less than 0.01; n = 3), but had no effect on calcium efflux. Nifedipine (1 microM) reduced (P less than 0.05; n = 6) the effect of cholesterol enrichment on unidirectional calcium uptake by 78 +/- 16%; and verapamil (10 microM), diltiazem (1 microM), and nifedipine (1 microM) each significantly inhibited the effect of cholesterol enrichment on intracellular calcium accumulation. Exposure of cholesterol-enriched VSMC to cholesterol-poor liposomes for 24 h returned both FC and calcium contents to control levels. Serum- and serotonin-stimulated calcium uptakes were potentiated 3.7- and 1.7-fold, respectively, in cholesterol-enriched VSMC, whereas endothelin, vasopressin, and thrombin-stimulated calcium uptakes were not affected. We conclude that VSMC FC content plays a role in regulating cellular calcium homeostasis, both under basal conditions and in response to selected agonists.

Animals↗
PubMed1989

Excess membrane cholesterol alters calcium channels in arterial smooth muscle.

We studied the effects of cholesterol enrichment on arterial function by evaluating its effects on 45Ca2+ uptake and tension development in the carotid artery of the rabbit. Arterial segments were enriched with cholesterol in vitro, using media containing liposomes composed of free (unesterified) cholesterol (FC) and phospholipid (PL) in a 2:1 molar ratio. Control segments were simultaneously perfused with 0.5:1 liposomal medium to compare the possible effects of PL. Rings from these arteries were then tested for basal and activated Ca2+ uptake and for contractile responses to norepinephrine (NE) and KCl. We found elevated 45Ca2+ uptake under basal and NE-activated conditions along with an increased contractile sensitivity (4-fold) to NE. These alterations correlated with a 78% increase in the FC/PL ratio reflecting cholesterol enrichment of cellular membranes. Cholesterol enrichment did not alter resting or maximal tensions, K+-activated Ca2+ uptake, or contractile sensitivity to K+. Pretreatment with 1 microM diltiazem abolished the cholesterol-induced increase in basal as well as NE-activated 45Ca2+ uptake but had no effect on either uptake in control vessels. These studies suggest that excess membrane cholesterol selectively increases NE contractile sensitivity by increasing basal or NE-activated Ca2+ influx (or both) as a result of fundamental alteration in the calcium channels in arterial smooth muscle cell membrane.

Animals↗
PubMed1989

Mutual interaction of vasoconstriction and endothelial damage in stenotic arteries.

Coronary artery vasomotion may be important in the pathogenesis of angina pectoris. Numerous experimental studies demonstrated accentuated arterial vasomotion in endothelium-damaged vessels. We examined interactions of stenosis, arterial vasoconstriction, and endothelium denudation in a stenosed artery preparation in vitro. Canine carotid arteries and porcine coronary arteries were perfused with a physiological salt solution under constant pressure and a fixed distal resistance. Pressures at the proximal and distal ends of the artery, as well as the flow, were continuously recorded. Hemodynamic responses to serotonin, norepinephrine, and angiotensin II were separately studied. In intact arteries without stenosis, the agonists produced a 30-40% reduction in lumen diameter without altering flow or distal pressure. After a luminal stenosis was created, vasoconstriction produced by the agonists decreased flow and increased the pressure gradient across the stenosis. Flow decreased to (or near) zero, indicating occlusion at the stenotic site. After endothelial loss, this effect was amplified, demonstrating occlusion of the artery and suppression of the flow at significantly (P less than 0.05) lower concentrations of agonist (0.1-0.3) compared with endothelial intact arteries. These studies illustrate 1) the necessity for the presence of stenosis in large arteries for vasoconstriction to impair flow and 2) the protecting effect of intact endothelium in blunting the effects of arterial vasoconstriction in stenosed vessels. Through the reciprocal interaction of arterial stenosis, vasoconstriction, and endothelial damage, ischemic events associated with certain types of vasomotion can be explained.

