bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of cyclic adenosine 3′,5′-monophosphate on amino acid transport and incorporation into protein in the rat aorta
Authors: McCumbee William D. , Mangiarua Elsa I.
Published: April 2011

To assess the effects of cyclic AMP on amino acid transport and incorporation into aortic tissue protein, rat aortic rings were incubated with the cyclic AMP analog, N6-monobutyryl cyclic AMP (MBcAMP), the phosphodiesterase inhibitor, 3-isoburyl-1-methylxanthine (MIX), and radiolabeled amino acids. Subsequently, the aortic rings were homogenized in 5% trichloroacetic acid (TCA) and processed for liquid scintillation counting. Radioactivity present in the TCA supernatant following centrifugation was used to estimate amino acid transport. TCA-precipitable radioactivity was used as a measure of amino acid incorporation into protein. MBcAMP induced an increase in the uptake of [3H]α-aminoisobutyric acid into aortic rings and an increase in the incorporation of radiolabeled proline and leucine into TCA-precipitable protein. Similar effects were observed with low concentrations of MIX (0.025–0.25 mM); however, at higher concentrations of MIX, there was an attenuation of the effect or frank inhibition. Maximum stimulation of transport was observed within 90–120 min of the addition of MIX or MBcAMP to the incubation medium, whereas the effect on amino acid incorporation was not detectable until after 12 h of exposure to MIX or MBcAMP. The effects of cyclic AMP on transport were observed in both the tunica media and the tunica adventitia, whereas the effects on amino acid incorporation into protein were observed only in the tunica media. These data are consistent with a possible role for cyclic AMP in promoting changes in the tunica media that could lead to the development of vascular hypertrophy.Key words: N6-monobutyryl cyclic AMP, 3-isobutyl-1-methylxanthine, vascular smooth muscle.
The area postrema: a cardiovascular control centre at the blood-brain interface?
Authors: Ferguson Alastair V.
Published: April 2011

The area postrema (AP) is one of the circumventricular organs of the brain and as such it is highly vascular and lacks the normal blood-brain barrier. Anatomical tracing studies have demonstrated afferent projections to AP originating from the paraventricular nucleus, lateral parabrachial nucleus (1-PBN), nucleus tractus solitarius (NTS), as well as the vagus nerve. AP neurons have been shown to project primarily to 1-PBN, and NTS. Receptor localization studies have reported dense aggregations of many specific peptide receptors in AP including those for angiotensin II (ANG), atrial natriuretic peptide (ANP), and endothelin (ET). Electrical stimulation studies have shown that activation of AP neurons at low frequencies (<15 Hz) results in decreases in blood pressure and heart rate, while higher frequency (>20 Hz) stimulation causes increases in blood pressure. These low frequency effects on blood pressure and heart rate appear to result from activation of separate components of the autonomic nervous system. Extracellular single unit recordings have identified two functionally separate populations of AP neurons: one responsive to circulating ANG and a second apparently responsive to changes in blood pressure. In addition, AP neurons are activated by increases in circulating ET. Afferent inputs to AP neurons from 1-PBN have separate excitatory (12% of AP neurons) or inhibitory (12% of AP neurons) effects on a relatively small proportion of AP neurons. In contrast, preliminary evidence suggests a much more broadly distributed excitatory input to approximately 70% of tested AP neurons originating from the aortic depressor nerve. These studies provide considerable evidence implicating the AP as a significant neural structure regulating the cardiovascular system.Key words: circumventricular organs, nucleus tractus solitarius, cardiovascular, angiotensin, endothelin, peptides.
Potentiation of the natriuretic effect of clonidine following indomethacin in the rat
Authors: Blandford Dorothea E. , Smyth Donald D.
Published: April 2011

Previous studies have demonstrated a diuretic effect of clonidine at low intrarenal infusion rates with a natriuretic effect being observed at high infusion rates (≥3 μg∙kg−1∙min−1). The natriuresis at high infusion rates may have been secondary to increased renal prostaglandin production. We therefore evaluated the effects of indomethacin (a cyclooxygenase inhibitor) on the response to cionidine in the anesthetized rat. Intrarenal infusions of saline (vehicle) or clonidine (0.1, 0.3, 1, and 3 μg∙kg−1∙min−1) were examined both in the presence and absence of pretreatment with indomethacin (5 mg/kg, i.p.). Clonidine produced a dose-related increase in urine volume and free water clearance at 0.3, 1, and 3 μg∙kg−1∙min−1 as compared with the vehicle group. Sodium excretion and osmolar excretion were increased only at the highest infusion rate investigated. Following indomethacin pretreatment, clonidine produced a greater increase in urine volume at each infusion rate investigated. The indomethacin pretreatment also resulted in a potentiation of the natriuretic effect of clonidine at all infusion rates. Interestingly, this was associated with an increase in osmolar clearance but not free water clearance. These effects of indomethacin were reversed by infusion of prostaglandin E2. An infusion of prostaglandin E2 attenuated the indomethacin-induced increase in both urine flow rate and sodium excretion, indicating that the effects of indomethacin were mediated by prostaglandin inhibition. These results suggest that endogenous prostaglandin production attenuates the renal effects of clonidine, and as well, that in the presence of α2-adrenoceptor stimulation, prostaglandin E2 mediates an antidiuretic and antinatriuretic effect.Key words: clonidine, indomethacin, prostaglandin E2, diuresis, natriuresis.
Effects of various secretagogues on [Ca2+]i in cultured human nasal epithelial cells
Authors: Harris Robert A. , Baimbridge Kenneth G. , Bridges Michael A. , Phillips John E.
Published: April 2011

