bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of metabolic feedback regulation in glucose production of running rats
Authors: Vissing J. , Sonne B. , Galbo H.
Published: December 2017

Hepatic glucose production (Ra) was studied in phlorizin (P)- and saline (C)-infused rats running for 35 min at 21 m/min in the postabsorptive state (series I) or 18 m/min in the fed state (series II). Phlorizin-induced increase in glucose clearance would increase or not affect Ra, depending on whether metabolic feedback mechanisms or central command from central nervous system (CNS), respectively, regulate Ra during exercise. Initial exercise-induced increases in Ra were similar in P and C rats of both series, although glucose clearance was higher and plasma glucose lower, however not hypoglycemic, in P rats. After 5 min of exercise, Ra remained similar in P and C rats in series I, whereas in series II, Ra increased almost twice as much in P compared with C rats. In both series muscle glycogenolysis and lipolysis were higher in P than in C rats. The results suggest a central command regulation of Ra from CNS motor centers and that this primary setting may be modulated by metabolic feedback mechanisms. Hypoglycemia is not needed to activate metabolic feedback. A variety of substrates rather than glucose specifically is mobilized by metabolic feedback mechanisms associated with decreased glucose availability.
Oscillating heat flow from rabbit's pinna
Authors: Mohler F. S. , Heath J. E.
Published: December 2017

Thermal characteristics of the pinnae of the ears of New Zealand White rabbits (Oryctolagus cuniculus) were measured with an infrared imaging system, and vasomotor oscillations were observed to occur spontaneously in the pinnae of all rabbits at an ambient temperature of 20 degrees C. Measured fluctuations in surface temperature were used to characterize the observed vasomotor oscillations, whereas heat loss from the pinnae was calculated using the mean pinna temperatures. The pulsing related to thermoregulation had a mean frequency of approximately 0.025 Hz with a mean amplitude of approximately 0.35 degrees C. When surface temperature was measured simultaneously from both pinnae of individual rabbits, the thermal pulsing was synchronous in the two pinnae. Many of the characteristics of the vasomotor rhythm measured in the pinnae of rabbits were consistent with an active and controlled oscillation, and a possible thermoregulatory role for a controlled vasomotor oscillation is discussed.
Postnatal undernutrition slows development of bronchiolar epithelium in rats
Authors: Massaro G. D. , McCoy L. , Massaro D.
Published: December 2017

The lung's small conducting airways are sites of dysfunction early in the course of chronic lung diseases that are prevalent in humans; furthermore, there is evidence that aspects of childhood environment may adversely influence small airway function in adulthood. Because there is considerable early postnatal morphological maturation of the bronchiolar epithelium in rats, these considerations led to the present study in which we assessed the effect of early postnatal undernutrition in rats on the anatomic development of the bronchiolar epithelium. We found undernutrition, produced by increasing rat litter size shortly after birth, led to delayed development of the mitochondria and rough endoplasmic reticulum of bronchiolar Clara cells. Of particular interest, underfeeding resulted in considerably diminished mitosis by Clara cells, decreased nuclear numerical density of bronchiolar ciliated cells, evidence of diminished conversion of Clara cells to ciliated cells, and an abnormal cellular composition of the small airway epithelium that persisted well beyond the period of underfeeding. We conclude that early neonatal events can have long-term effects on the bronchiolar epithelium.
Central and peripheral adrenoceptors affect glucose, free fatty acids, and insulin in exercising rats
Authors: Scheurink A. J. , Steffens A. B. , Benthem L.
Published: December 2017

The effects of intravenously and intrahypothalamically administered alpha- and beta-adrenoceptor antagonists on exercise-induced alterations in blood glucose, plasma free fatty acids (FFA), and insulin were investigated in rats. Exercise consisted of strenuous swimming against a counter current for 15 min. Before, during, and after swimming, blood samples were withdrawn through a permanent heart catheter. Intravenous administration of the alpha-blocker phentolamine led to a reduction in glucose and a substantial increase in insulin levels. Infusion of phentolamine through permanent bilateral cannulas into either the ventromedial or lateral area of the hypothalamus (VMH and LHA, respectively) completely prevented the increase in glucose while the decline in insulin was unaffected. Infusion of phentolamine into the VMH caused much higher plasma FFA levels than in controls. The beta-blocker timolol given intravenously caused a delayed increase in glucose and prevented the increase in FFA. Infusion of timolol into either VMH or LHA caused a delay in the increase in both glucose and FFA. The results suggest that 1) both peripheral and hypothalamic adrenoceptors are involved in energy metabolism during exercise and 2) FFA, glucose, and insulin concentrations in blood are independently regulated by VMH and LHA.
GABA-mediated inhibition of sympathoexcitatory neurons by midline medullary stimulation
Authors: McCall R. B.
Published: December 2017

The present investigation determined whether the effects of electrical stimulation of depressor sites in midline medullary raphe nuclei were a result of inhibition of sympathoexcitatory medullospinal neurons in the rostral ventrolateral medulla of anesthetized cats. Electrical stimulation of the raphe inhibited inferior cardiac sympathetic activity. Microinjections of glutamate mimicked the effects of electrical stimulation. Electrical stimulation inhibited sympathoexcitatory neurons in the rostral ventrolateral medulla. The onset of the sympathoinhibition recorded from the inferior cardiac nerve (72 ms) was equal to the sum of the onset latency of the sympathoexcitatory response elicited from the rostral ventrolateral medulla (49 ms) plus the conduction time in the raphe to rostral ventrolateral sympathoinhibitory pathway (23 ms). Raphe stimulation excited a second set of neurons in the rostral ventrolateral medulla with an onset of 21 ms. Microiontophoretically applied bicuculline increased the discharge of sympathoexcitatory neurons and blocked the raphe-evoked inhibition. Iontophoretic glutamate excited sympathoexcitatory neurons but failed to antagonize raphe-elicited inhibition. These data suggest that neuronal elements in medullary raphe nuclei tonically inhibit sympathoexcitatory medullospinal neurons in the rostral ventrolateral medulla by activating closely adjacent gamma-aminobutyric acid (GABA) interneurons.
Time course of thermal adaptation in plasma membranes of trout kidney. I. Headgroup composition
Authors: Hazel J. R. , Landrey S. R.
Published: December 2017

