bluuebunny/crossref_metadata_2025 huggingface dataset:
Basolateral membrane lipid dynamics alter Na–K ATPase activity in rabbit small intestine
Authors: Madsen Karen L. , Meddings Jonathan B. , Fedorak Richard N.
Published: April 2011

The role of basolateral membrane fluidity in regulating Na–K ATPase activity along the crypt–villus axis in rabbit distal small intestine was assessed. Basolateral membranes were prepared from isolated villus and crypt enterocytes at 24- to 28-fold enhancement. Villus basolateral membranes were significantly (p < 0.001) more fluid than crypt basoiateral membranes as measured by 1,6-diphenyl-1,3,5-hexatriene. No difference was seen between the two groups as measured by either 2-(9-anthroyloxy)-stearic fatty acid or 16-(9-anthroyloxy)-palmitic acid. Fluidity alterations were accompanied by an increased phospholipid content in villus membranes, which resulted in a decreased cholesterol:phospholipid ratio and an increased lipid:protein molar ratio. Na–K ATPase activity was significantly (p < 0.01) greater in villus basolateral membranes than in crypt membranes, and demonstrated a greater sensitivity to ouabain inhibition. Ouabain inhibition curves calculated from villus data fit well (p < 0.001) with a two binding site model, with a high affinity (Ki 16 nM) and a low affinity (Ki 4.2 μM) ouabain binding site. In crypt basolateral membranes, only a low affinity site was apparent (Ki 3.0 μM). Fluidizing crypt basolateral membranes in vitro with benzyl alcohol to levels seen in villus basolateral membranes resulted in the appearance of a high affinity ouabain binding site (Ki 110 nM) and an increased sensitivity of Na–K ATPase to ouabain inhibition. The fluidization of villus basolateral membranes eliminated the binding associated with the high affinity site. Treatment with methanol, as a control, did not alter Na–K ATPase activity. These results indicate that changes in basolateral membrane lipid dynamics may be involved in modulating Na–K ATPase activity and transport function.Key words:
The Physiology, Pharmacology, and Biophysics of Ganglionic Transmission
Authors: Smith Peter A. , Dryden William F. , Polosa Canio , Skok Vladimir I.
Published: April 2011

Over the last 20 years there has been a marked increase in the understanding of the biophysical properties of neurones in autonomic ganglia. During the same time period, there have been advances in immunohistochemistry which have shown that the autonomic ganglia are rich sources of a variety of neuroactive peptides and monoamines. Although physiological studies have underlined the role of enteric and prevertebral ganglia in the control of peristalsis and micturition, very little is known about the physiological role of many of the other autonomic ganglia.The objective of the International Brain Research Organization satellite symposium held in Edmonton, Alberta, during August 1991, was to bring together the biophysicists, morphologists, physiologists, and pharmacologists to evaluate the current status of our understanding of the autonomic ganglia. Posters and four sessions of invited talks were presented over a three-day period. The papers that appear in this issue detail the content of some of these talks.The organizers gratefully acknowledge the financial support provided by the Alberta Heritage Foundation for Medical Research, the Medical Research Council of Canada, Astra Pharma Inc., the University of Alberta Conference Fund, Nordic Laboratories, Merck Frosst Canada, Axon Instruments, Novopharm Ltd., Bio-Méga Inc., Chembiomed, Newport Instruments, the City of Edmonton, Charles River Canada, and Mandel Scientific.
Introduction to slow synaptic potentials and their neuromodulation by dopamine
Authors: Libet Benjamin
Published: April 2011

The existence of two muscarinically mediated slow postsynaptic potentials (PSPs) and a noncholinergic (peptidergic) late-slow PSP was established in the 1960s. These have synaptic delays and PSP durations 100–10 000 times those for the nicotinic (fast) excitatory post-synaptic potential (EPSP). Evidence is reviewed for and against the proposal that, in rabbit superior cervical ganglia, the slow (s-) inhibitory postsynaptic potential requires a second transmitter, dopamine, released by muscarinic action on interneurones (the small, intensely fluorescent cells). The s-EPSP in frog ganglia appears only in already depolarized cells by a muscarinic closure of the M (voltage-sensitive K+) channels. But the large s-EPSP in mammalian neurones, not depolarized, is generated largely via other mechanisms, especially one involving cyclic GMP. Dopamine also produces a long-term enhancement (LTE) of the muscarinic slow PSPs in rabbit superior cervical ganglia, whether dopamine is applied exogeneously or released intraganglionically by preganglionic nerve impulses at 10 s−1. LTE is producible heterosynaptically, and it persists well over 3 h; a noncholinergic (peptide?) transmitter may contribute to the initial 30 min of LTE. LTE is mediated by a D1 receptor coupled to cyclic AMP; it is blocked by cyclic GMP or low Ca2+ or calmidazolium (a calmodulin inhibitor). The modulatory process of LTE has certain similarities to, but also fundamental differences from, the long-term potentiation known in the hippocampus.Key words: muscarinic synapses, peptidergic synapses, dopamine actions, neuromodulation, postsynaptic long-term enhancement.
Molecular mechanisms of open-channel blockade in nicotinic acetylcholine receptors of autonomic ganglia neurons
Authors: Skok Vladimir I.
Published: April 2011

