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Biomedical subjects

S E Akopov

Publications and source records attributed to S E Akopov.

At least 19 recordsLinked to original sources
PubMed2001

Developmental changes in ryanodine- and IP(3)-sensitive Ca(2+) pools in ovine basilar artery.

To explore the hypothesis that cerebrovascular maturation alters ryanodine- and inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) pool sizes, we measured total intracellular Ca(2+) with (45)Ca and the fractions of intracellular Ca(2+) released by IP(3) and/or caffeine in furaptra-loaded permeabilized basilar arteries from nonpregnant adult and term fetal (139-141 days) sheep. Ca(2+) mass (nmol/mg dry weight) was similar in adult (1.60 +/- 0.18) and fetal (1.71 +/- 0.16) arteries in the pool sensitive to IP(3) alone but was significantly lower for adult (0.11 +/- 0.01) than for fetal (1.22 +/- 0.11) arteries in the pool sensitive to ryanodine alone. The pool sensitive to both ryanodine and IP(3) was also smaller in adult (0.14 +/- 0.01) than in fetal (0.85 +/- 0.08) arteries. Because the Ca(2+) fraction in the ryanodine-IP(3) pool was small in both adult (5 +/- 1%) and fetal (7 +/- 4%) arteries, the IP(3) and ryanodine pools appear to be separate in these arteries. However, the pool sensitive to neither IP(3) nor ryanodine was 10-fold smaller in adult (0.87 +/- 0.10) than in fetal (8.78 +/- 0.81) arteries, where it accounted for 72% of total intracellular membrane-bound Ca(2+). Thus, during basilar artery maturation, intracellular Ca(2+) mass plummets in noncontractile pools, decreases modestly in ryanodine-sensitive pools, and remains constant in IP(3)-sensitive pools. In addition, age-related increases in IP(3) efficacy must involve factors other than IP(3) pool size alone.

Animals↗
PubMed1998

Regulation of Ca2+ sensitization by PKC and rho proteins in ovine cerebral arteries: effects of artery size and age.

G protein-regulated Ca2+ sensitivity of vascular contractile proteins plays an important role in cerebrovascular reactivity. The present study examines the intracellular mechanisms that govern G protein-regulated Ca2+ sensitivity in cerebral arteries of different size and age. We studied beta-escin-permeabilized segments of common carotid, basilar, and middle cerebral arteries from nonpregnant adult and near-term fetal sheep. Activation of protein kinase C (PKC) by (-)-indolactam V or a phorbol ester produced receptor-independent increases in Ca2+ sensitivity. Such increases were more marked in immature arteries and were inversely correlated with artery size in both mature and immature arteries. However, inhibitors of PKC did not significantly affect increases in Ca2+ sensitivity in responses to either serotonin (5-hydroxytryptamine, 5-HT) or guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). Alternatively, deactivation of rho p21, a small G protein associated with Rho kinase, by exotoxin C3 fully prevented increases in Ca2+ sensitivity in responses to 5-HT or GTPgammaS in both adult and fetal arteries of all types. Neither inhibitors of PKC nor exotoxin C3 altered baseline Ca2+ sensitivity. We conclude that patterns of receptor- and/or G protein-mediated modulation of Ca2+ sensitivity are dependent on an intracellular pathway that involves activation of small G proteins and Rho kinase. In contrast, PKC has little, if any, role in agonist-induced Ca2+ sensitization under the present experimental conditions.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1998

Developmental changes in the calcium sensitivity of rabbit cranial arteries.