The phospholipid composition of plasma membranes from the kidney of rainbow trout, Salmo gairdneri, was determined over a period of 21 days as fish were acclimating between temperatures of 5 and 20 degrees C. Proportions of phosphatidylethanolamine (PE) were significantly higher (29.03 vs. 23.26%) in membranes of 5 degrees C- than 20 degrees C-acclimated trout, whereas levels of phosphatidylcholine (PC) were similar. During acclimation, changes in headgroup composition were restricted primarily to PE and PC, with proportions of the former increasing and the latter decreasing on cold exposure. Headgroup composition changed rapidly as indicated by variations in PC/PE, which dropped from 1.71 +/- 0.13 to 0.78 +/- 0.11 within 8 h of cold acclimation and rose from 1.31 +/- 0.15 to 2.0 +/- 0.13 by the 2nd day of warm acclimation. Differences between warm- and cold-acclimating fish in the proportion of both PC and PE attained during the acclimation time course exceeded the magnitude of the differences between fully acclimated fish. Because of differences in molecular geometry and physical properties between PC and PE, the observed changes in headgroup composition may result in thermal compensation of membrane function, and the more rapid response to cold as opposed to warm stress suggests a primary role in adaptation to cold temperatures. However, headgroup modulation is most likely to contribute to homeoviscous adaptation only during the initial stages of the acclimatory response.
Na-dependent L-proline transport by eel intestinal brush-border membrane vesicles
Authors: Vilella S. , Ahearn G. A. , Cassano G. , Storelli C.
Published: December 2017

L-[3H]proline uptake by brush-border membrane vesicles prepared from intestinal mucosa of the European eel, Anguilla anguilla, was stimulated by a transmembrane Na gradient (out greater than in). Kinetic analysis of L-proline influx, under short-circuited membrane potential conditions, indicated the presence of an apparent single Na-dependent carrier process (Kapp = 0.23 +/- 0.04 mM and Jmax = 7.96 +/- 0.87 nmol.mg protein-1.min-1) and a nonsaturable transfer component with an apparent diffusional permeability (P) of 1.53 +/- 0.35 microliter.mg protein-1.min-1. An imposed transmembrane potential (inside negative) increased apparent L-proline binding affinity (lowered Kapp) without appreciably altering maximal amino acid influx (Jmax). Hill analysis of L-proline influx over a wide range of external Na concentrations indicated a 1:1 stoichiometry for Na-proline cotransport. Use of amino acid inhibitors of L-proline influx suggested that L-proline transfer may occur by either a classical Na-dependent A System with a wide substrate specificity or by the combination of Na-dependent PHE (phenylalanine preferring) and IMINO (proline, alpha-methylaminoisobutyric acid preferring) Systems.
Intravenous vasopressin infusion decreases plasma ACTH concentration in conscious dogs
Authors: Brooks V. L. , Blakemore L. J. , Keil L. C.
Published: December 2017

Vasopressin infusion increases arterial and atrial pressures, which could stimulate arterial and cardiac baroreceptors to inhibit adrenocorticotropin (ACTH) secretion. Therefore, the current experiments were performed to test the hypothesis that vasopressin infusion decreases plasma ACTH concentration in conscious dogs. Vasopressin was infused for 90 min in three doses (0.5, 1.0, and 2.0 ng.kg-1.min-1) that produced increases in plasma levels within the physiological range. Only the highest dose of vasopressin increased mean arterial pressure, but left atrial pressure increased with all doses, and right atrial pressure increased with the two highest doses. A bradycardia was produced with all doses of vasopressin. Plasma ACTH concentration decreased from 44 +/- 12 to 25 +/- 7 (P less than 0.01), from 50 +/- 11 to 26 +/- 9 (P less than 0.001), and from 70 +/- 15 to 28 +/- 4 pg/ml (P less than 0.001) with infusion of 0.5, 1.0, and 2.0 ng.kg-1.min-1 vasopressin, respectively. In contrast, plasma cortisol concentration first increased (P less than 0.05) with each vasopressin dose, but after 15-30 min it decreased back to control levels. These results demonstrate that intravenous infusion of vasopressin decreases plasma ACTH concentration. Because the inhibition is associated with increases in atrial pressure and decreases in heart rate, it may be mediated via activation of the baroreceptor reflex.
Biosynthetic capacity of hummingbird liver
Authors: Suarez R. K. , Brownsey R. W. , Vogl W. , Brown G. S. , Hochachka P. W.
Published: December 2017

Hummingbirds have one of the highest mass-specific metabolic rates among vertebrate animals. High activities of pyruvate carboxylase (an enzyme involved in gluconeogenesis) and acetyl-CoA carboxylase (an enzyme involved in fatty acid synthesis) in hummingbird liver indicate that biosynthetic capacity is adjusted to cope with the high metabolic fuel requirements imposed by small size and hovering flight. This high biosynthetic capacity is supported by a correspondingly high oxidative capacity, as judged qualitatively by the abundance of mitochondria in electron micrographs and quantitatively by the presence of high citrate synthase activity (a Krebs cycle enzyme). To support their high metabolic fuel requirements, hummingbirds may possess the most biosynthetically active livers in nature.
Peak duration of serum melatonin and short-day responses in adult Siberian hamsters
Authors: Bartness T. J. , Goldman B. D.
Published: December 2017