Recent studies conducted on cultured canine tracheal cells have suggested that a complex relationship exists between cAMP and Ca2+ in the control of electrolyte secretion. The goal of this study was to determine if the Ca2+ second messenger system functions in a similar fashion in cultured human nasal epithelial cells, a tissue in which control of electrolyte secretion is known to be disrupted in the genetic disease, cystic fibrosis. Human nasal epithelial tissue was obtained as a by-product of surgery and put into monolayer cell culture. After 4–5 days in culture, cells were loaded with fura-2 and intracellular free Ca2+ measured as previously reported. We found that bradykinin increased intracellular free Ca2+ in all cells tested, whereas isoproterenol increased intracellular free Ca2+ in only half the cells tested, suggesting that more than one transporting cell type may be present in this tissue. Epinephrine and prostaglandin E2 had no effect on intracellular free Ca2+. We found that the voltage-sensitive Ca2+ channel blocker verapamil had no effect on the bradykinin-induced change in intracellular free Ca2+. Removal of Ca2+ from the bathing saline only slightly attenuated the increase in intracellular free Ca2+ that resulted from stimulation with bradykinin. We conclude that the source of the increased intracellular free CA2+, observed during stimulation with secretagogues, was primarily intracellular stores.Key words: airway epithelia, [Ca2+]i, calcium, bradykinin, cystic fibrosis, fura-2.
Insulin secretion and islet endocrine cell content at onset and during the early stages of diabetes in the BB rat: effect of the level of glycemic control
Authors: Pederson Raymond A. , Curtis Susan B. , Chisholm Connie B. , Gaba Neil R. A. , Campos Robert V. , Brown John C.
Published: April 2011

Although it is agreed that autoimmune destruction of pancreatic islets in diabetic BB rats is rapid, reports of endocrine cell content of islets from BB diabetic rats at the time of onset of diabetes vary considerably. Because of the rapid onset of the disease (hours) and the attendant changes in islet morphology and insulin secretion, it was the aim of this study to compare islet β-cell numbers to other islet endocrine cells as close to the time of onset of hyperglycemia as possible (within 12 h). As it has been reported that hyperglycemia renders the β cell insensitive to glucose, the early effects of different levels of insulin therapy (well-controlled vs. poorly controlled glycemia) on islet morphology and insulin secretion were examined. When measured within 12 h of onset, insulin content of BB diabetic islets, measured by morphometric analysis or pancreatic extraction, was 60% of insulin content of control islets. Despite significant amounts of insulin remaining in the pancreas, 1-day diabetic rats exhibited fasting hyperglycemia and were glucose intolerant. The insulin response from the isolated perfused pancreas to glucose and the glucose-dependent insulinotropic hormone, gastric inhibitory polypeptide (GIP), was reduced by 95%. Islet content of other endocrine peptides, glucagon, somatostatin, and pancreatic polypeptide, was normal at onset and at 2 weeks post onset. A group of diabetic animals, maintained in a hyperglycemic state for 7 days with low doses of insulin, were compared with a group kept normoglycemic by appropriate insulin therapy. No insulin could be detected in islets of poorly controlled diabetics, while well-controlled animals had 30% of the normal islet insulin content. Well-controlled diabetic animals were more glucose tolerant and exhibited greater in vivo and in vitro insulin responses to glucose and GIP than poorly controlled animals. These studies indicate that at the onset of diabetes in the BB rat, significant amounts of insulin remain in the islet, although secretion in response to glucose and GIP is severely blunted. Adjusting insulin dosage to achieve normoglycemia has a significant β-cell sparing effect in diabetic animals, which is reflected in only a small increase in glucose-stimulated insulin secretion. These data suggest that impaired glucose recognition by the BB diabetic β cell occurs prior to autoimmune destruction of the islet and may contribute to the onset and severity of the diabetic state in these animals.Key words: diabetes, BB rat, islet endocrine cell content, insulin secretion.
Blockade of reflex venous capacitance responses in liver and spleen by hexamethonium, atropine, and surgical section
Authors: Greenway C. V.
Published: April 2011

Since hexamethonium and surgical section have been used to prevent reflex splanchnic capacitance responses, we examined the effectiveness of these procedures in blocking responses to direct stimulation of preganglionic fibres in the splanchnic nerves. Liver blood volume was measured by plethysmography and splenic blood volume by weighing in cats anesthetized by pentobarbital. The cats were adrenalectomized to prevent adrenal catecholamine secretion in response to splanchnic nerve stimulation. Hexamethonium (10 and 20 mg/kg) alone or atropine (1 mg/kg) alone caused only a small variable block of the responses to preganglionic nerve stimulation. A combination of the two drugs essentially produced a complete block of the liver capacitance response, but a significant response still persisted in the spleen. Surgical section of the postganglionic nerve bundles around the hepatic and splenic arteries completely abolished the responses to preganglionic stimulation. It is concluded that a relatively complete block of reflex splanchnic capacitance responses requires either a combination of hexamethonium and atropine or surgical section of the postganglionic nerves.Key words: splanchnic nerves, ganglionic block, hepatic blood volume, splenic blood volume.
Effect of low extracellular calcium and ryanodine on muscle contraction of the mouse during postnatal development
Authors: Dangain Josette , Neering Ian R.
Published: April 2011