The results of recent attempts to estimate the dimensions of ionic channels in nicotinic acetylcholine receptors of sympathetic and enteric ganglia neurons are reviewed. The channel dimensions, obtained from comparison of the sizes of the open-channel blocking molecules with their blocking activities, are 6.1 × 8.3 Å (1 Å = 0.1 nm) in both sympathetic and enteric ganglia. None of the competitive ganglionic blockers fit within this channel size. In addition, a chemical structure that binds the open-channel blockers in ganglionic nicotinic acetylcholine receptors is suggested to be formed by serine and threonine residues, as found by comparing the differences between the structures of the neuronal and muscle nicotinic acetylcholine receptors with the differences in their pharmacology.Key words: nicotinic acetylcholine receptor, autonomic ganglia, open-channel blocking mechanisms.
Role of taurine in neural cell volume regulation
Authors: Schousboe Arne , Pasantes-Morales Herminia
Published: April 2011

Release of taurine and other amino acids was monitored from cultured astrocytes and neurons under isomotic and hyposmotic conditions as well as during exposure of the cells to 56 mM KCl. The release was correlated with swelling, as determined by the 3-O-methylglucose method. It was shown that release of taurine from astrocytes cultured from cerebral cortex and cerebellum of rats and mice regardless of the stimulating agent is a consequence of cell swelling. The release is unrelated to depolarization. This conclusion is also valid regarding release of taurine from cerebellar granule neurons. Comparison of release of different amino acids showed that not only taurine but also to some extent glutamate, aspartate, and glycine are released during cell swelling. On the other hand, glutamine is not released under these conditions. Studies of uptake of taurine under isosmotic and hyposmotic conditions as well as the dependency of the release on sodium and temperature strongly suggest that the release process is mediated by diffusional forces and not by a reversal of the high-affinity carrier. It is proposed that taurine may play an important role as an osmotically active substance in the brain involved in cell volume regulation.Key words: swelling, taurine release, neurons, astrocytes, amino acids.
Influence of atrial natriuretic factor on uptake, intracellular distribution, and release of norepinephrine in rat adrenal medulla
Authors: Vatta M. S. , Bianciotti L. G. , Fernández B. E.
Published: April 2011

Several studies have demonstrated that atrial natriuretic factor can bind to adrenal medulla cells. Furthermore, atrial natriuretic factor immunoreactivity has been identified in chromaffin cells. The aim of the present work was to investigate atrial natriuretic factor effects on the uptake, intracellular distribution, and release of norepinephrine in the rat adrenal medulla. Results showed that 100 nM atrial natriuretic factor induced a rapid increase of norepinephrine uptake during the first minute of the incubation period. This increase was maintained for up to 60 min. In addition, only neuronal norepinephrine uptake was increased by the natriuretic factor; non-neuronal norepinephrine uptake was unaltered. Atrial natriuretic factor modified the intracellular distribution of the amine store: the granular fraction of norepinephrine increased, while the cytosolic fraction decreased. On the other hand, different concentrations (10, 50, and 100 nM) of the atrial factor decreased spontaneous [3H]norepinephrine output in a concentration-dependent manner. Furthermore, atrial natriuretic factor (10 nM) also reduced high potassium solution evoked secretion of norepineprhine. These results suggest that atrial natriuretic factor modulates sympathetic activity in the rat adrenal medulla. These effects of atrial natriuretic factor may be related to the catecholamine peripheral mechanism involved in the regulation of arterial blood pressure, smooth muscle tone, metabolic activity, etc.Key words: adrenal medulla, atrial natriuretic factor, intracellular norepinephrine distribution, norepinephrine release, norepineprhine uptake.
Catabolism of intracerebroventricularly injected 5-hydroxytryptamine in mouse: effect of coinjection of tryptamine and several pretreatments
Authors: Sloley B. Duff , Orikasa Shuzo , Boulton Alan A.
Published: April 2011

The catabolism of intracerebroventricularly injected 5-hydroxytryptamine in mouse brain was investigated. Pretreatment of animals with the 5-hydroxytryptamine type 1 receptor antagonist metergoline, the 5-hydroxytryptamine type 2 receptor antagonist ketanserin, the 5-hydroxytryptamine reuptake inhibitor fluoxetine, or the selective 5-hydroxytryptamine neurotoxin 5,7-dihydroxytryptamine failed to alter the rate of catabolism of intracerebroventricularly administered 5-hydroxytryptamine. The monoamine oxidase inhibitor tranylcypromine effectively blocked degradation of injected 5-hydroxytryptamine and accumulation of 5-hydroxyindoleacetic acid. Coinjection of tryptamine with 5-hydroxytryptamine reduced the rate of conversion of 5-hydroxytryptamine to 5-hydroxyindoleacetic acid. These results indicate that intracerebroventricularly administered 5-hydroxytryptamine is removed by a monoamine oxidase dependent system. This catabolism is not affected by inhibition of presynaptic uptake, 5-hydroxytryptamine receptor type 1 or type 2 blockade, or destruction of serotonergic nerve terminals. The coadministration of tryptamine may prolong the residence period of 5-hydroxytryptamine through competition for monoamine oxidase.Key words: 5-hydroxytryptamine, tryptamine, monoamine oxidase, intracerebroventricular injection, catabolism.
Low zinc intake increases apparent oxidation of linoleic and α-linolenic acids in the pregnant rat
Authors: Cunnane S. C. , Yang J. , Chen Z.-Y.
Published: April 2011

