bluuebunny/crossref_metadata_2025 huggingface dataset:
Central oxytocin modulates exercise-induced tachycardia
Authors: Braga Douglas C. , Mori Eliana , Higa Keila T. , Morris Mariana , Michelini Lisete C.
Published: December 2017

We have shown that vasopressinergic projections to dorsal brain stem are activated during exercise and facilitate exercise tachycardia in both trained (T) and sedentary (S) rats (Dufloth DL, Morris M, and Michelini LC. Am J Physiol Regulatory Integrative Comp Physiol 273: R1271–R1282, 1997). In the present study, we investigated whether oxytocinergic projections to the nucleus of the solitary tract (NTS)-dorsal motor nucleus of the vagus (DMV) complex (NTS/DMV) are involved in the differential heart rate (HR) response to exercise in T and S rats. Arterial pressure (AP) and HR responses to dynamic exercise (0.4–1.4 km/h) were compared in S and T pretreated with vehicle (saline), oxytocin (OT; 20 pmol/200 nl) or OT-receptor antagonist (OTant; 20 pmol/200 nl) into the NTS/DMV. OT content in specific brain regions and plasma were measured in separate S and T groups at rest and immediately after exercise. Exercise increased OT content in dorsal (4.5-fold) and ventral brain stem (2.7-fold) and spinal cord (3.4-fold) only in T rats. No significant changes were observed in neurosecretory regions or medial eminence and posterior pituitary, but plasma levels of T rats were reduced immediately after exercise. Blockade of NTS/DMV OT receptors did not change basal mean AP (MAP) and HR or the MAP response to exercise. However, OTant potentiated exercise-induced tachycardia (average increase of 26%) only in the T group. Pretreatment with exogenous OT in the NTS/DMV blunted the tachycardic response both in S and T rats without changing the MAP response. Administration of OT-receptor antagonist or OT into the fourth cerebral ventricle had no effect on the cardiovascular response to dynamic exercise. Taken together, the results suggest that oxytocinergic projections to the NTS/DMV are stimulated when T rats exercise and that OT released at this level acts on OT receptors to restrain exercise-induced tachycardia.
Circadian rhythm of plasma sodium is disrupted in spontaneously hypertensive rats fed a high-NaCl diet
Authors: Fang Zhiwu , Carlson Scott H. , Peng Ning , Wyss J. Michael
Published: December 2017

High-NaCl diets elevate arterial pressure in NaCl-sensitive individuals, and increases in plasma sodium may trigger this effect. The present study tests the hypotheses that 1) plasma sodium displays a circadian rhythm in rats, 2) the plasma sodium rhythm is disturbed in spontaneously hypertensive rats (SHR), and 3) excess dietary NaCl elevates plasma sodium concentration in SHR. The results demonstrate that plasma sodium has a circadian rhythm that is inversely related to the circadian rhythm of arterial pressure. Although the plasma sodium rhythms of SHR and control rats are nearly identical, the plasma sodium concentrations are significantly higher in SHR throughout the 24-h cycle. Maintenance on a high-NaCl diet increases plasma sodium concentration similarly in both SHR and control rats, but it blunts the plasma sodium rhythm only in SHR. These results demonstrate that in rats, plasma sodium has a circadian rhythm and that high-NaCl diets increase plasma sodium concentration.
Arterial pulse pressure and vasopressin release during graded water immersion in humans
Authors: Gabrielsen Anders , Warberg Jørgen , Christensen Niels Juel , Bie Peter , Stadeager Carsten , Pump Bettina , Norsk Peter
Published: December 2017

Previous results indicate that arterial pulse pressure modulates release of arginine vasopressin (AVP) in humans. The hypothesis was therefore tested that an increase in arterial pulse pressure is the stimulus for suppression of AVP release during central blood volume expansion by water immersion. A two-step immersion model ( n = 8) to the xiphoid process and neck, respectively, was used to attain two different levels of augmented cardiac distension. Left atrial diameter (echocardiography) increased from 28 ± 1 to 34 ± 1 mm ( P < 0.05) during immersion to the xiphoid process and more so ( P < 0.05), to 36 ± 1 mm, during immersion to the neck. During immersion to the xiphoid process, arterial pulse pressure (invasively measured in a brachial artery) increased ( P < 0.05) from 44 ± 1 to 51 ± 2 mmHg and to the same extent from 42 ± 1 to 52 ± 2 mmHg during immersion to the neck. Mean arterial pressure was unchanged during immersion to the xiphoid process and increased during immersion to the neck by 7 ± 1 mmHg ( P < 0.05). Arterial plasma AVP decreased from 2.5 ± 0.7 to 1.8 ± 0.5 pg/ml ( P < 0.05) during immersion to the xiphoid process and significantly more so ( P < 0.05), to 1.4 ± 0.5 pg/ml, during immersion to the neck. In conclusion, other factors besides the increase in arterial pulse pressure must have participated in the graded suppression of AVP release, comparing immersion to the xiphoid process with immersion to the neck. We suggest that when arterial pulse pressure is increased, graded distension of cardiopulmonary receptors modulate AVP release.
Neural control of intestinal ion transport and paracellular permeability is altered by nutritional status
Authors: Hayden Ursula L. , Carey Hannah V.
Published: December 2017

