bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopaminergic metabolism in carotid bodies and high-altitude acclimatization in female rats
Authors: Joseph Vincent , Soliz Jorge , Soria Ruddy , Pequignot Jacqueline , Favier Roland , Spielvogel Hilde , Pequignot Jean Marc
Published: March 2015

We tested the hypothesis that ovarian steroids stimulate breathing through a dopaminergic mechanism in the carotid bodies. In ovariectomized female rats raised at sea level, domperidone, a peripheral D2-receptor antagonist, increased ventilation in normoxia (minute ventilation = +55%) and acute hypoxia (+32%). This effect disappeared after 10 daily injections of ovarian steroids (progesterone + estradiol). At high altitude (3,600 m, Bolivian Institute for High-Altitude Biology-IBBA, La Paz, Bolivia), neutered females had higher carotid body tyrosine hydroxylase activity (the rate-limiting enzyme for catecholamine synthesis: +129%) and dopamine utilization (+150%), lower minute ventilation (−30%) and hypoxic ventilatory response (−57%), and higher hematocrit (+18%) and Hb concentration (+21%) than intact female rats. Consistent signs of arterial pulmonary hypertension (right ventricular hypertrophy) also appeared in ovariectomized females. None of these parameters was affected by gonadectomy in males. Our results show that ovarian steroids stimulate breathing by lowering a peripheral dopaminergic inhibitory drive. This process may partially explain the deacclimatization of postmenopausal women at high altitude.
Regulation of ANP secretion by cardiac Na+/Ca2+ exchanger using a new controlled atrial model
Authors: Seul Kyung Hwan , Han Jeong Hee , Kang Keum Yee , Kim Sung Zoo , Kim Suhn Hee
Published: March 2015

The myocardial interstitium is important in regulating cardiac function. Between the atrial lumen and the pericardial space are transmural pathways, and movement of interstitial fluid (ISF) through these pathways is one of the main driving forces regulating translocation of substances from the interstitium into the blood. To define how ISF translocation from the interstitial space into the luminal space is regulated by each component of atrial hemodynamics, we devised a new rabbit atrial model in which each physical parameter could be controlled independently. Using this system, we also defined the physiological role of the cardiac Na+/Ca2+ exchanger on secretion of atrial natriuretic peptide (ANP) by depletion of extracellular Na+ ([Na+]o). Increases in stroke volume and atrial end-systolic volume increased ISF translocation and ANP secretion. However, an increase in atrial rate did not influence ISF translocation but, rather, increased ANP secretion. Gradual depletion of [Na+]o caused gradual increases in ANP secretion and intracellular Ca2+([Ca2+]i), which were blocked in the presence of Ca2+-free buffer and Ni2+, but not in the presence of KB-R7943, diltiazem, mibefradil, caffeine, or monensin. Amiloride and its analog blocked an increase in ANP secretion but not an increase in [Ca2+]i by [Na+]o depletion. Therefore, we suggest that ANP secretion and ISF translocation may be differently controlled by each physical factor. These results also suggest that the increase in ANP secretion in response to [Na+]o depletion may involve inhibition of Na+/Ca2+ and Na+/H+ exchangers but not an increase in [Ca2+]i.
Renal responses to plasma volume expansion and hyperosmolality in fasting seal pups
Authors: Ortiz Rudy M. , Wade Charles E. , Costa Daniel P. , Ortiz C. Leo
Published: March 2015

Renal responses were quantified in northern elephant seal ( Mirounga angustirostris) pups during their postweaning fast to examine their excretory capabilities. Pups were infused with either isotonic (0.9%; n = 8; Iso) or hypertonic (16.7%; n = 7; Hyper) saline via an indwelling catheter such that each pup received 3 mmol NaCl/kg. Diuresis after the infusions was similar in magnitude between the two treatments. Osmotic clearance increased by 37% in Iso and 252% in Hyper. Free water clearance was reduced 3.4-fold in Hyper but was not significantly altered in Iso. Glomerular filtration rate increased 71% in the 24-h period after Hyper, but no net change occurred during the same time after Iso. Natriuresis increased 3.6-fold in Iso and 5.3-fold in Hyper. Iso decreased plasma arginine vasopressin (AVP) and cortisol acutely, whereas Hyper increased plasma and excreted AVP and cortisol. Iso was accompanied by the retention of water and electrolytes, whereas the Hyper load was excreted within 24 h. Natriuresis is attributed to increased filtration and is independent of an increase in atrial natriuretic peptide and decreases in ANG II and aldosterone. Fasting pups appear to have well-developed kidneys capable of both extreme conservation and excretion of Na+.
Excitatory and inhibitory effects of tricaine (MS-222) on fictive breathing in isolated bullfrog brain stem
Authors: Hedrick Michael S. , Winmill Rachel E.
Published: March 2015

This study examined the direct effects of tricaine methanesulfonate (MS-222), a sodium-channel blocking local anesthetic, on respiratory motor output using an in vitro brain stem preparation of adult North American bullfrogs ( Rana catesbeiana). Bullfrogs were anesthetized with halothane, and the brain stem was removed and superfused with artificial cerebrospinal fluid containing MS-222 at concentrations ranging from 0.1 to 1,000 μM. At the lowest concentration of MS-222, respiratory frequency ( fR) increased significantly ( P < 0.05), but at higher concentrations, fRprogressively decreased and was abolished in all preparations at 1,000 μM ( P < 0.01). Respiratory burst amplitude and burst duration were not affected by MS-222. The frequency of nonrespiratory neural activity did not significantly change with the addition of MS-222 below 1,000 μM. These data indicate that MS-222 has a significant, direct effect on respiratory motor output from the central nervous system, producing both excitation and inhibition of fictive breathing. The results are consistent with other studies demonstrating that low concentrations of anesthetics generally cause excitation followed by depression at higher concentrations. Although the mechanisms underlying the excitatory effects of MS-222 in this study are unclear, they may include increased excitatory neurotransmission and/or disinhibition of inputs to the respiratory central pattern generator.
Glycerokinase activity in brown adipose tissue: a sympathetic regulation?
Authors: Kawashita N. H. , Festuccia W. T. L. , Brito M. N. , Moura M. A. F. , Brito S. R. C. , Garófalo M. A. R. , Kettelhut I. C. , Migliorini R. H.
Published: March 2015

