bluuebunny/crossref_metadata_2025 huggingface dataset:
TNF-α-induced c-Fos generation in the nucleus of the solitary tract is blocked by NBQX and MK-801
Authors: Emch Gregory S. , Hermann Gerlinda E. , Rogers Richard C.
Published: December 2017

Previous studies have shown that identified neurons of the nucleus of the solitary tract (NST) are excited by the cytokine tumor necrosis factor-α (TNF-α). Vagal afferent connections with the NST are predominantly glutaminergic. Therefore, we hypothesized that TNF-α effects on NST neurons may be via modulation of glutamate neurotransmission. The present study used activation of the immediate early gene product c-Fos as a marker for neuronal activation in the NST. c-Fos expression was evaluated after microinjections of TNF-α in the presence or absence of either the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide disodium (NBQX) or the N-methyl-d- aspartate (NMDA) antagonist MK-801. To assess the specificity of the interaction between TNF-α and glutamate, c-Fos expression was also evaluated after injection of oxytocin (OT) (which has a direct excitatory effect in this area of the brain stem) in the presence and absence of NBQX or MK-801. c-Fos labeling was significantly increased in the NST after TNF-α exposure. Coinjection of either NBQX or MK-801 with TNF-α prevented significant c-Fos induction in the NST. Microinjections of OT also induced significant NST c-Fos elevation, but this expression was unaffected by coinjection of either antagonist with OT. These data lead us to conclude that TNF-α activation of NST neurons depends on glutamate and such an interaction is not generalized to all agonists that act on the NST.
PVN activation is suppressed by repeated hypoglycemia but not antecedent corticosterone in the rat
Authors: Evans Scott B. , Wilkinson Charles W. , Bentson Kathy , Gronbeck Pam , Zavosh Aryana , Figlewicz Dianne P.
Published: December 2017

The mechanism(s) underlying hypoglycemia-associated autonomic failure (HAAF) are unknown. To test the hypothesis that the activation of brain regions involved in the counterregulatory response to hypoglycemia is blunted with HAAF, rats were studied in a 2-day protocol. Neuroendocrine responses and brain activation (c-Fos immunoreactivity) were measured during day 2 insulin-induced hypoglycemia (0.5 U insulin · 100 g body wt−1· h−1iv for 2 h) after day 1 hypoglycemia (Hypo-Hypo) or vehicle. Hypo-Hypo animals demonstrated HAAF with blunted epinephrine, glucagon, and corticosterone (Cort) responses and decreased activation of the medial hypothalamus [the paraventricular (PVN), dorsomedial (DMH), and arcuate (Arc) nuclei]. To evaluate whether increases in day 1 Cort were responsible for the decreased hypothalamic activation, Cort was infused intracerebroventricularly (72 μg) on day 1 and the response to day 2 hypoglycemia was measured. Intracerebroventricular Cort infusion failed to alter the neuroendocrine response to day 2 hypoglycemia, despite elevating both central nervous system and peripheral Cort levels. However, day 1 Cort blunted responses in two of the same hypothalamic regions as Hypo-Hypo (the DMH and Arc) but not in the PVN. These results suggest that decreased activation of the PVN may be important in the development of HAAF and that antecedent exposure to elevated levels of Cort is not always sufficient to produce HAAF.
Estrogen-induced recovery of autonomic function after middle cerebral artery occlusion in male rats
Authors: Saleh Tarek M. , Cribb Alastair E. , Connell Barry J.
Published: December 2017

Several studies have provided evidence to suggest that estrogen results in a significant reduction (∼50%) in the size of the ischemic zone in the middle cerebral artery occlusion (MCAO) model of stroke in a rat. The current study was done to demonstrate whether this estrogen-induced reduction in infarct size is associated with normalization of the autonomic dysfunction observed in an acute model of stroke in male rats. Experiments were done in anesthetized (thiobutabarbitol sodium; 100 mg/kg) male Sprague-Dawley rats instrumented to record baseline and reflex changes in cardiovascular and autonomic parameters. Estrogen was intravenously administered 30 min before, immediately before, or 30 min after MCAO. Estrogen administration resulted in a recovery of autonomic function and prevented the detrimental changes in autonomic tone observed following a stroke. In addition, infarct size was significantly increased in the presence of the estrogen antagonist ICI-182,780. These results suggest that both pre- or poststroke estrogen administration prevents or reverses acute stroke-induced autonomic dysfunction and that endogenous estrogen levels in males can contribute to this neuroprotection.
Physiological effect of circulating glucagon on the hepatic membrane potential
Authors: Lutz Thomas A. , Estermann Alois , Geary Nori , Scharrer Erwin
Published: December 2017

The pancreatic hormone glucagon hyperpolarizes the liver cell membrane under various conditions. Here we investigated the physiological relevance of this effect by testing the influence of infusions of glucagon antiserum on the liver cell membrane potential in vivo. Intracellular microelectrode recordings of liver cells (up to 60/rat over 2 h) were done in anesthetized male rats. Livers were fixed in place, and recordings were done 10–30 min after intraperitoneal injections of glucagon or hepatic portal vein infusions of glucagon or specific polyclonal glucagon antibodies raised in rabbits. The isotonic lactose vehicle was used as a control for glucagon, and equal amounts of nonimmunized rabbit IgG were used as a control for glucagon antibodies. Intraperitoneal glucagon (400 μg/kg) hyperpolarized the liver cell membrane up to 12 mV, and intraportal glucagon (10 or 60 μg/kg) dose dependently hyperpolarized the liver cell membrane by 3–7 mV. Intraportal infusion of glucagon antiserum (in vitro binding capacity of 4 ng glucagon/rat) significantly depolarized the liver cell membrane by ∼2.5 mV. The effects of both glucagon and glucagon antiserum reversed after 60–90 min. We conclude that glucagon is a physiologically important modulator of the liver cell membrane potential.
Stimulation of multiple MAPK pathways by mechanical overload in the perfused amphibian heart
Authors: Aggeli Ioanna-Katerina S. , Gaitanaki Catherine , Lazou Antigone , Beis Isidoros
Published: December 2017