This study examined the effect of fasting on the neural control of ion transport and paracellular permeability in piglet jejunum. Muscle-stripped tissues from fed or 48-h fasted piglets were mounted in Ussing chambers. Neural blockade with tetrodotoxin (TTX) or antagonists of muscarinic or nicotinic receptors caused reductions in basal short-circuit current that were approximately threefold greater in fasted piglets. The TTX-induced reduction in short-circuit current in fasted piglets was due to a decrease in residual ion flux and was abolished in the absence of[Formula: see text]. Intestinal paracellular permeability, as indicated by tissue conductance (Gt) and fluxes of inulin and mannitol, was significantly increased by fasting. TTX increased inulin flux and Gt in fed but not fasted piglets. In fasted piglets, carbachol reduced Gt by 29% and mannitol flux by 27% but had no effect on these parameters in the fed state. We conclude that fasting enhances enteric neural control of basal ion transport and increases paracellular permeability in piglet jejunum. Tonic release of enteric neurotransmitters regulates paracellular permeability in the fed state, and cholinergic stimulation restores fasting-induced elevations in paracellular permeability to fed levels.
Defenselike patterns of spinal sympathetic outflow involving the 10-Hz and cardiac-related rhythms
Authors: Gebber Gerard L. , Zhong Sheng , Lewis Craig , Barman Susan M.
Published: December 2017

Frequency- and time-domain analyses were used to compare the effects of stimulation of the defense region of the midbrain periaqueductal gray (PAG) on the 10-Hz and cardiac-related discharges of sympathetic nerves with different cardiovascular targets. In baroreceptor-denervated cats anesthetized with urethan, PAG stimulation at frequencies equal to or higher (up to 25 Hz) than that of the free-running 10-Hz rhythm produced an immediate and sustained decrease in vertebral sympathetic nerve (VN) 10-Hz activity but increased the 10-Hz discharges of the inferior cardiac (CN) and renal (RN) nerves. In baroreceptor-innervated cats, VN cardiac-related activity was initially unchanged by high-frequency (25-Hz) PAG stimulation, or it increased along with that in the CN and RN. Later, during high-frequency PAG stimulation, when the rise in blood pressure approached its peak, VN cardiac-related activity usually was reduced below control level. At this time, the increases in CN and RN cardiac-related discharges were largely sustained. The cardiac-related discharges of the three nerves were unaffected by PAG stimulation at frequencies just below or just above that of the heartbeat. We conclude that the defenselike pattern of spinal sympathetic outflow involving the 10-Hz rhythm is different in mechanism and character from that involving the cardiac-related rhythm.
Arterial baroreflex regulation of regional vascular conductance at rest and during exercise
Authors: Martínez-Nieves Brenda , Collins Heidi L. , DiCarlo Stephen E.
Published: December 2017

We tested the hypothesis that dynamic exercise resets the operating point and attenuates the spontaneous gain of the arterial baroreflex regulation of mesenteric and hindlimb vascular conductance in hypertensive rats. Eleven adult male spontaneously hypertensive rats were chronically instrumented with left carotid arterial catheters and Doppler ultrasonic flow probes around the superior mesenteric and left common iliac arteries. After the rats recovered, arterial baroreflex function was examined by recording reflex changes in conductance in response to spontaneous changes in mean arterial pressure before exercise and during steady-state treadmill running at 6 and 18 m/min. Dynamic exercise reduced the spontaneous baroreflex gain of mesenteric conductance (by 51 and 36%) and maximum mesenteric conductance (by 24 and 32%) at 6 and 18 m/min, respectively. In sharp contrast, dynamic exercise increased the spontaneous maximum iliac conductance (by 32 and 47%) without changing the spontaneous gain. Sinoaortic denervation eliminated the relationship between mean arterial pressure and conductance by reducing the mesenteric (92%) and iliac (68%) vascular conductance gain. These results demonstrate that dynamic exercise has differential effects on the regulation of mesenteric and iliac vascular conductance in hypertensive rats.
Hepatic versus gallbladder bile composition: in vivo transport physiology of the gallbladder in rainbow trout
Authors: Grosell M. , O'Donnell M. J. , Wood C. M.
Published: December 2017

Ion and water transport across the teleost Oncorhynchus mykiss gallbladder were studied in vivo by comparing flow and composition of hepatic bile, collected by chronic catheter, to volume and composition of terminally collected gallbladder bile. Differences in composition were comparable with those of other vertebrates, whereas bile flow (75 μl ⋅ kg−1⋅ h−1) was below values reported for endothermic vertebrates. The gallbladder concentrates bile acids five- to sevenfold and exhibits higher net Cl−than Na+transport in vivo, in contrast to the 1:1 transport ratio from gallbladders under saline/saline conditions. Transepithelial potential (TEP) in the presence of bile, at the apical surface, was −13 mV (bile side negative) but +1.5 mV in the presence of saline. Bile acid in the apical saline reversed the TEP, presumably by a Donnan effect. We propose that ion transport across the gallbladder in vivo involves backflux of Na+from blood to bile resulting in higher net Cl−than Na+flux. This Na+backflux is driven by a bile side negative TEP and low Na+activity in bile due to the complexing effects of bile acids.
Regulation of myogenin protein expression in denervated muscles from young and old rats
Authors: Kostrominova Tatiana Y. , Macpherson Peter C. D. , Carlson Bruce M. , Goldman Daniel
Published: December 2017

Myogenin is a muscle-specific transcription factor participating in denervation-induced increases in nicotinic ACh receptor (nAChR) gene expression. Although myogenin RNA expression in denervated muscle is well documented, surprisingly little is known about myogenin protein expression. Therefore, we assayed myogenin protein and RNA in innervated and denervated muscles from young (4 mo) and old (24–32 mo) rats and compared this expression to that of the nAChR α-subunit RNA. These assays revealed increased myogenin protein expression within 1 day of denervation, preceding detectable increases in nAChR RNA. By 3 days of denervation, myogenin and nAChR α-subunit RNA were increased 500- and 130-fold, respectively, whereas myogenin protein increased 14-fold. Interestingly, old rats (32 mo) had 6-fold higher myogenin protein and ∼80-fold higher mRNA levels than young rats. However, after denervation, expression levels were similar for young and old animals. The increased myogenin expression during aging, which tends to localize to small fibers, likely reflects spontaneous denervation and/or regeneration. Our results show that increased myogenin protein in denervated muscles correlates with the upregulation of its mRNA.
Role of adenosine in the hypoxia-induced hypothermia of toads
Authors: Branco Luiz G. S. , Steiner Alexandre A. , Tattersall Glenn J. , Wood Stephen C.
Published: December 2017

