bluuebunny/crossref_metadata_2025 huggingface dataset:
Hormone responses of proximal Na(+)-H+ exchanger in spontaneously hypertensive rats
Authors: Gesek F. A. , Schoolwerth A. C.
Published: December 2017

Na(+)-H+ exchange activity is increased in hypertensive rat strains and could be a predisposing factor in the pathogenesis of essential hypertension. Previously we demonstrated that proximal nephron Na(+)-H+ exchange is stimulated by alpha-adrenergic agonists and angiotensin II (ANG II) and inhibited by parathyroid hormone (PTH) and dopamine (DA). To test the hypothesis that hormonal regulation of proximal nephron Na(+)-H+ exchange could differ with hypertension, alterations in Na(+)-H+ exchange were determined by 1) amiloride analogue-suppressible 22Na+ uptake and 2) change in intracellular pH (pHi) as monitored with the fluorescent probe 2',7'-bis(carboxyethyl)-5(6)carboxyfluorscein acetoxymethyl ester. Spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats had similar tail-cuff pressures at 4 wk, but SHR blood pressure was significantly elevated at 8 and 16 wk compared with WKY. No significant differences were observed between SHR and WKY basal ethylisopropyl amiloride-suppressible 22Na+ uptakes or rates of pHi change. alpha-Adrenergic agents and ANG II significantly increased (P less than 0.05) Na(+)-H+ exchange, but, in contrast, 8- and 16-wk-old SHR tubules lacked responsiveness to PTH (10(-8) M) and DA (10(-6) M) observed in WKY. A significant reduction (57–79%, P less than 0.05) in norepinephrine and ANG II stimulation was observed with 8- and 16-wk-old WKY tubules incubated in combination with PTH or DA, but only a 3–33% reduction was produced in 8- and 16-wk-old SHR tubules. PTH- and DA-stimulated adenosine 3',5'-cyclic monophosphate accumulation was significantly reduced in SHR compared with WKY tubules at 4 and 8 wk. It appears that proximal nephron Na(+)-H+ exchange activity is a balance between ANG II and NE activation and PTH and DA inhibition. The data suggest SHR proximal hormone responses are different from WKY and may alter the balance of net Na(+)-H+ exchange activity, possibly contributing to the development or maintenance of hypertension in the SHR.
Induction of intramembranous particle clusters in mice with nephrogenic diabetes insipidus
Authors: Coffey A. K. , O'Sullivan D. J. , Homma S. , Dousa T. P. , Valtin H.
Published: December 2017

In mice with hereditary nephrogenic diabetes insipidus (NDI), the inability of vasopressin to increase hydraulic water permeability is reflected in a lack of intramembranous particle (IMP) clusters in apical membranes of inner medullary collecting ducts. The lack arises from anomalously high activity of one or two isozymes of adenosine 3',5'-cyclic monophosphate-phosphodiesterase (cAMP-PDE). We asked whether inhibition of these isozymes with rolipram and cilostamide would raise not only the tissue content of cAMP but also and simultaneously restore IMP clusters. Inner medullary collecting ducts from NDI mice were incubated in vitro. Tissue content of cAMP (fmol of cAMP per bundle) and number of IMP clusters (per 100 microns 2 of principal cell apical membrane) were, respectively: control, 44.8 +/- 13.0 and 4.16 +/- 1.49; arginine vasopressin (AVP), 31.7 +/- 8.0 and 3.98 +/- 1.56; rolipram and cilostamide, 109.7 +/- 21.0 and 58.09 +/- 15.74; and AVP plus rolipram and cilostamide, 305.7 +/- 75 and 48.63 +/- 11.03 (with the last four values showing significant difference from control and AVP only, respectively). In addition, treating NDI mice with rolipram and cilostamide in vivo reduced their high fluid turnover. We conclude that failure by AVP to increase cAMP in cells of collecting ducts, which results from anomalously high activity of one or two specific isozymes of cAMP-PDE, is the major or sole cause for the excretion of hypotonic urine in NDI mice (DI +/+ Severe strain).
Acidification of vasopressin-induced endosomes in toad urinary bladder
Authors: Emma F. , Harris H. W. , Strange K.
Published: December 2017

It is well established that water channels (WC) are removed from the apical membrane of vasopressin-sensitive epithelia by endocytosis. The processing and the ultimate fate of endocytosed WC is, however, incompletely understood. In many cells, endosome acidification plays an important role in the processing and sorting of endocytosed proteins. Endosome acidification in the toad urinary bladder was therefore examined in vivo by fluorescence ratio video microscopy after induction of endocytosis by vasopressin removal and transepithelial water flow in the presence of the pH-sensitive fluid phase marker 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-dextran. Fifteen minutes after induction of endocytosis, the majority of endosomes had a neutral or slightly acidic pH. The number of acidic endosomes increased progressively with time. Two hours after endocytosis began, 98% of the endosomes had a pH < 6.0. Bafilomycin completely blocked endosome acidification, indicating that H+ transport is mediated by a vacuolar H(+)-adenosinetriphosphatase. Bafilomycin had no effect on transepithelial water flow in bladders repetitively stimulated by vasopressin. These findings, as well as the work of other investigators, suggest that if WC recycling occurs, it is not dependent on acidification of the endosomal compartment. Acidification of vasopressin-induced endosomes most likely represents a terminal event in the endocytic pathway.
Impairment of renal medullary osmolyte accumulation in potassium-depleted rats
Authors: Nakanishi T. , Takamitsu Y. , Nakahama H. , Sugita M.
Published: December 2017

