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P W Watt

Publications and source records attributed to P W Watt.

At least 19 recordsLinked to original sources
PubMed1995

Effects of prolonged treatment of lactating goats with bovine somatotropin on aspects of adipose tissue and liver metabolism.

The effects of prolonged (22 weeks) treatment of lactating goats with bovine somatotropin on the metabolism of adipose tissue and liver has been investigated. Somatotropin treatment resulted in smaller adipocytes, decreased rate of fatty acid synthesis and decreased total acetyl-CoA carboxylase activity of adipocytes, but with no change in the proportion of this enzyme in the active state. The rate of acylglycerol glycerol synthesis from glucose of adipocytes tended to decrease as did total glucose utilization by the tissue. Glucose conversion to lactate was unchanged by somatotropin treatment but glucose conversion to other products was decreased. Maximum response of adipose tissue to insulin was unchanged but the sensitivity to insulin decreased on somatotropin treatment. Treatment with somatotropin had no effect on basal lipolysis and decreased maximum response to the beta-agonist isoproterenol, but this probably reflects the rate of isoproterenol-stimulated lipolysis varying with cell volume in adipocytes. No apparent change in response either to alpha 2-adrenergic agonists or to adenosine was apparent. The number of beta-adrenergic receptors was unchanged in adipocyte membranes but the number of alpha 2-adrenergic receptors increased. The rate of hepatic gluconeogenesis in vitro, the activity of key gluconeogenic enzymes and the modulation of the rate of gluconeogenesis by butyrate were unchanged except for the effect of this latter agent on gluconeogenesis from propionate. Hepatic ketogenic activity, as indicated by the activity of carnitine palmitoyl-CoA-transferase-1 and the concentrations of carnitine and acyl carnitines, was unchanged by treatment. Thus at the end of a prolonged period of treatment with somatotropin in lactating goats, lipid synthesis in adipose tissue is still decreased but no effects on liver lipid and carbohydrate metabolism were apparent.

Acetyl-CoA Carboxylase↗
PubMed1995

Pentagastrin increases pepsin secretion without increasing its fractional synthetic rate.

We studied the effects of increasing doses of pentagastrin on gastric secretion of pepsin and on incorporation of L-[1-13C]leucine into gastric aspirate protein as an index of pepsin synthesis. Pentagastrin (0.25-4.0 micrograms.kg-1.h-1) significantly increased pepsin output from basal 76 mg/h to < or = 181 mg/h but did not significantly alter incorporation of L-[1-13C]leucine from the basal fractional synthetic rate of 3.63 +/- 0.05%/h. In four subjects in whom infusion of tracer leucine was continued for > 1 day, aspiration of pepsin between 24 and 27 h demonstrated that plateau 13C labeling of leucine in pepsin had been attained, but at a value that was only 48% of the 13C labeling of plasma alpha-ketoisocaproic acid (alpha-KIC) [0.730 +/- 0.02 (SE) vs. 1.520 +/- 0.14 atoms %excess]. This suggests that actual rates of pepsin synthesis were approximately double those calculated on the basis of alpha-KIC labeling. The results are consistent with an interpretation that increasing doses of pentagastrin cause increased secretion of pepsinogen by recruitment of gastric chief cells, each synthesizing pepsinogen at an unaltered rate. Plateau 13C enrichment of alpha-KIC may not be a valid surrogate for plateau 13C leucine enrichment when fractional synthetic rates of some secreted proteins are calculated.

Adult↗
PubMed1995

Rapid tracer lactate influx into canine skeletal muscle.

