bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal dependence of endurance and locomotory energetics in a lizard
Authors: John-Alder H. B. , Bennett A. F.
Published: December 2017

The thermal dependencies of endurance and the rates of oxygen cnsumption (VO2) and carbon dioxide production (VCO2) were determined for the lizard Dipsosaurus dorsalis walking on a treadmill. The thermal dependencies of endurance and maximal VO2 (VO2 max) are nerly identical. The maximal sustainable speed and the speed at which VO2 max is attained at each experimental body temperature are the same. The net cost of locomotion (the slope of VO2 vs. speed) is termperature independent. Resting VO2 and the incremental change in VO2 required to support locomotion at a sustainable speed are higher at 40 degrees C than at 25 degrees C. Therefore, the total cost of locomotion (VO2 divided by speed) is greater at 40 degrees C. However, the minimum cost of transport, attained at the maximal sustainable speed, is temperature independent. The results clearly indicate that maintenance of a high body temperature is energetically expensive for Dipsosaurus, but that the associated expanded activity capacity enables this lizard to avoid an obligate increase in the energetic requirements of locomotion.
Amiloride-sensitive ammonium and sodium ion transport in the blue crab
Authors: Pressley T. A. , Graves J. S. , Krall A. R.
Published: December 2017

In the estuarine crab, Callinectes sapidus, net NH4+ efflux was twice as high in animals acclimated to 17% salinity seawater (SW) (0.495 +/- 0.084 mumol . h-1 . g wet wt-1, n = 7) than in animals acclimated to full-strength 35% SW (0.212 +/- 0.028 mumol . h-1 . g-1, n = 7). Amiloride (3 X 10(-4) M) in the external SW reversibly inhibited these effluxes by 63 +/- 6% (n = 6) and 67 +/- 6% (n = 5), respectively. Unidirectional Na+ influx was reversibly inhibited 42 +/- 6% (n = 7) by amiloride in 17% SW-acclimated crabs and 49 +/- 7% (n = 8) in 35% SW-acclimated crabs. This mutual sensitivity to amiloride is evidence for a Na+/NH4+ exchanger. Inhibition of unidirectional Na+ efflux by Na+-free SW indicates the presence of an obligate Na+/Na+ exchange component that accounts for at least 42% of the Na+ flux and is also amiloride sensitive. The lack of inhibition by amiloride of the net H+ efflux does not support the presence of a Na+/H+ exchanger. Acclimation of the crab to dilute SW may involve an increase in the activity of the Na+/NH4+ exchanger in the gills, but this mechanism contributes only a small fraction of the total Na+ transport.
Embryonic oxygen consumption and growth of Laysan and black-footed albatross
Authors: Pettit T. N. , Grant G. S. , Whittow G. C. , Rahn H. , Paganelli C. V.
Published: December 2017

The constraints placed on diffusive gas exchange by the eggshell and the adaptive features of embryonic respiration and metabolism in large Laysan and black-footed albatross eggs (300 g) during prolonged incubation (65 days) were examined in naturally incubated eggs on Sand Island, Midway, in the Northwestern Hawaiian Islands. A low eggshell gas conductance and slow growth rate were associated with a relatively low oxygen consumption (MO2) throughout incubation. Just prior to internal pipping (IP) of the inner shell membrane and penetration of the air space, the MO2 (pre-IP MO2) was approximately 1,250 ml O2 (STPD).day-1 for both species, resulting in air cell O2 and CO2 tensions of 106 and 40 Torr, respectively. During the 4- to 5-day pipping-to-hatching interval, O2 uptake increases rapidly as pulmonary respiration is initiated. Hatchling O2 consumption averaged 3,700 ml O2 (STPD).day-1 or about three times the pre-IP MO2. Data support the hypothesis that embryonic metabolism among Procellariiformes is related to the extent to which the incubation period deviates from the expected value based on initial egg mass.
Model for parathyroid hormone secretion and metabolism in calves
Authors: Jung A. , Mayer G. P. , Hurst J. G. , Neer R. , Potts J. T.
Published: December 2017

A model for parathyroid gland response to differing calcium and magnesium concentrations is proposed based on direct determinations of parathyroid hormone (PTH) secretion rate. A proportional control seems adequate for physiological variations of calcium and magnesium levels. At extreme hypocalcemia, nonlinearities are observed: a model involving the depletion of a storage compartment is proposed, the size of which is calculated. PTH distribution was studied in another group of animals; sampling was made from the saphenous artery and the thoracic duct. Concentrations of plasma and lymph-intact PTH and carboxy-terminal fragments were determined by means of two different radioimmunoassays. The analysis of the results leads to the formulation of a five-compartment model, which shows that the metabolism of intact PTH is only partly due to the formation of carboxy-terminal fragments, most being directly secreted or catabolized. Linking these models for secretion and distribution of PTH, simulation studies were undertaken and compared with published data. This model is then discussed in comparison with previous work concerning other polypeptide hormones.
Parathyroid gland response to epinephrine: a rate-sensitivity mechanism
Authors: Jung A. , Mayer G. P. , Hurst J. G. , Neer R. , Potts J. T.
Published: December 2017

