Full Length Papers
Red cell pulmonary transit times through the healthy human lung
- G. S. Zavorsky, K. R. Walley, J. A. Russell
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- Published online by Cambridge University Press:
- 12 March 2003, pp. 191-200
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It has previously been postulated that rapid red cell capillary transit through the human lung plays a role in the mechanism of diffusion limitation in some endurance athletes. Methodological limitations currently prevent researchers from directly measuring pulmonary capillary transit times in humans during exercise; however, first pass radionuclide cardiography allows direct measurement of red blood cell (RBC) transit times through the whole lung at various exercise intensities. We examined the relationship between mean whole lung red cell pulmonary transit times (cardiopulmonary transit times or CPTT) and different levels of flow in 88 healthy humans (76 males, 12 females) from several studies (mean age 31 years). The pooled data suggest that the relationship between CPTT and cardiac index (CI), beginning at rest and progressing through to maximum exercise demonstrates that CPTT reaches its minimum value when CI is about 8.1 l m2 min-1 (2.5-3 times the CI value at rest), and does not significantly change with further increases in CI. Cardiopulmonary blood volume (CPBV) index also does not change significantly until CI reaches 2.5 to 3 times the CI value at rest and then increases roughly linearly after that point. Consequently, the systematic increase in CPBV index with increasing pulmonary blood flow between 8.1 and 20 l m2 min-1 displays an adaptive response of the cardiopulmonary system by augmenting CPBV (and perhaps pulmonary capillary blood volume through distension and recruitment) to offset the reduction in CPTT, as no significant difference in mean CPTT is observed between these levels of flow (P > 0.05). Therefore, these data demonstrate that CPBV does not reach maximum capacity during strenuous or maximum exercise. This does not support the principle of quarter-power allometric scaling for flow when explaining modifications during exercise. Therefore, we speculate that the observed relationships between CPTT, CBPV index and flow may prevent mean CPTT (and perhaps mean pulmonary capillary transit times) from decreasing below the threshold time required for oxygenation. Experimental Physiology (2003) 88.2, 191-200.
Effects of endotoxin exposure on cationic amino acid transporter function in ovine peripheral blood mononuclear cells
- Megan F. Clark, Michael C. Reade, C. A. R. Boyd, J. Duncan Young
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- 12 March 2003, pp. 201-208
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Rodent models of sepsis differ from clinical human disease in that humans make substantially less whole-body nitric oxide and have different cellular responses to endotoxin. Sheep, when exposed to endotoxin, behave in a manner more similar to humans. Many studies of rodent peripheral blood mononuclear cells (PBMCs) exposed to endotoxin demonstrate increased cationic amino acid transporter function (particularly through the y+ transporter) to supply arginine substrate to upregulated nitric oxide synthase. Whether this is true in sheep is not known. We have studied cationic amino acid transport in sheep PBMCs stimulated with endotoxin, using labelled lysine. PBMCs stimulated both in vitro and in vivo show an initial reduction in total and y+ lysine transport (after 1-2 h exposure to endotoxin): a previously undescribed effect of endotoxin. In in vitro activated cells, the reduction in y+ transport was prevented by the lipoxygenase inhibitor, nordihydroguaretic acid (NDGA), and the phospholipase inhibitor 4-bromophenacyl bromide (4-BPAB), but not cyclohexamide or a number of other inhibitors of intracellular second-messenger pathways. In contrast after 14 h incubation, the expected increase in total and y+ lysine transport was seen. The increase in y+ transport could be prevented by cyclohexamide, dexamethasone, ibuprofen, the protein kinase C inhibitor sphingosine, NDGA and 4-BPAB. These results suggest that in response to endotoxin exposure there is an initial decrease in y+ activity mediated by a lipoxygenase product, followed by a substantial increase in y+ activity mediated by the products of either cyclo-oxygenase or lipoxygenase. Cyclo-oxygenase and/or lipoxygenase inhibition might be useful in reducing arginine transport, and hence nitric oxide production, in these cells. Experimental Physiology (2003) 88.2, 201-208.
