Chronic hypoxia alters nitric oxide-dependent pulmonary vascular responses in lungs of newborn pigs

Fike, Candice D., and Mark R. Kaplowitz. Chronichypoxia alters nitric oxide-dependent pulmonary vascular responses inlungs of newborn pigs. J. Appl.Physiol. 81(5): 2078-2087, 1996.Almost all ofthe studies evaluating the effect of chronic hypoxia on lung nitricoxide production have been performed in adult animals. Because resultsof studies in adult lungs should not be extrapolated to represent thenewborn lung, we performed studies to determine whether decreasednitric oxide production might be involved in the pathogenesis ofchronic hypoxia-induced pulmonary hypertension in newborns. We keptnewborn pigs in chambers filled with room air (control) or 11-12%O₂ for either 3-5 (short) or10-12 (long) days. Using isolated lungs, we measured pulmonary vascular responses to agents that either stimulate or inhibit thesynthesis of nitric oxide. To define the vascular sites of alteredproduction of nitric oxide, we applied the micropuncture technique andmeasured small venular pressures before and after treatment with anitric oxide synthesis inhibitor. Pulmonary vascular responses toacetylcholine were blunted in chronically hypoxic piglets of both theshort and long groups. The nitric oxide synthesis inhibitor had adifferent effect in the lungs of control piglets than in those ofchronically hypoxic piglets of the long but not of the short group. Forthe long group, the nitric oxide synthesis inhibitors causedconstriction of both arteries and veins in lungs of control but not ofchronically hypoxic piglets. These findings support the idea thatdecreased pulmonary vascular nitric oxide production occurs withchronic hypoxia in newborn pigs and might therefore contribute to thepathogenesis of pulmonary hypertension in newborns.

     

Anatomic distribution of pulmonary vascular compliance

Presson, Robert G., Jr., Said H. Audi, Christopher C. Hanger, Gerald M. Zenk, Richard A. Sidner, John H. Linehan, Wiltz W. Wagner, Jr., and Christopher A. Dawson. Anatomic distribution ofpulmonary vascular compliance. J. Appl.Physiol. 84(1): 303-310, 1998.Previously, thepressure changes after arterial and venous occlusion have been used tocharacterize the longitudinal distribution of pulmonary vascularresistance with respect to vascular compliance using compartmentalmodels. However, the compartments have not been defined anatomically.Using video microscopy of the subpleural microcirculation, we havemeasured the flow changes in ~40-µm arterioles and venules aftervenous, arterial, and double occlusion maneuvers. The quasi-steadyflows through these vessels after venous occlusion permitted anestimation of the compliance in three anatomic segments: arteries >40µm, veins >40 µm, and vessels <40 µm in diameter. We foundthat ~65% of the total pulmonary vascular compliance was in vessels<40 µm, presumably mostly capillaries. The transient portions ofthe pressure and flow data after venous, arterial, and double occlusionwere consistent with most of the arterial compliance being upstreamfrom most of the arterial resistance and most of the venous compliancebeing downstream from most of the venous resistance.

     

Nature and site of action of endogenous nitric oxide in vasculature of isolated pig lungs

Cremona, George, Tim Higenbottam, Motoshi Takao, Edward A. Bower, and Leslie W. Hall. Nature and site of action of endogenousnitric oxide in vasculature of isolated pig lungs. J. Appl. Physiol. 82(1): 23-31, 1997.The site ofaction of endogenous and exogenous nitric oxide (NO) in isolated piglungs was investigated by using arterial, double, and venous occlusion,which allowed precapillary, postcapillary, and venous segments to bepartitioned into arterial, precapillary, postcapillary, and venoussegments. N^G-nitro-L-arginine(L-NNA;10⁵ M) increased resistancein the arterial (35 ± 6.6%, P = 0.003), precapillary (39.3 ± 5.1%,P = 0.001), and venous (18.3 ± 4.8%, P = 0.01) segments,respectively. Sodium nitroprusside(10⁵ M) and NO (80 parts/million) reversed the effects ofL-NNA. Total pulmonary vascularresistance fell with increasing flow, due to a fall in precapillaryresistance and dynamic resistance, and was significantlylower than mean total resistance.L-NNA increased the resistancesbut did not alter the pattern of the pressure-flow relationships. It isconcluded that, in isolated pig lungs, the effect of endogenous NOseems to be dependent on flow in the arterial segment and independentof flow in the precapillary segment, but variation of its release doesnot appear to be fundamental to accommodation to changes in steadyflow.