A model for parathyroid gland response to an epinephrine infusion is proposed. It is based on direct measurements of the parathyroid hormone (PTH) secretion rate as measured directly after cannulation of the venous drainage of single superior parathyroid glands of calves. When epinephrine was infused into a jugular vein, a large increase of PTH secretion rate was observed at the beginning of the infusion. The PTH secretion rate thereafter fell, but it was still significantly above the control rate. At the end of the epinephrine infusion a sharp decrease was observed when the infusion was terminated. These observations are consistent with a rate-sensitive control mechanism. Calculation of the parameters yielded a model, which was then linked with a kinetic model for PTH distribution. Simulation studies were undertaken to predict plasma PTH concentration in response to an epinephrine infusion. Good agreement was found between predicted results and previously published work. The role of this rate-sensitive mechanism in the parathyroid gland is discussed.
Sympathetic immunoregulation: difference between high- and low-responder animals
Authors: del Rey A. , Besedovsky H. O. , Sorkin E. , Da Prada M. , Bondiolotti G. P.
Published: December 2017

A quantitative relationship is reported between the magnitude of the immune response of rats to sheep red blood cells and diminution of splenic norepinephrine (NE). A decrease in concentration and content of NE in the spleen on day 3 after immunization was evident in both high- and low-responder animals, whereas a diminished concentration of NE persisted only in the high responders. This continuing NE diminution in high-responder animals is associated with increase in spleen weight, probably attributable to blood accumulation. These findings are consonant with the concept that the sympathetic nervous system is involved in immunoregulation.
Renal handling of taurine in marine fish
Authors: Schrock H. , Forster R. P. , Goldstein L.
Published: December 2017

Net renal tubular excretion of taurine was demonstrated by clearance techniques in the dogfish, Squalus acanthias; the little skate, Raja erinacea; and in the winter flounder, Pseudopleuronectes americanus. Dogfish acclimated to 70% seawater had increased renal excretion of taurine resulting from higher glomerular filtration rates of taurine as well as from increased rats of tubular secretion. Tubular secretion of taurine prevailed in the dogfish and flounders measured, whereas it occurred in only 30% of the population of skates where tubular reabsorption predominated. Taurine uptake into incubated dogfish thin kidney slices was investigated. Uptake occurs mainly across the peritubular membrane, is carrier mediated, dependent on metabolic energy, and completely inhibited by ouabain and low Na in the medium. The active transport of taurine is also inhibited by beta-alanine but not by alpha-aminoisobutyric acid, glycine, gamma-aminobutyric acid, PAH, or probenecid.
Effect of swim training on development of obesity in the genetically obese rat
Authors: Walberg J. L. , Mole P. A. , Stern J. S.
Published: December 2017

Seven-week-old female lean and obese Zucker rats were swim trained or kept sedentary for 8 wk. Another group of obese rats was exercised plus food restricted. During exercise training, obese and lean rats ate more but gained less body weight than sedentary controls. Exercise favorably altered body composition, adipose cellularity, and plasma insulin of the obese rat. Exercise plus food restriction more dramatically affected body composition and adipose cellularity but was no more effective in depressing hyperinsulinemia than exercise alone. Following 8 wk of retirement, dorsal fat cell number remained depressed to formerly exercised obese rats whereas adipose cellularity in other depots, body composition, and plasma insulin were similar to control levels. Thus, exercise delayed but did not prevent the full development of obesity in the Zucker rat. Food restriction along with exercise resulted in more permanent effects on adipose cellularity than exercise alone but stunted muscle and skeletal growth.
Glucose and endocrine responses to hypothalamic electrical stimulation in rats
Authors: Dubuc P. U. , Leshin L. S. , Willis P. L.
Published: December 2017

The effect of ventromedial (VMN) or basolateral (LHA) hypothalamic electrical stimulation on glucose and hormone production was examined in conscious and anesthetized male rats. Barbiturate treatment alone led to large increases of corticosterone and smaller but significant increases of glucose, insulin, and glucagon. When hypothalamic stimulation was combined with anesthesia, interactions between the hypothalamic sites and the awake-anesthetized conditions were observed. This was most evident with LHA placements, as awake rats exhibited mild hypoglycemia and hypoglucagonemia in response to low-level (approximately 10 microA rms) current, but no effects on these values were seen with VMN electrodes. With barbiturate anesthesia, the same level of stimulation led to severe hyperglycemia in both VMN and LHA rats and a mild hyperglucagonemia in the LHA group. No consistent effects of stimulation on immunoreactive insulin or corticosterone were detected at either hypothalamic site or in any anesthesia condition. The present results point out the important role anesthetics may play in studies defining functional aspects of the hypothalamus. Furthermore, our inability to elicit consistent autonomic responses with electrical stimulation, when compared with the effectiveness of both metabolic agents and pharmacologic stimuli, suggests that the sites integrating autonomic function may be diffusely distributed over the basal diencephalon.
Aberrations of circadian body temperature rhythms in rats with medial preoptic lesions
Authors: Satinoff E. , Liran J. , Clapman R.
Published: December 2017

The normal amplitude of the circadian rhythm of telemetered body temperature (Tb) in male rats was 2 degrees C (between 36 and 38 degrees C). For several weeks after large medial preoptic lesions Tb cycled from as low as 29 degrees C to as high as 41 degrees C in a single day. With recovery, or in rats with smaller lesions, peak-to-trough Tb amplitudes decreased, ranging between 3 and 5 degrees C for many months, with normal or slightly raised troughs in the light part and grossly higher peaks in the dark part of a 12:12 light-dark cycle. Rats in whom some periventricular tissue was spared had normal amplitudes of Tb, but the whole curve was displaced 0.5-1.0 degrees C above control values. These effects persisted in constant darkness. We conclude that in the weeks after medial preoptic lesions thermoregulatory responses are not activated until Tb is abnormally high or low. As recovery progresses, or if the lesions are smaller to begin with, there may be an imbalance between heat loss and heat production systems so that heat production mechanisms are either always dominant or overshoot when activated.
The glabrous epidermis of cavies contains a powerful battery
Authors: Barker A. T. , Jaffe L. F. , Vanable J. W.
Published: December 2017