The mitogen-activated protein kinase (MAPK) signal transduction pathway activated by mechanical stress was investigated in the isolated perfused amphibian ( Rana ridibunda) heart. High perfusion pressure induced the rapid (30 s) and prolonged (30 min) phosphorylation of a p43-extracellular regulated kinase, a response almost completely inhibited by 25 μM PD-98059. c-Jun NH2-terminal kinase (JNK) was also phosphorylated with maximal values attained at 15 min and remained elevated over 30 min. In-gel kinase assays verified that phosphorylated JNKs are active, phosphorylating the transcription factor c-Jun. Furthermore, pressure overload rapidly stimulated the p38-MAPK phosphorylation (30 s), a transient process (5 min) abolished by 1 μM SB-203580. In-gel kinase assays revealed that with phosphorylation, active p38-MAPKs phosphorylate their substrate MAP kinase-activated protein kinase 2. Biochemical analysis along with immunohistochemical studies showed that with activation, the three MAPK subfamily members examined are localized not only in the cytoplasm but in the nucleus as well. Present results therefore demonstrate for the first time in an amphibian species the involvement of multiple MAPK pathways in the mechanical overload-induced adaptive responses of the heart as well as their possible physiological roles.
Hemodynamic response patterns to acute behavioral stressors resemble those to cocaine
Authors: Knuepfer Mark M. , Purcell Robert M. , Gan Qi , Le Khoi M.
Published: December 2017

Hemodynamic responses to cocaine vary greatly between animals, and the variability is related to the incidence of cocaine-induced cardiomyopathies and hypertension. The variability in cardiac output and systemic vascular resistance responses to cocaine in individuals is correlated with the responses to acute startle (air jet). This experiment was designed to determine whether responses to cocaine and to air jet are related to those evoked by a conditioned stimulus (tone preceding foot shock) and to an unconditioned stimulus (cold water). We verified the relationship in hemodynamic response patterns between cocaine and cold stress using selective receptor antagonists. Rats were instrumented with a pulsed Doppler flow probe on the ascending aorta for determination of cardiac output and with an arterial cannula for recording arterial pressure and heart rate. After recovery, some rats were tested multiple times with four different stimuli: air jet (6 trials), 15-s tone preceding 1-s foot shock (12 trials), cold water exposure (1 cm deep for 1 min, 4–12 trials), and cocaine (5 mg/kg iv, 4–6 trials) while hemodynamic parameters were recorded. Each stimulus was capable of eliciting a pressor response that was associated with variable changes in cardiac output. The cardiac output response to cocaine was correlated with the initial responses to each stressor in individual rats. Responses evoked by cold stress were most similar to those elicited by cocaine. Furthermore, nicardipine (25 μg/kg iv) or atropine methylbromide (0.5 mg/kg iv) pretreatment prevented the cardiac output differences to acute cold stress, as noted after cocaine administration. On the other hand, propranolol (1 mg/kg iv) exacerbated both the decrease in cardiac output and the stress-induced increase in systemic vascular resistance as previously reported with cocaine. Therefore, the initial response to cold water exposure is a reliable method of evoking characteristic hemodynamic response patterns that, as seen with cocaine, may provide a suitable model for identifying the causes for predilection to stress-induced cardiovascular disease.
Amylin potently activates AP neurons possibly via formation of the excitatory second messenger cGMP
Authors: Riediger Thomas , Schmid Herbert A. , Lutz T. , Simon E.
Published: December 2017

Amylin is secreted with insulin from the pancreas during and after food intake. One of the most potent actions of amylin in vivo is its anorectic effect, which is directly mediated by the area postrema (AP), a circumventricular organ lacking a functional blood-brain barrier. As we recently demonstrated, amylin also stimulates water intake most likely via its excitatory action on subfornical organ (SFO) neurons. Neurons investigated under equal conditions in an in vitro slice preparation of the rat AP were 15-fold more sensitive to amylin than SFO neurons. Amylin (10−11–10−8 M) excited 48% of 94 AP neurons tested; the remaining cells were insensitive. The average threshold concentration of the excitatory response was 10−10 M and, thus, close to physiological plasma concentrations. Coapplication of the amylin receptor antagonist AC-187 reduced amylin's excitatory effect. Amylin-mediated activation of AP neurons and antagonistic action of AC-187 were confirmed in vivo by c- fos studies. Peripherally applied amylin stimulated cGMP formation in AP and SFO neurons, as shown in immunohistochemical studies. This response was independent of nitric oxide (NO) formation in the AP, while coapplication of the NO synthase inhibitors N-monomethyl-l-arginine (100 mg/kg) and nitro-l-arginine methyl ester (50 mg/kg) blocked cGMP formation in the SFO. In contrast to the SFO, where NO-dependent cGMP formation seems to represent a general inhibitory transduction pathway, cGMP acts as an excitatory second messenger in the AP, since the membrane-permeable analog 8-bromo-cGMP stimulated 65% of all neurons tested ( n = 17), including seven of nine amylin-sensitive neurons (77%). The results indicate that the anorectic effect of circulating amylin is based on its excitatory action on AP neurons, with cGMP acting as a second messenger.
β-Adrenoceptor-mediated cell signaling in the neonatal heart and liver: responses to terbutaline
Authors: Auman J. T. , Seidler F. J. , Tate C. A. , Slotkin T. A.
Published: December 2017

