bluuebunny/crossref_metadata_2025 huggingface dataset:
Glyconeogenic and oxidative lactate utilization in skeletal muscle
Authors: McDermott John C. , Bonen Arend
Published: April 2011

In this article we present a synthesis of recent information concerning the fate of lactate in skeletal muscle. This is important since lactate is continuously produced by skeletal muscle at rest and at all levels of exercise. Therefore, the disposal of lactate as an 'intermediary' metabolite is discussed. The two primary fates of lactate in skeletal muscle are (1) oxidation and (2) glycogen synthesis (glyconeogenesis). From recent evidence it seems relatively clear that glycogen formation in muscle is primarily dependent on glucose, although in fast twitch muscles a considerable proportion of lactate can account for muscle glycogen formation, especially immediately after exercise when circulating lactate levels are elevated. Exactly how lactate is converted to glycogen is not known yet, but an extramitochondrial pathway that is divergent from the hepatic gluconeogenic pathway seems likely. Oxidation of lactate is quantitatively the most important means of disposing of lactate, whether in exercising or nonexercising muscle. The lactate gradient between muscle and blood may be an important factor dictating whether lactate is taken up or released by muscle, independent of whether the muscle is active or not. Finally a novel role for epinephrine is considered that may be important for the mitochondrial oxidation of lactate.Key words: lactate, glyconeogenesis, oxidation, skeletal muscle.
Relationship between potency of L-isoprenaline and β-adrenoceptor density estimated in single cells from tracheal smooth muscles of guinea pigs of different ages
Authors: Takayanagi Issei , Satoh Mitsutoshi , Kokubu Noriko , Kato Teruko
Published: April 2011

An age-related change in potency of L-isoprenaline in the presence of ascorbic acid, desmethylimipramine, corticosterone, pargyline, and phentolamine was obtained in tracheal strips from guinea pigs of differing ages between 6 and 40 weeks. The potency in the strips from 100-week-old guinea pigs did not significantly differ from that in strips from 40-week-old animals. Single cells were prepared from the tracheal muscles of 6-, 10-, 40-, and 100-week-old guinea pigs. The specific binding of [3H]dihydroalprenolol to the single cells was saturable. The dissociation constants of [3H]dihydroalprenolol were in good agreement with those of the membrane fractions from the guinea-pig tracheal muscles, and did not change with age. An excellent relationship between the potency of L-isoprenaline and the maximum binding of [3H]dihydroalprenolol estimated in the preparations from 6- to 40-week-old guinea pigs was found, suggesting that the increase in the potency of L-isoprenaline is due to the increase in the maximum binding or receptor density. The value in the preparations from 100-week-old guinea pigs deviated significantly from the regression line. This suggests the possibility that the decrease in potency in the strips from 100-week-old animals is due to a change in post β-receptor processes in responsiveness.Key words: guinea-pig trachea, single cells, β-receptor density, ageing, dissociation constant.
Signal transduction in smooth muscle as studied by the subcellular membrane approach
Authors: Kwan Chiu-Yin
Published: April 2011

Many of the contractile regulatory events in smooth muscle reside in various cellular membrane components as functional membrane constituents that interact in a variably complex manner. The physiological handling of ionized calcium (Ca2+), which serves multiple roles as an extracellular signal, a second messenger, and an activator interacting directly with myofilaments to effectuate contractile responses, referred to as Ca2+ signalling processes, represents an integral part of a more complicated membrane transduction mechanism. The subcellular membrane approach toward the understanding of Ca2+ signalling as well as the transduction mechanisms involving membrane receptors, GTP binding proteins, ion channels, membrane-bound enzymes, and the production of intracellular second messengers has made a significant contribution in smooth muscle research for the past decade. This review summarizes the current state of knowledge about the multiplicity of interactions between Ca2+ and various membrane constituents in the surface membranes and sarcoplasmic reticulum, such as Ca2+ binding, Ca2+ ATPase pumps, Ca2+ channels, and Ca2+Na+ or related ion exchangers. A number of recent novel findings from this laboratory have also been discussed. First of all, the technical refinement of membrane separation and characterization, which permits better identification of neuronal membranes in highly innervated smooth muscle tissues, led to the distinction of prejunctional and postjunctional membrane receptors. Secondly, unlike the Ca2+-release channels labelled with [3H]inositol 1,4,5-trisphosphate, the other type of internal membrane Ca2+-release channels labelled by [3H]ryanodine has been identified only recently in smooth muscle. Thirdly, the successful use of thapsigargin and cyclopiazonic acid as selective inhibitors for the sarcoplasmic reticulum Ca2+ pump in smooth muscle provided novel pharmacological tools to probe the refilling mechanisms of internal Ca2+ stores. Finally, the intriguing relationship between, and regulation of, α-adrenoceptor subtypes in vascular smooth muscles underscores the complexity of their transducing mechanisms and associated utilization of Ca2+.Key words: smooth muscle, sarcoplasmic reticulum, membrane receptors, calcium signalling, ion channels.
Cultured smooth muscle approach in the study of hypertension
Authors: Pang Stephen C. , Venance Shannon L.
Published: April 2011