The effect of brown adipose tissue (BAT) sympathetic hemidenervation on the activity of glycerokinase (GyK) was investigated in different physiological conditions. In rats fed a balanced diet, the activity of the enzyme was ∼50% lower in BAT-denervated pads than in intact, innervated pads. In rats adapted to a high-protein, carbohydrate-free diet, norepinephrine turnover rates and BAT GyK activity were already reduced, and BAT denervation resulted in a further decrease in the activity of the enzyme. Cold acclimation of normally fed rats at 4°C for 10 days markedly increased the activity of the enzyme. Cold exposure (4°C) for 6 h was insufficient to stimulate BAT GyK, but the activity of the enzyme was already increased after 12 h of cold exposure. The cold-induced BAT GyK stimulation was completely blocked in BAT-denervated pads. The data indicate that an adequate sympathetic flow to BAT is required for the maintenance of normal levels of GyK activity and for the enzyme response to situations, such as cold exposure, which markedly increase BAT sympathetic flow.
Regulation of transepithelial phosphate transport by PTH in chicken proximal tubule epithelium
Authors: Dudas Paul L. , Villalobos Alice R. , Gocek-Sutterlin Gayle , Laverty Gary , Renfro J. Larry
Published: March 2015

The effect of parathyroid hormone (PTH) and activation of protein kinase C (PKC) and protein kinase A (PKA) on transepithelial Pitransport was examined in monolayers of chick proximal tubule cells in primary culture (PTCs). Acute exposure of the PTCs to PTH (10−9M, basolateral side) significantly decreased the net reabsorption of Piby ∼66%. There was no effect after the addition of PTH to the luminal side. Activation of PKC by phorbol 12-myristate 13-acetate (PMA; 0.1 μM) dramatically decreased net Pireabsorption by ∼60%. Bisindolylmaleimide I (BIM; 1 μM), a highly selective PKC inhibitor, prevented PMA-induced inhibition. Activation of adenylate cyclase/PKA by forskolin (10 μM) mimicked the effect of PTH by significantly reducing net Pireabsorption by one-half. Addition of H-89 (10 μM), a potent inhibitor of PKA, abolished forskolin-induced inhibition. PTH inhibition was blocked by either BIM or H-89. Tissue electrophysiology remained stable after all treatments. There was a decreased immunoreactivity of the luminal Na+-Picotransporter NaPi-IIa after PTH treatment. These data indicate that PTH inhibition of Pireabsorption in this in vitro system is mediated by PKC and PKA.
Ontogeny and effect of cortisol on vasopressin-1b receptor expression in anterior pituitaries of fetal sheep
Authors: Young Sharla F. , Smith Jennifer L. , Figueroa Jorge P. , Rose James C.
Published: March 2015

Corticotroph responsiveness to arginine vasopressin (AVP) increases during late gestation in fetal sheep. The mechanism of this increase in AVP responsiveness is currently unknown but could be related to an increase in vasopressin type 1b (V1b) receptor expression in the pituitary during development. To determine if there are ontogenic changes in V1b receptor expression that may help explain the changes in ACTH responses to AVP, we studied pituitaries from three groups of fetal sheep [100, 120, or 140 days gestational age (dGA)]. V1b receptor mRNA and protein significantly decreased by 140 dGA. Peak V1b mRNA levels were detected at 100 dGA, while peak V1b protein levels were detected at 120 dGA. The reduction in V1b receptor expression in late gestation may be due to the naturally occurring peripartum increase in fetal plasma cortisol because cortisol infusion at 122–130 dGA decreased V1b receptor mRNA. Thus there is a marked decrease in the expression of the V1b receptor in the pituitary during fetal development, leaving the role of the V1b receptor in increasing AVP responsiveness uncertain.
Effects of aging and caloric restriction on mitochondrial energy production in gastrocnemius muscle and heart
Authors: Drew B. , Phaneuf S. , Dirks A. , Selman C. , Gredilla R. , Lezza A. , Barja G. , Leeuwenburgh C.
Published: March 2015

Mitochondria are chronically exposed to reactive oxygen intermediates. As a result, various tissues, including skeletal muscle and heart, are characterized by an age-associated increase in reactive oxidant-induced mitochondrial DNA (mtDNA) damage. It has been postulated that these alterations may result in a decline in the content and rate of production of ATP, which may affect tissue function, contribute to the aging process, and lead to several disease states. We show that with age, ATP content and production decreased by ∼50% in isolated rat mitochondria from the gastrocnemius muscle; however, no decline was observed in heart mitochondria. The decline observed in skeletal muscle may be a factor in the process of sarcopenia, which increases in incidence with advancing age. Lifelong caloric restriction, which prolongs maximum life span in animals, did not attenuate the age-related decline in ATP content or rate of production in skeletal muscle and had no effect on the heart. 8-Oxo-7,8-dihydro-2′-deoxyguanosine in skeletal muscle mtDNA was unaffected by aging but decreased 30% with caloric restriction, suggesting that the mechanisms that decrease oxidative stress in these tissues with caloric restriction are independent from ATP availability. The generation of reactive oxygen species, as indicated by H2O2production in isolated mitochondria, did not change significantly with age in skeletal muscle or in the heart. Caloric restriction tended to reduce the levels of H2O2production in the muscle but not in the heart. These data are the first to show that an age-associated decline in ATP content and rate of ATP production is tissue specific, in that it occurs in skeletal muscle but not heart, and that mitochondrial ATP production was unaltered by caloric restriction in both tissues.
Renal medullary nitric oxide deficit of Dahl S rats enhances hypertensive actions of angiotensin II
Authors: Szentiványi Mátyás , Zou Ai-Ping , Mattson David L. , Soares Paulo , Moreno Carol , Roman Richard J. , Cowley Allen W.
Published: March 2015