Terbutaline, a β2-adrenoceptor (β2-AR) agonist, is a widely used tocolytic that also crosses the placenta to stimulate fetal β-ARs. The current study examines the effects of terbutaline administered to neonatal rats. Terbutaline (10 mg/kg sc) given on postnatal day ( PN) 2–5 or PN 11–14 elicited significant downregulation of both cardiac and hepatic β-ARs, with a much greater effect in the liver. Despite the reduction in cardiac β-ARs, receptor desensitization was absent as evidenced by the maintained ability of isoproterenol to stimulate adenylyl cyclase (AC) in membrane preparations. The underlying mechanism was dissected by using stimulants that operate at different points in the AC signaling pathway, NaF, forskolin, and Mn2+. When administered in the early neonatal period, terbutaline failed to evoke any changes in cardiac AC activity; however, treatment on PN 11–14 evoked heterologous sensitization downstream from the receptor, evidenced by increases in the response to NaF and forskolin. In the liver, neonatal terbutaline administration elicited a small (≈10%) decrease in the AC response to isoproterenol, an effect much smaller than the downregulation of β-ARs (>40%). In this tissue, desensitization was again offset by heterologous sensitization of AC signaling. These results indicate that, in the developing organism, β-AR-mediated cell signaling responses are maintained in the face of receptor downregulation through heterologous induction of downstream signaling elements. These unique responses serve to sustain β-AR signaling in the perinatal period.
The function of the sarcoplasmic reticulum is not inhibited by low temperatures in trout atrial myocytes
Authors: Hove-Madsen Leif , Llach Anna , Tort Lluis
Published: December 2017

The effect of temperature on sarcoplasmic reticulum (SR) Ca2+uptake and release was measured in trout atrial myocytes using the perforated patch-clamp technique. Depolarization of the myocyte for 10 s to different membrane potentials ( Vm) induced SR Ca2+uptake. The relationship between Vmand SR Ca2+uptake was not significantly changed by lowering the experimental temperature from 21 to 7°C, and the relationship between total cytosolic Ca2+and SR Ca2+uptake was similar at the two temperatures with a pooled Vmax= 66 amol/pF and K0.5= 4 amol/pF. Quantification of the Ca2+release from the SR elicited by 10-ms depolarizations to different Vmshowed an increasing SR Ca2+release at more positive Vmbetween −50 and +10 mV, whereas SR Ca2+release stagnated between +10 and +50 mV. Lowering of the temperature did not affect this relationship significantly, giving an SR Ca2+release of 1.71 and 1.54 amol/pF at 21 and 7°C, respectively. Furthermore, clearance of the SR Ca2+content slowed down inactivation of the L-type Ca2+current at both temperatures (the fast time constant increased significantly from 10.4 ± 1.9 to 15.0 ± 2.0 ms at 21°C and from 38 ± 15 to 73 ± 24 ms at 7°C). Thus the SR has the capacity to remove the entire Ca2+transient at physiologically relevant stimulation frequencies at both 21 and 7°C, although it is estimated that ∼40% of the total Ca2+transient is liberated from and reuptaken by the SR with continuous stimulation at 0.5 Hz independently of the experimental temperature.
Cloning and functional expression of an MIP (AQP0) homolog from killifish (Fundulus heteroclitus) lens
Authors: Virkki Leila V. , Cooper Gordon J. , Boron Walter F.
Published: December 2017

The major intrinsic protein (MIP) of lens fiber cells is a member of the aquaporin (AQP) water channel family. The protein is expressed at very high levels in lens fiber cells, but its physiological function is unclear. By homology to known AQPs, we have cloned a full-length cDNA encoding an MIP from the lens of killifish ( Fundulus heteroclitus). The predicted protein (263 amino acids; GenBank accession no. AF191906 ) shows 77% identity to amphibian MIPs, 70% identity to mammalian MIPs, and 46% identity to mammalian AQP1. Expression of MIPfun in Xenopus laevis oocytes causes an ∼40-fold increase in oocyte water permeability. This stimulation is comparable to that seen with AQP1 and substantially larger than that seen with other MIPs. The mercurials HgCl2and p-chloromercuribenzenesulfonate inhibit the water permeability of MIPfun by ∼25%. MIPfun is not permeable to glycerol, urea, or formic acid but is weakly permeable to CO2.
Progesterone does not alter osmotic regulation of AVP
Authors: Calzone Wendy L. , Silva Celso , Keefe David L. , Stachenfeld Nina S.
Published: December 2017

