bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of plasma vasopressin after drinking in dehydrated humans
Authors: Geelen G. , Keil L. C. , Kravik S. E. , Wade C. E. , Thrasher T. N. , Barnes P. R. , Pyka G. , Nesvig C. , Greenleaf J. E.
Published: December 2017

To study the effects of nonosmotic and nonvolumetric factors that may influence secretion of vasopressin, serum Na+, K+, and osmolality (Osm), hemoglobin, hematocrit, plasma arginine vasopressin (AVP), aldosterone (PA), and renin activity (PRA) were measured in five men and three women (26–50 yr, 73 +/- 4 kg) before and after 24 h of mild dehydration (food but no fluid) and seven times during the 1st h after rehydration with 10 ml/kg of tap water (17.5 +/- 0.5 degrees C) consumed in 105 s (range 35-240 s). Dehydration increased mean serum Na+ 3.7 +/- 0.7 meq/l (P less than 0.05), osmolality 9.1 +/- 1.1 mosmol/kg (P less than 0.05), and AVP from a hydrated level of 1.7 +/- 0.2 to 3.3 +/- 0.5 pg/ml (delta = 1.6 pg/ml, P less than 0.05). After rehydration AVP fell to 2.4 +/- 0.3 pg/ml (P less than 0.05) within 3 min and reached the water-replete level of 1.8 +/- 0.3 pg/ml 9 min after drinking started. Serum Na+ and Osm did not change until 30–60 min after drinking. No significant changes occurred in PRA, hemogloblin, hematocrit, or calculated delta in plasma volume, but PA increased from 11.1 +/- 1.5 ng/dl after dehydration to 15.6 +/- 2.6 ng/dl (P less than 0.05) between 30 and 60 min after drinking. The rapid fall in plasma AVP after rehydration took place in the absence of the expected changes in the primary regulators of plasma AVP (i.e., osmolality and plasma volume), with no change in blood pressure. The results suggest that oropharyngeal factors, alone or combined with gastric stimuli, are implicated.
Renal and extra-renal excretion of calcium in the marine teleost, Gadus morhua
Authors: Bjornsson B. T. , Nilsson S.
Published: December 2017

The calcium turnover, with particular emphasis on the routes and rates of excretion, was investigated in the Atlantic cod, Gadus morhua. A very rapid internal redistribution of injected 45Ca was demonstrated, with the decline in the plasma concentration conforming to the power function f(t) = 8.83% X t-0.585. The clearance for 45Ca and [3H]inulin were both linearly correlated to urine flow and showed a ratio (Cca/CIn) of 2.6:1. Likewise a linear correlation between the renal and extra-renal excretion of 45Ca could be demonstrated with a ratio of 1:0.47, indicating that the renal route of excretion is of major importance in this species. The renal excretion of calcium was estimated to be 4.2 mumol X kg-1 X h-1 and the total calcium excretion to be 6.2 mumol X kg-1 X h-1. Calculations are presented, suggesting that the balance between intake and excretion of calcium can be explained in terms of growth of the animal, which would allow for an increase in the amount of body calcium of approximately 5 g X yr-1. It is also concluded that because about two-thirds calcium is excreted via the renal route, the kidneys may be the most important site for the regulation of calcium excretion in the cod.
Activation of branched-chain keto acid dehydrogenase by exercise
Authors: Kasperek G. J. , Dohm G. L. , Snider R. D.
Published: December 2017

The present study was conducted to investigate the metabolic regulation of leucine oxidation during exercise. Ten rats per group were run at 27 m/min (0% grade) on a treadmill for 30 and 120 min or until exhausted, and the total and basal activity of branched-chain keto acid dehydrogenase was examined in the muscle, liver, and heart. The total activity of the dehydrogenase in the heart, liver, or skeletal muscle was unchanged by exercise. However, exercise increased the basal activity levels of the dehydrogenase about 10-fold in muscle and 5-fold in heart. The basal dehydrogenase activity in the liver was unchanged by exercise. Activation of the dehydrogenase in both muscle and heart was statistically elevated after 30 min exercise and continued to increase during the remainder of the exercise bout. The basal activity of the dehydrogenase returned to resting levels by 10 min postexercise. The activation of the dehydrogenase in muscle and heart during exercise likely is due to dephosphorylation because activity of the enzyme in mitochondria isolated from exercised muscles reverts to control values when the mitochondria are incubated in the presence of ATP. Thus the increased leucine oxidation observed during exercise is due to activation of the branched-chain keto acid dehydrogenase by dephosphorylation. This is the first example of a large increase in branched-chain keto acid dehydrogenase activity caused by a physiological process. This demonstrates that the muscle's latent capacity of oxidize branched-chain amino acids is much larger than previously thought and that this capacity is used in exercising muscle.
Water and ion shifts in skeletal muscle of humans with intense dynamic knee extension
Authors: Sjogaard G. , Adams R. P. , Saltin B.
Published: December 2017