This study evaluated the effects of various lactate transport inhibitors and competitors on rapid tracer lactate influx into the canine gastrocnemius-plantaris muscle (GP). GPs of 25 anesthetized dogs were perfused with red blood cell-free media in situ. At 0.9 mM lactate concentration ([La]), GP oxygen uptake (2.6 +/- 0.1 ml.kg-1.min-1) and net lactate output (-0.039 +/- 0.007 mmol.kg-1.min-1) were similar to values during blood perfusion. Rapid tracer lactate influx was inferred by a paired-tracer dilution method at nominal perfusate [La] values of 1, 5, 10, 25, and 50 mM. The maximal tracer influx rate (Umax) decreased significantly with each increase in unlabeled [La]. A saturation effect was suggested by the fact that percent inhibition of Umax began to reach a plateau at the higher unlabeled [La] values. The inhibition of Umax was 20.5 +/- 2.9% at 5 mM, 34.1 +/- 3.3% at 10 mM, 47.3 +/- 2.7% at 25 mM, and 56.1 +/- 2.8% at 50 mM [La]. Umax was also inhibited by various inhibitors/competitors of lactate transport as follows (% inhibition): 50 mM alpha-cyano-4-hydroxy-cinnamate (69.2 +/- 4.9%), 1.5 mM phloretin (25.4 +/- 5.5%), 0.1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (0.3 +/- 1.9%), 0.5 mM p-chloromercuribenzenesulfonic acid (72.9%), 0.5 mM furosemide (+ 2.8%), 25 mM pyruvate (52.4 +/- 2.9%), and 50 mM DL-lactate (50.2 +/- 4.0%). These experiments support the notion that lactate influx into canine skeletal muscle is a function of both a linear (possible diffusive) component and a Michaelis-Menten (carrier-mediated) component.

Animals↗
PubMed1994

Measurement of human tissue protein synthesis: an optimal approach.

This paper reviews the evidence for and against the adoption of methods for the measurement of human tissue protein synthesis based upon the incorporation of stable isotopically labeled amino acids administered either as a continuous infusion or as a flooding dose. The practical advantages of the flooding dose method are the relative ease of application of the tracer and the ability to make a repeat measurement within approximately 2 h. For the method depending upon continuous infusion of labeled amino acid, the advantages include the use of labeled amino acids at true tracer doses (i.e., with no disturbance of metabolism) and the ability to make simultaneous measurements of whole body turnover and limb or organ turnover (given appropriate sampling techniques). The crucial question concerning the accuracy of the two methods (e.g., the 2-fold difference in the rate of skeletal muscle protein synthesis) remains unresolved, but in our opinion more evidence exists in favor of the values obtained from the continuous infusion method. Furthermore, as techniques for measurement of stable isotopically labelled amino acids improve, the length of time necessary for tracer infusion will fall, and the practical advantages of the flooding dose protocol will lessen in comparison.

Amino Acids↗
PubMed1994

Effect of a flooding dose of leucine in stimulating incorporation of constantly infused valine into albumin.

Recently, we demonstrated increased incorporation of [13C]valine tracer into muscle protein after administration of a flooding dose of L-leucine. We have now investigated the possibility of a similar effect on albumin synthesis in the same group of volunteers. We gave L-[1-13C]leucine (20 atom%, 0.05 g/kg) during the final 90 min of a 7.5-h primed constant infusion of L-[1-13C]valine (99 atom%, 1.5 mg/kg prime constant infusion of 1.5 mg.kg-1.h-1) in healthy male volunteers in the postabsorptive state. Blood samples, taken at 0.5- to 1-h intervals during the constant infusion and at 5- to 30-min intervals during the application of the flooding dose, were analyzed for the concentration and 13C enrichment of leucine, valine, and their ketoacids. Albumin was isolated and hydrolyzed, and the enrichments of incorporated valine and leucine were compared with the mean enrichment of various possible precursor pools to calculate the apparent rate of albumin protein synthesis according to the standard procedures. During constant infusion of [13C]valine tracer the rate of albumin synthesis (measured using alpha-ketoisovalerate labeling as a surrogate for the true precursor) was 0.250 +/- 0.041%h (SD), a value identical to that routinely obtained using constant leucine tracer infusion and alpha-ketoisocaproate labeling. During the application of the flooding dose of leucine, the rate of incorporation of tracer [13C]valine into albumin increased by 73% to 0.433 +/- 0.129%/h (P < 0.05); the apparent protein synthetic rate calculated from the incorporation of leucine applied during the flood was 0.402 +/- 0.057 (P < 0.001). These results raise further doubts about the validity of the flooding dose method for the measurement of rates of human protein synthesis.

Adult↗
PubMed1994

Effects of flow and contraction on lactate transport in the perfused rat hindlimb.