Studies were designed to examine the hypothesis that the renal medulla of Dahl salt-sensitive (Dahl S) rats has a reduced capacity to generate nitric oxide (NO), which diminishes the ability to buffer against the chronic hypertensive effects of small elevations of circulating ANG II. NO synthase (NOS) activity in the outer medulla of Dahl S rats (arginine-citrulline conversion assay) was significantly reduced. This decrease in NOS activity was associated with the downregulation of protein expression of NOS I, NOS II, and NOS III isoforms in this region as determined by Western blot analysis. In anesthetized Dahl S rats, we observed that a low subpressor intravenous infusion of ANG II (5 ng · kg−1 · min−1) did not increase the concentration of NO in the renal medulla as measured by a microdialysis with oxyhemoglobin trapping technique. In contrast, ANG II produced a 38% increase in the concentration of NO (87 ± 8 to 117 ± 8 nmol/l) in the outer medulla of Brown-Norway (BN) rats. The same intravenous dose of ANG II reduced renal medullary blood flow as determined by laser-Doppler flowmetry in Dahl S, but not in BN rats. A 7-day intravenous ANG II infusion at a dose of 3 ng · kg−1 · min−1 did not change mean arterial pressure (MAP) in the BN rats but increased MAP in Dahl S rats from 120 ± 2 to 138 ± 2 mmHg ( P< 0.05). ANG II failed to increase MAP after NO substrate was provided by infusion of l-arginine (300 μg · kg−1 · min−1) into the renal medulla of Dahl S rats. Intravenous infusion ofl-arginine at the same dose had no effect on the ANG II-induced hypertension. These results indicate that an impaired NO counterregulatory system in the outer medulla of Dahl S rats makes them more susceptible to the hypertensive actions of small elevations of ANG II.
Angiotensin II feedback is a regulator of renocortical renin, COX-2, and nNOS expression
Authors: Kammerl Martin C. , Richthammer Wolfgang , Kurtz Armin , Krämer Bernhard K.
Published: March 2015

Salt restriction leads to parallel increases of renin, cyclooxygenase-2 (COX-2), and neuronal nitric oxide synthase (nNOS) gene expression in the juxtaglomerular apparatus of rat kidneys. Because the upregulation of these genes is strongly enhanced if salt restriction is combined with inhibition of the renin-angiotensin-aldosterone system, our study aimed to find out whether the juxtaglomerular expressions of renin, COX-2, and nNOS are subject to a common direct negative feedback control by ANG II. For this purpose, male Sprague-Dawley rats were fed a low-salt diet (0.02% wt/wt) with or without additional treatment with the ANG I-converting enzyme (ACE) inhibitor ramipril (10 mg · kg body wt−1· day−1) for 1 wk, and renocortical renin, COX-2, and nNOS mRNAs were assayed. To narrow down possible indirect effects of the ACE inhibitor that may result from insufficient aldosterone production, the animals received mineralocorticoid substitution with fludrocortisone (6 mg · kg body wt−1· day−1). Thus mineralocorticoid substitution prevented the fall of systolic blood pressure and of glomerular filtration induced by ramipril in rats on low-salt diet.

Although fludrocortisone had no effect on basal renin, COX-2, and nNOS mRNA, it clearly attenuated the threefold increases of both renin and COX-2 mRNA in response to low-salt diet. In rats on low-salt diet, ramipril further increased renin mRNA ninefold, COX-2 mRNA fourfold, and nNOS 2.5-fold in the absence of fludrocortisone. In the presence of fludrocortisone, ramipril increased renin mRNA 10-fold, COX-2 mRNA 2.5-fold, and nNOS mRNA 2.5-fold. These data indicate that mineralocorticoid substitution lowers the overall expression of juxtaglomerular renin and COX-2 during low-salt intake and attenuates a further rise of COX-2 expression by ACE inhibition, but it does not change the stimulatory effect of ACE inhibition on renin and nNOS expression.

We conclude that the expression of renin, COX-2, and nNOS in the juxtaglomerular apparatus during low-salt diet is markedly limited by a direct feedback inhibition through ANG II.
Hypertension inl-NAME-treated diabetic rats depends on an intact sympathetic nervous system
Authors: Fitzgerald Sharyn M. , Brands Michael W.
Published: March 2015

We demonstrated previously that induction of diabetes in rats that were treated chronically with the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) causes a severe, progressive increase in mean arterial pressure. This study tested the role of the sympathetic nervous system in that response. Rats were instrumented with chronic artery and vein catheters and assigned randomly to four diabetic groups pretreated with vehicle (D), l-NAME (D+L), the α1- and β-adrenergic receptor antagonists terazosin and propranolol (D+B), or l-NAME, terazosin, and propranolol (D+LB). After baseline measurements were taken, rats were pretreated; 6 days later, streptozotocin was administered and 3 wk of diabetes ensued. D+L rats had a marked, progressive increase in arterial pressure that by day 20 was ∼60 mmHg greater than in D rats. The pressor response to l-NAME was significantly attenuated in diabetic rats cotreated with adrenergic blockers. During week 1 of diabetes, plasma renin activity (PRA) increased and then returned to control levels in D rats. PRA increased progressively in D+L rats, and chronic adrenergic receptor blockade restored the biphasic renin response in D+LB rats. These results suggest that the sympathetic nervous system may be involved in the hypertensive response to onset of diabetes inl-NAME-treated rats, possibly through control of renin secretion.
Enhanced vascular effects of the Ca2+channel agonist Bay K 8644 in pregnant rabbits
Authors: Venuto Rocco , Brown Gail , Schoenl Marion , Losonczy György
Published: March 2015