Dietary zinc deficiency impairs desaturation and elongation of linoleic acid, but nothing is so far known about its effects on net whole-body utilization of linoleic or α-linolenic acids. By measuring intake, whole-body accumulation, and excretion of linoleic and α-linolenic acids, together with accumulation of their long-chain products, we hypothesized that a quantitative estimate could be obtained of their whole-body disappearance (apparent oxidation). This was evaluated in pregnant and nonpregnant rats given a low-zinc diet (3.4 vs. 34 mg zinc/kg diet in zinc-adequate controls). In the nonpregnant controls, low zinc intake did not significantly affect food intake or weight gain but did reduce whole-body accumulation of desaturated and (or) elongated products of linoleic and α-linolenic acids. In pregnant rats, low zinc intake reduced food intake and weight gain and doubled whole-body disappearance of linoleic and α-linolenic acids relative to that in the zinc-adequate controls. In contrast to the maternal fatty acid changes, low zonc intake had no significant effect on linoleic acid accumulation in the fetuses. We conclude that low zinc intake during pregnancy prevents the normal accumulation of long-chain fatty acids and differentially depletes maternal whole-body stores of linoleic and α-linolenic acids.Key words: fetus, linoleic acid, oxidation, pregnancy, zinc.
Fever alters osmosensitivity of hypothalamic–vasopressin system in the rat
Authors: Cridland Ruth A. , Kasting Norman W.
Published: April 2011

The osmosensitivity of peripheral vasopressin release was studied during healthy thermoregulation and endotoxin-induced fever. There was an increase in osmosensitivity following bolus injection of saline in febrile rats. These animals displayed a steeper slope in the linear relationship between plasma osmolality and plasma vasopressin levels compared with afebrile animals. The change in regression slope was due to a significantly lower plasma osmolality in febrile rats. The plasma osmolality of animals infused with hypertonic saline was similarly decreased, but data analysis failed to show a significant change in the regression slope. Osmotic thresholds were not altered in either group. There was an increased urine output in febrile rats, and consequently these animals excreted greater amounts of salts than afebrile rats. This could account for the lower plasma osmolality observed in the febrile rat.Key words: endotoxin, fever, osmolality, vasopressin.
Newborn piglet lungs release endothelin-1: effect of α-thrombin and hypoxia
Authors: Perreault T. , Stewart D. J. , Cernacek P. , Wu X. , Ni F. , Marte J. de , Giaid A.
Published: April 2011

Endothelin-1 (ET-1) is a 21 amino acid vasoconstrictor peptide produced by endothelial cells, the expression of which is modulated by a variety of vasoconstrictors, vasodilators, and inflammatory mediators. Hypoxia has been shown to increase ET-1 expression and release in cultured endothelial cells from the systemic circulation, but reports are contradictory regarding the pulmonary circulation. In this study, the release of ET-1 and its cellular localization in the isolated perfused newborn piglet lung were examined under control conditions and after stimulation with hypoxia or α-thrombin (positive control). In the control condition, perfusion pressure remained stable during the study period, and a progressive increase in levels of immunoreactive ET-1 (irET-1) was noted. When α-thrombin was added to the perfusion fluid, a slow gradual increase in perfusion pressure was produced and the levels of irET-1 were significantly greater than those measured in the control preparations. Finally, hypoxia produced a significant increase in the perfusion pressure; however, the release of irET-1 did not differ significantly from the control, if anything, the net release across the lung was diminished. In all conditions, immunocytochemistry using antiserum to human–porcine ET-1 revealed the presence of high ET-1-like immunoreactivity in epithelial cells of bronchi, bronchioles, and terminal bronchioles. In addition, endothelial cells of large and medium-size pulmonary arteries were only moderately immunoreactive for ET-1. These findings indicate that the neonatal pig lung can produce and release ET-1, and that its release can be increased by certain stimuli like α-thrombin. On the other hand, acute hypoxia does not appear to be an important stimulus to ET-1 in the neonatal pulmonary circulation. Therefore, ET-1 is not likely to be involved in the hypoxic pulmonary vasoconstriction in the newborn piglet.Key words: neonatal pulmonary circulation, endothelium-derived constricting factor.
Inhibition by nifedipine of endothelin-induced adrenal catecholamine secretion in anesthetized dogs
Authors: Yamaguchi Nobuharu
Published: April 2011

The present study was conducted to investigate local effects of endothelin-1 (ET-1) on basal adrenal catecholamine (CA) secretion and underlying mechanisms of action of ET-1 in anesthetized dogs. ET-1 was locally administered to the left adrenal gland through a catheter inserted into the left adrenolumbar artery. Plasma CA concentrations in adrenal venous and aortic blood were determined by an HPLC–electrochemical method. The local infusions (1 min, 0.5 mL/min) of ET-1, in doses of 0.01, 0.1, and 1.0 μg/mL, resulted in a dose-dependent increase in epinephrine secretion, rising from an initial basal value of 6.9 ± 1.4 ng∙min−1∙g−1 to maximum values of 7.6 ± 1.5, 81.1 ± 38.3*, and 680.9 ± 107.6* ng∙min−1∙g−1 (*p < 0.05, n = 7), respectively. Neither mean arterial pressure nor plasma CA levels in aortic blood altered following ET-1 infusions. A similar dose-dependent increase in norepinephrine output was also observed with ET-1. Following the initial peak observed during infusion with the highest dose of ET-1, the output of both epinephrine and norepinephrine remained significantly elevated over a period of 30 min. This ET-1-induced, long-lasting increase in adrenal CA output was abolished by nifedipine (100 μg/mL) similarly administered 10 min before ET-1 infusion. The results indicate that ET-1 directly enhances the basal secretion of CA from dog adrenal medulla in vivo. The study suggests that the ET-1-induced increase in adrenal CA secretion is, at least in part, mediated by the opening of dihydropyridine-sensitive L-type calcium channels at the level of adrenal medullary chromaffin cells.Key words: adrenal catecholamines, anesthetized dogs, calcium channels, endothelin-1, epinephrine, intra-adrenolumbar arterial infusion, nifedipine, norepinephrine.
Barbiturate attenuation of agonist affinity in cerebral arteries correlates with anesthetic potency and lipid solubility
Authors: Germann Peter , Laher Ismail , Poseno Tina , Bevan John A.
Published: April 2011

