bluuebunny/crossref_metadata_2025 huggingface dataset:
An examination of transcapillary water flux in renal inner medulla
Authors: Sanjana VM , Johnston PA , Robertson CR , Jamison RL
Published: December 2017

We recently demonstrated that net fluid uptake occurs in the capillary system of the inner medulla. To define the site of fluid uptake, the concentration of protein was determined in plasma from descending vasa recta at the base and tip of the exposed papilla in Munich-Wister rats. The vasa recta plasma-to-arterial plasma protein concentration ratio (VR/P) was 1.43 +/- 0.09 at the base and 1.66 +/- 0.09 at the tip. These results, which indicate fluid loss from the descending vasa recta, are difficult to explain on the basic of hydraulic and oncotic forces alone. The osmolality of the contents of descending vasa recta increased between base and tip (delta = 72 +/- 30 mosmol/kg H2O). If the increase in osmolality of plasma in descending vasa recta lags behind that of the adjacent medullary interstitium, a transcapillary osmotic driving force exists favoring water loss from descending vessels. It is concluded that fluid uptake by the inner medullary circulation occurs beyond descending vasa recta in interconnecting capillaries or ascending vasa recta. In our view the most likely interpretation of these results is that fluid movement across vasa recta in the inner medulla is influenced by three forces: those owing to transcapillary differences in osmotic, oncotic, and hydraulic pressures.
Renal excretion of urate in mongrel and Dalmatian dogs: a micropuncture study
Authors: Roch-Ramel F , Wong NL , Dirks JH
Published: December 2017

Free-low micropunction experiments were performed in mongrel dogs and in Dalmatian coach hounds infused with urate to obtain Purate levels of 0.15-0.21 mM before and during the infusion of pyrazinioc acid (PZA). In the absence of PZA, mongrel dogs excreted approximately 50% and Dalmatians 140% of filtered loads of urate. In mongrel dogs net reabsorption occurred only in the proximal convoluted tubules. PZA enhanced net proximal reabsorption and revealed the occurrence of proximal secretion, whereas fractional urate excretion in the urine decreased only slightly. In Dalmation dogs urate fluxes across walls of proximal convoluted tubules resulted in either net reabsorption or net secretion, with no mean change. Net urate secretion occurred between superficial late-proximal and early-distal tubules, and considerably decreased fractional excretion of urate. The renal handling of PZA was similar in mongrel and in Dalmatian dogs.
Measurements of exit rates to distinguish between facilitated and simple diffusion
Authors: Hunter FR , Fayad R , Mayorga I
Published: December 2017

A modification of the method of Sen and Widdas (J. Physiol. London 160:392-403, 1962) was used to measure the rate of exit of several nonelectrolytes from erythrocytes of various species. In spite of additional errors introduced by the larger half-saturation values of the carriers (phi) and concentrations, it was possible to distinguish between systems with small values of phi, systems with relatively large values of phi, and systems involving only simple diffusion. Approximate values of phi in millimoles and of maximum transfer rate (K) in isotonic units per minute were obtained using times and initial slopes measured on experimental curves. The following values in the foregoing units were obtained: human glucose, phi = 1.8, 1.0, K = 0.8, 1.1; human glycerol, phi = 178, 94, K = 4.3, 3.3; sheep thiourea, phi = 56, 56, K = 0.9, 0.6; and rabbit glycerol, phi = 328, 64, K = 2.2, 1.0. Simple diffusion was demonstrated for the following systems: ox-ethylene glycol; ox-glycerol; sheep-ethylene glycol; and sheep glycerol.
Biliary excretion of dye in dogs infused with BSP or its glutathione conjugate
Authors: Barnhart JL , Combes B
Published: December 2017

A comparison of the maximal rates of biliary excretion (Tm), of dye in dogs infused with either BSP or its glutathione conjugate (BSP-GSH) was carried out. Tm was much higher when BSP-GSH rather than BSP was infused. This was accounted for by a significantly higher concentration of dye in bile of dogs receiving BSP-GSH. Evidence is presented that BSP and its conjugated metabolites compete for a common transport carrier and that BSP disproportionately depresses the biliary excretion of conjugated dye compounds. This latter observation accounts for the depressed dye Tm found during infusion of BSP. Choleresis invariably accompanied dye excretion. When BSP-GSH was infused, enhanced bile flow could be accounted for by the predicted osmotic activity of dye transported into bile. By contrast, the choleresis measured during infusion of BSP was significantly greater than that predicted. An additional mechanism for choleresis is operative, therefore, when unconjugated BSP is infused. Administration of taurocholate enhanced dye Tm when BSP-GSH was infused. Since increments of canalicular bile flow induced by theophylline and glucagon did not enhance dye excretion into bile, this effect by taurocholate appears to be related to taurocholate excretion per se rather than to the enhanced canalicular bile flow which accompanies its excretion.
Effects of norepinephrine on mechanics of arteries in vitro
Authors: Cox RH
Published: December 2017

The effects of smooth muscle activation on the pressure dependence of arterial wall characteristic impedance were studied with isolated segments of canine iliac and carotid arteries. Measurements of external diameter and transmural pressure were made before and after activation of the arterial smooth muscle (SM) by norepinephrine (NE) in concentrations of 0.5 and 5 mug/ml and used to compute values of characteristic impedance (Z0). In the absence of SM tone, values of Z0 for both arterial sites increased monotonically with transmural pressure. For the larger [NE], values of ZO exhibited a minimum at pressures of the order of 125 mmHg and increased for both larger and smaller values of pressure, For the smaller [NE], values of Z0 showed a similar pressure dependence but with a broader minimum. It is concluded that the previously demonstrated constancy of vascular impedance with changes in arterial pressure is at least the result of the presence of a tonic level of SM activation in conduit arteries.
Responses of abdominal vascular capacitance to stimulation of splachnic nerves
Authors: Karim F , Hainsworth R
Published: December 2017

