bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of living matter: physical foundations of biology
Authors: Benzinger T. H.
Published: December 2017

All major functions of life are exerted by reversible conformational changes of living matter, the genetically coded, giant molecules of proteins, polynucleotides, and biological membranes. Only thermodynamics can answer the questions why these reversible actions occur, why they are inevitable, and what the physical foundations may be on which biology rests. Classical Gibbs-Helmholtz thermodynamics was found to be inapplicable to the interpretation of reactions in living matter, because copious flows of heat without exchange of work obscure the subtle bond-forming or bond-breaking energy transformations that are driving the actions of living matter. An alternative thermodynamic formulation that is universally applicable was developed and applied to numerical examples: formation of a diatomic molecule from the elements, and two conformational changes, a protein folding and the winding of a polynucleotide helix. The subtle energy transformations, bond-forming or bond-breaking, that were causing the two reactions of living matter to proceed in vitro forward or in reverse have been identified as the thermal work function delta Wto(T) and the chemical bond energy delta Ho0. Since the chemical bond energies and the heat capacities delta CoP(T) between reaction temperature and the absolute zero, unchangeable attributes of matter, were the only ingredients used for the treatment, the complexity of the reactions has been reduced--as far as effects and ultimate causes are concerned--to the simplicity of low temperature physics, a solid physical foundation for all biological and medical sciences.
Influence of heating rate on control of heat loss from the tail in mice
Authors: Gordon C. J.
Published: December 2017

Although heating rate is important for stimulating thermoregulatory reflexes, it is not known if the control system differentiates between total heat gain and rate of heat gain. Exposing animals to microwaves inside a waveguide permits continuous monitoring of whole-body heat absorption. Tail skin temperature of restrained mice was recorded during whole-body exposure to 2,450-MHz microwave radiation at specific absorption rates (SAR) of either 11.5, 21.7, or 43.5 W . kg-1 and whole-body heat loads of 0.3-14 J . g-1. The integration of tail skin temperature with time, defined as the skin temperature index (STI), was measured as a function of absorbed heat load. At ambient temperatures of 20 and 25 degrees C the STI, averaged with respect to heat load, increased significantly with SAR. Depending on SAR, the sensitivity of heat loss from the tail to microwave exposure increased 32-71% per 1 degree C elevation in ambient temperature. The data indicate that heat loss from the tail increases with the whole-body heat load accrued from microwave exposure. When heat loss is averaged with respect to heat load, the rate of heat absorption and ambient temperature increase the sensitivity of thermoregulatory centers that control peripheral heat loss from the tail of mice.
Prostaglandin E2 and thromboxane B2 in cerebrospinal fluid of afebrile and febrile cat
Authors: Coceani F. , Bishai I. , Dinarello C. A. , Fitzpatrick F. A.
Published: December 2017

Levels of prostaglandin (PG) E2 and thromboxane (TX) B2, the stable metabolite of TXA2, were measured by radioimmunoassay in cerebrospinal fluid (CSF) collected from the third ventricle and the cisterna magna of conscious cats. In the absence of fever, PGE2 was usually below the threshold of the assay (0.05-0.37 ng/ml), while TXB2 was measurable in the majority of cases and its concentration was greater in the third ventricle (about 0.7 ng/ml) than in the cisterna magna (about 0.2 ng/ml). At either site, TXB2 content rose if any manipulation was required for the collection of samples. PGE2 levels increased to measurable values (max 1.1-1.4 ng/ml) during fever produced by intrathecal or intravenous administration of leucocytic pyrogen. In contrast, TXB2 concentration rose to an average of 2.2-4 ng/ml only when pyrogen (bacterial or leukocytic) was given intrathecally. Moreover, TXB2 elevation, unlike PGE2 elevation, was limited to the uprise phase of the fever. Imidazole, given either intraperitoneally (50 mg/kg) or intrathecally (3 mg), attenuated the pyrogen fever and suppressed any rise in TXB2 levels. At the same time, the drug tended to increase the PGE2 content of the CSF. Evidence was also obtained suggesting that a fraction of PGE2 is bound to CSF protein, and this event may be important to the inactivation of the compound. These findings are consistent with the concept that PGE2 is involved in the sequence of events underlying pyrogen fever. A role for thromboxane A2 in this process remains to be established.
Regulation of glucose production from lactate in experimental sepsis
Authors: Clemens M. G. , Chaudry I. H. , McDermott P. H. , Baue A. E.
Published: December 2017

Gluconeogenic and oxidative capabilities with lactate as a substrate were studied in perfused livers isolated from rats in late sepsis. Glucose release in the presence of 5 mM lactate was significantly depressed in livers from septic rats. When gluconeogenesis was stimulated by phenylephrine, livers from septic rats exhibited both a decreased sensitivity and lower maximal rate of glucose release when compared with livers from sham-operated rats. Oxygen consumption (VO2) by perfused livers from septic rats was also depressed under the above conditions. The addition of lysine in concentrations greater than 0.5 mM restored glucose production in livers from septic rats to a rate not different from sham-operated controls but did not restore VO2. However, inclusion of lysine (5 mM) in the perfusate was not able to restore sensitivity to stimulation by phenylephrine in livers from septic rats. Although hepatic ATP levels were depressed in sepsis, the decrease was not sufficient to explain the decreased rates of glucose production. We conclude from these results that primary cellular defects in gluconeogenic and oxidative capabilities occur during sepsis that are independent of inadequate perfusion.
Active transport of calcium across the urinary bladder and colon of the toad Bufo marinus
Authors: Rosoff C. J. , Baldwin G. F. , Bentley P. J.
Published: December 2017

