bluuebunny/crossref_metadata_2025 huggingface dataset:
Increase in somatostatin to glucagon ratio in islets of alloxan-diabetic dogs: effect of insulin-induced euglycemia
Authors: Rastogi K. S. , Brubaker P. L. , Kawasaki A. , Efendic S. , Vranic M.
Published: April 2011

We have previously shown that acute insulin-induced normalization of glycemia in alloxan-diabetic (A-D) dogs results in marked inhibition of total pancreatic glucagon content, but normalization of somatostatin content. We suggested that this glucagon deficiency might account for A-cell unresponsiveness in diabetes. To examine these changes in detail at the islet level, morphometric and immunologic analyses were carried out on pancreata from four normal (N), four hyperglycemic A-D dogs (HD), and four A-D dogs after acute normalization of glycemia with insulin (ND). The total number of islets per pancreas (3.9 × 106 ± 0.5 × 106; determined from the number of islets per square millimetre) was reduced by 60% (p < 0.001) in HD, and this was not affected by acute normalization of glycemia. Insulin content per islet was 1247 ± 205 pg in N, and this was reduced in both HD and ND to 2 and 5%, respectively (p < 0.001). Similarly, insulin-containing B-cell area was 76 ± 1% of the total islet area in N, and was unmeasurable in HD and ND. Glucagon content per islet was 89 ± 6 pg in N, and this was increased by 215% (p < 0.001) in HD, but was normalized in ND. The A-cell area increased concomitantly by 170% from 17 ±1 to 46 ± 2% (p < 0.01) of islet area in HD, and remained elevated in ND. In contrast, somatostatin content per islet was 3.0 ± 1.1 pg in N, but was increased by 567% (p < 0.01) in HD and fell to 200% (p = ns) of N in ND. D-cell area increased by 55% in HD, from 11.5 ± 0.8 to 17.8 ± 0.9% (p < 0.01), and remained elevated at 15.6 ± 1.1% (p < 0.01) in ND. The ratio of somatostatin to glucagon content in the islet was therefore 0.03 ± 0.01 in N, and this was increased by 167 (p = ns) and 333% (p < 0.05) in HD and ND, respectively. We speculate that the increase in the islet somatostatin to glucagon ratio in normoglycemic diabetic dogs may play a role in the suppression of glucagon responses in diabetes.Key words: islet, glucagon, somatostatin, diabetes, insulin-induced euglycemia.
Effects of staurosporine and calphostin C, two structurally unrelated inhibitors of protein kinase C, on vascular tone
Authors: Henrion Daniel , Laher Ismail
Published: April 2011

In isolated rings of the rabbit facial vein, facial artery, and aorta, calphostin C and staurosporine, inhibitors of protein kinase C, reduced myogenic tone and norepinephrine (1 μM), K+ (80 mM), and Ca2+ (1.6 mM) induced tone. In all instances, staurosporine was more potent than calphostin C. In contrast to staurosporine, the IC50 value of calphostin C against myogenic tone was similar to that recorded for protein kinase C in biochemical studies (0.086 vs. 0.050 μM) and the average IC50 values of calphostin C against norepinephrine (2.2 μM), K+ (3.3 μM), and Ca2+ (4.3 μM) in the three vessels were similar to that for myosin light-chain kinase in biochemical studies (>5.0 μM). In the facial vein, calphostin C was 59-foid more potent against myogenic tone than against Ca2+-induced tone and 8-fold more specific for myogenic tone than was staurosporine. In addition, at concentrations not affecting K+ (80 mM) induced tone, calphostin C suppressed 1-oleoyl-2-acetyl-sn-glycerol induced tone in the facial vein, whereas staurosporine only attenuated it by 65%. Thus calphostin C inhibits protein kinase C dependent tone in isolated blood vessels to a greater extent than does staurosporine.Key words: staurosporine, calphostin C, myogenic tone, protein kinase C, blood vessels.
Nitric oxide as putative nonadrenergic noncholinergic inhibitory transmitter in the opossum sphincter of Oddi
Authors: Allescher H. D. , Lu S. , Daniel E. E. , Classen M.
Published: April 2011