In chloralose-anesthetized dogs the abdominal circulation was vascularly isolated without opening the abdominal cavity. The region was perfused at constant flow through the aorta and drained at constant pressure from the inferior vena cava. Changes in resistance were calculated from changes in perfusion pressure and changes in capacitance were calculated by integrating changes in venous outflow. Stimulation of both splanchnic nerves at 20 Hz increased resistance by 135% and reduced capacitance by 7.20 ml kg-1. The capacitance responses at 1 and 2 Hz (3.42 and 5.43 ml kg-1) were 48 and 67% of the responses at 20 Hz, However, the resistance responses at 1 and 2 Hz (14 and 31% increase) were only 12 and 26% of the responses at 20 Hz. After occlusion of the splenic pedicle, capacitance responses were reduced by about 40%. Although changes in inferior vena caval pressure changed the volume of blood in the abdomen by 0.92 ml kg-1 cmH2O-1, the responses to stimulation were relatively constant in any one animal at constant venous pressures between 5 and 15 cmH2O.
Short-range stiffness of slow fibers and twitch fibers in reptilian muscle
Authors: Proske U , Rack PM
Published: December 2017

The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivision of its motor nerve, fibers of each type may be stimulated separately. When, during repetitive stimulation of nerve filaments, the muscle was lengthened or shortened, the tension changes included an initial short-range stiffness, followed by a later compliance. With increasing velocities of movement, the short-range stiffness increased toward a limiting value. For slow fibers this limiting value was reached with lower velocities of movement than for the twitch fibers. Provided that the same velocity of movement was used and the movements began from similar initial isometric tensions, the slow fibers resisted the movements with a greater stiffness than the twitch fibers. It is suggested that not all of the observed differences between the two fiber types can be interpreted simply in terms of differences in rates of formation and breakdown of cross-links.
Gastric H+ secretion in presence of substrates: absolute dependence on secretagogues
Authors: Kasbekar DK
Published: December 2017

Spontaneously secreting gastric mucosae of the bullfrog (Rana catesbeiana) were brought to resting states in the absence of both the exogenous secretagogue and energy-yielding substrate, either by treatment with burimamide or by the classical method of prolonged preincubation. Glucose, pyruvate, lactate, and tricarboxylic acid cycle intermediates were compared with short- and long-chain fatty acids as potential substrates on these resting mucosae to determine if the latter could initiate and sustain H+ secretion in the absence of added secretagogues. The experimental data indicate that fatty acids cannot stimulate acid secretion from the resting state by preempting the requirement for secretagogues. Although fatty acids may serve as preferred substrates in comparison with glucose, glycolytic intermediates, and tricarboxylic acid cycle intermediates, acid secretion is obligatorily dependent on the presence of endogenous or added secretagogues. The implications of this finding with respect to one of the recently proposed hypothesis for secretagogue regulation of gastric hydrochloric acid secretion are discussed.
Influence of sympathetic nerves on oxygen uptake or resting mammalian skeletal muscle,
Authors: Duran WN , Renkin EM
Published: December 2017

Gracilis muscles of anesthetized dogs were isolated and perfused with blood at constant flow. Oxygen uptake (Vo2) was measured by spectrophotometry of paired arterial and venous samples and monitored by continuous recording of HbO2 saturation. The sympathetic chain, connected to the isolated muscles, was stimulated electrically with supramaximal pulses. High frequencies (8-16/s) increased vascular resistance (R, ratio to control 1.86 +/- 0.6 SEM) and decreased Vo2 (0.61 +/- 0.02). Both effects could be maintained 10 min or longer. After stimulation there was an increase in Vo2, which could be less than equal to, or greater than the O2 deficit, depending on the stimulation frequency, the period of stimulation, and the blood flow. Low frequencies (0.5-4/s) increased R (1.39 +/- 0.04) and increased Vo2 during (1,18 +/- 0.03) and after stimulation. In several experiments there was an initial decrease in Vo2 which changed to an increase during the stimulation period while R remained elevated. These observations indicate that the decrease in Vo2 is due to closure of precapillary sphincters, whereas the increase is a direct effect on cell metabolism.
Effects of peptide hormone structure on H+ secretion by Necturus gastric mucosa
Authors: Berkowitz JM , Praissman M , LeFevre ME
Published: December 2017

The actions of human synthetic gastrin I(G), the C-terminal tetrapeptide of gastrin (T), and the C-terminal octapeptide of cholecystokinin (OP) on acid secretion and transepithelial potential difference (PD) of the isolated Necturus gastric mucosa were determined. All three peptides induced H+ secretion, but the maximum H+ output was less with OP than with G or T. G and OP produced their maximum H+ output at lower molar concentrations than T. G- and OP-stimulated secretion was long sustained, but T-stimulated secretion rapidly returned to basal levels. T- and G-stimulated secretion was partially inhibited by the addition of OP. Evidence is presented that T rapidly disappears from solutions exposed to gastric mucosa, whereas G does not. Washing sensitized the mucosa to subsequent addition of T. The results suggest that the action of the common C-terminal tetrapeptide of G, T, and OP is modified by the preceding amino acid sequences, and that T, the smallest of the three peptides, is rapidly degraded by gastric tissue in vitro. The implications of the work for the study of gastrointestinal hormone structure-function relationships in isolated tissue preparations are discussed.
Effects of potassium depletion on control of breathing in awake rats
Authors: Nattie EE , Tenney SM
Published: December 2017