Unidirectional fluxes of calcium were measured (in vitro) across the urinary bladder and colon of the toad Bufo marinus in the absence of electrochemical gradients. A net calcium flux was observed in each tissue, but the polarity differed; it occurred from the mucosal (luminal) to the serosal side of the colon and from the serosal to mucosal (urinary) side of the bladder. The active transport in each tissue appeared to involve different mechanisms; that across the colon exhibited a sodium dependence, possibly involving a sodium-calcium exchange, but this was not seen in the urinary bladder. The net flux in the latter was, however, abolished by metabolic inhibitors, possibly reflecting a role of a calcium-adenosine triphosphatase mechanism. The results are discussed in relation to the calcium metabolism of this amphibian.
Cellular mechanisms in shock and ischemia and their correction
Authors: Chaudry I. H.
Published: December 2017

Various metabolic, cellular, and subcellular alterations in cell function and morphology occur during shock or low flow conditions. Alterations in mitochondrial function during low flow conditions consist of decreases in the metabolic capability of mitochondria, alterations in mitochondrial cation contents, increased mitochondrial free fatty acids and Ca2+, and decreased adenine nucleotide translocase activity. The cell membrane transport of Na+ and K+, transmembrane potential, cellular ATP and cyclic nucleotide levels, and other phenomena are also significantly altered. The potential mechanisms responsible for altered mitochondrial and cellular functions during shock and the consequences of such alterations are discussed. Based on the cellular alterations that occur during shock, attempts have been made to support cell function during such conditions. These (along with volume replacement) include substrates, membrane-stabilizing solutions, and energy compounds. Although provision of substrates may improve cellular energy levels, they may not necessarily improve microcirculation. The use of ATP-MgCl2 as an adjunct in the treatment of shock and ischemia has been described, and potential mechanisms of the beneficial effects of this compound are discussed.
Photoperiodic regulation of body mass, food intake, and reproduction in meadow voles
Authors: Dark J. , Zucker I. , Wade G. N.
Published: December 2017

Adult male voles were maintained for 10 wk in long or short photoperiods (14 or 10 h of light/day). A third group of animals housed in the long photoperiod was implanted with capsules containing melatonin. Body weight and food intake were measured weekly; various tissues were weighed and analyzed at the time of autopsy. After 10 wk, voles in the short photoperiod weighed 20% less and consumed 30% less food than those housed in the long photoperiod. Total body water and lean body mass were reduced in the short-day animals, although the size of the brown adipose tissue was not affected. White adipose tissue lipoprotein lipase (LPL) activity was markedly reduced in the short-day voles who also manifested gonadal regression and suppression of spermatogenesis. Melatonin mimicked the effects of short photoperiods on LPL activity and on lean body mass; other parameters for melatonin-treated animals were intermediate between those of untreated long- and short-day voles. We hypothesize that winter weight losses experienced by meadow voles in the field are mediated by decreases in the duration of the daily photophase and that the reduction in body mass permits overwintering voles to reduce their energy requirements and the amount of time devoted to foraging. At least part of the seasonal decline in body mass appears due to a decrease in gonadal hormone secretion.
Hyperinsulinemia in rats with hypothalamic obesity: effects of autonomic drugs and glucose
Authors: Inoue S. , Mullen Y. S. , Bray G. A.
Published: December 2017

The present study examined the effects of autonomic drugs and glucose on the insulin and glucose concentrations of sham-operated rats and of rats with ventromedial hypothalamic (VMH) lesions and obesity. In the basal condition both epinephrine and atropine significantly decreased serum insulin levels in VMH-lesioned but not sham-operated rats. During glucose stimulation of insulin secretion in VMH-lesioned rats, epinephrine inhibited the increase of insulin by 83% and atropine inhibited it by 42%; whereas in sham-operated rats, epinephrine inhibited it by 70% and atropine inhibited it by 34%. Epinephrine with atropine completely blocked the increase of insulin in response to glucose in both VMH-lesioned and sham-operated rats. In the basal condition, epinephrine together with propranolol significantly decreased serum insulin levels in VMH-lesioned but not sham-operated rats. Epinephrine with phentolamine, on the other hand, markedly increased insulin in the VMH-lesioned rats and to a lesser degree in the sham-operated rats. During glucose stimulation epinephrine with propranolol inhibited the increase of insulin in both groups. Epinephrine with phentolamine or isoproterenol markedly increased serum insulin in VMH-lesioned rats. These results suggest that stimulation of the vagus nerve and increased sensitivity of the beta-receptors on the beta-cells of the islet contribute to the development of hyperinsulinemia. The sympathetic contribution may also be through suppression of alpha-adrenergic receptors.
Spontaneous obesity and weight loss: insulin action in the dormouse
Authors: Melnyk R. B. , Mrosovsky N. , Martin J. M.
Published: December 2017