Barbiturates are known to reduce agonist sensitivity (EC50) in vascular smooth muscle; we provide evidence that the reduced agonist sensitivity can be correlated with a reduction in agonist affinity for its receptor. The histamine receptor was chosen since this agonist caused a consistent and maximum contraction of the cerebral artery used in this study. Segments of the basilar artery of white New Zealand male rabbits were set up in a small-vessel myograph in physiological salt solution, kept at 37 °C, pH 7.4, and bubbled with a 95% oxygen and 5% carbon dioxide gas mixture. The equilibrium dissociation constant (KA) of histamine for its receptor was calculated according to Furchgott's method by making three concentration–response curves to histamine: control, in the presence of phenoxybenzamine (0.02 μM), and after addition of a barbiturate in concentrations between 0.1 and 1.0 mM. All barbiturates tested, i.e., thiamylal, thiopental, pentobarbital, and phenobarbital, significantly reduced both histamine sensitivity and affinity. There is a significant correlation between histamine sensitivity and receptor affinity for histamine in a series of arterial segments from different animals. The attenuation of both pharmacological properties was consistent with the known rank order of anesthetic potency and with lipophilicity (r = 0.98; p < 0.05). Receptor reserve did not correlate with sensitivity. Thus, most of the change in receptor sensitivity was due to a change in agonist affinity. We suggest that barbiturates alter agonist receptor affinity by causing a perturbation in the membrane lipid environment of the receptor, leading to a conformational change, although alterations in intracellular mechanisms cannot be excluded.Key words: affinity, barbiturates, cerebral arteries, receptors, sensitivity.
Chronic verapamil treatment attenuates the negative inotropic effect of ethanol in diabetic rat myocardium
Authors: Brown Ricardo A. , Bhasin Prashant , Savage Adedapo O. , Dunbar Joseph C.
Published: April 2011

It is well established that cardiomyopathy is a consistent feature of diabetic myocardium and that alcohol consumption increases the risk of cardiovascular disease among diabetic subjects. The objective of this investigation was to determine whether acute or chronic verapamil treatment attenuates the negative inotropic effect of ethanol (EtOH) in the diabetic rat heart. Wistar rats were made diabetic with streptozotocin (55 mg/kg, iv). Left-ventricular papillary muscles, from normal and diabetic (8 weeks) rats, were superfused with Tyrode's solution at 30 °C while driven at 0.5 Hz. A subgroup of diabetic and normal animals received daily injections of verapamil (8 mg/kg, ip; 8 weeks), whereas muscles from untreated animals were exposed to verapamil (2 μM) in vitro. Peak tension developed (PTD), time to peak tension (TPT), time to 90% relaxation (RT90), and the maximum velocities of tension development (+VT) and decay (−VT) were determined in the absence and presence of clinically relevant concentrations of EtOH (80–240 mg/dL, i.e., 17.4–52.1 mM). Ethanol at 80 mg/dL reduced PTD, + VT, and −VT only in preparations from diabetic animals. Higher concentrations of EtOH (120–240 mg/dL) decreased PTD, TPT, +VT, and −VT. The negative inotropic effect of EtOH (240 mg/dL) was attenuated only in diabetic myocardium chronically treated with verapamil, whereas acute verapamil treatment potentiated the negative inotropic effect of EtOH in both normal and diabetic myocardium. Thus, chronic verapamil therapy diminishes the negative inotropic effect of EtOH in diabetic myocardium and acute verapamil treatment exaggerates it. Altered expression of membrane-bound calcium channels may be involved in the negative inotropic response to EtOH in long-term diabetes.Key words: ethanol, papillary muscle, inotropism, myocardium, force of contraction, diabetes mellitus.
A role for thyroid hormones in cold-induced elevation of blood pressure and cardiac hypertrophy
Authors: Fregly Melvin J. , Rossi Fabian , Cade J. Robert
Published: April 2011

The systolic blood pressures of two groups of rats that were exposed to cold (5 °C) for 4 weeks were elevated significantly above that of warm-acclimated controls maintained at 24 °C. At this time these groups were given the antithyroid drug aminotriazole in their food at 0.3 g/kg. At the same time, one group was given 15.8 μg thyroxine (T4)/kg body mass per day, while the second received 31.6. The doses were chosen as replacement (15.8 μg/kg) and twice replacement (31.8 μg/kg) for the rats. The results of the study revealed that both groups receiving aminotriazole and T4 had reductions in blood pressure within 1 week of initiation of treatment. Blood pressures reached control level after 5 weeks. Cardiac hypertrophy accompanying cold-induced hypertension was reduced with the lower dose of T4 and prevented with the higher dose. Serum concentrations of T4 and triiodothyronine (T3) in the two treated groups were reduced, while serum thyroid-stimulating hormone concentration and thyroid mass were increased above that of the warm-acclimated control group. This suggests that the rats were hypothyroid relative to the warm-acclimated control group. However, the treated rats grew at the same rate as nontreated, cold-exposed controls and had similar food and water intakes, a similar dipsogenic response to acute administration of isoproterenol, and similar colonic temperatures. These measurements suggest that the rats were not functionally hypothyroid. Nevertheless, the results suggest that a paradigm in which the secretory ability of the thyroid gland is blocked, and T4 is returned at a constant, albeit suboptimal, level, reduced blood pressure and cardiac hypertrophy in cold-exposed rats. Hence, the increased turnover of thyroid hormones that characteristically accompanies exposure to cold plays a role in these changes. These studies also indicate that an increase in the rate of secretion of T4 is not required for survival in cold air.Key words: cold-induced hypertension, thyroxine, triiodothyronine, thyroid-stimulating hormone, aminotriazole, antithyroid drug, blood pressure, cardiac hypertrophy, catecholamines, norepinephrine, epinephrine, dopamine.
Heterogeneous distribution of a fatty acid analogue uptake in the myocardium of aged rats
Authors: Communal Catherine , Verdetti Jean , Estrade Colette , Humbert Thierry , Demenge Pierre
Published: April 2011