To determine the relationship between accumulation of osmolytes and maximal urinary concentration in potassium depletion, we tested the effects of experimental water diuresis or potassium depletion on osmolytes in the renal medulla of rats. Hyperosmotic stress was imposed by 4 days of water deprivation for the purpose of establishing the maximal concentrating ability or by the infusion of sodium for the purpose of loading the equal amounts of sodium to the renal medulla. In the diuresis group, water deprivation failed to increase betaine, sorbitol, and taurine contents to the same level as the untreated group, although sodium infusion increased betaine and sorbitol. In the potassium depletion group followed by water deprivation, urine osmolality (2,490 +/- 241 vs. 3,425 +/- 268 mosmol/kgH2O) and all osmolytes were significantly lower than in the untreated group. In response to hyperosmolality with sodium infusion, myo-inositol and glycerophosphorylcholine contents rose to the level of the untreated group. Medullary betaine (67.6 +/- 6.8 vs. 99.5 +/- 8.9), taurine (44.7 +/- 2.4 vs. 61.4 +/- 6.2) and sorbitol (35.6 +/- 4.4 vs. 57.0 +/- 8.4 mmol/kg protein) contents were reduced in potassium-depleted rats when the renal medulla was as hypertonic as in the untreated group. In conclusion, the processing of betaine, taurine, and sorbitol accumulation appeared to be impaired in potassium depletion.
Functional and molecular evidence for Shaker-like K+ channels in rabbit renal papillary epithelial cell line
Authors: Volk K. A. , Husted R. F. , Pruchno C. J. , Stokes J. B.
Published: December 2017

The rabbit papillary epithelial cell line GRB-PAP1 was used to determine the ion transport characteristics of a model of the distal nephron and terminal collecting duct. When grown on permeable supports, monolayers developed a significant electrical resistance and a benzamil-sensitive short-circuit current, indicating that they had the property of electrogenic Na+ transport. Using the whole cell patch-clamp technique, we found that the dominant current in these cells was a slowly inactivating, time- and voltage-dependent K+ current. This current was activated by voltages more positive than -30 mV. At +30 mV, the peak outward currents were > 300 pA. The magnitude of the outward currents and their reversal potentials depended strongly on the extracellular concentration of K+ and not on the extracellular concentration of Cl-. These currents were inhibited by either tetraethylammonium, 4-aminopyridine, charybdotoxin, or dendrotoxin. These characteristics, together with the kinetics of activation and inactivation, are the general characteristics of delayed rectifier channels seen in many muscle and neuronal cells. Because many of these types of channels share sequence homology with the Shaker family of channels cloned from Drosophila, we sought to identify a molecular correlate. Using reverse transcription followed by polymerase chain reaction to amplify Shaker-like sequences, we cloned and sequenced a single 881-bp fragment. The sequence shared identity with a recently reported rabbit Shaker channel that belongs to the subclass Kv 1.2. These data show that this renal papillary epithelial cell line, which has the capability of electrogenic Na+ transport, expresses functional delayed rectifier channels.
In vivo adaptation of bicarbonate reabsorption by rat distal tubules during acid loading
Authors: Levine D. Z. , Iacovitti M. , Buckman S. , Vandorpe D. , Harrison V. , Boisvert D. M. , Nadler S. P.
Published: December 2017

We carried out in vivo microperfusion experiments in acid-loaded rats to characterize the adaptive response of the unidirectional components secretory flux (Jsec) and reabsorptive flux (Jreab)] of distal tubule bicarbonate reabsorption and to test the hypothesis that Jreab is dependent on bafilomycin A1-sensitive H(+)-adenosinetriphosphatase activity. During 18 h of severe acidosis there was a significant decrease in Jsec (-15 +/- 3 vs. -38 +/- 5 pmol.min-1.mm-1, P < 0.05) and a significant increase in Jreab (37 +/- 6 vs. 0 +/- 5 pmol.min-1.mm-1, P < 0.05), which was insensitive to 10(-5) M bafilomycin A1, 10(-5) M Sch-28080, and 3 mM amiloride. After 3 days of acid loading, these same inhibitors reduced Jreab by approximately 60%. However, when water flux was completely inhibited by isosmotic perfusion, a significant Jreab (15 +/- 2 pmol.min-1.mm-1) resistant to 10(-5) M bafilomycin A1 persisted, as in severe acidosis. In reabsorbing distal tubules of overnight-fasted rats, Sch-28080 elicited no inhibition, whereas bafilomycin A1 and amiloride had significant effects (28 +/- 5, 24 +/- 4, respectively, vs. 50 +/- 4 pmol.min-1.mm-1 for fasted rats, P < 0.05). Thus, although Jsec is reduced in the transition from mild to severe metabolic acidosis of 18-h duration, the predominant effect is a stimulation of bafilomycin A1-resistant Jreab.
Atrial natriuretic peptide receptors are present and functional by midgestation in fetal sheep
Authors: Fraenkel M. B. , Potocnik S. J. , Wintour E. M.
Published: December 2017

This study examined the ontogeny of the mRNA for three atrial natriuretic peptide (ANP) receptors in the ovine fetal kidney and the effect of systemic ANP infusion in the very immature ovine fetus. mRNA was isolated from the kidneys of 60-, 100-, and 140-day fetuses (n = 4 at each age). Northern blots [5 micrograms poly(A)+ RNA per track] were probed for the guanylate cyclase (GC)-A, GC-B, and clearance receptors, using beta-actin as a control for variations in loading. The results were quantitated using laser densitometry. Levels of clearance receptor mRNA were significantly higher in 140-day than 60-day fetal kidneys (P < 0.05), whereas levels of mRNA for the GC-A and GC-B receptors remained steady. We propose that binding of ANP to an increased number of C receptors in the late-gestation fetal kidney could explain the previously documented increase in total ANP receptor number in late-gestation ovine kidneys without increased ANP biological activity. Systemic ANP infusion into four fetuses of approximately 74 days gestation resulted in a natriuresis and diuresis, indicating the presence of functional ANP receptors in the ovine kidney early in gestation.
Role of renal dopamine D1 receptors in natriuresis induced by calcium channel blockers
Authors: Eisner G. M. , Yamaguchi I. , Felder R. A. , Asico L. D. , Jose P. A.
Published: December 2017