Hemodynamic studies were performed to determine if blunting of vascular pressor responsiveness to vasoconstrictors during pregnancy may be due to impaired L-type voltage-dependent calcium channels (L-VDCC). Bay K 8644 (BAY), an L-VDCC agonist, was infused in pregnant and nonpregnant anesthetized rabbits (10, 20, 40, and 60 μg/kg) and pregnant and nonpregnant conscious, chronically instrumented (conscious) rabbits (10, 25, and 50 μg/kg). BAY infusions resulted in greater elevation of mean arterial pressure in both anesthetized pregnant ( n = 6) vs. nonpregnant ( n = 6) ( P < 0.05) and conscious pregnant ( n = 10) vs. nonpregnant ( n = 10) rabbits ( P < 0.05). Fractional increase over baseline of total peripheral resistance index was greater in pregnant (36 ± 5 to 78 ± 14%) vs. nonpregnant rabbits (14 ± 4 to 52 ± 6%) ( P< 0.02). Cardiac output index did not differ. There was a single high-affinity L-VDCC antagonist aortic binding site with similar number and affinity in pregnant ( n = 7) and nonpregnant ( n = 7) rabbits. In conclusion, stimulation of L-VDCC induces greater pressor responses in pregnant rabbits with heightened peripheral vasoconstriction. This does not appear to be due to a change in L-VDCC receptor parameters.
Pre- and postjunctional α2-adrenergic receptors in fetal and adult ovine cerebral arteries
Authors: Bishai John M. , Penninga Luit , Nijland Roel , Meulenaar Rogier , Gheorghe Ciprian P. , Zhao Yu , Buchholz John N. , Zhang Lubo , Longo Lawrence D.
Published: March 2015

In ovine cerebral arteries, adrenergic-mediated vasoconstrictor responses differ significantly with developmental age. We tested the hypothesis that, in part, these differences are a consequence of altered α2-adrenergic receptor (α2-AR) density and/or affinity. In fetal (∼140 days) and adult sheep, we measured α2-AR density and affinity with the antagonist [3H]idazoxan in main branch cerebral arteries and other vessels. We also quantified contractile responses in middle cerebral artery (MCA) to norepinephrine (NE) or phenylephrine in the presence of the α2-AR antagonists yohimbine and idazoxan and contractile responses to the α2-AR agonists clonidine and UK-14304. In fetal and adult cerebral artery homogenates, α2-AR density was 201 ± 18 and 52 ± 6 fmol/mg protein, respectively ( P< 0.01); however, antagonist affinity values did not differ. In fetal, but not adult, MCA, 10−7 M yohimbine significantly decreased the pD2 for NE-induced tension in the presence of 3 × 10−5 M cocaine, 10−5 M deoxycorticosterone, and 10−6 M tetrodotoxin. In fetal, but not adult, MCA, UK-14304 induced a significant decrease in pD2 for the phenylephrine dose-response relation. In addition, stimulation-evoked fractional NE release was significantly greater in fetal than in adult cerebral arteries. In the presence of 10−6 M idazoxan to block α2-AR-mediated inhibition of prejunctional NE release, the fractional NE release was significantly increased in both age groups. We conclude that in fetal and adult ovine cerebral arteries, α2-AR appear to be chiefly prejunctional. Nonetheless, the fetal cerebral arteries appear to have a significant component of postjunctional α2-AR.
Chronic cardiovascular and renal actions of leptin during hyperinsulinemia
Authors: Kuo Jay J. , Jones O. Barrett , Hall John E.
Published: March 2015

Hyperinsulinemia and hyperleptinemia occur concurrently in obese subjects, and both have been suggested to mediate increased blood pressure associated with excess weight gain. The goal of this study was to determine whether chronic hyperleptinemia exacerbates the effects of insulin on arterial pressure and renal function. Group I and II rats were infused with insulin (1.5 mU · kg−1 · min−1) for 21 days while maintaining euglycemia. After 7 days of insulin infusion, group II rats received leptin (1.0 μg · kg−1 · min−1) for 7 days, concomitant with insulin. Insulin plus glucose infusion reduced food intake to 55 ± 7% of control, while leptin + insulin lowered food intake further to 22 ± 4% of the initial control. Insulin initially raised mean arterial pressure (MAP) by 12 ± 1 mmHg; then MAP declined to 5–8 mmHg above control during continued hyperinsulinemia. Leptin + insulin infusion increased MAP by 7 ± 2 mmHg above the level observed in rats infused with insulin alone. Insulin raised heart rate (HR) by 17 ± 5 beats/min, whereas leptin + insulin increased HR by 34 ± 5 beats/min. Thus leptin appears to increase the effects of insulin to suppress appetite and to raise arterial pressure and HR.
Maturation-dependent changes of angiotensin receptor expression in fowl
Authors: Nishimura H. , Yang Y. , Hubert C. , Gasc J.-M. , Ruijtenbeek K. , De Mey J. , Boudier H. A. J. Struijker , Corvol P.
Published: March 2015