Voltages across various glabrous (and gland-free) regions of cavy skin range from 30 to 100 mV, inside positive; across hairy ones, 0 to 10 mV. (moreover, hairy areas also tend to maintain lower transcutaneous voltages in man.) When an incision is made through the glabrous epidermis of the cavy, a microampere flows through each millimeter of the cut's edge. These wound currents generate lateral, intraepidermal voltage gradients or fields of about 100-200 mV/mm near the cut; fields which decline with distance from the cut with a space constant of 0.3-0.4 mm. It is deduced from these data that the epidermis near a cut drives up to 300 microA/cm2 across itself; moreover, these currents and potentials can be grossly, rapidly, and (to some extent) reversibly reduced by amiloride. It is concluded that the hair and gland-free skin of cavies has a battery comparable in power and character to that of frogs; but it is suggested that this mammalian battery may primarily subserve epidermal wound healing rather than salt uptake.
Neuroendocrine control of Na+ balance in the fiddler crab Uca pugilator
Authors: Davis C. W. , Hagadorn I. R.
Published: December 2017

The hemolymph ionic composition and unidirectional Na+ fluxes were analyzed in fiddler crabs (Uca) acclimated to 500 mosmol seawater. Eyestalkless crabs had lower hemolymph osmotic, Na+, and Cl- concentrations. The Na+ efflux was increased from 13.6 +/- 0.6 in control crabs to 19.6 +/- 1.3 mueq.g-1.h-1 in eyestalkless crabs; this increase was shown to be due to a higher Na+ permeability in eyestalkless crabs. Hemolymph Na+ in eyestalkless crabs was increased by an injection of eyestalk extract. The Na+ influx was increased from 11.1 in intact to 15.8 mueq.g-1.h-1 in eyestalkless animals. A kinetic study showed that 1) the influx was higher at all external Na+ concentrations in eyestalkless and intact-Na+-depleted crabs than in intact controls, and 2) the influx mechanism exhibited allosterism. The elevated Na+ influx in eyestalkless crabs was decreased by an injected eyestalk extract. An injected brain extract caused in increase in the Na+ influx in intact animals. It is concluded that the Na+ uptake mechanism is activated by decreasing the hemolymph Na+ concentration and that a brain hormone mediates the effect.
Effect of ethanol ingestion on plasma vasopressin and water balance in humans
Authors: Eisenhofer G. , Johnson R. H.
Published: December 2017

The effects of 75 ml ethanol ingested over 60 min on plasma osmolality (Posmol) and plasma vasopressin (PAVP) in four normal subjects were studied. In the 1st h of the investigation PAVP fell, then rose, even though plasma ethanol levels were still rising. The rise in PAVP was preceded by a rise in Posmol corrected for the influence of ethanol. The fall in PAVP was followed by an increase in free water clearance and a decrease in urine osmolality, while the later rise in PAVP was followed by a decrease in free water clearance (CH2O) and a rise in urine osmolality. The relationship between PAVP and Posmol was then studied during intravenous (iv) hypertonic saline infusion in five subjects. The results were compared with those from a second infusion in the same subjects after ingestion of ethanol (0.5 ml/kg). Ethanol reduced vasopressin release in response to iv hypertonic saline infusion, and this correlated with a reduced decrease in CH2O. We conclude that ethanol inhibits PAVP release by decreasing the response of the osmosodium receptors to changes in plasma tonicity.
Regulation of brain temperature in pigeons: effects of corneal convection
Authors: Pinshow B. , Bernstein M. H. , Lopez G. E. , Kleinhaus S.
Published: December 2017

The effect of direct ventilation of the eyes on cooling in the brain was investigated in domestic pigeons (Columba livia, mean mass 0.27 kg) with thermocouples chronically implanted in the hypothalamus and anterior eye chamber. During conductive heating in still air body-brain temperature difference (delta T) was 2.6 degrees C. During exclusive ventilation of ocular surfaces, with air flowing at about flight speed, delta T increased to 3.5 degrees C and returned to preventilation values on cessation of ventilation. When the eyes were sealed then ventilated, delta T was not different from that in still air. Administration of phenylephrine caused iridial vasoconstriction and a significant decrease in intraocular temperature, but no changes in brain temperature. This suggests that compensation may occur via other evaporating cranial surfaces. Our findings suggest that the eyes contribute to the control of brain temperature by dissipating heat. Blood cooled while flowing through the ocular vasculature apparently contributes to the venous flow through the ophthalmic rete, serving as a heat sink for arterial blood flowing to the brain.
Blood chemistry homeostasis during prolonged fasting in the northern elephant seal
Authors: Costa D. P. , Ortiz C. L.
Published: December 2017

