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Biomedical subjects

M Vassileva

Publications and source records attributed to M Vassileva.

At least 19 recordsLinked to original sources
PubMed2004

Improvement of soil characteristics and growth of Dorycnium pentaphyllum by amendment with agrowastes and inoculation with AM fungi and/or the yeast Yarowia lipolytica.

The effectiveness of two microbiologically treated agrowastes [dry olive cake (DOC) and/or sugar beet (SB)] on plant growth, soil enzymatic activities and other soil characteristics was determined in a natural soil from a desertified area. Dorycnium pentaphyllum, a legume plant adapted to stress situations, was the test plant to evaluate the effect of inoculation of native arbuscular mycorrhizal (AM) fungi and/or Yarowia lipolytica (a dry soil adapted yeast) on amended and non-amended soils. Plant growth and nutrition, symbiotic developments and soil enzymatic activities were limited in non-amended soil where microbial inoculations did not improve plant development. The lack of nodules formation and AM colonization can explain the limited plant growth in this natural soil. The effectiveness and performance of inocula applied was only evident in amended soils. AM colonization and spores number in natural soil were increased by amendments and the inoculation with Y. lipolytica promoted this value. The effect of the inoculations on plant N-acquisition was only important in AM-inoculated plants growing in SB medium. Enzymatic activities as urease and protease activities were particularly increased in DOC amended soil meanwhile dehydrogenase activity was greatest in treatments inoculated with Y. lipolytica in SB added soil. The biological activities in rhizosphere of agrowaste amended soil, used as indices of changes in soil properties and fertility, were affected not only by the nature of amendments but also by the inoculant applied. All these results show that the lignocellulosic agrowastes treated with a selected microorganism and its further interaction with beneficial microbial groups (native AM fungi and/or Y. lipolytica) is a useful tool to modify soil physico-chemical, biological and fertility properties that enhance the plant performance probably by making nutrients more available to plants.

Agriculture↗
PubMed2003

Biotechnological solubilization of rock phosphate on media containing agro-industrial wastes.

Rock phosphate (RP) is an important natural material traditionally used for the production of phosphorus (P) fertilizers. Compared with chemical treatment, microbial solubilization of RP is an alternative environmentally mild approach. An overview of biotechnological techniques, mainly based on solubilization processes involving agro-industrial residues, is presented. Potential advantages of composting, solid-state fermentation, and liquid submerged fermentation employing free and immobilized microorganisms that produce organic acids and simultaneously solubilize RP are discussed. Subsequent introduction of the final fermented products into soil-plant systems promotes plant growth and P acquisition.

Agrochemicals↗
PubMed2001

Application of free and Ca-alginate-entrapped Glomus deserticola and Yarowia lipolytica in a soil-plant system.

This study was performed to investigate the applicability of microbial inoculants entrapped in alginate gel. Glomus deserticola (AM) was inoculated into soil microcosms, enriched with rock phosphate, as either free form or entrapped in calcium alginate alone or in combination with a P-solubilizing yeast culture (Yarowia lipolytica). Plant dry weight, soluble P acquisition, and mycorrhizal index were equal in treatments inoculated with free and alginate-entrapped AM. Dual inoculation with entrapped G. deserticola and free cells of Y. lipolytica significantly increased all analyzed variables. Highest rates of the latter were obtained when both fungal microorganisms were applied co-entrapped in the carrier. The yeast culture behaved as a 'mycorrhiza helper microorganism' enhancing mycorrhization of tomato roots. These results indicate that dual inoculation with an AM fungus and a P-solubilizing microorganism co-entrapped in alginate can be an efficient technique for plant establishment and growth in nutrient deficient soils.

Agriculture↗
PubMed2001

Immobilized cell technology applied in solubilization of insoluble inorganic (rock) phosphates and P plant acquisition.

This paper reviews current knowledge of the production of organic acids by immobilized microorganisms with a simultaneous solubilization of rock phosphate in fermentation and soil conditions. The most widely applied methods are based on the passive immobilization in preformed porous carriers and entrapment of the microbial cells in natural gels. In general, immobilized systems show higher acid producing and rock phosphate solubilizing activity than freely suspended cells. The potential of gel-entrapped P-solubilizers and mycorrhizal fungi as microbial soil inoculants is also pointed out. Some advantages and constraints of using immobilized cells are discussed and a special emphasis on further research is given.

Cells, Immobilized↗
PubMed1998

Application of an encapsulated filamentous fungus in solubilization of inorganic phosphate.