Hyperglycaemia inhibits thymidine incorporation and cell growth via protein kinase C, mitogen-activated protein kinases and nitric oxide in human umbilical vein endothelium
- Susana Rojas, Romina Rojas, Liliana Lamperti, Paola Casanello, Luis Sobrevia
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- 12 March 2003, pp. 209-219
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An elevated extracellular concentration of D-glucose (i.e. hyperglycaemia) inhibits cell proliferation and incorporation of the endogenous nucleoside thymidine into DNA in human umbilical vein endothelial cells (HUVECs). Cells in their log-phase of growth (3.7 ± 0.3 days, n = 27) incubated for 30 min with 25 mM D-glucose, but not with equimolar concentrations of L-glucose or D-mannitol, exhibited reduced [3H]thymidine incorporation and cell growth rate, with no change in cell viability (> 98 %), total DNA, protein content or cell volume. Incubation with D-glucose activated protein kinase C (PKC), endothelial NO synthase (eNOS), p42 and p44 mitogen-activated protein kinases (p42/44mapk), but inhibited superoxide dismutase (SOD). Incubation with D-glucose also increased cGMP and cAMP levels. The effect of D-glucose was blocked by the PKC inhibitor calphostin C, the MAP kinase kinase 1/2 (MEK1/2) inhibitor PD-98059, the eNOS inhibitor L-NAME, the protein kinase G (PKG) inhibitor KT-5823 and the protein kinase A (PKA) inhibitor KT-5720. In the presence of 5 mM D-glucose, [3H]thymidine incorporation and cell growth were reduced by the PKC activator phorbol 12-myristate 13-acetate (PMA), the NO donor S-nitroso-N-acetyl-L,D-penicillamine (SNAP), dibutyryl cGMP, dibutyryl cAMP and the Ca2+ ionophore A-23187. The effect of A-23187 was blocked by calphostin C and PD-98059. D-Glucose-dependent inhibition of thymidine incorporation and cell proliferation is associated with increased PKC, eNOS, and MEK1/2, but decreased SOD activity, and higher intracellular levels of cGMP, cAMP and Ca2+ in HUVECs. These are cellular mechanisms which may reduce endothelial cell growth in pathological conditions such as in diabetes mellitus or hyperglycaemia. Experimental Physiology (2003) 88.2, 209-219.
The effect of isoprenaline infusion on renal renin and angiotensinogen gene expression in the anaesthetised rat
- S. Mostafa Shid Moosavi, Edward J. Johns
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- 12 March 2003, pp. 221-227
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In this study, we investigated the ability of acute infusions of isoprenaline to alter renin and angiotensinogen gene expression in the kidney of rats anaesthetised with chloralose-urethane. Groups of rats received I.V. infusions of either saline or the β-adrenoceptor agonist isoprenaline at 400 ng kg-1 min-1 for 4 h. The isoprenaline infusion caused a sustained decrease in mean blood pressure of approximately 20 mmHg (P < 0.01), an increase in heart rate of 50 beats min-1 (P < 0.01) and reductions in urine flow and sodium excretion of 80-90 % (both P < 0.01). Renal blood flow and glomerular filtration rate were transiently reduced by 21 % (P < 0.01) and 61 % (P < 0.001), respectively, in the first hour, recovering to baseline levels after 4 h of infusion. At the end of the study, plasma renin activity was raised approximately 6-fold (P < 0.01) while renal renin and angiotensinogen mRNA levels were 1.8- and 1.5-fold higher (both P < 0.05) compared to the control group (saline infusion). The isoprenaline-induced renin secretion could have been mediated via the activation of β-adrenoceptors resulting in the exocytosis of renin-containing granules, with a smaller contribution being due to reduced renal haemodynamics. The increase in renal renin gene expression in response to isoprenaline was probably due primarily to the intracellular signalling processes acting directly on nuclear mechanisms. Similarly, the increased renal angiotensinogen gene expression most probably reflected a direct action of the isoprenaline. These findings provide evidence that catecholamines are involved in mechanisms that rapidly alter the expression of the genes of the renin-angiotensin system within the kidney. Experimental Physiology (2003) 88.2, 221-227.