Dormice (Glis glis) undergo spontaneous cyclic changes in food intake and body weight. These infradian cycles with a periodicity of about 2 mo are endogenously controlled, since they persist in conditions of constant temperature and photoperiod. To evaluate the role of insulin as an effector of hyperphagia and fattening in dormice, experiments were conducted to study pancreatic function and adipose tissue metabolism during several phases of the infradian cycle. During the weight loss phase, peripheral insulin resistance occurs in the absence of hyperinsulinism. This resistance is not corrected by weight loss. Weight loss phase animals showed poor glucose tolerance and an impaired in vitro glucose-stimulated insulin secretion; these were not attributable to reduced pancreatic insulin content. Although basal glucose transport and basal, as well as insulin-stimulated, glucose utilization in isolated adipocytes were depressed during the weight loss phase, insulin-stimulated transport was significant. The data offer no evidence that insulin has a direct causal role in the development of spontaneous obesity in this species.
Differential pattern of sympathetic outflow during upper airway stimulation with smoke
Authors: Peterson D. F. , Coote J. H. , Gilbey M. P. , Futuro-Neto H. A.
Published: December 2017

This study investigates directly the possibility that sympathetic discharge to the heart is decreased while it is increased to other organs during upper respiratory perfusion with cigarette smoke. Blood pressure (BP), heart rate, ECG, and respiratory movements were monitored in urethane-anesthetized rabbits. Insertion of two cannulas allowed respiration of room air while passing smoke across the upper respiratory irritant receptors and out through the nares. Through a retroplural incision, the left stellate ganglion was exposed and a cardiac branch isolated. Similarly, a left renal nerve was isolated. Multiunit nerve recordings were obtained from both nerves. In four control animals, cigarette smoke (50 ml) caused apnea, bradycardia (-116 beats/min) and increased BP (33 mmHg). Activity in the renal nerve increased (248% of control [C]) and activity in the cardiac nerve was reduced (62% C). In these animals after Flaxedil and artificial respiration, nerve activity responses were still pronounced (renal, 178% C; cardiac, 66% C). In four other barodenervated animals neural responses to smoke were similar to those observed with baroreceptors intact (renal, 211% C; cardiac, 51% C). In these animals after artificial ventilation and Flaxedil, responses were not significantly changed. These results indicate that smoke stimulation causes a differential pattern of sympathetic discharge. The responses observed cannot be accounted for by secondary adjustments through arterial baroreceptors, chemoreceptors, or pulmonary stretch receptors.
Impact of a circadian clock on the timing of human sleep
Authors: Winfree A. T.
Published: December 2017

This paper redescribes some recordings of human sleep and waking made in several laboratories during the past decade under conditions of temporal isolation. Since 1972 it has been noticed that sleep duration depends mainly on the timing of prior sleep onset relative to a rhythm of 24- to 25-h duration. The present paper emphasizes four additional points: 1) that the dependence sometimes includes a remarkable discontinuity, 2) that such dependence is characteristic of a rhythmically modulated threshold process; 3) that the rhythm's period gradually changes in some experiments; and 4) that no comparable regularity has been detected in the timing of sleep onset. This last impugns the reliability of models that treat sleep onset and wake onset as complementary but comparable processes.
Characteristics of afferent fiber innervation on acupuncture points zusanli
Authors: Lu G. W.
Published: December 2017

Acupoint zusanli is one of the most effective points in traditional Chinese medicine. Needling point zusanli has a significant suppressive effect on jaw movement response (JMR) and electromyogram of digastric muscle (dEMG) induced by peroneal nerve stimulation. This effect is weakened or abolished by sectioning the peroneal nerve and blocking A-beta- and some A-delta-fibers in the nerve. When the point zusanli is stimulated electrically a larger-than-normal proportion of A-beta-fibers is activated. Local afferent fiber composition at this point contains more myelinated fibers, more large-sized fibers, and more A-beta-fibers than nonacupoints. This predominance of large afferent fibers in the composition and activity of point zusanli is thought to be one of the fundamental characteristics of the point in regard to its structure and function and contributes to its powerful acupuncture effect.
Information content of data with respect to models
Authors: Berman M. , Van Eerdewegh P.
Published: December 2017

A measure is proposed for the information content of data with respect to models. A model, defined by a set of parameter values in a mathematical framework, is considered a point in a hyperspace. The proposed measure expresses the information content of experimental data as the contribution they make, in units of information bits, in defining a model to within a desired region of the hyperspace. This measure is then normalized to conventional statistical measures of uncertainty. It is shown how the measure can be used to estimate the information of newly planned experiments and help in decisions on data collection strategies.
Is the "pool-fraction" paradigm a valid model for assessment of in vivo turnover in non-steady state?
Authors: Cobelli C. , Ruggeri A. , Toffolo G. , Avogaro A. , Nosadini R.
Published: December 2017

Quantification of in vivo turnover of endogenous substances in nonsteady state is of fundamental importance for understanding a variety of physiological and clinical metabolic situations. Toward this end, a pool-fraction model has become a paradigm in the glucose and ketone body areas. We discuss the basic assumptions on which the pool-fraction model is based and the criteria on which it has been validated. Specific comments are then made on its current and potential use for quantifying the non-steady-state turnover of glucose, ketone bodies, and insulin. We conclude that the quantitative reliability of predictions provided by the pool-fraction model is quite poor and that new developments are needed for quantifying the non-steady-state situation.
Energy balance and regulation of body weight after intestinal bypass surgery in rats
Authors: Atkinson R. L. , Brent E. L. , Wagner B. S. , Whipple J. H.
Published: December 2017