We have examined the effects of low Ca2+ solutions, Co2+, and ryanodine on the isometric tension and contraction speed of isolated, developing mouse EDL muscles. Twitch responses of young muscles (7–14 days postnatal) were more sensitive to lowered [Ca2+]0 than those of more fully developed muscles (22–35 days postnatal). Responses of EDL muscles from a middle-aged group (15–21 days postnatal) were intermediate between the two other groups. Overall, the time course of contraction in a single twitch was accelerated by low [Ca2+]o. Ca2+-free solution induced a 7.95 and 9.25 mV depolarization in young and "old" muscle fibres, respectively. The presence of cobalt ions (5 mM) in the Krebs solution had a similar effect as Ca2+-free Krebs in terms of reduction of the isometric twitch and tetanic tensions of EDL muscles from the various age groups. In contrast, the shortening of the contraction time seen with Ca2+-free solution did not take place following exposure to Co2+-containing solutions. Finally, young (7–14 days postnatal) muscles were less sensitive to the inhibitory action of ryanodine on the twitch compared with more fully developed muscles (22–35 days postnatal). Taken together, our results indicate that from birth to maturity, there is a gradual change in the spectrum of calcium utilization for the contractile process.Key words: mammalian muscle, calcium, development, ryanodine, contraction, sarcoplasmic reticulum.
Prorenin and gene activation
Authors: Morris Brian J. , Smith D. Lynne
Published: April 2011

After the discovery of an inactive, putative renin precursor that could be proteolytically activated, and the proteases involved in vivo, Morris and co-workers directly demonstrated that renin is indeed synthesized as a "pro" form, and from genetic coding sequences they provided the structure of human prorenin. The gene is inactive and must be activated in prorenin-synthesizing tissues. To study the mechanism involved, we have performed transient expression analyses of putative regulatory DNA of the human gene (REN). 5′-Flanking DNA, extending from residue −144 to −2400, was linked to a reporter gene, viz. that for chloramphenicol acetyl transferase (CAT), and its ability to drive a heterologous (thymidine kinase, tk) promoter was examined by transfecting plasmid constructs into ceils in culture and measuring CAT activity 48 h later. Because suitable renin-synthesizing cells were not available, choriocarcinoma (JEG-3) and cervical carcinoma (HeLa) cells were used. Although this DNA caused a reduction in CAT activity relative to the positive control, examination of a range of subfragments suggested that the −2400 to −144 region did not contain negative regulatory elements. In contrast, all fragments containing the −149 to +13 DNA segment gave CAT activities that were lower than the promoterless control. Together, the data were consistent with the presence of negative regulatory element(s) in that fragment of DNA that contained the REN promoter. On the basis of mouse gene studies, it has been suggested that the inactivity of the renin gene in tissues that do not synthesize prorenin is not due to repression, but rather, cells that do express the gene may possess unique trans-acting factor(s) that stimulate enhancer(s) in the renin DNA, therefore activating the renin promoter. Nuclear extracts of JEG-3, but not HeLa, cells contained a binding activity for the −340 to −192 segment, but the relationship, if any, of this to the model proposed is unclear. Thus, having demonstrated the synthesis, structure, and activation of prorenin, the mechanism of activation of the gene represents the next challenge.Key words: gene regulation, transient expression assay, JEG-3 ceils, HeLa cells, prorenin.
Measurement of inactive renin in normal, nephrectomized, and adrenalectomized rats
Authors: Poulsen Knud , Nielsen Arne Høj , Johannessen Arne
Published: April 2011

In a new method for measurement of inactive rat plasma renin, the trypsin generated angiotensin I immunoreactive material, which was HPLC characterized as similar to tetradecapeptide renin substrate, is removed by a cation exchange resin before the renin incubation step. The method also corrects for trypsin destruction of endogenous angiotensinogen by the addition of exogenous angiotensinogen. When measured with this method inactive renin in rat plasma decreased after nephrectomy and increased after adrenalectomy. This is in accordance with findings in humans. A sexual dimorphism of prorenin (inactive renin) in rat plasma, similar to that reported in humans and mice, was demonstrated. Thus, inactive renin in the rat is no exception among species, and the rat might be a suitable animal model for further studies dealing with the physiology of prorenin in plasma and tissues.Key words: angiotensinogen, inactive renin, renin.
Trypsin activation of human and cat prorenin: a comparative study
Authors: Rubattu Speranza , Gahnem Fuad , Sealey Jean E.
Published: April 2011

Prorenin can be converted to renin by limited proteolysis with trypsin. In the current study we compared conditions for activation of human renal and ovarian prorenin and cat renal prorenin with either liquid-phase trypsin or trypsin bound to sepharose (solid phase). Higher concentrations of trypsin were required to activate cat prorenin than human prorenin. Human prorenin was destroyed by high concentrations of trypsin, while cat prorenin was not destroyed by up to 2 mg/mL solid-phase trypsin. For both human and cat prorenin, addition of the competitive serine protease inhibitor benzamidine–HCl increased the concentration of trypsin needed to activate prorenin, resulting in slightly higher levels of human prorenin but lower levels of cat prorenin. For human samples, activation with solid-phase trypsin resulted in slightly higher estimates of prorenin than liquid-phase trypsin. These results demonstrate species differences in the susceptibility of prorenin to trypsin cleavage. Cat prorenin requires more trypsin to be activated and is less susceptible to destruction than human prorenin.Key words: prorenin, inactive renin, cat human, trypsin.
Adrenoceptor regulation of canine skeletal muscle blood flow during carbon monoxide hypoxia
Authors: Kubes P. , Nesbitt K. A. , Cain S. M. , Chapler C. K.
Published: April 2011