The present experiments examine developmental changes in cerebrovascular Ca2+ sensitivity. Common carotid (COM), basilar (BAS) and femoral (FA) arteries from adult (n = 16), 8- to 9-day-old (n = 15) and 24- to 25-day-old rabbits (n = 12) were denuded of the endothelium and permeabilized with beta-escin. Bath calcium concentrations were controlled via EGTA-Ca2+ buffer solutions. Adult pCa-force relations were right-shifted relative to those of 8- to 9-day-old rabbits but were similar to those of 24- to 25-day-olds. Adult pD2 (-log ED50) values for Ca2+ averaged 6.36 +/- 0.03 (COM), 6.77 +/- 0.04 (BAS) and 6.40 +/- 0.04 (FA). Corresponding 8- to 9-day-old values were 6.85 +/- 0.03, 7.08 +/- 0.08 and 6.76 +/- 0.05. In all arteries studied, the addition of 5-hydroxytryptamine (5-HT) subsequent to contraction by a constant submaximal (EC30) concentration of Ca2+ produced a dose-dependent and GDP3S-sensitive increase in tension attributable to an increase in Ca2+ sensitivity. The magnitudes of 5-HT-induced increases in Ca2+ sensitivity were significantly greatest in 8- to 9-day-old rabbits, intermediate in 24- to 25-day-old rabbits, and least in adults. GTPgammaS mimicked the effects of 5-HT and prevented further increases in Ca2+ sensitivity induced by 5-HT in all arteries from all age groups. GDPbetaS completely reversed all effects of 5-HT on Ca2+ sensitivity. From these data we conclude that baseline Ca2+ sensitivity is elevated in newborn relative to adult rabbits, at least in femoral, common carotid and basilar arteries. In these arteries, 5-HT can increase Ca2+ sensitivity via a G-protein-dependent mechanism which is more effective in neonatal than adult arteries. These effects of maturation on vascular Ca2+ sensitivity may play an important role in developmental changes in vascular reactivity.

Aging↗
PubMed1998

Maturational modification of hypoxic relaxation in ovine carotid and cerebral arteries: role of endothelium.

In light of evidence that hypoxia inhibits cerebrovascular calcium influx and that the contractile importance of calcium influx is greater in neonatal than adult cerebral arteries, the present studies evaluate the hypothesis that the mechanisms involved in hypoxic cerebral vasodilation are different in newborn and adult cerebral arteries. Intact segments of ovine common carotid (COM) and middle cerebral (MCA) arteries from 3- to 7-day-old newborn lambs and nonpregnant adults were mounted in tissue baths, contracted with 1 microM 5-HT, and exposed to hypoxia for 20 min (PO2 approximately 12 Torr). In endothelium-intact arteries, the magnitude of relaxation was similar and near maximal in all groups (range 82-92%) and did not vary with either age or artery type. However, the magnitude of hypoxic relaxation after endothelium removal was attenuated more in adult (COM 37 +/- 6%, MCA 53 +/- 7%) than in newborn (COM 75 +/- 5%, MCA 93 +/- 1%) arteries. In addition, endothelium-dependent responses to A23187, which like hypoxia increases endothelial cell concentrations of calcium, were attenuated in immature compared to mature arteries. Reductions of extracellular calcium concentration from 1.6 to 0.8 mM eliminated all age-dependent differences in relaxation responses to hypoxia. Together these data demonstrate that in newborn arteries, the endothelium-dependent component of hypoxic vasodilation is minimal, especially in intracerebral arteries, and robust relaxant responses to hypoxia depend on the high sensitivity of immature smooth muscle cells to decreases in PO2. In contrast, in adult arteries the smooth muscle sensitivity to decreases in PO2 is minimal and the endothelial component of hypoxic relaxation is particularly important in responses to hypoxia.

Adenosine Diphosphate↗
PubMed1998

Maturation alters the contractile role of calcium in ovine basilar arteries.