An angiotensin (ANG) receptor homologous to the type 1 receptor (AT1) has been cloned in chickens (cAT1). We investigated whether cAT1expression in various tissues shows maturation/age-dependent changes. cAT1mRNA levels detected in renal glomeruli [in situ hybridization (ISH)] and kidney extract (RT-PCR) are significantly ( P < 0.01) higher in 19-day embryos (EB) than in chicks (CH, 2–3 wk) and pullets/cockerels (PL/CK, 14–16 wk). The levels in adrenal glands (concentrated in subcapsular regions) are high in EB and further increased in CH and PL/CK. cAT1mRNA is also detectable in smooth muscle (SM)/adventitia of EB and CH aorta and in the adventitia, but not SM, from PL/CK aortas. The endothelia from small arteries and arterioles, but not from aorta, express cAT1mRNA (ISH). In all age groups, ANG II induces profound endothelium-dependent relaxation of abdominal aorta, partly (37–47%) inhibitable ( P < 0.01) by Nω-nitro-l-arginine methyl ester (l-NAME, 10-4M), suggesting the presence of ANG receptor in endothelium. l-NAME-resistant ANG II relaxation, examined in a limited number of EB or CH aortas, was reduced by 125 mM K+or apamin plus charybdotoxin. The results suggest that 1) cAT1is present in kidney, adrenal gland, and vascular endothelium (heterogeneity exists among arteries) of EB, CH, and PL/CK, and in aortic SM/adventitia of EB/CH but only in adventitia of PL/CK; 2) levels of cAT1gene expression change during maturation in a tissue-specific manner; and 3) ANG II-induced relaxation may be partly attributable to nitric oxide and potassium channel activation.
M3-receptor knockout mice: muscarinic receptor function in atria, stomach fundus, urinary bladder, and trachea
Authors: Stengel Peter W. , Yamada Masahisa , Wess Jürgen , Cohen Marlene L.
Published: March 2015

Negative chronotropic and smooth muscle contractile responses to the nonselective muscarinic agonist carbamylcholine were compared in isolated tissues from M3-muscarinic receptor knockout and wild-type mice. Carbamylcholine (10−8–3.0 × 10−5 M) induced a concentration-dependent decrease in atrial rate that was similar in atria from M3-receptor knockout and wild-type mice, indicating that M3 receptors were not involved in muscarinic receptor-mediated atrial rate decreases. In contrast, the M3 receptor was a major muscarinic receptor involved in smooth muscle contraction of stomach fundus, urinary bladder, and trachea, although differences existed in the extent of M3-receptor involvement among the tissues. Contraction to carbamylcholine was virtually abolished in urinary bladder from M3-receptor knockout mice, suggesting that contraction was predominantly due to M3-receptor activation. However, ∼50–60% maximal contraction to carbamylcholine occurred in stomach fundus and trachea from M3-receptor knockout mice, indicating that contraction in these tissues was also due to M2-receptor activation. High concentrations of carbamylcholine relaxed the stomach fundus from M3-receptor knockout mice by M1-receptor activation. Thus M3-receptor knockout mice provided unambiguous evidence that M3 receptors 1) play no role in carbamylcholine-induced atrial rate reduction, 2) are the predominant receptor mediating carbamylcholine-induced urinary bladder contractility, and 3) share contractile responsibility with M2 receptors in mouse stomach fundus and trachea.
GABA-mediated neurotransmission in the ventrolateral NTS plays a role in respiratory regulation in the rat
Authors: Wasserman Adam M. , Ferreira Manuel , Sahibzada Niaz , Hernandez Yvonne M. , Gillis Richard A.
Published: March 2015

Our purpose was to determine whether endogenously released GABA in the ventrolateral nucleus of the solitary tract (vlNTS) of the rat influences respiration. Experiments were carried out in anesthetized, vagotomized and spontaneously breathing rats, and diaphragm electromyogram activity was measured while drugs affecting GABAergic neurotransmission were microinjected into the vlNTS and medial NTS (mNTS). Bilateral microinjection of nipecotic acid, 5 or 25 nmol, into the vlNTS (but not in the mNTS) produced dose-dependent increases in inspiratory duration (Ti) frequently culminating in apneustic breathing. Neither unilateral microinjection of bicuculline nor CGP-35348 (GABAB receptor antagonist) reversed this response; however, a combination of both GABA receptor antagonists effectively reversed apneustic breathing. Bilateral microinjection of either muscimol or baclofen into the vlNTS mimicked the effect of nipecotic acid. Microinjection of the bicuculline produced apnea, whereas microinjection of CGP-35348 produced a decrease in Ti and an increase in expiratory duration. Immunohistochemical analysis of the vlNTS region revealed GABAA receptors densely localized to processes, whereas GABAB immunoreactivity was localized to cell bodies. Our data indicate that GABA activity in the vlNTS is important for respiratory function.
Aortic blood flow subtraction: an alternative method for measuring total renal blood flow in conscious dogs
Authors: Sandgaard N. C. F. , Andersen J. L. , Holstein-Rathlou N.-H. , Bie P.
Published: March 2015

We have measured total renal blood flow (TRBF) as the difference between signals from ultrasound flow probes implanted around the aorta above and below the renal arteries. The repeatability of the method was investigated by repeated, continuous infusions of angiotensin II and endothelin-1 seven times over 8 wk in the same dog. Angiotensin II decreased TRBF (350 ± 16 to 299 ± 15 ml/min), an effect completely blocked by candesartan (TRBF 377 ± 17 ml/min). Subsequent endothelin-1 infusion reduced TRBF to 268 ± 20 ml/min. Bilateral carotid occlusion (8 sessions in 3 dogs) increased arterial blood pressure by 49% and decreased TRBF by 12%, providing an increase in renal vascular resistance of 69%. Dynamic analysis showed autoregulation of renal blood flow in the frequency range <0.06–0.07 Hz, with a peak in the transfer function at 0.03 Hz. It is concluded that continuous measurement of TRBF by aortic blood flow subtraction is a practical and reliable method that allows direct comparison of excretory function and renal blood flow from two kidneys. The method also allows direct comparison between TRBF and flow in the caudal aorta.
Norepinephrine release in brown adipose tissue remains robust in cold-exposed senescent Fischer 344 rats
Authors: Gabaldón Annette M. , Gavel David A. , Hamilton Jock S. , McDonald Roger B. , Horwitz Barbara A.
Published: March 2015

