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Biomedical subjects

C F Nassar

Publications and source records attributed to C F Nassar.

At least 37 records · Page 2Linked to original sources
PubMed1991

Effects of aminophylline and terbutaline sulfate on the contractility of feline diaphragm.

1. The effect of aminophylline and terbutaline sulfate, separately and in combination, on the contractility of the feline diaphragm was investigated. 2. Diaphragmatic contractility increased significantly (P less than 0.05) to 28.3% above control level as long as theophylline plasma levels were maintained between 10-20 mg/l (mean 13.9 +/- 0.8 mg/l). 3. Diaphragmatic contractility showed a significant (P less than 0.05) 41.5% increase after i.v. administration of terbutaline sulfate as a maintenance dose of 1.4 micrograms/kg-hr, and the increase leveled off after 180 min. 4. Administering the two drugs in combination showed a significant (P less than 0.05) 27.3% increase which suggests a non-synergistic effect of aminophylline and terbutaline sulfate on diaphragmatic contractility. 5. By enhancing the contractility of the diaphragm, aminophylline and terbutaline sulfate may improve the clinical status of patients with airway obstructive diseases and help in preventing respiratory muscle fatigue.

Aminophylline↗
PubMed1991

Effect of chlorpromazine on proline absorption across rat jejunum.

The effect of chlorpromazine on proline absorption across jejunum in anaesthetized rats was investigated. Intravenous infusion of chlorpromazine reduced significantly (P less than 0.01) proline absorption across the jejunum. Intraluminal perfusion of chlorpromazine into the jejunal segment reversed net absorption of proline to net secretion. Net water absorption was increased significantly (P less than 0.01) when chlorpromazine was infused intravenously or perfused intraluminally. Unidirectional influx of proline across the mucosal surface was significantly inhibited (P less than 0.01) after preincubation with 1 mM chlorpromazine.

Animals↗
PubMed1989

Digoxin-stimulated calcium transport across rat diaphragm interactions with aminophylline and verapamil.

1. The effect of digoxin on calcium transport across muscle strips isolated from rat diaphragms was investigated. 2. Digoxin at concentrations ranging between 0.2-5.0 ng/ml in the incubation solution increased significantly (P less than 0.5) intracellular calcium in the diaphragm muscle strips in a dose-dependent pattern. 3. The inclusion of digoxin (2 ng/ml) and aminophylline (18.75 micrograms/ml) in the incubation medium showed a significant increase (P less than 0.001) in calcium uptake suggesting a synergistic effect on intracellular calcium accumulation. 4. The presence of digoxin with verapamil in the incubation medium showed a partial alleviation of the inhibitory effect of verapamil on calcium transport. 5. The effect of increasing calcium concentration in the presence of digoxin and digoxin plus aminophylline in the incubation medium, showed a nonsaturable linear relationship between calcium concentration and intracellular calcium accumulation.

Aminophylline↗
PubMed1989

Characteristics and displaceability of neurotensin binding sites in the rat cerebral cortex and corpus striatum.

1. Neurotensin binding to synaptosomes isolated from the rat cerebral cortex and corpus striatum reached saturation after 4 min of incubation. 2. The rates of binding were found to be higher in the corpus striatum than in the cerebral cortex. 3. Concentration study revealed the presence of two different and independent classes of neurotensin binding sites with a negative cooperative interaction within each class of binding sites. 4. At saturation levels, the low affinity binding component was found to have a flat regional difference, while the high affinity binding component showed regional differences in terms of maximal binding capacity, suggesting a higher number of high affinity binding sites in the striatum than in the cortex. 5. In the competition related experiments, dopamine was found to displace around 70% of neurotensin binding sites in the corpus striatum and the cerebral cortex. 5. Substance P displaced around 50% of [3H]neurotensin in the cerebral cortex. Whereas, 50% and 70% displacement were observed in the striatum at high and low affinity binding sites, respectively. 6. These results show the overlap in the binding sites of neurotensin, dopamine and substance P.

Animals↗
PubMed1988

Prostacyclin-inhibition of lysine accumulation by the rat left ventricle.