The present studies examine how agonist-induced increases in cytosolic Ca2+ concentration and sensitivity vary with maturation. Basilar arteries from term fetal (138-141 d) and nonpregnant adult sheep were denuded of endothelium, mounted for measurements of contractile tension, and then loaded with Fura-2 to enable estimation of cytosolic Ca2+ responses to both potassium and serotonin (5-hydroxytryptamine, 5-HT). In response to potassium, normalized values of intracellular Ca2+ and tension increased in parallel in both fetal and adult preparations; no age-related differences were apparent. In contrast, 5-HT increased Ca2+ sensitivity significantly more in fetal than in adult arteries. In the absence of extracellular Ca2+, 5-HT increased cytosolic Ca2+ in adult but not fetal arteries. In addition, responses to repeated applications of 5-HT in the absence of extracellular Ca2+ were exhausted more rapidly in fetal than in adult arteries. We interpret these data to indicate that vascular maturation involves important shifts in the mechanisms mediating cerebrovascular pharmacomechanical coupling. Specifically, the data suggest that normal development involves a reduction in the Ca2+ sensitizing effects of agonists with parallel increases in the agonist-induced intracellular Ca2+ release. In so doing, these studies offer one possible reason why vascular reactivity varies dramatically with age. From a pathophysiologic perspective, these studies also advance the possibility that failure to shift from the increased Ca2+ sensitivity typical of immature arteries may lead to vascular hyperreactivity in adult arteries.

Animals↗
PubMed1997

Increased nitric oxide deactivation by polymorphonuclear leukocytes in patients with intermittent claudication.

PURPOSE: Local activation of polymorphonuclear leukocytes (PMNLs) is considered an important aspect of the pathogenesis of intermittent claudication, although concrete mechanisms of their effects on circulatory homeostasis in peripheral atherosclerotic disease remain unclear. This study evaluated the ability of PMNLs to deactivate nitric oxide (NO), a key regulator of regional circulation, as a possible factor determining PMNL involvement into ischemic disorders in patients who have intermittent claudication before and after vascular reconstruction. METHODS: A total of 57 patients who had peripheral occlusive disease in an aortofemoral segment before surgical treatment (group 1) and 65 patients who had similar occlusive lesions and other clinical and demographic data 6 to 12 months after undergoing inflow vascular reconstruction (group 2) were examined. All patients from group 2 had anatomically patent grafts; their satisfaction and level of function after surgical treatment were assessed by a five-point questionnaire. The sex- and age-matched control group included 35 subjects. NO activity was bioassayed by measuring its ability to increase cyclic guanosine monophosphate (cGMP) accumulation in rat fetal lung-cultured fibroblasts (RFL-6 cells). The ability of PMNLs to deactivate NO was characterized as the percent decrease in NO-induced cGMP accumulation in RFL-6 cells. RESULTS: Stimulated PMNLs caused inhibition of the activity of authentic NO; accumulation of cGMP induced by sodium nitroprusside was not affected. PMNLs from patients with peripheral atherosclerotic disease either before or after vascular reconstruction had a more marked capacity of NO inactivating than the cells from healthy subjects. For both groups of patients, levels of PMNL-induced NO deactivation were higher for patients with diabetes, and especially both diabetes and arterial hypertension. For both groups of patients, there was no correlation between levels of PMNL-induced NO deactivation and resting ankle-brachial indexes (ABIs). In contrast, close correlation was revealed between levels of PMNL-induced NO deactivation and postexercise ABIs and percent decrease in resting ABIs after exercise in patients evaluated either before or after surgical treatment. CONCLUSIONS: The ability of stimulated PMNLs to deactivate NO is elevated in peripheral occlusive disease and may be implicated in the pathogenesis of intermittent claudication. In patients who underwent successful recanalization of magistral arteries, levels of PMNL-induced NO deactivation remained higher than in control subjects. The increase in the ability of PMNL to deactivate NO positively correlated to ABI decreases after exercise in patients with peripheral occlusive disease either before or after surgical treatment.

Animals↗
PubMed1997

Comparison of isradipine and enalapril effects on regional carotid circulation in patients with hypertension with unilateral internal carotid artery stenosis.