This study evaluated the possibility that intestinal bypass surgery alters energy balance and regulation of body weight. In two sets of experiments, male Sprague-Dawley rats underwent bypass or sham bypass surgery. In experiment 1, half of each group was overfed and half was underfed. Bypass reduced net calorie intake (intake - fecal loss) at 2 wk but not at 6 wk. Body weights were maintained at a much lower level in the bypass rats, yet apparent energy expenditure was greater. In experiment 2, bypass rats were compared with sham bypass and sham bypass who were food restricted for paired-weight-loss to bypass (PWL sham). Net calorie intake and body weights of bypass and sham bypass followed a similar pattern as in experiment 1. At similar levels of body weight postoperatively, bypass rats required more calories per kilogram than did the PWL shams, suggesting that bypass resets downward the level at which body weight is regulated. Calorie requirements correlated with food intake better than with absolute body weight. Further studies to determine the mechanism of altered energy expenditure may provide methods for weight loss without extensive surgery.
Further in vivo evidence for antagonist-to-antidiuretic action of arginine vasopressin
Authors: Ishikawa S. , Kim J. K. , Schrier R. W.
Published: December 2017

The effect of a new arginine vasopressin (AVP) analogue, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-ethyltyrosine, 4-valine]AVP or d(CH2)5Tyr(Et)VAVP, was examined on exogenous and endogenous AVP in the conscious rat. An intravenous injection of 8 micrograms/kg body wt of the AVP analogue completely blocked the antidiuretic effect of exogenous AVP (4 ng/kg body wt iv). Similarly, 8 micrograms/kg of the AVP analogue totally abolished the antidiuretic effect of infused AVP (0.1 mU X kg-1 X min-1) in the homozygous Brattleboro rats with central diabetes insipidus. The antagonism of this antidiuretic effect of exogenous AVP occurred in the absence of changes in urinary solute excretion, glomerular filtration rate (GFR), and mean arterial pressure. Intraperitoneal administration of the AVP analogue (30 micrograms/kg body wt) decreased the mean urinary osmolality in rats after 24 h of fluid deprivation from 3,098 +/- 140 to 797 +/- 155 mosmol/kg H2O (P less than 0.001). The duration of the antagonism of endogenous AVP was approximately 4.5 h. The antagonism of AVP was not dependent on the vascular properties of AVP, since the AVP analogue also blocked the antidiuretic effect of exogenous 1-deamino-8-D-AVP (DDAVP), an AVP analogue with negligible vascular properties. These in vivo results therefore indicate that d(CH2)5Tyr(Et)VAVP is a specific antagonist of the hydrosmotic effect of exogenous and endogenous AVP. In contrast to some previous analogues, this effect of the AVP analogue occurred in the absence of any known diuretic factors including an increase in GFR, solute excretion, and blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Decrease in adenylate cyclase activity in dog livers during endotoxic shock
Authors: Ghosh S. , Liu M. S.
Published: December 2017

The effects of endotoxin administration on adenylate cyclase in dog liver plasma membranes were studied. The basal, fluoride-, guanine nucleotide-, isoproterenol-, and glucagon-stimulated adenylate cyclase activities were decreased by 61, 62, 69, 83, and 63%, respectively, 2 h after in vivo administration of endotoxin. Endotoxin (100 micrograms/ml) in vitro decreased the guanine nucleotide-, isoproterenol-, and glucagon-stimulated adenylate cyclase activities by 24, 25, and 21%, respectively. These data demonstrate that endotoxin administered in vivo or in vitro had an inhibitory effect on the adenylate cyclase enzyme system in dog liver plasma membranes. Because of the involvement of the adenylate cyclase-adenosine 3',5'-cyclic monophosphate (cAMP) system in the regulation of hepatic carbohydrate metabolism, the finding that endotoxin administration decreased adenylate cyclase activity in the liver should contribute to the understanding of the pathophysiology of altered hepatic glucose homeostasis during shock.
A possible role for the brain renin-angiotensin system in the regulation of LH secretion
Authors: Steele M. K. , Gallo R. V. , Ganong W. F.
Published: December 2017

To investigate the possibility that angiotensin II (ANG II) is involved in the regulation of luteinizing hormone (LH) secretion, ANG II was injected intraventricular ANG II caused an increase in plasma LH concentrations in 10 min, whereas intravenous ANG II in the same dose had no significant effect. Intraventricular administration of the ANG II antagonist, saralasin, during the afternoon of proestrus induced a significant decrease in the number of rats ovulating and abolished the ovulatory surge in LH secretion seen in saline-injected control animals. Intravenous saralasin in two different doses failed to inhibit ovulation and produced only a small decrease in the LH surge. In animals treated with intraventricular saralasin, the increase in plasma LH concentration produced by intravenous injection of 50 ng of LH-releasing hormone (LHRH) was normal, indicating no alteration in the sensitivity of the gonadotrops to LHRH. Intraventricular administration of the converting-enzyme inhibitor, enalapril diacid, inhibited ovulation and the ovulatory surge, whereas systemically administered enalapril diacid had no effect on LH secretion. The data suggest that ANG II generated in the brain may play a significant role in the regulation of LH secretion on the day of proestrus.
Metabolic organization of liver during spawning migration of sockeye salmon
Authors: French C. J. , Hochachka P. W. , Mommsen T. P.
Published: December 2017