Interactions between neural and hormonal mediators of renal vascular tone in anaesthetized rabbits
- Sarah-Jane Guild, Carolyn J. Barrett, Roger G. Evans, Simon C. Malpas
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- 12 March 2003, pp. 229-241
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We investigated how sympathetic nerve activity and vasoactive hormones interact in controlling renal haemodynamics in pentobarbitone-anaesthetized rabbits. Renal blood flow was progressively reduced by electrical stimulation (0.5-3 Hz) of the renal nerves, during renal arterial infusion of saline, vasoconstrictors (angiotensin II and [Phe2,Ile3,Orn8]-vasopressin), or vasodilators (acetylcholine, adrenomedullin and the nitric oxide donor methylamine hexamethylene NONOate (MAHMA NONOate). A frequency-rich stimulus was also applied to test whether the vasoactive agents affect the dynamic control of renal blood flow by sympathetic nerve activity. The vasodilators tended to increase renal blood flow, but only the effect of MAHMA NONOate was statistically significant. [Phe2,Ile3,Orn8]-vasopressin reduced medullary perfusion (by 61 ± 12 %) but not renal blood flow or cortical perfusion. Angiotensin II reduced renal blood flow (33 ± 3 %) and cortical perfusion (14 ± 5 %) but not medullary perfusion. Steady-state responses of renal blood flow and cortical perfusion during renal nerve stimulation were attenuated during infusion of acetylcholine and [Phe2,Ile3,Orn8]-vasopressin, while angiotensin II attenuated responses of medullary perfusion, and MAHMA NONOate and adrenomedullin had no significant effects. The dynamic response to sympathetic nerve activity (renal blood flow responded as a low pass filter with a pure time delay of ~664 ms) was not altered by the vasoactive agents. We conclude that some vasoactive agents can modulate steady-state renal haemodynamic responses to sympathetic nerve activity in a regionally specific manner, independent of their effects on baseline renovascular tone. However, they have little impact on the dynamic response of renal blood flow to sympathetic nerve activity. Experimental Physiology (2003) 88.2, 229-241.
Chronic blockade of neuronal nitric oxide synthase does not affect long-term control of blood pressure in normal, saline-drinking or deoxycorticosterone-treated rats
- Rosemary Wangensteen, Juan Sainz, Isabel Rodríguez-Gomez, Juan Manuel Moreno, Antonio Osuna, Félix Vargas
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- 12 March 2003, pp. 243-250
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It has been reported that long-term selective inhibition of neuronal nitric oxide synthase (nNOS) produces elevated blood pressure (BP) in normal rats. The present study was designed to analyse the possible influences of the sodium-retaining hormone deoxycorticosterone acetate (DOCA) and of an increased sodium intake on BP effects induced by the chronic blockade of nNOS with 7-nitroindazole (7NI). Two experiments were performed using 7NI at a dose of either 10 mg kg-1 day-1 (experiment 1) or 30 mg kg-1 day-1 (experiment 2). The following groups were used in both experiments: control rats, and rats that received either 1 % saline drinking water (Salt), deoxycorticosterone acetate (DOCA), 7NI, 7NI plus 1 % saline (7NI + Salt) or 7NI plus DOCA (7NI + DOCA). The tail systolic BP (SBP) was measured in all rats once a week. At the end of the experimental period, the mean arterial pressure (MAP) and metabolic, morphological and renal variables were measured. There were no significant differences in the tail SBP, final MAP or glomerular filtration rate between the experimental groups and the control group. In both experiments, the plasma renin activity (PRA) was significantly inhibited in the Salt groups and suppressed in the DOCA groups. The PRA significantly increased in the 7NI groups, whereas the 7NI + Salt and 7NI + DOCA groups showed a significant inhibition in PRA, especially compared to the 7NI groups in the two experiments. We conclude that chronic nNOS blockade is unable to increase BP in normal, saline-drinking or DOCA-treated rats. Furthermore, the nNOS blockade does not interfere with the counterbalance between renin and an increased sodium intake or retention. Experimental Physiology (2003) 88.2, 243-250.
Effect of brain serotoninergic stimulation on sodium appetite of euthyroid and hypothyroid rats
- D. Badauê-Passos Jr, R. R. Ventura, L. F. S. Silva, E. L. Olivares, L. C. Reis
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- 12 March 2003, pp. 251-260
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The aim of the present work was to investigate the role of the serotoninergic system in the control of sodium appetite of hypothyroid rats (HTR) by administering drugs that affect the serotoninergic activity, and to compare the same homeostatic behaviour in euthyroid rats (ETR) also given these drugs. Fenfluramine (FEN; 5.0 mg kg-1, I.P.), which releases serotonin in the brain, significantly reduced the intake of 1.8 % NaCl in HTR subjected to water and sodium depletion (depleted) or water, sodium and food deprivation (deprived) by 31 and 45 %, respectively, 120 min after FEN injection, compared to HTR that received vehicle alone. Similarly, administration of FEN to ETR reduced 1.8 % NaCl intake in depleted and deprived rats by 64 and 46 %, respectively. The presynaptic serotonin reuptake inhibitor fluoxetine (20.0 mg kg-1, I.P.) led to the inhibition of sodium appetite in HTR during the initial 30 min in depleted rats and for up to 60 min post-injection in deprived rats, while sodium appetite inhibition persisted for longer periods in ETR. The 5HT2C receptor agonist mCPP (5.0 mg kg-1, I.P.) caused a drastic reduction in sodium appetite in HTR and ETR in depleted and deprived rats, respectively, after 120 min. Prior administration of the 5HT2C receptor antagonist LY53857 (5.0 mg kg-1, I.P.) completely blocked the inhibitory action of mCPP on sodium appetite in both HTR and ETR. In summary, our results suggest that the recruitment of serotoninergic neurons involved in the modulation of sodium appetite seems to be decreased in hypothyroidism due to a probable deficiency in the cerebral signalling pathway. Experimental Physiology (2003) 88.2, 251-260.