To test the hypothesis that progesterone, independent of estrogen, decreases the plasma osmotic threshold for arginine vasopressin (AVP) release and thirst onset, we compared AVP and thirst responses to hypertonic saline infusion (HSI) during administration of oral contraceptives (OCs) containing progesterone (OCP) with responses to infusion of OCs containing progesterone and estrogen (OCEP). Eight women (29 ± 2 yr) were infused with 3% NaCl (120 min, 0.1 ml · kg body wt−1 · min−1) and consumed fluid (90 min, 15 ml/kg body wt) in the early follicular and midluteal phases of a 28-day menstrual cycle and also after 4 wk of OCP and after 4 wk of OCEP in a randomized crossover design. Baseline plasma osmolality (Posm) was lower in the luteal phase (280 ± 1 mosmol/kgH2O) and during OCEP (283 ± 1 mosmol/kgH2O) than in the follicular phase (286 ± 1 mosmol/kgH2O, P < 0.05) but was unaffected by OCP (284 ± 1 mosmol/kgH2O). Posmremained lower in the follicular phase than in the luteal phase and with OCEP throughout the first 50 min of HSI. The mean abscissal plasma AVP concentration-Posm intercept was unaffected by OCP (267 ± 1 mosmol/kgH2O) but was greater in the follicular phase (273 ± 2 mosmol/kgH2O) than in the luteal phase (266 ± 4 mosmol/kgH2O) and with OCEP (268 ± 2 mosmol/kgH2O, P < 0.05). There were no differences in osmotic thresholds for thirst onset across experimental days. Despite the lower osmotic threshold for AVP release during the luteal phase and with OCEP, fluid balance, renal free water clearance, and Na+ regulation during HSI were unaffected by menstrual phase or OC treatment, indicating a lower osmotic operating point for body water balance. OCP did not affect osmotic AVP regulation, suggesting that progesterone does not affect osmotic fluid regulation through a mechanism independent of estrogen.
Evidence for central venous pressure resetting during initial exposure to microgravity
Authors: Convertino Victor A. , Ludwig David A. , Elliott James J. , Wade Charles E. ,   (With the Technical Assistance of Gary Muniz and Richard Owens)
Published: December 2017

We measured central venous pressure (CVP); plasma volume (PV); urine volume rate (UVR); renal excretion of sodium (UNa); and renal clearances of creatinine, sodium, and osmolality before and after acute volume infusion to test the hypothesis that exposure to microgravity causes resetting of the CVP operating point. Six rhesus monkeys underwent two experimental conditions in a crossover counterbalance design: 1) continuous exposure to 10° head-down tilt (HDT) and 2) a control, defined as 16 h/day of 80° head-up tilt and 8 h prone. After 48 h of exposure to either test condition, a 120-min course of continuous infusion of isotonic saline (0.4 ml · kg−1 · min−1 iv) was administered. Baseline CVP was lower ( P = 0.011) in HDT (2.3 ± 0.3 mmHg) compared with the control (4.5 ± 1.4 mmHg) condition. After 2 h of saline infusion, CVP was elevated ( P = 0.002) to a similar magnitude ( P = 0.485) in HDT (ΔCVP = 2.7 ± 0.8 mmHg) and control (ΔCVP = 2.3 ± 0.8 mmHg) conditions and returned to preinfusion levels 18 h postinfusion in both treatments. PV followed the same pattern as CVP. The response relationships between CVP and UVR and between CVP and UNa shifted to the left with HDT. The restoration of CVP and PV to lower preinfusion levels after volume loading in HDT compared with control supports the notion that lower CVP during HDT may reflect a new operating point about which vascular volume is regulated. These results may explain the ineffective fluid intake procedures currently employed to treat patients and astronauts.
Behavioral analysis of anorexia produced by hindbrain injections of AMPA receptor antagonist NBQX in rats
Authors: Zheng Huiyuan , Patterson Christiane , Berthoud Hans-Rudolf
Published: December 2017

The caudal brain stem integrates short-term feedback signals from the oral cavity and the food-handling abdominal viscera, as well as long-term homeostatic, cognitive, and emotional signals from the forebrain, to control ingestive behavior. Glutamate, acting on various receptor subtypes, plays a prominent role in this integrative process. Fourth ventricular injection of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptor blocker 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo[ f]quinoxaline-7-sulfonamide (NBQX, 0.5–5 nmol/3 μl) dose dependently suppressed intake of 15% sucrose in food-deprived and non-food-deprived rats compared with saline injection. Two consecutive paired NBQX injections (5 nmol) into the fourth ventricle did not produce conditioned taste aversion to saccharin, but LiCl did. Intraburst lick rate and lick efficiency were not affected, but burst size and number and initial lick rate were significantly decreased by NBQX. Local injection of NBQX (2 nmol) into and near the nucleus tractus solitarius also suppressed sucrose intake. These results suggest a general role for non- N-methyl-d-aspartate receptors in the transmission of positive (feedforward) signals, but do not identify the exact processing step involved, such as taste input, sensory-motor processing, or descending facilitation. More localized injections and response measures will be necessary.
Defense of body weight depends on dietary composition and palatability in rats with diet-induced obesity
Authors: Levin Barry E. , Dunn-Meynell Ambrose A.
Published: December 2017

Sprague-Dawley rats selectively bred for diet-induced obesity (DIO) or diet resistance (DR) were characterized on diets of differing energy content and palatability. Over 10 wk, DR rats on a high-energy (HE) diet (31% fat) gained weight similarly to DR rats fed chow (4.5% fat), but they became obese on a palatable liquid diet (Ensure). DIO rats gained 22% more weight on an HE diet and 50% more on Ensure than chow-fed DIO rats. DIO body weight gains plateaued when switched from HE diet to chow. But, Ensure-fed DIO rats switched to chow spontaneously reduced their intake and weight to that of rats switched from HE diet to chow. They also reduced their hypothalamic proopiomelanocortin and dynorphin but not neuropeptide Y mRNA expression by 17–40%. When reexposed to Ensure after 7 wk, they again overate and matched their body weights to rats maintained on Ensure throughout. All Ensure-fed rats had a selective reduction in dynorphin mRNA in the ventromedial hypothalamic nucleus. Thus genetic background, diet composition, and palatability interact to produce disparate levels of defended body weight and central neuropeptide expression.
Activities of arginase I and II are limiting for endothelial cell proliferation
Authors: Li Hui , Meininger Cynthia J. , Kelly Katherine A. , Hawker James R. , Morris Sidney M. , Wu Guoyao
Published: December 2017