Long photoperiod-housed, adult Siberian hamsters were pinealectomized and given daily subcutaneous infusions of melatonin (MEL) to determine which characteristic of the MEL secretion profile is critical for short photoperiod-induced physiological responses. Long-duration MEL infusions (10 or 12 h) given for 5 wk elicited short-day-type responses [i.e., decreased body, testes, and epididymal white adipose tissue (EPIWAT) weights, EPIWAT lipoprotein lipase activity, carcass lipid content, and serum follicle-stimulating hormone and prolactin levels]. In contrast, short- or intermediate-duration (5 or 8 h) MEL infusions or saline infusions were without effect. Long-duration MEL infusions elicited short-day-type responses independently of both the time of day when MEL was administered and of the MEL dose if the latter was greater than or equal to 6.25 ng MEL/daily infusion. The continuity of the 10-h MEL infusions was important for triggering short-day-type responses; 10-h MEL infusions interrupted at their midpoint by 2 h of no infusion were ineffective even though dose and total duration were held constant. The body and lipid mass decreases were independent of the gonads, since castrated and gonad-intact hamsters responded similarly to the daily 10-h MEL infusions. Decreased body weight resulting from long-duration MEL infusions were never accompanied by decreased food intake. We conclude that the peak nocturnal duration of MEL is the critical parameter of the MEL secretion profile for triggering short-day-induced responses in adult Siberian hamsters.
Renal dose response and pharmacokinetics of atrial natriuretic factor in dogs
Authors: Cernacek P. , Maher E. , Crawhall J. C. , Levy M.
Published: December 2017

The present studies investigated the dose-plasma level-response relationships with the use of increasing doses of atrial natriuretic factor [ANF-(99-126)] administered by constant infusion in conscious dogs. The preinfusion plasma immunoreactive ANF increased 12, 19, 23, and 35 times during 45-min consecutive infusions of 50, 75, 125, and 175 ng.kg-1.min-1, respectively. Over this pharmacological range, natriuresis increased linearly with the infused dose (r = 0.99, n = 5) to a maximum response of +1,550%, despite the significant gradual fall of blood pressure, which attained a minimum of 83 mmHg (-26%) at 125 ng.kg-1.min-1. There was no change of glomerular filtration rate (GFR) or renal plasma flow at any dose. A very similar renal response was found in 13 other dogs infused with the highest dose only in which the pharmacokinetic parameters of ANF-(99-126) were estimated. Metabolic clearance rate during the infusion was 1.09 +/- 0.19 l/min. The postinfusion decay curve of plasma immunoreactive ANF was best described by a biexponential function. Plasma disappearance half time was 1.44 min during the rapid phase and 10.3 min during the slow phase of elimination. The results show that 1) natriuretic response to ANF in the pharmacological range is dose dependent and occurs despite a pronounced hypotension, 2) increase in GFR is not a prerequisite of ANF-induced natriuresis, and 3) ANF is rapidly eliminated from the circulation, suggesting an intensive uptake and/or degradation in the target tissues.
Intracellular signals and volume regulatory response in skate erythrocytes
Authors: McConnell F. M. , Goldstein L.
Published: December 2017

The volume regulatory response of erythrocytes (RBCs) of the little skate Raja erinacea subjected to 30% dilution of their medium is mimicked by the application of phorbol ester or calcium ionophore, implicating protein kinase C and phosphoinositide metabolism in that response. To investigate the signaling link between dilution of the medium and cell response, we measured levels of inositol phosphates (associated with intracellular calcium release) and of diacylglycerol (the physiological activator of protein kinase C) in control and hyposmotically treated RBCs. Labeled inositol monophosphate (IP1) was significantly higher in osmotically shocked than in control cells. Inositol bis- and trisphosphate levels (IP2 and IP3) were low and did not alter with dilution treatment. Separation of the isomers in the IP1 fraction indicated that the dilution effect was likely to result from the breakdown of phosphatidylinositol directly, without the involvement of the IP3 and related messenger molecules. Hyposmotic treatment also elevated the diacylglycerol content of the skate RBCs, providing evidence for the activation of protein kinase C as part of the volume regulatory response. The results are interpreted as indicating that the response to hypotonic media in skate erythrocytes is mediated primarily by protein kinase C and any involvement of calcium is associated with that pathway rather than with the production and metabolism of IP3.
Sympathoadrenal influence on glucose, FFA, and insulin levels in exercising rats
Authors: Scheurink A. J. , Steffens A. B. , Bouritius H. , Dreteler G. H. , Bruntink R. , Remie R. , Zaagsma J.
Published: December 2017

The effects of sympathoadrenal manipulations on the exercise-induced alterations in blood glucose, plasma free fatty acids (FFA), and insulin were investigated in intact and adrenodemedullated rats. Exercise consisted of strenuous swimming against a countercurrent for 15 min. Before, during, and after swimming, blood samples were taken through a permanent heart catheter. Adrenodemedullation (Adm) markedly reduced the exercise-induced increase in both glucose and FFA. This effect was counteracted by intravenous infusion of epinephrine (E, 20 ng/min). Intravenous infusion of 50 ng E/min into Adm rats caused an exaggerated increase in glucose. In two additional experiments 1) specific adrenoceptor agonists and antagonists were administered to exercising intact and Adm rats, and 2) E or norepinephrine (NE; 20 ng/min) was infused into intact resting rats. The results suggest that E from the adrenal medulla directly affects glucose and insulin but not FFA concentrations in the blood. NE released from peripheral sympathetic nerve endings probably acts in two different ways: as neurotransmitter on liver and pancreas and as a hormone on adipose tissue.
Hyperprolactinemia prevents short photoperiod-induced changes in brown fat
Authors: Kott K. S. , Moore B. J. , Fournier L. , Horwitz B. A.
Published: December 2017