Serum electrolytes, 3 enzymes, and 11 metabolites were monitored for 32-68 days in weaned, naturally fasting elephant seal pups. Serum glucose, urea nitrogen and creatinine levels declined as the fast progressed, whereas total protein, albumin, and globulin levels remained nearly constant. By contrast, triglycerides, cholesterol, uric acid, and bilirubin were quite variable and no definite trends were apparent. Alkaline phosphatase activity appeared to increase during fasting, while serum glutamic oxalacetic transaminase and lactate dehydrogenase remained fairly uniform. Comparisons of averaged blood chemistry values from singly and multiply sampled fasting pups to that of four nursing pups showed significant differences in the levels of blood urea nitrogen, creatinine, cholesterol, bilirubin, and albumin, but sampling uncertainty limited physiological interpretation. Electrolyte levels in all animals were maintained within narrow limits under all conditions with little interindividual variation. These results further document the remarkable homeostasis achieved during prolonged fasting in elephant seals and support the hypothesis that fat is the primary energy substrate during the protracted natural fasts characteristic of this species.
Fastigial nucleus stimulation and excitatory spinal sympathetic activity in dog
Authors: Dormer K. J. , Foreman R. D. , Ohata C. A.
Published: December 2017

To locate the cerebellar-activated descending sympathetic pathways in the dog the fastigial nucleus (FN) was electrically stimulated in chloralose-anesthetized dogs while recording from sympathetic preganglionic neurons. Physiological interventions included lesions in the dorsolateral funiculus (DLF) of the spinal cord, myelotomy, arterial pressure changes, bilateral occlusion of the carotid arteries, and administration of clonidine. Multiunit activity at the T2 on T3 white ramus communicans was recorded on-line during rest and FN stimulation. Descending sympathetic activity (averaging 3.5 m/s) in the DLF was increased in response to FN stimulation but was significantly reduced by ipsilateral and eliminated by bilateral FN lesions. When testing for the effects of baroreceptor reflexes on the sympathetic pathway phenylephrine-induced hypertension decreased, but moderate hemorrhage increased the amount of preganglionic activity at rest and during FN stimulation. During hypertension and simultaneous carotid artery occlusion the amount of sympathetic activity that could be evoked was comparable to that evoked during normotensive states. Clonidine (IV) reduced the FN sympathoexcitation, but direct stimulation of the DLF indicated that clonidine had sympathoinhibitory activity at both medullary and spinal sites. In summary, rostral FN primarily excited ipsilateral descending sympathetic pathways in DLF, and this sympathoexcitation was partially inhibited by baroreceptor intervention.
Classification of raphe neurons with cardiac-related activity
Authors: Morrison S. F. , Gebber G. L.
Published: December 2017

The cardiac-related component of sympathetic nerve discharge (SND) results from entrainment of a rhythm of brain stem origin by the baroreceptor reflexes [Gebber, Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H143-H155, 1980]. As a consequence, changes in heart rate are accompanied by shifts in the phase relations between SND and the arterial pulse wave. This observation presented us with the opportunity of distinguishing brain stem neurons whose discharges are locked to SND from other neuronal types that exhibit cardiac-related activity. Raphe neurons in the cat medulla with cardiac-related activity were identified using post-R wave interval analysis. The discharges of one group of these neurons remained locked to inferior cardiac SND during changes in ventricular rate which shifted the phase relations between SND and the arterial pulse wave. Most importantly, the lag between unit spike occurrence and the peak of the cardiac-related component of SND was unchanged during ventricular pacing (as demonstrated with cross-correlation analysis). It is suggested that these neurons were contained in brain stem networks which control SND. The discharges of two additional types of raphe neurons remained locked to the arterial pulse wave during ventricular pacing. Neurons of the first type exhibited an increase in discharge probability in late diastole and early systole. Neurons of the second type exhibited a period of reduced activity time-locked to systole.
Evolution of angiotensin II-induced catecholamine release
Authors: Carroll R. G. , Opdyke D. F.
Published: December 2017

The interaction between angiotensin II (ANG II) and catecholamines was examined in nonmammalian vertebrates. ANG II challenge caused a significant pressor response in representatives of the seven vertebrate classes. Additionally, plasma levels of both epinephrine and norepinephrine increased following intravascular ANG II injection in the conscious lumpfish, bullfrog, and turtle, and the anesthetized chicken. Phentolamine pretreatment totally abolished ANG II pressor action in the hagfish and chicken and diminished the ANG II pressor response in other classes of vertebrates. The ability of ANG II to release catecholamines appears to be a phylogenetically ancient interaction and indicates that catecholamines may play an important role in the physiological expression of ANG II action in lower vertebrates.
Fluctuations in basal levels and effects of altered nutrition on plasma somatostatin
Authors: Hansen B. C. , Vinik A. , Jen K. L. , Schielke G. P.
Published: December 2017

Rapid oscillations in basal plasma levels of insulin, C-peptide, glucagon, and glucose in rhesus monkeys have been reported previously. We now report large minute-to-minute fluctuations in plasma somatostatinlike immunoreactivity (SLI) in undisturbed, chair-adapted, and chronically cannulated male rhesus monkeys. Plasma samples were drawn from eight monkeys at 1- to 2-min intervals for 30-40 min following an overnight fast. Large fluctuations in SLI levels with periods of 4.4-9.4 min/cycle and possibly secondary periods of 14-18 min/cycle with average amplitudes of +/- 23% relative to the respective mean SLI levels were observed both within a single experiment and across monkeys under basal conditions. No consistent relationship was found between SLI fluctuations and that of insulin or glucagon. When portal and central blood samples were drawn precisely simultaneously no consistent portal-central gradient was found. Patterns of fluctuations in central and portal SLI levels were not correlated. Overfeeding significantly increased insulin levels but did not alter SLI levels. After 5 days of food deprivation basal SLI levels were unchanged. These data indicate the need to exercise care in the interpretation of single samples in the measurement of plasma SLI levels. Somatostatin secreted into the blood under basal, unstimulated conditions appears to be unrelated to nutritional balance.
A new approach to compartmental analysis
Authors: Sherif M. H.
Published: December 2017

