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Biomedical subjects

R Jacob

Publications and source records attributed to R Jacob.

At least 163 records · Page 9Linked to original sources
PubMed1986

Intrabiliary glutathione hydrolysis. A source of glutamate in bile.

High concentrations of glutathione (GSH) and two of its constituent amino acids, glutamate and glycine, are normally found in rat bile. To examine the role of intrabiliary GSH hydrolysis as a source of these amino acids, as well as of cystine in bile, the biliary excretion of GSH and free amino acids was measured in normal male Sprague-Dawley rats; in animals given either phenol 3,6-dibromphthalein disulfonate or diethyl maleate, inhibitors of GSH secretion into bile; and after a retrograde intrabiliary infusion of (alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125), an irreversible inhibitor of gamma-glutamyl transferase activity. Total concentration of amino acids in normal rat bile ranged from 4 to 7 mM and was more than double the concentration in plasma (2-3 mM). Although most amino acids were detected in bile, glutamate and glycine were the most prevalent (1.2 and 1.0 mM, respectively), followed by the branched chain amino acids valine and leucine. The administration of phenol 3,6-dibromphthalein disulfonate (180 mumol/kg, intravenous), or of diethyl maleate (1 mmol/kg, intraperitoneal), resulted in a marked decrease in the biliary excretion of GSH, as well as a decrease in the excretion of glutamate, cystine, and glycine; however, the effects of these agents were not specific for the amino acid constituents of GSH. Following retrograde intrabiliary infusion of AT-125 (10 mumol/kg), there was an immediate and sustained doubling in the rate of biliary excretion of both GSH and glutathione disulfide and a marked decrease in the rate of excretion of glutamate. Varying the dose of AT-125 (0-20 mumol/kg) resulted in an inverse linear relation between hepatic gamma-glutamyl transferase activity and the biliary excretion of intact GSH. These findings suggest that most, if not all, of the free glutamate in excreted bile is formed from the intrabiliary hydrolysis of GSH. Prior to hydrolysis within the biliary tree, substantial concentrations of GSH must be transported from liver cells into bile; minimal canalicular concentrations of this tripeptide are estimated at 5 mM.

Amino Acids↗
PubMed1986

Correlation between total catecholamine content and redistribution of myosin isoenzymes in pressure loaded ventricular myocardium of the spontaneously hypertensive rat.

In the spontaneously hypertensive rat (SHR) with established hypertension left ventricular mass closely correlated with the proportion of ventricular myosin (VM)-3. A 60% VM-3 content was reached corresponding, under the present housing conditions, to an average age of 40 weeks without any significant change in total noradrenaline content. However, all 72-week-old SHR showed marked reduction in total noradrenaline content which corresponded to noradrenaline depletion. At this stage, the proportion of VM-3 varied greatly; some of the SHR exhibited a higher proportion of VM-3 than would be expected from their ventricular weight. The excessive redistribution in the direction of VM-3 might, therefore, be considered as a reaction secondary to noradrenaline depletion. Total dopamine content was also reduced in 72-week-old SHR. In younger SHR, a positive correlation was found for dopamine content and left ventricular weight. It is concluded that a redistribution of the myosin isoenzymes up to 60% VM-3 in SHR is not associated with deterioration of ventricular performance to the extent that an excessive neurohumoral drive ensues. However, in the late stage of haemodynamic overload, a functional state is reached which is prone to noradrenaline depletion. A causative factor involved in this process could be the extreme redistribution of the myosin isoenzyme population, besides other factors such as fibrosis and dilatation. Which functional determinants or structural elements are finally decisive for the transition into a myocardium with depleted noradrenaline stores requires further investigation.

Animals↗
PubMed1986

Significance of physical exercise in hypertension. Influence of water temperature and beta-blockade on blood pressure, degree of cardiac hypertrophy and cardiac function in swimming training of spontaneously hypertensive rats.