Previous studies demonstrated that short photoperiod exposure significantly decreases circulating prolactin levels. The present study investigated the possibility that concomitant changes in brown fat tissue mass, protein content, thermogenic capacity, and carcass composition are dependent on this change in prolactin levels. Male golden (Syrian) hamsters were sham operated and exposed to a short (10L:14D) or long (14L:10D) photoperiod. A third group was implanted with exogenous pituitaries under the right kidney capsule and exposed to a short photoperiod. In experiment I, 4 wk of short- vs. long-photoperiod exposure did not result in significant changes in circulating prolactin levels, nor was there an increase in brown fat mass, protein content, or thermogenic capacity. Four weeks of short-photoperiod exposure did significantly increase carcass lipid content. However, this increase did not occur in hamsters exposed to 4 wk of short photoperiod but made hyperprolactinemic (implanted with two exogenous pituitaries). Ten weeks of short photoperiod significantly reduced circulating prolactin levels. Concomitantly, brown fat mass, protein content, and thermogenic capacity, as well as carcass fat, were increased. These short-photoperiod-induced changes were not observed in similarly exposed hamsters that were made hyperprolactinemic via two implanted pituitaries. In experiment II, similar changes in brown fat and body composition occurred in sham-operated hamsters exposed to 10 wk of short photoperiod. These changes were prevented in hamsters exposed to 10 wk of short photoperiod but made hyperprolactinemic via only one implanted pituitary. These results suggest that decreased prolactin is a necessary condition for the increased brown fat mass, protein content, and thermogenic capacity that occurs when golden hamsters are exposed to short photoperiod.
Effects of bombesin on food intake and gastric acid secretion in cats
Authors: Bado A. , Lewin M. J. , Dubrasquet M.
Published: December 2017

The brain and gut peptide bombesin has been reported both to stimulate gastric secretion and to induce satiety. To understand how the peripheral administration of bombesin affects food intake and whether gastric mechanisms are involved, a comparative study of the doses of bombesin active on gastric secretion, gastric emptying, and food intake was undertaken in cats provided with a gastric fistula and a denervated Heidenhain pouch. The smallest dose of intravenous bombesin that stimulated significantly basal acid secretion (20 pmol.kg-1.h-1) by the gastric fistula also enhanced meal-stimulated acid secretion by the Heidenhain pouch (+138%, P less than 0.01), delayed gastric emptying of a liquid protein meal (-30%, P less than 0.01), and suppressed food intake when the test meal was allowed to reach the stomach (-15%, P less than 0.01). Conversely, in sham-feeding experiments, the same dose of bombesin increased food intake (+35%, P less than 0.01). In full-day experiments conducted in nonfasted cats, bombesin decreased both the food intake in the 4-h period after the infusion and the daily food intake, whereas octapeptide cholecystokinin induced a transient satiety but did not decrease daily food intake. These results indicate that in cats the interaction of bombesin with "pregastric" mechanisms is not sufficient to induce satiety and that a relation could exist between the effects of bombesin on gastric secretion, emptying, and food intake. A single class of receptors might be involved in these peripheral effects of bombesin.
Evolution of mammalian endothermic metabolism: mitochondrial activity and cell composition
Authors: Hulbert A. J. , Else P. L.
Published: December 2017

Body composition was measured and compared in Amphibolurus vitticeps and Rattus norvegicus (a reptile and a mammal with the same weight and body temperature). Homogenates were prepared from liver, kidney, brain, heart, lung, and skeletal (gastrocnemius) muscle, and mitochondria were isolated. Cytochrome oxidase activities of both tissue homogenates and isolated mitochondria were measured (at 37 degrees C) as was protein content. Phospholipids were extracted from liver and kidney, and the fatty acid composition was determined. The brain, liver, kidney, heart, and skeletal muscle were significantly larger in the mammal, whereas the skin, reproductive organs, lung, and digestive tract showed no significant difference in size. All mammalian tissues examined contained approximately 50% more protein and phospholipid than the respective reptilian tissue. Although the mammalian phospholipids contained significantly less total unsaturated fatty acids, these unsaturated fatty acids were significantly more polyunsaturated than in the reptilian tissues. Tissue cytochrome oxidase activity was significantly greater in mammals when expressed on a wet weight basis but not when expressed on a tissue protein basis. Mitochondrial cytochrome oxidase activity (on a protein basis) was the same in both species in liver, kidney, and brain, but in heart, lung, and skeletal muscle mammalian mitochondria were twice as active as reptilian mitochondria. The implications of these differences in tissue composition were discussed relative to the evolution of mammalian endothermy.
Carotid sinus baroreflex control of beta-endorphin release in anesthetized dogs
Authors: Brunner M. J. , Wehberg K. E. , Williams J. C. , Cahill C. A.
Published: December 2017