The systemic vasculature is known to undergo marked change in both human and experimental hypertension. The in vitro study of individual cellular components from the blood vessel wall and the regulation of their intracellular biochemical processes will aid in developing an understanding of the pathogenesis of hypertension. Vascular smooth muscle cells derived from the aorta and mesenteric arteries of normotensive and hypertensive rats can be successfully maintained in culture, providing a system free of confounding variables such as blood pressure. To assist in fully understanding the pathophysiology of hypertension, this cell culture model can be used to examine interactions between receptor and ligand, the transduction of an associated signal, characterization of subsequent intracellular responses and ultimately, quantification of a physiological and functional consequence of these events, for example, proliferation. The application of in vitro techniques to hypertension research will continue to contribute new knowledge to increase our understanding of the mechanisms behind the hypertensive disease process.Key words: experimental hypertension, spontaneously hypertensive rat, vascular smooth muscle, aorta, mesenteric arteries, cell culture technique.
Hypertension during chronic exposure to cold: comparison between Sprague–Dawley and Long–Evans strains
Authors: Riesselmann Anne , Baron Andreas , Fregly Melvin J. , Bergen Patricia van
Published: April 2011

It is now well established that chronic exposure of rats to cold (5–6 °C) induces an elevation of systolic, diastolic, and mean blood pressures and cardiac hypertrophy within 3 weeks. Since rats of the Long–Evans (LE) strain are known to be resistant to the induction of deoxycorticosterone salt induced hypertension, their cardiovascular responses to chronic exposure to cold were compared with those of rats of the Sprague–Dawley (SD) strain. The results of these studies revealed clear differences between the LE and SD strains of rats. Thus, rats of the SD strain had a significant elevation in their blood pressure; a significantly increased urinary output of norepinephrine and epinephrine; a significantly greater dipsogenic responsiveness to acute administration of angiotensin II, and significant increases in weights of the heart, kidneys, adrenals, and brown adipose tissue compared with their warm-adapted controls. All of these changes are characteristic of rats acclimated to cold. In contrast, rats of the LE strain appear to be less responsive to cold in that blood pressure failed to rise as sharply and to attain as high a level. Furthermore, urinary outputs of norepinephrine and epinephrine were significantly lower in cold-treated rats of the LE strain compared with cold-treated rats of the SD strain, but dipsogenic responsiveness to angiotensin II was unchanged. Although increases in the weight of the previously mentioned organs were also observed in cold-treated rats of the LE strain compared with their warm-adapted controls, weights of the heart and interscapular brown adipose tissue of both groups were significantly less than those of counterparts of the SD strain. Thus, the results show striking differences between the two strains and suggest that a reduced secretion of catecholamines by the LE strain may be a factor in the failure of the blood pressure of these rats to reach the level of cold-exposed rats of the SD strain. Additional studies will be required to verify this suggestion.Key words: strains of rats, Long–Evans, Sprague–Dawley, cold, cold-induced hypertension, blood pressure, angiotensin II induced drinking.
Relaxant effects on iloprost in canine cerebral artery
Authors: Zhang H. , Weir B. , Doi M. , Kasuya H. , Cook D.
Published: April 2011

Iloprost caused relaxation of rings of canine cerebral arteries precontracted with prostaglandin F2α or the thromboxane A2 analogue U46619, but it was without effect on arteries precontracted with potassium chloride. Pretreatment with iloprost did not significantly affect the concentration–response curve to any agent. Contractile responses to oxyhemoglobin were completed relaxed by iloprost. In arteries from animals with moderate cerebrovascular spasm, the response to prostaglandin F2α was also reduced by iloprost. The observation that iloprost relaxes the response to oxyhemoglobin to prostaglandin F2α in spastic arteries may be of interest in the management of cerebral vasospasm.Key words: iloprost, eicosanoid, oxyhemoglobin, relaxation, vasospasm.
Competitive antagonism of pressor responses to angiotensin II and angiotensin III by the angiotensin II-1 receptor ligand losartan
Authors: Abdelrahman Aly , Pang Catherine C. Y.
Published: April 2011

Losartan (DuP 753) and PD123177 are nonpeptide angiotensin (ANG) receptor ligands for subtypes of ANG II receptors ANG II-1 and ANG II-2, respectively. We examined the effects of losartan and PD123177 on dose – mean arterial pressure (MAP) response curves for ANG II and ANG III in eight groups (n = 6 each) of conscious rats. Saline (0.9% NaCl), losartan (1 × 10−6 and 9 × 10−6 mol/kg), and PD123177 (2 × 10−5 mol/kg) were i.v. bolus injected 15 min before the construction of ANG II dose–response curves in groups I, II, III, and IV, respectively. Groups V–VIII were treated similarly to I–IV except that ANG III was given in place of ANG II. Losartan dose dependently shifted the dose–response curves of ANG II and ANG III to the right with similar dissociation constants (−log KI of 6.6 ± 0.7 and 6.6 ± 0.1 mol/kg, respectively) and no change in the maxima. PD123177 affected neither maximum MAP nor ED50 values for ANG II or ANG III. Our results show that losartan but not PD123177 is a competitive antagonist of the MAP effects of ANG II and ANG III.Key words: nonpeptide angiotensin receptor antagonist, angiotensin II, angiotensin III, blood pressure, losartan.
Central peptidergic mechanisms controlling reproductive hormone secretion: Novel methodology reveals a role for the natriuretic peptides
Authors: Samson Willis K. , Alexander Blake D. , Skala Karl D. , Huang F.-L. Steven , Fulton R. Jerrold
Published: April 2011