In previous studies swimming training (ST) of spontaneously hypertensive rats (SHR) at 36 degrees water temperature (WT) led to a decrease in blood pressure (BP). A similar effect of ST has not been described in human hypertension. Our purpose was to investigate the influence of WT on this training effect, the influence of ST on LV hypertrophy and the involvement of adrenergic stimuli in the latter. Male SHR (20 weeks old) were divided randomly into 4 groups. 1) SHR sedentary 2) SHR ST 36 degrees 3) SHR ST 26 degrees 4) SHR ST 36 degrees + atenolol (50 mg/kg/die). ST was performed 2 X 90 min/day for 31 days and then reduced to 2 X 60 min/day. After 7 weeks of ST BP was lower in all ST groups compared with SHR sedentary (p less than 0.001). BP was higher in ST 26 degrees than in ST 36 degrees (p less than 0.05). No additional effect of atenolol on BP was observed. The increase in the degree of LV hypertrophy during ST (ST 36 degrees: +15%; ST 26 degrees: +26%) could be prevented by atenolol (ST 36 degrees + atenolol: -1.5%). ST 36 degrees led to improved ventricular and myocardial performance with decreased LV wall stress ("luxury hypertrophy"), while in ST 26 degrees ventricular dilatation occurred with increased systolic wall stress and elevated LVEDP. It was uncertain whether this should be interpreted as a state of LV pre-insufficiency in ST 26 degrees in spite of no indications of impaired myocardial contractile capability. Peripheral vascular resistance (PVR) was significantly reduced by ST. The reduction was more evident in ST 26 degrees, but was partially compensated for by an increased cardiac output. The weights of adrenal glands increased (p less than 0.001), most markedly for ST 26 degrees. The level of thyroid hormones (T3 and fT3) was increased in ST 26 degrees. In summary, ST proved to be effective in lowering BP of SHR. WT had great influence with respect to cardiovascular adaptation and mechanisms involved in ST of SHR. Cardioadrenergic drive was of great significance for the process of hypertrophy during ST in SHR.

Animals↗
PubMed1986

Pathophysiological mechanisms in cardiac insufficiency induced by chronic pressure overload--an attempt to analyze specific factors in animal experiment.

Experimental results obtained from studies on Goldblatt rats and spontaneously hypertensive rats as well as theoretical considerations render possible an approximate analysis and evaluation of the relative significance of specific factors at different levels of the heart for the manifestation of cardiac failure under chronic pressure overload. In our experimental models congestive failure was never observed independently of structural dilatation. Thus, as a rule dilatation had already set in before symptoms of heart failure became manifest. However, at moderate dilatation of the ventricle, e.g., at double the end-diastolic volume, the geometrical state per se cannot be the cause of hydropic decompensation whereas extreme dilatation would, in principle, cause cardiac pumping failure even in the absence of any impairment of myocardial "contractility". Generally, a more or less marked impairment of myocardial contractile capability was found, which exceeded the effects due to the altered isoenzyme pattern of myosin. As a rule, a reduction in myocardial "contractility" could be ascertained before a marked degree of dilatation was reached. Diffuse fibrosis impairs the contractile capability of the myocardium and certainly contributes to the manifestation of heart insufficiency; although, as a rule, it should not be the main cause. The adaptive transformation of myocardium towards a slower muscle (isoenzyme pattern of myosin; sarcoplasmatic reticulum) as such does not lead to resting insufficiency, not even under persisting pressure load. Further investigations on processes of excitation-mechanical coupling in the advanced stage of cardiac overload are indicated. The absence of sympathetic support to the heart, e.g., following blockade of beta-adrenergic receptors can, in the advanced stage, elicit a transition from the stage of pre-insufficiency to manifest failure. However, this was only observed when dilatation had already occurred. A network of factors are responsible for cardiac insufficiency due to pressure overloading, whereby the respective significance of each component varies, depending on the experimental model used.

Animals↗
PubMed1986

Amino acid and glucose metabolism in the postabsorptive state and following amino acid ingestion in the dog.