We questioned whether carbon monoxide hypoxia (COH) would affect peripheral blood flow by neural activation of adrenoceptors to the extent we had found in other forms of hypoxia. We studied this problem in hindlimb muscles of four groups of anesthetized dogs (untreated, α1-blocked, α1 + α2-blocked, and β2-blocked). Cardiac output increased, but hindlimb blood flow [Formula: see text] and resistance (RL) remained at prehypoxic levels during COH (O2 content reduced 50%) in untreated animals. When activity in the sciatic nerve was reversibly cold blocked, [Formula: see text] doubled and RL decreased 50%. These changes with nerve block were the same during COH, suggesting that neural activity to hindlimb vasculature was not increased by COH. In animals treated with phenoxybenzamine (primarily α1-blocked), RL dropped (~50%) during COH, an indication that catecholamines played a significant role in maintaining tone to skeletal muscle. Animals with both α1 + α2-adrenergic blockade (phenoxybenzamine and yohimbine added) did not survive COH. RL was higher in β2-block than in the untreated group during COH, but nerve cooling indicated that β2-adrenoceptor vasodilation was accomplished primarily by humoral means. The above findings demonstrated that adrenergic receptors were important in the regulation of [Formula: see text] and RL during COH, but they were not activated by sympathetic nerve stimulation to the limb muscles.Key words: α1-adrenoreceptor blockade, α2-adrenoreceptor blockade, peripheral vascular resistance, skeletal muscle, blood flow.
Pharmacological evidence for N-methyl-D-aspartate receptors on nigrostriatal dopaminergic nerve terminals
Authors: Johnson Kenneth M. , Jeng Yow-Juin
Published: April 2011

The efflux of tritium from rat striatal synaptosomes labelled with [3H]dopamine was utilized as an index of dopamine (DA) release for the purpose of characterizing the receptors underlying the effects of L-glutamate. N-Methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA), and kainate each induced DA release in the absence of Mg2+, though NMDA was much more efficacious and only the NMDA response was inhibited by Mg2+. The response to L-glutamate was potentiated in a concentration-dependent manner by glycine. Further, it was completely inhibited by the competitive NMDA antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid and by the NMDA channel blocker phencyclidine. Finally, the response to L-glutamate was unaffected by either tetrodotoxin or the kainite–AMPA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. These data demonstrate the presence of NMDA receptors on dopaminergic nerve terminals that mediate the ability of L-glutamate to release DA and suggest an additional mechanism by which information from the nigrostriatal and corticostriatal pathways may be integrated.Key words: N-methyl-D-aspartate, receptors, dopamine, nigrostriatal, synaptosomes.
cis-Dominance of rat atrial natriuretic factor gene regulatory sequences in transgenic mice
Authors: Seidman C. E. , Schmidt E. V. , Seidman J. G.
Published: April 2011

We have produced transgenic mice that express the prokaryotic marker protein chloramphenicol acetyltransferase under the control of regulatory sequences derived from the rat atrial natriuretic factor gene. The transgene, which contains 2.4 kilobases of the rat atrial natriuretic factor gene regulatory region, was found to direct 4000-fold more chloramphenicol acetyltransferase expression in adult atria than in ventricles. Low-level activity was also detected in the hypothalamus, demonstrating that these sequences contain the signals necessary for cardiac and central nervous system expression of the hormone atrial natriuretic factor. Developmental analyses showed early, high-level transgene expression in fetal atrial and ventricular tissues but marked reduction of ventricular transgene expression following birth. Further, the developmental expression patterns of the endogenous murine atrial natriuretic factor gene and rat transgene were found to be quite distinct. Although both the rat and mouse atrial natriuretic factor genes are activated early in embryogenesis, perinatal ventricular expression appears to differ in these two rodent species. The transgene is expressed in a pattern analagous to the neonatal rat rather than the endogenous murine gene. These studies demonstrate that the cis-acting signals required for correct tissue specificity and developmental regulation of the rat atrial natriuretic factor gene are encoded in this 2.4-kilobase fragment and that these sequences act in a dominant fashion.Key words: ANF, transgenic mice, tissue-specific expression.
Pathophysiology of congestive heart failure: role of atrial natriuretic factor and therapeutic implications
Authors: Perrella Mark A. , Margulies Kenneth B. , Burnett Jr. John C.
Published: April 2011

Endogenous atrial natriuretic factor (ANF) serves a functional role to maintain sodium homeostasis and inhibit activation of the renin–angiotensin–aldosterone system in acute congestive heart failure despite arterial hypotension. However, as heart failure progresses, maximal synthesis and release of ANF from both the atrial and ventricular myocardium may occur resulting in relative ANF deficiency. This relative deficiency of ANF results in a progressive inability to excrete sodium and antagonize the renin–angiotensin–aldosterone system. Consequently, agents that increase circulating ANF and (or) enhance its local action have potential therapeutic efficacy. Recent studies suggest that inhibitors of neutral endopeptidase 24.11, which block ANF degradation, potentiate the natriuretic action of endogenous ANF independent of systemic or renal hemodynamics. This action does not parallel increases in plasma ANF and is associated with marked increases in urinary ANF and cyclic guanosine monophosphate consistent with enhanced local action of the peptide. In addition, agents that selectively bind to biologically inactive ANF clearance receptors increase endogenous plasma ANF and promote increases in renal sodium excretion. These studies suggest a therapeutic role for neutral endopeptidase inhibition and clearance receptor blockade, while advancing our understanding of the pathophysiology of ANF in congestive heart failure.Key words: congestive heart failure, atrial natriuretic factor, cyclic guanosine monophosphate, natriuresis, renin–angiotensin–aldosterone system.
Atrial natriuretic peptides in essential hypertension: basal plasma levels and relationship to sodium balance
Authors: Sagnella G. A. , Markandu N. D. , Buckley M. G. , Miller M. A. , Singer D. R. J. , Cappuccio F. P. , MacGregor G. A.
Published: April 2011