A perfused rat hindlimb preparation was used to assess the effects of perfusate flow and electrical stimulation to mimic exercise on the rates of lactate influx (measured by a dual tracer technique with [3H]mannitol as the extracellular marker) and net lactate production. The same perfused muscle system was also used for assessing the effects of alpha-cyano-4-hydroxycinnamate (CIN, 15 mM), phloretin (0.6 mM), and pyruvate on tracer lactate influx. Unidirectional lactate influx, oxygen uptake (VO2), and net lactate flux were all significantly dependent on perfusate flow rate (all P < 0.05). The hindlimb was in net lactate production at all flow rates studied. Electrical stimulation (60 Hz, 100 ms, 20 V trains at 0.6 min-1) at perfusate lactate concentration of 1 mM significantly increased the hindlimb VO2 from 8.0 +/- 1.1 to 16.0 +/- 2.2 ml.kg-1.min-1 and production of lactate from -69 +/- 31 to -823 +/- 77 nmol.min-1.g-1 (both P < 0.001) but did not affect tracer-measured unidirectional lactate influx (nonstimulated: 235.4 +/- 78.1; stimulated: 235.0 +/- 31.0 nmol.min-1.g-1). At a perfusate flow of 0.55 ml.g-1.min-1 the unidirectional influx of 1 mM lactate was markedly inhibited (90 +/- 5%) by 15 mM CIN. CIN also significantly reduced VO2 from 6.2 +/- 0.16 to 4.45 +/- 0.57 ml.kg-1.min-1 (P < 0.05, n = 5). Phloretin (0.6 mM, n = 3) had no significant effect on lactate influx.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mechanisms involved in the adaptations of the adipocyte adrenergic signal-transduction system and their modulation by growth hormone during the lactation cycle in the rat.

The mechanisms responsible for the diminished lipolytic response of adipocytes to catecholamines after litter removal from lactating rats and their modulation by growth hormone have been investigated. Lactation, litter removal and growth-hormone treatment did not alter the ability of noradrenaline to activate protein kinase A (A-kinase), showing that the defect in signal transduction in rats after litter removal is after A-kinase. Litter removal had no effect on hormone-sensitive lipase activity itself, but the proportion of the lipase associated with the fat droplet was decreased; growth-hormone treatment increased hormone-sensitive lipase activity and the proportion associated with the fat droplet. In addition, a number of other adaptations in the beta-adrenergic signal-transduction system occur during the lactation cycle and in response to growth hormone treatment, including changes in receptor number, adenylate cyclase activity and cyclic AMP phosphodiesterase activity, but a defect in the ability of hormone-sensitive lipase to associate with the lipid droplet appears to be the major reason for the diminished response to catecholamines on litter removal.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Protein turnover in the human fetus studied at term using stable isotope tracer amino acids.

Before elective cesarean delivery (4 h), we infused L-[1-13C]leucine and L-[15N]phenylalanine into the maternal circulation and measured enrichment and concentration of amino acids and carbon dioxide in cord blood of six normal human fetuses at delivery. There were net fetal uptakes of leucine (2.22 +/- 0.29 mumol.kg-1.min-1) and phenylalanine (0.80 +/- 0.11 mumol.kg-1.min-1) with net outputs of CO2 (6.11 +/- 1.12 ml.kg-1.min-1) and the transamination product of leucine, alpha-ketoisocaproate (1.04 +/- 0.32 mumol.kg-1.min-1). Fetal amino acid oxidation accounted for a substantial proportion of the flux from the mother (leucine, 0.36 +/- 0.09 mumol.kg-1.min-1 and phenylalanine, 0.18 +/- 0.04 mumol.kg-1.min-1). Fetal whole body accretion of leucine carbon (0.82 +/- 0.21 mumol.kg-1.min-1) was 69% of the umbilical uptake, and that of phenylalanine (0.62 +/- 0.08 mumol.kg-1.min-1) was 78%. Fetal whole body protein synthesis was approximately 13 g.kg-1.day-1, i.e., much faster than in adults but similar to that in the newborn. Net protein accretion was 2-4 g.kg-1.day-1. The placental supply of leucine and phenylalanine exceeds the fetal demand for protein synthesis by only a small amount, suggesting that the safety margin of placental transfer may be small for these amino acids. The results suggest that the method could be applied safely to studies of fetal growth retardation.