The direct tubular natriuretic effect of calcium channel blockers (CCBs) may be due to an interaction between CCBs and a renal tubular dopamine receptor. We therefore studied the effects of two chemically unrelated CCBs, diltiazem and isradipine, infused into the right renal artery of 5% saline-loaded anesthetized rats alone or in the presence of a D1 antagonist, SKF-83742. Isradipine (0.03 microgram.kg-1.min-1) or diltiazem (20 but not 10 micrograms.kg-1.min-1) alone produced an increase in urine flow and an approximate doubling of absolute and fractional sodium excretion, which was not seen in the left kidney or in the control animals (analysis of variance, Scheffe's test, P < 0.05). SKF-83742 alone given systemically or into the right renal artery did not affect these parameters but did block the actions of diltiazem or isradipine. There was no change in mean arterial pressure, renal blood flow, or glomerular filtration rate in any of the experiments. In additional studies, we found that a combined infusion of dopamine (0.1 microgram.kg-1.min-1) and diltiazem (10 micrograms.kg-1.min-1) (doses that by themselves did not alter renal function) produced a twofold or greater increase in urine flow and absolute and fractional sodium excretion; glomerular filtration rate was not significantly changed. Intrarenal arterial CCBs, without a change in renal hemodynamics, produce a natriuresis that is blocked by a D1 antagonist. Concomitant administration of diltiazem and dopamine (each in subeffective doses when used alone) produces a synergistic effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Instantaneous and steady-state gains in the tubuloglomerular feedback system
Authors: Layton H. E. , Pitman E. B. , Moore L. C.
Published: December 2017

The load of water and solute entering each nephron of the mammalian kidney is regulated by the tubuloglomerular feedback (TGF) mechanism, a negative feedback loop. Experiments in rats have shown that key variables of this feedback system may exhibit TGF-mediated oscillations. Mathematical modeling studies have shown that the open-feedback-loop gain is a crucial parameter for determining whether oscillations will emerge. However, two different formulations of this gain have been used. The first is the steady-state gain, a readily measurable quantity corresponding to the steady-state reduction in single-nephron glomerular filtration rate (SNGFR) subsequent to a sustained increased in ascending limb flow rate. The second is an instantaneous gain, a variable arising from theoretical considerations corresponding to the maximum reduction in SNGFR resulting from an instantaneous shift of the ascending limb flow column, with the assumption that the SNGFR response is also instantaneous. Here we show by an analytic argument how the steady-state and instantaneous open-feedback-loop gains for the ascending limb are related. In the case of no solute backleak into the ascending limb, the two formulations of gain are equivalent; however, in the presence of solute backleak, the instantaneous gain is larger in magnitude than the steady-state gain. With typical physiological parameters for the rat, calculations with a model previously devised by us show that the gains differ by 5-10%. Hence, experimental measurements of the steady-state gain may provide useful lower-bound estimates of the instantaneous gain of the feedback system in the normal rat. However, the gains may diverge significantly in pathophysiological states where ascending limb transport is compromised by abnormally high NaCl permeability.
A novel cGMP-activated Cl- channel in renal proximal tubules
Authors: Darvish N. , Winaver J. , Dagan D.
Published: December 2017

Cl- channels activated by natriuretic peptides were detected in cultured rat proximal convoluted tubule (PCT) cells with the use of patch-clamp methodology. Bath application of atrial natriuretic peptide (ANP) activates a 150-pS Cl- channel with the open probability (Po) of the channel increasing from 0.0008 +/- 0.0003 to 0.021 +/- 0.008. 8-Bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP), a membrane-permeable analogue of cGMP, increased channel activity in the on-cell mode. In inside-out patches the channel was activated by cGMP in a dose-dependent manner. Channel activity decreased after washing out and increased on reapplication of cGMP. A similar activation was observed also in presence of either of two protein kinase inhibitors, N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride or KT5823, or a phosphatase inhibitor. Bath application of urodilatin mimicked the action of ANP. Po of the channel was found to be independent of both voltage and Ca2+, and gating activity could be blocked by the stilbene, 4,4-dinitrostilbene-2,2-disulfonic acid. These results demonstrate a Cl- conductance in PCT cells modulated by ANP and urodilatin via their second messenger, cGMP.
Desensitization of endothelin-1 binding by vasopressin via a cAMP-mediated pathway in rat CCD
Authors: Takemoto F. , Uchida S. , Katagiri H. , Oka Y. , Nakao A. , Kurokawa K.
Published: December 2017