Possible mechanisms for the variable ventilatory response to metabolic acid-base disturbances have been examined in normal and K-depleted rats. Ventilatory measurements are correlated with CSF acid-base data. The ratios VE/VO2 and 1/PaCO2 are utilized as indices of alveolar ventilation. The log of these indices correlates closely with CSF [H+] independent of [K+] except at very low CSF [H+] where the change in log 1/PaCO2 and log VE/VO2 per change in CSF [H+] is much diminished in low-K rats. This finding suggests the presence of an additional stimulus to breathing in the low-K rat opposing the inhibitory effect of low CSF [H+]. Otherwise the chemical control of ventilation appears to be normal. However, low-K rats always breath with a low-flight-Vt pattern and occasionally with abnormal rhythms. The similarity of the low K breathing pattern to that reported in awake animals with vagotomy and pneumotaxic center (PC) lesions suggests that the altered breathing pattern in depletion involves vagal and/or PC pathways. The similarity of the low-K breathing pattern to that observed with reserpine administration together with the known relationships of K and catecholamine metabolism lead to the speculation that K depletion alters breathing via an effect on central catecholamine metabolism. However, other mechanisms involving changes in membrane excitability and intracellular pH in K depletion might also be involved.
Renal responses of Australian lungfish to vasotocin, angiotensin II, and NaCl infusion
Authors: Sawyer WH , Blair-West  , Simpson PA , Sawyer MK
Published: December 2017

The Australian lungfish (Neoceratodus forsteri) responds to intravenous injections of 0.63 ng/kg or more of arginine vasotocin with increased dorsal aortic blood pressure, inulin clearance, urine flow, and tubular rejection of Na+. Single injections of 1 ng/kg or more of angiotensin II or norepinephrine also increase dorsal aortic pressure but do not cause consistent diuresis and natriuresis, Continuous infusions of angiotensin II or repeated injections of norepinephrine produce sustained hypertension and more modest diuresis and natriuresis than are seen after injections of arginine vasotocin that cause less hypertension. Infusions of isosmolar or hyposmolar NaCl solutions increase blood pressure, inulin clearance, urine flow, and tubular Na+ rejection in a manner resembling the response to argininge vasotocoin injections. These data are consistent with the hypothesis that arginine vasotocin is released in response to volume expansion in lungfishes and that it may act on the kidney as a diuretic and natriuretic hormone. They do not rule out a more direct action of expansion on renal functions.
Renal tubular reabsorptive response to hypernatremia
Authors: Bresler EH , Nielsen KT , Miller MC  , Stoud MR
Published: December 2017

Renal tubular reabsorptive response to rapid infusions of isotonic saline and 5% NaCl solutions were measured during brisk ethacrynic acid diuresis in anesthetized dogs. When adjustments were made for effects of variations in volume expansion, as indexed by plasma protein concentration ([Pprot]), tubular reabsorption of sodium per unit filtrate volume (TNa/GFR) was found to be significantly and positively correlated with plasma sodium concentration ([PNa]) despite hypernatremia and total body surfeit of sodium. The proportions of sodium and water reabsorbed were also homeostatically inappropriate, since the sodium concentration in the reabsorbate was somewhat in excess of that in contemporary plasma ultrafiltrate. These findings signify that glomerulotubular balance holds when the filtered load of sodium is increased by an increment in [pNa] as well as GFR. It is proposed that the moiety of tubular reabsorption (some 75% of GFR) studied here is more closely related to regulation of volume than of osmolality of sodium concentration, and the primary regulation exerted is on tubular volume reabsorption (bulk fluid reabsorption) rather than on the amount of sodium reabsorbed.
Uptake of bile acids by perfused rat liver
Authors: Reichen J , Paumgartner G
Published: December 2017

The uptake of 14C-labeled cholic, taurocholic, and chenodeoxycholic acid by the perfused rat liver was studied to characterize the mechanism responsible for hepatic uptake of bile acids. A rapid-injection multiple indicator-dilution technique and the three-compartment model of Goresky were employed. The kinetics of hepatic uptake of the three bile acids could be described by the Michaelis-Menten equation. The maximal uptake velocities (Vmax) were 24.9 +/- 2.2 (mean +/- SD), 20.8 +/- 1.2, 1.2, and 11.4 +/- 0.9 nmol/s-g liver for cholic, taurocholic, and chenodeoxycholic acid, respectively. The corresponding apparent half-saturation constants (Km) were 526 +/- 125, 258 +/- 43, and 236 +/- 48 nmol/g liver. Competitive inhibition could be demonstrated between cholate and taurocholate as well as between cholate and chenodeoxycholate. Substitution of 94% of the Na+ in the perfusion medium decreased the Vmax and the apparent Km of taurocholate uptake by 68 and 55%, respectively. These findings are consistent with the hypothesis that bile acids are taken up into the hepatocyte by Na+-dependent carrier-mediated transport.
Circulatory responses of the near-term sheep fetus to prostaglandin E2
Authors: Rankin JH , Phernetton TM
Published: December 2017