The identification of the atrial natriuretic peptides (ANP) as a new hormonal system has provided a new perspective on the mechanisms controlling renal sodium excretion and abnormalities in sodium homeostasis. The present article focuses on the potential importance of ANP (ANF 99–126) in essential hypertension with particular reference to circulating ANP levels and the relationship between the ANP and the renin–angiotensin system in the control of sodium balance and blood pressure. There is now considerable evidence demonstrating that a substantial proportion of patients with essential hypertension have raised circulating ANP levels. Given the known biological actions of ANP, these raised levels point to important compensatory mechanisms. This is further supported by studies during alterations in dietary sodium intake, as sodium restriction highlighted important relationships between ANP and the renin angiotensin system. The potential importance of ANP in essential hypertension is strengthened by recent demonstration of natriuretic and antihypertensive actions associated with small increases in circulating ANP as induced by administration of exogenous ANP. Furthermore, the recent development of orally active inhibitors of ANP metabolism now provides a basis to determine the therapeutic importance of specific manipulation of endogenous ANP levels in patients with essential hypertension.Key words: ANF, essential hypertension, sodium balance.
Evaluation of SQ 28 603, an inhibitor of neutral endopeptidase, in conscious monkeys
Authors: Seymour Andrea A. , Abboa-Offei Benoni , Asaad Magdi M. , Rogers W. Lynn
Published: April 2011

The potent neutral endopeptidase inhibitor SQ 28 603 (N-(2-(mercaptomethyl)-1-oxo-3-phenylpropyl)-β-alanine) significantly increased excretion of sodium from 4.9 ± 2.3 to 14.3 ± 2.1 μequiv./min and cyclic 3′,5′-guanosine monophosphate from 118 ± 13 to 179 ± 18 pmol/min after intravenous administration of 300 μmol/kg (~80 mg/kg) in conscious female cynomolgus monkeys. SQ 28 603 did not change blood pressure or plasma atrial natriuretic peptide concentrations in the normal monkeys. In contrast, 1-h infusions of 3, 10, or 30 pmol∙kg−1∙min−1 of human atrial natriuretic peptide lowered blood pressure by −3 ± 4, −9 ± 4, and −27 ± 3 mmHg (1 mmHg = 133.322 Pa), increased cyclic guanosine monophosphate excretion from 78 ± 11 to 90 ± 6, 216 ± 33, and 531 ± 41 pmol/min, and raised plasma atrial natriuretic peptide from 7.2 ± 0.7 to 21 ± 4, 62 ± 12, and 192 ± 35 fmol/mL without affecting sodium excretion. In monkeys receiving 10 pmol∙kg−1∙min−1 of atrial natriuretic peptide, 300 μmol/kg of SQ 28 603 reduced mean arterial pressure by −13 ± 5 mmHg and increased sodium excretion from 6.6 ± 3.2 to 31.3 ± 6.0 μequiv./min, cyclic guanosine monophosphate excretion from 342 ± 68 to 1144 ± 418 pmol/min, and plasma atrial natriuretic peptide from 124 ± 8 to 262 ± 52 fmol/mL. In conclusion, SQ 28 603 stimulated renal excretory function in conscious monkeys, presumably by preventing the degradation of atrial natriuretic peptide by neutral endopeptidase.Key words: atrial natriuretic peptide, neutral endopeptidase, natriuresis, cyclic guanosine monophosphate.
The guanylyl cyclase–receptor family
Authors: Garbers David L.
Published: April 2011

Guanylyl cyclase activity exists in the soluble and particulate fractions of most tissue homogenates. Recently, the mRNA encoding members of the enzyme family from both the soluble and particulate fraction have been cloned. The soluble form exists as a heterodimer, both subunits containing cyclase catalytic-like amino acid sequences. Both subunits must be expressed to observe enzyme activity. The particulate (plasma membrane) forms contain a single putative transmembrane domain that separates an extracellular, ligand-binding domain from an intracellular, protein kinase-like and cyclase catalytic region. The protein kinase-like domain appears to serve as an important regulatory element of the receptor.Key words: receptors, plasma membrane, guanylyl cyclase, cGMP, protein kinase.
Neutral metalloendopeptidase inhibitors as ANF potentiators: sites and mechanisms of action
Authors: Sybertz Jr. Edmund J. , Chiu Peter J. S. , Watkins Robert W. , Vemulapalli Subbarao
Published: April 2011