Adult↗
PubMed1992

Flooding with L-[1-13C]leucine stimulates human muscle protein incorporation of continuously infused L-[1-13C]valine.

To investigate why flooding methods give higher rates than constant-infusion methods for muscle protein synthesis, we studied seven healthy postabsorptive male volunteers (20-42 yr; 67-74 kg) during a 7.5-h primed constant infusion of L-[1-13C]valine (99 atoms %, 1.5 mg/kg prime, 1.5 mg.kg-1.h-1); at 6.5 h they were given a flood of L-[1-13C]leucine (20 atoms %, 0.05 g/kg). Musculus tibialis anterior biopsies were taken at 0.5, 6, and 7.5 h, and blood was sampled as appropriate. The enrichment of valine and leucine in muscle protein (isotope ratio mass spectrometry of protein amino acid-derived 13CO2) was compared with the average enrichment of various amino acid pools (gas chromatography-mass spectrometry). During infusion of [13C] valine the rate of muscle protein synthesis measured using alpha-ketoisovalerate (alpha-KIV) as precursor surrogate was 0.043 +/- 0.002%/h (SE). After flooding with leucine, the incorporation rate of [13C]valine increased by 70% (P less than 0.05), i.e., apparent muscle protein synthetic rate (based on alpha-[13C]KIV) increased to 0.065 +/- 0.009%/h (P less than 0.05); the rate calculated from the [13C]leucine flood was 0.060 +/- 0.005%/h (P less than 0.01). The synthetic rates calculated using the constant-infusion method were higher after flooding, irrespective of the precursor chosen, raising serious concern about the validity of the flooding-dose method.

Adult↗
PubMed1992

Stimulation of protein synthesis in pig skeletal muscle by infusion of amino acids during constant insulin availability.

Incorporation of L-[1-13C]leucine into muscle protein and leg exchange of L-[15N]phenylalanine were used to assess the effects over 240 min of amino acid supply on leg protein turnover in anesthetized, overnight-fasted (Landrace x Great White) female pigs. In all pigs, plasma insulin and glucagon stability was ensured by infusion of somatostatin (8 micrograms.kg-1.h-1), insulin (6 mU.kg-1.h-1), and glucagon (72 ng.kg-1.h-1). Mixed amino acid infusion (260 mg.kg-1.h-1) caused a 2- to 2.5-fold elevation of arterial plasma phenylalanine and leucine; in a control group (no amino acid infusion), an increase in phenylalanine and leucine concentration was observed as a result of the hormone clamp. Plasma insulin and glucagon concentrations were steady and not significantly different between control and amino acid-infused groups during the final 240 min, but plasma glucose fell (P less than 0.05) in both groups (4.57 +/- 0.17 to 3.15 +/- 0.73 mM). Muscle protein synthetic rate (estimated from the change in L-[1-13C]leucine incorporation compared with labeling of [13C]leucyl-tRNA) was greater in amino acid-infused (0.076%/h) than in control (0.053%/h) pigs. In the control group, leg amino acid balance was negative (Phe alone, -10.2 +/- 9.4 nmol Phe.100 g-1.min-1; total amino acids, -0.27 +/- 1.04 micrograms amino N.100 g-1.min-1), but during amino acid infusion, balance was positive (Phe alone, +33.6 +/- 8.8 nmol Phe.100 g-1.min-1; total amino acids, +58.2 +/- 4.9 micrograms amino N.100 g-1.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1991

Isolation of aminoacyl-tRNA and its labeling with stable-isotope tracers: Use in studies of human tissue protein synthesis.