The effect of prostaglandin E2 (PGE2) on the fetal circulation was measured in chronically catheterized ewes using radioactive microspheres. The injection of 10 mug/kg PGE2 into six fetuses resulted in a biphasic pressor response with a hypotensive period followed by a prolonged period of hypertension. The fetal arterial pressure rose from 45 to 63 mmHg (P less than 0.002). The placental membrane flow changed from 36 to 16 ml/min (P less than 0.004), the fetal renal blood flow changed from 8.6 to 7.1 ml/min per kg of fetus (P less than 0.001). It was postulated that the hypotensive response was due to a direct effect of PGE2 on the heart and the hypertensive response was due to PGE2 releasing a vasoconstricting agent into the fetal circulation. In nine experiments the PGE2 was administered to the maternal lcirculation. This caused a fetal hypertension and a vasoconstriction of the fetal renal, placental membrane, and umbilical circulations. These changes were similar in time course and magnitude to those described above. It is postulated that PGE2 crosses the placenta and that the fetal responses seen in this series are similar to those seen when PGE2 is administered to the fetal circulation.
Ascending pressor and depressor pathways in the cat spinal cord
Authors: Chung JM , Wurster RD
Published: December 2017

Blood pressure responses to stimulation of the cervical dorsolateral sulcus (DLS) of the spinal cord and lumbar dorsal roots were studied in anesthetized, vagotomized, and paralyzed cats. Stimulation of the lumbar dorsal roots elicited pressor responses with high-frequency stimulation (50 Hz, 10 V, 1 ms) and depressor responses with low-grequency stimulation (1 Hz, 10 V, 1 ms). Pressor responses were converted to depressor responses after bilateral lesions were made in the DLS area rostral to the site of stimulation. These results suggest that the ascending spinal pressor pathways are localized in the DLS region. Furthermore, these depressor responses were abolished by placing additional bilateral lesions in the dorsolateral funiculus (DLF) rostral to the site of stimulation. These data indicate the presence of ascending depressor pathways in the DLF which are anatomically separate from pressor pathways. Both pathways were found to be bilateral systems, and decussation of fibers appears to be complete within three segments rostral to their entry into the spinal cord. Ascending depressor pathways have a low optimal frequency of activation, as opposed to the ascending pressor pathways which have a relatively high optimal frequency of activation. Neurophysiological evidence obtained by recording unit activity from the cervical sympathetic trunk confirmed the localization of the ascending pressor and depressor pathways.
Changes in CNS responsiveness during hibernation
Authors: Beckman AL , Stanton TL
Published: December 2017

The ability of the midbrain reticular formation (MRF) to produce thermogenic responses and to trigger arousal from hibernation was tested during successive quarters of individual hibernation bouts. Golden-mantled ground squirrels (Citellus lateralis) were implanted with bilateral cannula guides into the MRF. Single, bilateral, 1-mul injections of acetylcholine (ACh) at concentrations of 50, 100, or 200 mug/mul were delivered in each quarter of the same bout or in selected quarters of different bouts. The results show that the magnitude of thermogenic responses evoked by ACh stimulation of the MRF was depressed during the early portion of the bout and increased as time in the bout elapsed. Furthermore, the magnitude of responses evoked during hibernation was depressed in comparison to those evoked during euthermia, indicating the influence of inhibition on the responsiveness of the CNS during hibernation. We suggest that during hibernation, a progressive change in responsiveness of the CNS, perhpas focused in the MRF, controls the duration of each hibernation bout.
Renal gluconeogenesis and increased glucose utilization in shock
Authors: Archer LT , Benjamin B , Lane MM , Hinshaw LB
Published: December 2017

The roles of renal gluconeogenesis and glucose utilization in control, hemorrhaged, and endotoxin-injected animals were investigated using anesthetized, eviscerated, nonnephrectomized and nephrectomized dogs. Results demonstrate an increased glucose utilization in both hemorrhagic and endotoxic shock which was marked after endotoxin. Since blood glucose values dropped more in nephrectomized, hemorrhaged animals, in contrast to the nonnephrectomized, hemorrhaged dogs, the kidneys were assumed to perform a significant gluconeogenic role. The kidneys did not appear to perform gluconeogenesis in endotoxin shock since blood glucose levels were comparable in eviscerated, endotoxin-treated animals whether nephrectomized or not. To ascertain the tissue responsible for the increased glucose utilization in endotoxin shock, a study was performed with endotoxin added to blood in vitro (estimated LD100 concentration). The endotoxin-treated blood (n = 7) demonstrated an increased glucose utilization compared with saline controls (n = 7) (P less than or equal 0.02). Acclerated glucose utilization rates were comparable between the eviscerated, nephrectomized animals and in vitro experiments. These data suggest that excessive glucose demand by certain blood components may partially explain the lethal hypoglycemia of endotoxin shock.
Cardiovascular and metabolic responses during burn shock in the guinea pig
Authors: Wolfe RR , Miller HI
Published: December 2017