Inhibition of the enzyme neutral metalloendopeptidase potentiates responses to atrial natriuretic factor and elicits reductions of blood pressure in desoxycorticosterone acetate sodium hypertensive rats. The present study evaluated the role of atrial natriuretic factor and bradykinin in the antihypertensive response to neutral metalloendopeptidase inhibition through the use of antibodies and antagonists, respectively. In addition, the pharmacokinetic mechanism by which neutral metalloendopeptidase inhibition interferes with atrial natriuretic factor metabolism was explored. The antihypertensive response to the neutral metalloendopeptidase inhibitor SCH 34826 was abruptly reversed by i.v. injection of a polyclonal antiserum to atrial natriuretic factor. In contrast, the antihypertensive response to SCH 34826 was unaffected by injection of the bradykinin antagonist Thi5,8-D-Phe7 bradykinin. The renal response to atrial natriuretic factor, SCH 34826, and phosphoramidon was inhibited by the bradykinin antagonist. The NEP inhibitor SCH 39370 significantly delayed the disappearance of TCA precipitable radioactivity from plasma following i.v. bolus dosing with 125I-labelled ANF 99–126. The effects were enhanced in the presence of the C receptor ligand. The results indicate that atrial natriuretic factor, but not bradykinin, plays an important role in the antihypertensive response to SCH 34826. Bradykinin plays a permissive role in the diuretic responses to atrial natriuretic factor and inhibitors of neutral metalloendopeptidase. Lastly, neutral metalloendopeptidase inhibition significantly alters the clearance and metabolism of tracer quantities of atrial natriuretic factor.Key words: neutral metalloendopeptidase, SCH 34826, bradykinin, SCH 39370, atrial natriuretic factor metabolism, antihypertensive activity.
The role of selenium in thyroid hormone metabolism
Authors: Arthur John R.
Published: April 2011

In animals, decreases in selenium-containing glutathione peroxidase activity and the resultant impairment of peroxide metabolism can account for many, but not all of the biochemical and clinical changes caused by selenium deficiency. Recently, however, type I iodothyronine 5′-deiodinase has also been shown to be a selenium-containing enzyme. This explains the impairment of thyroid hormone metabolism caused by selenium deficiency in animals with a normal vitamin E status. Since iodothyronine 5′-deiodinases are essential for the production of the active thyroid hormone 3,5,3′-triiodothyronine, some of the consequences of selenium deficiency may result from thyroid changes rather than inability to metabolise peroxides. In particular, the impaired thyroid hormone metabolism may be responsible for decreased growth and resistance to cold stress in selenium-deficient animals. A further consequence of the role of selenium in thyroid hormone metabolism is the exacerbation of some of the thyroid changes in iodine deficiency by a concurrent selenium deficiency. Selenium status may therefore have a major influence on the outcome of iodine deficiency in both human and animal populations.Key words: selenium, thyroid hormones, iodothyronine deiodinases, iodine, nutritional disorders.
Tribute to Graham W. Mainwood
Authors: Biro George P. , Parry David J. , Renaud Jean-Marc
Published: April 2011

Graham Mainwood's scientific contributions were largely in the field of skeletal and cardiac muscle physiology. His early work centered around the electrophysiology of cardiac muscle and its regulation by the vagus nerve. Later he became interested in the electrophysiology of frog sartorius muscle, which led him to study the mechanism of muscle fatigue. One of his most important contributions was to show the inhibitory effect of reduced extracellular pH on the recovery of force following fatigue. Subsequently, he studied the role of creatine phosphate in the potentiation of the twitch following a tetanus. Finally toward the end of his career he returned to his first love: cardiac muscle. In collaboration with the NMR group at the NRC, Ottawa, Ontario, he worked on finding the optimally constituted cardioplegic solution for the preservation of the human heart for transplant purposes.In addition to these scientific achievements, there were many facets of Graham's character that enriched the lives and work of those he touched. He was always ready with a welcoming smile and some words of encouragement. His formidable intellect was always tempered by personal humility. He was always ready to help, advise, encourage, and provide constructive criticism.He expended great efforts on behalf of Canada's struggling scientific community to raise the level of awareness of the importance of science and its support. He participated extensively in all lobbying activities, wrote articles, and with his insight, helped many to understand difficult ideas, without trivializing them. Besides these serious and time-consuming activities, Graham's wonderful wit also lit up our lives in many ways. Many who attended Canadian Physiological Society meetings in the 1970s and 80s will remember fondly his after-dinner doggerel.Those of us at the University of Ottawa were further privileged in reading many of his acerbic and incisive contributions to an in-house newsletter that also contained some of his delightful cartoons. These stimulated many of us to carry further the struggle against diminishing funding and priority accorded science in Canada since the 1970s by successive governments.At least one of the authors of each of the papers in this special issue has had, at some time, a significant level of interaction with Graham. We will all miss the unique blend of devotion to excellence, intellect, wit, and humanity that was Graham Mainwood. These labours are dedicated to his memory.
Stroma-free hemoglobin: its presence in plasma does not improve oxygen supply to the resting hindlimb vascular bed of hemodiluted dogs
Authors: Biro George P. , Anderson Peter J. , Curtis Scott E. , Cain Stephen M.
Published: April 2011