Amino acid and glucose metabolism was studied in nine awake 18-hour fasted dogs with chronic portal, arterial, and hepatic venous catheters before and for three hours after oral ingestion of amino acids. The meal was composed of a crystalline mixture of free amino acid, containing neither carbohydrate nor lipid. Following the amino acid meal, plasma glucose concentration declined slowly and this occurred despite a rise in hepatic glucose release. Portal plasma insulin rose transiently (30 +/- 7 to 50 +/- 11 microU/mL, P less than 0.05) while the increase in portal glucagon was more striking and persisted throughout the study (162 +/- 40 to 412 +/- 166 pg/mL). Over the three hours following amino acid ingestion, the entire ingested load of glycine, serine, phenylalanine, proline, and threonine was recovered in portal blood as was 80% of the ingested branched chain amino acids (BCAA). The subsequent uptake of these glucogenic amino acids by the liver was equivalent to the amount ingested, while hepatic removal of BCAA could account for disposal of 44% of the BCAA absorbed; the remainder was released by the splanchnic bed. During this time, ongoing gut production of alanine was observed and the liver removed 1,740 +/- 170 mumol/kg of alanine, which was twofold greater than combined gut output of absorbed and synthesized alanine. In the postcibal state, the total net flux of alanine and five other glucogenic amino acids from peripheral to splanchnic tissues (1,480 mumol/kg 3 h) exceeded the net movement of branched chain amino acids from splanchnic to peripheral tissues (590 mumol/kg/3 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1986

Na/H exchange in cultured chick heart cells: secondary stimulation of electrogenic transport during recovery from intracellular acidosis.

Intracellular acidosis is capable of stimulating a rapid amiloride-sensitive Na/H exchange mechanism in the cell membrane of cultured chick heart cells. The sequence of changes of intracellular sodium and potassium contents during recovery from an acid load in heart cells was determined by atomic absorption spectrophotometry and correlated with electrophysiological measurements. Induction of an intracellular acid load by removal of NH4Cl from the bathing solution caused a rapid rise in sodium content that was amiloride-sensitive. Following a peak, sodium content declined concomitant with a rise in potassium content; these changes were ouabain-sensitive and corresponded with a ouabain-sensitive membrane hyperpolarization beyond the calculated potassium equilibrium potential. These observations indicate that pHi regulation in cardiac muscle, following an intracellular acid load involves extrusion of H+ by electroneutral Na/H exchange with the consequent rise in Nai stimulating the electrogenic Na/K pump to return Nai to control level. In the presence of amiloride (10(-4) M), the hyperpolarization was slower although still present: this suggests the existence of another sodium uptake mechanism which contributes to stimulation of electrogenic transport.

Action Potentials↗
PubMed1986

Vitamin K deficiency in chronic alcoholic males.

Twenty male alcoholic subjects were studied initially within 1 day after stopping alcohol and again after about 1 week. Vitamin and mineral measurements were made on blood and abnormal prothrombin molecules quantitated for vitamin K status. Nine of the 20 patients received menadiol after the initial blood sample. Twelve of the alcoholics had significant elevations of abnormal prothrombin. Of these 12, all five who received vitamin K reduced the abnormal prothrombin levels toward normal but no change was observed in the seven who did not receive vitamin K. All nine patients receiving vitamin K lowered the abnormal prothrombin level significantly whereas there was no change in those 11 who did not receive vitamin K. The prothrombin time by the one-stage technique was normal in all patients. These data suggest that the production of abnormal prothrombin is frequently present in alcoholics and this may represent a subclinical vitamin K deficiency.

Adult↗
PubMed1986

Coupled sodium-calcium transport in cultured chick heart cells.

In cultured embryonic chick heart cells, alterations of extracellular Na (Nao) and Ca (Cao), intracellular Na (Nai) and Ca, extracellular pH, and membrane potential resulted in changes in Na and Ca contents that were consistent with sarcolemmal Na-Ca exchange. 24Na efflux measurements revealed a large ouabain-insensitive component, one-third of which was inhibited by removal of Cao. Incubating the cells in Na-free solution resulted in a rapid, 1.5- to 2-fold increase in total cell Ca that remained elevated for at least 15 min. Cells exposed for 15 min to Nao less than or equal to 20 mM became maximally loaded with Ca, whereas Ca loading fell off sharply at values of Nao greater than 20 mM. The movement of Na against its electrochemical gradient was shown to be associated with Ca accumulation. During Na-K pump inhibition (in 10(-4) M ouabain), Na initially rose 2- to 3-fold to a level below its equilibrium value; then, lowering Cao for 30 min from 1.25 to 0.75 mM caused a 26% elevation in Nai, whereas raising Cao from 1.25 to 2.7 mM resulted in a 25% fall in Nai against its electrochemical gradient. These data are consistent with Nai being maintained by a Na-Ca exchange during Na-K pump inhibition. In the presence of ouabain (10(-4) M), Ca uptake into intracellular organelles, e.g., mitochondria, was suggested by an increase in total cell Ca as well as the occurrence of mitochondrial matrix granules, which were shown qualitatively by X-ray analysis to contain Ca. Although matrix granules also occurred in mitochondria during Na-free incubation, they did not contain detectable amounts of Ca when examined under identical conditions of fixation and analysis.