Six subjects performed one-legged dynamic knee-extension. Blood samples were drawn from the femoral artery and vein, and muscle biopsies were obtained from the quadriceps muscle. Leg blood flow was measured by the thermodilution technique, and 3H-inulin was infused for determination of extra- and intracellular muscle water shifts. During the submaximal work load (S) muscle lactate increased, whereas muscle pH remained almost constant; after maximal exercise (M) the values markedly increased for lactate and decreased for pH. Except for a release of lactate from the exercising muscles, K was continuously released throughout S, and this release increased during M. Immediately when the muscles relaxed, the K release was converted to a K re-uptake. The calculated K loss, based on v- a and flow values, agreed with the decrease in muscle K content from 458 mmol/kg dw at rest to 414 mmol/kg dw at exhaustion (P less than 0.05), as analyzed on the muscle biopsies. Muscle water content increased during S mainly because of an increased extracellular H2O, whereas during M the largest increase occurred in intracellular H2O (H2Oi). Because of the simultaneous K loss and H2Oi increase in the exercising muscle the intracellular [K] was calculated to decrease from 165 mM at rest to 129 mM at exhaustion. This decrease and an increase in extracellular [K] from 4.5 mM at rest to greater than 6.0 mM at exhaustion affects the muscle membrane excitability. Muscle fatigue may thus not only be caused by changes within the cell, affecting energy metabolism or actin-myosin reaction, but may be located at the membrane protecting the cell against overload.
Cardiovascular responses to elevation of intra-abdominal hydrostatic pressure
Authors: Barnes G. E. , Laine G. A. , Giam P. Y. , Smith E. E. , Granger H. J.
Published: December 2017

Intra-abdominal fluid volume and hydrostatic pressure were elevated by positive pressure infusion of Tyrode solution into the peritoneal cavity of anesthetized dogs. The compliance of the peritoneal cavity fell from 10.8 to 0.56 ml X mmHg-1 X kg-1 of body wt as intra-abdominal pressure increased from 0 to 40 mmHg. Intrathoracic pressure also increased as elevated peritoneal pressure caused diaphragmatic bulging. Cardiac output and stroke volume were reduced by 36% after an intra-abdominal pressure rise of 40 mmHg; in contrast, heart rate did not change. Flow in the celiac, superior mesenteric, and renal arteries was reduced by 42, 61, and 70%, respectively. Pressure in the femoral vein increased to 46 mmHg, while flow in the femoral artery decreased by 65%. Whole-body O2 consuxmption, pH, and arterial PO2 decreased as intra-abdominal pressure rose. The peritoneal cavity, with its high initial compliance, affords the body an ideal location for the temporary accumulation of small to moderate volumes of fluid during episodes of increased vascular pressure or permeability. The marked alterations in the hemodynamic properties of the cardiovascular system are indicative of the physiological changes that occur when intra-abdominal fluid accumulation becomes excessive and peritoneal pressure rises to high levels.
Hyperdipsia in rats after electrolytic lesions of nucleus medianus
Authors: Gardiner T. W. , Stricker E. M.
Published: December 2017

Ablation of the ventral portion of nucleus medianus (vNM) in rats produced a temporary adipsia or hypodipsia that was accompanied by pronounced urinary fluid losses. When ad libitum drinking resumed, about half of the brain-damaged animals became hyperdipsic, exhibiting chronic two- to threefold elevations in their daily water intakes during the nocturnal hours of the day-night cycle. Rats that remained normodipsic after vNM ablation usually exhibited hyperdipsia if they were food-deprived overnight. The basis for the hyperdipsia produced by vNM ablation was not clear. The elevated water intakes appeared not to result from chronic urinary fluid losses, because hyperdipsic rats were able to concentrate their urine during the day, when they drank little. Moreover, the animals did not seem to be volume depleted; their plasma renin activities were not elevated, and they drank normally in association with meals. These and other findings suggest that vNM lesions damage neural substrates that control drinking behavior, and the hyperdipsia results from this rather than from physiological changes produced by the lesion.
Exercise training-induced hypervolemia in greyhounds: role of water intake and renal mechanisms
Authors: McKeever K. H. , Schurg W. A. , Convertino V. A.
Published: December 2017

The purpose of this study was to determine if the chronic hypervolemia that accompanies endurance exercise training is due only to an increase in the rate of water intake or if there were contributions from renal mechanisms. Four greyhound dogs, previously sedentary for 3 yr, were utilized. During the 28-day experiment each dog was trained on a treadmill ergometer for 14 consecutive days at 65% of its pretraining maximal work intensity. After training, plasma volume increased 472 ml (27.5%, P less than 0.05). The rate of water intake increased 328 ml/day (33%, P less than 0.05), whereas urine output increased 87 ml/day (20.8%, P less than 0.05). The mean resting 24-h values for clearance of sodium increased 0.29 ml/min (90.3%, P less than 0.05), and clearance of potassium decreased 1.51 ml/min (16.1%, NS). Glomerular filtration rate, free water clearance, and osmotic clearance were not significantly altered. These data suggest that the primary mechanism for the exercise training-induced hypervolemia in dogs is a net positive water balance via increased water consumption without significant contribution from an increase in renal water reabsorption.
Oral stimulation alters digestion of intragastric oil meals in rats
Authors: Ramirez I.
Published: December 2017

Rats were fed corn oil by gastric catheter, and plasma levels of triglycerides were measured 1-6 h later. In previous studies intragastric feeding of oil resulted in a more rapid rise in plasma triglycerides, followed by a more rapid fall, than oral feeding of the same amount of oil. In the present study administration of a small amount of oil or saccharin to the mouths of rats immediately before intragastric feeding prolonged the elevation in blood triglycerides 4 h later. This latter effect appeared only in rats having previous experience with oil paired with the taste. Oral stimulation with saccharin also increased the amount of fat remaining in the stomach 1 h after the intragastric meal. The amount of free fatty acids remaining in the stomach 1 h after intragastric feeding was not significantly influenced by oral stimulation, suggesting that lingual lipase is not responsible for the observed effects. These findings demonstrate that a taste which has been paired with fat intake can acquire the ability to influence the digestion of fat.
Urinary responses to cold temperature during water immersion
Authors: Knight D. R. , Horvath S. M.
Published: December 2017