We isolated aminoacyl-tRNA (60-70% yield) from human and rat tissues and measured, by GC/MS, its labeling in vivo by [15N]- and [13C]leucine. Tracer dilution artifacts seemed unlikely since, after infusion of L-[1-13C,15N]leucine into rats, (i) muscle leucyl-tRNA labeling exceeded tissue free leucine labeling, (ii) values were largely unaffected by storing over 5 min at 22 degrees C, and (iii) L-[2,4,5-methyl-13C]leucine was not incorporated into leucyl-tRNA during homogenization. Leucyl-tRNA labeling in liver and muscle suggested charging from extra- and intracellular pools: e.g., after infusing L-[1-13C,15N]leucine, rat muscle tissue free leucine 13C labeling (8.97 +/- 0.30 atom % excess) exceeded that by 15N (3.37 +/- 0.33 atom % excess), and both were significantly lower (P less than 0.02) than venous plasma (13C, 12.1 +/- 1.8; 15N, 5.54 +/- 0.6 atom % excess) indicating tracer dilution by transamination and by proteolysis; however, leucyl-tRNA labeling by either isotope (13C, 10.26 +/- 0.50; 15N, 4.72 +/- 0.72 atom % excess) was significantly above mixed tissue free leucine (P less than 0.05). Labeling of leucyl-tRNA in human erector spinae muscle (obtained after preoperative L-[1-13C]leucine infusion) was, at 4.98 +/- 0.43 atom % excess, lower (27%) than venous plasma leucine (P less than 0.05) and intermediate between muscle free leucine (9% lower; P less than 0.01) and venous alpha-ketoisocaproate (11% higher; P less than 0.02). Human placental leucyl-tRNA labeling (after predelivery tracer infusion) was 37% lower (P less than 0.05) than maternal uterine vein labeling but not significantly different from placental free leucine or umbilical arterial leucine.

Animals↗
PubMed1991

Effects of corticosteroid on the transport and metabolism of glutamine in rat skeletal muscle.

Intramuscular glutamine falls with injury and disease in circumstances associated with increases in blood corticosteroids. We have investigated the effects of corticosteroid administration (0.44 mg/kg dexamethasone daily for 8 days, 200 g female rats) on intramuscular glutamine and Na+, muscle glutamine metabolism and sarcolemmal glutamine transport in the perfused hindlimb. After dexamethasone treatment intramuscular glutamine fell by 45% and Na+ rose by 25% (the respective muscle/plasma distribution ratios changed from 8.6 to 4.5 and 0.12 to 0.15); glutamine synthetase and glutaminase activities were unchanged at 475 +/- 75 and 60 +/- 19 nmol/g muscle per min. Glutamine output by the hindlimb of anaesthetized rats was increased from 31 to 85 nmol/g per min. Sarcolemmal glutamine transport was studied by paired-tracer dilution in the perfused hindlimb: the maximal capacity (Vmax) for glutamine transport into muscle (by Na(+)-glutamine symport) fell from 1058 +/- 310 to 395 +/- 110 nmol/g muscle per min after dexamethasone treatment, accompanied by a decrease in the Km (from 8.1 +/- 1.9 to 2.1 +/- 0.4 mM glutamine). At physiological plasma glutamine concentration (0.75 mM) dexamethasone appeared to cause a proportional increase in sarcolemmal glutamine efflux over influx. Addition of dexamethasone (200 nM) to the perfusate of control rat hindlimbs caused acute changes in Vmax and Km of glutamine transport similar to those resulting from 8-day dexamethasone treatment. The reduction in muscle glutamine concentration after dexamethasone treatment may be primarily due to a reduction in the driving force for intramuscular glutamine accumulation, i.e., in the Na+ electrochemical gradient. The prolonged increase in muscle glutamine output after dexamethasone treatment (which occurs despite a reduction in the size of the intramuscular glutamine pool) appears to be due to a combination of (a) accelerated sarcolemmal glutamine efflux and (b) increased intramuscular synthesis of glutamine.

Amino Acids↗
PubMed1991

Chronic control of the beta- and alpha 2-adrenergic systems of sheep adipose tissue by growth hormone and insulin.

1. Sheep adipose tissue retained responsiveness to catecholamines when maintained in tissue culture for 48 h; both the rate of basal lipolysis and sensitivity to beta-agonists were increased after tissue culture. 2. Tissue culture in the presence of growth hormone resulted in an increased maximum response and sensitivity to the beta-agonist isoprenaline, but had no effect on basal lipolysis. 3. Tissue culture in the presence of insulin increased the basal rate of lipolysis and increased the ratio of the rate of noradrenaline-stimulated/isoprenaline-stimulated lipolysis, indicating a decrease in the 2-adrenergic effect of noradrenaline. 4. Tissue culture in the presence of growth hormone increased ligand binding to beta-adrenergic receptors. 5. Tissue culture in the absence of exogenous hormones increased ligand binding to alpha 2-adrenergic receptors; this was prevented by actinomycin D and partly prevented by insulin. 6. These studies show that both growth hormone and insulin chronically modulate the adrenergic system of sheep adipose tissue; the effects of growth hormone are primarily on the beta-adrenergic system, whereas insulin modulates the alpha 2-adrenergic system.