Keratinocyte growth factor and epidermal growth factor can reverse the intestinal atrophy associated with elemental diets in mice
- Masaya Sasaki, Anthony J. FitzGerald, Nikki Mandir, Jorge Berlanga-Acosta, Robert A. Goodlad
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- 12 March 2003, pp. 261-267
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Elemental diets are associated with intestinal atrophy and reduced intestinal integrity. Growth factors such as keratinocyte growth factor (KGF) and epidermal growth factor (EGF) have considerable potential for the therapeutic reversal of such atrophy and may have greater actions if given in combination. We examined the effects of recombinant human KGF (rHuKGF), EGF and their combination on tissue mass, cell proliferation and crypt fission throughout the intestine of mice fed elemental diets. rHuKGF significantly increased the relative wet weight of the intestine, with EGF having a lesser effect. Cell proliferation of the stomach, small intestine and colon were significantly increased by rHuKGF, but EGF only increased proliferation in the small intestine. Crypt fission in the small intestine and colon was significantly decreased by rHuKGF. An interactive effect of rHuKGF and EGF on the weight of stomach and the proliferation of the fundus and antrum was observed. Moreover, an interactive effect of the agents was also seen on crypt fission in the colon. We concluded that (1) rHuKGF and EGF have significant trophic effects on the stomach, small intestine and colon, (2) these actions vary between different sites in the gastrointestinal tract, and (3) interactive effects occur. Experimental Physiology (2003) 88.2, 261-267.
Apoptosis-dependent acute lung injury and repair after intratracheal instillation of noradrenaline in rats
- Bruce D. Uhal, Heather Rayford, Jiaju Zhuang, Xiaopeng Li, Jeremy Laukka, Valerie Soledad-Conrad
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- 12 March 2003, pp. 269-275
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Earlier work in this laboratory showed that noradrenaline (NA) induces apoptosis in primary cultures of alveolar epithelial cells (AECs). Apoptosis of alveolar epithelial cells may promote the collapse of lung barrier function. On this basis we hypothesized that exogenous NA, administered by intratracheal (I.T.) instillation, might induce AEC apoptosis in vivo followed by acute lung injury. Delivery of NA (10 µM) I.T. into male Wistar rats increased labelling of both fragmented DNA, measured by in situ end labelling (ISEL), and the active form of caspase 3 (anti-Casp3) 6 and 20 h after administration (P < 0.05), but instillation of the vehicle alone (PBS) had no effect. Both ISEL and anti-Casp3 labelling were attenuated by concurrent I.T. delivery of the broad-spectrum caspase inhibitor ZVADfmk. After 6 h, most ISEL- and Casp3-positive cells were located in the surfaces of alveolar walls, but after 20 h more were found in alveolar spaces (P < 0.05). Instillation of NA also increased the bronchoalveolar lavage (BAL) content of fluorescent albumin (BODIPY-alb), which had previously been injected intravenously; the increase was reversed by concurrent ZVADfmk administration. These data suggest that NA-induced apoptosis of AECs in vivo is sufficient to invoke transient collapse of AEC barrier function that is rapidly repaired. Experimental Physiology (2003) 88.2, 269-275.