Polyamines are essential for cell proliferation; therefore, we hypothesized that arginase I or arginase II activities, via production of ornithine for polyamine synthesis, may be limiting for proliferation of endothelial cells (EC). Bovine coronary venular EC stably transfected with a lacZ gene (lacZ-EC, control), rat arginase I cDNA (AI-EC), or mouse arginase II cDNA (AII-EC) were utilized to test this hypothesis. Cell-proliferation assays showed that EC proliferation was markedly increased in AI-EC and AII-EC compared with lacZ-EC. Expression of proliferating cell nuclear antigen was also enhanced in AI-EC and AII-EC. DL-α-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, was used to establish that increased polyamine synthesis was involved in mediating the enhanced growth of AI-EC and AII-EC. Addition of 5 mM DFMO to the culture medium completely abolished the differences in cellular putrescine concentrations and reduced the differences in spermidine concentrations among AI-EC, AII-EC, and lacZ-EC. The DFMO treatment also prevented an increase in AI-EC and AII-EC proliferation compared with lacZ-EC. Addition of 10 and 50 μM putrescine dose-dependently increased AI-EC, AII-EC, and lacZ-EC growth to the same extent. These results demonstrate that either arginase isoform can potentially play a role in modulating EC proliferation by regulating polyamine synthesis.
Effect of acetazolamide on normoxic and hypoxic exercise in humans at sea level
Authors: Schoene R. B. , Bates P. W. , Larson E. B. , Pierson D. J.
Published: December 2017

Acetazolamide (A) is a potent inhibitor of carbonic anhydrase. It has been shown to be efficacious in preventing acute mountain sickness as well as decreasing the O2 desaturation that occurs during sleep in individuals with chronic mountain sickness who live at altitude. Very little data, however, are available about its effect on exercise. We studied six healthy males in a double-blind cross-over design using acetazolamide and placebo (P) during normoxic and hypoxic (fractional inspired O2 = 0.118) progressive work exercise to exhaustion on a bicycle ergometer. A metabolic acidosis was documented in all subjects on A (P less than 0.045). Before exercise, subjects on A had 2.0 and 3.5 l/min increase in minute ventilation (VE) during normoxia (P = not significant) and hypoxia (P less than 0.005), respectively, and a 2.2% increase in arterialized O2 hemoglobin saturation (SaO2) during hypoxia. During normoxic and hypoxic exercise, VE/kpm and SaO2/kpm were significantly higher while the respiratory exchange ratio (R) was significantly lower on A. These effects were greater on hypoxia. During normoxia, maximal O2 consumption (1/min) was lower on A [3.1 +/- 0.4 (A) vs. 3.8 +/- 0.2 (P), P less than 0.025] and higher during hypoxia on A[2.6 +/- 0.7 (A) vs. 2.4 +/- 0.1 (P), P less than 0.05]. The increase in exercise VE on A may result in an increased alveolar and subsequent arterial O2 tension which may be important for exercise at altitude. Carbonic anhydrase inhibition may also affect CO2 transport in the lung, which may explain the lower R.
Gas mixing in dog lungs studied by single-breath washout of He and SF6
Authors: Meyer M. , Hook C. , Rieke H. , Piiper J.
Published: December 2017

Simultaneously measured helium (He) and sulfur hexafluoride (SF6) single-breath washout was studied in 16 anesthetized paralyzed dogs ventilated with a special hydraulically operated ventilatory servo system. After equilibration of lung gas with 1% He and 1% SF6, the maneuver consisting of inspiration of a test gas-free mixture at constant rate (VI), a variable time of breath holding, and an expiration at constant rate (VE), was performed. Fractional concentrations of He and SF6, recorded against expired volume, were analyzed in terms of slope of the alveolar plateau (S) and series (Fowler) dead space (VD). In control conditions (VI = 0.5 l/s, VE = 0.1 l/s) S was about 10% of alveolar-to-inspired concentration difference per liter expirate both for He and SF6. Both SHe and SSF6 were inversely related to VI and VE, the relative changes being more pronounced with varying VE. SHe/SSF6 was higher or lower than unity depending on VI and VE. Both SHe and SSF6 decreased with increasing preinspiratory lung volume. Breath holding up to 10 s slightly decreased SHe and SSF6 while SHe/SSF6 was unchanged. The contribution of continuing gas exchange to S assessed from comparative measurements using the reversed (single breath washin) technique ranged from 6 to 23% in the various conditions. The VDHe/VDSF6 ratio was 0.84 and was little affected in the various settings. Results indicate that the substantial alveolar gas inhomogeneity in the dog lung and the mechanism accounting for S are little diffusion dependent. By exclusion sequential filling and emptying of lung units is believed to constitute the most important mechanism responsible for the sloping alveolar plateau.
Bronchoconstriction: upper airway dilating muscle and diaphragm activity
Authors: Haxhiu M. A. , Deal E. C. , Van de Graaff W. B. , Van Lunteren E. , Salamone J. A. , Cherniack N. S.
Published: December 2017