The concept that hypoxia elicits a drop in body temperature (Tb) in a wide variety of animals is not new, but the mechanisms remain unclear. We tested the hypothesis that adenosine mediates hypoxia-induced hypothermia in toads. Measurements of selected Tbwere performed using a thermal gradient. Animals were injected (into the lymph sac or intracerebroventricularly) with aminophylline (an adenosine receptor antagonist) followed by an 11-h period of hypoxia (7% O2) or normoxia exposure. Control animals received saline injections. Hypoxia elicited a drop in Tbfrom 24.8 ± 0.3 to 19.5 ± 1.1°C ( P < 0.05). Systemically applied aminophylline (25 mg/kg) did not change Tbduring normoxia, indicating that adenosine does not alter normal thermoregulatory function. However, aminophylline (25 mg/kg) significantly blunted hypoxia-induced hypothermia ( P < 0.05). To assess the role of central thermoregulatory mechanisms, a smaller dose of aminophylline (0.25 mg/kg), which did not alter hypoxia-induced hypothermia systemically, was injected into the fourth cerebral ventricle. Intracerebroventricular injection of aminophylline (0.25 mg/kg) caused no significant change in Tbunder normoxia, but it abolished hypoxia-induced hypothermia. The present data indicate that adenosine is a central and possibly peripheral mediator of hypoxia-induced hypothermia.
Expression of a duplicate Na,K-ATPase β1-isoform in the European eel (Anguilla anguilla)
Authors: Cutler Christopher P. , Brezillon Stephane , Bekir Songul , Sanders Ian L. , Hazon Neil , Cramb Gordon
Published: December 2017

Recent studies on teleost fish have suggested that their genomes have undergone ancient polyploidization events resulting in the duplication of the genome. A duplicate copy of the Na,K-ATPase β1-isoform (called β233) has been identified in the European eel ( Anguilla anguilla). The β233-isoform shares high levels of nucleotide (74.8%) and amino acid (69.9%) homology with the eel β1-subunit as well as other vertebrate β1-sequences. Compared with the widely expressed β1-isoform, expression of β233-mRNA is mainly restricted to epithelial tissues. Seawater acclimation induced increases in β233-mRNA levels in kidney, gill, and intestine of migratory “silver” but not the nonmigratory “yellow” adult eels, suggesting that the factors responsible for this upregulation are themselves developmentally regulated. Expression of a variably glycosylated 40- to 52-kDa β233-protein in both gill “chloride” and intestinal epithelial cells suggests that the β233-isoform of Na,K-ATPase may play an important functional role in the major osmoregulatory tissues of euryhaline fish such as the eel.
Receptor-specific influence of endothelin-1 in the erectile response of the rat
Authors: Dai Y. , Pollock D. M. , Lewis R. L. , Wingard C. J. , Stopper V. S. , Mills T. M.
Published: December 2017

Specific receptor antagonists were used to examine the role of endothelin-1 (ET-1) in the erectile response of the rat. In these studies, intact rats were cannulated to permit the continuous recording of mean arterial pressure (MAP) and intracavernosal pressure (CCP). Erection was induced by electrical stimulation of the autonomic ganglion, which regulates blood flow to the penis. The animals were subjected to intracavernosal injection with vehicle only (Cont) or with an antagonist to the endothelin-A receptor (ETA) or to the endothelin-B receptor (ETB). Blockade of the ETAor the ETBhad no effect on the erectile response (CCP/MAP) during maximal ganglionic stimulation. When ET-1 was injected into Cont rats, there was a marked vasoconstriction with a sharp rise in MAP and a decline in CCP as the cavernosal arterioles constricted and limited inflow. The injection of the ETAantagonist prevented the vasoconstriction after ET-1 injection into Cont rats, whereas blockade of the ETBhad no effect on the vasoconstrictive effect to ET-1. Similar results were obtained during submaximal ganglionic stimulation. With minimal levels of ganglionic stimulation, ET-1 injection led to a moderated degree of vasodilation in the presence of the ETAantagonist. The ETBantagonist failed to alter the CCP response during minimal stimulation, but it did have a marked effect on the MAP response to ET-1 injection. The results of these studies confirm that cavernosal tissue of the rat penis is highly responsive to ET-1. However, the failure of the ET-1 antagonists to affect penile erection in response to ganglionic stimulation reflects a minimal role of ET-1 in the erectile response in the rat.
Effect of renal denervation on renin gene expression, concentration, and secretion in mature ovine fetus
Authors: Draper Michael L. , Wang Jinjuan , Valego Nancy , Block William A. , Rose James C.
Published: December 2017

To determine the role of the renal nerves on renin secretion and expression in the mature ovine fetus, we performed bilateral renal denervation on eight fetuses of time-dated pregnant ewes (126.8 ± 0.6 days gestation) and compared renin in them to seven fetuses that underwent sham denervation (126.7 ± 0.6 days gestation). Fetal arterial and venous catheters were implanted, and after 5–7 days of recovery isoproterenol was infused. Plasma active renin was lower in denervated animals than in intact animals under basal conditions and at each dose of isoproterenol. Plasma prorenin levels were lower in denervated fetuses but unaffected by isoproterenol. Denervation did not change renal renin, prorenin, or renin mRNA, but it did block isoproterenol-induced increases in renin mRNA in renocortical cells in vitro. We conclude that the renal nerves are required for renin secretory mechanisms and responsiveness of renin mRNA to β-adrenergic stimulation but not for the expression of renin in the fetal kidney. We propose that one or more of the factors that maintain renin expression in the perinatal period may be absent or may be replaced by the renal nerves in the adult.
Octreotide-induced drinking, vasopressin, and pressure responses: role of central angiotensin and ACh
Authors: Hajdu I. , Obál F. , Gardi J. , Laczi F. , Krueger J. M.
Published: December 2017