If cold temperature combines with ambient water pressure to stimulate the Henry-Gauer reflex in humans, then free water clearance (CH2O) should be greater during immersion in cold water (29.8 degrees C) than during exposure to cold air (14.8 degrees C) or immersion in thermoneutral water (35 degrees C). Urinary responses to these environments were compared with control measurements made during 6 h of sitting in thermoneutral air (27.6 degrees C). CH2O was not significantly greater in cold water than in the other environments. Rather, the diuretic response was characterized by an increased osmolar clearance (P less than 0.05). Cold temperature and water pressure additively raised urinary output during cold water immersion, with ambient water pressure accounting for two-thirds of the urinary water loss. An elevated rate of sodium excretion (P less than 0.05) began significantly earlier in cold water than in thermoneutral water. This effect of low temperature might have resulted from cold-induced vasoconstriction, since cold temperatures was observed to reduce the foot volume. Sodium excretion was inversely proportional to vital capacity, indicating a responsiveness of the kidney to expansion of the central blood volume. In addition to the effects of water pressure and cold temperature, urinary function was also sensitive to time. The rate of potassium excretion was significantly elevated at min 199 of exposure to all environments. Failure of CH2O to increase above control values indicated that the human diuretic response to cold water immersion is atypical for the Henry-Gauer reflex.
Forced internal desynchronization between circadian temperature and activity rhythms in squirrel monkeys
Authors: Gander P. H. , Lydic R. , Albers H. E. , Moore-Ede M. C.
Published: December 2017

In an attempt to force internal desynchronization between the rest-activity rhythm and the body temperature rhythm of the squirrel monkey (Saimiri sciureus), five animals were studied in a 14:14 light-dark cycle. In four animals a 28-h spectral component was found to predominate in the rest-activity rhythm, whereas an unentrained circadian component (tau = 25.9 +/- 0.4 h) predominated in the body temperature rhythm. Plots of the cycle-by-cycle acrophases of the two rhythms confirm that they desynchronize, due to the failure of the temperature rhythm to entrain to the light-dark cycle. These data from intact animals provide further support for the hypothesis that the squirrel monkey circadian timing system has at least two pacemakers. A rhythm for which the supra-chiasmatic nuclei (SCN) have previously been shown to be essential (rest-activity) simultaneously exhibited a different period from a rhythm (body temperature) that has been shown to persist after destruction of the SCN.
Sources of carbon dioxide in penguin air sacs
Authors: Powell F. L. , Hempleman S. C.
Published: December 2017

CO2 tensions in the caudal air sacs of birds cannot be quantitatively predicted by current models of avian respiration, mainly because the contribution of neopulmonic parabronchial gas exchange has not been determined. To overcome this problem we studied penguins that have purely paleopulmonic lungs. Three penguins were anesthetized, intubated, and ventilated at a constant respiratory rate and different tidal volumes (VT). PO2 and PCO2 were measured in arterial blood and end-expired, mixed-expired, interclavicular air sac, and caudal thoracic air sac gas. Interclavicular air sac and end-expired gas had similar compositions. Caudal thoracic air sac gas was intermediate in composition to end-expired and inspired gas, and its PCO2 was 1.5–3.5 times greater than the value predicted from reinhaled dead space. This difference between measured and predicted caudal thoracic air sac PCO2 increased with VT but showed no relationship to changes in dead space-to-VT ratio. The difference is not explained by stratification or diffusive gas exchange across air sac walls. The results can be explained by postulating that inspired gas passes over exchange surfaces on its path to caudal air sacs. This is unexpected in the purely paleopulmonic lungs of penguins and suggests that airflow may not be caudocranial in all paleopulmonic parabronchi.
Menstrual cycle phase and time of day alter reference signal controlling arm blood flow and sweating
Authors: Stephenson L. A. , Kolka M. A.
Published: December 2017

The changes occurring in the esophageal temperature (Tes) thresholds for initiation of heat loss responses as affected by the circadian period and menstrual cycle were studied. Four women exercised at 60% peak Vo2 in 35 degrees C (ambient water vapor pressure 1.73 kPa) for 30 min at 0400 and 1600 during the follicular (F) and luteal (L) phase. Tes, arm sweating rate (msw), and forearm blood flow (FBF) were measured frequently. At rest, Tes averaged 0.3 degrees C higher during L than F at both 0400 and 1600 and approximately 0.4 degrees C higher at 1600 than at 0400 during both phases. During exercise transients, the slopes of the FBF:Tes and the msw:Tes relationships were not different among treatments. The thresholds for initiation of sweating and cutaneous vasodilation were higher at 1600 than 0400 during both phases. Thresholds during F at 0400 averaged 36.44 degrees C for msw and 36.80 degrees C for vasodilation. The thresholds during L at 1600 averaged 37.46 and 37.53 degrees C for sweating and vasodilation, respectively. Our data indicate that the thermoregulatory effector activity during exercise is a function of numerous inputs, and one of these may be hormonal or hormonal-like in action. Controlling time of day and menstrual cycle phase are as important as controlling for aerobic power, age, and fitness in studying female thermoregulatory responses during exercise.
Mathematical model of fetal circulation and oxygen delivery
Authors: Huikeshoven F. J. , Hope I. D. , Power G. G. , Gilbert R. D. , Longo L. D.
Published: December 2017