A variety of neural factors can influence reproductive hormone secretion by neuromodulatory actions within the hypothalamus or neuroendocrine actions within the anterior pituitary gland. Passive immunoneutralization and antagonist administration protocols have suggested physiological roles for a number of these factors; however, both experimental approaches have severe technical limitations. We have developed novel methodology utilizing cytotoxin cell targeting with neuropeptides linked to the toxic A chain of the plant cytotoxin ricin. With this methodology we can target and destroy in vivo or in vitro cells bearing receptors for that peptide. Ricin A chain conjugated to atrial natriuretic peptide (ANP), a neuropeptide known to pharmacologically inhibit luteinizing hormone-releasing hormone (LHRH) release, was injected into the cerebroventricular system of intact, cycling rats and ovariectomized rats. Cytotoxin conjugate treatment significantly lengthened the estrous cycle. In ovariectomized rats the luteinizing hormone surge induced by steroid priming was completely inhibited. LHRH content of the median eminences of these rats was not significantly altered. These data suggest that ANP binding to clearance receptors in the hypothalamus displaces the C-type natriuretic peptide (CNP) from the shared clearance receptor, making more CNP available to inhibit LHRH release. In the absence of cells bearing the clearance receptor all available CNP binds to the ANPR-B receptor and exerts its effect via an inhibitory interneuron, since LHRH fibers are spared by this treatment.Key words: atrial peptides, hypothalamus, reproduction, cytotoxin, gonadotropins.
Central arginine vasopressin and endogenous antipyresis
Authors: Pittman Quentin J. , Wilkinson Marshall F.
Published: April 2011

Arginine vasopressin (AVP) is a centrally synthesized nonapeptide that exerts classical endocrine effects as well as a host of centrally mediated actions. A strong case can be argued in support of a neurotransmitter–neuromodulator role for AVP. Acting within the central nervous system (CNS), AVP has been demonstrated to be involved in the modulation of febrile body temperature. Because AVP acts to reduce pyrogen-induced fevers, but not normal body temperature, its actions are deemed to be antipyretic. However, to demonstrate an endogenous antipyretic function, AVP must be shown to be active during conditions where fever is naturally suppressed. This review will focus on five such conditions where the absence of pyrogen-induced fever can be linked to the endogenous activity of AVP within the brain. In the neonatal rat pup, the use of specific antagonists to the AVP receptor has revealed a role for CNS AVP in the absence of fever following peripheral injections of bacterial endotoxin. These results may help to explain a similar lack of fever in other newborn species. In parturient animals a reduced or absent febrile response has been linked to the increased presence of AVP within the septal area of the brain. The combined use of AVP receptor antagonism as well as immunohistochemistry has shown enhanced AVP activity within the ventral septal area of the rat and guinea pig brain during tolerance to intravenous pyrogens. These results suggest that the mechanism of fever suppression following repeated systemic injections of bacterial pyrogen includes centrally acting AVP. Recent observations from our laboratory have revealed a suppression of fever during the rising phase of arterial blood pressure in the one-kidney, one-clip model of hypertension. The normal febrile response to prostaglandin E1 can be restored in this instance by blockade of ventral septal AVP receptors. A similar situation of lack of response to pyrogens occurs in hypotensive animals in which pressor mechanisms are activated to restore blood pressure to normal. In this, and the previous four examples, centrally acting AVP has been linked to the natural suppression of pyrogen-induced fevers. Using these models of endogenous antipyresis we will continue to investigate this phenomenon to assess the benefits to the organism as well as to examine other nonthermal host defence responses.Key words: fever, antipyretic, pyrogen, host defence, vasopressin.
Pharmacology of MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-indol-2-yl]-2,2-dimethyl propanoic acid), a potent, orally active leukotriene biosynthesis inhibitor
Authors: Brideau C. , Chan C. , Charleson S. , Denis D. , Evans J. F. , Ford-Hutchinson A. W. , Fortin R. , Gillard J. W. , Guay J. , Guévremont D. , Hutchinson J. H. , Jones T. R. , Leger S. , Mancini J. A. , McFarlane C. S. , Pickett C. , Piechuta H. , Prasit P. , Riendeau D. , Rouzer C. A. , Tagari P. , Vickers P. J. , Young R. N. , Abraham W. M.
Published: April 2011

MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-indol-2-yl]-2,2-dimethyl propanoic acid, previously L-686,708) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human and elicited rat polymorphonuclear leukocytes (PMNLs) (IC50 values 3.1 and 6.1 nM, respectively) and in human, squirrel monkey, and rat whole blood (IC50 values 510, 69, and 9 nM, respectively). MK-0591 had no effect on rat 5-lipoxygenase. MK-0591 has a high affinity for 5-lipoxygenase activating protein (FLAP) as evidenced by an IC50 value of 1.6 nM in a FLAP binding assay and inhibition of the photoaffinity labelling of FLAP by two different photoaffinity ligands. Inhibition of activation of 5-lipoxygenase was shown through inhibition of the translocation of the enzyme from the cytosol to the membrane in human PMNLs. MK-0591 was a potent inhibitor of LT biosynthesis in vivo, first, following ex vivo challenge of blood obtained from treated rats and squirrel monkeys, second, in a rat pleurisy model, and, third, as monitored by inhibition of the urinary excretion of LTE4 in antigen-challenged allergic sheep. Inhibition of antigen-induced bronchoconstriction by MK-0591 was observed in inbred rats pretreated with methysergide, Ascaris-challenged squirrel monkeys, and Ascaris-challenged sheep (early and late phase response). These results indicate that MK-0591 is a potent inhibitor of LT biosynthesis both in vitro and in vivo indicating that the compound will be suitable for assessing the role of leukotrienes in pathological situations.Key words: leukotriene, 5-lipoxygenase, leukotriene inhibitor, bronchoconstriction, inflammation, 5-lipoxygenase activating protein.
Yohimbine-precipitated clonidine withdrawal: An experimental model of the antihypertensive drug withdrawal syndrome
Authors: Penning Donald H. , Jhamandas Khem
Published: April 2011