Near the end of life, old F344 rats undergo a transition, marked by spontaneous and rapidly declining function. Food intake and body weight decrease, and these rats, which we call senescent, develop severe hypothermia in the cold due in part to blunted brown fat [brown adipose tissue (BAT)] thermogenesis. We tested the hypothesis that this attenuation may involve diminished sympathetic signaling by measuring cold-induced BAT norepinephrine release in freely moving rats using linear microdialysis probes surgically implanted into interscapular BAT 24 and 48 h previously. In response to 2 h at 15°C, senescent rats increased BAT norepinephrine release 6- to 10-fold but did not maintain homeothermy. This increase was comparable to that of old presenescent (weight stable) rats that did maintain homeothermy during even greater cold exposure (2 h at 15°C followed by 1.5 h at 8°C). Tail temperatures, an index of vasoconstrictor responsiveness to cold, exhibited similar cooling curves in presenescent and senescent rats. Thus cold-induced sympathetic signaling to BAT and tail vasoconstrictor responsiveness remain robust in senescent rats and cannot explain their cold-induced hypothermia.
Habitual physical activity facilitates stress-induced HSP72 induction in brain, peripheral, and immune tissues
Authors: Campisi Jay , Leem Ted H. , Greenwood Ben N. , Hansen Michael K. , Moraska Albert , Higgins Karianne , Smith Taro P. , Fleshner Monika
Published: March 2015

The mechanism(s) for how physically active organisms are resistant to many damaging effects of acute stressor exposure is unknown. Cellular induction of heat-shock proteins (e.g., HSP72) is one successful strategy used by the cell to survive the damaging effects of stress. It is possible, therefore, that the stress-buffering effect of physical activity may be due to an improved HSP72 response to stress. Thus the purpose of the current study was to determine whether prior voluntary freewheel running facilitates the stress-induced induction of HSP72 in central (brain), peripheral, and immune tissues. Adult male Fischer 344 rats were housed with either a mobile running wheel (Active) or a locked, immobile wheel [sedentary (Sed)] for 8 wk before stressor exposure. Rats were exposed to either inescapable tail-shock stress (IS; 100 1.6-mA tail shocks, 5-s duration, 60-s intertrial interval), exhaustive exercise stress (EXS; treadmill running to exhaustion), or no stress (controls). Blood, brain, and peripheral tissues were collected 2 h after stressor termination. The kinetics of HSP72 induction after IS was determined in cultured mesenteric lymph node cells. Activation of the stress response was verified by measuring serum corticosterone (RIA). Tissue and cellular HSP72 content were measured using HSP72 ELISA in cell lysates. Both Active and Sed rats had elevated levels of serum corticosterone after stress. In contrast, Active but not Sed rats exposed to IS and/or EXS had elevated HSP72 in dorsal vagal complex, frontal cortex, hippocampus, pituitary, adrenal, liver, spleen, mesenteric lymph nodes, and heart. In addition, Active rats exposed to IS demonstrated a faster induction of lymphocyte HSP72 compared with Sed rats. Thus Active rats responded to stress with both greater and faster HSP72 responses compared with Sed rats. These results indicate that previous physical activity potentiates HSP72 expression after a wide range of stressors. Facilitated induction of HSP72 may contribute to the increased stress resistance previously reported in physically active organisms.
CO2transduction in avian intrapulmonary chemoreceptors is critically dependent on transmembrane Na+/H+exchange
Authors: Hempleman Steven C. , Adamson Thomas P. , Begay Rowin S. , Solomon Irene C.
Published: March 2015

Avian intrapulmonary chemoreceptors (IPC) are vagal respiratory afferents that are inhibited by high lung Pco2and excited by low lung Pco2. Previous work suggests that increased CO2inhibits IPC by acidifying intracellular pH (pHi) and that pHiis determined by a kinetic balance between the rate of intracellular carbonic anhydrase-catalyzed CO2hydration/dehydration and transmembrane extrusion of acids and/or bases by various exchangers. Here, the role of amiloride-sensitive Na+/H+exchange (NHE) in the IPC CO2response was tested by recording single-unit action potentials from IPC in anesthetized ducks, Anas platyrhynchos. For each of the IPC tested, blockade of the NHE using dimethyl amiloride (DMA) elicited a marked (>50%) dose-dependent decrease in mean IPC discharge ( P < 0.05), suggesting that NHE is important for pHiregulation and CO2transduction in IPC. In addition, activation of the NHE using 12-O-tetradecanoylphorbol 13-acetate stimulated six of the seven IPC tested, although the overall effect was not statistically significantly ( P = 0.07). Taken together, these findings suggest that CO2transduction in IPC is dependent on transmembrane NHE although it is likely to be much slower than carbonic anhydrase-catalyzed hydration-dehydration of CO2.
Adrenomedullin binding protein-1 modulates vascular responsiveness to adrenomedullin in late sepsis
Authors: Zhou Mian , Ba Zheng F. , Chaudry Irshad H. , Wang Ping
Published: March 2015

Adrenomedullin (AM), a potent vasodilatory peptide, plays an important role in initiating the hyperdynamic response during the early stage of sepsis. Moreover, the reduced vascular responsiveness to AM appears to be responsible for the transition from the early, hyperdynamic to the late, hypodynamic phase of sepsis. Although the novel specific AM binding protein-1 (AMBP-1) enhances AM-mediated action in a cultured cell line, it remains to be determined whether AMBP-1 plays any role in modulating vascular responsiveness to AM during sepsis. To study this, adult male rats were subjected to sepsis by cecal ligation and puncture (CLP). The thoracic aorta was harvested for determination of AM-induced vascular relaxation. Aortic levels of AMBP-1 were determined by Western blot analysis, and AM receptor gene expression in the aortic tissue was assessed by RT-PCR. The results indicate that AMBP-1 significantly enhanced AM-induced vascular relaxation in aortic rings from sham-operated animals. Although vascular responsiveness to AM decreased at 20 h after CLP (i.e., the late, hypodynamic stage of sepsis), addition of AMBP-1 in vitro restored the vascular relaxation induced by AM. Moreover, the aortic level of AMBP-1 decreased significantly at 20 h after CLP. In contrast, AM receptor gene expression was not altered under such conditions. These results, taken together, suggest that AMBP-1 plays an important role in modulating vascular responsiveness to AM, and the reduced AMBP-1 appears to be responsible for the vascular AM hyporesponsiveness observed during the hypodynamic phase of sepsis.
Subdiaphragmatic vagotomy fails to inhibit intravenous leptin-induced IL-1β expression in the hypothalamus
Authors: Hosoi Toru , Okuma Yasunobu , Ono Atsushi , Nomura Yasuyuki
Published: March 2015