1. Left ventricular slices of male Sprague-Dawley rats were incubated with a fixed concentration of 0.5 microCi/ml 3H-lysine and several concentrations of unlabelled lysine ranging from 0.2 to 5.0 mM in control and prostacyclin-treated experiments. The time of incubation ranged from 0.5 to 90 min. 2. Left ventricular slices were cut to have an optimal thickness of 0.47 +/- 0.09 mm. 3. Lysine was taken up against a concentration gradient. Saturation was reached at 0.5 mM and steady state accumulation of lysine was attained within 60 min. 4. Prostacyclin in concentrations ranging from 1.2 x 10(-8) to 4.8 x 10(-8) M inhibited lysine transport in left ventricular slices significantly (P less than 0.01).

Animals↗
PubMed1988

Cytoskeletal control of calcium absorption across the rat small intestine.

1. The effect of colchicine, cytochalasin-B and procaine on calcium transport across the rat small intestine was investigated. The results obtained show the following: 2. Colchicine and cytochalasin-B at different concentrations inhibited significantly (P less than 0.001) calcium accumulation in rat intestinal cells, whereas procaine at different concentrations increased significantly (P less than 0.001) calcium accumulation in the rat small intestine. 3. Unidirectional influx of calcium across the rat small intestine was significantly inhibited (P less than 0.01) in the presence of colchicine and cytochalasin-B in the preincubation medium. Procaine, on the other hand, caused a significant increase (P less than 0.01) in the unidirectional influx of calcium across the rat intestinal cells. 4. The cell water content was not altered in the presence of the different drugs indicating that the changes in calcium transport across the rat intestinal cells are not due to alterations in the structure of the cell membrane.

Animals↗
PubMed1988

Enzymatic inhibition of lysine transport across the small intestine in vivo.

1. Trypsin, at different concentrations, significantly inhibited lysine absorption (P less than 0.05) in a dose-dependent pattern. 2. Maximum inhibition equivalent to 35% below control value was reached with 10 micrograms/ml (100 BAEE units) trypsin with a non-reversible inhibitory effect. 3. Chymotrypsin at 10 micrograms/ml produced a significant decrease (P less than 0.05) of lysine absorption although it did not exceed 5%. Perfusion of both enzymes did not show an additive inhibitory effect. 4. Lysine absorption showed a 39% decrease with 10 micrograms/ml trypsin and 1 X 10(-4) M ouabain, whereas ouabain alone produced 34% inhibition. 5. Lysine absorption showed a 71% decrease with 10 micrograms/ml trypsin in a sodium-free medium, and 70% inhibition with Na-free medium alone. 6. The inhibition of lysine absorption after trypsin treatment could be due to inhibition of the active component of lysine transport.

Animals↗
PubMed1988

Taurine transport across the small intestine of adult and suckling rats.

1. Taurine accumulation in intestinal cells of adult and suckling rats reached steady-state after 60 min with an In/Out ratio of 1.46 and 4.66 in the adult and suckling rats respectively. 2. The accumulative capacity of the intestinal strips isolated from suckling rats is almost four times higher than that of adult rats. 3. The steady-state uptake of taurine by the adult and suckling rats intestinal cells is saturable, sodium-dependent and inhibited by ouabain. 4. The calculated Vmax of the mediated component of the steady-state uptake in the suckling rats is three times greater than that of the adult rats, and the affinity is seven fold greater in the suckling as compared to the adult. 5. Taurine influx across the mucosal membrane in the suckling rat is significantly greater than that of the control adult.

Animals↗
PubMed1988

Dopaminergic and adrenergic binding affinities in rabbit retinal synaptosomes.