Angiotensin II↗
PubMed1989

Stenotic amplification of vasoconstriction responses.

Based on simple hemodynamic principles, arterial stenoses could accentuate the effects of arterial vasoconstriction by reducing intraluminal pressure. To examine this mechanism we employed an in vitro stenotic carotid artery preparation. Eight carotid arteries, obtained from anesthetized heartworm-positive dogs, were isolated and perfused with a physiological salt solution under constant pressure (100 mmHg) and with a fixed distal resistance. After creating an intraluminal stenosis, proximal pressure, distal pressure, and flow were continuously recorded as norepinephrine was incrementally added to the perfusion reservoir. At each norepinephrine concentration, arterial dimensions were recorded on 35-mm film and measured by quantitative dimensional analysis. These data were approximated by a four-parameter logistic equation. The proximal diameter data were considered to represent solely the effects of arterial vasoconstriction, while the stenotic diameter data were considered to be affected both by arterial vasoconstriction and by stenotic pressures. The stenotic diameters shortened significantly more than the proximal diameter (1.2 +/- 2 vs. 0.5 +/- 0.1 mm, P less than 0.01). The shape of the stenotic diameter dose-response curve was similar to the distal pressure curve and was significantly (P less than 0.05; - 3.4 +/- 0.7) steeper than the proximal diameter curve (-0.7 +/- 0.1). Furthermore, the half maximum effective doses (ED50) were significantly interrelated for distal pressure and stenotic diameter data and unrelated for proximal diameter data. In five additional experiments, to eliminate the stenotic pressure changes, the flow was maintained constant. Maintaining stenotic vasoconstriction response (0.6 +/- 2 mm). The results of the present study show exaggerated stenotic vasoconstriction caused by a stenotic pressure decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Cholesterol-induced changes in rabbit arterial smooth muscle sensitivity to adrenergic stimulation.

We evaluated the effects of exposure to high cholesterol levels for 3 h on arterial smooth muscle responses to adrenergic stimulation. Femoral arteries from Dutch belted rabbits were perfused in vitro with a constant-flow variable-pressure perfusion apparentus. After equilibration the vessels were perfused for 180 min more with media supplemented with cholesterol-phospholipid (C/PL) liposomes of molar ratios of 2:1 or 0.5:1. Although resting vascular resistance was unchanged, norepinephrine (NE) concentration-response analyses revealed a fivefold increase in NE sensitivity (P less than 0.001) in the arteries perfused with the cholesterol-enriched liposomes (2:1) compared with control arteries perfused with the 0.5:1 liposome medium. The arteries perfused with the cholesterol-enriched liposomes demonstrated a 60% increase in cholesterol content and a marked (90%) reduction in Na+-K+-ATPase activity. The increased sensitivity of the cholesterol-enriched arteries was not mediated by acute reductions in Na-pump activity, altered endothelial function, adrenergic nerve function, or prostaglandin production. Cholesterol-induced sensitization to NE did demonstrate an absolute dependence on extra-cellular calcium. These findings suggest that an increase in the free cholesterol content of the arterial smooth muscle cell plasma membrane alters membrane permeability to extracellular calcium during adrenergic stimulation.

Acetylcholine↗
PubMed1989

Effects of aging on agonist-activated 86Rb efflux in arteries of Fischer 344 rats.