This randomized, double-blind, placebo-controlled study was aimed at detecting cerebrovascular effects of isradipine and enalapril in patients with moderate hypertension depending on the presence and grade on unilateral stenosis of internal carotid artery (ICA). We evaluated carotid vascular resistance by using Doppler analysis and regional cerebral blood flow (rCBF) by using 133Xe-clearance technique before and after a single 5-mg oral dose of isradipine, enalapril, or placebo. Their effects were randomly and consecutively tested in 73 patients with essential hypertension subdivided into three groups: without carotid occlusive lesions, with moderate (50-75%), and with severe (76-99%) unilateral asymptomatic ICA stenosis. There were no differences in age, gender, and antihypertensive effects of the drugs between these three subgroups. Three major variants of cerebrovascular drug effects were observed: absence of changes (variant I), decrease in carotid vascular resistance with increase in rCBF and elimination of side-to-side asymmetry (variant II), and increase in carotid vascular resistance with further reduction of rCBF ipsilaterally ICA stenosis, and increased side-to-side asymmetry (variant III). Frequency of variant III was significantly higher in patients with severe ICA stenosis. Enalapril produced variant I of cerebrovascular effects in most patients examined; variant III was observed only in 13% of patients with severe ICA stenosis. Isradipine produced variant I of cerebrovascular effects much less frequently than did enalapril. For this drug, variant II was most typical in patients without ICA stenosis and with moderate ICA stenosis. In 43.5% of patients with severe ICA stenosis, however, isradipine produced reduction of cerebral perfusion. Presumably the presence of ICA stenosis, especially >75%, increases the risk of cerebrovascular disorders in antihypertensive therapy. In patients with severe ICA stenosis, treatment with enalapril appears to be safer than that with isradipine.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Physiological variations in ovine cerebrovascular calcium sensitivity.

Cerebrovascular reactivity to biogenic amines varies in relation to both arterial diameter and age. The present study examines the hypothesis that these patterns of reactivity are secondary to corresponding variations in the Ca2+ sensitivity of the contractile proteins. To test this hypothesis, we permeabilized segments of common carotid (Com), basilar, main branch middle cerebral, and second-branch middle cerebral (MCA-B) arteries from nonpregnant adult and near-term fetal sheep using beta-escin. Permeabilization methods were carefully validated and adjusted for each artery type. Baseline myofilament Ca2+ sensitivity in both adults and fetuses increased significantly from the Com to the MCA-B and was generally higher in fetuses than in adults. Serotonin dose dependently increased Ca2+ sensitivity via a G protein-dependent mechanism in all arteries. The magnitudes of this effect did not vary among artery types but were significantly greater in fetal than in adult arteries. This effect of serotonin was mimicked by guanosine 5'-O-(3-thiotriphosphate), a nonhydrolyzable analog of guanosine 5'-triphosphate, and its effects were also much greater in fetal than in adult arteries. We conclude that patterns of cerebrovascular reactivity to biogenic amines were determined, at least in part, by underlying variations in baseline myofilament Ca2+ sensitivity and/or its alteration by G protein-dependent mechanisms.

Animals↗
PubMed1997

Intracranial-extracranial differences in the Ca2+ sensitivity of rabbit arteries.

We have previously demonstrated that the ratio of calcium uptake to force production varies widely with age, artery size, and method of contraction in cerebral arteries. The present experiments were conducted to examine the possibility that these differences involve corresponding variations in contractile force-calcium relations. Common carotid (COM), basilar (BAS), and middle cerebral (MCA) arteries from adult were denuded of endothelium and mounted in vitro for measurement of contractility. Following equilibration at optimum resting diameter, the arteries were permeabilized (beta-escin, 50 microg/ml) and depleted of intracellular Ca2+ by treatment with 1 microM A23187. Ca2+ depletion was verified by absence of any contracile response to either 25 mM caffeine or 1 microM inositol 1,4,5-trisphosphate. Then, in the continuous presence of 1 microM calmodulin, bath calcium concentration was raised from zero through 10 microM in half-log increments and the corresponding contractions were recorded. For all permeabilized arteries, the maximum force produced by 10 microM Ca was greater than or equal to that produced by 120 mM potassium-Krebs in the same segment before skinning. The pD2 (-log ED50) values for calcium averaged 6.39 +/- 0.03, 6.77 +/- 0.04, and 6.92 +/- 0.03 in COM, BA, and MCA segments, respectively. In arteries contracted by a constant submaximal concentration of calcium (0.1 microM for BAS and MCA, 0.3 microM for COM), the addition of 5HT produced a dose-dependent and GDPbetaS-sensitive increase in tension of up to 44% maximum. GTPgammaS mimicked the effects of 5HT and prevented further increases in Ca force induced by 5HT. Together, these data demonstrate that cerebrovascular calcium sensitivity is an anatomically heterogenous, physiologically regulated parameter responsive to agonist-induced perturbations.