The hemodynamic and metabolic responses of fatally burned, nonfatally burned, and unburned control guinea pigs were compared. The burns were induced in temporarily anesthetized animals by immersion to either the xyphoid process (70% fatal) or the midabdomen (100%survival) in boiling water for 3 s. Although cardiac output was reduced in all animals postburn, the survivors (MAG) has higher cardiac outputs at lower arterial pressures than the nonsurvivors (XPN). The postburn lactate levels in the XPN were higher than in the MAG, and the postburn values for pH, oxygen consumption, and core temperature were lower in the XPN. In each group, hyperglycemia was evident for 8 h postburn and terminal plasma glucose concentrations were usually elevated or similar to the prevalue. It was concluded that fatal and nonfatal burn shock were distinguished primarily by differences in tissue perfusion.
Autoregulation of cerebral blood flow and its relation to cerebrospinal fluid pH
Authors: Hernandez-Perez MJ , Anderson DK
Published: December 2017

Internal carotid artery blood flow (IFBF) was determined in each of nine Macaca mulatta by means of a flow transducer implanted around an internal carotid artery. The monkeys were lightly anesthetized, intubated, and paralyzed. Normoxia and normocarbia were maintained stable throughout the experiment. ICBF was monitored while mean arterial blood pressure (MABP) was lowered by withdrawal of blood. MABP was kept within the known limits of autoregulation in order not to compromise CBF. Cerebrospinal fluid (CSF) from the cisterna magna was analyzed for pH PCO2, and PO2 before and after a 30-min hypotensive period in which MABP was lowered from 116 +/- 4 to 70 +/- 2 mmHg (mean +/- SE). Corresponding HCO3- concentrations were calculated. The decrease in MABP did not result in a significant reduction in ICBF but elicited a 37% reduction in calculated cerebrovascular resistance, indicating normal autoregulation. Mena CSF pH was not significantly decreased (P less than 0.05); it changed from 7.320 +/- 0.010 to 7.317 +/- 0.010 after the induced hypotensive period. Thus CSF pH does not appear to have a significant role in cerebral blood flow autoregulation.
Preglomerular resistance and glomerular perfusion in the rat and dog
Authors: Chenitz WR , Nevins BA , Hollenberg NK
Published: December 2017

Glomerular blood flow in the rat, measured with radioactive microspheres, averaged 233 +/- 59 nl/min per glomerulus, significantly less than the glomerular flow rate in the dog (568 +/- 115; P less than 0.005). The difference in glomerular blood flow rate could not be attributed to differences in mean or cortical flow rates, the fraction of acrdiac output received, cardiac output normalized to body weight, or the fractional distribution of blood flow or glomeruli from outer to inner cortex in the two species. The size of microspheres reaching the glomerulus, however, was significantly larger in the dog than in the rat (P less than 0.0005) suggesting that afferent arterioles were larger in the dog than rat. The difference in afferent resistance calculated from the size of microspheres delivered to the glomeruli was larger than the difference in glomerular blood flow. With a similar arterial pressure, a lower afferent resistance suggests a higher glomerular capillary pressure in the dog, consistent with a number of suggestions that filtration equilibrium is less likely in this species.
Changes in canine saliva ion concentration induced by increased intraluminal pressure
Authors: Siegel KA
Published: December 2017

Hydrostatic pressure was applied to a cannula inserted into Wharton's duct of adult dogs anesthetized with pentobarbital and the effect of pressure on saliva flow rate and ionic composition of saliva was measured. Increasing the back pressure on a secreting gland resulted in a decrease in flow rate. Over the range of 0-100 mmHg back pressure the decrease in flow was proportional to the applied back pressure. The potassium concentration of saliva collected in the absence of back pressure and at raised pressure was similar even though back pressure reduced flow. In contrast, sodium concentration decreased when back pressure caused salivary flow rate to be reduced. However, when examined at the same flow rates the concentration of sodium is increased when back pressure is applied to the gland as compared to absence of back pressure. Under conditions of constant stimulation the total output of sodium and potassium into saliva decreases as back pressure is increased; but when equal flow rates are compared total sodium output increases in the presence of applied back pressure, whereas potassium output remains constant.
Lung surfactant: some historical perspectives leading to its cellular and molecular biology
Authors: Tierney D. F.
Published: December 2017

By appreciating the influence of surface forces on lung mechanics, discovering pulmonary surfactant, and then recognizing its deficiency states a small number of investigators began the first 30 years of pulmonary surfactant research. These investigators had different backgrounds and took diverse approaches to understand surface forces in the lung. Their careers provide a fascinating study of the means by which new discoveries are made. After recognizing the critical importance of surfactant, investigators turned to a series of questions that obviously needed to be answered and they attempted to learn the following: 1) how to quantitate surfactant; 2) its biochemical and structural composition; 3) how it leaves the alveolar surface after secretion; and 4) its role in lung diseases. This research established the basis for pursuing the cellular and molecular biology of surfactant.
Release of intracellular calcium by two different second messengers in airway epithelium
Authors: McCann J. D. , Bhalla R. C. , Welsh M. J.
Published: December 2017