In renal collecting ducts, endothelin-1 (ET-1) inhibits Na+ reabsorption and antagonizes the effects of arginine vasopressin (AVP). Whether AVP may affect ET-1 action in the collecting ducts that mainly express the ETB receptor subtype, however, remains unknown. Since ETB, but not ETA, possesses a consensus amino acid sequence for possible phosphorylation by protein kinase A (PKA), we hypothesized that AVP may influence ET-1 binding to the ETB receptor via PKA. In microdissected rat cortical collecting ducts, the specific ET-1 binding decreased by 35% (15.6 +/- 4.4 vs. 24.0 +/- 3.6 amol/mm in control) following 20-min preincubation with 10(-7) M AVP. This decrease in ET-1 binding was mimicked by 10(-5) M forskolin and by 10(-4) M dibutyryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP), indicating that this heterologous desensitization may be caused by a cAMP-dependent mechanism. Moreover, N-(2([3-(4-bromophenyl)-2-propenyl]-amino]-ethyl)-5- isoquinolinesulfonamide (H-89) and the Rp diastereoisomer of cAMP, Rp-cAMPS, which are both PKA-specific inhibitors, eliminated AVP-induced ETB receptor desensitization. The reduction in ET-1 binding was characterized by a decrease in binding affinity [dissociation constant (Kd) = 4 vs. 2 nM in control] with no change in maximal binding capacity. In contrast, forskolin and DBcAMP had no effect on ET-1 binding in endothelium-denuded aortic strips, which mainly express ETA subtype. These results showed that AVP rapidly downregulates the ETB receptor by reducing Kd through a PKA-dependent pathway. Thus ET-1 and AVP may act in a mutually antagonizing manner in the renal collecting ducts.
Increased Tyr phosphorylation of ZO-1 during modification of tight junctions between glomerular foot processes
Authors: Kurihara H. , Anderson J. M. , Farquhar M. G.
Published: December 2017

The slit diaphragms between the glomerular epithelial foot processes represent a variant of the tight junction that are rapidly replaced by typical tight junctions after perfusion with protamine sulfate (PS). To investigate the mechanism of signaling involved, tyrosine phosphorylation of glomerular proteins was analyzed in newborn, PS-treated, and control rats using antiphosphotyrosine immunoglobulin G. In glomeruli of normal adults, phosphotyrosine (Ptyr) staining was confined largely to mesangial cells by immunofluorescence, whereas in newborn and PS-treated rats, the Ptyr signal was dramatically increased in the glomerular epithelium. By immunogold labeling, it was found that newly phosphorylated proteins were concentrated along the newly formed tight junctions (cell-cell junctions) and the basal membrane of the foot processes (cell-matrix junctions). By immunoblotting, several prominent bands were detected with anti-Ptyr in glomerular lysates of controls; in PS-treated rats, additional bands were detected at 225, 180, and 100 kDa. The 225-kDa protein was identified as ZO-1 by immunoprecipitation with anti-ZO-1 followed by immunoblotting with anti-Ptyr. These findings indicate that ZO-1 is one of the targets for tyrosine phosphorylation after PS treatment. They indicate that phosphorylation of tight junction and other proteins occurs during the formation of tight junctions in glomeruli under circumstances where there are rapid changes in epithelial cell shape.
Upper airway muscle activity and the thoracic volume dependence of upper airway resistance
Authors: Aronson R. M. , Carley D. W. , Onal E. , Wilborn J. , Lopata M.
Published: December 2017

Although a thoracic volume dependence of upper airway resistance and caliber is known to exist in seated subjects, the mechanisms mediating this phenomenon are unknown. To test the hypothesis that actively altered end-expiratory lung volume (EELV) affects upper airway resistance in the supine position and to explore the mechanisms of any EELV-induced resistance changes, we studied five normal males during wakefulness. Supraglottic upper airway resistance (Ruaw) was calculated at an inspiratory flow of 0.1 l/s. The genioglossal electromyogram was obtained with indwelling wire electrodes and processed as moving time average. End-tidal CO2 was monitored by infrared analyzer. Observations were made during four 20-breath voluntary maneuvers: two at high and two at low EELV in each subject. Each maneuver was preceded by a control period at functional residual capacity. At high lung volume the EELV was increased by 2.23 +/- 0.54 (SD) liters; Ruaw decreased to 67.8 +/- 35.1% of control, while tonic and phasic genioglossal activities declined to 79.0 +/- 23.1 and 72.4 +/- 29.8%, respectively. At low lung volume the EELV was decreased by 0.86 +/- 0.23 liters. Ruaw increased to 178.2 +/- 186.8%, while tonic and phasic genioglossal activities increased to 243.0 +/- 139.3 and 249.1 +/- 146.3%, respectively (P less than 0.0001 for all). The findings were not explained by CO2 perturbations or respiratory pattern. Multiple linear regression analysis indicated that the genioglossal responses blunted the EELV-induced changes in upper airway patency.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of phrenic nerve afferents in the control of breathing
Authors: Frazier D. T. , Revelette W. R.
Published: December 2017

A long-held belief is that respiratory-related reflexes mediated by afferents in the diaphragm are weak or absent. However, recent data suggest that diaphragmatic afferents are capable of altering ventilatory motor drive as well as influencing perception of added inspiratory loads in humans. This review describes the sensory elements of the diaphragm, their central projections, and their functional significance in the control of respiratory muscle activation. The reflexes elicited by electrical stimulation of phrenic nerve afferents and the contribution of diaphragmatic afferents in respiratory load compensation and perception are considered. There is growing evidence that phrenic nerve afferents are activated under a variety of conditions. However, the significance of this input to the central nervous system is yet to be discerned.
Effect of mean airway pressure on gas exchange during high-frequency oscillatory ventilation
Authors: Boynton B. R. , Villanueva D. , Hammond M. D. , Vreeland P. N. , Buckley B. , Frantz I. D.
Published: December 2017