In hemodilution, red cell spacing in the microcirculation is increased, flow distribution may become more heterogeneous, and, as a result, oxygen supply to tissues may suffer. We tested the hypothesis that oxygen extraction from diluted blood may be enhanced by the presence of hemoglobin in the plasma phase in relatively low concentrations. In anesthetized dogs, the hindlimb vascular bed was isolated and perfused with the animal's own blood by a roller pump. One group of dogs (n = 6) was hemodiluted (hematocrit = 15.0 ± 1.0%) with a 6% solution of dextran. A second group of dogs (n = 6) was similarly hemodiluted (hematocrit = 16.0 ± 0.4%) with dextran containing stroma-free hemoglobin solution whereby plasma-phase hemoglobin concentration was raised to 1.1 ± 0.1 g∙dLé−1. Systemic hemodynamic observations were made repeatedly over the subsequent 2.5 h, while blood flow to the hindlimb was progressively reduced in stepwise decrements. The hemoglobin-hemodiluted group showed increased systemic arterial blood pressure and total peripheral resistance when compared with the control (dextran diluted) group. The isolated hindlimb also showed evidence of increased vascular resistance in the hemoglobin-treated group. In each individual animal, critical oxygen delivery and extraction were determined by finding the intercept of the supply-independent and supply-dependent portions of the oxygen uptake/oxygen delivery relationship. Neither the critical oxygen delivery rates (5.75 ± 0.83 vs. 6.41 ± 0.53 mL∙kg−1 min−1) nor critical oxygen extraction ratios (0.75 ± 0.03 vs. 0.76 ± 0.04) were found to be significantly different in the two groups. We conclude that hemoglobin in solution in the plasma at a concentration of about 1 g∙dL−1 induces significant increase in vascular resistance and fails to augment oxygen extraction from diluted blood by the resting hindlimb.Key words: stroma-free hemoglobin solution, oxygen extraction, vasoconstriction, isolated hindlimb vascular bed, oxygen supply.
Impairment of cardiac contractility and sarcoplasmic reticulum Ca2+ ATPase activity by hypochlorous acid: reversal by dithiothreitol
Authors: Eley D. W. , Eley J. M. , Korecky B. , Fliss H.
Published: April 2011

Isolated rat hearts perfused with 100 μM hypochlorous acid (HOCl), a powerful oxidant produced by activated neutrophils, exhibited progressive impairment of contractile performance suggestive of a cytosolic Ca2+ overload (increased left ventricular end-diastolic pressure, increased aortic root perfusion pressure, and depressed pulse pressure). Sarcoplasmic reticulum (SR) enriched microsomal preparations isolated from HOCl-perfused hearts showed a significant decline, when compared with control hearts, in both Ca2+ ATPase activity (123 ± 40 vs. 473 ± 46 nmol Pi∙mg−1 protein∙min−1) and Ca2+ uptake (12 ± 5 vs. 46 ± 4 nmol Ca2+∙mg−1 protein∙min−1). The sulfhydryl content in Ca2+ ATPase and other proteins, as determined by [14C]iodoacetamide binding, was also progressively depleted in HOCl-perfused hearts. Perfusion of the HOCl-treated hearts with dithiothreitol (DTT), a disulfide reducing agent, resulted in a time-dependent attenuation, and eventual partial reversal, of the dysfunction in both contractility and SR Ca2+ ATPase activity. Protein thiol levels were concomitantly restored to near control values. The data indicate that HOCl-induced contractile dysfunction in heart is related to the inactivation of the SR Ca2+ ATPase as a result of thiol oxidation and suggest that DTT is capable of reversing this dysfunction in situ by reducing the oxidized sulfhydryls in the Ca2+ ATPase.Key words: hypochlorous acid, dithiothreitol, cardiac sarcoplasmic reticulum, Ca2+ ATPase, protein sulfhydryl.
Effects of chronic treatment of rats with "designer" amphetamines on brain regional monoamines
Authors: Martin-Iverson Mathew T. , Lodge Bruce A.
Published: April 2011

(+)-Amphetamine and two structurally related analogues, 4-methoxyamphetamine and a recent "designer drug," 4-ethoxy-amphetamine, were given to rats via subcutaneous osmotic minipumps for 1–14 days. Regional brain levels of the drugs as well as monoamine neurotransmitters and some of their major acidic metabolites were determined. Amphetamine produced depletions of dopamine in the striatum after at least 3 days of treatment but not in the nucleus accumbens or olfactory tubercle, even after 14 days of treatment. In contrast, the two ring-substituted amphetamine analogues increased levels of the monoamines and decreased levels of their acid metabolites. These data indicate that the two ring-substituted amphetamine analogues, at least one of which is a potent hallucinogen, have potent monoamine oxidase inhibition properties that are sustained during chronic treatment. Furthermore, these two compounds do not share amphetamine's regionally selective neurotoxic effects on dopamine-releasing terminals, even though brain and striatal drug levels are the same or higher than those of amphetamine.Key words: (+)-amphetamine, 4-methoxyamphetamine, 4-ethoxyamphetamine, designer amphetamines, monoamines, rats, chronic treatment.
Myocardial calcium cycling defect in furazolidone cardiomyopathy
Authors: O'Brien Peter James , Shen Hua , Weiler Janice E. , Mirsalimi S. Mehdi , Julian Richard J.
Published: April 2011