The aim of this study was to determine the extent and location of damaged myocardial areas in senescent rats. The viability of myocardial cells was evaluated in virgin young (4 months old) and aged (29 months old) female Wistar rats by analysing the uptake of a slowly metabolisable radiolabelled fatty acid analogue, 15-p-iodophenyl-β-methylpentadecanoic acid (IMPPA). The biodistribution of IMPPA was measured in various organs, and regional myocardial uptake was specifically assessed using quantitative autoradiography. Myocardial enzymatic activity and DNA content were also evaluated with nitro blue tetrazolium (NBT) and propidium iodide (PÏ) staining, respectively. In senescent rats, cardiac and renal IMPPA uptake showed a significant (50%) reduction compared with young adult rats and the uptake was not significantly changed in the liver, spleen, lungs, and skeletal muscle. Total ventricular NBT staining and IMPPA uptake were almost homogeneous in young adult rats, whereas they were very heterogeneous in aged rats. In the latter, approximately 11% of the total ventricular volume showed a significantly decreased (by 60% or more) IMPPA uptake compared with normal values, and this reduction was greater in ventricle base than in apex. The myocardial areas unlabelled or poorly labelled by IMPPA represented 4, 5, 6, and 21% of the right ventricular, left ventricular epicardial, septal, and left ventricular endocardial volume, respectively, and were poorly stained with NBT. In some of these areas, PI staining indicated the presence of living cells unable to pick up NBT staining. In conclusion, in young adult rats, no myocardial lesions were observed using three different labelling techniques. However, important and significant myocardial lesioned areas were detected in senescent rats and were located preferentially in the left ventricular endocardium, as shown by a decrease in NBT staining and IMPPA uptake. These likely corresponded to a reduced number of cardiomyocytes and (or) a reduced aerobic substrate utilization, along with the development of fibrosis.Key words: senescent female rats, fatty acid analogue uptake, myocyte loss, lesioned and borderline areas.
Isoproterenol exerts cyclic AMP independent effects on DNA synthesis in cultured adventitial fibroblasts from spontaneously hypertensive and Wistar–Kyoto rats
Authors: Venance Shannon L. , Bennett Brian M. , Pang Stephen C.
Published: April 2011

Understanding the mechanism behind the growth response evident in the vasculature of the spontaneously hypertensive rat (SHR) remains elusive. Fibroblasts from the aortic adventitial layer of the SHR manifest the heightened proliferative rate in vitro relative to Wistar–Kyoto (WKY) rats that is conspicuous in cultured aortic smooth muscle cells. The adenylyl-cyclase/cyclic AMP signal transduction pathway is believed to be altered in hypertensive people and animals such that responses to β-adrenoceptor activation are blunted. The present study examined the effects of β-adrenoceptor-mediated versus direct activation of adenylylcyclase on intracellular cyclic AMP accumulation and subsequent DNA synthesis in cultured aortic fibroblasts. We hypothesized that elevation of cyclic AMP levels by both isoproterenol and forskolin would normalize the proliferative capacity of SHR fibroblasts. Forskolin increased intracellular cyclic AMP levels and inhibited epidermal growth factor stimulated thymidine incorporation in an equivalent manner in both SHR and WKY adventitial fibroblasts, implying that there is no difference in adenylylcyclase activity. Isoproterenol elevated cyclic AMP levels to a significantly greater degree in the SHR than did forskolin, and yet, relative to forskolin, attenuated growth factor induced DNA synthesis to a lesser extent. These data suggest that isoproterenol, via β-adrenoceptor activation, exhibits both cyclic AMP dependent and cyclic AMP independent effects in adventitial fibroblasts. The cyclic AMP independent effects of isoproterenol oppose the expected observations due to cyclic AMP and may offer an explanation to the blunted responses to β-adrenoceptor activation evident both in vitro and in vivo.Key words: spontaneously hypertensive rats, cultured adventitial fibroblasts, aorta, isoproterenol, forskolin, DNA synthesis, cyclic AMP.
Preservation of sarcoplasmic reticulum Ca2+-sequestering function in homogenates of different fibre type composition following sprint activity
Authors: Dossett-Mercer J. , Green H. J. , Chin E. , Grange F.
Published: April 2011