Animals↗
PubMed1986

Removal of infused amino acids by splanchnic and leg tissues in humans.

To compare the contributions of splanchnic and skeletal muscle tissues to the disposal of intravenously administered amino acids, regional amino acid exchange was measured across the splanchnic bed and leg in 11 normal volunteers. Postabsorptively, net release of amino acids by leg (largely alanine and glutamine) was complemented by the net splanchnic uptake of amino acids. Amino acid infusion via peripheral vein (0.2 g X kg-1 X h-1) caused a doubling of plasma insulin and glucagon levels and a threefold rise in blood amino acid concentrations. Both splanchnic and leg tissues showed significant uptake of infused amino acids. Splanchnic tissues accounted for approximately 70% of the total body amino acid nitrogen disposal; splanchnic uptake was greatest for the glucogenic amino acids but also included significant quantities of branched-chain amino acids. In contrast, leg amino acid uptake was dominated by the branched-chain amino acids. Based on the measured leg balance, body skeletal muscle was estimated to remove approximately 25-30% of the total infused amino acid load and approximately 65-70% of the infused branched-chain amino acids. Amino acid infusion significantly stimulated both the leg efflux and the splanchnic uptake of glutamine (not contained in the infusate). We conclude that when amino acids are infused peripherally in normal humans, splanchnic viscera (liver and gut) are the major sites of amino acid disposal.

Adolescent↗
PubMed1986

Effect of free fatty acids on blood amino acid levels in human.

Raised plasma free fatty acid (FFA) levels effectively impede glucose uptake in vivo, thereby conserving plasma glucose and sparing glycogen. To test whether FFA have any effect on blood amino acid levels, we infused Intralipid plus heparin or saline into healthy volunteers under four different experimental conditions: A) overnight fast; B) euglycemic hyperinsulinemia (approximately 100 microU/ml); C) hyperglycemic (approximately 200 mg/100 ml) hyperinsulinemia (approximately 50 microU/ml); and D) hyperglycemic (approximately 300 mg/100 ml) normoinsulinemia (approximately 20 microU/ml). In the fasting state (A), lipid infusion was associated with lower blood levels of most amino acids, both branched chain and glucogenic. This effect, however, could not be ascribed to lipid infusion alone, because plasma insulin levels were also stimulated. The clamp studies (B, C, and D) allowed to assess the influence of lipid on blood amino acid levels at similar plasma insulin and glucose levels. It was thus observed that lipid infusion has a significant hypoaminoacidemic effect of its own under both euglycemic (B) and hyperglycemic (C) conditions; this effect involved many glucogenic amino acids (alanine, glycine, phenylalanine, serine, threonine, and cystine) but none of the branched-chain amino acids (leucine, isoleucine, and valine). In marked contrast, normoinsulinemic hyperglycemia (D), with or without lipid infusion, caused no change in the blood level of any measured amino acid. We conclude that lipid infusion has a hypoaminoacidemic action. We also suggest that this action is permitted by insulin and may involve specific metabolic interactions (e.g., reduced availability of glucose-derived pyruvate or glycerophosphate) as well as enhanced uptake by the liver.

Adolescent↗
PubMed1986

Characterization of glutamine transport by liver plasma membrane vesicles.