Segments of thoracic aorta (DTA), tail artery (TA), and mesenteric artery branches (MAB) were obtained from male Fischer 344 rats at ages of 1, 2, 6, 12, 24, and 30 mo and were used to determine the effects of aging on agonist-activated 86Rb (and 42K) efflux. At all three arterial sites, basal efflux decreased during development (1-6 mo), but no further changes were observed with aging (6-30 mo). The initial efflux response to 10 microM norepinephrine (NE) in the presence of 1 microM propranolol exhibited either no change (DTA) or an increase (TA and MAB) during development (1-6 mo), but all three sites showed a large decrease during aging (6-30 mo). Changes in the steady-state response to NE paralleled changes in the basal efflux at all ages and arterial sites. The initial efflux response to 75 mM K+-physiological salt solution (PSS) for the DTA in the presence of 1 microM phentolamine and 1 microM propranolol decreased during development followed by an increase during aging, whereas for the TA and MAB, there were no significant changes with age. The steady-state efflux response to K+ decreased during development at all three sites but was increased only for the DTA during aging. The steady-state efflux response to K+ was not altered for the TA and MAB during aging. Efflux responses using 42K were qualitatively similar, but rate constants were quantitatively larger than those with 86Rb at all three arterial sites and at all ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1989

Effects of endothelium regeneration on canine coronary artery function.

During coronary catheterization under general anesthesia, the endothelium of a portion of the proximal left circumflex coronary artery of dogs was removed (injured). Segments from the denuded and normal (distal circumflex and left anterior descending coronary) regions were removed immediately in some animals (acute studies) or 5 wk after the injury in other animals (chronic studies). No significant differences in passive mechanics or active stress normalized to medial thickness were found between segments from normal and denuded regions in acute studies or normal and injured segments in chronic studies. Intimal thickening was found in the chronically injured segments, which averaged 32% of the total media-adventitia thickness. No significant differences were found in potassium dose-response relations in acute or chronic studies. Maximum responses to serotonin were increased in acutely denuded but not in chronically injured segments. Sensitivity to serotonin was increased in chronically injured but not acutely denuded segments. Endothelium-dependent relaxation responses produced by acetylcholine, bradykinin, and the Ca2+ ionophore A23187 were all depressed in chronically injured segments compared with normal, as were relaxation responses to sodium nitroprusside. In acutely denuded segments, the former agents produced only small contractions at high doses, whereas nitroprusside relaxations were augmented compared with sites with intact endothelium. Relaxation responses to isoproterenol and forskolin were not significantly affected by acute denudation or by chronic injury. The results of this study suggest a "chronic" depression of relaxation responses mediated by the guanosine 3',5'-cyclic monophosphate pathway and increased serotonin vasoconstriction sensitivity in arteries 5 wk after an endothelial denudation injury.

Animals↗
PubMed1988

Altered Na+-K+-ATPase, cell Na+ and lipid profiles in canine arterial wall with chronic cigarette smoking.

1. We evaluated the influence of cigarette smoking on arterial wall membranes, using Na+-K+-ATPase activity, free cholesterol (FC) and phospholipid (PL) contents as indices of membrane structural and functional integrity. 2. Segments of aorta, carotid and femoral arteries were obtained from normal dogs (controls) and dogs subjected to chronic cigarette smoking for 2 yr (12 cigarettes a day). 3. Na+-K+-ATPase activity was assessed in segments of carotid and femoral arteries using a ouabain-sensitive 86Rb uptake procedure for intact tissues. 4. Free cholesterol and phospholipids were separated, identified, and quantitated from extracts of aortic samples by means of two dimensional thin-layer chromatography. 5. Na+-K+-ATPase activity was reduced in the smoker group in both carotid and femoral arteries. This reduced enzyme activity was accompanied by a rise in cell Na+ levels at both arterial sites. 6. Aortic FC was elevated and the PL profile was altered in the smoker group; as a result, phosphatidylcholine was reduced, whereas lysophosphatidylcholine, phosphatidic acid, and cardiolipin were elevated. 7. Phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and sphingolipid levels were unchanged. In addition, the FC/PL ratio was increased in the smokers. 8. Taken together, the changes in Na+-K+-ATPase activity, FC/PL ratio and phospholipid profiles observed are consistent with the hypothesis that chronic cigarette smoking causes a reorganization of the phospholipid bilayer in the smooth-muscle cell membrane of the arterial wall.

Animals↗