Although earlier studies have established broad outlines of biochemical changes during salmon spawning migration, the metabolic organization of specific organs has hitherto remained unknown. In this study, we assessed the performance of isolated liver cells from anorexic female sockeye salmon (Oncorhynchus nerka) at four sampling sites along their 1,150-km spawning migration. Isolated hepatocytes maintain high rates of gluconeogenesis and CO2 release from amino acids and lactate throughout the migration. Alanine, derived from proteolysis of white muscle, constitutes the single most important source for de novo synthesis of glucose. Just before spawning, when glycogen reserves reach a maximum, gluconeogenesis from alanine is specifically inhibited, whereas its conversion to CO2 and the utilization of other substrates are relatively unchanged. Spawning, apparently supported by carbohydrate catabolism, is accompanied by depletion of glycogen reserves from muscle as well as liver and a stimulation of gluconeogenesis from amino acids. At the onset of migration, palmitate oxidation accounts for about half the CO2 released by liver cells; its contribution decreases during the migration and is negligible after spawning.
Pulse-wave propagation in the arterial system of the diamond python Morelia spilotes
Authors: Avolio A. P. , O'Rourke M. F. , Webster M. E.
Published: December 2017

Pulse-wave velocity (PWV) and pulse-wave amplification (PWA) were measured over a proximal [51 +/- 3 (SE) cm] and distal segment (60 +/- 6 cm) of the common descending aorta of 10 anesthetized diamond python snakes (Morelia spilotes). For proximal and distal segments, PWV values were 551 +/- 66 and 921 +/- 116 cm/s and PWA were 0.91 +/- 0.05 and 0.91 +/- 0.06, respectively. PWV for proximal and distal segments were significantly different (P less than 0.02), but PWA were not. PWA for separate harmonics of heart frequency showed no significant increase above unity. Increase of PWV between distal and proximal aorta indicates a reduction in arterial distensibility, a phenomenon that in other species is associated with amplification of the pressure pulse; this was not observed in snakes. Using a simple elastic tube model 56 cm in length and 3 mm in diameter it was found that the amplification produced by the measured PWV changes is offset by attenuation due to viscous damping. Thus similarity of pulse-wave contour throughout the snake's aorta is attributable to the opposing effects of elastic nonuniformity and viscous damping.
Systemic and renal effects of angiotensin II in the freshwater turtle Pseudemys scripta elegans
Authors: Brown S. R. , Stephens G. A. , Todt M. J.
Published: December 2017

This study examined the renal and systemic effects of angiotensin II (ANG II) in the freshwater turtle, Pseudemys scripta elegans. We infused [Asn1, Val5]ANG II at doses of 1, 10, 100, and 500 ng X kg-1 X min-1 in conscious turtles while monitoring blood pressure, glomerular filtration rate (GFR), urine volume, and plasma and urine electrolytes. Saline (0.6%) was infused for two 1-h control periods at 1 ml X kg-1 X h-1 followed by a 1-h infusion of saline with ANG II added. Saline alone was then infused for either two or three 1-h recovery periods. Control values before ANG II infusion averaged 21 mmHg for blood pressure, 1.8 ml X h-1 for urine volume, and 8.0 ml X kg-1 X h-1 for GFR. At 1 (n = 7) and 10 ng X kg-1 X min-1 (n = 6) ANG II produced no significant changes in blood pressure or renal function. Angiotensin infusion at the higher rates of 100 (n = 6) and 500 ng X kg-1 X min-1 (n = 11) significantly elevated blood pressure during ANG II infusion (29 and 44 mmHg, respectively), while electrolyte excretion remained unchanged. Despite the increased blood pressure, GFR and urine volume tended to decrease. At all infusion rates, plasma electrolytes remained unchanged. The results suggest that ANG II is a potent constrictor of preglomerular vessels in the kidney of the turtle.
CO2 balance of a heterothermic rodent: comparison of sleep, torpor, and awake states
Authors: Bickler P. E.
Published: December 2017

CO2 homeostasis of different thermal states have been compared in a heterothermic ground squirrel, Spermophilus tereticaudus. Gas exchange (MO2, MCO2), lung ventilation (VE), and body temperature (Tb) were simultaneously measured during sleep, shallow torpor (Tb 25-29 degrees C), deep torpor (Tb 11-15 degrees C), awake heterothermia (Tb 30-42.5 degrees C), and transitions between these states. CO2 retention (falling MCO2/MO2 and VE/MCO2) accompanied entrance into sleep and torpor. CO2 retention lowered MO2 in sleeping and torpid squirrels beyond that caused by reduced Tb. In torpor at steady state, MCO2/MO2 (R) and ventilation returned to control values, and no further CO2 retention occurred. Arousal from sleep or torpor was accompanied by transiently high VE/MCO2 and R values as CO2 was released from the body fluids. R and VE/MCO2 values during heterothermia in awake squirrels (Tb 32-42.5 degrees C) showed that total body CO2 content remained unchanged until Tb reached 40 degrees C with onset of hyperventilation. Altered CO2 content of the body fluids is thus not a general feature of mammalian heterothermy. The difference in CO2 homeostasis of torpid and heterothermic awake animals may have implications for the difference in metabolic intensity of these states.
Regulation of bone repletion in rats subjected to varying low-calcium stress
Authors: Drivdahl R. H. , Liu C. C. , Baylink D. J.
Published: December 2017