To better understand the fetal circulation and its regulation we constructed a dynamic model of fetal circulation as a transport system. The fetal vascular system is divided into 16 compartments which incorporate the peculiarities of the fetal circulation that produce a difference in oxygen concentration in blood supplying the upper and lower body. Recently published data is used to provide a firm experimental base for the model. The model is used to examine how the results on parts of the fetal cardiovascular system and fetal oxygen consumption are compatible and form a coherent description. We also studied the effects of disturbances from the normal steady state produced by changes in patterns of and resistances to blood flow. A maternal placental blood flow of less than 200 ml X min-1 X kg fetal wt-1 produces a steady-state value of oxygen tension in the fetal ascending aorta of less than 17 mmHg, which is incompatible with normal oxygen delivery. A minimal value of umbilical flow providing an adequate oxygen supply to the fetal body is 87 ml X min-1 X kg fetal wt-1. Due to the geometry of the fetal circulation, the highest normal oxygen tension in the fetal ascending aorta is approximately 25 mmHg, only 8 mmHg above the lowest normal tension of 17 mmHg. Dynamic studies using the model demonstrate differences in response of fetal arterial oxygen tension to temporal cord occlusion and temporal decrease in maternal placental flow.
Isolated perfused head of rainbow trout. II. Ionic fluxes
Authors: Perry S. F. , Booth C. E. , McDonald D. G.
Published: December 2017

Branchial ionic transport processes were evaluated and compared in Ringer-perfused and blood-perfused heads of rainbow trout. Rates of Na+ and Cl- influx were similar to in vivo levels at the onset of perfusion. Na+ uptake deteriorated more rapidly over time during Ringer perfusion, whereas Cl- uptake was relatively stable regardless of the perfusate employed. Transepithelial potentials (TEP) were similar to values reported for intact freshwater teleosts and were unstable only during the initial period of blood perfusion. The TEP was extremely dependent on the external concentration of NaCl. Ammonia excretion (JNH4+net) was normal during both types of perfusion, although blood did have a stabilizing effect on JNH4+net over time of perfusion. JNH4+net was stimulated by the addition of carbonic anhydrase to Ringer, without a concomitant increase in Na+ uptake. Branchial net fluxes of Na+ and Cl- were stable but slightly negative and in this regard represented slightly stressed intact animals. Net acid flux (JH+net), however, was similar to in vivo rates. Na+ and Cl- uptake displayed Michaelis-Menten kinetics. The affinity constant (Km) for Na+ uptake was typical of intact fish during both Ringer and blood perfusion, whereas Km for Cl- uptake was abnormally high in both cases. The results are discussed with reference to the suitability of the perfused trout head preparation for studying gill ionic fluxes in vitro.
Effect of hypokinesia-hypodynamia on rat muscle oxidative capacity and glucose uptake
Authors: Fell R. D. , Steffen J. M. , Musacchia X. J.
Published: December 2017

Whole-body hypokinetic-hypodynamic (H/H) suspension, unlike other models of muscle disuse, allows voluntary contractile activity. This study examined the oxidative capacity and insulin sensitivity of rat hindlimb muscles subjected to 7 days of suspension H/H conditions. Oxidative capacity was determined by measuring citrate synthase activity and cytochrome c concentration in soleus and gastrocnemius muscles. A perfused hindquarter preparation was used to measure glucose uptake rates at rest with physiological and supramaximal concentrations of insulin in the perfusate. Citrate synthase activity was 17% lower in soleus and 23% lower in gastrocnemius muscles from H/H rats. Similarly, a 29% decrease in H/H rat gastrocnemius cytochrome c concentration was observed. Rates of glucose uptake were lower in muscles from H/H rats compared with controls at physiological levels of insulin and did not increase in response to a further increase in insulin concentration. Muscles undergoing a significant loss in mass after 7 days suspension were found to have increased glycogen concentrations. In conclusion, data presented in this study suggest that hindlimb muscle disuse, brought about by whole-body suspension, results in a decreased aerobic capacity in load bearing muscles and a lowered insulin sensitivity in perfused rat hindlimb muscles.
Neuropeptide action in nucleus tractus solitarius: angiotensin specificity and hypertensive rats
Authors: Casto R. , Phillips M. I.
Published: December 2017

We have reported that microinjection of angiotensin II (ANG II) into the nucleus tractus solitarius of urethan-anesthetized normotensive rats produces an increase in mean arterial pressure (MAP) over the dose range 50-500 pmol. The effect in spontaneously hypertensive rats (SHR) is now reported. Over the range 100-500 pmol SHR exhibit increases in MAP and heart rate greater than Wistar-Kyoto or Sprague-Dawley rats. SHR did not exhibit exaggerated responses to intravenous phenylephrine, suggesting a central site of increased responsiveness to ANG II. We also found depressor effects in Sprague-Dawley at lower doses (0.1 and 1 pmol). The decreases in MAP were extremely variable and not dose related. A selected dose of additional neuropeptides identified in the NTS was tested. Somatostatin, bradykinin, and vasoactive intestinal peptide (0.5 nmol) were without cardiovascular effects. Oxytocin and vasopressin, however, produced significant increases in MAP. Substance P produced a very small but significant increase in heart rate and MAP. Interaction between the vasopressin and ANG II pressor effects was studied, and each proved to be independent.
Potentiated muscular thermogenesis in cold-acclimated muscovy duckling
Authors: Barre H. , Geloen A. , Chatonnet J. , Dittmar A. , Rouanet J. L.
Published: December 2017