The sphincter of Oddi has a typical nonadrenergic noncholinergic inhibitory innervation; however, the transmitter of this inhibition has not been identified. The aim of the present study was to evaluate whether metabolites of the L-arginine – nitric oxide synthase pathway mediate neural inhibition in the sphincter of Oddi of the opossum. Electrical field stimulation at various frequencies (3, 5, and 10 pulses/s), performed in the presence of guanethidine (10−6 M) to exclude adrenergic responses, caused a slight, but significant excitatory response of the sphincter of Oddi. The responses were more pronounced at the duodenal side of the sphincter of Oddi than on the hepatic side. When the electrical field stimulation was repeated after blockading muscarinic receptors, using atropine (10−6 M), a potent inhibitory response was obtained. The inhibitory response to each of the various stimulation parameters was similar. Addition of L-arginine methyl ester (L-NAME, 2 × 10−4 M) abolished and reversed the inhibitory effect of electrical field stimulation, resulting in a potent stimulatory effect. Higher frequencies (5 and 10 pulses/s) were more potent in causing a stimulatory response than lower frequencies (3 pulses/s). The excitatory effect of electrical field stimulation was blocked or reversed to inhibition when the amino acid L-arginine (2 × 10−3 M) was added to the bath. In a second series of experiments, the inhibitory effect of electrical field stimulation in the presence of atropine and guanethidine was not prevented after the addition of methylene blue (5 × 10−5 M), a substance that, in vascular smooth muscle, has been demonstrated to block cyclic GMP dependent inhibitory responses. These data demonstrate that the sphincter of Oddi is characterized by an excitatory innervation that is partly cholinergic and partly nonadrenergic noncholinergic (NANC), while the NANC inhibitory response of this sphincter muscle is mediated by the release of endogenous nitric oxide or related compounds.Key words: nonadrenergic, noncholinergic, nitric oxide, L-arginine, sphincter of Oddi, methylene blue.
Lipid absorptions passing through the unstirred layers, brush-border membrane, and beyond
Authors: Thomson A. B. R. , Schoeller C. , Keelan M. , Smith L. , Clandinin M. T.
Published: April 2011

Lipids are components of our diet and luminal secretions, with physicochemical characteristics that determine their digestion and absorption in the gastrointestinal tract. Lipids include triglycerides, phospholipids, and cholesterol. Dietary lipids contain approximately 97% triglycerides, with small amounts of phospholipids and cholesterol. These components are important in cell membrane composition, fluidity, peroxidation, prostaglandin and leukotriene synthesis, and cellular metabolic processes. Lipids are implicated in the mechanisms of brain development, inflammatory processes, atherosclerosis, carcinogenesis, aging, and cell renewal. Duodenal hydrolysis of dietary lipids and biliary phospholipids and cholesterol is carried out by pancreatic lipase, colipase, phospholipase A2, and cholesterol esterase. Bile acid solubilization results in mixed micelles and liposomes, in gel and liquid crystal phases. Lipid digestion products pass across the intestinal unstirred water layer. For long-chain fatty acids and cholesterol, passage across the unstirred water layer is rate limiting, whereas passage of short- and medium-chain fatty acids is limited by the brush-border membrane. Within the unstirred water layer, an acidic microclimate aids micellar dissociation so that protonated, and to a lesser extent, nonprotonated monomers then pass across the intestinal brush-border membrane. Absorptive mechanisms have been studied extensively in relation to lipid composition, fatty acid chain length, degree of unsaturation, essential fatty acid content, phospholipid components, and cholesterol. Enterocytes may take up lipids from the intestinal lumen or from lipoproteins of the bloodstream, but these pools are likely to be functionally distinct. Recent advances are reviewed, including recent advances in the area of microclimates, compartmentation, lipid binding proteins, intracellular trafficking, intestinal lipoproteins, release of lipids across the basolateral membrane, and dietary effects.Key words: diet effects, lipid binding proteins, lipoproteins.
Are dietary protein requirements altered in diabetes mellitus?
Authors: Hoffer L. John
Published: April 2011