Weanling Sprague-Dawley rats subjected to varying degrees of low-Ca dietary stress (depletion) showed graded increases in the rate of endosteal bone formation when normal dietary Ca was restored (repletion). There was a strong positive correlation between the rate of bone resorption in depletion and the rate of bone formation attained after 1 wk of repletion. However, bone formation declined rapidly within the first 4 wk of repletion, despite the persistence of a substantial endosteal bone volume deficit. Furthermore the medullary area (indicative of bone volume) did not by itself determine the bone formation rate. Bone volume in test groups was restored to control levels after 6 mo of repletion, and this result could be predicted by a kinetic analysis. Thus, although very high rates of formation in early repletion decline rapidly, smaller increments relative to controls must be sustained for long periods. Our data indicate that increased formation rats at all stages of repletion are a consequence of elevations in both osteoblast number and osteoblast activity.
Hemodynamics and potentials in isolated flounder gills: effects of catecholamines
Authors: Stagg R. M. , Shuttleworth T. J.
Published: December 2017

Branchial hemodynamics and transepithelial potentials were investigated in an isolated perfused gill preparation from the flounder (Platichthys flesus L.). An analysis of the pressure-flow profiles suggests that the gill is compliant but that the physical relationships of pressure and flow are complex. Epinephrine has a bimodal effect with an initial vasoconstriction followed by a vasodilation, the latter response being much smaller than that usually seen in teleosts. Pharmacological analysis shows 1) an alpha-mediated vasoconstriction of the arterial and venous pathway, associated with a redistribution of flow away from the venous pathway, and 2) a small beta-mediated vasodilation of the arterial pathway only. An electrical potential (inside positive) was measured across the isolated gill, bathed and perfused with an identical saline. This potential was recorded, despite the venous system being open to the external bath, and was independent of both arterial and venous flows. Epinephrine caused a significant decline in this potential, which could be resolved into a large inhibitory alpha-mediated response and a small beta-mediated stimulation.
Glycogenolytic substances, hepatic and systemic lactate, and food intake in rats
Authors: Racotta R. , Islas-Chaires M. , Vega C. , Soto-Mora M. , Russek M.
Published: December 2017

Changes in hepatic lactate and glucose and systemic blood lactate produced by intraperitoneal injections of epinephrine, isoproterenol, glucagon, and insulin showed a high correlation (r = 0.9) with the changes in food intake elicited by the same substances. The changes in systemic blood glucose showed no correlation with the changes in feeding, which suggests that central glucoreceptors are not playing an important role in the observed changes in feeding. The intramuscular epinephrine had no significant effect on food intake, in spite of changes in systemic and hepatic lactate and glucose similar to those elicited by intraperitoneal epinephrine. However, intramuscular epinephrine had no hepatic glycogenolytic effect. This suggests that the changes in glucose and lactate elicited by intraperitoneal epinephrine result from hepatic glycogenolysis, whereas the changes elicited by intramuscular epinephrine result from muscular glycogenolysis and inhibition of insulin. Thus hepatic glucose and lactate are good predictors of feeding only when they are produced endogenously by hepatic glycogenolysis. It was concluded that hepatic lactate cannot be the substance sensed by hepatic metabolic receptors. However, due to a possible change in the hepatic lactate-to-pyruvate ratio elicited by intraperitoneal epinephrine, hepatic pyruvate may still be correlated with feeding during the action of both intramuscular and intraperitoneal epinephrine. Therefore the hypothesis that pyruvate is the substance monitored by hepatic metabolic receptors should be tested.
Calmodulin-induced feeding in the cat: attenuation by calcium chelator EGTA
Authors: Myers R. D. , Lee T. F.
Published: December 2017

Cannulas for intracerebroventricular injection of calmodulin (CaM), Ca2+, and other substances were implanted stereotaxically in the cat. Postoperatively, measures of food intake were taken on each day during a 1.0-h interval until feeding had stabilized. Then the Ca2+-binding protein, CaM, was infused intracerebroventricularly into the fasted cat 15 min before the 1.0-h feeding session. CaM (0.15-0.60 nM) significantly enhanced the animal's normal feeding response, which was accompanied by a slight decline in body temperature. Infusion of 6.25-50.0 mM excess Ca2+ reduced body temperature in a concentration-dependent manner with food intake augmented by 6.25-25.0 mM Ca2+. Chelation of Ca2+ in the brain with 0.5-2.5 mM ethyleneglycol-bis(beta-aminoethyl ether)-N,N'-tetra-acetic acid (EGTA) similarly infused intracerebroventricularly into the cat simultaneously suppressed feeding and elevated core temperature. Threshold doses of EGTA selectively attenuated CaM-induced eating but not feeding elicited by the catecholamine neurotransmitter, norepinephrine. Overall these results suggest that CaM, by complexing with cellular Ca2+, could serve as an intermediary factor in governing steady-state activity of neurons in the brain. In turn, this essential cation may mediate specific regulatory processes within the diencephalon that underlie the postulated "setpoint" mechanism for the control of feeding.
Acid-base status of fish at different temperatures
Authors: Cameron J. N.
Published: December 2017