To examine the effect of exercise on sarcoplasmic reticulum function in muscle tissue of different fibre composition, adult male Wistar rats weighing 388 ± 23 g (x ± SE) ran intermittently on a treadmill until fatigue. Fatigue was induced by 15–20 min of running performed at 52 m/min on an 8° incline in periods of 2.5 min of exercise separated by 2 min of recovery. Analysis of sarcoplasmic reticulum Ca2+ ATPase activity determined in homogenates indicated no difference (p > 0.05) between age-matched control and exercised tissue for the soleus (SOL; 0.121 ± 0.012 vs. 0.156 ± 0.018 μmol∙mg−1 protein∙min−1), red gastrocnemius (RG; 0.381 ± 0.022 vs. 0.354 ± 0.022), or white gastrocnemius (WG; 0.526 ± 0.05 vs. 0.471 ± 0.031). Similarly, both total ATPase and Mg2+ ATPase activities were unaffected by the exercise in any of the tissues examined. Exercise also failed to alter sarcoplasmic reticulum Ca2+ uptake in homogenates of the SOL (1.43 ± 0.15 vs. 1.38 ± 0.19 nmol∙mg−1 protein∙min−1), RG (3.74 ± 0.29 vs. 3.59 ± 0.24), and WG (5.98 ± 0.48 vs. 5.41 ± 0.50). At fatigue, glycogen depletion was similar in all tissue types and amounted to 65.1% in the SOL (172 ± 9 vs. 60 ± 16 mmol∙glucosyl units−1∙kg−1 dry weight), 74.4% in RG (164 ± 8 vs. 42 ± 6), and 79% in the WG (167 ± 9 vs. 35 ± 9). It is concluded that exercise by itself does not alter sarcoplasmic reticulum Ca2+-sequestering function in tissues of primarily different fibre composition when determined in homogenates in vitro. The integrity of sarcoplasmic reticulum function is preserved despite an apparent extensive recruitment of all tissue types during the exercise.Key words: sarcoplasmic reticulum function, Ca2+ uptake, Ca2+ ATPase activity, muscle fibre types.
Effect of oral administration of ursodeoxycholic acid on rat hepatic and intestinal UDP-glucuronosyltransferase
Authors: Pozzi Enrique J. Sánchez , Catania Viviana A. , Luquita Marcelo G. , Roma Marcelo G. , Garay Emilio A. Rodríguez , Mottino Aldo D.
Published: April 2011

The effect of oral administration of the bile acid ursodeoxycholic acid on rat hepatic and intestinal microsomal UDP-glucuronosyltransferase was studied. The bile acid was administered during 8 days at a daily dose of 500 mg/kg body weight. Enzyme activity was assessed in native and activated microsomes, using bilirubin and p-nitrophenol as substrates. Activation was achieved either by including UDP-N-acetylglucosamine in the incubation mixture or by preincubating native microsomes with an optimal concentration of Lubrol Px. Irrespective of activation status of the microsomes, ursodeoxycholic acid treatment increased enzyme activities toward both substrates in intestine, but not in liver. The analysis of the degree of activation by Lubrol Px revealed that, at least for bilirubin, ursodeoxycholic acid decreased the latency of the intestinal enzyme. The analysis of the lipid composition of microsomes showed several changes in response to ursodeoxycholic acid in intestine but not in liver. Thus, a decrease in cholesterol/phospholipid ratio and an increase in the unsaturation index of total-lipid fatty acids, which correlated well with a membrane "fluidification," were observed. These modifications appear to be related to the lower latency of bilirubin UDP-glucuronosyltransferase in intestine from treated rats and could be responsible, at least in part, for the improvement of enzyme activity in this group. Whatever the mechanism involved, the increment of intestinal UDP-glucuronosyltransferase activities toward both substrates may be relevant as a complement to the hepatic enzymes in those liver diseases in which ursodeoxycholic acid is used as a therapeutic agent.Key words: bilirubin, p-nitrophenol, ursodeoxycholic acid, UDP-glucuronosyltransferase, microsomal lipids.
Paradoxic bradycardia (vasodepressor reaction) induced by inferior vena cava occlusion: the role of α- and β-adrenergic receptors and their interaction
Authors: Waxman Menashe B. , Asta John A. , Cameron Douglas A.
Published: April 2011

Vasodepressor reactions, characterized by paradoxic bradycardia, were induced in rats when the inferior vena cava was occluded during an infusion of isoproterenol. The effects of α-adrenergic receptors and their interaction with β-adrenergic receptors on the vasodepressor reaction were examined. Inferior vena cava occlusion was performed for 60 s, and the maximum changes in R–R were measured in 44 rats: (i) in control conditions, during phenylephrine (α1-adrenergic agonist), and during a combined infusion of phenylephrine and isoproterenol the R–R shortened significantly (−16.8 ± 1.4, −24.1 ± 2.2, and −4.9 ± 1.2 ms, respectively); (ii) isoproterenol and phentolamine and prazosin (nonselective and selective α-adrenergic antagonists) prolonged the R–R paradoxically (+89.2 ± 9.5, +58.9 ± 4.1, and +64.4 ± 10.2 ms, respectively); (iii) atropine and right vagotomy did not affect the phentolamine-induced R–R prolongation (+66.0 ± 2.4 and +73.8 ± 13.7 ms, respectively), but it was blocked by left vagotomy (−9.6 ± 1.1 ms); (iv) propranolol inhibited the prazosin-induced R–R prolongation (−14.3 ± 2.8 ms,); (v) epinephrine (α- and β-adrenergic agonist) shortened the R–R interval (−9.5 ± 2.2 ms), but following prazosin, epinephrine induced R–R prolongation (+13.7 ± 6.0 ms,); (vi) norepinephrine induced R–R prolongation (+21.0 ± 6.7 ms). It was concluded that (i) paradoxic bradycardia (vasodepressor reaction) dependent on vagal afferents can be induced by reduced venous return in the presence of excess exogenous β1-adrenergic stimulation (isoproterenol) or when endogenous α-adrenergic tone is antagonized (phentolamine or prazosin); (ii) the reaction can be blocked by α1-adrenergic stimulation; and (iii) epinephrine does not induce paradoxic bradycardia, whereas norepinephrine does, and this may be due to the stronger α-stimulating properties of epinephrine.Key words: vasovagal reaction, sympathetic tone.
Improvement in cardiac function in streptozotocin-diabetic rats by salt loading
Authors: Dai Soter , Fraser Heather , Yuen Violet G. , McNeill John H.
Published: April 2011