     

Nitric oxide decreases lung liquid production in fetal lambs

Cummings, James J. Nitric oxide decreases lung liquidproduction in fetal lambs. J. Appl.Physiol. 83(5): 1538-1544, 1997.To examine theeffect of nitric oxide on fetal lung liquid production, I measured lungliquid production in fetal sheep at 130 ± 5 days gestation (range122-137 days) before and after intrapulmonary instillation ofnitric oxide. Thirty-one studies were done in which net lung luminalliquid production (Jv) was measured by plotting the change in lung luminal liquid concentration ofradiolabeled albumin, an impermeant tracer that was mixed into the lungliquid at the start of each study. To see whether changes inJvmight be associated with changes in pulmonary hemodynamics, pulmonary and systemic pressures were measured and left pulmonary arterial flowwas measured by an ultrasonic Doppler flow probe. Variables weremeasured during a 1- to 2-h control period and for 4 h after a smallbolus of isotonic saline saturated with nitric oxide gas (10 or 100%)was instilled into the lung liquid. Control (saline) instillations(n = 6) caused no change in anyvariable over 6 h. Nitric oxide instillation significantly decreasedJv and increased pulmonary blood flow;these effects were sustained for 1-2 h. There was also asignificant but transient decrease in pulmonary arterial pressure. Thusintrapulmonary nitric oxide causes a significant decrease in lungliquid and is associated with a decrease in pulmonary vascularresistance. In a separate series of experiments either amiloride orbenzamil, which blocks Na⁺transport, was mixed into the lung liquid before nitric oxide instillation; still, there was a similar reduction in lung liquid production. Thus the reduction in lung liquid secretion caused bynitric oxide does not appear to depend on apicalNa⁺ efflux.

     

Segmental pulmonary vascular responses to ATP in rat lungs: role of nitric oxide

Hakim, Tawfic S., Lara Ferrario, Jeffrey C. Freedman, RobertE. Carlin, and Enrico M. Camporesi. Segmental pulmonary vascularresponses to ATP in rat lungs: role of nitric oxide. J. Appl. Physiol. 82(3): 852-858, 1997.ATP exhibits vascular pressor and depressor responses in a dose-and tone-dependent manner. The vascular site of ATP-induced contractionor dilation has not previously been characterized. Using the vascularocclusion technique, we investigated the effects of ATP in isolated rat lungs perfused with autologous blood (hematocrit = 20%) and described its action during resting and elevated tone in terms of changes inresistances of the small and large arteries and veins. During restingtone, ATP (10⁵M)

     

Effects of chronic exercise and deconditioning on platelet function in women

Wang, Jong-Shyan, Chauying J. Jen, and Hsiun-Ing Chen.Effects of chronic exercise and deconditioning on plateletfunction in women. J. Appl. Physiol.83(6): 2080-2085, 1997.To investigate the effects of chronicexercise and deconditioning on platelet function in women, 16 healthysedentary women were divided into control and exercise groups. Theexercise group cycled on an ergometer at 50% maximal oxygenconsumption for 30 min/day, 5 days/wk, for two consecutive menstrualcycles and then were deconditioned for three menstrual cycles. Duringthis period, platelet adhesiveness on a fibrinogen-coated surface,ADP-induced platelet aggregation and intracellular calciumconcentration elevation, guanosine 3,5-cyclic monophosphate (cGMP) content in platelets, and plasma nitric oxide metabolite levels were measured before and immediately after a progressive exercise test in the midfollicular phase. Ourresults indicated that, after exercise training,1) resting heart rates and bloodpressures were reduced, and exercise performance was improved;2) resting platelet function wasdecreased, whereas plasma nitrite and nitrate levels and platelet cGMPcontents were enhanced; and 3) thepotentiation of platelet function by acute strenuous exercise wasdecreased, whereas the increases in plasma nitrite and nitrate levelsand platelet cGMP contents were enhanced by acuteexercise. Furthermore, deconditioning reversed these training effects. This implies that training-induced platelet functional changes in women in the midfollicular phase may be mediatedby nitric oxide.