A quantitative assessment of the carotid sinus baroreflex release of endogenous plasma beta-endorphin-like immunoreactive material has been established. The carotid sinuses of 12 pentobarbital sodium-anesthetized dogs were isolated bilaterally and perfused with a constant pressure maintained by infusion or withdrawal of normal saline. Mean arterial pressure (MAP) and heart rate (HR) were monitored. Carotid sinus pressure (CSP) was changed from 200 to 50 mmHg in 25 mmHg steps before and after vagotomy. At each interval of CSP, 10 ml mixed venous blood were collected, and beta-endorphin-like peptides were extracted from plasma and assayed. Concentrations of plasma beta-endorphin-like material were determined by radioimmunoassay. Sigmoidal responses of MAP and HR were revealed during changes in CSP. No significant differences in beta-endorphin-like immunoreactivity (beta-END-L-I) were measured at CSP of 200 and 50 in the intact condition (35.9 +/- 3.9 and 35.0 +/- 6.4 fm/ml, respectively). However, after vagotomy, beta-END-L-I measured at 50 mmHg CSP was significantly elevated to 53.3 +/- 5.2 fm/ml compared with the value of 35.5 +/- 7.2 fm/ml at CSP of 200 mmHg. The results suggest that the release of beta-endorphin is modulated by the action of the carotid baroreflex as a normal component of an integrated efferent response. However, this response is normally buffered by reflexes with vagal afferents.
Role of renal sympathetic nerves in renin inhibition by elevated left atrial pressure
Authors: Scheuer D. A. , Thrasher T. N. , Ramsay D. J.
Published: December 2017

We have reported that the renin response to systemic hypotension during a simultaneous increase in left atrial pressure (LAP) depends, in part, on intact renal nerves. Because efferent neural control of renin release is mediated by renal sympathetic nerves, we tested the hypothesis that withdrawal of renal sympathetic tone is an essential component of the inhibitory mechanism. In conscious dogs, the ascending aorta was partially constricted to produce a simultaneous decrease, of up to 30%, in renal perfusion pressure (RPP) and a rise in LAP. Sympathetic neural control of renin release was reversibly blocked with propranolol. Propranolol infusion did not affect the increases in LAP or atrial natriuretic factor (ANF) during ascending aortic constriction. There was no increase in renin (P greater than 0.1) during ascending aortic constriction, with or without propranolol infusion. Identical reductions in RPP during constriction of the abdominal aorta caused renin to rise (P less than 0.03). Therefore acute withdrawal of renal sympathetic tone is not necessary for the inhibition of the renin response to systemic hypotension by elevated LAP.
In vitro diencephalic neuronal thermosensitivity in normotensive and hypertensive rats
Authors: Travis K. A. , Boulant J. A.
Published: December 2017

Because morphological differences exist in hypothalamic neurons from spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats, the present study recorded neuronal spontaneous activity and thermosensitivity from diencephalic tissue slices of these two strains. With the use of extracellular recordings from horizontal tissue slices, neurons were characterized according to location, firing rate at 37 degrees C, and firing rate response to changes in local tissue temperature. Compared with WKY neurons, SH neurons had higher firing rates in the preoptic-anterior hypothalamus and lower firing rates in the dorsomedial hypothalamus. In addition, SH warm-sensitive neurons were less thermosensitive over the hyperthermic range (37-40 degrees C), and SH temperature-insensitive neurons had higher spontaneous firing rates. These differences in spontaneous activity and thermosensitivity provide a neuronal basis to explain the elevation of core temperature observed in SH rats.
Sympathetic activity remains synchronized in presence of a glutamate antagonist
Authors: Gebber G. L. , Barman S. M. , Zviman M.
Published: December 2017

Sun et al. like activity in the rostral ventrolateral medulla (RVLM) of the rat after an intracisternal injection of the glutamate receptor antagonist, kynurenate (KYN). They proposed that these neurons are primarily responsible for sympathetic nerve discharge (SND). The fact that RVLM pacemaker neurons discharge independently of each other after intracisternal KYN leads to the prediction that SND will be desynchronized by this drug. The results of the current study show that this is not the case. Postganglionic SND was recorded in rats and cats before and after intracisternal injection of KYN in doses that blocked the baroreceptor reflexes. Whereas the background level of SND was unchanged in rats, KYN markedly reduced SND in cats. Independent of this difference, KYN failed to desynchronize SND in either species. Power density spectra of SND in rats and cats contained sharp peaks between 2 and 10 Hz before and after intracisternal KYN. These results require a reassessment of the pacemaker hypothesis on the origin of SND. Moreover, KYN-induced depression of SND in the cat points to the importance of brain stem synaptic mechanisms in the genesis of sympathetic tone in this species.
Reticulospinal vasomotor neurons in the RVL mediate the somatosympathetic reflex
Authors: Morrison S. F. , Reis D. J.
Published: December 2017

Sympathoexcitatory neurons in the C1 area of the rostral ventrolateral medulla (RVL) that project to the spinal intermediolateral nucleus play an important role in the maintenance of basal sympathetic tone and in the reflex adjustments of sympathetic activity to internal and external stimuli. We sought to determine whether the sympathetic response to somatic afferent activation, the somatosympathetic reflex, also arises from the excitation of reticulospinal vasomotor neurons in the RVL. In urethan-anesthetized, paralyzed, ventilated rats, single sciatic nerve stimuli evoked an early (latency: 26 ms) and a late (latency: 117 ms) excitation of antidromically identified, RVL-spinal, sympathoexcitatory neurons that paralleled and preceded the biphasic increases in splanchnic nerve activity (peak latencies: 87 and 176 ms). The differences between the respective latencies of the RVL unit responses and those recorded in the splanchnic nerve were comparable to the conduction time in the sympathoexcitatory pathway from the RVL to the splanchnic nerve. Both the threshold intensity and the response amplitude vs. stimulus intensity relationship for the sympathetic response were comparable to those for the A-delta-fiber component of the dorsal root response to sciatic stimulation. We conclude that the rat somatosympathetic reflex consists of an early excitatory component due to the early activation of RVL-spinal sympathoexcitatory neurons with rapidly conducting axons and a later peak that may arise from the late activation of these same neurons as well as the early activation of RVL vasomotor neurons with more slowly conducting spinal axons.
Plasma atriopeptin during exercise in dogs under beta-blockade
Authors: Peronnet F. , Adjoa S. A. , Beliveau L. , Bichet D. , Nadeau R. , Brisson G.
Published: December 2017