The capacity for nonshivering thermogenesis (NST) was examined in 26- to 27-day cold-acclimated (CA) muscovy ducklings reared for 21 days at 4 degrees C. Metabolic rate and integrated electromyographic (EMG) muscle activity were measured at ambient temperature ranging from -10 to 28 degrees C. Compared with controls reared at 30 degrees C, CA ducklings were more resistant to cold and had higher peak metabolic rate in extreme cold. Shivering threshold temperature of CA ducklings was 14.2 degrees C lower than lower critical temperature, whereas for controls the two temperatures were similar. Thus CA ducklings exhibited an NST in moderate cold. In addition, at temperatures that produced shivering, EMG activity in CA duckling muscle was lesser than that of controls, even at a higher metabolic rate. Because these ducklings are devoid of brown adipose tissue, these results indicated an increased thermogenic efficiency of muscular activity in CA ducklings.
Ultra- and circadian fluctuations in arterial pressure and electromyogram in conscious dogs
Authors: Blinowska K. , Marsh D. J.
Published: December 2017

Mean arterial blood pressure was measured for 2 days in conscious dogs to estimate the frequency of ultradian fluctuations and to compare the magnitudes of the ultra- and circadian fluctuations. The ultradian fluctuation had an average frequency of 0.38 +/- 0.04 cycle/h and 60% more power than the circadian rhythm. The ultradian fluctuation was consistently more powerful during daylight than nighttime hours, but there was no consistent change in the frequency with time of day. Electromyogram (EMG) activity was also measured to test a possible causal relationship between the two variables. There were both circ- and ultradian fluctuations in EMG activity, and the peak cross-spectral power was also in these frequency bands. The coherence function was also high, but the phase angle between the two variables was so variable, both in sign and in magnitude, that it was judged unlikely that there was tight coupling between them.
Ionic requirements for intracellular pH regulation in rainbow trout hepatocytes
Authors: Walsh P. J.
Published: December 2017

The ionic requirements for pH regulation in isolated rainbow trout (Salmo gairdneri) hepatocytes were determined by manipulation of intracellular pH (pHi; measured by the dimethyloxazolidinedione distribution technique) by NH4Cl prepulse and changes in external [CO2] in the presence and absence of various drugs and external ions. The presence of a Na+/H+(NH+4) exchange system is supported by the following results: 1) the rate of recovery from an acid load is decreased by amiloride (0.5 mM) or reduction of external [Na+]; 2) the rate of 22Na uptake is increased during recovery from an acid load, and this increase in amiloride sensitive. The presence of a Cl-/HCO3- exchange system is supported by the observations that 1) pHi is increased, and 2) rates of recovery of pHi from acid loading are enhanced, by exposure to 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (0.5 mM) and reductions in external [Cl-]. Further studies are required to determine the role of these exchange processes during physiological pHi perturbations.
Postnatal development of pulmonary alveoli: modulation in rats by thyroid hormones
Authors: Massaro D. , Teich N. , Massaro G. D.
Published: December 2017

We studied the effect of thyroid hormones on the postnatal development of the gas exchange region of rat lungs. Treatment with triiodothyronine (T3, 0.1 microgram . g body wt-1 . day-1) accelerated the increase of the surface-to-volume ratio (S/V) and surface area (Sa) and decrease of the mean chord length (Lm) of the gas exchange structures of pups killed at age 7 days. Propylthiouracil (PTU, 100 micrograms twice daily) from age 1 to 13 days, with death at age 14 days, diminished the rise of S/V and Sa and the fall of Lm compared with diluent-injected pups. Providing drinking water with 0.01% PTU to dams from gestation day 20 (term 22 days) to postnatal day 14 also diminished the rise of S/V and fall of Lm. Treatment of pups nursed by dams drinking 0.01% PTU with thyroxine (0.1 microgram/g body wt) every other day from age 1 to 13 days significantly diminished the effect of PTU on S/V, Sa, and Lm. We conclude thyroid hormones can modulate the postnatal architectural development of the gas exchange region of the rat lung.
Elastic energy storage in rigored skeletal muscle cells under physiological loading conditions
Authors: Tidball J. G. , Daniel T. L.
Published: December 2017

The capability of heavy meromyosin (HMM) to store energy in reversible deformations has been investigated previously; yet, whether HMM is the site of most elastic energy storage in skeletal muscle cells has not been established. We conducted dynamic loading tests on single rigored muscle cells over the physiological range of sarcomere lengths. These tests enabled us to calculate the energy stored in reversible deformations or dissipated in the cell during each cycle of oscillation. Our findings show that these cells are capable of storing approximately 0.5 J . kg-1 of elastic energy during the last 50 ms of passive extension in vivo by agonists and before their own active contraction. Possible sites of this energy storage are HMM subunit 2, the proximal portion of HMM subunit 1, and parallel structures. However, energy storage increases monotonically as myofilament overlap decreases in the physiological range. This negative correlation suggests that HMM subunits are not the primary sites of elastic energy storage. Our electron-microscopic observations show that collagen fibrils at the cell's surface become oriented parallel to the cell's long axis over the range of sarcomere lengths where energy storage increases. This provides a mechanism for the observed increases in elastic energy storage.
Alterations in beta-adrenergic stimulation of myocardial adenylate cyclase in endotoxic rats
Authors: Romano F. D. , Jones S. B.
Published: December 2017