We studied the effect of mean airway pressure (Paw) on gas exchange during high-frequency oscillatory ventilation in 14 adult rabbits before and after pulmonary saline lavage. Sinusoidal volume changes were delivered through a tracheostomy at 16 Hz, a tidal volume of 1 or 2 ml/kg, and inspired O2 fraction of 0.5. Arterial PO2 and PCO2 (PaO2, PaCO2), lung volume change, and venous admixture were measured at Paw from 5 to 25 cmH2O after either deflation from total lung capacity or inflation from relaxation volume (Vr). The rabbits were lavaged with saline until PaO2 was less than 70 Torr, and all measurements were repeated. Lung volume change was measured in a pressure plethysmograph. Raising Paw from 5 to 25 cmH2O increased lung volume by 48-50 ml above Vr in both healthy and lavaged rabbits. Before lavage, PaO2 was relatively insensitive to changes in Paw, but after lavage PaO2 increased with Paw from 42.8 +/- 7.8 to 137.3 +/- 18.3 (SE) Torr (P less than 0.001). PaCO2 was insensitive to Paw change before and after lavage. At each Paw after lavage, lung volume was larger, venous admixture smaller, and PaO2 higher after deflation from total lung capacity than after inflation from Vr. This study shows that the effect of increased Paw on PaO2 is mediated through an increase in lung volume. In saline-lavaged lungs, equal distending pressures do not necessarily imply equal lung volumes and thus do not imply equal PaO2.
Surface area-independent assessment of lung microvascular permeability with an amphipathic tracer
Authors: Olson L. E. , Pou A. , Harris T. R.
Published: December 2017

A combination of an amphipathic-indicator-dilution (ID) diffusing tracer 1,4[14C]butanediol (B) and a hydrophilic tracer ([14C]urea) (U) was hypothesized to provide a capillary surface area- (S) independent assessment of lung microvascular permeability (P). We performed ID studies on isolated perfused dog lungs and administered randomly two interventions, increasing P by alloxan infusion and reduction in S by lobar ligation. The ratio of PS product of U (PSU) to that for butanediol (PSB) was sensitive to changes in P yet insensitive to changes in S. We performed ID studies in which the dependence of PSU and PSB on flow, hematocrit, and plasma protein binding were examined. Measurements of PSU and PSB after flow and hematocrit were changed suggested that these factors have no significant independent effects. From ID and in vitro studies we also found that no significant binding of B to plasma proteins (albumin) occurred. We concluded that ID techniques using B and U provide a consistent measure of P, despite changes in S, hematocrit, plasma protein concentration, and recruitment.
In vitro perfused-superfused cat carotid body for physiological and pharmacological studies
Authors: Iturriaga R. , Rumsey W. L. , Mokashi A. , Spergel D. , Wilson D. F. , Lahiri S.
Published: December 2017

An in vitro perfused carotid body preparation was developed to study its chemosensory responses to physiological and pharmacological stimuli. The carotid bifurcation with the carotid body was vascularly isolated and excised from pentobarbital sodium-anesthetized cats. The CB was perfused in a chamber by gravity (80 Torr) with modified Tyrode's solution (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-NaOH at pH 7.40) equilibrated at a given Po2 and superfused with the same medium at (Po2 of 20 Torr). The temperature was maintained at 35.5 +/- 0.5 degrees C. The frequency of chemosensory discharges (CD) was recorded from the whole carotid sinus nerve (n = 24), and the responses were tested by repeated interruptions of perfusate flow (SF), perfusion with hypoxic medium, and injections of nicotine and cyanide (0.1 nmol to 1 mumol) and hypercapnic medium. During hyperoxic perfusion, SF resulted in a sigmoidal increase in CD, reaching a maximum that was 23.6 +/- 4.4-fold greater than the basal activity. Restoration of flow returned CD promptly to basal values. After normoxic perfusion, SF led to a similar maximal activity more rapidly, but the duration was shorter. Reduction of the perfusate PO2 (Po2 from 450 Torr to 150, 30, and less than 10 Torr) caused a nonlinear increase in CD. CO2 stimuli (PCo2 38-110 Torr) resulted in a linear increase in CD. Nicotine or cyanide increased CD in a dose-dependent manner. The preparation retained its initial responsiveness for 2-3 h, making extensive experimental studies feasible.(ABSTRACT TRUNCATED AT 250 WORDS)
Pleural pressure distribution and its relationship to lung volume and interstitial pressure
Authors: Lai-Fook S. J. , Rodarte J. R.
Published: December 2017

The mechanics of the pleural space has long been controversial. We summarize recent research pertaining to pleural mechanics within the following conceptual framework, which is still not universally accepted. Pleural pressure, the force acting to inflate the lung within the thorax, is generated by the opposing elastic recoils of the lung and chest wall and the forces generated by respiratory muscles. The spatial variation of pleural pressure is a result of complex force interactions among the lung and other structures that make up the thorax. Gravity contributes one of the forces that act on these structures, and regional lung expansion and pleural pressure distribution change with changes in body orientation. Forces are transmitted directly between the chest wall and the lung through a very thin but continuous pleural liquid space. The pressure in pleural liquid equals the pressure acting to expand the lung. Pleural liquid is not in hydrostatic equilibrium, and viscous flow of pleural liquid is driven by the combined effect of the gravitational force acting on the liquid and the pressure distribution imposed by the surrounding structures. The dynamics of pleural liquid are considered an integral part of a continual microvascular filtration into the pleural space. Similar concepts apply to the pulmonary interstitium. Regional differences in lung volume expansion also result in regional differences in interstitial pressure within the lung parenchyma and thus affect regional lung fluid filtration.
Neutrophil accumulations due to pulmonary thromboxane synthesis mediate acid aspiration injury
Authors: Goldman G. , Welbourn R. , Klausner J. M. , Kobzik L. , Valeri C. R. , Shepro D. , Hechtman H. B.
Published: December 2017