Plasma membrane vesicles were prepared from livers of fed normal and diabetic rats and used to characterize the membrane transport process responsible for glutamine uptake by the liver cell. In vesicles from normal rats the initial velocity of glutamine uptake was fourfold more rapid (0.20 +/- 0.02 vs. 0.05 +/- 0.02 nmol X mg protein-1 X 10 s-1) when Na+ replaced K+ in the extravesicular buffer. In the presence of a Na+-gradient glutamine uptake by vesicles was saturable, with a Km of 1.3 +/- 0.5 mM and a Vmax of 10 +/- 2.3 nmol X mg-1 X min-1. Lithium could fully substitute for Na+ in stimulating glutamine entry. In the presence of an imposed K+-gradient glutamine uptake was a linear function of its extravesicular concentration. In accord with the sodium-stimulated uptake of glutamine occurring via a sodium symport process, we observed that glutamine stimulated the initial rate of 22Na+ entry into vesicles by four- to fivefold. We further observed that glutamine entry was more rapid when lipophilic anions accompanied sodium in the incubation buffer, suggesting that Na+-glutamine flux is electrogenic. Preloading of vesicles with glutamine did not effect subsequent entry of labeled glutamine (no transstimulation), whereas intravesicular alanine did enhance alanine but not glutamine entry. Alloxan diabetes, which is known to stimulate the Na+-alanine cotransporter in these vesicles did not increase glutamine entry at any concentration tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1986

Continuous subcutaneous insulin infusion (CSII) reduces counter-regulatory hormone concentrations in a patient receiving enteral hyperalimentation.

A 61-year-old male, while recovering from a Whipple's procedure for pancreatic carcinoma, was treated for 13 days with an insulin infusion pump for diabetes exacerbated by enteral hyperalimentation. Treatment with continuous subcutaneous insulin infusion resulted in improved blood glucose control. Associated with this improvement was a reduction in plasma cholesterol, triglyceride and free fatty acid levels. Plasma epinephrine, norepinephrine, glucagon and cortisol concentrations were also lowered although growth hormone levels remained unchanged. It is concluded that enhanced metabolic control during hyperalimentation results in a decrease in counter-regulatory hormone levels and an improvement in the catabolic state in this patient. These preliminary observations provide evidence for maintaining euglycemia in diabetic patients while receiving nutritional support.

Blood Glucose↗
PubMed1986

Myocardial and ventricular mechanics as influenced by disopyramide.

The effects of disopyramide (D) on the mechanics of isolated myocardium as well as on the whole ventricle were examined in the rat model. Moreover bipolar leads of the apex and an area at the base of the left ventricle were set up to get indications for changes in the spread of excitation. D in concentrations of 10(-8) to 10(-4) mol/l did not affect the diastolic elastic properties of isolated myocardium. Isometric contraction amplitude was nearly unaltered, while rate of isometric contraction and relaxation were slightly increased. In the whole ventricle in situ D (2 to 10 mg/kg b.w. administered i.v.) induced a dose-dependent decrease in left ventricular isovolumetric peak pressure (16%), max.pos. dP/dt (40%) and max.neg. dP/dt (30%; for highest doses respectively), while time to peak pressure and relaxation time 90% were prolonged. Therapeutic dose of D (2 mg/kg b.w.i.v.) induced no decrease in essential systolic parameters of the whole ventricle under auxotonic conditions. Left ventricular pressure, dP/dt max.pos. and neg., left ventricular end-diastolic pressure and cardiac output were nearly unaltered. Heart rate showed a tendency to decrease, while total time of contraction and left ventricular ejection time increased. Higher doses of D led to marked cardiac depressant effects. The time interval between the excitation of the apex and an area at the base of the heart was increased. It was concluded that the negative dromotropic effect of D and thereby an altered pattern of left ventricular contraction are essential components in the elimination of the pressure gradient between left ventricle and aorta, observed in patients with muscular subaortic stenosis, and are presumably involved in the cardiac depressant effect of the drug in over-therapeutic doses.

Animals↗
PubMed1985

Cytosolic free calcium in chick heart cells. Its role in cell injury.