The effect of in vivo endotoxin administration on adenylate cyclase in rat ventricular membranes was studied. Basal, fluoride-, and 5'-guanylylimidodiphosphate-stimulated adenylate cyclase activities were not affected throughout the period of endotoxicosis. Isoproterenol-stimulated adenylate cyclase activity was not different at 0.5 or 3 h after endotoxin. At the agonal stage, the isoproterenol dose-response curve was shifted significantly to the right in myocardial membranes from endotoxic rats, but there was no significant decrease in maximum stimulated activity. These data indicate that endotoxicosis does not inhibit the adenylate cyclase enzyme system but does decrease stimulation of adenylate cyclase via beta-adrenergic receptors when the animal is approaching death.
pH-induced hysteretic properties of phosphofructokinase purified from rat myocardium
Authors: Hand S. C. , Carpenter J. F.
Published: December 2017

Phosphofructokinase (PFK) purified from the rat myocardium is reversibly inactivated under a pH regime approximating that reported for ischemic hearts. At pH 6.5 and 37 degrees C, the enzyme displays a hysteretic loss of activity during 60-min incubations, declining to 48% of control (pH 7.1, 37 degrees C) values. Citric acid increases the degree of inactivation (28% of control), whereas fructose 1,6-bisphosphate reduces the decline in activity. Simultaneous measurements of 90 decreases light scattering and catalytic activity suggest the inactivation is temporally linked to dissociation of active tetrameric enzyme into an inactive form of lower molecular weight. Fluorescence enhancement of the extrinsic probe sodium mansate, which binds preferentially to dimeric PFK, indicates that the equilibrium dimer concentration (cp1 infinity) increases as pH is lowered. This increase in cp1 infinity exhibits a strong inverse correlation (r = 0.984) with catalytic activity across the pH range of 8.0 to 6.5. Returning solution pH to 7.0 or above promotes a time-dependent reactivation and repolymerization of PFK. The rate of reactivation is increased at higher enzyme concentrations and in the presence of trimethylamine-N-oxide, a nitrogenous osmolyte noted for its ability to promote protein aggregation reactions. Thus these results demonstrate the capacity of rat heart PFK to undergo reversible inactivation and dissociation in vitro and represent the first phase of a two-part study testing the hypothesis that these pH-induced hysteretic processes are operative in the ischemic myocardium. The data are evaluated in terms of the potential roles of hysteretic enzymes in metabolic regulation.
Plasma clearance, metabolism, and tissue accumulation of 3H-labeled catecholamines in trout
Authors: Nekvasil N. P. , Olson K. R.
Published: December 2017

Plasma clearance, metabolism, and tissue accumulation of [3H]norepinephrine (NE) and [3H]epinephrine (E) were measured after injection into the dorsal aorta of chronically catheterized trout, Salmo gairdneri. Sucrose, an inert volume marker, was injected with the catecholamines (CAs). Ion-exchange chromatography was used to separate unmetabolized CAs from deaminated and O-methylated metabolites in plasma. Both CAs are cleared from plasma at an exponential two-component rate. By 10 min postinjection, CA-specific extraction lowered plasma [3H]NE by 65% and [3H]E by 50%. Over 80% of the 3H remaining in plasma 10 min after injection was metabolized to O-methylated and deaminated products. Thus trout are able to quickly and efficiently lower circulating CA levels through tissue accumulation and metabolism. Kidney, liver, spleen, and atrium accumulate more CA than other tissues, although most tissues bind CA to some extent. Gills preferentially accumulate CAs over sucrose. Skeletal muscle has a low affinity for CAs but by virtue of its large mass may be an important organ in CA metabolism. NE is removed from the circulation faster, and more NE is bound to tissues than E. A blood-brain barrier for E but not NE was observed.
Secretory NaCl and volume flow in renal tubules
Authors: Beyenbach K. W.
Published: December 2017

This review attempts to give a retrospective survey of the available evidence concerning the secretion of NaCl and fluid in renal tubules of the vertebrate kidney. In the absence of glomerular filtration, epithelial secretory mechanisms, which to this date have not been elucidated, are responsible for the renal excretion of NaCl and water in aglomerular fish. However, proximal tubules isolated from glomerular fish kidneys of the flounder, killifish, and the shark also have the capacity to secrete NaCl and fluid. In shark proximal tubules, fluid secretion appears to be driven via secondary active transport of Cl. In another marine vertebrate, the sea snake, secretion of Na (presumably NaCl) and fluid is observed in freshwater-adapted and water-loaded animals. Proximal tubules of mammals can be made to secrete NaCl in vitro together with secretion of aryl acids. An epithelial cell line derived from dog kidney exhibits secondary active secretion of Cl when stimulated with catecholamines. Tubular secretion of NaCl and fluid may serve a variety of renal functions, all of which are considered here. The occurrence of NaCl and fluid secretion in glomerular proximal tubules of teleosts, elasmobranchs, and reptiles and in mammalian renal tissue cultures suggests that the genetic potential for NaCl secretion is present in every vertebrate kidney.
Intracisternal insulin alters sensitivity to CCK-induced meal suppression in baboons
Authors: Figlewicz D. P. , Stein L. J. , West D. , Porte D. , Woods S. C.
Published: December 2017