     

Evidence that nitric oxide increases glucose transport in skeletal muscle

Balon, Thomas W., and Jerry L. Nadler. Evidence thatnitric oxide increases glucose transport in skeletal muscle.J. Appl. Physiol. 82(1): 359-363, 1997.Nitric oxide synthase (NOS) is expressed in skeletal muscle.However, the role of nitric oxide (NO) in glucose transport in thistissue remains unclear. To determine the role of NO in modulatingglucose transport, 2-deoxyglucose (2-DG) transport was measured in ratextensor digitorum longus (EDL) muscles that were exposed to either amaximally stimulating concentration of insulin or to an electricalstimulation protocol, in the presence ofN^G-monomethyl-L-arginine,a NOS inhibitor. In addition, EDL preparations were exposed to sodiumnitroprusside (SNP), an NO donor, in the presence of submaximal andmaximally stimulating concentrations of insulin. NOS inhibition reducedboth basal and exercise-enhanced 2-DG transport but had no effect oninsulin-stimulated 2-DG transport. Furthermore, SNP increased 2-DGtransport in a dose-responsive manner. The effects of SNP and insulinon 2-DG transport were additive when insulin was present inphysiological but not in pharmacological concentrations. Chronictreadmill training increased protein expression of both type I and typeIII NOS in soleus muscle homogenates. Our results suggest that NO maybe a potential mediator of exercise-induced glucose transport.

     

Nitric oxide and thermoregulation during exercise in the horse

Mills, Paul C., David J. Marlin, Caroline M. Scott, andNicola C. Smith. Nitric oxide and thermoregulation during exercise in the horse. J. Appl. Physiol. 82(4):1035-1039, 1997.The effect of inhibition of nitric oxideproduction on sweating rate (SR) and on core, rectal, and tail skintemperatures was measured in five Thoroughbred horses during exerciseof variable intensity on a high-speed treadmill. A standard exercisetest consisting of three canters [~55% maximumO₂ uptake(O_{2 max})], withwalking (~9%O_{2 max}) and trotting(~22% O_{2 max})between each canter, was performed twice (control or test), in randomorder, by each horse.N^G-nitro-L-arginine methyl ester(L-NAME; 20 mg/kg), acompetitive inhibitor of nitric oxide synthase, was infused into thecentral circulation and induced a significant reduction in the SRmeasured on the neck (31.6 ± 6.4 vs. 9.7 ± 4.2 g · min¹ · m²;69%) and rump (14.7 ± 5.2 vs. 4.8 ± 1.6 g · min¹ · m²;67%) of the horses during canter (P < 0.05). Significant increases in core, rectal, and tailskin temperatures were also measured (P < 0.05).L-Arginine (200 mg/kg iv)partially reversed the inhibitory effects ofL-NAME on SR, but core, rectal,and tail skin temperatures continued to increase(P < 0.05), suggesting a cumulationof body heat. The results support the contention that nitric oxidesynthase inhibition diminishes SR, resulting in elevated core andperipheral temperatures leading to deranged thermoregulation duringexercise. The inhibition of sweating byL-NAME may be related toperipheral vasoconstriction but may also involve the neurogenic controlof sweating.

     

Physiological and Genomic Consequences of Intermittent Hypoxia: Selected Contribution: Altered vascular reactivity in arterioles of chronic intermittent hypoxic rats