Authorities in the United States and Canada have recently advised persons with diabetes to limit their protein intake to the level recommended for normal adults, and consider further reductions in the presence of incipient renal disease. This recommendation ignores metabolic data indicating that conventional insulin therapy fails to fully normalize the abnormal protein metabolism characteristic of untreated diabetes. The residual abnormality is an increased or poorly regulated rate of amino acid catabolism. It is proposed in this review that the large amount of protein in the customary diet compensates for this increased amino acid catabolism, and thus protects many diabetic individuals from protein malnutrition. If this is true, protein restriction to a level that still meets the requirement of an individual with normal insulin metabolism could be too little for someone with diabetes. The current assumption that the protein requirement in diabetes is equal to the value set for normal individuals should be reconsidered.Key words: diabetes mellitus, protein metabolism, diet, nutrition, malnutrition.
Pathways for the uptake and conservation of docosahexaenoic acid in photoreceptors and synapses: biochemical and autoradiographic studies
Authors: Bazan Nicolas G. , Turco Elena B. Rodriguez de , Gordon William C.
Published: April 2011

Docosahexaenoic acid (22:6n−3) esterified into phospholipids represents by far the most prevalent fatty acid of rod photoreceptor disc membranes and synaptic terminals. During synaptogenesis and photoreceptor biogenesis, plasma lipoproteins, secreted mainly by the liver, are the main source of plasma 22:6n−3 for the central nervous system. This systemic route (the long loop) also operates in mature animals for morphogenesis and maintenance of excitable membranes (e.g., during constant renewal of photoreceptor disc membranes). When radiolabeled 18:3n−3, the dietary precursor of 22:6n−3, is systemically supplied to 3-day-old mouse pups, it is elongated and desaturated in the liver, leading to the synthesis of 22:6n−3 – lipoproteins that shuttle the fatty acid through the bloodstream to retina and brain. When radiolabeled 22:6n−3 was used, a more efficient labeling of brain and retinal lipids was achieved. The retinal pigment epithelium is involved, not only in the uptake of 22:6n−3 from circulating lipoproteins in the choriocapillaris but also in the recycling of 22:6n−3 from degraded phagosomal phospholipids back to the inner segments of photoreceptors (the short loop), following each phagocytic event. An interplay among efficient 22:6n−6 delivery from the liver, selective uptake by retinal pigment epithelium photoreceptor cells, and avid retinal retention may contribute to the enrichment of excitable membranes of the retina with 22:6n−3 – phospholipids.Key words: docosahexaenoic acid, phospholipids, photoreceptors.
Partners in defense, vitamin E and vitamin C
Authors: Chan Alvin C.
Published: April 2011

In addition to the enzymic mechanism of free-radical removal, essential nutrients that can scavenge free radicals, such as vitamins E and C, constitute a strong line of defense in retarding free radical induced cellular damage. Distinct pathways for the repair of oxidized vitamin E in human cells have been recently identified. Within 0.5 min after the addition of arachidonic acid to a human platelet homogenate, over half of the platelet vitamin E and added arachidonate were metabolized by platelet cyclooxygenase and lipoxygenase pathways. After adding nordihydroguaiaretic acid, a lipoxygenase inhibitor and a strong reductant, over 60% of the oxidized vitamin E was regenerated. To test other physiological, water-soluble reductants that may help regenerate vitamin E, eicosatetraynoic acid, a lipoxygenase inhibitor that is not an antioxidant, was used. In this system, both ascorbate and glutathione provided significant vitamin E regeneration. Kinetic analysis and studies of vitamin E regeneration in a protein-denaturing system revealed that ascorbate regenerates vitamin E by a nonenzymic mechanism, whereas glutathione regenerates vitamin E enzymatically. These studies suggest that significant interaction occurs between water- and lipid-soluble molecules at the membrane–cytosol interface and that vitamin C may function in vivo to repair the membrane-bound oxidized vitamin E.Key words: vitamin C, vitamin E, vitamin E cycle, glutathione, human platelets.
Tissue glutathione, nutrition, and oxidative stress
Authors: Bray Tammy M. , Taylor Carla G.
Published: April 2011

Glutathione, a cysteine-containing tripeptide, is the most abundant nonprotein thiol in mammalian cells. Glutathione plays an important role in the detoxification of xenobiotic compounds and in the antioxidation of reactive oxygen species and free radicals. Because of its multiple functions in various tissues and its involvement in many diseases and malnutrition, a clear understanding of the interrelationships among tissue glutathione, nutrition, and oxidative stress is clinically relevant. The focus of this review is to discuss the regulation of tissue glutathione concentration by diet and nutritional status, and to apply this information to those diseases and malnutrition in which decreased tissue glutathione and increased oxidative stress are implicated. A potential strategy to rapidly restore glutathione for both antioxidant and immune defense systems before therapeutic treatment in malnourished patients is discussed.Key words: glutathione, dietary regulation, oxidative stress, malnutrition.
Peripheral modulation of duodenal and colonic motility and arterial pressure by neuropeptide Y, neuropeptide Y fragment 13–36, peptide YY, and pancreatic polypeptide in rats: cholinergic mechanisms
Authors: Wager-Pagé S. A. , Raizada E. , Veale W. , Davison J. S.
Published: April 2011