We have previously demonstrated that in furazolidone-induced congestive heart failure in turkeys the specific Ca2+-ATPase activity of myocardial sarcoplasmic reticulum (SR) is 60% increased in compensation for a 50% depression in net Ca2+-sequestration activity. This study tested the hypothesis that SR Ca2+-uptake and Ca2+-ATPase activities were uncoupled in this cardiomyopathy because of increased Ca2+-release channel activity. A novel microassay was used to monitor Ca2+ transport by myocardial homogenates using the fluorescent Ca2+ dye indo 1 to indicate extravesicular ionized Ca2+. The method is applied to cyropreserved biopsy specimens of myocardium and requires only 50 mg tissue. Both SR Ca2+-pump and SR Ca2+-channel activity were estimated using the channel-inhibitor ruthenium red (RR) and the mitochondrial inhibitor sodium azide. The specificity of the RR inhibition was confirmed using ryanodine. Cardiomyopathy was induced in 2-week-old turkey pouits by the addition of 0.07% furazolidone to their feed for 4 weeks. Compared with controls, myocardial maximal Ca2+-channel activity relative to maximal Ca2+-pump activity was 22% greater and duration of Ca2+-channel activity was 100% increased. However, the heart failure birds had 43 and 53% decreases in absolute maximal Ca2+-pumping and Ca2+-channel activities, respectively. The abnormal Ca2+-channel activity resulted in 200% greater time before initiation of net Ca2+ sequestration and 700% greater final myocardial Ca2+ concentrations. For all birds, the Ca2+-accumulating activity was highly correlated with Ca2+-release activity (all p < 0.05). These data indicate that in this animal model of congestive heart failure there is defective SR Ca2+-channel function resulting in abnormal Ca2+ homeostasis. However, this defect can only partially explain our previous finding of furazolidone-induced uncoupling of Ca2+ uptake from Ca2+-ATPase activities. The consequent myocardial Ca2+ overload predisposes the heart to fatigue and irreversible failure.Key words: sarcoplasmic reticulum, calcium sequestration, furazolidone cardiomyopathy, indo 1 spectrofluorometry.
Effects of neonatal sympathectomy on brown fat development and susceptibility to high fat diet induced obesity in mice
Authors: Desautels M. , Dulos R. A.
Published: April 2011

Injections of 6-hydroxydopamine in mouse neonates caused extensive and long lasting damage to the sympathetic nervous system and impaired brown fat development. Brown adipose tissue (BAT) thermogenic capacity of sympathectomized mice (up to 120 days old) was reduced because of marked reductions in the tissue mitochondrial protein content and the mitochondrial concentration of uncoupling protein, as assessed by [3H]GDP binding and immunoassay. Neonatal sympathectomy did not affect BAT DNA content. Sympathectomized mice also had reduced epinephrine-stimulated rates of oxygen consumption. BAT of sympathectomized mice failed to respond by increases in [3H]GDP binding to isolated mitochondria and uncoupling protein concentration when animals were offered a palatable high-fat dietary supplement that increased calorie intake of both normal and sympathectomized mice. The high-fat diet caused increases in body weight, carcass fat, and gonadal white fat pad weights in sympathectomized animals that were similar to those of control mice. These results show that inactivation of BAT metabolism did not accentuate the development of obesity caused by a dietary supplement rich in fat and suggest that stimulation of BAT metabolism was not very effective in counteracting the obesity-inducing effect of this diet.Key words: body weight, body temperature, energy balance, mitochondria, uncoupling protein.
Influence of acetone on the severity of the liver injury induced by haloalkane mixtures
Authors: Charbonneau Michel , Greselin Erminio , Brodeur Jules , Plaa Gabriel L.
Published: April 2011

Acetone potentiation of haloalkane-induced liver injury is a well-known phenomenon. Acetone-treated rats challenged with a trichloroethylene–CCl4 mixture exhibit a more severe liver injury than that predicted by the addition of the single potentiating effects of each. The purpose of the present study was to determine if acetone exerted similar interactions with other haloalkane mixtures. The testing protocol used was designed and performed to allow categorization of interactions occurring among two or three agents. Rats were treated (p.o.) with corn oil or acetone (10.2 mmol/kg) and were administered (i.p.) 18 h later 1,1-dichloroethylene (0.6 mmol/kg), trichloroethylene (5.6 mmol/kg), tetrachloroethylene (19.6 mmol/kg), 1,1,1-trichloroethane (10.0 mmol/kg), 1,1,2-trichloroethane (1.1 mmol/kg), 1,1,2,2-tetrachloroethane (1.0 mmol/kg), CHCl3 (6.2 mmol/kg), CCl4 (1.0 mmol/kg), or a mixture of two haloalkanes (all 28 combinations were tested). Liver injury was assessed 24 h later using plasma alanine aminotransferase activity and a quantitative histological evaluation. In corn oil pretreated rats, the hepatotoxic responses observed for the 28 mixtures were additive for 26 of 28 mixtures and supra-additive for 2 of 28, whereas in acetone-pretreated rats the responses observed were additive for 17 of 28, infra-additive for 10 of 28, and supra-additive for 1 of 28. Mixtures containing 1,1,1-trichloroethane or tetrachloroethylene resulted only in no change in toxicity or infra-additivity. Increased toxic responses (additivity and supra-additivity) were observed with certain binary mixtures containing CCl4, CHCl3, 1,1,2-trichloroethane, or 1,1-dichloroethylene. Tetrachloroethylene yielded infra-additive responses when combined in a binary mixture with other haloalkanes, CCl4 in particular. The effect exerted by acetone on the liver injury induced by haloalkane mixtures appears to be predictable on the basis of the particular haloalkanes present in the mixture. Halogenated methanes, chemicals with minimal use in the industrial workplace, showed the greatest potential for additive and supra-additive interactions with other haloalkanes. The approach described is a useful method for examining the potential toxicity of mixtures.Key words: acetone, haloalkanes, liver injury, mixtures, interactions.