When recirculation of compounds and/or mixing transients are appreciable, traditional compartment analysis can lead to erroneous results. In this paper, a novel approach that overcomes many of these difficulties is presented. It unifies classical compartment analysis and indicator-dilution theory. It is conceptually simple and can be easily extended to many situations. Several examples for the case of a single compartment demonstrate the superiority of the suggested model to more traditional approaches.
Preoptic-hypothalamic periventricular lesions reduce natriuresis to volume expansion
Authors: Bealer S. L. , Haywood J. R. , Gruber K. A. , Buckalew V. M. , Fink G. D. , Brody M. J. , Johnson A. K.
Published: December 2017

The present experiment was designed to determine if electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V) altered the natriuresis typically seen during isotonic volume expansion. Control and AV3V-lesioned rats received intravenous infusions of 0.9% NaCl at 0.5 ml/min until 10% body weight was given. Arterial blood pressure was monitored, and urine was collected throughout the experiment. Following expansion, blood was processed for analysis of natriuretic hormonelike activity by chromatographic separation of plasma extracts followed by measuring antinatriferic activity across the isolated toad bladder. Urinary sodium excretion and urine volume during expansion were significantly less in rats with lesions surrounding the AV3V region than in control rats. Toad bladder bioassay showed a high level of natriuretic hormonelike activity in control animals following volume expansion, but no natriuretic hormonelike activity in plasma from volume-expanded rats with AV3V lesions. These data demonstrate that AV3V periventricular ablation attenuates the natriuresis induced by isotonic-volume expansion. In addition, preliminary results indicate the AV3V region may be a central site critical for natriuretic hormonelike activity and control of extracellular fluid volume.
Control of arterial pressure in aquatic sea snakes
Authors: Lillywhite H. B. , Pough F. H.
Published: December 2017

Cardiovascular responses to head-up tilt, acutely graded hemorrhage, and pharmacologic stimulation by principal autonomic drugs were studied in four species of marine snakes, principally Aipysurus laevis (family Hydrophiidae). Arterial pressure varied inversely with tilt angle and blood volume deficit in conscious snakes outside of water, indicating that physiological regulation was poor or lacking. Calculated arterial pressures at head level typically diminished to zero in A. laevis tilted to angles greater than or equal to 30 degrees. Arterial pressure (corrected for external water pressure) did not change when these snakes were tilted in seawater. Changes of arterial pressure induced by tilt, blood loss, or autonomic drugs elicited reflex adjustments in heart activity, but the magnitude of these responses was less than that observed in terrestrial species of snake. It is concluded that baroreflexes are present but comparatively ineffective in sea snakes. Snakes tolerated large losses of blood volume, and extravascular fluids were absorbed into the circulation during hemorrhage; both hemorrhage and estimated hemodilution volumes exceeded 100% of the initial blood volume in Acalyptophis peronii. Thus, in marine snakes major fluid shifts between nonvascular and vascular compartments significantly compensate hypovolemia but, because of minor autonomic adjustments, do not result in a well-regulated arterial pressure.
Humoral and cardiovascular responses to feeding in pigs
Authors: Houpt K. A. , Baldwin B. A. , Houpt T. R. , Hills F.
Published: December 2017

In young pigs, allowed to feed after various periods of food deprivation, the changes in plasma levels of insulin, glucose, and corticosteroids were measured. Food was presented in bowls or obtained by operant response. In pigs deprived of food for 17 h there was a marked rise in insulin from 15 +/- 1 to 91 +/- 10 microU/ml and glucose from 94 +/- 2 to 112 +/- 4 mg/dl when feeding began, while the corticosteroid levels were reduced from 48 +/- 8 to 29 +/- 9 ng/ml. Evidence for a cephalic phase of insulin secretion was seen in 17-h fasted pigs. In pigs fed ad libitum there were no significant changes in the levels of insulin, glucose, or corticosteroids. The changes observed in the 5-h fasted pigs were intermediate. No differences were seen between bowl-fed and operant pigs. Pressure transducers were surgically implanted in the carotid arteries of three pigs. When 17-h fasted pigs started to eat there was a marked rise of blood pressure from 114 +/- 3 to 147 +/- 5 mmHg and a similar increase was seen when satiated pigs drank milk.
Effect of p-chlorophenylalanine on thermoregulation in unrestrained rats
Authors: Giacchino J. L. , Schertel E. R. , Horowitz J. M. , Horwitz B. A.
Published: December 2017

p-Chlorophenylalanine (PCPA), a serotonin depletor, was used to investigate thermoregulation of unrestrained unanesthetized rats exposed to warm (approximately 32 degrees C) and cold (approximately 3 degrees C) environments. PCPA (300 mg/kg, ip) was administered approximately 48-96 h prior to the experimental trials. After 60 min of warm exposure, PCPA-treated rats had a significantly smaller increase in mean tail temperature (3.05 degrees C) and a greater increase in mean core temperature (1.47 degrees C) than did the control rats (6.13 and 1.20 degrees C, respectively) as measured via chronically implanted thermistors. A noninvasive method, infrared photography, was also used to monitor skin temperatures following heat exposure. Changes were qualitatively similar to those seen with thermistors, although differences between control and PCPA-treated groups were not statistically significant. During cold exposure, thermistor measurements indicated that the decrease in mean core temperature of the PCPA-treated rats (0.62 degrees C) did significantly differ from that of the controls (1.11 degrees C), whereas tail temperatures did not. These data confirm other studies implicating serotonin in the thermoregulation of rats. In particular, these results show that in a warm environment, PCPA may alter, albeit subtly, peripheral vasodilation in unrestrained rats.
Suppressed basal antidiuretic hormone release during cyclooxygenase inhibition in conscious dogs
Authors: Walker B. R.
Published: December 2017