The pancreatic polypeptide-fold (PP-fold) peptides neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) (500 pmol/kg) increased duodenal and colonic intraluminal pressure of urethane-anesthetized rats following intravenous (iv) bolus injections. Increases in mean arterial pressure (MAP) accompanied the excitatory effects of NPY and PYY on gastrointestinal motility in these rats during the same time period. Atropine attenuated PYY's excitatory effect on duodenal pressure of rats. Excitatory effects of NPY, PYY, and PP (iv) on rat colon were not mediated via the muscarinic receptors. In the presence of hexamethonium, a nicotinic antagonist, PP (iv) increased colonic pressure to a greater extent than when administered alone. This observation suggested that PP had an inhibitory effect on colonic motility, which was not apparent as a result of the larger excitatory component. The nicotinic antagonist did not modulate the effects of peripherally administered NPY or PYY on duodenal or colonic motility in anesthetized rats. The Y2 receptor ligand, NPY (13–36) (iv) (500 pmol/kg), increased duodenal and colonic pressure in rats to the same extent as the full NPY molecule. Therefore, the peripheral effect of PYY and NPY on duodenal and colonic motility in rats may be mediated via Y2 receptors. NPY and PYY (iv) initially increased MAP, which then return to baseline values. Unlike NPY and PYY (iv) which produced short-term hypertensive effects, PP (iv) decreased MAP. Atropine did not attenuate the hypertensive effects of PYY and NPY (iv); however, the hypotensive effect of PP (iv) was blocked by atropine. The effects of the PP-fold peptides on MAP were not altered in the presence of hexamethonium. MAP in anesthetized rats was not modulated by NPY (13–36) (iv). Peripheral modulation of MAP by the PP-fold peptides does not correspond with alterations in gastrointestinal motility observed in these studies.Key words: pancreatic polypeptide-fold peptides, duodenum, colon, atropine.
Forskolin and isoproterenol effect discrete responses on epidermal growth factor induced DNA synthesis in aortic smooth muscle cells
Authors: Venance S. L. , Bennett B. M. , Pang S. C.
Published: April 2011

Defining the mechanisms regulating the proliferation of vascular smooth muscle is necessary to better understand the pathogenesis of atherosclerosis and hypertension. In the present investigation, we examined the effects of incubation with forskolin or isoproterenol on the proliferation of cultured rat aortic smooth muscle cells. Forskolin, a direct activator of adenylate cyclase, and isoproterenol, a β-adrenergic agonist, increased intracellular cyclic AMP levels in a concentration-dependent manner, subsequent to a 5-min exposure. Isobutylmethylxanthine at 100 μM attenuated epidermal growth factor stimulated DNA synthesis by 35% without affecting intracellular cyclic AMP levels. Forskolin dose-dependently augmented this inhibition. In contrast, a 24-h exposure of cells to isoproterenol resulted in a biphasic effect on growth factor stimulated thymidine incorporation. Both forskolin and isoproterenol attenuated thymidine incorporation to the same degree up to 12 h poststimulation, the onset of S phase. By 16 h poststimulation, [3H]thymidine incorporation in smooth muscle cells treated with isoproterenol was significantly enhanced by 50%, whereas forskolin treatment continued to attenuate DNA synthesis by 40%. Somewhat surprisingly, this disparity in effect on DNA synthesis was evident in spite of heterologous desensitization to rechallenge by either forskolin or isoproterenol subsequent to a 24-h incubation with either drug. These results suggest that the isoproterenol enhancement of epidermal growth factor stimulated DNA synthesis in rat aortic smooth muscle cells may be cyclic AMP independent.Key words: smooth muscle cells, proliferation, cyclic AMP.
Sexual differences in hypothalamic adenosine 3′,5′-cyclic monophosphate content
Authors: Zubin P. , Defagot C.
Published: April 2011