The involvement of central angiotensinergic and cholinergic mechanisms in the effects of the intracerebroventricularly injected somatostatin analog octreotide (Oct) on drinking, blood pressure, and vasopressin secretion in the rat was investigated. Intracerebroventricular Oct elicited prompt drinking lasting for 10 min. Water consumption depended on the dose of Oct (0.01, 0.1, and 0.4 μg). The drinking response to Oct was inhibited by pretreatments with the intracerebroventricularly injected angiotensin-converting enzyme inhibitor captopril, the AT1/AT2 angiotensin receptor antagonist saralasin, the selective AT1 receptor antagonist losartan, or the muscarinic cholinergic receptor antagonist atropine. The dipsogenic effect of Oct was not altered by prior subcutaneous injection of naloxone. Oct stimulated vasopressin secretion and enhanced blood pressure. These responses were also blocked by pretreatments with captopril or atropine. Previous reports indicate that the central angiotensinergic and cholinergic mechanisms stimulate drinking and vasopressin secretion independently. We suggest that somatostatin acting on sst2 or sst5 receptors modulates central angiotensinergic and cholinergic mechanisms involved in the regulation of fluid balance.
Age-related thermoregulatory differences during core cooling in humans
Authors: Frank Steven M. , Raja Srinivasa N. , Bulcao Christian , Goldstein David S.
Published: December 2017

The current study assessed sympathetic neuronal and vasomotor responses, total body oxygen consumption, and sensory thermal perception to identify thermoregulatory differences in younger and older human subjects during core cooling. Cold fluid (40 ml/kg, 4°C) was given intravenously over 30 min to decrease core temperature (Tc) in eight younger (age 18–23) and eight older (age 55–71) individuals. Compared with younger subjects, the older subjects had significantly lower Tc thresholds for vasoconstriction (35.5 ± 0.3 vs. 36.2 ± 0.2°C, P = 0.03), heat production (35.2 ± 0.4 vs. 35.9 ± 0.1°C, P = 0.04), and plasma norepinephrine (NE) responses (35.0 vs. 36.0°C, P < 0.05). Despite a lower Tc nadir during cooling, the maximum intensities of the vasoconstriction ( P = 0.03) and heat production ( P = 0.006) responses were less in the older compared with the younger subjects, whereas subjective thermal comfort scores were similar. Plasma NE concentrations increased fourfold in the younger but only twofold in the older subjects at maximal Tc cooling. The vasomotor response for a given change in plasma NE concentration was decreased in the older group ( P = 0.01). In summary, aging is associated with 1) a decreased Tc threshold and maximum response intensity for vasoconstriction, total body oxygen consumption, and NE release, 2) decreased vasomotor responsiveness to NE, and 3) decreased subjective sensory thermal perception.
Brief hypoxic stress suppresses postbacteremic NF-κB activation and TNF-α bioactivity in perfused liver
Authors: Loftis Laura L. , Johanns Cheryl A. , Lechner Andrew J. , Matuschak George M.
Published: December 2017

Reductions in hepatic O2delivery are common early after gram-negative bacteremic sepsis owing to cardiopulmonary dysfunction and derangements in sinusoidal perfusion. Although gram-negative endotoxin and cellular hypoxia independently enhance activation of nuclear factor-κB (NF-κB) via generation of reactive O2species (ROS), the combination of these stimuli downregulates hepatic TNF-α gene expression. Here we tested the hypothesis that hypoxic suppression of postbacteremic TNF-α gene expression is transcriptionally mediated by reduced activation of NF-κB. Buffer-perfused rat livers ( n = 52) were studied over 180 min after intraportal infection at t = 0 with 109live Escherichia coli (EC), serotype O55:B5, or 0.9% NaCl controls under normoxic conditions, compared with 0.5 h of constant-flow hypoxia (Po2∼41 ± 7 Torr) beginning at t = 30 min, followed by 120 min of reoxygenation. In parallel studies, tissue was obtained at peak hypoxia ( t = 60 min). To determine the role of xanthine oxidase (XO)-induced ROS in modulating NF-κB activity after hypoxia/reoxygenation (H/R), livers were pretreated with the XO inhibitor allopurinol, with results confirmed in organs of tungstate-fed animals. Electrophoretic mobility shift assays were performed on nuclear extracts of whole liver lysates using32P-labeled oligonucleotides specific for NF-κB. Compared with normoxic EC controls, hypoxia reduced postbacteremic NF-κB nuclear translocation and TNF-α bioactivity, independent of reoxygenation, tissue levels of reduced glutathione, or posthypoxic O2consumption. XO inhibition reversed the hypoxic suppression of NF-κB nuclear translocation and ameliorated decreases in cell-associated TNF-α. Thus decreases in hepatic O2delivery reduce postbacteremic nuclear translocation of NF-κB and hepatic TNF-α biosynthesis by signaling mechanisms involving low-level generation of XO-mediated ROS.
Thermal compensation of peripheral oxygen transport in skeletal muscle of seasonally acclimatized trout
Authors: Egginton S. , Cordiner S. , Skilbeck C.
Published: December 2017