Acid aspiration leads to lung injury associated with high levels of plasma thromboxane (Tx). This study tests the role of Tx synthesis by the aspirated lung segment in mediating local and remote neutrophil (PMN) sequestration, alveolar diapedesis, and permeability edema. Anesthetized rats underwent tracheostomy and insertion of a fine-bore cannula into the anterior segment of the left lung. This was followed by the installation of either 0.1 ml saline (n = 18) or the Tx synthase inhibitor OKY 046 (0.1 mg/kg in 0.1 ml, n = 18). Twenty minutes later either 0.1 ml 0.1 N HCL or 0.1 ml saline was similarly introduced (n = 18). Three hours later, in the saline-HCl group, the rise in Tx concentration in both plasma (1,340 pg/ml) and bronchoalveolar lavage (BAL) fluid (2,100 pg/ml) was higher than that in the saline-saline aspirated control group (350 and 115 pg/ml, respectively; both P less than 0.05). In the acid-aspirated lung PMN sequestration [87 PMN/10 high-power fields (HPF)] and diapedesis (96 x 10(4) PMN/ml in BAL) were higher than control values of 7 PMN/10 HPF and 3 x 10(4) PMN/ml (both P less than 0.05). Acid aspiration induced local permeability edema with a high protein concentration in BAL of 3,350 micrograms/ml and an increase in lung wet-to-dry weight ratio (W/D) of 6.6, both higher than control values of 482 micrograms/ml and 3.4, respectively (P less than 0.05). Leukosequestration in the aspirated side started at 30 min and was progressive over a 3-h monitoring period.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of withdrawal of respiratory CO2 oscillations on respiratory control at rest
Authors: Takahashi E. , Tateishi I. , Yamamoto K. , Mikami T.
Published: December 2017

We examined the effect of sudden withdrawal of respiratory oscillations of arterial PCO2 (CO2 oscillations) at resting metabolic rate on the control of respiration in 11 anesthetized paralyzed vagotomized dogs in normoxic normocapnia. A double-lumen endotracheal tube was inserted so that the left and right lungs were ventilated independently. By alternately ventilating each lung, we could completely abolish CO2 oscillations without affecting the mean blood gas levels (withdrawal of CO2 oscillations). The CO2 oscillation was calculated from arterial pH oscillation measured by a rapidly responding intra-arterial pH electrode. Respiratory center output was monitored by use of a moving time average of the phrenic neurogram. A 3-min period of withdrawal of CO2 oscillations was bracketed by two control periods (simultaneous ventilation of lungs for 3 min) to avoid the confounding effect of the baseline drift in the respiratory center output. The amplitude of the CO2 oscillations in the control was 2.33 +/- 0.89 (SD) Torr. When the difference in the mean level of arterial PCO2 between the control and withdrawal of CO2 oscillations was minimized (-0.09 +/- 0.54 Torr; P greater than 0.25), we found negligible change in the minute phrenic activity during withdrawal of CO2 oscillations (-0.02 +/- 6.11% of the control, P greater than 0.98, n = 49; 99% confidence interval -2.36 to 2.32%). Thus we conclude that the maintenance of normal respiration at rest is not critically dependent on a phasic afferent input to the respiratory center arising from respiratory CO2 oscillations.
Effects of substance P and calcitonin gene-related peptide on the pulmonary circulation
Authors: Adnot S. , Cigarini I. , Herigault R. , Harf A.
Published: December 2017

To assess the in vivo effects of the neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP) on the pulmonary vascular bed, the hemodynamic responses to both CGRP and SP were examined in the in situ-perfused lung lobe of open-chest anesthetized pigs. Peptides were infused into the lobar artery under conditions of elevated pulmonary vascular tone by prostaglandin F2 alpha (PGF2 alpha, 20 micrograms/min). Pulmonary airway lobar dynamic compliance (Cdyn) and airway resistance (Re) were computed from simultaneously measured airway pressure and airflow entering the lobe through a Carlens endobronchial divider. PGF2 alpha infusion slightly reduced Cdyn (-20%) and increased Re (+11%) while lobar arterial pressure rose from 14 +/- 1 to 31 +/- 2 mmHg (n = 12). In these conditions, lobar artery infusion of SP (0.5-50 pmol/min) or CGRP (15-5,000 pmol/min) produced a dose-dependent decrease in the pressor response to PGF2 alpha, reaching -54 +/- 3 and -64 +/- 7%, respectively, without alterations in lung mechanics. On a molar basis, SP was more effective than CGRP; its vasodilatory effect was more rapid and of shorter duration. Higher CGRP infusion rates were not studied because of marked systemic hypotension. SP infused at 150, 500, and 1,000 pmol/min significantly reduced Cdyn by 12 +/- 2, 24 +/- 4, and 62 +/- 7%, respectively, but also induced a rise in lobar arterial pressure and a fall in systemic arterial pressure. The results show that both SP and CGRP are potent pulmonary vasodilators. In contrast to CGRP, which did not affect lung mechanics, high infusion rates of SP decreased Cdyn and increased Re.(ABSTRACT TRUNCATED AT 250 WORDS)
Exercise endurance and arterial desaturation in normobaric hypoxia with increased chemosensitivity
Authors: Giesbrecht G. G. , Puddy A. , Ahmed M. , Younes M. , Anthonisen N. R.
Published: December 2017

We studied whether exercise endurance under normobaric hypoxia can be enhanced by increasing hypoxic ventilatory sensitivity with almitrine bismesylate (ALM). On both ALM and placebo (PL) days, resting subjects breathed a hypoxic gas mixture (an inspired O2 fraction of 10.4-13.2%), which lowered resting arterial O2 saturation (SaO2) to 80%. After 15 min of rest there was a 3-min warm-up period of exercise at 50 W (light) on a cycle ergometer, followed by a step increase in load to 60% of the previously determined maximum power output with room-air breathing (moderate), which was maintained until exhaustion. With PL, SaO2 decreased rapidly with the onset of exercise and continued to fall slowly during moderate exercise, averaging 71.0 +/- 1.8% (SE) at exhaustion. With ALM, saturation did not differ from PL during air breathing but significantly exceeded SaO2 with PL, by 3.4% during resting hypoxia, by 4.0% at the start of exercise, and by 5.9% at exhaustion. Ventilation was not affected by ALM during air breathing and was slightly, although not significantly, increased during hypoxic rest and exercise. ALM was associated with an increased heart rate during room air breathing but not during hypoxia. Endurance time was 20.6 +/- 1.6 min with ALM and 21.3 +/- 0.9 min with PL. During hypoxic exercise, the potential benefit of greater saturation with ALM is apparently offset by other unidentified factors.
Rate of decline in blood lactate after cycling exercise in endurance-trained and -untrained subjects
Authors: Bassett D. R. , Merrill P. W. , Nagle F. J. , Agre J. C. , Sampedro R.
Published: December 2017