Leptin is known to be an important circulating signal for regulation of food intake and body weight. Recent evidence has suggested that leptin is involved in infection and inflammation. The afferent vagus nerve is known to be an important component for transmitting peripheral immune signals to the brain, such as interleukin (IL)-1β expression in the brain, anorexia, and fever responses. In the present study, we investigated whether intravenous leptin-induced IL-1β expression in the hypothalamus is mediated via afferent vagus nerve. IL-1β transcripts in the hypothalamus were significantly increased on RT-PCR assessment 1 h after the administration of leptin (1 mg/kg iv) to mice. Subdiaphragmatic vagotomy did not significantly modify intravenous leptin-induced IL-1β expression in the hypothalamus compared with that in sham-treated mice. These data suggest that circulating leptin directly acts in the brain independently of afferent vagus nerve input originating from the subdiaphragmatic organs.
Postnatal intracerebroventricular exposure to neuropeptide Y causes weight loss in female adult rats
Authors: Varma Amit , He Jing , Weissfeld Lisa , Devaskar Sherin U.
Published: March 2015

We investigated the effect of repetitive postnatal (2–7 days) intracerebroventricular administration of neuropeptide Y (NPY) on food intake and body weight gain in the 3- to 120-day-old Sprague-Dawley rats. NPY caused a 32% transient increase in body weight gain with elevated circulating insulin concentrations within 24 h. This early intervention led to the persistence of hyperinsulinemia and relative hyperleptinemia with euglycemia in the 120-day-old female alone. This perturbation was associated with 50% suppression in adult female hypothalamic NPY concentrations and a 50–85% decline in NPY immunoreactivity in the paraventricular and arcuate nuclei. This change was paralleled by a ∼20% decline in food intake and body weight gain at 60 and 120 days. However, when exogenous NPY was stereotaxically reinjected into the paraventricular nucleus of the ∼120-day-old adult females who were pretreated with NPY postnatally, an increase in food intake and body weight gain was noted, attesting to no disruption in the NPY end-organ responsivity. We conclude that postnatal intracerebroventricular NPY has long-lasting effects that predetermine the resultant adult phenotype in a sex-specific manner.
NK1 receptor and its interaction with NMDA receptor in spinal c-fos expression after lower urinary tract irritation
Authors: Mitsui Takahiko , Kakizaki Hidehiro , Matsuura Shinobu , Tanaka Hiroshi , Ameda Kaname , Yoshioka Mitsuhiro , Koyanagi Tomohiko
Published: March 2015

The role of neurokinin 1 (NK1) receptor and possible interaction between NK1 and N-methyl-d-aspartic acid (NMDA) glutamatergic receptors were investigated on spinal c- fos expression after lower urinary tract irritation with acetic acid infusion in rats. At both levels of the first (L1) and sixth lumbar (L6) spinal cord, where most of hypogastric nerve and pelvic nerve afferent terminals project, respectively, the selective NK1 receptor antagonist CP-99,994 dose dependently reduced the total number of c- fos protein (Fos)-positive cells. However, CP-100,263, the enantiomer of CP-99,994 with a very low affinity for NK1receptor, did not have any effect on the total number of Fos-positive cells. Coadministration of a low dose (1 mg/kg) of CP-99,994 and NMDA receptor antagonist (MK-801), either of which alone did not affect c- fos expression, significantly inhibited c- fosexpression at both levels of the spinal cord. Regarding regional differences, the number of Fos-positive cells decreased significantly at all regions of the L6 level, but only at the dorsal horn of the L1 level. These results indicate that NK1 receptor is involved in spinal c- fosexpression after lower urinary tract irritation and that NK1 and NMDA receptors have a synergistic interaction in the spinal processing of nociceptive input from the lower urinary tract.
Activated epidermal growth factor receptor (ErbB1) protects the heart against stress-induced injury in mice
Authors: Pareja Miguel , Sánchez Olga , Lorita Jordi , Soley Maria , Ramírez Ignasi
Published: March 2015

Acute, high-intensity stress induces necrotic lesions in the heart. We found that restraint-and-cold (4°C) exposure (RCE) raises plasma lactate dehydrogenase (LDH), creatine kinase (CK), and transaminase activity in a time-dependent manner, with a peak value 7 h after stimulus cessation. At 24 h, signs of necrotic lesions were observed in paraffin sections stained with hematoxylineosin: focal accumulation of mononuclear cells in subendocardial areas of the left ventricle wall and focal hemorrhage in papillary muscles. In contrast, intermale fighting (IF) did not increase plasma CK activity, although LDH and transaminase activities did increase. In IF, no histological evidence of heart injury was observed. Because IF, but not RCE, increased plasma epidermal growth factor (EGF) concentration by ∼1,000-fold, we hypothesized that EGF receptor (ErbB1) activation may protect the heart against stress-induced injury. To examine this hypothesis, we injected the ErbB1 tyrosine kinase inhibitor tyrphostin AG-1478 (25 mg/kg ip) immediately before mice were exposed to IF. After 3 h, plasma activities of LDH-1 and CK increased. Plasma enzyme activities were as low in control mice (injected with vehicle alone) as in nonfighting mice. In the last experiment, we injected EGF (0.25 mg/kg ip) 20 min before exposing mice to RCE. After 7 h, plasma LDH-1 and CK activities were significantly lower in these animals than in mice injected with vehicle. The effect required ErbB1 activation, because simultaneous administration of AG-1478 completely abolished the effect of exogenous EGF. We conclude that activated ErbB1, by endogenous or exogenous ligands, may protect the heart against stress-induced injury.
Unique endothelin receptor binding in kidneys of ETBreceptor deficient rats
Authors: Taylor Traci A. , Gariepy Cheryl E. , Pollock David M. , Pollock Jennifer S.
Published: March 2015