The effect of bronchoconstriction on the activity of the diaphragm and the upper dilating airway muscles were studied by administering graded doses of methacholine to anesthetized dogs spontaneously breathing oxygen. The electrical activity of the genioglossus, posterior cricoarytenoid, and alae nasi was compared with that of the diaphragm at different levels of pulmonary resistance. Induced bronchoconstriction was associated with increases in the electrical activity of all muscles examined. Bilateral cervical vagotomy diminished but did not prevent the bronchoconstrictor effects of methacholine. When greater concentrations of methacholine were administered to produce bronchoconstriction comparable with that produced prevagotomy, both genioglossus and diaphragm activity increased. This study indicates that the upper airway muscles and the diaphragm respond to bronchoconstriction. The activation of the upper airway muscles with bronchoconstriction may decrease upper airway resistance serving to partially offset increases in pulmonary resistance and to modulate airflow patterns during bronchoconstriction.
Interaction between norepinephrine and hypoxia on carotid body chemoreception in rabbits
Authors: Milsom W. K. , Sadig T.
Published: December 2017

The effects of both bolus injection and constant infusion of various levels of norepinephrine (NE) on the activity of single-carotid chemoreceptor nerve fibers was studied in pentobarbital-anaesthetized rabbits under normoxic and hypoxic conditions. All animals were paralyzed and artificially ventilated. The dominant effect of NE was to excite carotid body chemoreceptor fibers in a dose-dependent fashion. There was an inverse relationship between the effect of NE on afferent fiber discharge and arterial O2 tension at all levels of exogenous NE above threshold levels. Propranolol (PROP) in sufficient dosage abolished the chemoreceptor response to NE and also markedly reduced the chemoreceptor response to hypoxia. These results support suggestions that beta-adrenergic receptors may be an integral part of the O2 chemosensory mechanism. They also demonstrate a nonadditive interaction between the effects of NE and hypoxia on the chemoreceptor afferent fibers. A reduction in resting discharge levels after infusion of PROP further suggests that endogenous catecholamines may contribute to carotid body chemoreceptor activity even under normoxic normocapnic conditions.
Effects of coronary flow reduction on lung vascular tissue transport in sheep
Authors: Harris T. R. , Collins J. C. , Roselli R. J.
Published: December 2017

This study was performed to measure the effects of a sustained reduction in coronary flow on lung lymph flow and protein content. Ten halothane-anesthetized sheep with cannulated lymphatic vessels were provided with a carotid-to-left anterior descending coronary artery cannula containing an electromagnetic flowmeter. One group of five animals was observed at base line and after coronary flow was reduced to 38% of base line. A second group of five animals acted as controls and was observed at base line, for 111 min of increased left atrial pressure, and a second period of normal pressures. Sustained coronary flow reduction led to significant increases in pulmonary arterial pressure, left atrial pressure, lymph flow, total protein lymph-to-plasma concentration ratio (L/P), and protein lymph clearance (L/P X lymph flow). Analysis of the pressure, lymph, protein, and indicator data with a two-pore model of the microvascular barrier showed that the observations were consistent with the concept that coronary flow reduction decreased functioning lung capillary surface but increased the size of the large pore and the number of small pores relative to the number of larger pores. Control studies showed increases in lymph flow and decreases in L/P with increased pressure but no significant changes in any variable between the first and second period of normal pressures. We conclude that coronary flow reduction increases lung vascular-tissue transport by decreasing the resistance of the microvascular barrier to protein and fluid movement. However, increased pressure secondary to left ventricular dysfunction plays a role in the magnitude of this response.
Multiple inert gas elimination technique
Authors: Hlastala M. P.
Published: December 2017

The understanding of pulmonary gas exchange has undergone several major advances since the early 1900‣s. One of the most significant was the development of the multiple inert gas elimination technique for assessing the ventilation-perfusion (VA/Q) distribution in the lung. By measuring the mixed venous, arterial, and mixed expired concentrations of six infused inert gases, it is possible to distinguish shunt, dead space, and the general pattern of VA/Q distribution. As with all mathematical models of complex biological phenomena, there are limitations that can result in errors of interpretation if the technique is applied uncritically. In addition, methodological limitations also can lead to both experimental error and errors of interpretation. Despite these limitations, the multiple inert gas elimination technique remains the most powerful tool developed to date to analyze pulmonary gas exchange.
Net O2, CO2, lactate, and acid exchange by muscle during progressive working contractions
Authors: Chirtel S. J. , Barbee R. W. , Stainsby W. N.
Published: December 2017

The net O2 uptake (VO2), CO2 output (VCO2), lactate output (L), and non-CO2 acid output (HA) by the gastrocnemius-plantaris muscle group of the dog were measured during progressively loaded isotonic tetanic contractions. Shortening during the 1/s contractions was maintained constant as load was increased by raising the stimulus voltage applied to the motor nerve. Contractions at each load continued for 5 min with two arterial and four venous blood samples obtained during the last minute at each load. Work rate (W) during the contractions was calculated from the load and the shortening. The VO2 increased linearly with time and W. The VCO2 generally followed VO2 with a modest lag during the first two work periods. L increased with time, W, and VO2. Maximal L was lower than that seen during repetitive maximal twitch contractions. HA also increased with time, W, and VO2 and was much larger than L at the higher work rates. It is concluded that L and HA are independent variables during progressive working contractions, as they were during repetitive twitch contractions. Both L and HA patterns may be explained as summations of the respective exchanges of L and HA with time by sequentially recruited groups of muscle fibers.
Comparison of subjects' perception of inspiratory and expiratory resistance
Authors: Muza S. R. , McDonald S. , Zechman F. W.
Published: December 2017