The purpose of this study was to describe plasma atriopeptin concentrations at rest and in response to moderate treadmill exercise (10 min, 4 km/h, 26% slope) performed with or without nonspecific beta-adrenergic blockade (1 mg/kg iv propranolol) in 10 mongrel dogs [19 +/- 2 (SE) kg]. A small (20%) but significant (P less than 0.05) increase in plasma atriopeptin concentration was observed from rest (43 +/- 5 pg/ml) to exercise (52 +/- 6 pg/ml) without beta-blockade. Propranolol significantly reduced heart rate at rest (89 +/- 7 vs. 104 +/- 7 beats/min) and during exercise (96 +/- 10 vs. 176 +/- 11 beats/min), and this was associated with a larger increase in plasma atriopeptin concentration during exercise (rest 46 +/- 6 pg/ml; exercise 171 +/- 22 pg/ml). Exercise under beta-blockade is associated with an increased preload of the heart. These results further support the hypothesis that atriopeptin release during exercise is under the control of atrial stretch. The higher plasma atriopeptin concentration observed during exercise under beta-blockade may contribute to the reduction of the response of plasma renin activity (1.0 +/- 0.1 vs. 3.0 +/- 0.6 ng.ml-1.h-1) and aldosterone concentration (87 +/- 36 vs. 138 +/- 25 pg/ml). Vasopressin concentration was lower at rest and during exercise under propranolol (3.5 +/- 1.3 vs. 4.9 +/- 0.9 and 6.1 +/- 2.2 vs. 9.9 +/- 1.5 pg/ml, respectively), which might reflect a dissociation between activity of the renin-angiotensin system and vasopressin release.
Postabsorptive glucose decreases excitatory effects of taste on ingestion
Authors: Bedard M. , Weingarten H. P.
Published: December 2017

To test the hypothesis that postprandial rises of plasma glucose attenuate the motivation derived from positive tastes, we analyzed the effects of intraperitoneal (ip) injections of glucose on sham feeding, a preparation in which food intake is motivated primarily by taste sensations. Ip glucose suppressed sham feeding, with maximal suppressions approximately 42% but only when glucose was administered contiguous with oropharyngeal stimulation. The food intake inhibition produced by ip glucose interacted with palatability; smaller doses of glucose were required to suppress less concentrated sucrose solutions. Closing the gastric cannula increased the potency with which ip glucose inhibited eating, suggesting synergy of postabsorptive glucose with other postgastric satiety signals. The inhibition of eating produced by ip glucose did not result from malaise. Thus postabsorptive rises of plasma glucose decrease the ability of taste cues to drive ingestion and suggest that this phenomenon may contribute to spontaneous meal termination.
Hormonal responses to gradual changes in dietary sodium intake in humans
Authors: Sagnella G. A. , Markandu N. D. , Buckley M. G. , Miller M. A. , Singer D. R. , MacGregor G. A.
Published: December 2017

The effects of gradual (50 mmol/day) increases in dietary sodium intake from 10 to 350 mmol/day on plasma atrial natriuretic peptide (ANP), aldosterone, and plasma renin activity (PRA) were studied in six normal subjects. With the increases in sodium intake there was a progressive increase in urinary sodium from 12.2 +/- 4.4 to 314.8 +/- 31.4 mmol/24 h; plasma ANP increased gradually from 9.9 +/- 1.1 to 23.3 +/- 2.2 pg/ml, with the increases being closely associated with the changes in cumulative sodium balance. Plasma aldosterone decreased significantly from 2,519.7 +/- 147.4 pmol/l on the 10 mmol/day to 1,393.3 +/- 125.4 pmol/l when the sodium intake was increased to 50 mmol/day and decreased further to 251.6 +/- 78.7 pmol/l by the end of the study. The changes in PRA paralleled those in plasma aldosterone with the exception of no significant change in plasma PRA within 24 h of the initial increase in sodium intake. This marked sensitivity in the responses of both the ANP and the renin-aldosterone system to small increases in sodium intake clearly points to their importance in the renal adaptations to alterations in dietary sodium intake.
Mechanism of ion transport by avian salt gland primary cell cultures
Authors: Lowy R. J. , Dawson D. C. , Ernst S. A.
Published: December 2017

Confluent sheets formed from primary culture of avian salt gland secretory cells exhibit a short-circuit current (Isc) in response to cholinergic and beta-adrenergic stimulation [Lowy, R. J., D. C. Dawson, and S. A. Ernst. Am J. Physiol. 249 (Cell Physiol. 18): C41-C47, 1985]. To establish the ionic basis for the Isc, transmural fluxes of 22Na and 36Cl were measured. Under short-circuit conditions there was little net flux of either ion in the absence of agonists. Addition of carbachol elevated net serosal-to-mucosal Cl flux to 1.71 mu eq.h-1.cm-2, whereas a smaller increase to 0.85 mu eq.h-1.cm-2 occurred with isoproterenol. Neither agonist altered net Na flux. The stimulated Isc accounted for 70% of the net Cl flux induced by carbachol and nearly 100% of that induced by isoproterenol. Replacement of Cl by gluconate or Na by choline abolished (carbachol) or greatly reduced (isoproterenol) the Isc, which could be restored in a dose-dependent fashion by ion restitution. Active ion transport was preferentially inhibited by basal (vs. apical) addition of ouabain, furosemide, or barium. The results provide evidence that cholinergic and beta-adrenergic agonists elicit active transmural Cl secretion. They further suggest that transport is dependent on the Na+-K+-adenosine-triphosphatase, a Na-Cl cotransport process, and a basal K conductance, all features of a secondary active Cl secretory mechanism.
Individual correlation of morphology, muscle mechanics, and locomotion in a salamander
Authors: Bennett A. F. , Garland T. , Else P. L.
Published: December 2017