To better understand regulation of Cl- secretion by airway epithelia, we measured the intracellular Ca2+ concentration ([Ca2+]c) using the Ca2+ indicator fura-2 and a fluorescent microscope imaging system. We examined receptor-mediated changes in [Ca2+]c in response to two Cl- secretagogues: the beta-adrenergic agonist isoproterenol and the peptide hormone bradykinin. Isoproterenol increased cell adenosine 3',5'-cyclic monophosphate (cAMP) levels but did not alter cellular accumulation of inositol phosphates. Bradykinin stimulated inositol phosphate accumulation but, in the presence of indomethacin, did not alter cAMP levels. Despite the difference in second messenger pathways, both bradykinin and isoproterenol transiently increased [Ca2+]c. Bradykinin stimulated inositol phosphate accumulation and increased [Ca2+]c with similar potencies, suggesting that bradykinin elevated [Ca2+]c by stimulating inositol phosphate production. The response to isoproterenol was inhibited by a beta-adrenergic antagonist, but not an alpha-adrenergic antagonist, and was mimicked by a membrane permeant analogue of cAMP. Isoproterenol also increased [Ca2+]c and cAMP at similar potencies. These results suggest that isoproterenol increased [Ca2+]c via cAMP. Both agonists increased [Ca2+]c when the extracellular [Ca2+] was reduced, suggesting that they release Ca2+ from intracellular stores. The ability of cAMP to increase [Ca2+]c suggests a mechanism by which cAMP- and Ca2+-activated membrane transport processes can be regulated in a coordinating manner.
Postnatal stimulation of rat surfactant protein A synthesis by dexamethasone
Authors: Floros J. , Phelps D. S. , Harding H. P. , Church S. , Ware J.
Published: December 2017

The effects of postnatal dexamethasone treatment in vivo on the synthesis of surfactant protein A (SP-A) were examined at the protein and RNA levels. Rats ranging from 1 day old to adult were injected with 200 micrograms of dexamethasone/kg body wt or with vehicle alone and were killed 24 h after injection. One portion of the lung was metabolically labeled with [35S]methionine, the proteins immunoprecipitated using an antiserum to SP-A, and analyzed electrophoretically. Both newly synthesized intracellular and secreted SP-A levels were increased by dexamethasone, reaching averages of 2.3 and 4.5 times control values, respectively. Another portion of the lung tissue was used for RNA analysis. SP-A mRNA levels were also elevated an average of 1.4 times control values by hormone treatment. Dose-response experiments using 16-day-old pups showed that both total SP-A, as measured by enzyme-linked immunosorbent assay, and total SP-A mRNA levels were elevated with dexamethasone treatment, reaching maximal stimulation at 2 mg. We conclude that postnatal dexamethasone treatment in vivo results in increased levels of both newly synthesized SP-A and SP-A mRNA, suggesting that pretranslational events may in part contribute to this process.
Regulation of lung cell proliferation by polypeptide growth factors
Authors: King R. J. , Jones M. B. , Minoo P.
Published: December 2017

In the last 10 years there has been an increased appreciation of the changes in lung cell populations that occur in association with the acute respiratory failure often induced by traumatic injury. Early events result in an accumulation in the lung of platelets, neutrophils, monocytes, and macrophages, a release of substances having potent cardiopulmonary and metabolic effects, and an ensuing edema and transudation of materials from the interstitium and capillaries into the alveoli. Further progression of the injury results in significant decreases in the number of endothelial and type I epithelial cells and a subsequent hyperplasia of fibroblasts and type II-like epithelial cells. Major sequelae of the latter stage of the disease are interstitial and interalveolar fibrosis, probably resulting from the increased number of fibroblasts present. The activity and composition of pulmonary surfactant are often perturbed. This review will discuss mechanisms that may be involved in these processes, with major emphasis on cell-cell interactions mediated through polypeptide growth factors. We describe the properties of certain growth factors commonly associated with inflammatory and wound healing reactions, discuss their cellular origins, and speculate on their possible roles in mediating the structural and physiological responses seen in the lung during acute respiratory failure. The majority of work done with lung cells has concentrated on interactions between macrophages and fibroblasts, and it is evident that macrophages are capable of producing mitogens affecting the proliferation of fibroblasts. However, from the results of studies that are less developed, it is possible that epithelial cells and immunologically stimulated cells could also be involved in these actions. We conclude that the homeostasis of lung cell populations may be influenced by both growth-stimulating and growth-inhibiting substances and potentially could involve interactions through growth factors of fibroblasts, macrophages, lymphocytes, alveolar epithelial cells, endothelial cells, and platelets. At this time the information on these purported interactions is quite limited and there are far more questions than answers.
Endotoxin increases lung Cu,Zn superoxide dismutase mRNA: O2 raises enzyme synthesis
Authors: Iqbal J. , Clerch L. B. , Hass M. A. , Frank L. , Massaro D.
Published: December 2017

Administration of endotoxin to adult rats increases lung Cu,Zn superoxide activity after 72 h of exposure to greater than 95% O2. The increased activity is brought about mainly by a faster rate of Cu,Zn superoxide dismutase synthesis; rats treated with endotoxin but not exposed to hyperoxia do not exhibit these findings (Hass, Frank, and Massaro, J. Biol. Chem. 257: 9379-9383, 1982). We now report that 48 h after treatment of adult rats with endotoxin there was a decreased rate of Cu,Zn superoxide dismutase synthesis by lung slices from air- and O2- exposed rats, although, in both groups, the lung concentration of Cu,Zn superoxide dismutase mRNA was increased approximately 45%. Exposure of endotoxin-treated rats to greater than 95% O2 or air for an additional 24 h (72 h all told) resulted in continued elevation of Cu,Zn superoxide dismutase mRNA only in lungs of O2- exposed rats. In vitro exposure of lung slices from air-breathing saline- or endotoxin-treated rats to 95% O2 for 6 h led to an increased rate of Cu,Zn superoxide dismutase synthesis only in slices from endotoxin-treated rats. We conclude that endotoxin treatment leads to an increased concentration of Cu,Zn superoxide dismutase mRNA in rat lungs, but a sustained elevation of the mRNA, and its translation into an increased rate of Cu,Zn superoxide dismutase synthesis requires exposure of the lung to hyperoxia.
Endotoxin stimulates platelet-derived growth factor production from cultured human pulmonary endothelial cells
Authors: Albelda S. M. , Elias J. A. , Levine E. M. , Kern J. A.
Published: December 2017