Seasonal changes in ultrastructure of locomotory muscle were quantified after acclimatization to natural temperature and photoperiod. Only modest changes were seen in the volume density (Vv) of mitochondria in slow fibers ranging from 0.21 ± 0.01 (summer) to 0.24 ± 0.01 (winter), despite an increase in fiber size from 945 ± 19 to 1,594 ± 46 μm2, respectively, resulting in a significantly greater total mitochondrial volume at low temperatures. In contrast, intracellular lipid stores showed a marked change with season, from a maximum Vvof lipid droplets of 0.16 ± 0.01 in winter, progressively declining through spring and summer to a minimum of 0.07 ± 0.01 in autumn. For both organelles, the surface density reflected changes in Vv, indicating little modification of structure. Seasonal effects may dominate those of environmental temperature on mitochondrial separation, which in winter and spring fish at 4oC averaged 0.64 ± 0.06 and 1.20 ± 0.07 μm, respectively. The extracellular transport of oxygen also varies with season, the peak capillary density in autumn (2,851 ± 88 mm−2) resulting in a minimum tissue supply (domain) area of 529 ± 9μm2per capillary. As a consequence, the predicted intracellular Po2(∼2.5 kPa) is similar throughout the year.
Role of endothelin-1 in stress response in the central nervous system
Authors: Kurihara Yukiko , Kurihara Hiroki , Morita Hiroyuki , Cao Wei-Hua , Ling Guang-Yi , Kumada Mamoru , Kimura Sadao , Nagai Ryozo , Yazaki Yoshio , Kuwaki Tomoyuki
Published: December 2017

Endothelin (ET)-1 is a 21-amino acid peptide that induces a variety of biological activities, including vasoconstriction and cell proliferation, and its likely involvement in cardiovascular and other diseases has recently led to broad clinical trials of ET receptor antagonists. ET-1 is widely distributed in the central nervous system (CNS), where it is thought to regulate hormone and neurotransmitter release. Here we show that CNS responses to emotional and physical stressors are differentially affected in heterozygous ET-1-knockout mice, which exhibited diminished aggressive and autonomic responses toward intruders (emotional stressors) but responded to restraint-induced (physical) stress more intensely than wild-type mice. This suggests differing roles of ET-1 in the central pathways mediating responses to different types of stress. Hypothalamic levels of ET-1 and the catecholamine metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) were both increased in wild-type mice subjected to intruder stress, whereas MHPG levels were not significantly affected in ET-1-knockout mice. Furthermore, immunohistochemical analysis showed that ET-1 and tyrosine hydroxylase, an enzyme in the catecholamine synthesis pathway, were colocalized within certain neurons of the hypothalamus and amygdala. Our findings suggest that ET-1 modulates central coordination of stress responses in close association with catecholamine metabolism.
Coupling of left ventricular and aortic volume elasticity in the rabbit
Authors: Wronski T. , Persson P. B. , Seeliger E. , Harnath A. , Flemming B.
Published: December 2017

Changes in volume elasticity (VE) of the left ventricle and aorta could be important for blood flow. A procedure is presented to rapidly assess VE of the left ventricle and aorta by analyzing changes in the eigenfrequency. Six control rabbits and 11 rabbits with atheromatosis (12 wk of high-cholesterol feeding) were studied. In control rabbits, during the first half of the systole, left ventricular VE continuously increased to +43% ( P < 0.05). Then VE gradually declined to an end-diastolic minimum (20% of the average systolic levels, P < 0.05). Aortic VE changes were in the opposite direction to the ventricle. Aortic VE continuously decreased throughout the systole; the last value was 20% lower than at the beginning of the systole ( P < 0.05). Conversely, diastolic VE of the aorta took on greater values. This inverse time course between ventricle and aorta may reduce energy requirements for conveying blood. High cholesterol-fed rabbits did not reveal the inverse behavior of ventricular and aortic VE, e.g., aortic VE increased during the systole (119%, P < 0.05).
Effect of single wrist exercise on fibroblast growth factor-2, insulin-like growth factor, and growth hormone
Authors: Eliakim Alon , Oh Youngman , Cooper Dan Michael
Published: December 2017

Anabolic effects of exercise are mediated, in part, by fibroblast growth factor-2 (FGF-2), insulin-like growth factor-I (IGF-I), and growth hormone (GH). To identify local vs. systemic modification of these mediators, 10 male subjects performed 10 min of unilateral wrist-flexion exercise. Blood was sampled from catheters placed in basilic veins of both arms. Lactate was significantly increased only in the exercising arm. FGF-2 decreased dramatically ( P < 0.01) in both the resting (from 1.49 ± 0.32 to nadir at 0.11 ± 0.11 pg/ml) and exercising arm (1.80 ± 0.60 to 0.29 ± 0.14 pg/ml). Small but significant increases were found in both the resting and exercising arm for IGF-I and IGF binding protein-3 (IGFBP-3). GH was elevated in blood sampled from both the resting (from 1.04 ± 0.68 to a peak of 2.57 ± 0.53 ng/ml) and exercising arm (1.04 ± 0.66 to 2.43 ± 0.42 ng/ml, P < 0.05). Unilateral wrist exercise was not sufficiently intense to increase circulating lactate or heart rate, but it led to systemic changes in GH, IGF-I, IGFBP-3, and FGF-2. Low-intensity exercise involving small muscle groups can influence the circulating levels of growth factors.
Fever and motor activity in rats following day and night injections ofStaphylococcus aureuscell walls
Authors: Luker Frank I. , Mitchell Duncan , Laburn Helen P.
Published: December 2017