Animals↗
PubMed1997

Mechanisms of platelet-induced angiospastic reactions: potentiation of calcium sensitivity.

Platelet aggregation and adherence to the vessel lumina are common events in various physiological and pathological conditions. However, the mechanisms whereby aggregating platelets cause vasoconstriction remain unclear. We hypothesized that aggregating platelets may alter the Ca2+ sensitivity of the contractile apparatus in smooth muscle cells. We tested this hypothesis using rabbit common carotid arteries permeabilized with beta-escin. In these preparations, the receptor-effector coupling is functionally intact, while the intracellular ionic composition, in particular calcium concentration, may be clamped. Aggregating platelets in the presence of 100 microM GTP left-shifted the pCa-force curve. On average, the pD2 for calcium was 6.30 +/- 0.05 and 6.86 +/- 0.07 in the absence and presence of platelets, respectively (p < 0.01). This increase in calcium sensitivity was prevented by blockade of G-proteins with guanosine 5'-O-(2-thiodiphosphate). Platelets modulated calcium sensitivity at concentrations markedly lower than those that produce contractions of intact vessels. These data suggest that platelet activation in the vicinity of the vessel wall may sensitize the smooth muscle contractile apparatus to calcium via a G-protein-dependent mechanism. This phenomenon may enhance vessel responses to vasoactive substance that produce vessel contraction via elevation of intracellular calcium concentrations.

Animals↗
PubMed1996

Dynamics of polymorphonuclear leukocyte accumulation in acute cerebral infarction and their correlation with brain tissue damage.

BACKGROUND AND PURPOSE: This study was performed to study the dynamics of polymorphonuclear leukocyte (PMNL) accumulation in human cerebral infarction and its association with neurological outcome and brain lesion. METHODS: A total of 88 patients diagnosed as having hemispheric ischemic stroke were examined. PMNL accumulation was studied using technetium-99m hexamethylpropyleneamine oxime (99mTc HMPAO)-labeled leukocyte brain single-photon emission computed tomography (SPECT). Volume of brain infarction was evaluated by CT scan. The Mathew Scale was used for neurological assessment. Dynamics of PMNL accumulation was studied at 3 to 6, 6 to 12, and 12 to 24 hours and 6 to 9, 28 to 30, and 90 days after stroke onset. In parallel, at admission, at 6 to 9 days, and at 28 to 30 days neurological outcome and infarction volume were evaluated. RESULTS: Generally, PMNL accumulation progressively increased during 6 to 24 hours after stroke, remained at a high level up to 6 to 9 days and then declined. With the use of cluster analysis, all patients were subdivided into three groups: patients with severe PMNL accumulation that dramatically increased within 12 hours after stroke onset and persisted even at 28 to 30 days (group A); those with moderate PMNL accumulation that significantly decreased at 30 days (group B); and those with mild PMNL accumulation that decreased at 6 to 9 days (group C). Baseline neurological deficit and brain tissue damage at admission appear to be at a similar level for all groups of patients. In dynamics, however, in patients with severe PMNL accumulation, neurological outcome was worse and infarction volume larger than in patients with less marked PMNL accumulation. CONCLUSIONS: The present clinical study confirms that PMNLs intensively accumulate in the regions of cerebral infarction. The present study revealed that this accumulation correlated with the severity of the brain tissue damage and poor neurological outcome.