Hypothalamic adenosine 3′,5′-cyclic monophosphate (cAMP) concentration was measured in the morning (10:00) and afternoon (16:00) in castrated and intact rats of both sexes to evaluate a possible sexual difference. Castration produced different effects on the hypothalamic cAMP concentration. In females, ovariectomy significantly reduced total hypothalamic cAMP concentration, whereas in males, orchidectomy elevated hypothalamic cAMP content. This observation was independent of the time of day at which the animals were killed. On the other hand, administration of the α-adrenoreceptor blocking agent phenoxybenzamine or theβ-adrenoreceptor blocker propranolol lowered the concentration of cAMP in the hypothalamus. However, this effect was selective and related to the time of day when the animals were killed. Phenoxybenzamine reduced the hypothalamic cAMP content in males killed in the afternoon, whereas the effect of propranolol was significant in males killed in the morning. These results indicate a response of hypothalamic cAMP to adrenoreceptor blockers in male rats opposite to that reported previously from our laboratory in female rats, suggesting that the functional behavior of the hypothalamic adrenergic response is strongly sex related.Key words: cyclic AMP, hypothalamus, gonadal steroids, norepinephrine concentration, α- and β-adrenoreceptor blockers, circadian rhythm.
Phosphatidylcholine metabolism in hypoxic and phospholipase C exposed rat ventricular myocytes
Authors: Myrmel Truls , Steigen Terje K. , Bjordal Erling , Larsen Terje S.
Published: April 2011

A phospholipase C specific for choline and ethanolamine acyl and plasmalogen glycerophospholipids (PC-PLC) has been described in myocardial tissue. In the present study we investigated whether an endogenous PC-PLC is activated in hypoxic, substrate-free incubations of rat ventricular myocytes. The phosphatidylcholine pool of the myocytes was prelabelled with [14C]choline during a 4-h preincubation (pulse) period. The myocytes were subsequently washed and incubated for another 2 h (chase period) in normoxic, hypoxic, or hypoxic buffer supplemented with PC-PLC from Bacillus cereus. We hypothesized that an increase in the total (intracellular plus extracellular) content of [14C]phosphocholine (one of the products resulting from PC-PLC action on phosphatidylcholine) throughout the chase period would indicate PC-PLC activity. Instead, an apparent decrease was observed for this parameter in all myocyte groups (17–29%), even in the one exposed to exogenous PC-PLC. However, 60 min after the start of the chase period, the level of total [14C]phosphocholine was higher in hypoxic (p = 0.022) and hypoxic + PC-PLC exposed (p = 0.013) myocytes compared with normoxic controls. The total content of [14C]choline increased significantly (p < 0.017) in all myocyte groups during the incubation period (98–153%) as a result of an increment of this metabolite in the buffer. Furthermore, the values measured in hypoxic and hypoxic + PC-PLC exposed myocytes during the first hour of the chase period were significantly (p < 0.017) higher than the corresponding values in normoxic myocytes. The present results do not allow firm conclusions regarding endogenous PC-PLC activation in energy-depleted rat cardiac myocytes. On the other hand, the data suggest activation of phosphocholine phosphatase or phospholipase D under these conditions.Key words: phosphatidylcholine, phospholipase C, phospholipase D, myocytes, hypoxia.
Selective sequestration of nitric oxide by subcellular components of vascular smooth muscle and platelets: relationship to nitric oxide stimulation of the soluble guanylyl cyclase
Authors: Liu Zhenguo , Nakatsu Kanji , Brien James F. , Beaton E. Danielle , Marks Gerald S. , Maurice Donald H.
Published: April 2011