1. Dopamine binding to amacrine membrane vesicles isolated as synaptosomal fractions P1 and P2 from rabbit retinas showed saturation within less than a minute. 2. Dopamine binding to retinal synaptosomal membranes (RSM) in P1 and P2 is a two-component system: the first saturated at 1.00 microM 14C-dopamine in P1 and 1.25 microM in P2, and the second saturated at 2.00 microM in both pellets. 3. The affinity of RSM receptors to dopamine in P1 was equal to that in P2 (Km = 2.00 microM), whereas the calculated Vmax of dopamine binding was increased in P2 (1.25 pmol/micrograms protein) as compared to P1 (0.625 pmol/micrograms protein). 4. Dopamine binding to the beta-adrenergic sites showed a lower affinity (Km = 10 microM) in P2 relative to P1 (Km = 4.0 microM), whereas Vmax in P2 (5.0 pmol/micrograms protein) was 4-fold higher than P1 (1.25 pmol/micrograms protein). 5. The P1 and P2 fractions of rabbit RSM contain dopaminergic and beta-adrenergic binding sites with higher concentration of dopaminergic receptors and lower concentration of beta-adrenergic receptors in P2 relative to P1.

Animals↗
PubMed1988

Prostacyclin-enhanced calcium sequestration by microsomes isolated from rat left ventricle.

The objective of these experiments was to investigate the direct effect of prostacyclin on calcium binding and uptake by microsomal vesicles isolated from rat left ventricle. The protein content of the preparation was found to be 2.73 +/- 0.18 mg microsomal protein/g of left ventricular wet weight. Steady-state calcium binding and uptake by microsomal vesicles was reached at 6 minutes in control animals and 20 sec in prostacyclin-treated experiments. Prostacyclin increased steady-state calcium binding and uptake from a control of 52.48 +/- 4.16 up to 109.31 +/- 3.06 nmol/mg protein (p less than 0.05) and from 238.07 +/- 12.37 up to 314.85 +/- 1.23 nmol/mg protein (p less than 0.05) respectively. Doubling the concentration of prostacyclin from initial dose of 1.2 x 10(-8) M did not alter calcium binding and uptake further.

Animals↗
PubMed1987

Cysteamine-induced duodenal ulcer: effects on calcium absorption across rat duodenum.

The effect of cysteamine-induced duodenal ulcers on calcium transport across rat duodenum was investigated. Intracellular calcium accumulation measured after 24 hr and 3 days of cysteamine injection showed a significant increase (P less than 0.001) in the duodenal strips isolated after 3 days with no change noticed in those isolated after 24 hr, although the morphological changes in both were very similar. The relationship between increasing calcium concentration in the incubation medium and intracellular calcium concentration is a saturable process that conforms to the Michaelis-Menten type of kinetics. The average maximal flux (Vmax) increased from 8.93 nmole/hr-gdw in normal to 12.5 nmole/hr-gdw in 3-day-ulcerated rats, with no apparent change in the Michaelis constant (Kt) (0.8 mM). Unidirectional influx of calcium across the mucosal membrane was significantly increased (P less than 0.001) in 3-day-ulcerated duodenum suggesting that the increase in calcium transport could be due to the activation of the active step at the mucosal border.

Animals↗
PubMed1987

Dopamine receptors in the hypertrophied rat heart.

1. Dopamine (DA) binding sites in the left and right ventricle of hypertensive rats were assessed after two weeks of induction of hypertension by left renal artery occlusion. 2. The ratio of left ventricular (LV) weight to total body weight was significantly increased in hypertensive rats from 2.046 +/- 0.120 mg g-1 to 3.125 +/- 0.090 mg g-1 (P less than 0.01) while no significant difference was noted in the right ventricle (RV). 3. The hypertrophied LV was associated with a 78% increase in its protein content, however, the ratio of protein content to ventricular wet weight was not significantly different from controls. No change in RV protein content and concentration was observed. 4. Dopamine affinity of sarcolemmal protein was not significantly different in control and experimental LV and RV and the ratio of DA affinity in LV:RV was 10:1. 5. Saturation of LV with DA was reached at around 7 min whereas RV was saturated at approximately 15 min.

Animals↗
PubMed1987

Interactions and effects of aminophylline, terbutaline sulfate and verapamil on calcium transport across rat diaphragm.