In the water-breathing fishes, rising temperatures are accompanied by progressive reduction in pH, reductions in bicarbonate concentration, and slight rises in CO2 partial pressure. The pH-temperature slope of both intra- and extracellular compartments varies considerably, from -0.009 to -0.033/degrees C, with a rather consistent pattern of red muscle greater than white muscle greater than heart. Three different approaches to acid-base analysis, the imidazole-alphastat model, the strong-ion difference analysis, and the delta-bicarbonate approach, were applied to a set of data from the fresh-water channel catfish (Ictalurus punctatus). A principal difficulty encountered in using all three approaches was that assumptions were required regarding the chemical behavior of the intracellular buffers, but the delta-bicarbonate approach has the practical advantage of emphasizing parameters that can be measured directly. Closed-system models are not generally applicable to fish, and the interest for future work lies in deciphering the significance of tissue-to-tissue variations in pH regulation and in elucidating the mechanisms of the strong-ion transfers.
Influence of thermal acclimation on glucose production and ketogenesis in isolated eel hepatocytes
Authors: Jankowsky D. , Hotopp W. , Seibert H.
Published: December 2017

Hepatocytes were isolated by collagenase perfusion of the liver from adult eels (Anguilla anguilla L.) acclimated to different temperatures. Whereas the relative weight of the liver increased in cold-acclimated fish, hepatocytes from 10- and 20 degrees C-acclimated animals did not differ in cellular weight, dry weight, or protein content. Endogenous rates of oxygen consumption and respiratory control ratios were independent of acclimation temperature. There was no effect of temperature on triacylglycerol content, but glycogen concentration was significantly higher in hepatocytes of cold-acclimated fish. Liver cells from cold-acclimated eels exhibited higher rates of glucose release and ketogenesis than those from warm-acclimated animals. It is concluded that the increase in acetoacetate production induced by cold acclimation results primarily from a higher rate of lipolysis. Cellular interactions between ketogenesis and gluconeogenesis are demonstrated and discussed.
Low-temperature dormancy in fish
Authors: Crawshaw L. I.
Published: December 2017

The importance of low ambient temperature in the physiology of winter dormancy was studied in the brown bullhead (Ictalurus nebulosus) and the largemouth bass (Micropterus salmoides). The bullheads frequently entered a sleep-like state at low temperatures; the likelihood of being aroused from this state was inversely proportional to the ambient temperature. Spontaneous activity for both species was relatively constant from 17 to 7 degrees C; at lower temperatures activity decreased. The selected temperature was lowered in both species as a consequence of acclimation to 3 degrees C; if given the opportunity, fish of both species moved to temperatures above 25 degrees C within 1 day in spite of the consequent acid-base and metabolic imbalances. In bass, food intake was very low for acclimation temperatures of 8 degrees C and below; at higher temperatures the relationship between food intake and acclimation temperature required 4 wk to stabilize. Quiescent brown bullheads exhibited discontinuous breathing. Alteration of brain temperature with implanted thermodes indicated that the main locus of control of this breathing pattern is in the medulla; lesser influences emanate from the anterior hypothalamus and the midbrain. Metabolism was measured at a series of acclimation temperatures between 3 and 17 degrees C for both species. No evidence of a discontinuous function (metabolic shutdown) was seen for either species.
Temperature sensitivity of the renin-angiotensin system in Ambystoma tigrinum
Authors: Corwin E. , Malvin G. M. , Katz S. , Malvin R. L.
Published: December 2017

The presence of a renin-angiotensin system was demonstrated in the poikilotherm Ambystoma tigrinum, commonly called the tiger salamander. Standard radioimmunoassay techniques were employed to measure the intrarenal renin activity (IRA) and the plasma renin activity (PRA) of A. tigrinum kept at either 5 or 20 degrees C. Basal IRA and PRA values were not affected by the temperature at which the animals were maintained. Intraperitoneal injection of the beta-adrenergic agonist isoproterenol, however, increased PRA only in those animals maintained at 20 degrees C. This is consistent with the hypothesis of a temperature sensitivity of the renal adrenergic system in vivo. In addition, we were able to demonstrate the existence of a contractile response of Ambystoma vascular smooth muscle to angiotensin II that was blocked by the competitive inhibitor saralasin.
Intracranial volume adjustments and cerebrospinal fluid pressure in the osmotically swollen rat brain
Authors: Melton J. E. , Nattie E. E.
Published: December 2017

Acute dilutional hyponatremia (DH) (plasma [Na+] approximately equal to 110 meq/l over 3 h) was produced by intraperitoneal dialysis with distilled water in pentobarbital-anesthetized rats with either closed (SC) or open (SO) skulls. SO rats showed marked brain protrusion during DH, but the loss of brain Na+ and Cl- and gain in brain water was the same as that seen in SC rats. During DH, cerebrospinal fluid pressure (PCSF) rose five to six times within 90 min postdialysis and then fell toward control values in both SC and SO rats. This pattern did not correlate with changes in brain water, suggesting that volume adjustments in another intracranial compartment, possibly bulk CSF, are partially responsible for changes in PCSF. The pressure-volume characteristics of the intracranial space, as measured by the pressure-volume index (PVI), were unaffected by osmotic brain swelling. Comparison of PCSF values observed during DH with values predicted from PVI data showed that actual PCSF is, at most, half the predicted value. This again suggests reduction of a nontissue intracranial compartment, which, from relative size considerations, is probably bulk CSF.
Anteroventral hypothalamus and hemorrhagic shock: cardiovascular and neuroendocrine responses
Authors: Feuerstein G. , Johnson A. K. , Zerbe R. L. , Davis-Kramer R. , Faden A. I.
Published: December 2017