Six healthy male adults were studied at five levels of suprathreshold added resistance (delta R) applied thrice to either inspiration (I) or expiration (E) in a random sequence. Subjects squeezed on isometric handgrip dynamometer to express the perceived magnitude of the load. Peak mouth pressure (Pm), flow, grip (G), and delta R were analyzed to derive the exponent for Steven's power law. We observed that the slope for log G vs. log delta R was significantly greater for I loads than for E loads (P less than 0.05), but the intercepts for E loads were significantly elevated. However, the slopes and intercepts for log G vs. log Pm during the same I and E loads were not significantly different. When subjects were instructed to target I or E flow to a preset level, we observed no difference between the slopes and intercepts for log G vs. log delta R during I and E loading. These results suggest that 1) the sensory information utilized in judging the magnitude of added resistance is more likely related to the force generated by the respiratory muscles (Pm) rather than delta R per se; and 2) similar muscle receptors and neural processing systems are utilized in the estimation of added loads involving either inspiratory or expiratory muscle groups.
Effect of substrate intake and physiological state on background 13CO2 enrichment
Authors: Wolfe R. R. , Shaw J. H. , Nadel E. R. , Wolfe M. H.
Published: December 2017

The natural enrichment of 13C in energy substrates varies, and this variation must be taken into account when stable isotopic tracers are used in metabolic studies. This is conventionally accomplished by measuring background samples taken before the tracer infusion begins and subtracting these values from postinfusion values. Whereas this approach is satisfactory if no perturbation occurs between the collection of the background samples and the collection of postinfusion sample, the data presented in this paper show that any change in the metabolic state can significantly alter the background enrichment of expired CO2. This study not only confirmed that the introduction of natural energy sources may alter the background enrichment of CO2, but we also found that changes in substrate oxidation induced by different physiological states, such as exercise, can cause significant changes in expired CO2 enrichments. Conclusions from studies in which oxidation of substrates were measured by means of a 13C tracer but potential changes in background enrichments were not accounted for must, therefore, be reassessed.
Interstitial fluid pressure gradient measured by micropuncture in excised dog lung
Authors: Bhattacharya J. , Gropper M. A. , Staub N. C.
Published: December 2017

We have directly measured lung interstitial fluid pressure at sites of fluid filtration by micropuncturing excised left lower lobes of dog lung. We blood-perfused each lobe after cannulating its artery, vein, and bronchus to produce a desired amount of edema. Then, to stop further edema, we air-embolized the lobe. Holding the lobe at a constant airway pressure of 5 cmH2O, we measured interstitial fluid pressure using beveled glass micropipettes and the servo-null method. In 31 lobes, divided into 6 groups according to severity of edema, we micropunctured the subpleural interstitium in alveolar wall junctions, in adventitia around 50-micron venules, and in the hilum. In all groups an interstitial fluid pressure gradient existed from the junctions to the hilum. Junctional, adventitial, and hilar pressures, which were (relative to pleural pressure) 1.3 +/- 0.2, 0.3 +/- 0.5, and -1.8 +/- 0.2 cmH2O, respectively, in nonedematous lobes, rose with edema to plateau at 4.1 +/- 0.4, 2.0 +/- 0.2, and 0.4 +/- 0.3 cmH2O, respectively. We also measured junctional and adventitial pressures near the base and apex in each of 10 lobes. The pressures were identical, indicating no vertical interstitial fluid pressure gradient in uniformly expanded nonedematous lobes which lack a vertical pleural pressure gradient. In edematous lobes basal pressure exceeded apical but the pressure difference was entirely attributable to greater basal edema. We conclude that the presence of an alveolohilar gradient of lung interstitial fluid pressure, without a base-apex gradient, represents the mechanism for driving fluid flow from alveoli toward the hilum.
Role of pulmonary lymphatics and interstitium in visceral pleural fluid exchange
Authors: Kinasewitz G. T. , Groome L. J. , Marshall R. P. , Diana J. N.
Published: December 2017

If the pulmonary lymphatics and/or interstitium of the lung participate in visceral pleural (VP) fluid exchange, then increasing the water content of the interstitial compartment by lymphatic ligation (L) should increase the filtration and/or decrease the absorption of fluid across the VP membrane. To test this hypothesis, the hydraulic conductivity (Lp) and diffusional permeability for protein (Pd) of the visceral pleura were determined in eight spontaneously breathing anesthetized chronic L dogs and seven sham-operated (S) controls. The left lung was enclosed in a water-impermeable membrane, creating a VP space; fluid flux was determined as the filtration or reabsorption of water and protein in the VP space. Intravascular and pleural pressures and the protein concentration of plasma and pleural fluid were monitored during two or more experimental periods in which different mixtures of plasma and saline were introduced in the VP space. At similar pulmonary capillary pressures, the extravascular lung water of the L animals [5.36 (+/- 0.32) g/g dry blood-free lung] was significantly (P less than 0.001) greater than that of the S dogs [3.79 (+/- 0.13)]. The Lp of the L dogs [6.8 (+/- 1.6) X 10(-7) ml X s-1 X cm-2 X Torr-1] was virtually identical (P greater than 0.8) to the 6.7 (+/- 1.4) ml X s-1 X cm-2 X Torr-1 of the S controls. Similarly, Pd in the L group [4.3 (+/- 0.5) X 10(-6) cm/s] was similar (P greater than 0.5) to that of the S animals [5.1 (+/- 1.1) X 10(-6) cm/s]. We conclude that neither the pulmonary lymphatics nor the interstitium of the lung contribute to VP fluid exchange.
Repeated lung injury due to alpha-naphthylthiourea causes right ventricular hypertrophy in rats
Authors: Hill N. S. , O'Brien R. F. , Rounds S.
Published: December 2017