Both in vitro and in vivo experiments suggest that prostaglandins may affect antidiuretic hormone (ADH) release centrally. In addition, other studies show that prostaglandins administered peripherally may cause ADH release. However, these latter studies have been flawed by hemodynamic alterations and the use of anesthetics, which make interpretation difficult. The present study was designed to test for involvement of prostaglandins produced outside the central nervous system in ADH release in conscious dogs. Administration of meclofenamate (2 mg/kg and 2 mg X kg-1 X h 1, iv) resulted in a consistent fall in plasma ADH levels in five dogs. This diminution of ADH release occurred with no change in systemic hemodynamics, arterial blood gases, or plasma osmolality, suggesting that prostaglandins are important mediators of basal ADH release in the conscious dog. Because meclofenamate does not cross the blood-brain barrier, prostaglandins produced outside the central nervous system appear to be involved in this process. The specific prostaglandin involved or the site of action of prostaglandins on ADH release is not clear at this time.
Metabolic responses to fasting and refeeding in lean and genetically obese rats
Authors: Rothwell N. J. , Saville M. E. , Stock M. J.
Published: December 2017

Injection of norepinephrine (NE) (25 micrograms/100 g body wt) caused a similar rise in metabolic rate in lean and obese (fa/fa) Zucker rats, but 3-day fasting suppressed the response in lean rats and enhanced the rise in obese mutants. Triiodothyronine (T3) injection (10 micrograms/100 g body wt) caused a significantly greater rise in oxygen consumption (Vo2) in obese than lean rats, but the response was attenuated by fasting in all animals. The thermic response to a single meal of either mixed composition, carbohydrate, or protein (40 kJ) was much smaller in obese rats than lean, but the response to the mixed nutrient meal was similar for all rats after a 3-day fast. Refeeding 3-day fasted lean rats with a single carbohydrate meal (40 kJ) caused a rise in plasma T3 levels after 3 h and a delayed increase in metabolic rate 24 h later. Injection of NE instead of refeeding caused a similar delayed rise in metabolic rate. Carbohydrate refeeding had no effect on plasma T3 levels or oxygen consumption in 3-day fasted obese Zuckers, but injection of NE did produce a significant increase in metabolic rate after 24 h. Refeeding 3-day fasted rats with protein (40 kJ) caused a rise in oxygen consumption 24 h later in lean animals but had no effect in obese animals. The data from lean Zucker rats confirm previous findings in Sprague-Dawley rats and suggest that the thermic response to refeeding involves a complex interaction between the sympathetic nervous system and thyroid hormones. Obese Zuckers responded normally to NE and T3, indicating that their reduced thermogenesis after food may be due to insensitivity to nutrient availability or an inability to activate the sympathetic nervous system.
Fastigial stimulation in rats releases adrenomedullary catecholamines
Authors: Del Bo A. , Ross C. A. , Pardal J. F. , Saavedra J. M. , Reis D. J.
Published: December 2017

Electrical stimulation of the rostral fastigial nucleus (FN) in anesthetized, paralyzed, and artificially ventilated rats with a 10-s stimulus train elicited a stimulus-locked elevation of arterial pressure (AP) and heart rate (HR) (the fastigial pressor response, FPR) and elevated plasma catecholamines (CA) within 20 s from the onset of stimulus. Norepinephrine (NE) increased from 139 +/- 24 to 280 +/- 43 pg/ml (P less than 0.05, n = 8) and epinephrine (E) from 70 +/- 26 to 360 +/- 107 pg/ml (P less than 0.02, n = 8). Acute adrenalectomy increased basal plasma NE (362 +/- 108 pg/ml, P less than 0.05, n = 6) and reduced E (9 +/- 4 pg/ml, P less than 0.02, n = 6). The magnitude and duration of the FPR and the relative increase of NE were unchanged; however, the elevation of E was abolished. Chemosympathectomy, produced by 6-hydroxydopamine hydrobromide (100 mg/kg iv, 24 h before the experiment), lowered resting AP (from 122 +/- 2 to 77 +/- 1 mmHg, P less than 0.001) and NE (16 +/- 5 pg/ml, P less than 0.01), but not E. After chemosympathectomy, FN stimulation induced a pressor response of greater magnitude and longer latency and duration than in controls, increased NE 3.5-fold (from 16 +/- 5 to 56 +/- 14 pg/ml, P less than 0.05, n = 5) and E 9-fold (from 38 +/- 11 to 336 +/- 88, P less than 0.05, n = 5). The increases in CA were abolished by adrenalectomy. Chemosympathectomy shifted the pressor-dose-response curves of NE and E to the left; thus, the enhanced pressor response to FN stimulation after chemosympathectomy was possibly a consequence of supersensitivity to circulatory CA. Stimulation of cerebellar FN increased plasma CA, as a consequence of coexcitation of both neural and adrenomedullary components of the autonomic nervous system. However, in rats with intact sympathetic nerves the release of adrenomedullary CA did not contribute to the elevation in AP.
Decrease in liver norepinephrine in response to exercise and hypoglycemia
Authors: Winder W. W. , Beattie M. A. , Piquette C. , Holman R. T.
Published: December 2017