Spores of Aspergillus niger were encapsulated in agar, calcium alginate and k-carrageenan and further applied in citric acid production during six repeated batch cultivations. Rock phosphate (RP) at concentrations of 3 g l-1 and 7 g l-1 was supplemented to the culture medium to test encapsulated-fungus solubilizing capability. The highest average citric acid productivity of 0.15 g l-1 h-1 was reached with alginate-bead-encapsulated A. niger on RP-free culture medium while agar seemed to be the most suitable carrier on RP-supplemented medium. Accordingly, the highest average soluble P concentration of 0.20 g l-1 batch-1 was obtained with agar-cell beads as compared with other encapsulated systems.

Agar↗
PubMed1995

Different effects of H1 and H2 blockers on the tone and the contractile activity of guinea pig stomach fundus.

The action of H1 and H2 blockers on the spontaneous and evoked contractile activity of gastric fundus smooth muscles as well as the effects of H2 antagonists on the release of acetylcholine (ACh) from gastric myenteric neurons were studied. The experiments were performed on smooth muscle strips (25 x 3 mm) cut out in circular direction from guinea pig fundus region. In concentrations of 1 x 10(-7) M to 1 x 10(-4) M, the H1 blockers diphenhydramine (DPH), mepyramine (MEP) and dimethpyrindene (DMPD), but not the H2 blockers ranitidine (RAN), cimetidine (CIM) and roxatidine (ROX), increased in a concentration-dependent manner the smooth muscle tone, the maximum contractions being about 50% of the contractile effects of 1 x 10(-5) M ACH and 5 x 10(-5) M histamine (HA). The concentration-dependent contractions of the stomach fundus strips in response to electrical field stimulation (EFS) were enhanced by RAN, CIM and ROX (but not by MEP and DPH), all in concentrations of 1 x 10(-7) M to 1 x 10(-4) M. EFS increased the resting [3H]-ACh release by 67.8%, the S2/S1 ratio being 0.85 +/- 0.04. ROX in a concentration of 1 x 10(-5) M significantly increased (by 16.1%) the EFS-induced release with a S2/S1 ratio of 1.22 +/- 0.04. The ROX effect on the [3H]-ACh release was reduced or even abolished by 1 x 10(-6) M tetrodotoxin (TTX) and 1 x 10(-6) M scopolamine or in Ca(2+)-free medium, while 1 x 10(-6) M hexamethonium did not change it. It might be concluded that H2 blockers have no direct myogenic effect and do not interfere with muscarinic receptors in guinea pig stomach fundus. The H2 antagonists enhance the EFS-evoked contractions of the gastric smooth muscle most probably by increasing the release of ACH.

Acetylcholine↗
PubMed1993

Effect of neurotensin on the canine gallbladder motility: in vivo and in vitro experiments.

Neurotensin (NT) (10(-8)-10(-6)) exerted a dose-dependent increase in the tone and release of [3H]ACh in the guinea-pig gallbladder muscle strips but was inefficient in the canine gallbladder muscle strips. However, in conscious dogs NT (2.5-20 ng/kg intravenously (i.v.)) dose-dependently increased the gallbladder pressure. Similar was the effect of CCK8 (1-10 ng/kg i.v.) and carbachol (0.5-2 micrograms/kg i.v.). The NT- or CCK8-induced gallbladder pressure was inhibited by atropine (10-50 micrograms/kg i.v.) or hexamethonium (0.5-3 mg/kg i.v.). Somatostatin (1-2 micrograms/kg i.v.) or VIP (0.5-1 microgram/kg i.v.) also reduced or even abolished the NT- or CCK8-induced gallbladder pressure. The NT-induced increase of the tone of guinea-pig gallbladder preparations was accompanied by an increase of [3H]ACh release, suggesting the involvement of cholinergic innervation.

Acetylcholine↗
PubMed1990

Effects of somatostatin and motilin on the motor and myoelectrical activity of the canine stomach and small intestine in vivo.

The experiments were performed on six starved dogs with chronic fistula in the stomach and small intestine and with chronically implanted electrodes on the smooth-muscle wall of these organs. Motilin (15-25 ng/kg i.v.) induced fastedtype peristaltic contractions accompanied by migrating myoelectrical spike activity in the stomach and small intestine. Somatostatin (0.5-2 micrograms/kg i.v.) inhibited the spontaneous contractile activity and the spike potentials in both organs. The antagonistic effect of somatostatin on the spontaneous and motilin-induced contractions resembled the effect of atropine and probably resulted from the decreased acetylcholine release in the cholinergic neurons.

Action Potentials↗
PubMed1989

Streptozotocin-induced diabetes in rat. III. Antioxidant protection of vascular complications by flunarizine and aligeron.