In this study, a model of the clonidine withdrawal syndrome in normotensive rats was used to investigate the mechanisms and sites of the cardiovascular responses associated with this withdrawal. Clonidine (400 μg∙kg−1∙day−1), an α2-adrenergic receptor agonist, was administered to rats via indwelling osmotic minipumps for 7 days. Withdrawal was precipitated by an intravenous injection of the α2-adrenergic receptor antagonist yohimbine under α-chloralose anaesthesia, and the blood pressure and heart rate responses were recorded. Yohimbine (0.25, 0.50, and 1.0 mg/kg i.v.) in clonidine-treated rats provoked an immediate rise in blood pressure and heart rate. Similar injections in saline-treated rats produced slight hypotension and modestly increased the heart rate. Intracerebroventricular (i.c.v.) yohimbine injection (30 or 120 μg/kg in 10 μL volume) failed to elicit signs of withdrawal in clonidine-treated animals, but a subsequent intravenous injection of yohimbine (0.5 mg/kg) provoked brisk signs of withdrawal. Hexamethonium (2 mg/kg) pretreatment did not abolish the increase in the heart rate, but it delayed the blood pressure increase. Pretreatment with atropine sulfate (1 mg/kg) did not block the yohimbine-induced increase in heart rate or blood pressure. This study demonstrates that yohimbine can effectively produce cardiovascular signs of withdrawal in rats chronically exposed to clonidine. The lack of i.c.v. yohimbine suggests that the antagonist-precipitated withdrawal may not have a central origin. The failure of atropine to attenuate the blood pressure and heart rate responses, and the failure of hexamethonium to block the heart rate response and the late phase of blood pressure response, suggest that central cholinergic hyperactivity is not substantially involved in the yohimbine-precipitated clonidine withdrawal. It is suggested that under the conditions of clonidine exposure used here, the yohimbine-precipitated response may arise from increased activity of peripheral sympathetic mechanisms.Key words: yohimbine, clonidine withdrawal syndrome.
Vasodepressor reaction induced by inferior vena caval occlusion and isoproterenol
Authors: Waxman Menashe B. , Asta John A. , Cameron Douglas A. , Endrenyi Laszlo
Published: April 2011

Testing for the susceptibility for vasodepressor reaction in humans involves the combination of restriction of venous return by passive upright tilting and the administration of isoproterenol. To explore the basis of the vasodepressor test in humans, the present experiment examined whether a reduced cardiac volume coupled with adrenergic stimulation causes a vasodepressor reaction in rats. Vasodepressor reaction was defined as paradoxical heart rate slowing in conjunction with hypotension during inferior vena caval occlusion. Inferior vena caval occlusion was performed for 60 s and the maximum changes in R-R were measured during seven states as follows. (A) Under control conditions inferior vena caval occlusion alone accelerated the rate in 32 of 32 rats (ΔR-R, −13.9 ± 1.7 ms, p < 0.001). (B) When inferior vena caval occlusion was performed during an infusion of isoproterenol (0.5–1.0 μg∙min−1), a vasodepressor reaction was observed in all rats as the heart rate slowed (ΔR-R, +138.1 ± 14.8 ms, p < 0.001). The vasodepressor reaction was further examined during isoproterenol and inferior vena caval occlusion under five additional states. (C) After atropine the vasodepressor reaction was unchanged (ΔR-R, +132.7 ± 24.8 ms, p < 0.001). (D) After bilateral vagotomy the paradoxical slowing was eliminated. (E) After intrapericardial lidocaine the paradoxic slowing was eliminated. (F) After bilateral stellectomy nonsignificant slowing was still present, but this was markedly reduced when compared with B (p < 0.001). (G) Following chronic chemical sympathetic denervation with 6-hydroxydopamine the paradoxic bradycardia was eliminated. Conclusions: (1) Reduced cardiac volume combined with adrenergic stimulation can stimulate a vasodepressor reaction; (2) the vasodepressor reaction requires signalling by the afferent but not efferent vagal fibers; (3) the bradycardia is mainly due to withdrawal of sympathetic efferent tone.Key words: vasodepressor reaction, venous return, isoproterenol.
Reduced Ca2+-induced Ca2+ release from skeletal muscle sarcoplasmic reticulum at low pH
Authors: Williams Jay H. , Ward Christopher W.
Published: April 2011

The purpose of this investigation was to determine the effects of reduced pH on Ca2+-induced Ca2+ release (CICR) from skeletal muscle sarcoplasmic reticulum (SR). Frog semitendinosus fiber bundles (1–3/bundle) were chemically skinned via saponin treatment (50 μg/mL, 20 min), which removes the sarcolemma and leaves the SR functional. The SR was first depleted of Ca2+ then loaded for 2 min at pCa (log free Ca2+ concentration) 6.6. CICR was then evoked by exposing the fibers to pCa 5–7 for 5–60 s. CICR was evoked both in the absence of ATP and Mg2+ and in the presence of β,γ-methyieneadenosine-5′-triphosphate (AMPPCP, a nonhydrolyzable form of ATP) and Mg2+. Ca2+ remaining in the SR was then assayed via caffeine (25 mM) contracture. In all cases, CICR evoked at pH 6.5 resulted in larger caffeine contractures than that evoked at 7.0, suggesting that more Ca2+ was released during CICR at the higher pH. Accordingly, rate constants for CICR were significantly greater at pH 7.0 than at pH 6.5. These results indicate that reduced pH depresses CICR from skeletal muscle SR.Key words: sarcoplasmic reticulum, skeletal muscle, calcium ions, hydrogen ions, fatigue.
Electrolytes, protein, and lactate dehydrogenase isozymes of parotid saliva in mineralocorticoid-treated rats
Authors: Yu Zong-Han
Published: April 2011