G protein-coupled receptor kinases 2 and 5 are differentially expressed in rat skeletal muscle and remain unchanged following β2-agonist administration
- Simon W. Jones, David J. Baker, Paul L. Greenhaff
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- 12 March 2003, pp. 277-284
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Chronic stimulation of β2-receptors with β2-agonists causes desensitisation, which in skeletal muscle is accompanied by myosin heavy chain (MHC) remodelling, similar to that observed in heart failure patients. However, the mechanisms for this skeletal muscle remodelling are not well established. G protein-coupled receptor kinases (GRKs) specifically phosphorylate and desensitise G protein-coupled receptors during periods of agonist activation. However, desensitisation associated with prolonged agonist activation alters β-adrenergic signalling, and downstream affects gene expression. We hypothesised that skeletal muscle remodelling induced by β2-agonist administration could be regulated by GRK expression. Therefore the aim of this study was firstly to characterise which, if any, of the six known isoforms of GRK were expressed in skeletal muscle and then secondly to determine whether remodelled skeletal muscle induced by chronic β2-agonist administration was accompanied by altered expression of GRK isoforms. Male Wistar rats were administered a β2-agonist daily for 8 weeks, and the expression of MHC and GRKs examined in gastrocnemius and soleus muscles. Treatment with β2-agonist caused a change in MHC in soleus from types I to IIA, and in gastrocnemius from MHC types IIA/IIX to IIB. Western blotting revealed that GRK2 and GRK5 were expressed in skeletal muscle. Furthermore, despite changes in MHC and differential muscle-specific expression of GRK isoforms, there was no significant change in expression of GRK2 and GRK5 in soleus or gastrocnemius following β2-agonist administration. In conclusion the level of GRK expression is unlikely to be responsible for MHC switching following chronic β2-receptor stimulation. Experimental Physiology (2003) 88.2, 277-284.
Static fusimotor action during locomotion in the decerebrated cat revealed by cross-correlation of spindle afferent activity
- R. Durbaba A. Taylor, S. R. Rawlinson, P. H. Ellaway
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- 12 March 2003, pp. 285-296
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Cross-correlation of the discharges of muscle spindle afferents in ankle extensor and flexor muscles has been used to reveal the activity of static gamma (γS) motoneurones innervating chain intrafusal muscle fibres during locomotion. In the anaesthetised cat, the cross-correlation of spindle afferents, jointly innervated by a γS-efferent with chain fibre contacts, showed short duration synchrony (2-8 ms) when the efferent was stimulated repetitively. In pre-mammillary decerebrated cats, the cross-correlograms of discharges of some pairs of spindle afferents showed similar short duration peaks of synchronisation and these were interpreted as being due to a common γS drive to chain intrafusal muscle fibres. The incidence of synchrony was low, and was similar at rest (5 % of pairs) and during treadmill locomotion (7 % of pairs). Phase dependence of synchrony was evident during locomotion in the flexor muscle. The synchrony of muscle spindle afferent discharge is discussed in relation to estimates of the numbers of spindles contacted by individual γS-efferents. Experimental Physiology (2003) 88.2, 285-296.
Cerebral metabolism is influenced by muscle ischaemia during exercise in humans
- Mads K. Dalsgaard, Lars Nybo, Yan Cai, Niels H. Secher
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- 12 March 2003, pp. 297-302
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Maximal exercise reduces the cerebral metabolic ratio (O2/(glucose + 1/2lactate)) to < 4 from a resting value close to 6, and only part of this decrease is explained by the 'intent' to exercise. This study evaluated whether sensory stimulation of brain by muscle ischaemia would reduce the cerebral metabolic ratio. In 10 healthy human subjects the cerebral arterial-venous differences (a-v differences) for O2, glucose and lactate were assessed before, during and after three bouts of 10 min cycling with equal workload: (1) control exercise at light intensity, (2) exercise that elicited a high rating of perceived exertion due to a 100 mmHg thigh cuff, and (3) exercise followed by 5 min of post-exercise muscle ischaemia that increased blood pressure by ~ 20 %. Control exercise did not significantly affect the a-v differences. However, during the recovery from exercise with thigh cuffs the cerebral metabolic ratio decreased from a resting value of 5.4 ± 0.2 to 4.0 ± 0.4 (mean ± S.E.M.; P < 0.05) as a discrete lactate efflux from the brain at rest shifted to a slight uptake. Also, following post-exercise muscle ischaemia, the cerebral metabolic ratio decreased to 4.5 ± 0.3 (P < 0.05). The results support the hypothesis that during exercise, cerebral metabolism is influenced both by the mental effort to exercise and by sensory input from skeletal muscles. Experimental Physiology (2003) 88.2, 297-302.
Book Review
Book Review: Degeneration and Regeneration in the Nervous System
- P.H. Ellaway
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- 12 March 2003, p. 303
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