Recurrentepisodic hypoxia (EH) is a feature of sleep apnea that may beresponsible for some chronic cardiovascular sequelae such as systemichypertension. Chronic EH (8 h/day for 35 days) causes elevation ofdiurnal resting (unstimulated) mean arterial blood pressure (MAP) inthe rat. We used in vivo video microscopy to examine arteriolarreactivity in the cremaster muscle of male Sprague-Dawley ratssubjected to 35 days of EH. Cremaster muscles of EH (n = 6) and control (n = 6) rats were exposed to varying doses of norepinephrine (NE) (10¹⁰ to 10⁵M), ACh (10⁹ to 10⁵ M), and endothelin-1(10¹² to 10⁸ M). In a separate experiment,EH (n = 5) and control (n = 6) ratswere given one dose of a nitric oxide synthase (NOS) inhibitor N^G-nitro-L-arginine methylester (L-NAME; 10⁵ M). We also examinedendothelial NOS mRNA from the kidneys of EH-stimulated and control(unstimulated) rats. Telemetry-monitored EH rats showed a 16-mmHgincrease in MAP over 35 days, whereas control rats showed no change.The response to NE and endothelin-1 were similar for EH and controlrats. ACh vasodilatation of arterioles in EH rats was significantlyattenuated compared with that of controls. The degree ofvasoconstriction in response to blockade of the nitric oxide system byL-NAME was significantly less (83% of baseline diameterwith L-NAME) for arterioles of EH rats compared with thatfor controls (61% of baseline diameter), implying lower basal restingnitric oxide release in the EH rats. Whole kidney mRNA endothelial NOSlevels were not different between groups. These data support thehypothesis that chronic elevation of blood pressure associated with EHinvolves increased peripheral resistance from decreased basal releaseor production of nitric oxide after 35 days of EH.

     

Ventilatory effects of specific carotid body hypocapnia and hypoxia in awake dogs

Smith, Curtis A., Craig A. Harms, Kathleen S. Henderson, andJerome A. Dempsey. Ventilatory effects of specific carotid bodyhypocapnia and hypoxia in awake dogs. J. Appl.Physiol. 82(3): 791-798, 1997.Specific carotidbody (CB) hypocapnia in the 10-Torr (less than eupneic) rangereduced ventilation in the awake and sleeping dog to the same degree asdid CB hyperoxia [CB PO₂ (PCB_O2);>500 Torr; C. A. Smith, K. W. Saupe, K. S. Henderson, and J. A. Dempsey. J. Appl. Physiol. 79:689-699, 1995], suggesting a powerful inhibitory effect ofhypocapnia at the carotid chemosensor over a range ofPCO₂ encountered commonly inphysiological hyperpneas. The primary purpose of this study was toassess the ventilatory effect of CB hypocapnia on the ventilatoryresponse to concomitant CB hypoxia. The secondary purpose was to assess the relative gains of the CB and central chemoreceptors to hypocapnia. In eight awake female dogs the vascularly isolated CB was perfused withhypoxic blood (mild,PCB_O2 50 Torr or severe, PCB_O2 36 Torr) in a background of normocapnia or hypocapnia (10 Torr lessthan eupneic arterial PCO₂) in theperfusate. The systemic (and brain) circulation was normoxicthroughout, and arterial PCO₂ was notcontrolled (poikilocapnia). With CB hypocapnia, the peak ventilation(range 19-27 s) in response to hypoxic CB perfusion increased 48%(mild) and 77% (severe) due to increased tidal volume. When CBhypocapnia was present, these increases in ventilation were reduced to21 and 27%, respectively. With systemic hypocapnia, with the isolatedCB maintained normocapnic and hypoxic for >70 s, the steady-statepoikilocapnic ventilatory response (i.e., to systemic hypocapnia alone)decreased 15% (mild CB hypoxia) and 27% (severe CB hypoxia) from thepeak response, respectively. We conclude that carotid body hypocapniacan be a major source of inhibitory feedback to respiratory motoroutput during the hyperventilatory response to hypoxic carotid bodystimulation.

     

Determination of production of nitric oxide by lower airways of humans---theory

Hyde, Richard W., Edgar J. Geigel, Albert J. Olszowka, JohnA. Krasney, Robert E. Forster II, Mark J. Utell, and Mark W. Frampton.Determination of production of nitric oxide by the lower airwaysof humanstheory. J. Appl. Physiol.82(4): 1290-1296, 1997.Exercise and inflammatory lung disorderssuch as asthma and acute lung injury increase exhaled nitric oxide(NO). This finding is interpreted as a rise in production of NO by thelungs (NO)but fails to take into account the diffusing capacity for NO(DNO) that carries NO into thepulmonary capillary blood. We have derived equations to measureNO from thefollowing rates, which determine NO tension in the lungs(PL) at any moment from 1) production(NO);2) diffusion, whereDNO(PL) = rate of removal by lung capillary blood; and3) ventilation, whereA(PL)/(PB  47) = the rate of NO removal by alveolar ventilation(A) and PB is barometric pressure. During open-circuit breathingwhen PL is not in equilibrium,d/dtPL[V_L/(PB  47)] (where V_L is volumeof NO in the lower airways) = NO  DNO(PL)  A(PL)/(PB  47). When PL reaches asteady state so that d/dt = 0 andA iseliminated by rebreathing or breath holding, then PL = NO/DNO.PL can be interpreted as NOproduction per unit of DNO. Thisequation predicts that diseases that diminishDNO but do not alterNO willincrease expired NO levels. These equations permit precise measurementsof NO thatcan be applied to determining factors controlling NO production by thelungs.