The existence of the sympathetic innervation of the liver has been known for many years, but the role of this system in regulation of liver metabolism is unclear. The purpose of these experiments was to identify physiological conditions for activation of liver sympathetics. Liver norepinephrine (NE) was measured in normal resting rats and in rats exposed to swimming, treadmill running, fasting, and insulin-induced hypoglycemia. Liver NE decreased significantly in response to swimming (-71% of control), treadmill running (-53% of control), and hypoglycemia (-24% of control). Rats that are endurance trained by daily bouts of treadmill running for 3 mo show no decrease in liver NE in response to a 60-min run on the treadmill, whereas nontrained rats show a 50% decrease in liver NE with the same amount of exercise. We conclude that the liver sympathetics are activated in response to swimming, treadmill exercise and hypoglycemia, and that endurance training causes a reduction in the degree of exercise-induced activation of these neurons.
Forearm blood flow and metabolism during stylized and unstylized states of decreased activation
Authors: Jevning R. , Wilson A. F. , O'Halloran J. P. , Walsh R. N.
Published: December 2017

We have measured forearm oxygen consumption and blood flow changes during two wakeful rest behaviors. We have observed acute reduction of forearm respiration (28%) during an acute stylized rest state (TM) and a nonsignificant small decline (11%) during unstylized ordinary eyes-closed rest. These changes were not associated with significant change of forearm blood flow or glycolytic metabolism. Hence, forearm oxygen consumption decline was due almost solely to decreased rate of oxygen extraction. Small variation of forearm blood flow implies that little of the previous findings of increased nonrenal, nonhepatic circulation during TM or increased nonrenal circulation during ordinary rest can be accounted for by altered muscle blood flow, which therefore is consistent with possible increased cerebral blood flow. However, reduced muscle metabolism was a likely contributor to the forearm metabolic decline. The lack of coupling between metabolic and blood flow changes during TM indicates limitation of obligatory coupling between cardiovascular and metabolic function in the rest state of TM.
Cardiovascular functions during voluntary apnea in dogs
Authors: Lin Y. C. , Carlson E. L. , McCutcheon E. P. , Sandler H.
Published: December 2017

We studied cardiovascular responses to apnea during voluntary snout immersion in conscious, chronically instrumented dogs. Voluntary snout immersion up to eye level for a duration of greater than 15 s ensured that the dog was engaged in active apnea. In a control apnea of 15-35 s, heart rate decreased by 43% from a control value of 104 beats/min. Changes in cardiac output paralleled those of heart rate. Mean aortic blood pressure did not vary during apnea, which, coupled with a reduced cardiac output, indicated a 65% increase in estimated total peripheral resistance compared with preapnea values. Treatment with atropine sulfate (0.2 mg/kg) eliminated the bradycardia response, but the peripheral vasoconstriction persisted. Treatment with propranolol (0.5 mg/kg) eliminated postapnea hypertension. Changes in myocardial contractility during apnea were observed by measuring hemodynamic parameters while maintaining a constant heart rate with cardiac pacing. Myocardial contractility was decreased during apnea as indicated by decreases in stroke volume (-13%), stroke work (-22%), cardiac output (-13%), left ventricular (dP/dt)max (-11%), and cardiac power (-24%). These changes were prevented by atropine treatment, indicating the depressed contractility was a result of vagus nerve activity. The circulatory adjustments in the dog during apnea are potential mechanisms for oxygen conservation, although the effectiveness is uncertain for the animal as a whole. It is clear that by appropriate reduction in cardiac power output, the heart itself plays an active role in conservation of limited oxygen during apnea.
Distribution and discharge properties of airway receptors in the opossum, Didelphis marsupialis
Authors: Farber J. P. , Fisher J. T. , Sant'Ambrogio G.
Published: December 2017

The distribution and discharge characteristics of airway mechanoreceptors were evaluated using vagal recording in the pentobarbital-anesthetized, artificially ventilated, open-chest adult opossum (Didelphis marsupialis), a marsupial mammal. Of the 114 receptors studied, 20 (18%) were rapidly adapting. Of the slowly adapting receptors (SARs) evaluated, 21 (22%) were in the trachea and 72 (77%) were located more peripherally; the latter group was designated as bronchial SARs. Fifteen (21%) of the bronchial SARs were found in the contralateral lung. Sixty-five percent of tracheal SARs were active at 0 cmH2O transpulmonary pressure (Ptp), whereas 85% were recruited at less than or equal to 2.5 cmH2O Ptp, which corresponds to the functional residual capacity (FRC). Only 53% of bronchial SARs were active at FRC. Tracheal and bronchial SARs with firing thresholds up to 3 cmH2O Ptp showed similar rates of discharge during static lung inflations as Ptp was increased to 20 cmH2O. Static discharge rates of bronchial receptors with firing thresholds greater than 3 cmH2O were lower than for the other groups. After rapid inflation of the lungs (0.3 s) to 10 cmH2O Ptp, SARs showed an adaptation index (percent decrease in firing rate from initial levels) of 26.5%; slow inflation (1.2 s) yielded a significantly lower adaptation index (17.4%). The discharge of both tracheal and bronchial SARs was inhibited during CO2 inhalation. Specific comparisons of airway receptors in the opossum with those of other mammals yield several quantitative and qualitative differences.
Dehydration induces sodium depletion in rats, rabbits, and sheep
Authors: McKinley M. J. , Denton D. A. , Nelson J. F. , Weisinger R. S.
Published: December 2017