The interaction of Gram-negative bacterial cell wall products (endotoxins) with endothelial cells is thought to be responsible for many of the damaging manifestations of Gram-negative sepsis. Because cultured human endothelial cells are relatively resistant to the direct cytotoxic actions of endotoxin, it is possible that many of the systemic effects of endotoxin may be caused by stimulation of endothelial cells to produce biologically active mediators which could then act on targets such as smooth muscle cells, fibroblasts, and leukocytes. We hypothesized that one such endothelial cell-derived mediator could be platelet-derived growth factor (PDGF), a protein that causes proliferation of mesenchymal cells, chemotaxis of leukocytes, fibroblasts and smooth muscle cells, and vasoconstriction. We therefore examined the effect of endotoxin on PDGF-like protein production by cultured adult human pulmonary artery endothelial cells. Twenty-four hours of endotoxin exposure resulted in a threefold increase in the steady-state levels of mRNA coding for PDGF B-chain (c-sis) and a two- to threefold increase in the amount of newly synthesized PDGF released into the media, as measured by immunoprecipitation of [35S]methionine-labeled protein with anti-PDGF antiserum. We conclude that human pulmonary artery endothelial cells in culture are stimulated both to produce increased amounts of PDGF mRNA and to release PDGF-like protein after exposure to endotoxin. This increased release of PDGF-like protein by human endothelial cells may play a role in the inflammatory infiltrate, vasospasm, and fibroblast proliferation that characterize the host response to endotoxin.
Brief perinatal hypoxia impairs postnatal development of the bronchiolar epithelium
Authors: Massaro G. D. , Olivier J. , Massaro D.
Published: December 2017

We placed pregnant rats in 10% O2 on the last day of gestation for less than or equal to 9 h plus 1-2 h (with their pups) after the onset of delivery. In the pups this brief perinatal hypoxia led to an altered cellular composition of the bronchiolar epithelium that persisted at least to age 30 days; it was characterized by a higher nuclear numerical density (Nvn) of Clara cells, a lower Nvn of ciliated cells, and a lower percentage and Nvn of Clara cells in mitoses compared with control rats. The perinatal hypoxia also led to a significantly lower volume and volume density of the secretory apparatus (rough endoplasmic reticulum and secretory granules) on day 7 in 10% O2-born rats. The data on the Nvn of Clara and ciliated cells and on Clara cell mitoses are consistent with the notion that exposure to 10% O2 impaired the differentiation of Clara cells into ciliated cells and this impairment persisted well beyond the period of exposure.
Phospholipid transfer proteins in mammalian lung
Authors: Lumb R. H.
Published: December 2017

Proteins that catalyze the transfer of phospholipids between membranes are known to occur in the mammalian lung and may play roles in the pulmonary surfactant system. These roles may include 1) packaging of newly synthesized as well as recycled surfactant phospholipid into lamellar bodies, the intracellular storage form of surfactant phospholipid, 2) extracellular movement of phospholipid between the compartments in the alveolar subphase, and 3) delivery of phospholipid to membrane sites during signal transduction events. The nature and distribution of these proteins are discussed as they relate to the pulmonary surfactant system.
Tumor necrosis factor-induced lung injury is not mediated by platelet-activating factor
Authors: Chang S. W. , Ohara N. , Kuo G. , Voelkel N. F.
Published: December 2017

Both tumor necrosis factor (TNF) and platelet-activating factor (PAF) have been incriminated as mediators of endotoxic shock. Since TNF stimulates PAF synthesis in vitro, we tested the hypothesis that PAF mediates TNF-induced lung injury in vivo using specific PAF receptor antagonists. Intravenous infusion of purified human recombinant TNF resulted in peripheral neutrophilia, lymphocytopenia, and hemoconcentration, caused hemorrhagic injury to the cecum, and increased lung tissue levels of thromboxane B2 and 6-ketoprostaglandin F1 alpha. In addition, plasma glutathione disulfide (GSSG), an in vivo index of oxidative stress, was significantly increased. TNF (0.01-1 mg/kg) caused a dose-dependent increase in lung permeability-surface area product (PS) measured in isolated perfused lungs removed from rats 90 min after injection of TNF. [Lung PS in controls and after 0.01, 0.1, and 1.0 mg/kg of TNF were 0.022 +/- 0.001, 0.027 +/- 0.002, 0.033 +/- 0.001, and 0.036 +/- 0.005, respectively (P less than 0.05 from control for TNF 0.1 and 1 mg/kg).] Pretreatment of the rats with the PAF receptor antagonists WEB 2086 (10 mg/kg) and SRI 63-441 (10 mg/kg), at doses that previously protected against endotoxin-induced lung injury, did not significantly affect TNF-induced (0.1 mg/kg) changes in hematocrit, plasma GSSG, or lung PS. Moreover, WEB 2086 (10 mg/kg) did not inhibit TNF-induced (1 mg/kg) lymphocytopenia or the increases in lung tissue eicosanoid products. We conclude that TNF causes oxidative stress, eicosanoid activation, and acute lung injury in rats by a mechanism largely independent of PAF receptor activation.
Translocation of protein kinase C is associated with inhibition of 5-HT uptake by cultured endothelial cells
Authors: Myers C. L. , Lazo J. S. , Pitt B. R.
Published: December 2017

