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Biomedical subjects

P Bakos

Publications and source records attributed to P Bakos.

At least 19 recordsLinked to original sources
PubMed2000

Continuous spinal anaesthesia/analgesia for the perioperative management of high-risk patients.

The intraoperative effects of continuous spinal anaesthesia, and the efficacy of postoperative continuous spinal analgesia in 48 elderly high risk patients undergoing major abdominal, vascular or orthopaedic surgery is reported. Intraoperative anaesthetic technique proved to be safe and provided satisfactory results in the immediate postoperative period. Furthermore, the postoperative analgesic regimen which involved intrathecal fentanyl and bupivacaine, and intravenous tenoxicam, provided effective analgesia for all patients. The intrathecal analgesic regimen was administered continuously through a PCA pump which had the facility to provide bolus doses when requested in predetermined lockout intervals. The mean doses of fentanyl and bupivacaine infused intrathecally for the first 24 h postoperatively were 14.5 +/- 1.5 microg h(-1) (mean +/- SD) and 0.72 +/- 0.08 mg h(-1) (mean +/- SD), respectively, while the requirements for analgesia decreased progressively overtime but lasted for 118 h. The technique provided effective analgesia with low pain scores that was reflected by the ease in performing physical exercises and the pleasant co-operation with the physiotherapist. Only minor complications related to anaesthesia/analgesia were encountered.

Aged↗
PubMed2000

Continuous spinal anesthesia/analgesia for perioperative management of morbidly obese patients undergoing laparotomy for gastroplastic surgery.

BACKGROUND: The authors determined prospectively the safety of continuous spinal anesthesia combined with general anesthesia and the efficacy of postoperative pain relief with continuous spinal analgesia for morbidly obese patients undergoing vertical banded gastroplasty. METHODS: 27 patients (13 men, 14 women) with a mean body mass index (BMI) of 50.4 +/- 7.8 and several co-morbidities were studied. All patients were anesthetized with the same anesthetic regimen, which included midazolam, fentanyl, propofol, muscle relaxants, nitrous oxide, isoflurane and intrathecal bupivacaine. Postoperative pain relief was provided for 5 days and all patients received the same regimen, which included intrathecal bupivacaine, fentanyl and intravenous tenoxicam. The intrathecal analgesic regimen was administered continuously through a pump which had the facility of providing bolus doses when requested in predetermined lockout intervals. Intra-operative monitoring included hemodynamic and respiratory parameters. Additional postoperative monitoring included respiratory rate, degree of sedation, sensory level of anesthesia, motor response and intensity of pain. RESULTS: Intraoperative anesthetic technique was safe and provided satisfactory results in the immediate postoperative period. Furthermore, the postoperative analgesia regimen provided effective analgesia in all patients. The mean doses of fentanyl and bupivacaine infused intrathecally for the first 24 postoperative hours were 14.1 +/- 2.0 microg.h(1) and 0.7 +/- 0.1 mg.h(1) respectively, while the requirements of analgesia decreased progressively with time. The technique provided effective analgesia with low pain scores, which was reflected by ease in mobilizing and performing physical exercises with the physiotherapist. Only minor complications related to anesthesia and analgesia were encountered. CONCLUSION: To our knowledge, this technique of anesthesia and postoperative analgesia has not been described before in morbidly obese patients. This regimen merits further controlled trials to establish its place in the perioperative management of morbidly obese patients.

Adult↗
PubMed1996

Contribution of surface epithelial cells to total conductance of Necturus gastric fundus mucosa.

Microelectrode techniques were used to quantify the contribution of surface epithelial cells (SEC) to transepithelial conductance (gt) of Necturus gastric fundus mucosa. Transepithelial voltage (Vt) and resistance (Rt) as well as the basolateral cell membrane potential (Vb) and voltage divider ratio of SEC were measured. Freshly mounted preparations did not respond to luminal amiloride (10 microM), but within 2-3 h a significant response developed (delta Vt = 3.8 +/- 1.2 mV, delta Rt = 63 +/- 23 omega cm2, and delta Vb = -6.9 +/- 1.3 mV), indicating activation of an apical Na+ conductance in SEC. Using circuit analysis equations, we calculate that SEC contribute 10.4% to gt under control conditions and 13.0% after Na+ conductance activation. Histamine (0.1 mM), which stimulates the oxyntopeptic cells (OC), increased Vt and decreased Rt but did not significantly alter the membrane resistances of SEC. As a result, the contribution of SEC to gt fell to 7.4 or 9.3%, respectively. The data confirm that SEC are poorly permeable and that the major conductance path across gastric mucosa leads through OC in the glands. The reason for the protracted in vitro activation of the apical Na+ conductance in SEC is not known.