Effects of salt loading by drinking 0.9% NaCl solution on the myocardial performance in nondiabetic and diabetic Wistar rats were studied using the isolated working heart apparatus. Body weight and fluid and food intakes of these animals were monitored. Blood pressure and plasma levels of glucose, insulin, cholesterol, and triglycerides were also measured. Diabetes was induced by intravenous injection of streptozotocin (60 mg/kg). Diabetic rats were found to develop myocardial dysfunction at 8 weeks after STZ injection, accompanied by significant increases in food and fluid intakes, slowed body weight gain, hyperglycemia, hypoinsulinemia, and hyperlipidemia but without significant changes in blood pressure. Salt loading did not cause significant changes in any of the parameters studied in nondiabetic rats. However, in streptozotocin-diabetic rats given saline to drink, the impaired myocardial function was significantly improved and was associated with a significant reduction in hyperphagia and hyperlipidemia. Plasma glucose levels significantly decreased at weeks 1–3 but increased to the levels of untreated diabetic animals at weeks 4–7. There was an increase in fluid intake, but neither blood pressure nor plasma insulin levels were significantly affected. It is suggested that the improvements in cardiac function and hyperlipidemia in diabetic rats by salt loading may be related to each other; however, the mechanisms for these effects are not clear but are unlikely to be due to changes in glycemic control.Key words: streptozotocin diabetes, salt loading, cardiac dysfunction.
Effects of a new dihydropyridine derivative, S12968 (pranedipine), and its stereoisomer, S12967, on renal effects of endothelin-1
Authors: Montañés Immaculada , Flores Olga , Eleno Nélida , López-Novoa José M.
Published: April 2011

The purpose of the present study was to assess in rats the prevention by two enantiomers of a new dihydropyridine derivative (pranedipine) (called S12967 for the dextrogyre(+) and S12968 for the levogyre (−) molecules) of the renal and cardiovascular effects induced by endothelin-1. The injection of endothelin-1 (1 nmol/kg body weight) induced a sharp and transient decrease in urine flow, sodium and potassium excretion, glomerular filtration rate, renal plasma flow, and renal blood flow, a significant increase in renal vascular resistance, and a small but significant increase in arterial pressure. Treatment with S12968 alone (0.3 mg/kg) induced a 2.5-fold increase in urine flow and potassium excretion and a 4.5-fold increase in sodium excretion. Pretreatment with S12968 completely blocked the endothelin-1 induced increase in arterial pressure, did not affect the acute effect of endothelin-1 on urine flow, sodium and potassium excretion, filtration rate, and renal blood flow, but blunted the effect on renal vascular resistance. Administration of S12967 alone (1 mg/kg) did not induce changes in either renal function or arterial pressure. In S12967-treated animals, endothelin-1 also induced a transient increase in arterial pressure and renal vascular resistance but failed to change renal function in a significant manner. In summary, the above reported experiments show that at the higher, nonhypotensive doses, the levogyre enantiomer (S12968) of a new dihydropyridine derivative (pranedipine) completely prevented the hypertensive effect of endothelin 1, and partially prevented the effect of endothelin-1 on renal vascular resistance. The dextrogyre enantiomer (S12967) had almost no effect on either mean arterial pressure or renal vascular resistance but completely blocked the endothelin-1-induced decrease in urine flow and urinary sodium excretion.Key words: calcium antagonists, endothelin, dihydropyridines, kidney, renal function (rat).
Effect of ovarian steroids on hypothalamic norepinephrine-induced adenylate cyclase activity
Authors: Zubin Palmira , Defagot Cristina
Published: April 2011

The adenylate cyclase activity induced by norepinephrine (10−8–10−9 M) was studied in hypothalamic particulate fractions from female rats. The effect of estradiol on this activity was studied in rats that were ovariectomized in diestrus 1, injected with estradiol benzoate (50 μg/kg body weight), and killed 48 h later. The effect of progesterone was studied in fractions from female cycling rats injected in the morning of diestrus 2 with progesterone (2 mg/rat); these animals were killed 30 or 48 h after the steroid injection. The blockade of norepinephrine-induced adenylate cyclase activity by α- and β-blocking agents (10−8–10−9 M) was also evaluated. The enzymatic activity was determined by monitoring the capacity to produce cAMP from ATP at saturated levels; cAMP was assayed by radioimmunoassay. At 48 h after administration, estradiol benzoate increased the norepinephrine-induced adenylate cyclase activity in the hypothalamus. This effect was not changed by the presence of phenoxybenzamine, an α-adrenoceptor blocker, but was greatly reduced by propranolol, the β-adrenoreceptor blocker. In contrast, the progesterone, at 30 and 48 h after injection, decreased the hypothalamic adenylate cyclase activity, and this effect was preferentially antagonized in the presence of phenoxybenzamine rather than propranolol. These results suggest that estrogen and progesterone act selectively on one or another type of adrenergic receptor at the hypothalamic level.Key words: hypothalamus, ovarian steroids, norepinephrine turnover, adenylate cyclase activity, α- and β-adrenoreceptors.
Relationship between ATPase activity, Ca2+, and force in α-toxin- and β-escin-treated smooth muscle
Authors: Kerrick W. Glenn L. , Hoar Phyllis E.
Published: April 2011