We have previously reported that intravenous administration of the octapeptide of cholecystokinin (CCK-8) is more effective in reducing single meal size in baboons at noontime than in the morning. We have also reported that immunoreactive insulin levels in the cerebrospinal fluid (CSF) are elevated after animals have recently eaten. To test whether elevated CSF insulin levels can alter the efficacy of intravenous CCK to reduce meal size we administered subthreshold doses of CCK-8 to baboons infused with either synthetic CSF or CSF and insulin (100 microU X kg-1 X day-1) via the cisterna magna. Intravenous CCK-8 alone reduced 30-min meal size from 504 +/- 121 to 378 +/- 113 kcal (n = 7, P = NS). Chronic intracisternal insulin infusion enhanced CCK-8's suppressive effects such that 30-min meal size was reduced from 544 +/- 74 to 240 +/- 108 kcal (n = 7, P less than 0.005). Intracisternal insulin infusion had no significant effect on total food intake, basal plasma insulin and glucose levels, or postprandial plasma insulin and glucose levels. These findings suggest that central insulin may contribute to food intake regulation by modulating the ability of brain-gut peptides to alter single meal size.
Plasma renin and angiotensin in dehydrated and rehydrated rats
Authors: Di Nicolantonio R. , Mendelsohn F. A.
Published: December 2017

The role of the renin-angiotensin system in the stimulation and termination of dehydration-induced drinking was examined in the rat. Rats dehydrated for 48 h had significantly elevated renin, angiotensin II, plasma Na+ concentration, osmolality, and hematocrit when compared with replete controls. Although plasma Na+ concentration, osmolality, and hematocrit of dehydrated rats had returned to control replete levels by 2-4 h after the return of water, the plasma renin and angiotensin II levels exhibited a further increase on rehydration and remained significantly above dehydration levels for 2-4 h after the return of water. The levels of renin and angiotensin II in rehydrated rats were maintained at levels in excess of the dipsogenic threshold for circulating angiotensin II during the 8-h period after rehydration, indicating that termination of the drinking is not dependent on a reduction of circulating angiotensin II. Finally, rehydrated rats did not drink significantly more than replete controls in the 1- to 8-h postrehydration period despite plasma angiotensin II levels in excess of that of the dipsogenic threshold for angiotensin II, indicating that mechanisms exist which override the dipsogenic action of circulating angiotensin II.
Mechanisms of hemodynamic responses to electrical stimulation of subfornical organ
Authors: Mangiapane M. L. , Brody M. J.
Published: December 2017

The rat subfornical organ (SFO) is involved in the pressor response to circulating angiotensin II, and recent evidence indicates that SFO electrical stimulation also produces a pressor response. In the present experiments we examined the hemodynamic, neural, and humoral mechanisms that underlie the pressor response to electrical stimulation of the SFO. Rats were anesthetized with urethan and instrumented with femoral arterial catheters and with pulsed Doppler flow probes on the superior mesenteric and renal arteries and on the abdominal aorta. Constant-current stimulation, delivered to the SFO via tungsten microelectrodes, resulted in stimulus-locked frequency-dependent pressor responses and vasoconstriction in all vascular beds tested. The stimulation-evoked increases in vascular resistance were greatest in the mesenteric circulation and least in the renal. Movement of the electrode away from the SFO produced significantly smaller responses. Ganglionic blockade abolished the responses to electrical stimulation, whereas vasopressin blockade significantly attenuated the responses. The responses of baroreceptor-denervated rats were qualitatively similar to but approximately double in magnitude of those of normal rats. We conclude that electrical stimulation of the SFO elicits widespread regional vasoconstriction that is most pronounced in the mesenteric circulation. The sympathetic nervous system appears responsible for these effects, but there may be facilitation of the responses by vasopressin.
Modulation of gastric and arterial pressure by nucleus tractus solitarius in rat
Authors: Spencer S. E. , Talman W. T.
Published: December 2017

By using L-glutamate as a physiological tool to selectively stimulate neurons in specific subnuclear regions of the nucleus tractus solitarius (NTS), we have sought to differentiate those regions that modulate cardiovascular activity from those that modulate gastric activity. Microinjections of L-glutamate (300 pmol/25 nl) into the dorsomedial NTS of alpha-chloralose-anesthetized rats elicited dose-dependent falls in arterial pressure (AP) of 37.5 +/- 7.7 Torr from a base line of 130 +/- 5.8 Torr and gastric pressure (GP) of 0.8 +/- 0.1 cmH2O and inhibited the usual 5-6 waves/min phasic activity. Microinjection into the ventromedial NTS did not affect AP but transiently lowered GP by 1.6 +/- 0.2 cmH2O and eliminated phasic waves. The GP changes were vagally mediated. Microinjections into the area postrema or the hypoglossal nucleus elicited neither AP nor GP changes. Microinjections in other NTS areas at the same rostral-caudal level did not alter GP consistently. This study suggests that local stimulation of neurons in a specific region of the NTS elicits vagally mediated alterations of tonic GP and phasic activity and that AP and GP can be influenced independently in the medial NTS region.
An opioid antagonist, naltrexone, reduces preference for sucrose in humans
Authors: Fantino M. , Hosotte J. , Apfelbaum M.
Published: December 2017