Body temperature and physical activity are affected by both circadian cycles and pyrogens. We injected intraperitoneally 2.5 × 109cell walls of the gram-positive organism Staphylococcus aureus or sterile saline at three different times in the circadian temperature and activity rhythm of Sprague-Dawley rats. Irrespective of whether pyrogen injections were made when the rats were inactive (injection at 0900), just before the nighttime rise in activity and body temperature (1630), or during high activity (2100), the peak body temperature attained and the time to reach peak temperature were indistinguishable. The fever response, as measured by the thermal-response index, was greatest, however, when body temperature and activity were in the lowest phase. Physical activity was inhibited by night but not day injection of S. aureus. Our results provide the first description of experimental fever resulting from a gram-positive pyrogen in rats and the first time an aspect of sickness behavior (suppressed motor activity) has been associated with fever resulting from simulated gram-positive bacterial infection.
Prostaglandin dehydrogenase mRNA in baboon intrauterine tissues in late gestation and spontaneous labor
Authors: Wu W. X. , Ma X. H. , Smith G. C. S. , Mecenas C. A. , Koenen S. V. , Nathanielsz P. W.
Published: December 2017

The present study was designed to characterize prostaglandin dehydrogenase (PGDH) mRNA expression in critical intrauterine tissues of pregnant baboons in late gestation and at spontaneous labor. In addition, we determined regulatory effects of betamethasone in vivo on chorionic and placental PGDH mRNA expression. PGDH mRNA was present in chorion, decidua, lower uterine segment, fundal myometrium, and cervix in late gestation but undetectable in amnion. PGDH mRNA significantly decreased in decidua and cervix during late gestation and in chorion and fundus during spontaneous labor. PGDH mRNA in lower uterine segment, decidua, cervix, and placenta was unchanged during spontaneous labor from late gestation levels. Betamethasone had no effect on chorionic and placental PGDH mRNA expression. In summary, our data suggest that PGDH mRNA expression is tightly controlled in gestation- and tissue-specific manners. Decreased chorionic and fundal PGDH abundance during labor and decreased decidua and cervical PGDH mRNA in late gestation allow local uterine prostaglandin accumulation and assist prostaglandin transfer to myometrium. Local differences in PGDH function may regulate tissue- and region-specific requirements for prostaglandins to promote and complete labor.
Water ingestion provides an early signal inhibiting osmotically stimulated vasopressin secretion in rats
Authors: Huang Wan , Sved Alan F. , Stricker Edward M.
Published: December 2017

Dehydrated dogs are known to inhibit secretion of vasopressin (VP) within minutes after drinking water, before plasma osmolality (Posmol) diminishes. The present studies determined whether water ingestion causes a similar rapid inhibition of neurohypophyseal hormone secretion in rats. Adult rats were infused with 1 M NaCl (2 ml/h iv) for 240 min to stimulate VP and oxytocin (OT) secretion. After 220 min of infusion, rats were given water to drink for 5 min, and blood samples were taken 5 and 15 min later for RIA. Plasma VP (pVP) was much lower when rats ingested water than when they drank nothing even though Posmol was not significantly altered. Plasma OT (pOT) was affected similarly. In contrast, no effects on pVP or pOT occurred when rats drank isotonic NaCl solution for 5 min in amounts comparable to the water intakes (∼5.5 ml). These results suggest that neurohypophyseal secretion of VP and OT in rats is inhibited rapidly by water drinking, and that this inhibition is mediated by a visceral signal of osmotic dilution rather than by the act of drinking per se.
α2-Adrenergic receptor-mediated increase in NO production buffers renal medullary vasoconstriction
Authors: Zou Ai-Ping , Cowley Allen W.
Published: December 2017

The present study was designed to investigate the role of nitric oxide (NO) in modulating the adrenergic vasoconstrictor response of the renal medullary circulation. In anesthetized rats, intravenous infusion of norepinephrine (NE) at a subpressor dose of 0.1 μg · kg−1· min−1did not alter renal cortical (CBF) and medullary (MBF) blood flows measured by laser-Doppler flowmetry nor medullary tissue Po2(Pmo2) as measured by a polarographic microelectrode. In the presence of the NO synthase inhibitor nitro-l-arginine methyl ester (l-NAME) in the renal medulla, intravenous infusion of NE significantly reduced MBF by 30% and Pmo2by 37%. With the use of an in vivo microdialysis-oxyhemoglobin NO-trapping technique, we found that intravenous infusion of NE increased interstitial NO concentrations by 43% in the renal medulla. NE-stimulated elevations of tissue NO were completely blocked either by renal medullary interstitial infusion ofl-NAME or the α2-antagonist rauwolscine (30 μg · kg−1· min−1). Concurrently, intavenous infusion of NE resulted in a significant reduction of MBF in the presence of rauwolscine. The α1-antagonist prazosin (10 μg · kg−1· min−1renal medullary interstitial infusion) did not reduce the NE-induced increase in NO production, and NE increased MBF in the presence of prazosin. Microdissection and RT-PCR analyses demonstrated that the vasa recta expressed the mRNA of α2B-adrenergic receptors and that medullary thick ascending limb and collecting duct expressed the mRNA of both α2A- and α2B-adrenergic receptors. These subtypes of α2-adrenergic receptors may mediate NE-induced NO production in the renal medulla. We conclude that the increase in medullary NO production associated with the activation of α2-adrenergic receptors counteracts the vasoconstrictor effects of NE in the renal medulla and may play an important role in maintaining a constancy of MBF and medullary oxygenation.
Behavioral feedback regulation of circadian rhythm phase angle in light-dark entrained mice
Authors: Mistlberger R. E. , Holmes M. M.
Published: December 2017