     

Endothelial cell dilatory pathways link flow and wall shear stress in an intact arteriolar network

Frame, Mary D. S., and Ingrid H. Sarelius. Endothelialcell dilatory pathways link flow and wall shear stress in an intactarteriolar network. J. Appl. Physiol.81(5): 2105-2114, 1996.Our purpose was to determine whether theendothelial cell-dependent dilatory pathways contribute to theregulation of flow distribution in an intact arteriolar network. Cellflow, wall shear stress (T),diameter, and bifurcation angle were determined for four sequentialbranches of a transverse arteriole in the superfused cremaster muscleof pentobaribtal sodium (Nembutal, 70 mg/kg)-anesthetized hamsters(n = 51). Control cell flow wassignificantly greater into upstream than into downstream branches[1,561 ± 315 vs. 971 ± 200 (SE) cells/s,n = 12]. Tissue exposure to 50 µMN-nitro-L-arginine + 50 µM indomethacin (L-NNA + Indo) produced arteriolar constriction of 14 ± 4% and decreasedflow into the transverse arteriole. More of the available cell flow wasdiverted to downstream branches, yet flow distribution remainedunequal. Control T was higherupstream than downstream (31.3 ± 6.8 vs. 9.8 ± 1.5 dyn/cm²).L-NNA + Indo decreasedT upstream and increasedT downstream to become equal inall branches, in contrast to flow. To determine whether constriction ingeneral induced the same changes, 5%O₂ (8 ± 4% constriction) or10⁹ M norepinephrine (NE;4 ± 3% constriction) was added to the tissue (n = 7). WithO₂, flow was redistributed tobecome equal into each branch. With NE, flow decreased progressivelymore into the first three branches. The changes in flow distributionwere thus predictable and dependent on the agonist. WithO₂ or NE, the spatial changes inflow were mirrored by spatial changes inT. Changes in diameter and incell flux were not related forL-NNA + Indo (r = 0.45),O₂(r = 0.07), or NE(r = 0.36). For all agonists, when thebifurcation angle increased, cell flow to the branch decreasedsignificantly, whereas if the angle decreased, flow was relativelypreserved; thus active changes in bifurcation angle may influence redcell distribution at arteriolar bifurcations. Thus, when theendothelial cell dilatory pathways were blocked, the changes in flowand in T were uncoupled; yet when they were intact, flowand T changed together.

     

Role of inhibition of nitric oxide production in monocrotaline-induced pulmonary hypertension