The purpose of this study was to compare the rate of decline in blood lactate (La) levels in nine trained men [maximal O2 consumption (VO2max) 65.5 +/- 3.3 ml.kg-1.min-1] and eight untrained men (VO2max 42.2 +/- 2.8 ml.kg-1.min-1) during passive recovery from a 3-min exercise bout. Trained and untrained subjects cycled at 85 and 80% VO2max, respectively, to produce similar peak blood La concentrations. Twenty samples of arterialized venous blood were drawn from a heated hand vein during 60 min of recovery and analyzed in an automated La analyzer. The data were then fitted to a biexponential function, which closely described the observed data (r = 0.97-0.98). There was no difference in the coefficient expressing the rate of decline in blood La for trained and untrained groups (0.0587 +/- 0.0111 vs. 0.0579 +/- 0.0100, respectively). However, trained subjects demonstrated a faster time-to-peak La (P = 0.01), indicative of a faster efflux of La from muscle to blood. Thus the rate of decline in blood La after exercise does not appear to be affected by training. The faster decline previously reported for trained subjects may be due to the use of a linear rather than a biexponential curve fit.
Influence of cold, exercise, and caffeine on catecholamines and metabolism in men
Authors: Graham T. E. , Sathasivam P. , MacNaughton K. W.
Published: December 2017

Recently we found that caffeine ingestion did not enhance either thermal or fat metabolic responses to resting in cold air, despite an increase in plasma epinephrine and free fatty acids. Theophylline, another methylxanthine, has been shown to be effective during exercise but not at rest during cold stress. Therefore we hypothesized that caffeine ingestion before exercise in cold air would have a thermal-metabolic impact by increasing fat metabolism and increasing oxygen consumption. Young adult men (n = 6) who did not normally have caffeine in their diet performed four double-blind trials. Thirty minutes after ingesting placebo (dextrose, 5 mg/kg) or caffeine (5 mg/kg) they either exercised (60 W) or rested for 2 h in 5 degrees C air. Cold increased (P less than 0.05) plasma norepinephrine while both caffeine and exercise increased (P less than 0.05) epinephrine. Serum free fatty acids and glycerol were increased, but there were no differences between rest and exercise or placebo and caffeine. Caffeine had no influence on either respiratory exchange ratio or oxygen consumption either at rest or during exercise. The exercise trials did not significantly warm the body, and they resulted in higher plasma norepinephrine concentrations and lower mean skin temperatures for the first 30 min. The data suggest that skin temperature stimulates plasma norepinephrine while caffeine has little effect. In contrast, caffeine and exercise stimulate plasma epinephrine while cold has minimal effect. Within the limits of this study caffeine gave no thermal or metabolic advantage during a cold stress.
Evidence that the effect of physical exercise on NK cell activity is mediated by epinephrine
Authors: Kappel M. , Tvede N. , Galbo H. , Haahr P. M. , Kjaer M. , Linstow M. , Klarlund K. , Pedersen B. K.
Published: December 2017

The present study was designed to test the hypothesis that the changes in natural killer (NK) cell activity in response to physical exercise were mediated by increased epinephrine concentrations. Eight healthy volunteers 1) exercised on a bicycle ergometer (60 min, 75% of maximal O2 uptake) and 2) on a later day were given epinephrine as an intravenous infusion to obtain plasma epinephrine concentrations comparable with those seen during exercise. Blood samples were collected in the basal state, during the last minutes of exercise or epinephrine infusion, and 2 h later. The NK cell activity (lysis/fixed number of mononuclear cells) increased during exercise and epinephrine infusion and dropped below basal levels 2 h afterward. The increased NK cell activity during exercise and the epinephrine infusion resulted from an increased concentration of NK (CD16+) cells in the peripheral blood. On the other hand, the decreased NK cell activity demonstrated 2 h after exercise and epinephrine infusion did not simply reflect preferential removal of NK cells from the blood, because the proportion of CD16+ cells was normalized. On the basis of the finding that indomethacin abolished the suppressed NK cell activity in vitro and the demonstration of a twofold increase in the proportion of monocytes (CD14+ cells) 2 h after exercise and epinephrine infusion, we suggest that, after stress, prostaglandins released by monocytes are responsible for downregulation of NK cell function. Our findings support the hypothesis that increased plasma epinephrine during physical stress causes a redistribution of mononuclear subpopulations that results in altered function of NK cells.
Influence of posture on lung volumes and impedance of respiratory system in healthy smokers and nonsmokers
Authors: Michels A. , Decoster K. , Derde L. , Vleurinck C. , Van de Woestijne K. P.
Published: December 2017

In 105 adults we investigated the influence of the body positions, sitting with respect to supine, on lung volumes and on the input resistance, (Rrs) and reactance (Xrs) of the respiratory system. Rrs and Xrs were measured between 2 and 26 Hz by means of a forced oscillation technique. Vital capacity (VC) and expiratory reserve volume (ERV) are smaller in the supine position; this reduction decreases with age and is less for ERV in male smokers than in nonsmokers. The Rrs values are larger in the supine position, and the slope of the Rrs-frequency curves tends to become less positive or negative, depending on sex, age, and smoking habits. Xrs decreases at lower frequencies. The changes in Rrs due to posture are larger in young smokers than in young nonsmokers. This is not explained by changes in ERV and may reflect changes in the intrinsic properties of the airways induced by smoking.
Cyclooxygenase inhibitors prevent ethchlorvynol-induced injury in rat and rabbit lungs
Authors: Zanaboni P. B. , Bradley J. D. , Webster R. O. , Dahms T. E.
Published: December 2017