Induced and spontaneous wheel running can alter the phase and period (τ) of circadian rhythms in rodents. The relationship between spontaneous running and the phase angle (ψ) of entrainment to 24-h light-dark (LD) cycles was evaluated in C57BL/6j mice. With a wheel freely available, ψ was significantly correlated with the absolute ( r = 0.32) and relative ( r = 0.44) amount of activity during the first 2 h of the activity period. When wheels were locked during the first half of the night in LD and then unlocked in constant dark (DD), mice exhibited a delayed ψ and lengthened τ compared with mice that had wheels locked during the second half of the night. In DD, τ correlated negatively with total daily activity. To evaluate if wheel running modulates the phase-resetting actions of LD, phase shifts to light pulses were measured at two time points in DD, when daily activity levels differed by 40%. Phase delays to light were 56% greater when activity levels were lower. However, in a counterbalanced follow-up experiment, phase advances and delays to light pulses were not affected by the availability of wheels, although an effect of time in DD was replicated. Spontaneous activity can regulate ψ and τ without altering the response of the pacemaker to light.
Antenatal glucocorticoids alter premature newborn lamb neuroendocrine and endocrine responses to hypoxia
Authors: Ervin M. Gore , Padbury James F. , Polk Daniel H. , Ikegami Machiko , Berry Lynne M. , Jobe Alan H.
Published: December 2017

Glucocorticoids are administered for preterm labor to improve postnatal adaptation. We assessed the effect of antenatal betamethasone (Beta) treatment on preterm newborn lamb neuroendocrine [catecholamine, arginine vasopressin (AVP)] and endocrine [triiodothyronine (T3), ANG II, and atrial natriuretic factor (ANF)] adaptive responses following delivery and a hypoxic challenge. Beta treatment included direct fetal injection at 0.2 (F0.2; n = 8) or 0.5 (F0.5; n = 7) mg/kg estimated fetal body weight or maternal injection with 0.2 ( n = 8) or 0.5 mg/kg (M0.5; n = 8). Control animals received fetal and maternal intramuscular injections of saline ( n = 8). After 24 h, lambs were delivered by cesarean section, surfactant treated, and ventilated for 4 h. Relative to the control lambs, 3 h after delivery, there was a marked suppression of plasma cortisol, epinephrine, norepinephrine, and ANG II levels and elevated plasma T3and ANF levels, systolic blood pressure, and left ventricular contractility (dP/d t; F0.5and M0.5) values in F0.5and both maternal Beta-treated groups. However, Beta treatment augmented the cardiac output, cortisol, norepinephrine, AVP, and ANF responses to 20 min of hypoxia (Po2= 25–30 mmHg). We concluded that short-term (24 h) antenatal glucocorticoid exposure 1) alters preterm newborn postnatal blood pressure regulation in the face of marked depression of plasma cortisol, catecholamine, and ANG II levels and 2) augments the postnatal neuroendocrine and endocrine responses to a hypoxic challenge.
Leptin responses to physical inactivity induced by simulated weightlessness
Authors: Blanc Stéphane , Normand Sylvie , Pachiaudi Christiane , Duvareille Monique , Gharib Claude
Published: December 2017

Physical inactivity induced by head-down bed rest (HDBR) affects body composition (BC). Leptin is involved in BC regulation by acting on fuel homeostasis. We investigated whether leptin and counterregulatory hormone levels are affected by a 7-day HDBR. Fasting blood was sampled daily (0700) in males ( n = 8) and on alternating days in females ( n = 8) for measurements of leptin, insulin, norepinephrine (NE), epinephrine (Epi), growth hormone (GH), cortisol, nonesterified fatty acid (NEFA), and glucose. BC was measured by H2 18O dilution. Energy intake (men 10.5 ± 0.2 MJ/day, women 7.9 ± 0.3 MJ/day) and BC were unchanged by HDBR. Increased levels of leptin (men 40%, P = 0.003; women 20%, P = 0.050), insulin (men 34%, P= 0.018; women 25%, P = 0.022), and the insulin-to-glucose ratio (men 30%, P = 0.049; women 25%, P = 0.031) were noted. GH, NE, Epi, and cortisol levels were unaltered. NEFA dropped in both sexes, but glucose decreased only in women. In conclusion, HDBR increased leptin levels independently of stress response, changes in fat mass, energy intake, or gender. These changes were correlated to the insulin-resistance development in men. Further analyses are required, but the results have to be considered for longer HDBR periods with 1) the well-described drop in energy intake and 2) the BC changes.
Subcutaneous lipectomy causes a metabolic syndrome in hamsters
Authors: Weber R. V. , Buckley M. C. , Fried S. K. , Kral J. G.
Published: December 2017

The insulin resistance syndrome X is related to excess intra-abdominal adipose tissue. With lipectomy of >50% of subcutaneous adipose tissue (SQAT) in nonhibernating, adult female Syrian hamsters on high-fat (HF; 50 calorie%) diet and measurements of oral glucose tolerance, oral [14C]oleic acid disposal, serum triglycerides, serum leptin, liver fat, perirenal (PR) adipose tissue cellularity, and body composition, we studied the role of SQAT. Sham-operated (S) animals on HF or low-fat (LF; 12.5 calorie%) diets served as controls. After 3 mo there was no visible regrowth of SQAT but HF diet led to similar levels of body weight and body fat in lipectomized and sham-operated animals. Lipectomized (L) animals had more intra-abdominal fat as a percentage of total body fat, higher insulinemic index, a strong trend toward increased liver fat content, and markedly elevated serum triglycerides compared with S-HF and S-LF. Liver and PR adipose tissue uptake of fatty acid were similar in L-HF and S-HF but reduced vs. S-LF, and were inversely correlated with liver fat content and insulin sums during the oral glucose tolerance test. In summary, lipectomy of SQAT led to compensatory fat accumulation implying regulation of total body fat mass. In conjunction with HF diet these lipectomized hamsters developed a metabolic syndrome with significant hypertriglyceridemia, relative increase in intra-abdominal fat, and insulin resistance. We propose that SQAT, via disposal and storage of excess ingested energy, acts as a metabolic sink and protects against the metabolic syndrome of obesity.
Effects of time of day, gender, and menstrual cycle phase on the human response to a water load
Authors: Claybaugh John R. , Sato Aileen K. , Crosswhite Linda K. , Hassell L. Harrison
Published: December 2017