Acute lung injury due to alpha-naphthylthiourea (ANTU) is associated with increased permeability edema, transient pulmonary hypertension, and increased vascular reactivity. We sought to determine whether repeated administration of ANTU caused right ventricular hypertrophy. Rats were injected weekly for 4 wk with ANTU or an equivalent volume of the vehicle Tween 80. Rats injected repeatedly with ANTU in doses of 5–10 mg/kg body wt had increased ratios of right ventricular to left ventricular plus septal weights. The right ventricular hypertrophy in ANTU-treated rats was associated with right ventricular systolic hypertension. Repeated injections of ANTU also caused transient pulmonary edema after each dose, as evidenced by increased wet-to-dry lung weight ratios after 4 h, which returned to normal by 24 h. Lungs isolated from ANTU-injected rats had greater pressor responses to hypoxia and to angiotensin II than lungs from Tween 80-injected rats. Pressure-flow curves of isolated lungs, arterial blood gases, and hematocrits were similar in rats treated repetitively with ANTU or Tween alone. Lung histology was also similar in ANTU and control lungs, as were measurements of arterial medial thickness and ratios of numbers of arteries/100 alveoli, indicating that substantial vascular remodeling had not occurred. Thus, four weekly ANTU injections in rats caused right ventricular hypertrophy, probably due to pulmonary hypertension. We speculate that the pulmonary hypertension was due, at least in part, to sustained vasoconstriction, which somehow resulted from repeated acute lung injury.
Upper airway negative-pressure effects on respiratory activity of upper airway muscles
Authors: Mathew O. P.
Published: December 2017

Influence of upper airway negative-pressure change on the respiratory activity of various upper airway muscles was investigated in 13 anesthetized rabbits. Phasic inspiratory activity increased or appeared during virtually all negative-pressure trials in nasolabial, cricothyroid, and posterior cricoarytenoid muscles. No phasic inspiratory activity was seen in the sternothyroid (ST) and sternohyoid (SH) muscles before negative-pressure applications but appeared during 80% of trials in ST and 62% of trials in SH. During maintained negative pressure, a gradual decline in activity was often observed in the nasolabial and laryngeal muscles, whereas a rapid decline in activity was seen in the cervical strap muscles. Reflex effects of negative pressure was markedly reduced or abolished by sectioning the internal branch of the superior laryngeal nerve bilaterally. Reflex augmentation of upper airway muscle activity reported here may have functional significance in the maintenance of upper airway patency. It could prevent upper airway collapse when negative pressure swings in the upper airway increase or facilitate recovery when large negative pressure swings are produced by obstructed inspiratory efforts.
Lung compliance changes on high-frequency ventilation in normal dogs
Authors: Weinmann G. G. , Simon B. A. , Mitzner W.
Published: December 2017

To test the hypothesis that high-frequency ventilation (HFV) promotes lung stability we compared the temporal course of dynamic lung compliance changes after two inflations on HFV with those occurring on conventional mechanical ventilation (CMV) at two different lung volumes, specifically with and without 5 cmH2O positive end-expiratory pressure (PEEP). In our first set of experiments we ventilated six anesthetized paralyzed dogs first with CMV, then with HFV, then again with CMV using tidal volumes of 15 ml/kg at rates of 16–18 times/min for CMV and less than 90 ml and a rate of 15 Hz for HFV. In our second set of experiments we ventilated six dogs for 4 h, the 1st h with CMV at 0 cmH2O end-expiratory pressure, the 2nd h with CMV with 5 cmH2O PEEP, the 3rd h with HFV at the same mean pleural pressure, and the 4th h again with CMV with 5 cmH2O PEEP. We found the decreases in dynamic compliance with time following hyperinflations were similar on HFV and CMV (P greater than 0.5) at both lung volumes. With the lower lung volume the initial dynamic compliance following hyperinflation also tended to fall progressively from one hour to the next despite the inflations. However, with PEEP the initial dynamic compliance over successive hours tended to rise from one hour to the next. We found that changes in dynamic compliance were not necessarily reflected in the venous admixture or alveolar to arterial O2 partial pressure gradients. We thus conclude that lung stability in normal dogs is not improved during HFV, and blood gases cannot be used to predict compliance changes.
Hypocapnia and sustained hypoxia blunt ventilation on arrival at high altitude
Authors: Huang S. Y. , Alexander J. K. , Grover R. F. , Maher J. T. , McCullough R. E. , McCullough R. G. , Moore L. G. , Sampson J. B. , Weil J. V. , Reeves J. T.
Published: December 2017

Hypoxia at high altitude stimulates ventilation, but inhibitory influences in the first days after arrival limit the ventilatory response. Possible inhibitory influences include hypocapnia and depression of ventilation during sustained hypoxia. Our approach was to compare hypoxic ventilatory responses at low altitude with ventilation at high altitude. In 12 subjects we compared responses both to isocapnic hypoxia and poikilocapnic (no CO2 added) hypoxia during acute (less than 10 min) and sustained (30 min) hypoxia in Denver (1,600 m) with ventilations measured on each of 5 days on Pikes Peak (4,300 m). On Pikes Peak, day 1 ventilation [minute ventilation = 10.0 1/min, BTPS; arterial O2 saturation (Sao2) = 82%] was less than predicted by either acute isocapnic or poikilocapnic tests. However, sustained poikilocapnic hypoxia (Sao2 approximately = 82%) in Denver yielded ventilation similar to that on Pikes Peak on day 1. By Pikes Peak days 4 and 5, endtidal PCO2, pHa, and Sao2 approached plateaus, and ventilation (12.4 1/min, BTPS) on these days was as predicted by the acute isocapnic test. Thus the combination of hypocapnia and sustained hypoxia may have blunted the ventilatory increase on Pikes Peak day 1 but apparently not after 4 or 5 days of acclimatization.