The effect of terbutaline sulfate on calcium transport across muscle strips isolated from rat diaphragms, and its effect on this process when used in combination with aminophylline was investigated using labelled calcium in a two-compartment system. The results show that terbutaline sulfate causes a dose-dependent increase in intracellular calcium concentration which reached saturation at a terbutaline sulfate concentration of 2 ng/ml. The inclusion of both aminophylline and terbutaline sulfate at a concentration range of 6.25-50 micrograms/ml and 0.5-4 ng/ml respectively in the incubation medium, did not show a synergistic effect on intracellular calcium accumulation. Although verapamil, a calcium channel blocker, inhibited significantly (P less than 0.01) calcium accumulation in the muscle strips of the diaphragm, it did not inhibit completely the increase in intracellular calcium concentration noticed in the presence of aminophylline or terbutaline sulfate. This would suggest that aminophylline and terbutaline sulfate have an effect on the calcium channels in the muscle strips of the diaphragm.

Aminophylline↗
PubMed1987

Effect of vagal nerve stimulation on L-leucine absorption in the cat jejunum.

The effects of vagal nerve stimulation in the neck and in the lower thorax were studied on L-leucine absorption in/the cat jejunum. Four series of in vivo experiments were performed in 26 cats using single pass perfusion technique with samples collected every 10 min and examined for their phenol red and radioactive L-leucine concentrations. The first two series acted as controls for the time it took to reach steady-state absorption and for the effects on L-leucine absorption of mechanical handling of the vagus nerve. In the third series, vagal stimulation in the neck (with a 20-second train of shocks at 7 Hz repeated every 10 min for either 16 or 4 stimulus sessions) resulted in a 3-fold increase in L-leucine absorption which was maintained throughout the stimulation period (up to 160 min). L-Leucine absorption started increasing within 10 min and peaked around 30-40 min after the initiation of stimulation and returned to control levels within 40 min after cessation of stimulation. In the fourth series, similar increases and returns to control L-leucine absorption levels were noted following vagal stimulation in the lower thorax (with a 20-min train of shocks at 7 Hz given for 3 sessions). The findings suggest a definite role of the vagus nerve in the control of leucine transport across the small intestine.

Animals↗
PubMed1986

Effect of enzymatic treatment on calcium absorption by small intestine: a comparative study between rat and rabbit transport mechanisms.

Calcium absorption by the small intestine of rat and rabbit reached steady state after 60 min of incubation with intracellular to extracellular ratio of 2.0. Trypsin and neuraminidase significantly inhibited (P less than 0.05) calcium accumulation in rat small intestine. These enzymes showed no significant effect (P greater than 0.05) on calcium transport across rabbit small intestine. The inhibitory action of trypsin and neuraminidase on calcium accumulation by the rat small intestine does not involve the influx of calcium into the intestinal cells.

Animals↗
PubMed1986

The kinetics of calcium influx into rat liver slices.

The unidirectional influx of calcium across rat liver slices is a carrier-mediated process which displays saturation kinetics. The presence of Mg2+ in the incubation medium competitively inhibits calcium influx into rat liver slices. Metabolic inhibitors such as ouabain and 2,4-dinitrophenol at a concentration of 1 X 10(-4) and 2.5 X 10(-4) M respectively, inhibited significantly (P less than 0.001) calcium influx across the liver slices. Calcium influx is dependent on the presence of sodium in the extracellular medium, and is significantly reduced (P less than 0.01) when sodium concentration in the preincubation solution is reduced to zero.

Animals↗
PubMed1986

Effect of enzymatic digestion on phenylalanine transport across the small intestine.

Phenylalanine accumulation in mucosal strips isolated from rat small intestine was significantly inhibited (P less than 0.01) after preincubation with trypsin, chymotrypsin, phospholipase D and neuraminidase. Unidirectional phenylalanine influx across the small intestine was significantly reduced (P less than 0.01) when the mucosal strips were preincubated with the above mentioned enzymes. Intestinal cell water and volume were not significantly changed (P greater than 0.6) when the intestinal tissues were preincubated with these enzymes.

Animals↗