Amiloride↗
PubMed1995

Vasopressin and oxytocin in stress.

Though oxytocin and vasopressin are similar in structure and are produced in the same brain regions, they show specific responses under stress conditions. In humans, increases in peripheral blood vasopressin appear to be a consistent finding during many acute stress situations, while in rats, vasopressin secretion is unresponsive to several stimuli known to induce ACTH and catecholamine release. Even decreases in vasopressin levels during stress were described. In accordance with others, we observed enhanced vasopressin release in response to stress stimuli with an osmotic component such as hypertonic saline injection but also during exposure of rats to a warm environment. Immobilization stress which fails to induce vasopressin release was reported to increase hypothalamic vasopressin mRNA and plasma vasopressin levels in chronically adreno-demedullated rats. Unlike vasopressin, oxytocin may be considered a typical stress hormone responding to osmotic as well as other stress stimuli. We found that acute exposure of rats to immobilization stress resulted in an increase in oxytocin mRNA level. In addition, we have shown that magnocellular neurons of the paraventricular nucleus, but not the supraoptic nucleus, are essential for oxytocin release during immobilization stress. The release of posterior pituitary hormones represents an important component of the stress response.

Animals↗
PubMed1995

Ion transport in rat antral mucosa in vitro: general characteristics.

Although numerous studies have shown the existence of various types of ion conductance in antral part of gastric fundus mucosa epithelia of amphibian, practically no data are available on ion conductance in higher animal species. Present experiments were undertaken to check the possible existence of ion conductance in rat gastric antral mucosa and to investigate its general electrophysiological characteristics. Antral epithelia were isolated from adult Sprague Dawley rats. The tissues were mounted to a modified Ussing-type chamber and continually perfused with identical Krebs-Henseleit bicarbonate buffer on both sides. Antrum generated a transepithelial electrical potential difference (Vt = -10 +/- 2.6 mV) and short-circuit current (Isc = 76 +/- 15 microA.cm-2) with a transepithelial electrical resistance (Rt = 135 +/- 16.8 Ohm.cm2). Ion replacement experiments showed that it is mainly Na+ transport that contributes to Vt and Isc as evidenced by a) Na+ and/or Cl- removal, b) the effects of amiloride a sodium channel blocker, on the apical (secretory) surface, c) the effects of the Na(+)-K(+)-ATPase inhibitor ouabain on the basolateral (nutrient) side of the epithelium. Microelectrode experiments confirmed the existence of Na+ and/or Cl- conductance of the apical cell membrane. Antral mucosa also showed a gradual and time-dependent increase in sensitivity to amiloride (10(-5) mol/l). Maximum inhibition of Vt and Isc by amiloride in dose-dependent manner was detected after 1-2 h. This amiloride-sensitive sodium transport (maximal level 31.5 +/- 5.9 microA.cm-2) represented approximately 50% of the whole transepithelial ion conductance. Results of experiments with ouabain (10(-4 mol/l) suggest the presence of functional Na(+)-K(+)-ATPase and/or Na(+)-ATPase in the basolateral cell membranes. Which signals trigger this epithelial ion transport, which hormones are responsible for its regulation and what is the physiological significance of this ion conductance remains to be elucidated.

Amiloride↗
PubMed1994

Influence of salmon melanin concentrating hormone on vasopressin analogue (dDAVP) activity and sodium transport in frog skin.

Salmon melanin-concentrating hormone (sMCH) is a peptide known to regulate skin pigmentation both in fish and tetrapod (frog and lizard). To evaluate the influence of sMCH on ionic transport in frog skin, standard voltage-clamp technique for the measurement of transepithelial short-circuit current (ISC) reflecting net sodium transport was used. It was found that sMCH alone applied at concentrations of 0.5; 5 or 10 mumol/l failed to influence ISC. The application of 5 mumol/l of sMCH, however, inhibited ISC across the skin stimulated by a synthetic analogue of vasopressin (dDAVP), whereas no influence on natriferic effect of 1 mumol/l forskolin by the studied peptide was observed. The results indicate that cAMP was presumably not involved in the mediation of sMCH action in frog skin. We assume that the interaction of sMCH with the basolateral membrane could lead either (1) to changes of membrane structure including organization of its lipid surrounding or (2) to modification of AVP/dDAVP receptor activity and binding capacity. The nature of these interactions and change(s) in cell membrane and signal(s) which trigger processes responsible for the inhibitory effect of sMCH on dDAVP-stimulated frog skin sodium transport remains to be elucidated.

Animals↗
PubMed1992

Osmotic swelling and membrane conductances in A6 cells.