In rats with streptozotocin-induced diabetes antioxidant protection of diabetic angiopathy was performed by flunarizine (10 mg/kg/day) and aligeron (10 mg/kg/day), applied intraperitoneally during 2.5 months of diabetes. Diabetic vascular complications were assessed by morphologic determination of PAS-positive mucopolysaccharides and measurement of vascular wall thickness in addition to quantitative estimation of lipid hydroperoxides, thromboxane A2/prostacyclin disbalance and plasma beta-thromboglobulin changes. Both drugs prevented development of diabetic angiopathy in rats by inhibition of lipid peroxidation, prostanoid synthesis and platelet activity, but the effect of flunarizine was more pronounced, which could be explained by its additional blocking effect of abnormal calcium flux into vascular cells. The free radical scavenging action of flunarizine and aligeron was investigated.

Animals↗
PubMed1988

Pathogenesis of cardiovascular disorders in streptozotocin-induced diabetes in rat. I. Cardiovascular, renal and morphologic changes in different stages of diabetes.

Some cardiovascular (heart rate and mean arterial pressure), and renal (glomerular filtration rate-GFR; renal plasma flow-RPF; filtration fraction-FF; blood urea nitrogen-BUN and albuminuria) parameters, coupled with morphologic examination, was undertaken in early (2 months) and late (6 months) stage of streptozotocin-induced diabetes mellitus in rats. The results showed a temporally (early) bradycardia and gradually increase of blood pressure with morphologic changes typical for diabetic cardiopathy. The increased GFR (by 92%), associated with significantly decreased RPF (by 37%), increased FF (by 133%), increased kidney weight/body weight ratio (by 88%), increased BUN (by 52%) and distinct albuminuria (13.53 +/- 2.08 mg/24 h/100 g b. w.), together with typical morphologic changes, suggested the development of diabetic nephropathy which was progressive with the duration of the disease.

Animals↗
PubMed1988

Pathogenesis of cardiovascular disorders in streptozotocin-induced diabetes in rat. II. Correlation between lipid peroxides, thromboxane A2/prostacyclin, and platelet aggregation in different stages of diabetes.

An attempt was undertaken to assess the relationship between the imbalance of lipid peroxides, thromboxane A2/prostacyclin and increased platelet aggregability during early (2 months) and late (6 months) stage of streptozotocin diabetes in rat. Thromboxane A2 and prostacyclin (PGI2) were estimated by their stable metabolic products TXB2 and 6-keto-PGF1 alpha respectively. The results showed: 1. There is a significant imbalance in TXA2 (a potent promoter of platelet aggregation) and PGI2 (a potent vasodilator and inhibitor of platelet aggregation). The ratio TXA2/PGI2 was increased by 38% in the early and by 69% in the late stage of diabetes. 2. Serum lipid peroxides increased significantly during early (four times) and late (five times) stage of diabetes. 3. There is a very good correlation between increased lipid peroxides and increased TXA2/PGI2 ratio (r = 0.71) in diabetic rats. 4. A pronounced increase in thrombin-induced platelet aggregation is consistent with the increased levels of lipid peroxides (r = 0.65) and TXA2/PGI2 ratio (r = 0.60). 5. All described changes correlate with the duration of the disease.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

Streptozotocin-induced diabetes in rat. I. Influence of hypertension and myocardial infarction on the development of vascular complications.

Streptozotocin diabetes in rats was complicated by spontaneous hypertension (SHR) and myocardial infarction (MIC), considered as "risk groups". Renal function was assessed on the basis of blood urea nitrogen (BUN) and albuminuria. BUN increased by 36% in Wistar diabetic group, by 100% in SHR + diabetes, and by 51% in MIR + diabetes. Morphologic changes were assessed by estimation of PAS-positive glycosaminoglycans and measurement of vascular wall thickness of glomerular arterioles. The risk groups showed exaggerated tendency for development of diabetic angiopathy. A significant imbalance between TXA2 and prostacyclin was found, which was reflected by TXB2/6-keto-PGF1 alpha (the stable metabolites of TXA2 and prostacyclin, respectively) ratio, which increased by 38% in Wistar diabetic rats, by 61% in SHR + diabetes, and by 133% in MIR + diabetes. These changes correlated very well with increased platelet aggregability (r = 0.70; p less than 0.05) and with increased lipid peroxide level (r = 0.60; p less than 0.05), but neither with total plasma cholesterol (r = 0.20), nor with plasma triglycerides (r = 0.34). Lipid peroxides increased 5-fold in Wistar diabetic rats, 6-fold in SHR + diabetes, and 5.5-fold in MIR + diabetes. A causative relationship between TXA2/PGI2 imbalance and lipid peroxide changes on one hand, and diabetic angiopathy, on the other, was suggested.