Measurements were made on locomotor performance (burst run and swim speed, run and swim endurance), morphology (body, tail, and hindlimb length, body mass), and skeletal muscle mechanics (isometric: twitch and tetanic tension, rates of force development and relaxation; isotonic: maximal velocity of shortening and power output) in a size range of individual salamanders (Ambystoma tigrinum nebulosum) at 10 and 20 degrees C. The size dependence of each factor was determined, and the interindividual correlations among factors were measured after removal of size effects. Locomotor performance is positively related to body size: larger animals are faster and have higher endurance. Isometric tensions (standardized for muscle cross-sectional area) and isotonic properties are mass independent; rates of isometric force development and relaxation are negatively related to body mass. Locomotor performance capacities are not intercorrelated among individuals. Isometric force and rates of force development are highly intercorrelated as are maximal shortening velocity and power output. Several statistical techniques failed to uncover correlations among sets of variables (performance, morphology, muscle mechanics): neither fast individuals nor individuals with high endurance necessarily have relatively fast muscles or long limbs or tails after the effects of body size have been removed.
Atrial natriuretic factor induces natriuresis during pacing tachycardia in dogs
Authors: Christensen G. , Bugge J. F. , Ilebekk A. , Kiil F.
Published: December 2017

To examine whether release of atrial natriuretic factor (ANF) can explain the increase in sodium excretion during supraventricular tachycardia, we compared the natriuretic responses with right atrial pacing tachycardia and ANF infusion in six barbiturate-anesthetized dogs. When we raised the dogs' heart rates from 148 +/- 12 to 263 +/- 12 beats/min for 30 min, plasma immunoreactive (IR) ANF rose from 42.1 +/- 3.4 to 139.0 +/- 25.6 pg/ml. Sodium excretion increased from 36.2 +/- 12.8 to 132.4 +/- 40.8 mumol/min in the exposed denervated kidney. When we infused 12.5 ng.min-1.kg body wt-1 of ANF at a spontaneous heart rate of 146 +/- 12 beats/min, plasma IR-ANF rose from 46.0 +/- 5.1 to 121.7 +/- 17.5 pg/ml, which was similar to that observed during pacing tachycardia. Sodium excretion increased from 40.6 +/- 11.3 to 193.6 +/- 46.0 mumol/min, which was higher than that observed during pacing tachycardia. Renal blood flow was lower during pacing tachycardia than during ANF infusion, but glomerular filtration rate and aortic blood pressure were not significantly different during the two procedures. Because sodium excretion was 30% lower during pacing tachycardia, even though plasma IR-ANF was as high as during ANF infusion, we conclude that ANF induces the acute rise in sodium excretion during pacing tachycardia but that hemodynamic changes may attenuate the natriuretic response.
Metabolic effects of aminophylline in rats
Authors: Vonlanthen M. G. , McCarter R. J. , Casto D. T.
Published: December 2017

Whole body metabolic rate is elevated after administration of methylxanthines, but the mechanism by which this occurs is not clear. We have investigated the hypothesis that this increase in metabolic rate is in part due to increased physical activity. Metabolic rate and spontaneous cage activity of Fischer 344 rats were measured over a 24-h period before and during aminophylline treatment. Weight, food, and water consumption were also measured. Our results show an increase in metabolic rate with a simultaneous increase in spontaneous activity over the 24-h period. These results are consistent with the hypothesis that increased physical activity is in part responsible for the increase in cellular metabolism that follows administration of aminophylline.
Diabetes mellitus in Brattleboro rats: cardiovascular, fluid, and electrolyte status
Authors: Tomlinson K. C. , Gardiner S. M. , Bennett T.
Published: December 2017

Because plasma arginine vasopressin (AVP) levels are raised during streptozotocin (STZ)-induced diabetes mellitus (DM), it is possible that AVP contributes to the pattern of change in fluid and electrolyte handling and cardiovascular status after STZ treatment. Therefore we have made daily measurements of cardiovascular and metabolic variables in normal (Long-Evans) and AVP-deficient (Brattleboro) rats treated with saline or STZ. Twenty-four days after STZ, both strains had similar weight loss and increases in fluid intake, but the increase in food intake was greater in Long-Evans than in Brattleboro rats. After STZ, bradycardia developed in both strains, but only Brattleboro rats had reduced blood pressure. Plasma variables were measured 25 days after STZ. Packed cell volume and plasma sodium concentration were reduced in STZ-treated Long-Evans rats compared with saline-treated controls but were unchanged in STZ-treated Brattleboro rats. The results indicate that although AVP deficiency does not seriously affect the ability to maintain fluid and electrolyte balance after STZ treatment, there may be consequences for cardiovascular control.
Cardiovascular effects of dynorphin A-(1-13) and arginine vasopressin in fetal lambs
Authors: Dunlap C. E. , Valego N. K.
Published: December 2017