Small quantities of parotid saliva were obtained from 7 of 11 rats in which hypokalemia was induced by treatment with deoxycorticosterone acetate (DOCA). Thirst in the treated rats was indicated by an increase in water consumption. A decrease of 28% in plasma potassium levels indicated that the DOCA-treated rats had become hypokalemic; chloride decreased 6–7% while sodium was unchanged. Saliva showed significant increases in potassium and protein and a decrease in sodium; lactate dehydrogenase-2 and -4 bands appeared darker on the electrophoretic profile. These changes are relevant to the clinical manifestations and diagnosis of hypokalemia.Key words: parotid saliva, hypokalemia, lactate dehydrogenase, electrolytes.
Inactivation of cytochrome P450 and inhibition of ferrochelatase by analogues of 3,5-diethoxycarbonyl-l,4-dihydro-2,4,6-trimethylpyridine with 4-nonyl and 4-dodecyl substituents
Authors: McCluskey S. A. , Riddick D. S. , Mackie J. E. , Kimmett S. M. , Whitney R. A. , Marks G. S.
Published: April 2011

Cytochrome P450- and heme-destructive effects of the 4-nonyl and 4-dodecyl analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) were determined using hepatic microsomal preparations obtained from untreated, β-naphthoflavone-treated, and phenobarbital-treated chick embryos. The 4-nonyl analogue of DDC was less efficacious than 4-ethyl DDC and 4-hexyl DDC, but more efficacious than 4-dodecyl DDC with respect to cytochrome P450-destructive activity. In all hepatic microsomal preparations, cytochrome P450 destruction by 4-nonyl DDC was accompanied by loss of microsomal heme. In contrast, 4-dodecyl DDC caused loss of heme only in hepatic microsomal preparations obtained from phenobarbital-treated chick embryos. The ability of 4-nonyl DDC and 4-dodecyl DDC to lower ferrochelatase activity was compared with that of 4-ethyl DDC and 4-hexyl DDC in cultured chick embryo hepatocytes. As the length of the 4-alkyl group was increased, the ferrochelatase-lowering efficacy and potency of the DDC analogue decreased. The 4-dodecyl DDC analogue was unable to lower ferrochelatase activity, which accorded with the finding that the administration of 4-dodecyl DDC to phenobarbital-treated rats did not lead to the accumulation of an N-alkylprotoporphyrin. The ability of 4-nonyl DDC to lower ferrochelatase activity was attributed to the formation of N-nonylprotoporphyrin IX following the administration of 4-nonyl DDC to phenobarbital-treated rats.Key words: cytochrome P450, ferrochelatase, heme.
In vivo catechol activity in the rat locus coeruleus following different nociceptive stimuli and naloxone
Authors: Hong M. , Milne B. , Loomis C. W. , Jhamandas K.
Published: April 2011

The nucleus locus coeruleus (LC) has been implicated in the processing of spinal reflexes following noxious stimuli. It has been demonstrated that noxious stimuli activate LC neuronal firing, but little is known about the neurochemical changes that might occur following such activation. To determine the effects of different noxious stimuli on LC neuronal activity, anaesthetized rats were exposed to mechanical (tail pinch), thermal (55 °C water), and chemical (5% Formalin injected in the hind paw) stimuli; the catechol oxidation current (CA∙OC), an index of noradrenergic neuronal activity, in the locus coeruleus was monitored using differential normal pulse voltammetry. In addition, the effect of the opioid antagonist naloxone on the CA∙OC in the LC was examined. Exposure to both mechanical and chemical stimuli significantly increased CA∙OC indicating an increase in LC noradrenergic neuronal activity, while the thermal stimulus had no effect. Treatment with naloxone (1 mg/kg i.v.) had no effect on CA∙OC in the LC. The results show a differential responsiveness of LC noradrenergic neurons to different modes of noxious stimuli and fail to demonstrate a tonic opioid regulation of these neurons in the anaesthetized rat.Key words: nociception, in vivo voltammetry, locus coeruleus, opioid, noradrenergic activity, naloxone.
Role of the adrenal gland in the thermal response to morphine withdrawal in rats
Authors: Katovich Michael J. , Pitman David , Schechtman Orit
Published: April 2011

Administration of naloxone to morphine-dependent rats results in an elevation of tail skin temperature and a fall in core temperature. Previous studies have demonstrated a role of the adrenal gland in the thermal responses that accompany morphine withdrawal in the rat. In the present study, experiments were designed to determine if the duration of adrenalectomy significantly influenced the thermal response observed in morphine withdrawal. In addition we evaluated the influence of the adrenal medulla and glucocorticoid replacement in adrenalectomized rats in mediating the thermal responses of the morphine-dependent rat. Ovariectomized rats were addicted to morphine and subsequently withdrawn by administration of naloxone. This treatment results in a significant rise in tail skin temperature and subsequent fall in colonic temperature. These thermal responses were not observed in morphine-naive rats. Adrenalectomy resulted in a significant attenuation of the rise in tail skin temperature associated with withdrawal. This reduced tail skin temperature response was not different among animals adrenalectomized for 1, 7, 14, 21, or 28 days. Likewise, the moderate increase in core temperature associated with morphine treatment was not observed in the adrenalectomized rats. Serum corticosteroid determinations confirmed the loss of the adrenal steroids in the adrenalectomized rats. In a subsequent experiment it was determined that adrenal demedullation did not reduce the tail skin temperature response during morphine withdrawal, and corticosteroids restored the naloxone-induced surge in tail skin temperature in morphine-dependent, adrenalectomized rats. Collectively, these data suggest a role for the adrenal gland, especially the cortical region, in allowing for full expression of the skin temperature changes associated with withdrawal in morphine-dependent animals.Key words: corticosterone, tail skin temperature, morphine withdrawal, adrenal gland, thermal response, naloxone.
Characterization of lipid uptake into rabbit jejunal brush border membrane vesicles
Authors: Keelan M. , Burdick S. , Wirzba B. , Thomson A. B. R.
Published: April 2011