Hyposmotic basolateral perturbations (-30 mosmol/kg) in cultured renal layers (A6) increased basolateral membrane conductance more than 2-fold within 10 min; the increase was partly due to upregulation of K+ conductance, but other conductive pathways were also activated. The raise in apical membrane amiloride-sensitive Na+ conductance was less pronounced; it appears to be due to secondary effects.

Animals↗
PubMed1992

Hydroosmotic activities of arginine-vasopressins modified either in positions 1, 2 and 4 or at N-terminal extensions.

Vasopressin and its synthetic analogs were studied for their effect on transepithelial water flux in frog urinary bladder. As compared with AVP, 1-deamino-8-D-arginine vasopressin (dDAVP) was about 40 times less effective in stimulating osmotic water flow. The vasopressin analogs obtained by modification in positions 1 and 2 were: [1-(1-mercapto-4-tert-butylcyclohexaneacetic acid)] AVP (I); [1-(1-mercapto-4-methylcyclohexaneacetic acid)]AVP (II); [1-(1-mercapto-4-methylcyclohexaneacetic acid)-2-O-methyltyrosine]AVP (III); and those modified in position 4 were: [1-(1-mercaptocyclohexaneacetic acid)-4-arginine] AVP (IV); [1-(2-mercaptopropionic acid)-4-arginine]AVP (V). Any of the above analogs did not influence basal, but antagonized vasopressin-stimulated water flux. N-terminally extended analogs of AVP: Ala-AVP (VI); Ser-Ala-AVP (VII) and Thr-Ser-Ala-AVP (VIII) stimulated osmotic water flux to the same extent in concentration 200 times higher as that of AVP. We conclude from these studies that vasopressin analogs (I-V) competitively antagonize vasopressin-stimulated hydroosmotic activity in frog urinary bladder probably at the epithelial vasotocin V1 and/or V2 receptor site. N-terminal extension of the vasopressin molecule did not influence the capacity of AVP to induce V2 receptor-mediated action, even when used at higher concentrations.

Amino Acid Sequence↗
PubMed1990

Suppression of natriferic activity of the vasopressin molecule by modifications in positions 1, 2 and 4.

The capacity of five synthetic analogs of [8-arginine] vasopressin (AVP) to stimulate frog skin sodium transport (natriferic activity) was characterized electrophysiologically using the method of short-circuit current, and compared to that of synthetic AVP. The analogs used were [8-arginine] vasopressins modified in positions 1 and 2: [1-(1-mercapto-4-tert-butylcyclohexaneacetic acid)] AVP (I); [1-(1-mercapto-4-methylcyclohexaneacetic acid)] AVP (II); [1-(1-mercapto-4-methylcyclohexaneacetic acid)-2-O-methyltyrosine] AVP (III); and in position 4: [1-(1-mercaptocyclohexaneacetic acid)-4-arginine] AVP (IV); [1-(2-mercaptopropionic acid)-4-arginine] AVP (V). The addition of synthetic vasopressins I, II and V to the frog skin resulted in a weaker stimulation of the skin sodium transport, measured as the level of the short-circuit current (Isc), as compared to that induced by synthetic AVP. In relation to natriferic activity, analogs III and IV did not change the electrical parameters of the skin. It is concluded that introduction of cyclic structure at the beta-carbon in position 1 of the vasopressin molecule decreased its natriferic activity by about 70%. The same reduction of the activity was caused by the replacement of the glutamine residue in position 4 with arginine, and deamination in position 1. Cyclic structure bound in position 1 together with methylation of tyrosine in position 2 resulted in a full suppression of natriferic activity. Similarly, introduction of cyclic group in position 1 in combination with substitution of glutamine in position 4 with arginine totally abolished natriferic activity.

Amino Acid Sequence↗
PubMed1990

Reversible inactivation of water and sodium transport systems in frog urinary bladder and skin in the presence of detergents.

Detergents (Triton X-100, dodecyl sulphate, saponin) added in concentrations of 0.1-10 mg/ml to solution at the outer frog skin surface reversibly reduced potential difference (PD) and short-circuit current (Isc); when added at the inner surface. Triton X-100 initially induced a short increase in the PD and Isc followed by a pronounced decrease similarly as after the application of any of the detergents used. When added to either serosal or mucosal surface of frog urinary bladder, the detergents reversibly abolished the reactivity to vasopressin. Triton X-100 blocked foskolin and cAMP-induced effects on membrane water permeability. The results suggest that hydrophobic elements of membrane play a crucial role in the regulation of membrane permeability for ions and water and of the responsiveness of the cells to vasopressin. Differences in sensitivity to detergents could be observed between the apical and the basolateral cell membrane.