The effect of three chemically dissimilar cyclooxygenase inhibitors on ethchlorvynol-(ECV) induced acute lung injury was studied in isolated buffer-perfused rat and blood-perfused rabbit lungs. ECV caused the microvascular fluid filtration coefficient (Kf) to increase by greater than threefold in the rat lungs and twofold in the rabbit lungs. ECV caused increased pulmonary vascular resistance (PVR) and microvascular pressure measured by the double occlusion technique (Pdo) compared with the vehicle control group in the rat experiments. However, ECV had no effect on PVR or Pdo in the rabbit experiments. Pretreatment with the cyclooxygenase inhibitors indomethacin, ibuprofen, and meclofenamate prevented the increase in microvascular permeability in both the rat and rabbit lung preparations. The cyclooxygenase inhibitors also prevented the ECV-induced PVR and Pdo increases in the rat lungs but had no effect on PVR or Pdo in the rabbit lungs. These results indicate that cyclooxygenase products of arachidonate metabolism mediate the ECV-induced Kf increase in both isolated rat and rabbit lungs.
Effects of volume history and vagotomy on pulmonary and chest wall mechanics in cats
Authors: Shardonofsky F. R. , Skaburskis M. , Sato J. , Zin W. A. , Milic-Emili J.
Published: December 2017

Using the technique of rapid airway occlusion during constant-flow inflation, we studied the effects of inflation volume, different baseline tidal volumes (10, 20, and 30 ml/kg), and vagotomy on the resistive and elastic properties of the lungs and chest wall in six anesthetized tracheotomized paralyzed mechanically ventilated cats. Before vagotomy, airway resistance decreased significantly with increasing inflation volume at all baseline tidal volumes. At any given inflation volume, airway resistance decreased with increasing baseline tidal volume. After vagotomy, airway resistance decreased markedly and was no longer affected by baseline tidal volume. Prevagotomy, pulmonary tissue resistance increased progressively with increasing lung volume and was not affected by baseline tidal volume. Pulmonary tissue resistance decreased postvagotomy. Chest wall tissue resistance increased during lung inflation but was not affected by either baseline tidal volume or vagotomy. The static volume-pressure relationships of the lungs and chest wall were not affected by either baseline tidal volume or vagotomy. The data were interpreted in terms of a linear viscoelastic model of the respiratory system (J. Appl. Physiol. 67: 2276–2285, 1989).
Activity of pulmonary surfactant after blocking the associated proteins SP-A and SP-B
Authors: Kobayashi T. , Nitta K. , Takahashi R. , Kurashima K. , Robertson B. , Suzuki Y.
Published: December 2017

This study investigated the role of sympathetic withdrawal on blood flow responses in cutaneous arteriovenous anastomoses (AVAs) and capillaries to direct and indirect heat stress. This was achieved by clamping sympathetic activity (SC) to the tail of anesthetized rats so that constrictor tone remained invariant during exposure of either the animal's tail (direct heating) or body (indirect heating) to a 35 degrees C environment. Flow through the AVAs in the tail was evaluated by laser-Doppler flowmetry (LDF), while capillary flow was investigated by videodensitometry measurements of blood cell velocity (CBV) in single capillaries within the subepidermal vascular plexus. Both direct and indirect heating significantly increased LDF and CBV. In comparison to blood flow responses in sham-operated control rats, the SC procedure resulted in significantly lower LDF responses to both direct and indirect heat stress. By contrast, the response of CBV was not significantly affected by SC during either mode of heating. These results indicate that the withdrawal of sympathetic constrictor tone plays a role in the response of cutaneous AVAs, but not precapillary arterioles, to direct as well as indirect heat stress. Additional studies on unanesthetized animals showed that superimposing body heating on a base of local heating elicited a further increase in LDF, suggesting that local heating does not deplete neural mediated dilatory reserve.
Atrial natriuretic peptide in acute hypoxia-induced pulmonary hypertension in rats
Authors: Jin H. , Yang R. H. , Chen Y. F. , Jackson R. M. , Itoh H. , Mukoyama M. , Nakao K. , Imura H. , Oparil S.
Published: December 2017

To test the hypothesis that exogenous atrial natriuretic peptide (ANP) prevents the acute pulmonary pressor response to hypoxia, ANP (20-micrograms/kg bolus followed by 1-microgram.kg-1.min-1 infusion) or vehicle was administered intravenously to conscious rats beginning 3 min before exposure to hypoxia or room air for 90 min. Exogenous ANP abolished the acute pulmonary pressor response to hypoxia in association with marked and parallel increases in plasma ANP and guanosine 5′-cyclic monophosphate (cGMP) and with a significant increase in lung cGMP content. To examine whether endogenous ANP modulates the acute pulmonary pressor response to hypoxia, rats were pretreated with a monoclonal antibody (Ab) to ANP and exposed to hypoxia. Mean pulmonary arterial pressure (MPAP) in the Ab-treated rats was not different from control over the first 6 h of hypoxic exposure. Thereafter, the Ab-treated group had significantly higher MPAP than control. Our data suggest that 1) exogenous ANP blocks the pulmonary pressor response to acute hypoxia via stimulation of cGMP accumulation in the pulmonary vasculature, and 2) endogenous ANP may modulate the subacute, but not acute, phase of hypoxic pulmonary hypertension.