The anteroventral third ventricle (AV3V) region was shown to be a site of central integration of sympathetic pressor pathways and central pressor and vasopressin (VP) release by angiotensin II (ANG II). Since the AV3V area seems to have an important role in the regulation of the three major pressor systems, we investigated the role of the AV3V in cardiovascular recovery after hemorrhage, a known stimulus for sympathetic, ANG II, and VP release. Conscious AV3V-lesioned (n = 19) and sham-operated rats (n = 14) underwent bleeding (40% of blood volume) through an arterial line. Mean blood pressure, heart rate, and plasma ANG II, VP, and catecholamines were monitored over 24 h. The exact site of lesion was determined by microscopic examination. The mean blood pressure and heart rate of both groups of rats were not different before or after hemorrhage. Plasma catecholamines, ANG II, and VP responses were also the same as were hematocrit and water consumption 24 h after the bleeding. Despite the lack of difference between control and lesioned animals with regard to cardiovascular, humoral, and neuroendocrine responses to hypovolemia, the AV3V-lesioned rats had a significantly higher early mortality rate. These data indicate that the AV3V may be an important region in recuperation and survival after hemorrhagic shock, but through mechanisms unrelated to activation of VP, renin-ANG II, or the sympathetic nervous system.
Local cerebral glucose utilization in fetal and neonatal sheep
Authors: Abrams R. M. , Ito M. , Frisinger J. E. , Patlak C. S. , Pettigrew K. D. , Kennedy C.
Published: December 2017

The newborn mammalian brain of several species has been shown to have a lower average rate of energy metabolism and a narrower range of rates in its various components than is found in maturity. In a further study of cerebral energy metabolism during development, we have employed the [14C]deoxyglucose method for measuring local cerebral glucose utilization in fetal and neonatal sheep. After establishing the lumped constant to be 0.40 and finding the rate constants for the kinetic behavior of deoxyglucose in plasma and brain to be close to those in other species, we measured the rates of glucose utilization in 44 regions of the brain. The rates were low and homogeneous in midgestation, except for those of brain stem nuclei of the auditory and vestibular systems and those of the hippocampus which were relatively high. In the last 7 wk, local rates rose approximately threefold. After birth there was a further average increase of 50% above full-term levels. The study shows that cerebral energy metabolism rises in most structures during prenatal maturation, a time when sensory stimulation is at a relatively low level and behavioral responses are minimal.
cAMP-mediated regulation of chloride secretion by the opercular epithelium
Authors: May S. A. , Degnan K. J.
Published: December 2017

Catecholamine regulation of the Cl- secretion rate (short-circuit current, Isc) and adenosine 3',5'-cyclic monophosphate (cAMP) levels of the opercular epithelium was investigated by using 3-isobutyl-1-methylxanthine (IBMX), forskolin, and adrenergic agonists. In this tissue alpha-adrenergic agonists inhibit, and beta-adrenergic agonists stimulate, the Isc (J. Physiol. London 294: 483-495, 1979). IBMX and forskolin stimulated the Isc 125 and 85%, respectively, and simultaneously produced 2.5- and 70.0-fold elevations in the cAMP levels, respectively. These findings confirm previous observations demonstrating that stimulation of the Isc in this tissue is mediated by elevations in cAMP (J. Comp. Physiol. B 145: 29-35, 1981). Isoproterenol, a beta-agonist, had no effect on the Isc of either IBMX- or forskolin-stimulated tissues but increased the cAMP level an additional 5.8-fold in IBMX-stimulated tissues. Clonidine, an alpha-agonist, inhibited the Isc in IBMX-stimulated tissues only and had no effect on cAMP levels in either IBMX- or forskolin-stimulated tissues. These findings demonstrate that catecholamine-induced inhibition of the Isc can occur while the cAMP level remains elevated, indicating that this effect is not mediated by lowering cAMP levels. This observation is strong evidence for a cAMP-independent mechanism for catecholamine-induced inhibition of Cl- secretion in the opercular and similar epithelia.
Cardiovascular actions of microinjections of angiotensin II in the brain stem of rats
Authors: Casto R. , Phillips M. I.
Published: December 2017

The blood pressure and heart rate responses to microinjection of angiotensin II (ANG II) into the brain stem of urethan-anesthetized rats were studied. Microinjection of ANG II into the area postrema (AP) resulted in significant elevation of blood pressure and significant reduction of heart rate. Microinjection into the region of the nucleus tractus solitarius (NTS) yielded a significant dose-dependent elevation in blood pressure and consistent increases in heart rate. The response to microinjection of ANG II into the region of the NTS was not due to leakage into the peripheral circulation, since intravenous administration of the ANG II antagonist, saralasin, did not attenuate the response. In fact, the cardiovascular response was increased after peripheral ANG II blockade, and the heart rate, which was consistently but not significantly elevated by NTS injection alone, was significantly elevated after saralasin pretreatment. Thermal ablation of the AP did not change the heart rate or the pressor response to microinjection of ANG II into the region of the NTS, indicating that the response was not mediated through the AP.