Animals↗
PubMed1988

Streptozotocin-induced diabetes in rat. II. Lipid and lipid peroxide changes of lipoprotein fractions in diabetes complicated by hypertension and myocardial infarction.

Lipid peroxide levels and plasma lipids were studied in plasma lipoprotein fractions of streptozotocin diabetic rats, spontaneous hypertensive rats (SHR) + diabetes, and in myocardial infarction rats (MIR) + diabetes. The duration of diabetes in all experimental groups was 2.5 months. We found a tendency of elevation of cholesterol in VLDL and fall in HDL2 but the differences were not significant. Total plasma triglycerides were increased in the three diabetic groups, and the increase was due to LDL fraction but again the differences were not significant. The lipid peroxide (LP) level in total plasma showed a significant increase in the three diabetic groups: in Wistar diabetic rats LP increased 3 times, in MIR + diabetes 3.5 times, and in SHR + diabetes 5 times. The increase of LP in the three diabetic groups was due to LDL with good correlation (r = 0.60) between LP and triglycerides in LDL of the three diabetic groups. The results are in agreement with the concept of the importance of lipoprotein fraction changes: increased cholesterol, triglycerides and lipid peroxides in atherogenic (VLDL and LDL) fractions, and decreased levels in antiatherogenic (HDL, HDL2) fractions in diabetes mellitus.

Animals↗
PubMed1987

Discrepancy between aldosterone production and renin-angiotensin system activity in Brattleboro rats.

It was demonstrated before that in addition to their typical changes in water-sodium-potassium balance Brattleboro rats, homozygous for hypothalamic diabetes insipidus (DI), revealed a discrepancy between aldosterone level and plasma renin activity (PRA). In the present study PRA was significantly increased (79%), and concomitantly juxtaglomerular (JG) index was increased, reflecting an increased secretory activity of renin-producing JG cells. Plasma concentration of aldosterone was significantly lower (-36%) in DI rats than in their Long Evans (LE) controls. Adrenal blood flow rates were not significantly different in both groups of rats but aldosterone concentrations in the adrenal venous effluents were significantly lower (-66%) in DI rats than in LE rats, suggesting that in vivo production rate of aldosterone was reduced in DI rats. This assumption was confirmed by morphometric data of zona glomerulosa. Our results demonstrated a significant reduction (50%) of angiotensin II receptors in the adrenal glands of DI rats, referring to the number of binding sites and to Kd. This finding threw light on the dissociation between a decreased aldosterone production and stimulated renin-angiotensin system in DI rats.

Adrenal Glands↗
PubMed1987

Mode of action of neurotensin on the spontaneous and electrically-induced contractions of gastric smooth muscle.

Mechanical activity was recorded from muscle preparations isolated from the guinea-pig stomach. Neurotensin (10(-11) M to 10(-7) M) produced dose-dependent tonic contractions and showed a higher affinity but lower efficiency compared to acetylcholine (ACH). Atropine and tetrodotoxin had no effect on the neurotensin responses. Blockade of prostaglandin (PG) synthesis by indomethacin or cortisone (5 X 10(-6) M) shifted to the right the dose-response curve for neurotensin (NT) and significantly reduced the NT maximum responses. The data suggest the involvement of PG-mechanisms in the myogenic effect of neurotensin. The electrically-induced, atropine-sensitive contractions (5 to 10 Hz, 0.3 to 0.5 ms) of the muscle strips were inhibited by NT (10(-11) M to 10(-9) M). This inhibition was overcome by yohimbine (10(-6) M) or prostaglandin F2a. It is concluded that NT modulates cholinergic neurotransmission in gastric smooth muscle probably via presynaptically located adrenoceptors.

Acetylcholine↗
PubMed1987

Opioid peptides in experimental myocardial infarction. I. The effect of naloxone.

The effect of intravenous administration of the opioid antagonist naloxone in rats with acute left coronary artery ligation was studied. The results demonstrated that naloxone in a dose 2 mg/kg b. w. affords its protection on infarcted animals by two mechanisms: Reduces by 22% the incidence of early arrhythmias that occur within 15-20 minutes of acute myocardial ischaemia, and are responsible for the early (up to the 30th minutes) postligation death; Reverses the hypotension that results from the development of cardiogenic shock after 30 minutes myocardial infarction. The total mortality after naloxone treatment was significantly reduced by 22%. Naloxone does not influence significantly the size of the infarcted area but the incidence of left ventricle wall perforations was decreased by 38%. Both effects of naloxone are attributed to the antagonism of opioid receptors either directly on the myocardium or through blocking the central action of beta-endorphin. A direct effect of naloxone on the cardiac muscle action potential cannot be excluded.

Acid-Base Equilibrium↗