Acute exposure (30 min-1 h) of bovine pulmonary artery endothelial cells in culture (BPAEC) to phorbol myristate acetate (PMA 10(-10)-10(-6) M) resulted in concentration-dependent decrement in serotonin (5-HT) uptake. Neither cell viability (trypan blue exclusion or release of deoxyglucose) nor activity of another plasma membrane function, angiotensin-converting enzyme activity, were affected. A decrease in 5-HT uptake was also noted with phorbol 12,13 dibutyrate and mezerein, but not with 4-alpha-phorbol 12,13 didecanoate, which does not stimulate protein kinase C (PKC). Inhibition of 5-HT uptake by PMA (160 nM) was reversed in a concentration-dependent manner by pretreatment of cells with the PKC inhibitor staurosporine (3-100 nM). BPAEC were treated with PMA (160 nM) for 1 h, and activities of PKC in cytosolic and membrane compartments were determined. PMA did not significantly affect total cellular PKC activity but resulted in a translocation of activity from cytosol to membrane (control membrane activity 67 +/- 4%; PMA-treated membrane activity 97 +/- 1% of total cellular PKC). Thus we propose that translocation of PKC from cytosol to membrane results in inhibition of 5-HT uptake by BPAEC.
Erythrocytes fail to induce glutathione in response to diethyl maleate or hyperoxia
Authors: Phelps D. T. , Deneke S. M. , Baxter D. F. , Fanburg B. L.
Published: December 2017

We have previously found that exposure of pulmonary artery endothelial cells to hyperoxia or low concentrations of diethyl maleate (DEM) results in elevation of both cellular glutathione (GSH) and uptakes of glutamate and cystine. The present study confirms that this elevation occurs for a variety of lung cells (bovine pulmonary artery endothelial and smooth muscle cells and rat lung fibroblast and epithelial-like cells) but not for human, rat, and chicken erythrocytes. In fact, human and rat erythrocyte GSH levels were reduced substantially at DEM concentrations from 0.05 to 0.5 mM, whereas the GSH level of chicken erythrocytes was almost totally eliminated by 0.05 mM DEM. Also, all erythrocytes failed to accumulate measurable amounts of radioactive glutamate or cystine. The findings suggest the presence of different mechanisms for the regulation of cellular GSH in lung cells from those of erythrocytes. They are consistent with a requirement for a cystine-glutamate transporter and transcriptional and translational events for the elevation of cellular GSH in response to hyperoxia or low levels of DEM in the lung cells.
Selective expression of an amiloride-inhibitable Na+ conductance from mRNA of respiratory epithelium in Xenopus laevis oocytes
Authors: Kroll B. , Bautsch W. , Bremer S. , Wilke M. , Tummler B. , Fromter E.
Published: December 2017

Poly(A)+RNA was prepared from primary cultures of human nasal polyp epithelia and from native bovine tracheal epithelia. Six to fifty nanograms mRNA were injected into prophase-arrested immature Xenopus laevis oocytes. One to four days later the oocytes were probed with electrophysiological techniques for induction of novel ion conductances. Oocytes injected with mRNA had lower membrane potentials (Vm) and resistances (Rm) than controls. By use of step changes in extracellular Na+ concentration and applying amiloride, a Na+ conductance could be identified in mRNA-injected oocytes, which was inhibited by submicromolar concentrations of amiloride with the same kinetics (Ki = 1.3 X 10(-7) mol/l) as in the original tissue. After complete inhibition of this conductance by 10(-5) mol/l amiloride, Vm and Rm approached the respective values of controls. The data indicate that oocytes express functional epithelial Na+ channels but apparently no other epithelial ion conductances from injected mRNA of respiratory epithelium.
Immunotargeting: a contemporary approach to the study of lung development
Authors: Funkhouser J. D. , Peterson R. D.
Published: December 2017

This commentary discusses an immunological approach to lung development that has been termed immunotargeting. The approach involves the use of monoclonal antibody technology to identify cell membrane antigens unique to cells of particular lineage or stage of differentiation. Methods of using the antibodies to focus on important unresolved questions relating to development, particularly of the pulmonary epithelium, are discussed. Antigens and membrane molecules, which have already been identified and which may be useful in this type of approach to respiratory epithelial cell differentiation, are enumerated and briefly described.
Release of cyclooxygenase products from primary cultures of tracheal epithelia of dog and human
Authors: Widdicombe J. H. , Ueki I. F. , Emery D. , Margolskee D. , Yergey J. , Nadel J. A.
Published: December 2017

Release of cyclooxygenase products from primary cultures of dog or human tracheal epithelium was measured by radioimmunoassay. In both species, bradykinin, platelet-activating factor (PAF), and A23187 (a calcium ionophore) caused increases in the rate of release of prostaglandin (PG) E2 and smaller increases in PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2 output. Isoproterenol, vasoactive intestinal peptide (VIP), methacholine, and leukotrienes C4 and D4 had no effect on release of these cyclooxygenase products. Gas chromatography-mass spectrometry showed that the ratio of PGE2 to PGD2 released from dog cells by A23187 was 30:1. Short-circuit current across dog cells was stimulated by bradykinin, A23187, PAF, VIP, methacholine, and isoproterenol. Only the responses to bradykinin and A23187 were reduced by pretreatment with indomethacin.