The absorption of lipids is generally accepted to be mediated by a process of passive diffusion, although some recent data have raised the possibility of a mediated component. Brush border membrane vesicles (BBMV) have been widely used to study nutrient transport, but have only recently been used to examine the uptake of lipids. Using a BBMV technique validated with studies of the uptake of D-glucose, we examined the uptake of linoleic acid into the jejunum of adult rabbits. The uptake of 100 μM linoleic acid was constant between 2 and 20 min, with no overshoot observed at earlier periods. Linoleic acid uptake was suppressed by 88% with 0.6 mM phloridzin and by 58% with 0.2 mM phloretin, but uptake of linoleic acid was unaffected by the absence of sodium, by the presence of a sodium gradient, or by varying the osmolarity of the buffer. Lysis of the BBMV incubated with linoleic acid by the addition of ice-cold deionized water did not alter the amount of linoleic acid associated with the BBMV. The linoleic acid concentration curve was linear up to 160 μM, when carried out under initial rate conditions and in the presence of 2 mM taurocholic acid. These results are compatible with the process of passive uptake of linoleic acid into BBMV of rabbit jejunum, but do not exclude the possible physiological importance of a membrane fatty acid binding protein.Key words: absorption, cholesterol, fatty acids, ileum, jejunum, transport.
Antioxidant changes in heart hypertrophy: significance during hypoxia–reoxygenation injury
Authors: Kirshenbaum Lorrie A. , Singal Pawan K.
Published: April 2011

Because hypertrophied rat hearts display an increase in antioxidant enzyme activities and because hypoxia – reoxygenation injury is known to involve free radicals, we tested the hypothesis that the hypertrophied heart may be more resistant to this type of injury. Hypertrophied rat hearts after 10 weeks of chronic pressure overload showed elevated superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities and a decrease in lipid peroxidation as indicated by malondialdehyde (MDA) content. Glucose-free hypoxia for 15 min resulted in a complete failure of developed tension and about 200% increase in resting tension in both hypertrophied and sham control groups (p < 0.05). Upon reoxygenation for up to 30 min, hypertrophied hearts recovered developed tension to 60% and resting tension was higher by only 80% of prehypoxic values. In contrast, sham hearts showed only a 25% recovery of developed tension, whereas resting tension remained 130% higher than prehypoxic control values. During hypoxia, the SOD activity was significantly reduced in both sham and hypertrophied groups, whereas GSHPx was reduced only in the sham group. Upon reoxygenation there was no further change in these enzyme activities. Both the SOD and GSHPx activities in the hypertrophied group remained significantly higher than the corresponding reoxygenated sham hearts. During hypoxia, there was no apparent change in MDA content in either the sham or hypertrophied hearts. However, reoxygenation resulted in a significant increase in MDA content in both sham and hypertrophied hearts, but the MDA content was significantly less in the hypertrophied group (p < 0.05). It is suggested that maintenance of an adequate endogenous antioxidant reserve during hypoxia may be important in recovery upon reoxygenation.Key words: antioxidants, hypoxia–reoxygenation injury, heart hypertrophy.
Bradykinin binding to B2 kinin receptors and stimulation of phosphoinositide turnover and arachidonic acid release in primary cultures of cells from late pregnant rat myometrium
Authors: Tropea Margaret M. , Munoz Consuelo M. , Leeb-Lundberg L. M. Fredrik
Published: April 2011

Primary cultures of cells from late pregnant rat myometrium contain B2 kinin receptors through which bradykinin (BK) stimulates inositol phosphate (InsP) formation and arachidonic acid (20:4) release. Equilibrium binding at 4 °C revealed that [3H]BK identified a maximal number of cell surface B2 kinin receptor binding sites on rat myometrial cells of 308 ± 78 fmol/106 cells with apparently a single equilibrium dissociation constant of 1.8 ± 0.2 nM. At 37 °C, [3H]BK binding was associated with a time-dependent decrease in the reversibility of the binding. This decrease was due in part to formation of slowly dissociating cell surface receptor [3H]BK binding and in part to internalization of the receptor-bound [3H]BK. Exposure of labeled cells to BK resulted in dose-dependent increases in [3H]InsP3, [3H]InsP2 ([3H]Ins(1,4)P2), and [3H]InsP1 [([3H]Ins(1)P1) formation and [3H]20:4 release. Pretreatment with 100 ng/mL pertussis toxin did not perturb BK stimulation of [3H]InsP formation but partially (~30%) inhibited BK stimulation of [3H]20:4 release. BK stimulation of [3H]20:4 release was directly proportional to the number of receptor sites occupied by BK. In contrast, stimulation of [3H]InsP formation required a threshold level of receptor occupancy, which decreased as a function of time of BK exposure. These results show that BK interacts with B2 kinin receptors on rat myometrial cells with apparently a single affinity through which BK stimulates [3H]InsP formation and [3H]20:4 release. BK stimulation of [3H]InsP formation requires a threshold BK concentration, which decreases with time, and we suggest that the decrease is due to a time-dependent formation of a BK receptor binding state from which BK slowly dissociates.Key words: bradykinin, receptors, myometrium, inositol phosphates, arachidonic acid.
Atrial natriuretic peptide inhibits compensatory responses when cardiac performance is depressed
Authors: Ackermann Uwe , Atchison Deborah Jean , Choo Lin P'ing
Published: April 2011