Estrogen and progesterone interference with renal actions of arginine vasopressin (AVP) has been shown. Thus we hypothesized that women will have a higher water turnover than men and that the greatest difference will be during the luteal phase of the menstrual cycle. Seven men (32 ± 3 yr) and six women (33 ± 2 yr) drank 12 ml water/kg lean body mass on different days at 0800 and at 2000 following 10 h of fast and a standardized meal at 0600 and 1800. Women participated on days 4–11 and 19–25 of the menstrual cycle. Initial urine and plasma osmolalities and urine flow rates were similar in all experiments. The cumulative urine voided over 3 h following the morning drink was less in men (73 ± 12% of the water load) compared with women in either the follicular (100 ± 3%) or luteal phases (102 ± 10%) of the menstrual cycle. Nighttime values (30–43% of the water load) were lower in all experiments and were not different between sexes or menstrual cycle phases. Plasma AVP was higher at night and may contribute to this diurnal response. The data are generally consistent with the stated hypothesis; however, possibly owing to the greatly reduced urine flow in both sexes at night, a difference between sexes was not observed at that time.
Norepinephrine mediates glucoprivic-induced increase in GABA in the ventromedial hypothalamus of rats
Authors: Beverly J. L. , de Vries M. G. , Beverly M. F. , Arseneau L. M.
Published: December 2017

Noradrenergic mechanisms in the hypothalamus may be involved in counterregulatory responses to glucoprivic episodes. After 2-deoxy-d-glucose (2-DG; 1.2 mmol/kg iv), extracellular norepinephrine (NE) concentration in the ventromedial hypothalamus (VMN) increased in a bimodal fashion to 251 ± 39% ( P < 0.001) and 150 ± 17% ( P < 0.001) of baseline during the first 30 min. In the lateral hypothalamus (LHA), NE decreased by 30 min (61 ± 4%, P < 0.001) and no consistent changes were measured in the paraventricular nucleus (PVN). Because the NE response in the VMN after 2-DG followed the same pattern as GABA, the interaction between NE and GABA was evaluated. In the VMN, GABA had little effect on extracellular NE concentrations but NE increased GABA concentrations 166 ± 13%, ( P < 0.01). In the presence of yohimbine (α2-adrenoceptor antagonist) the first GABA peak after 2-DG was absent, and the second GABA peak was absent in the presence of timolol (β-adrenoceptor antagonist). These results support an interaction among noradrenergic and GABAergic systems in the VMN during glucoprivation and that increased NE mediates the increase in extracellular GABA after 2-DG.
Right ventricular systolic pressure load alters myocyte maturation in fetal sheep
Authors: Barbera A. , Giraud G. D. , Reller M. D. , Maylie J. , Morton M. J. , Thornburg K. L.
Published: December 2017

The effects of right ventricular (RV) systolic pressure (RVSP) load on fetal myocyte size and maturation were studied. Pulmonary artery (PA) pressure was increased by PA occlusion from mean 47.4 ± 5.0 (±SD) to 71 ± 13.6 mmHg ( P < 0.0001) in eight RVSP-loaded near-term fetal sheep for 10 days. The maximal pressure generated by the RV with acute PA occlusion increased after RVSP load: 78 ± 7 to 101 ± 15 mmHg ( P< 0.005). RVSP-load hearts were heavier (44.7 ± 8.4 g) than five nonloaded hearts (31.8 ± 0.2 g; P < 0.03); heart-to-body weight ratio (10.9 ± 1.1 and 6.5 ± 0.9 g/kg, respectively; P < 0.0001). RVSP-RV myocytes were longer (101.3 ± 10.2 μm) than nonloaded RV myocytes (88.2 ± 8.1 μm; P < 0.02) and were more often binucleated (82 ± 13%) than nonloaded myocytes (63 ± 7%; P < 0.02). RVSP-loaded myocytes had less myofibrillar volume than did nonloaded hearts (44.1 ± 4.4% and 56.1 ± 2.6%; P < 0.002). We conclude that RV systolic load 1) leads to RV myocyte enlargement, 2) has minor effects on left ventricular myocyte size, and 3) stimulates maturation (increased RV myocyte binucleation). Myocyte volume data suggest that RV systolic loading stimulates both hyperplastic and hypertrophic growth.
Panting in reindeer (Rangifer tarandus)
Authors: Aas-Hansen Øyvind , Folkow Lars P. , Blix Arnoldus Schytte
Published: December 2017

Two winter-insulated Norwegian reindeer ( Rangifer tarandus tarandus) were exposed to air temperatures of 10, 20, 30, and 38°C while standing at rest in a climatic chamber. The direction of airflow through nose and mouth, and the total and the nasal minute volumes, respectively, were determined during both closed- and open-mouth panting. The animals alternated between closed- and open-mouth panting, but the proportion of open-mouth panting increased with increasing heat load. The shifts from closed- to open-mouth panting were abrupt and always associated with a rise in respiratory frequency and respiratory minute volume. During open-mouth panting, the direction of airflow was bidirectional in both nose and mouth, but only 2.4 ± (SD) 1.1% of the air was routed through the nose. Estimates suggest that the potential for selective brain cooling is markedly reduced during open-mouth panting in reindeer as a consequence of this airflow pattern.