Smooth muscle was made permeable with α-toxin and β-escin. ATPase activity was measured using a phosphoenolpyruvate – pyruvate kinase regenerating system for ATP that was monitored by NADH fluorescence changes, and Ca2+ was measured using fura 2 fluorescence. α-Toxin- and β-escin-treated bundles of cells had a high ATPase activity, which was reduced 80% when exposed to 1% Triton X-100. This Triton-sensitive ATPase activity was increased by approximately 20% when GTP or GTPγS was added to the solutions and was of much greater magnitude than the Ca2+-activated ATPase associated with contraction. This high membrane ATPase activity will cause a gradient of ATP into and ADP out of the bundle of cells. Thus modulation of this ATPase by G-protein–receptor mechanisms could alter the force at a constant Ca2+ concentration by changing the ADP/ATP ratio within the cells. Measurements of the fura 2 fluorescence ratio (340/380) in α-toxin-treated bundles of cells following sudden changes in extracellular Ca2+ showed that the cells were not freely permeable to Ca EGTA. Similar experiments in β-escin-treated cells showed the cells to be much more permeable to Ca EGTA. These experiments indicate that great care must be taken in α-toxin- and β-escin-treated fibers to make sure that the intracellular ATP, ADP, and Ca2+ are held constant.Key words: α-toxin, skinned fibers, β-escin, ATPase activity, intracellular calcium, calcium ion activation, smooth muscle, force, fura 2, ADP.
Calponin and smooth muscle regulation
Authors: Carmichael Jeffrey D. , Winder Steven J. , Walsh Michael P. , Kargacin Gary J.
Published: April 2011

Calponin has been implicated in the regulation of smooth muscle contraction as a result of its ability to inhibit the actin-activated Mg ATPase of smooth muscle myosin. This inhibitory effect is abolished by phosphorylation of calponin by Ca2+/calmodulin-dependent protein kinase II or protein kinase C, and restored following dephosphorylation by a type 2A protein phosphatase. Confocal immunofluorescent images of isolated smooth muscle cells colabeled with antibodies to calponin and actin or to calponin and tropomyosin indicate that calponin is present on thin filaments throughout the cell cytoplasm. Both calponin phosphorylation and myosin light chain phosphorylation increased in intact smooth muscle tissue strips when they contracted in response to carbachol or the phosphatase inhibitor okadaic acid. These results support the hypothesis that calponin phosphorylation–dephosphorylation plays a role in regulating smooth muscle contraction.Key words: calponin, smooth muscle, confocal microscopy, phosphorylation–dephosphorylation.
Potential role for phenotypic modulation of bronchial smooth muscle ceils in chronic asthma
Authors: Halayko Andrew J. , Stephens Newman L.
Published: April 2011

Asthma is considered to be a chronic inflammatory disease of the airways and is highlighted by excessive airway narrowing in response to various stimuli. Subepithelial fibrosis and increased airway smooth muscle mass are characteristic pathological features of the disease. Airway remodelling in asthma involves cellular hyperplasia and hypertrophy of bronchial myocytes. Smooth muscle cells from a variety of tissues have been shown to be multifunctional mesenchymal cells capable of expressing considerable phenotypic plasticity in vivo in response to injury and pathological stimuli. The growth response of vascular smooth muscle cells following arterial injury has been fairly well characterized, and it appears many of the chemical mediators responsible are common to the inflamed bronchi seen in asthmatics. Specific studies regarding the effects of phenotypic modulation of airway smooth muscle and the potential contribution of this phenomenon to the pathogenesis of chronic asthma have not been carried out. Limited evidence, some indirect, suggests that contractile properties of smooth muscle from inflamed tissues are altered; if this is the case in asthma, then considerations of the effects of airway smooth muscle hypertrophy should be broadened beyond that of only contributing to bronchial hyperresponsiveness via an increase in bronchial wall thickness. Recruitment and modulation of smooth muscle cells to functionally different phenotypes, which contribute to fibrosis by secreting extracellular matrix materials and promote cellular hyperplasia by producing growth factors, are known to occur in atherogenic blood vessels; and evidence suggests that airway smooth muscle cells might play a similar role in asthma. We report the identification of markers of differentiation for airway smooth muscle cells. These markers should be useful tools in the elucidation of phenotypic heterogeneity of smooth muscle in asthmatic airways and, thereby, allow for the definition of a clearer role for bronchial smooth muscle cells in the pathogenesis of chronic asthma.Key words: airway smooth muscle cells, asthma, phenotype, pathogenesis, proliferation.
Auxotonic loading and airway smooth muscle shortening
Authors: Li Weilong , Stephens Newman L.
Published: April 2011

Isometric and isotonic contractions represent two extremes in loading regimens that can be imposed on a contracting smooth muscle preparation in vitro. Under physiological conditions, however, it is likely that smooth muscle in hollow organs contracts against auxotonic loads, the magnitude of which is a function of muscle shortening. Therefore, attempts to determine physiologically significant contractile properties of smooth muscle should be made under auxotonic loading conditions. An electronic loader was built to provide four auxotonic loading modes: linear, logarithmic, sigmoidal, and exponential. These shortening-dependent auxotonic loads were imposed on an actively shortening canine tracheal smooth muscle. Results confirmed that (i) active force generated by the muscle is load dependent but that (ii) at the same load borne by the muscle in its steady state, i.e., at the same maximum force generated by the muscle, the maximum shortenings under different loading modes were significantly altered. The shortening was maximal under the exponential loading mode, which provided the smallest load in the early phase of contraction, while it was the least under the logarithmic loading mode, which provided the greatest load in that phase. We concluded that the shortening achieved by an airway smooth muscle was a function not only of the magnitude of the final load imposed on the muscle but, more importantly, of the time course of loading. An explanation was provided by a previous report, which stated that cross-bridge cycling rate of smooth muscle was maximum in the early phase of activation and decreased thereafter, and that about 70% of the total shortening of the muscle was completed in the first 2 s of a light-loaded isotonic contraction with a contraction time of 10 s. A heavier load applied during the early phase of contraction will inhibit the major portion of the shortening, whereas a light load applied during this early stage will allow more shortening. Alteration in the viscoelastic properties of tissues that attach to airway smooth muscle and load it auxotonically could strongly affect the muscle's ability to shorten in vivo.Key words: auxotonic shortening, airway smooth muscle, loading history.