Mathew, Rajamma, Elizabeth S. Gloster, T. Sundararajan, Carl I. Thompson, Guillermo A. Zeballos, andMichael H. Gewitz. Role of inhibition of nitric oxide productionin monocrotaline-induced pulmonary hypertension. J. Appl. Physiol. 82(5): 1493-1498, 1997.Monocrotaline (MCT)-induced pulmonary hypertension (PH) isassociated with impaired endothelium-dependent nitric oxide(NO)-mediated relaxation. To examine the role of NO in PH,Sprague-Dawley rats were given a single subcutaneous injection ofnormal saline [control (C)], 80 mg/kg MCT, or the same doseof MCT and a continuous subcutaneous infusion of 2 mg · kg¹ · day¹of molsidomine, a NO prodrug (MCT+MD). Two weeks later, plasma NO₃ levels, pulmonary arterialpressure (Ppa), ratio of right-to-left ventricular weights (RV/LV) toassess right ventricular hypertrophy, and pulmonary histology wereevaluated. The plasma NO₃ level inthe MCT group was reduced to 9.2 ± 1.5 µM(n = 12) vs. C level of 17.7 ± 1.8 µM (n = 8; P < 0.02). In the MCT+MD group,plasma NO₃ level was 12.3 ± 2.0 µM (n = 8). Ppa and RV/LV in theMCT group were increased compared with C [Ppa, 34 ± 3.4 mmHg(n = 6) vs. 19 ± 0.8 mmHg(n = 8) and 0.41 ± 0.01 (n = 9) vs. 0.25 ± 0.008 (n = 8), respectively;P < 0.001]. In the MCT+MDgroup, Ppa and RV/LV were not different when compared with C [19 ± 0.5 mmHg (n = 5) and 0.27 ± 0.01 (n = 9), respectively;P < 0.001 vs. MCT]. Medial wall thickness of lung vessels in the MCT group was increased comparedwith C [31 ± 1.5% (n = 9)vs. 13 ± 0.66% (n = 9);P < 0.001], and MDpartially prevented MCT-induced pulmonary vascular remodeling [22 ± 1.2% (n = 11);P < 0.001 vs. MCT and C].These results indicate that a defect in the availability of bioactive NO may play an important role in the pathogenesis of MCT-induced PH.

     

Cytochrome c mRNA in skeletal muscles of immobilized limbs

Booth, Frank W., Wei Lou, Marc T. Hamilton, and Zhen Yan.Cytochrome c mRNA in skeletalmuscles of immobilized limbs. J. Appl.Physiol. 81(5): 1941-1945, 1996.Even thoughimmobilization of a slow skeletal muscle in a lengthened positionprevents muscle atrophy, it is unknown whether this treatment wouldprevent a decrease in mitochondrial quantity. We found that, regardless of muscle length in immobilized limbs, the mRNA of a marker for mitochondrial quantity, cytochrome c,decreased. Cytochrome c mRNA permilligram of muscle was 62 and 72% less 1 wk after fixation of thesoleus muscle in shortened and lengthened positions, respectively, thanage-matched controls. Cytochrome cmRNA per milligram wet weight was 36 and 32% less in the tibialisanterior muscle fixed for 1 wk in the shortened and lengthenedpositions, respectively, compared with age-matched controls. Recently,in the 3-untranslated region of cytochromec mRNA a novel RNA-protein interactionthat decreases in chronically stimulated rat skeletal musclewas identified.[Z. Yan, S. Salmons, Y. L. Dang, M. T. Hamilton, and F. W. Booth. Am. J. Physiol. 271 (CellPhysiol. 40): C1157- C1166,1996]. The RNA-protein interaction inthe 3-untranslated region of cytochrome c mRNA in soleus and tibialis anteriormuscles was unaffected by fixation in either shortened or lengthenedposition. We conclude that, whereas lengthening muscle during limbfixation abates the loss of total muscle protein, the percentagedecrease in cytochrome c mRNA isproportionally greater than total protein. This suggests that thedesign of countermeasures to muscle atrophy should include differentexercises to maintain total protein and mitochondria.

     

Mechanism controlling sleep organization of the obese Zucker rats

Megirian, David, Jacek Dmochowski, and Gaspar A. Farkas. Mechanism controlling sleep organization ofthe obese Zucker rat. J. Appl.Physiol. 84(1): 253-256, 1998.We tested thehypothesis that the obese (fa/fa)Zucker rat has a sleep organization that differs from that of leanZucker rats. We used the polygraphic technique to identify and toquantify the distribution of the three main states of the rat:wakefulness (W), non-rapid-eye-movement (NREM), and rapid-eye-movement(REM) sleep states. Assessment of states was made with light present(1000-1600), at the rats thermoneutral temperature of 29°C.Obese rats, compared with lean ones, did not show significantdifferences in the total time spent in the three main states. Whereasthe mean durations of W and REM states did not differ statistically,that of NREM did (P = 0.046). However,in the obese rats, the frequencies of switching from NREM sleep to W,which increased, and from NREM to REM sleep, which decreased, werestatistically significantly different(P = 0.019). Frequency of switchingfrom either REM or W state was not significantly different. We concludethat sleep organization differs between lean and obese Zucker rats andthat it is due to a disparity in switching from NREM sleep to either Wor REM sleep and the mean duration of NREM sleep.