Gariepy and colleagues (Gariepy CE, Williams SC, Richardson JA, Hammer RE, and Yanagisawa M. J Clin Invest 102: 1092–1101, 1998.) developed rescued spotting-lethal rats that carry a naturally occurring deletion of the endothelin (ET) type B receptor gene resulting in a lack of functional renal ETBreceptor expression. It has been shown that rats homozygous ( sl/sl) for the deletion have elevated plasma ET-1 levels; thus, the purpose of this study was to determine whether this deletion would result in a downregulation of ETAreceptors in renal tissue. ET-1 and ET-3 binding experiments were performed with cortex, outer medullary, and inner medullary membranes of heterozygous ( sl/+) and sl/sl ETBreceptor-deficient rats.125I-labeled ET-1 binding in sl/sl cortex and outer medulla was significantly lower than cortex and outer medulla from sl/+ rats. In contrast to sl/+ rats, [125I]ET-3 binding was not detected in the cortex and outer medulla of sl/sl rats, indicating a lack of ETBreceptor expression. The inner medulla of sl/+ rats also demonstrated an abundance of ETBreceptors. Surprisingly, however, we also observed significant [125I]ET-3 binding in the sl/sl inner medulla. Furthermore, ET-3 binding in the inner medulla could be blocked with an ETAreceptor antagonist in sl/sl rats but not in tissue from sl/+ rats. These studies indicate that rats deficient in ETBreceptors have decreased renal cortical and outer medullary ETAreceptor number, most likely in response to elevated plasma ET-1 levels. In addition, homozygous ETB-deficient rats express a novel inner medullary ET-3 binding site.
Quinine and citric acid elicit distinctive Fos-like immunoreactivity in the rat nucleus of the solitary tract
Authors: Travers Susan P.
Published: March 2015

The present experiment investigated Fos-like immunoreactivity (FLI) in the nucleus of the solitary tract (NST) after intraoral infusions of 0.1 M citric acid, 0.3 M NaCl, and 0.3–30 mM quinine monohydrochloride (QHCl) in awake, behaving rats. Increases in QHCl concentration produced increases in the numbers of FLI-labeled neurons in the rostral part of the intermediate (ir) and rostral (r) NST, but the topographic distribution of FLI was consistent across QHCl concentrations and distinctive compared with effects of citric acid. Quinine elicited FLI concentrated in the medial third of the nucleus; acid elicited more broadly distributed FLI concentrated farther laterally. Surprisingly, in contrast to QHCl and citric acid, NaCl produced FLI that was indistinguishable from that produced by water. Although the functional significance of these patterns is unknown, citric acid and QHCl are nonpreferred stimuli but produced different oromotor behaviors. QHCl (30 mM) elicited ∼3.2 times as many gapes as citric acid (0.1 M), and acid elicited more ingestive responses. Parallel differences in FLI expression suggest that different NST regions may have distinctive roles in triggering oromotor behaviors.
Cardiac adenosine production in rat genetic models of low and high exercise capacity
Authors: Walker Jon P. , Barbato John C. , Koch Lauren Gerard
Published: March 2015

We previously demonstrated that Copenhagen (COP) and DA inbred rat strains show a wide difference in a test for aerobic treadmill running that correlated positively with isolated cardiac function. The purpose of this study was to test adenosine production as a candidate intermediate phenotype that may explain part of the difference in running and cardiac performance in these genetic models for low and high aerobic capacity. Adenosine production was measured as the activity of soluble 5′-nucleotidase and membrane-bound ecto-5′-nucleotidase in the membrane pellet and supernatant fractions of left and right ventricular muscle and gracilis muscle taken from 10 DA and 10 COP rats. Ecto-5′-nucleotidase activity in the membrane pellet of hearts from both DA and COP accounted for the vast majority of the total tissue adenosine production (>90% in the left ventricle and >80% in the right ventricle). Ecto-5′-nucleotidase activity in the pellet fraction was significantly higher in the left (22.4%) and right (46.1%) ventricles of DA rats compared with COP rats, with no differences in total protein content. There were no significant differences between the strains for 5′-nucleotidase activity in the cardiac supernatant, the gracilis pellet, or the gracilis supernatant. These data support the hypothesis that an increase in cardiac adenosine production may contribute to the greater aerobic running capacity of the DA rats.
Model of functional cardiac aging: young adult mice with mild overexpression of serum response factor
Authors: Zhang Xiaomin , Azhar Gohar , Furr Maxwell C. , Zhong Ying , Wei Jeanne Y.
Published: March 2015

Serum response factor (SRF) is an important transcription factor that may have a role in the maintenance of cardiac structure and function. The level of SRF mRNA expression increases ∼16% in the hearts of mice during adult aging. To model the effect of mild SRF elevation in the aging heart, transgenic mice with low levels of SRF overexpression were generated. By 6 mo of age, the transgenic mice had a 19% increase of heart-to-body weight ratio compared with nontransgenic mice. In addition, they had a 12% increase in myocyte size, a 6.7% increase in collagen deposition, and altered gene expression of a number of muscle-specific and cardiac genes. Doppler echocardiography revealed that these transgenic mice had increased left ventricular wall thickness and decreased left ventricular (LV) volumes, increased LV stiffness with 20% reduction in early diastolic LV filling (peak E), and 35% decline in peak E-to-peak A (late diastolic filling) ratio. The observed changes, especially those in the E/A ratio, are similar to those seen clinically in late life as a part of human adult myocardial aging.