Eight healthy nonobese volunteers were asked to rate, on a pleasure-displeasure scale, sucrose and salty solutions as well as alimentary and nonalimentary odors. Effects of intragastric glucose load (vs. water load) and naltrexone (vs. placebo) were tested. Naltrexone produces a significant decrease for sweetened solution on the pleasure scale, a shift even stronger than that of the glucose load itself. Such a decrease is also observed for alimentary odors but not for responses to nonalimentary stimuli. Thus the opioid system is involved in ingestive behavior in humans, and this action is perhaps specific.
Comparative effects of CCK-8 on feeding, sham feeding, and exocrine pancreatic secretion in rats
Authors: Reidelberger R. D. , Solomon T. E.
Published: December 2017

Cholecystokinin (CCK) is thought to be a hormonal regulator of exocrine pancreatic secretion and is postulated to be a satiety hormone. We compared the dose-response effects of CCK octapeptide (CCK-8) on feeding, sham feeding, and pancreatic secretion to gauge whether the feeding effect might be physiological. Pancreatic responses to intravenous CCK-8 (40, 200, 1,000, or 4,000 pmol . kg-1 . h-1) in fasted unanesthetized rats were compared with effects of CCK-8 (0, 200, 1,000, or 4,000 pmol . kg-1 . h-1) on ingestion of liquid diet in fasted rats with gastric cannulas either closed (normal feeding) or open (sham feeding). Maximal pancreatic amylase output occurred at 200 pmol . kg-1 . h-1 of CCK-8; output declined at higher doses. Food intake was significantly inhibited only at 1,000 and 4,000 pmol . kg-1 . h-1 of CCK-8; the effect was similar when gastric cannulas were closed and open. These results, together with available data on the low postprandial levels of plasma CCK, suggest that circulating levels of CCK normally present after food intake are not sufficient to produce satiety. Furthermore, suppression of feeding by CCK does not appear to be mediated solely by a mechanism that senses gastric distension, because CCK-8 had similar effects in the presence and absence of gastric distension. Whether CCK interacts with other neural or humoral factors to produce satiety by a hormonal mechanism remains to be determined.
Oral hypertonic saline causes transient fall of vasopressin in humans
Authors: Seckl J. R. , Williams T. D. , Lightman S. L.
Published: December 2017

After dehydration, oral rehydration causes a fall in plasma arginine vasopressin (AVP) that precedes changes in plasma osmolality. To investigate further the stimulus for this effect, its specificity, and association with thirst, six volunteers were deprived of water for 24 h and given a salt load on two separate occasions. On each study day they then drank rapidly 10 ml/kg of either tap water or hypertonic saline (360 mosmol/kg). There was a significant fall in plasma AVP from 2.0 +/- 0.3 to 1.2 +/- 0.4 pmol/l (P less than 0.05) 5 min after drinking water and from 1.8 +/- 0.3 to 0.9 +/- 0.2 pmol/l (P less than 0.05) after hypertonic saline. Plasma osmolality fell 30-60 min after water and was unchanged after saline. Plasma renin activity, oxytocin, and total protein all remained unchanged. All subjects reported diminished thirst after hypertonic saline. Gargling with water reduced thirst but did not affect plasma AVP. There appears to be a drinking-mediated neuroendocrine reflex that decreases plasma AVP irrespective of the osmolality of the liquid consumed. The sensation of thirst did not correlate with plasma osmolality and was not always related to plasma AVP concentration.
Dexamethasone accelerates postnatal alveolar wall thinning and alters wall composition
Authors: Massaro D. , Massaro G. D.
Published: December 2017

The gas exchange region of newborn rats is composed of large thick-walled gas exchange saccules that become subdivided by septum formation between ages 4 and 14 days. Dexamethasone given daily from age 4 to 13 days irreversibly prevents septation. We now asked if dexamethasone (0.1 micrograms) given daily from age 4 to 13 days accelerates alveolar wall thinning and alters wall composition. Compared with controls, within 2 days dexamethasone-treated pups had a 20% thinner gas exchange wall, a 35% lower volume density (Vv) and absolute volume of interstitial fibroblasts, and a 45% greater Vv of type II cells. At age 14 days the volumes of type I cells, fibroblasts, and acellular matrix were approximately 35% less in dexamethasone-treated pups, but the volumes of type II and endothelial cells did not exhibit significant intergroup differences. We conclude dexamethasone accelerates alveolar wall thinning and suggest dexamethasone diminishes replication of fibroblasts more rapidly than it diminishes division of type II, impairs conversion of type II to I, and does not decrease replication of endothelial cells.
Urinary bladder function and its control in healthy females
Authors: Griffiths D. J. , Constantinou C. E. , van Mastrigt R.
Published: December 2017

Recordings in eight healthy female volunteers of bladder (detrusor) pressure and flow rate, obtained during bladder filling and during voiding, both through the urethra and through a catheter, demonstrate that a model of bladder function in which the detrusor muscle is considered as completely passive during filling and fully activated during voiding is inadequate. Assessment of the detrusor contraction strength by a new method (described in APPENDIX A) shows that in ideal normal voidings the contraction strength rises to values of 11-24 W/m2 and is sustained or rises slightly until the bladder is empty. During unstable detrusor contractions, which even in these healthy women are observed during bladder filling and also during inhibited voidings through the urethra, the contraction is weaker. During voidings through a catheter the detrusor contraction is weak, variable, and fades away before the bladder is empty. An elementary feedback analysis demonstrates that the effect of the micturition reflex governing detrusor behavior differs according to whether or not voiding is taking place. The reflex does not lead to a simple on-off mechanism but to a more complex behavior that is consistent with the observations and that appears to be important for the understanding of pathological obstructed micturition.