Animals↗
PubMed1990

Stimulation of the sodium transport across the frog skin by three N-terminally extended arginine-vasopressins.

The standard Ussing method was used to electrophysiologically characterize the effects of three analogs of arginine-vasopressin (AVP) on the frog skin, a model Na-transporting epithelium. The analogs tested were N-terminally extended Arg8-vasopressins: Ala-AVP, Ser-Ala-AVP and Thr-Ser-Ala-AVP; synthetic Arg8-AVP was used as the reference agent. The vasopressins were applied to the basolateral side of the frog skin in concentrations ranging between 10(-8) to 10(-5) mol.l-1. All the three analogs increased both the short-circuit current (Isc) and the open-circuit transepithelial potential (Voc), and decreased the transepithelial d.c. resistance (Rt) similarly as did synthetic Arg8-AVP. The results show that N-terminal extension of the Arg8-AVP did not alter the natriferic properties of AVP.

Animals↗
PubMed1990

Comparison of the effects of dDAVP and AVP on the sodium transport in the frog skin.

The effect of 1-deamino-8-D-arginine-vasopressin, dDAVP, the synthetic analogue of vasopressin, upon the active sodium transport across the frog skin was studied using standard microelectrode technique and compared with the effect of synthetic arginine-vasopressin, AVP. dDAVP applied to the basolateral side of the epithelium stimulated the active sodium transport as reflected by the increase of short-circuit current, Isc, and transepithelial electrical potential difference, Voc. Potential difference across both the apical, Vo, and the basolateral, Vi, cell membranes decreased. The driving force of transepithelial sodium transport, ENa, did not change. The transepithelial electrical resistance, Rt, ohmic resistance of the active sodium transport, RNa, and apical cell membrane resistance, Ro, rapidly decreased, while the resistance of the basolateral cell membrane, Ri, and the resistance of the shunt pathway, Rs, remained unchanged. It is concluded that dDAVP primarily increases sodium permeability of the apical cell membrane which subsequently stimulates sodium pump activity. This action is similar to that of AVP.

Animals↗
PubMed1989

Microelectrode study of insulin effect on apical and basolateral cell membrane of frog skin: comparison with the effect of 1-deamino-8-D-arginine-vasopressin (dDAVP).

The standard microelectrode technique was used to electrophysiologically characterize the effect of insulin on both apical and basolateral cell membranes of the frog skin, a model Na-transporting epithelium. Insulin applied to the basolateral side of the epithelium stimulated the sodium transport as shown by both increased short-circuit current, Isc, (P less than 0.02) and transepithelial potential difference, Voc, (P less than 0.002). Potential difference across the apical cell membrane, Vo, decreased (P less than 0.002) as did the apical cell membrane resistance, Ro, (P less than 0.05). The driving force of sodium ions, ENa, increased after insulin (P less than 0.005). These findings confirm that insulin acts both to increase the apical cell membrane permeability for ions and to stimulate the sodium pump in the basolateral membrane. The effects of insulin were compared with those of a vasopressin analog (dDAVP), known to stimulate transepithelial sodium transport by increasing the permeability of the apical cell membrane for sodium ions. dDAVP applied at the height of insulin effect further stimulated transepithelial transport, but insulin applied at the height of dDAVP action did not. It is concluded that the direct stimulation of the sodium pump by insulin may not represent a decisive component in the stimulation of transepithelial transport across the frog skin. A more potent stimulus for sodium transport is obviously the increased permeability of the apical membrane for ions.

Animals↗
PubMed1987

Water and sodium transport: effects of calcium channel blocker and calmodulin antagonists on the apical and basolateral membranes of amphibian epithelia.

Ca2+ channel blocker (sensit) and calmodulin antagonists (thioridazine, perphenazine, oxyprothepine) applied to the mucosal side of frog urinary bladder, weakened the response of epithelial cells to vasopressin. Thioridazine (2.7 X 10(-5) mol X l-1) and sensit (1.7 X 10(-4) mol X l-1) applied to the serosal side rapidly increased the permeability of the epithelia for sodium and potassium ions along the concentration gradient (from serosa to mucosa). The same concentrations of these blockers when applied to the mucosal side of frog urinary bladder selectively decreased vasopressin stimulated water permeability and did not influence ionic permeability. Both thioridazine and sensit decreased the short-circuit current across frog skin. The results show that the Ca2+ channel blocker and the calmodulin antagonists tested influenced water and ionic transport across the epithelial cell membranes, and had different effects upon the apical and the basolateral cell membranes.

Animals↗