     

Expression of the inducible nitric oxide synthase gene in diaphragm and skeletal muscle

Thompson, Marita, Lisa Becker, Debbie Bryant, Gary Williams,Daniel Levin, Linda Margraf, and Brett P. Giroir. Expression ofthe inducible nitric oxide synthase gene in diaphragm and skeletal muscle. J. Appl. Physiol. 81(6):2415-2420, 1996.Nitric oxide (NO) is a pluripotent molecule thatcan be secreted by skeletal muscle through the activity of the neuronalconstitutive isoform of NO synthase. To determine whether skeletalmuscle and diaphragm might also express the macrophage-inducible formof NO synthase (iNOS) during provocative states, we examined tissuefrom mice at serial times after intravenous administration ofEscherichia coli endotoxin. In thesestudies, iNOS mRNA was strongly expressed in the diaphragm and skeletalmuscle of mice 4 h after intravenous endotoxin and was significantlydiminished by 8 h after challenge. Induction of iNOS mRNA was followedby expression of iNOS immunoreactive protein on Western immunoblots.Increased iNOS activity was demonstrated by conversion of arginine tocitrulline. Immunochemical analysis of diaphragmatic explants exposedto endotoxin in vitro revealed specific iNOS staining in myocytes, inaddition to macrophages and endothelium. These results may be importantin understanding the pathogenesis of respiratory pump failure duringseptic shock, as well as skeletal muscle injury during inflammation ormetabolic stress.

     

Phosphorylation of rat muscle acetyl-CoA carboxylase by AMP-activated protein kinase and protein kinase A

Winder, W. W., H. A. Wilson, D. G. Hardie, B. B. Rasmussen,C. A. Hutber, G. B. Call, R. D. Clayton, L. M. Conley, S. Yoon, and B. Zhou. Phosphorylation of rat muscle acetyl-CoA carboxylase byAMP-activated protein kinase and protein kinase A. J. Appl. Physiol. 82(1): 219-225, 1997This studywas designed to compare functional effects of phosphorylation of muscleacetyl-CoA carboxylase (ACC) by adenosine 3,5-cyclicmonophosphate-dependent protein kinase (PKA) and by AMP-activatedprotein kinase (AMPK). Muscle ACC (272 kDa) was phosphorylated and thensubjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresisfollowed by autoradiography. Functional effects of phosphorylation weredetermined by measuring ACC activity at different concentrations ofeach of the substrates and of citrate, an activator of the enzyme. Themaximal velocity(V_max) and theMichaelis constants(K_m) for ATP,acetyl-CoA, and bicarbonate were unaffected by phosphorylation by PKA.Phosphorylation by AMPK increased theK_m for ATP andacetyl-CoA. Sequential phosphorylation by PKA and AMPK, first withoutlabel and second with label, appeared to reduce the extent of label incorporation, regardless of the order. The activation constant (K_a) forcitrate activation was increased to the same extent by AMPKphosphorylation, regardless of previous or subsequent phosphorylation by PKA. Thus muscle ACC can be phosphorylated by PKA but with noapparent functional effects on the enzyme. AMPK appears to be the moreimportant regulator of muscle ACC.

     

Regression of hypoxic hypertension-induced changes in the elastic laminae of rat pulmonary arteries

Liu, S. Q. Regression of hypoxic hypertension-inducedchanges in the elastic laminae of rat pulmonary arteries.J. Appl. Physiol. 82(5):1677-1684, 1997.The elastic laminae of the pulmonary arteries(PAs) undergo a progressive structural change in hypoxic hypertension.This study focused on the reversibility of altered PA elastic laminaeof the rat due to hypoxic hypertension. The structure andcross-sectional area of the PA medial elastic laminae were examined byusing electron-microscopic and image-analytic approaches duringrecovery from 12 h and 10 days of hypoxic hypertension. At 12 h ofhypoxic hypertension, the elastic laminae, which appeared homogeneousin normal control animals, were reorganized into structures composed ofrandomly oriented filaments, with an increase in the cross-sectionalarea of 70%. At 10 days of hypoxic hypertension, the elastic laminaeappeared homogeneous in structure and normal in cross-sectional areadespite continuous exposure to hypoxia. During recovery from 12 h ofhypoxic hypertension, the medial elastic laminae regained theirhomogeneous structure and normal cross-sectional area afterday 2. During recovery from 10 days ofhypoxic hypertension, the medial elastic laminae changed from homogeneous to filamentous structures, with a progressively altered cross-sectional area that increased by 89% from recoveryday 0 to day10 and returned to the normal level onday 30. These changes were associatedwith alterations in the PA wall tensile stress. These results indicatedthat structural changes in the PA elastic laminae were reversible andthat the regression process depended on the duration of exposure tohypoxia, the state of the elastic laminae, and possibly the tensilestress level in the PA wall.