Aged↗
PubMed1996

[The clinico-biochemical characteristics of periodontal diseases in subjects who are under conditions of constant, permanent stress].

A comparative study of prevalence of periodontal diseases in an indigenous Armenian population and a population of refugees in Armenia has been performed. The refugees population was considered a population of subjects under permanent stress conditions. It has been shown that in the refugees population there are higher prevalence of periodontal diseases, first of all periodontitis, and more marked heaviness of injures in periodontal tissues that those in the indigenous population. These changes were accompanied with elevated signs of disturbances of hemo-endothelial balance. In particular, there were profound alterations of normal ratio of 6-keto-PGF1a/NXB2 and increased level of markers for endothelial disorganization, thrombomodulin and von Willebrand factor, in the blood. It is that stress-induced disturbances of the hemo-endothelial balance among the refugees may contribute to developing periodontal diseases in this population.

6-Ketoprostaglandin F1 alpha↗
PubMed1996

Nitric oxide (EDRF) enhances the vasorelaxing effect of dihydropyridine calcium antagonists in isolated human middle cerebral arteries.

Experiments were performed on perfused human middle cerebral artery (MCA) precontracted with prostaglandin F2a. Nifedipine, isradipine and lacidipine induced dose-dependent relaxant effects on MCA segments. Effects of nifedipine were rather similar on MCA segments with and without endothelium; however, responses of endothelium-denuded vessel segments to isradipine and especially lacidipine were lower than those of vessels with intact endothelium. The vasodilator effects of these agents, especially isradipine and lacidipine, on vessel segments with intact endothelium in the presence of a NO-synthase inhibitor, N-nitro-L-arginine, were significantly attenuated whereas a cyclooxygenase inhibitor, indomethacin, did not significantly alter vasodilator responses of MCA segments to all calcium antagonists tested. It is suggested that the endothelium modulates vascular relaxation to dihydropyridines by an enhancement of calcium antagonist actions by basally released EDRF/NO at the level of vascular smooth muscles or by a dihydropyridine-induced increase in the release of EDRF/NO.

Adult↗
PubMed1996

[Nitric oxide (NO) inactivation by polymorphonuclear leukocytes as a mechanism for the development of periodontal lesions].

To investigate the mechanism by which polymorphonuclear leukocytes (PMNLs) contribute to tissue injury in periodontitis, NO-activity was bioassayed by measuring its ability to increase cGMP accumulation in cultured fibroblasts in the absence or presence of PMNLs isolated from blood and gingival fluid in healthy volunteers and patients with periodontitis. Non-activated PMNLs do not NO-induced stimulation of cGMP accumulation in the detector cells. However, activated PMNLs inhibited NO-induced cGMP accumulation whereas the effects of sodium nitroprusside was unaffected. Peripheral PMNLs periodontitis impaired NO-dependent cGMP accumulation more markedly than from healthy volunteers. PMNLs from periodontal pockets in periodontal patients destroyed NO significantly higher than in venous blood of the same patients without additional activation. It is assumed that the deactivation of NO by activated PMNLs is a one of the pathomechanisms of disorders in periodontitis.

Adult↗
PubMed1996

[The stimulation of nitric oxide synthesis as a possible protective function of the saliva and its disorders in periodontal diseases].

Effects of mixed non-stimulated saliva on NO synthesis in polymorphonuclear leukocytes (PMNs) have been studied. Saliva from healthy volunteers in concentration-dependent manner potentiates the NO formation. In patients with gingivitis and periodontitis this effect of saliva was altered and in some patients saliva did not stimulate NO synthesis or began to suppress it. By means of cluster-analysis, a classification of these effects of saliva in periodontal diseases has been elaborated. It was shown that in gingivitis and especially periodontitis a number of patients with depressed or inverted effects of saliva on NO synthesis significantly increased.

Adult↗