The cardiovascular effects of the kappa-opioid receptor agonist, dynorphin A-(1-13) (D13), were compared with those of arginine vasopressin (AVP) in intact and bilaterally vagotomized (VGX) fetal lambs. Intravenous injection of AVP (114 ng/kg) produced a significant rise in mean arterial pressure (MAP) lasting 15-20 min in both intact and VGX lambs. AVP produced a bradycardia in intact fetuses concurrently with the MAP response and had no effect on heart rate (HR) in VGX fetuses. D13 (500 micrograms/kg) also produced significant increases in MAP in intact and VGX fetuses that lasted 45-60 min. D13 produced a bradycardia in intact fetal lambs but, unlike AVP, significantly increased HR in VGX fetuses. HR responses to D13 had time courses similar to MAP responses in both intact and VGX fetal lambs. Pretreatment with a vasopressin V1-receptor antagonist significantly attenuated pressor responses to AVP in both treatment groups and to D13 in intact fetuses and abolished the D13 pressor response in VGX fetuses. The antagonist also completely blocked HR responses to AVP in intact and to D13 in VGX fetuses and attenuated the D13 HR response in intact fetuses. Therefore the effects of D13 on ovine fetal cardiovascular function appear to be mediated in part through AVP pathways. D13 also appears to have a positive chronotropic effect on the heart that is normally masked by inhibitory vagal activity.
Increase in sympathetic outflow by paraventricular nucleus stimulation in awake rats
Authors: Kannan H. , Hayashida Y. , Yamashita H.
Published: December 2017

Our previous studies demonstrated that stimulation of the hypothalamic paraventricular nucleus (PVN) in anesthetized rats evoked a depressor response accompanied with a decrease in sympathetic outflow (H. Kannan, A. Niijima, and H. Yamashita, J. Auton. Nerv. Syst. 19: 83-86, 1987; H. Yamashita, H. Kannan, M. Kasai, and T. Osaka, J. Auton. Nerv. Syst. 19: 229-234, 1987). Because anesthesia may alter cardiovascular responses, we examined in conscious rats the effects of PVN stimulation on arterial pressure, heart rate, and renal sympathetic nerve activity. Electrical stimulation through chronically implanted electrodes evoked increases in arterial pressure and renal sympathetic nerve activity with a slight decrease in heart rate. The magnitude of responses was dependent on the frequency and the intensity of the stimulus. Latency of the excitatory response of the renal sympathetic nerve activity was approximately 70 ms. Microinjection of L-glutamate (0.5 M, 200 nl) into the PVN area also elicited increases in blood pressure and renal sympathetic nerve activity. These results suggest that activation of PVN neurons in conscious rats produces pressor responses due to an increase in the sympathetic outflow. These findings contrast with those obtained previously in anesthetized rats.
Fever response in laboratory-maintained and free-ranging chuckwallas (Sauromalus obesus)
Authors: Muchlinski A. E. , Stoutenburgh R. J. , Hogan J. M.
Published: December 2017

The fever response was studied in laboratory-maintained and free-ranging chuckwallas. Five animals were used in a self-pairing laboratory experiment in which each animal was first injected with a sterile, pyrogen-free saline solution. Approximately 7 days later, each individual was injected with a solution of 4.75 x 10(9) Aeromonas sobria (formerly A. hydrophila). Saline-injected individuals had a mean preferred body temperature (MPBT) of 36.8 +/- 0.4 (SE) degrees C, whereas bacteria-injected animals had a MPBT of 39.1 +/- 0.6 (SE) degrees C (an increase of 2.3 degrees C). The within-animal variance associated with MPBT was significantly decreased in bacteria-injected animals. In the natural environment, 10 chuckwallas were divided into five pairs, so that both animals of a pair could be monitored simultaneously. One animal in a pair was given an injection of sterile, pyrogen-free saline, whereas the other animal received an injection of 4.75 x 10(9) A. sobria. On day 2, both the MPBT and the rate of heating were greater in bacteria-injected animals. The between-animal variation in fever MPBT was greater than the mean increase in MPBT of fever animals. Also, the absolute level of the MPBT during the fever response was related to time of the year, with spring-active animals having the highest fever MPBTs.
Effect of renal decapsulation on renal interstitial hydrostatic pressure and natriuresis
Authors: Khraibi A. A. , Knox F. G.
Published: December 2017

The objective of this study was to investigate the possible causal role of renal interstitial hydrostatic pressure (RIHP) in the natriuretic and diuretic responses of the Wistar rat. The relationship between renal perfusion pressure (RPP), RIHP, and fractional excretion of sodium (FENa) was established in the acutely decapsulated kidney and the contralateral control kidney of the same rat. The renal response to acute saline volume expansion was also studied in control and decapsulated kidney. When RPP was allowed to increase from 100 +/- 1.2 to 123 +/- 1.3 mmHg in male Wistar rats (n = 10), RIHP and FENa increased significantly from 3.3 +/- 0.4 mmHg and 0.57 +/- 0.15% to 4.3 +/- 0.4 mmHg and 1.77 +/- 0.41% in the decapsulated kidney and from 4.1 +/- 0.4 mmHg and 0.86 +/- 0.17% to 6.9 +/- 0.5 mmHg and 2.56 +/- 0.38% in control kidney. During saline volume expansion, RIHP and FENa increased significantly from 6.3 +/- 0.5 mmHg and 1.30 +/- 0.43% to 9.8 +/- 0.5 mmHg and 7.53 +/- 0.88% in the decapsulated kidney. In the control kidney, RIHP and FENa were 8.3 +/- 0.6 mmHg and 1.81 +/- 0.35% during control period and increased significantly to 12.7 +/- 0.4 mmHg and 9.31 +/- 0.50% during acute saline volume expansion. We conclude that the renal capsule is essential for the full increase in RIHP and for the full expression of the natriuretic and diuretic responses of pressure natriuresis and acute volume expansion of Wistar rats.