The role of cytosolic free Ca2+ (Caf) in cell injury was investigated using two methods for measuring Caf in freshly disaggregated embryonic chick heart cells. The null-point method, using arsenazo III, is based on determining the extracellular Ca2+ concentration at which no net Ca2+ movement occurs when plasma membrane permeability is increased. With this technique, the null point Caf averaged 0.23 +/- 0.07 microM (n = 6) in the basal state. Using quin2, an intracellular fluorescent dye, to measure Caf a value of 0.05 +/- 0.01 microM (n = 5) was obtained. Elevation of Caf by various agents was associated with an increase in cell injury as measured by the release of the cytosolic enzyme, LDH. However, the relationship between Caf and LDH release was not a direct one under all experimental conditions, indicating that the level of Caf is not the sole determinant of cell injury.

Adenosine Triphosphate↗
PubMed1985

Na/H exchange in cultured chick heart cells. pHi regulation.

The purpose of this study was to establish the existence of Na/H exchange in cardiac muscle and to evaluate the contribution of Na/H exchange to pHi regulation. The kinetics of pHi changes in cultured chick heart cells were monitored microfluorometrically with 6-carboxyfluorescein and correlated with Nai content changes analyzed by atomic absorption spectrophotometry; transmembrane H+ movements were evaluated under pH stat conditions. After induction of an intracellular acid load by pretreatment with NH4Cl, a regulatory cytoplasmic alkalinization occurred with a t1/2 of 2.9 min. pHi regulation required external Na+ and was concomitant with transmembrane H+ extrusion as well as a rapid rise in Nai content in an Na/H ratio of 1:1. Microelectrode recordings of membrane potential demonstrated directly the electroneutral character of pHi regulation. Acid-induced net Na+ uptake could be either stimulated by further decreasing pHi or inhibited by decreasing pHo; Na+ uptake was unaffected by tetrodotoxin (10 micrograms/ml), quinidine (10(-3) M), DIDS (10(-4) M), Clo-free solution, or HCO3-free solution. Amiloride (10(-3) M) maximally inhibited both pHi regulation and Na+ uptake; the ID50 for amiloride inhibition of Na+ uptake was 3 microM. Nao-dependent H+ extrusion showed half-maximal activation at 15 mM Nao; Li+, but not K+ or choline+, could substitute for Na+ to support H+ extrusion. Cao-free solution also stimulated acid-induced Na+ uptake. We conclude that pHi regulation following an acid load in cardiac muscle cells is by an amiloride-sensitive, electroneutral Na/H exchange. Stimulation of Na/H exchange up to 54 pmol/cm2 X s indicates the rapidity of this exchange across cardiac cell membranes. Na/H exchange may also participate in steady state maintenance of pHi.

Amiloride↗
PubMed1985

Potassium-chloride cotransport in cultured chick heart cells.

The polystrand preparation of cultured chick heart cells has a unidirectional transmembrane Cl- efflux that is twice K+ efflux. However, Cl- conductance of this heart cell membrane is low [regardless of extracellular K+ (K+o)], suggesting the existence of electroneutral Cl--dependent transport mechanisms. Furosemide (10(-3) M) decreases the 36Cl tracer efflux rate constant from a control value of 0.67 to 0.33 min-1. Extracellular Na+--free solution, which depletes intracellular Na+ within 1 min, has no significant effect on 36Cl efflux. K+o-free solution plus 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 10(-4) M) promotes the loss of Cl- against the Cl- electrochemical gradient; Cl- loss is furosemide sensitive in a dose-dependent manner. Incubating polystrands in 133 mM K+o, normal extracellular Cl- (Cl-o) solution causes net K+ and Cl- uptake in a 1:1 stoichiometry as well as a furosemide-sensitive volume increase; 130 mM extracellular choline or Li+ cannot mimic this high-K+o-induced volume increase. Removal of Cl-o from 133 mM K+o solution prevents K+ uptake and causes a Cl- loss as well as a furosemide-sensitive volume decrease. Adjusting Cl-o concentrations in high-K+o solution plus DIDS, so that the Cl- chemical gradient equally opposes the K+ chemical gradient, prevents high-K+o-induced volume changes. These data suggest that the cardiac cell membrane contains a furosemide-sensitive K+-Cl- cotransport mechanism.

Animals↗