We tested the hypothesis that the atrial natriuretic peptide (ANP) mediated decrease in baroreceptor sensitivity that is seen in normal rats is more pronounced in a state of depressed cardiac performance. Holtzman rats (n = 15) were injected with Adriamycin (1 mg/kg i.p. 3 times/week for 8–10 weeks). Control rats (n = 17) were injected with 0.9% saline. Experiments were done in conscious animals that had been catheterized for i.v. infusions and for measurement of arterial blood pressure (ABP) and heart rate (HR). ANP (250 ng∙kg−1∙min−1) or saline vehicle was infused i.v. Graded periodic bolus injections of phenylephrine or sodium nitroprusside were given to assess baroreceptor sensitivity (beats∙min−1∙mmHg−1) up to 60 mmHg (1 mmHg = 133.3 Pa) above and below resting ABP. The following day the experiment was repeated with the ANP–vehicle regimen reversed. Finally, the rats were anesthetized and the rate of left ventricular pressure increase (dP/dt) was measured. Data evaluation included calculation of least squares linear regression slopes of peak ΔHR vs. peak ΔABP, applying corrections for experimental errors in both the dependent and independent variables. Adriamycin rats (A) did not differ significantly from control rats (C) with respect to either initial ABP (A = 105 ± 5; C = 100 ± 3; mean mmHg ± SEM) or initial HR (335 ± 9 vs. 312 ± 13 beats∙min−1). However, their indices of cardiac performance were significantly depressed. The maximum rates of left ventricular pressure increase, +dP/dtmax, were A = 2877 ± 108 and C = 4569 ± 223 mmHg/s (p < 0.0001) and the maximum rates of decrease, −dP/dtmin, were A = −2459 ± 52 and C = −4076 ± 287 mmHg/s (p < 0.0001). Adriamycin-treated rats also showed significantly depressed baroreceptor sensitivity. This was particularly marked during blood pressure decreases in the presence of ANP. In this experimental setting, transient decreases in ABP resulted in physiologically inappropriate bradycardia. The results suggest that elevated plasma levels of ANP may have detrimental effects on mechanisms of cardiovascular compensation during heart failure.Key words: baroreflex, blood pressure regulation, adriamycin.
Fuel selection and the production of ammonium by the kidney: studies using insulin
Authors: Halperin Mitchell L. , Goguen Jeannette M. , Chen Ching-Bun
Published: April 2011

The purpose of this study was to explore the interrelations among energy turnover, the selection of fuels, and the production of ammonium (NH4+) in the kidney during chronic metabolic acidosis. Experiments were carried out in dogs because of the extensive background literature in this species. The specific question addressed was, will a diminished rate of oxidation of fatty acids in the kidney permit the rate of extraction of glutamine and the production of NH4+ to rise? Chronic metabolic acidosis was induced by the ingestion of NH4Cl for 5 days to stimulate the rate of production of NH4+. Insulin was administered to diminish the delivery of fatty acids to the kidney. The concentration of fatty acids in plasma fell from 350 ± 104 to 188 ± 45 μM, yet there was no significant increase in the rates of production of NH4+, consumption of oxygen, or extraction of glutamine after insulin. Notwithstanding, there was a significant rise in the rate of extraction of lactate by the kidney when expressed per 100-mL glomerular filtration rate. Because there was a significant decline in the level of glutamine in plasma (512 ± 76 to 359 ± 42 μM) 1 h after giving insulin, a second series of experiments was carried out. When glutamine was infused after the insulin period, there was no longer a fall in the concentration of this metabolite. Notwithstanding, the rates of extraction of glutamine and production of NH4+ were not higher in the presence of insulin. These data suggest that the rate of oxidation of fatty acids did not limit the rate of oxidation of glutamine in the kidneys of fed dogs with chronic metabolic acidosis. Rather, there was an enhanced oxidation of lactate when the delivery of fatty acids was decreased.Key words: acid–base balance, ammonium, energy turnover, glutamine metabolism, insulin, oxygen consumption.
Effects of N6-endonorbornan-2-yl-9-methyladenine, N0861, on negative chronotropic and vasodilatory actions of adenosine in the canine heart in vivo
Authors: Pelleg Amir , Hurt Carl M.
Published: April 2011

The pharmacology of N6-endonorbornan-2-yl-9-methyladenine (N0861), a new selective antagonist of adenosine at the A1 adenosine receptor subtype (A1-AdoR), was studied in vivo using a canine model. First, the pharmacokinetics of N0861 were determined in anesthetized dogs. The time-dependent decay of plasma levels of N0861 fitted a two-compartment polyexponential model with α-phase t1/2 = 3.80 min and β-phase t1/2 = 80.55 min. Secondly, the effect of N0861 on the negative chronotropic and vasodilatory actions of adenosine in the canine heart were determined. N0861 attenuated the negative chronotropic action of adenosine (1–6 μmol/kg; rapid bolus into the right atrium) on sinus node pacemaker activity in a dose-dependent manner (pA2 = 4.23). For example, the maximal prolongation of sinus cycle length induced by 6 μmol/kg adenosine was 82 ± 13% under baseline conditions and 57 ± 10, 34 ± 5 and 34 ± 6% during infusion of N0861 at incremental rates leading to plasma levels of 7.75 ± 1.02, 14.15 ± 0.87, and 19.71 ± 1.83 μg/mL, respectively. In contrast, N0861 did not inhibit but had a tendency to potentiate the vasodilatory action of adenosine (thought to be mediated by the A2 adenosine receptor subtype (A2-AdoR)) on the left anterior descending and circumflex coronary arteries. These data indicate that two different receptors, similar to the typical A1-AdoR and A2-AdoR, mediate the electrophysiologic and vasodilatory actions of adenosine in the canine heart, respectively, and that N0861 is a selective antagonist of adenosine at A1-AdoR in the canine heart in vivo.Key words: adenosine, N0861, atrioventricular block, A1 adenosine receptor, dog heart.
Effects of deoxycorticosterone acetate on glucose metabolism in nondiabetic and streptozotocin-diabetic rats
Authors: Dai Soter , Fraser Heather , McNeill John H.
Published: April 2011