     

Chronic hormone replacement therapy alters thermoregulatory and vasomotor function in postmenopausal women

Brooks, E. M., A. L. Morgan, J. M. Pierzga, S. L. Wladkowski, J. T. O'Gorman, J. A. Derr, and W. L. Kenney. Chronic hormone replacement therapy alters thermoregulatory and vasomotor function in postmenopausal women. J. Appl.Physiol. 83(2): 477-484, 1997.This investigationexamined effects of chronic (2 yr) hormone replacement therapy (HRT),both estrogen replacement therapy (ERT) and estrogen plus progesteronetherapy (E+P), on core temperature and skin blood flow responses ofpostmenopausal women. Twenty-five postmenopausal women [9 not onHRT (NO), 8 on ERT, 8 on E+P] exercised on a cycle ergometer for1 h at an ambient temperature of 36°C. Cutaneous vascularconductance (CVC) was monitored by laser-Doppler flowmetry, and forearmvascular conductance (FVC) was measured by using venous occlusionplethysmography. Iontophoresis of bretylium tosylate was performedbefore exercise to block local vasoconstrictor (VC) activity at oneskin site on the forearm. Rectal temperature (T_re) was ~0.5°C lower forthe ERT group (P < 0.01) comparedwith E+P and NO groups at rest and throughout exercise. FVC: mean body temperature (T_b) and CVC:T_b curves were shifted~0.5°C leftward for the ERT group(P < 0.0001). Baseline CVC wassignificantly higher in the ERT group(P < 0.05), but there was nointeraction between bretylium treatment and groups once exercise wasinitiated. These results suggest that1) chronic ERT likely acts centrally to decrease T_re,2) ERT lowers theT_re at which heat-loss effector mechanisms are initiated, primarily by actions on active cutaneous vasodilation, and 3) addition ofexogenous progestins in HRT effectively blocks these effects.

     

Effect of cigarette smoke extract on arteriolar dilatation in vivo

Mayhan, William G., and Glenda M. Sharpe. Effect ofcigarette smoke extract on arteriolar dilatation in vivo.J. Appl. Physiol. 81(5):1996-2003, 1996.The goal of this study was to determine whethercigarette smoke extract alters dilatation of arterioles in vivo inresponse to agonists that produce activation of ATP-sensitive potassiumchannels and activation of adenylate cyclase. By using intravitalmicroscopy, we measured diameter of arterioles contained within themicrocirculation of the hamster cheek pouch during suffusion withagonists in the absence and presence of cigarette smoke extract (0.1, 0.5, and 1.0%). Before treatment with cigarette smoke extract,activation of ATP-sensitive potassium channels with aprikalim andcromakalim produced dose-related dilatation of cheek poucharterioles. Similarly, activation of adenylate cyclasewith isoproterenol and forskolin produced dose-related dilatation ofcheek pouch arterioles before treatment with cigarette smoke extract.Superfusion of 0.1% cigarette smoke extract did not change baselinediameter of arterioles and did not alter responses of cheek poucharterioles to activation of ATP-sensitive potassium channels andadenylate cyclase. Superfusion of 0.5 and 1.0% cigarette smoke extractalso did not alter baseline diameter of arterioles but did impairdilatation of arterioles in response to activation of ATP-sensitivepotassium channels and adenylate cyclase. These findings suggest thatcigarette smoke extract impairs dilatation of resistance arterioles inresponse to activation of important cellular dilator pathways.