Adipose Tissue↗
PubMed1991

Adenosine and the control of adrenergic regulation of adipose tissue lipolysis during lactation.

Adenosine is a locally active factor that is produced intracellularly and extracellularly in adipose tissue. Adenosine binds to receptors in the plasma membrane of adipocytes; this activates a guanine triphosphate binding protein that inhibits adenylate cyclase activity and, hence, lipolysis. Lactation results in an enhanced responsiveness of adipocytes to beta-agonists, which stimulate lipolysis, and, paradoxically, to adenosine, which inhibits lipolysis. These adaptations are partly due to increases in ligand binding and to changes in postreceptor components of the signal transduction systems. Somatotropin is implicated in the chronic adaptations of the beta-adrenergic system, whereas insulin, somatotropin, glucocorticoids, and at least one unidentified factor have a role in the chronic control of the adenosine system of adipocytes.

Adenosine↗
PubMed1990

Glutamine transport and metabolism in denervated rat skeletal muscle.

Rat skeletal muscle glutamine fell by 40% from 4.18 to 2.5 mumols/g wet weight (P less than 0.01) after 4 days of denervation. Over the same period net glutamine efflux from denervated hindlimbs [i.e., arteriovenous (a-v) concentration differences x blood flow] increased 3.5-fold (from -6.72 +/- 1.73 to -26 +/- 4.81 nmol.min-1.g-1, P less than 0.001). Gastrocnemius glutamine synthetase activity fell 48% after denervation (from 475 +/- 81 to 248 +/- 39 nmol.min-1.g-1, P less than 0.001), but glutaminase activity was not significantly altered (17 nmol.min-1.g-1). The maximal activity (Vmax) of the unidirectional Na(+)-dependent glutamine transporter (system Nm) was depressed by 45% from 1,020 +/- 104 to 571 +/- 9 nmol.min-1.g-1 (P less than 0.01), but the concentration at which transport was half maximal (Km) was not significantly altered (control 8.1 +/- 0.6 mM; denervated 6.52 +/- 0.12). Hindlimb denervation resulted in an increase of intramuscular Na+ by 17% and a fall of K+ by 12%, and the resting membrane potential in isolated muscles decreased from -75 +/- 10 to -59.5 +/- 5.5 mV. Membrane potential of perfused denervated muscle, isolated after acute addition of the Na+ channel blocker tetrodotoxin (TTX, 3 microM), repolarized to -66.4 +/- 3.2 mV. In perfused denervated preparations TTX caused an acute recovery of Vmax of unidirectional glutamine transport to 848 +/- 75 nmol.min-1.g-1; Km was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Skeletal muscle glutamine transport, intramuscular glutamine concentration, and muscle-protein turnover.

This article reviews work we have carried out to investigate (1) the transport mechanisms responsible for the high distribution ratio of free glutamine commonly observed in skeletal muscle; (2) the fall in the distribution ratio that accompanies starvation, injury and chronic disease, whether directly involving muscle or not; and (3) the effect of modulation of intracellular free-glutamine concentration on protein synthesis and breakdown in skeletal muscle. We suggest that the results are consistent with the controlling role of the muscle membrane glutamine-sodium cotransporter in the regulation of the intracellular glutamine pool, the existence of pathophysiological mechanisms for the modulation of intramuscular glutamine and anabolic effects of glutamine in promoting protein synthesis, with a smaller effect in reducing protein breakdown. The mechanisms by which glutamine affects skeletal muscle protein turnover, and thus muscle protein balance, and the extent of the net flow of amino acids between the periphery and the viscera are unknown as yet, but the results suggest that modulation of transporter activity may offer the possibility of therapeutic intervention to reduce muscle wasting associated with injury and disease.

Animals↗