A previous study in our laboratory showed that streptozotocin (STZ) induced diabetic, deoxycorticosterone acetate (DOCA) induced hypertensive rats exhibited significantly lower levels of plasma glucose than did normotensive diabetic animals. The present experiments further investigate the effects of DOCA treatment on fasting levels of plasma glucose and insulin and on their changes after oral glucose challenge in nondiabetic and STZ-diabetic rats. It was found that, in nondiabetic rats, DOCA-induced hypertension was associated with normal glucose levels and glucose tolerance but with significantly lower levels of plasma insulin. DOCA-treated diabetic animals showed significantly lower levels of plasma glucose, but their plasma insulin concentrations were not significantly different from those of the DOCA vehicle treated diabetic rats. DOCA-treated diabetic rats also had significantly higher plasma levels of cholesterol and triglycerides. It is suggested that DOCA may have a direct or indirect action on the assimilation, production, or utilization of glucose, perhaps leading to an improvement in insulin sensitivity and subsequently a decrease in insulin secretion.Key words: glucose metabolism, insulin, deoxycorticosterone acetate, streptozotocin.
Glucose uptake by adipocytes of obese rats: effect of one bout of acute exercise
Authors: Burstein R. , Zissholtz A. , Zick-Bachar Y. , Epstein Y. , Shapiro Y. , Karnieli E.
Published: April 2011

The effect of one bout of acute exercise on impaired glucose metabolism was studied in obese (480 ± 20 g), untrained rats, at rest (n = 10) and after 60 min of swimming (n = 5). Using the euglycemic, hyperinsulinemic (10 mU∙kg−1∙min−1) clamp, glucose clearance rate increased from 7.6 ± 0.9 at rest to 9.7 ± 0.5 mL∙kg−1∙min−1 after exercise (p < 0.05). Glucose (3-O-[14C]methylglucose) transport (GT) into epididymal adipocytes was also studied. Animals were sacrificed at rest (n = 21) or after swimming (n = 18) and their epididymal adipocytes were incubated with or without insulin. In the absence of insulin, GT was 0.13 ± 0.02 and 0.26 ± 0.07 fmol∙cell−1∙min−1 at rest and after exercise, respectively. In the presence of insulin (25–1000 μU∙mL−1) GT increased at rest from 0.97 ± 0.08 to 1.13 ± 0.07 fmol∙cell−1∙min−1, and after exercise from 1.35 ± 0.05 to 1.87 ± 0.11 fmol∙cell−1∙min−1. GT was significantly higher after exercise compared with rest (p < 0.004). At rest, maximal insulin effect was achieved at 100 μU∙mL−1, whereas with exercise, GT increased gradually with the insulin dosage. The following may be concluded: (i) the biological effect of insulin is amplified in obese rats by one bout of exercise and (ii) exercise affects GT into enlarged adipocytes by enhancing tissue responsiveness to insulin and by a cellular mechanism unrelated to the insulin action.Key words: glucose uptake, euglycemic clamp, glucose transport, obesity, exercise.
Is accelerated oxidation of lactate required for dichloroacetate to lower the level of lactate in blood?
Authors: Kamel Kamel S. , Cheema-Dhadli Surinder , Halperin Mitchell L.
Published: April 2011

We examined mechanisms by which dichloroacetate (DCA), an activator of pyruvate dehydrogenase (PDH), led to a decrease in the concentration of lactate in blood in a unique "metabolic setting," where the concentration of lactate in blood was 5.4 ± 0.5 mmol/L. Elevated levels of lactate were induced in anaesthetized rabbits by the administration of a large dose of insulin. The rate of consumption of oxygen was 1.2 ± 0.1 mmol/min, the respiratory quotient was close to unity, and close to half of the PDH was in its active form; therefore, virtually all ATP synthesis should require flux through PDH. Hence, we predicted that DCA should not cause a significant decrease in the concentration of lactate in blood in this model. In contrast, if DCA was effective, new insights could be obtained into its mechanisms of action, at least in this setting. During steady-state hyperlactatemia, DCA was given as its sodium salt, 2 mmol/kg (n = 10); a control group (n = 5) received equimolar NaCl. Forty minutes later, the level of lactate in blood in the DCA group was 1.3 ± 0.2 mmol/L, significantly lower than in the NaCl group (4.2 ± 0.6 mmol/L). To determine the organ(s) responsible for removing lactate, arteriovenous differences were measured in organs drained by the jugular, femoral, and hepatic veins. There was no net uptake of lactate in these drainage beds after DCA was administered. From a quantitative analysis of the rate of removal of lactate and the rate of consumption of oxygen, it seems unlikely that the majority of the decrease in lactate could be directly attributed to an increase in its oxidation.Key words: lactic acidosis, dichloroacetate, pyruvate dehydrogenase, metabolism.