The effect of water deprivation for 1 day on Na balance was measured in rats, rabbits, and sheep. In all three species, dehydration induced a considerable increase in the daily output of Na in urine. This resulted in the water-deprived animals becoming Na depleted as well as water deficient. Experiments were also designed to control for the reduced food intake that results from water deprivation in rats and rabbits. The results showed that decreased food intake was not the cause of the natriuresis and subsequent Na depletion that occurred during dehydration. When water was again made available to the dehydrated animals, a period of urinary Na retention ensued. This Na retention usually continued until the Na deficit that had accrued during the period of dehydration had been ameliorated. It seems likely that natriuresis in response to dehydration is common in mammals. We postulate that such a natriuretic response may serve a homeostatic function in buffering increases in plasma [Na] and osmolality that result from dehydration.
Toward a physical approach to integrative physiology. I. Brain dynamics and physical causality
Authors: Basar E.
Published: December 2017

This report treats the fundamental question raised by Yates [Am. J. Physiol. 238 (Regulatory Integrative Comp. Physiol. 7): R277-R290, 1980.]: “Why should neuroscience look to physics for its theories?” This is the viewpoint of an experimentalist who needs a physical approach to brain theories to interpret the results of physically oriented experiments on electroencephalogram and evoked potentials. The fundamental physical theories are briefly outlined; the phenomena of enhancement of brain potentials, frequency stabilization effects, and phase-resetting phenomena of populations of neurons in the brain are explained. The results of experiments are interpreted in the light of a variety of physical theories: coupled oscillators, induced magnetization, laser physics, and synergetics. Further, analogies with nonlinear mechanics, theory of dissipative structures, and the S-matrix formalism of quantum mechanics are provided to predict the brain's excitability. The homeokinetic approach of Iberall, the electromagnetic theory of Adey, and the quantumlike theories of Walter are discussed. It is concluded that brain scientists need an ensemble of physical approaches and concepts to understand various brain mechanisms.
Transient solutions of equations for countercurrent capillary exchange
Authors: Homer L. D. , Weathersby P. K.
Published: December 2017

A model for passive countercurrent capillary exchange is presented, and solutions for transient responses are obtained. The model is applied to an analysis of hydrogen gas exchange in the renal medulla. Estimates of medullary flow per gram tissue are in reasonable agreement with estimates obtained with vascular tracers and similar to the values for whole kidney. Semilog plots of tissue washout curves appear nearly linear but will overestimate flow if the countercurrent process is inefficient and will underestimate flow if the countercurrent exchange is efficient. Analysis of the countercurrent process also provides some insights into the importance of tracer exchange between capillaries in vascular beds not arranged in orderly countercurrent networks. Capillaries in other vascular beds that are close enough together to permit considerable exchange of inert gas tracers may simulate countercurrent effects if some of the adjacent capillaries are in countercurrent or staggered cocurrent arrangements.
Open-loop analysis of the pulmocutaneous baroreflex in the toad Bufo marinus
Authors: West N. H. , Van Vliet B. N.
Published: December 2017

In the conscious toad, Bufo marinus, heart rate responses to manipulations of arterial pressure by vascular occlusion confirm that receptors sensitive to changes in intravascular pressure are located in the pulmocutaneous arteries. The cardiovascular responses to electrical stimulation of the central end of the laryngeal branch of the vagosympathetic trunk indicate that their afferents lie within this nerve. Inflation of an isolated pulmocutaneous sac in conscious toads in which the contralateral laryngeal nerve was cut resulted in a reduction of mean aortic pressure, with an associated bradycardia in some animals. Maximum open-loop gain for the relationship between sac pressure and aortic pressure was 0.35 +/- 0.06 (n = 5), resulting in a predicted maximum closed-loop gain of 0.25 +/- 0.03. Maximum gain occurred at 4.0-6.0 kPa, which was higher than the normal range of mean pulmocutaneous pressures in conscious undisturbed B. marinus, suggesting that the baroreceptors may be more effective in compensating for a rise than for a fall in pressure. This functional characteristic of the receptors suggests that not only may they modulate mean pressure in both the systemic and pulmocutaneous circuits, but that they may be particularly important in protecting the lung vasculature from excessive hydrostatic pressures.>
Acid-base and ionic balance in Ambystoma tigrinum and Necturus maculosus during hypercapnia
Authors: Stiffler D. F. , Tufts B. L. , Toews D. P.
Published: December 2017

The aquatic urodeles Ambystoma tigrinum and Necturus maculosus responded to hypercapnia quite differently. A. tigrinum, after 2-h exposure to 22 Torr partial pressure of CO2 (PCO2), decreased arterial pH (pHa) from 7.85 to 7.32 and increased arterial pressure of CO2 (PaCO2) to 26 Torr. Plasma [HCO-3] [( HCO-3]pl) remained constant at about 17 mM. Prolonged exposure (24 h) led to a 26% extracellular compensation as pHa rose to 7.46 while [HCO-3]pl increased to 24 mM. Plasma [K+] increased and [Cl-] decreased while [Na+] remained unchanged. Recovery in normocapnic water reversed these changes. N. maculosus did not display similar compensatory changes. Two-hour exposure to 17 Torr PCO2 resulted in a decline of pHa from 7.66 to 7.24, which was not compensated (pHa = 7.19) after 24 h. There were no significant changes in plasma [Na+], [K+], [Cl-], or [HCO-3]. The pHa decline reversed after recovery in normocapnic water, however. The fact that compensation for hypercapnic in A. tigrinum was accompanied by changes in Cl- and K+ concentrations may indicate the participation of epithelial transport mechanisms involving these ions in acid-base balance.