Sequestration of nitric oxide (NO) by subcellular fractions isolated from bovine pulmonary arterial medial layer (BPA) and rabbit platelets (RP) was studied utilizing a novel chemiluminescence – headspace gas technique. Sequestration in all fractions was similarly rapid (5 min) and remained constant for at least 30 min. When incubated with 108 pmol of NO, the BPA mitochondrial, microsomal, and nuclear fractions sequestered 22.8 ± 1.9, 20.5 ± 2.2 and 15.2 ± 3.6% of the NO, respectively (n = 14). However, significantly more of the 108 pmol of NO, 36.8 ± 2.8 and 32.9 ± 3.6%, respectively, was sequestered by the BPA homogenate (about 2 mg protein/mL) and BPA cytosolic fraction (about 1 mg protein/mL) (n = 19). Also, RP cytosolic fraction (about 3 mg protein/mL) sequestered a greater amount of NO than any BPA fraction when incubated with 108 pmol of NO (83.0 ± 1.0%; n = 3). Analysis of the binding data obtained for the BPA homogenate and cytosolic fraction was consistent with the existence of two binding sites, one site with a Kd of approximately 100 nM and another with a Kd of approximately 1 μM. Both the BPA homogenate fraction and the cytosolic fraction as well as the RP cytosolic fraction were shown to have soluble guanylyl cyclase activity. The nitrovasodilator sodium nitroprusside (SNP) caused a concentration-dependent increase in the activity of this enzyme in all these fractions. Maximum stimulations caused by 1 mM SNP in BPA homogenate fraction, BPA cytosolic fraction, and RP cytosolic fraction were equivalent to 2-, 4- and 3-fold increases in catalytic activity, respectively. No effect of SNP was observed in BPA mitochondrial, microsomal, or nuclear fraction. Prior incubation of BPA and RP cytosolic fractions with authentic NO significantly stimulated the soluble guanyiyl cyclase activity. In both the BPA and RP cytosolic fractions, maximal stimulation brought about by prior incubation with authentic NO was equivalent to approximately 60% of that caused by 100 μM SNP. Thus, incubation of subcellular fractions from two nitrovasodilator-sensitive tissues with authentic NO resulted in significant sequestration of the free radical in these fractions and a concentration-dependent activation of the soluble guanylyl cyclase. In conclusion, the chemiluminescence – headspace gas technique is a suitable method for the study of NO sequestration in subcellular fractions of various tissues. Also, this study demonstrates that NO is sequestered preferentially by subcellular fractions of BPA and RP that contain soluble guanylyl cyclase activity, and that the sequestration of NO in these fractions stimulates the catalytic activity of this enzyme.Key words: nitric oxide, vascular smooth muscle, platelets, soluble guanylyl cyclase.
Effects of long-term cocaine administration and exercise on cardiac metabolism and isomyosin expression
Authors: Morris G. S. , Fiore P. V. , Hamlin R. L. , Sherman W. M.
Published: April 2011

Although chronic cocaine use is cardiotoxic, its use remains problematic in athletics. Hence adaptive changes induced in the heart by superimposing chronic cocaine use on an exercise training are of interest but remain poorly understood. Therefore this study investigated the effects of cocaine treatment combined with exercise training on the metabolic and contractile properties of the heart. Male Sprague–Dawley rats were assigned to one of four groups: normal sedentary (NS, n = 6), cocaine sedentary (CS, n = 6), normal trained (NT, n = 6), and cocaine trained (CT, n = 6). Trained animals were sprint trained 4 times/week. CS and CT animals received cocaine (25 mg/kg, ip) 6 times/week, 15 min before each exercise bout and 2 additional times per week. After 12 weeks, all animals were sacrificed, and the hearts were removed and analyzed for citrate synthase activity, 3-hydroxyacyl-CoA dehydrogenase activity, Ca2+-activated myofibrillar ATPase activity, and myosin isoform distribution. None of the groups demonstrated altered cardiac metabolic properties, but cocaine alone and in conjunction with exercise reduced myofibrillar ATPase activity (p < 0.05) and increased expression of the low ATPase myosin isoform, V3. These data suggest that the potential of the citric acid cycle and β-oxidation is not sensitive to chronic cocaine treatment, but the distribution of cardiac myosin among its three isoforms is affected. Furthermore, high-intensity treadmill training does not interact with cocaine to further alter these properties.Key words: cocaine, exercise, cardiac metabolism, myosin.
Evaluation of bronchoconstriction induced by neurokinins and its inhibition by selective nonpeptide antagonists in conscious guinea pigs, using a double-chamber plethysmograph technique
Authors: Chan Chi-Chung , Tousignant Christine , Ho Elaine , Brideau Christine , Savoie Chantal , Rodger Ian W.
Published: April 2011

Bronchoconstriction induced by inhaled neurokinins, leukotriene D4 (LTD4), and histamine was examined in conscious guinea pigs, using a double-chamber plethysmograph. The reliability of the plethysmograph was established by obtaining stable baseline values of key pulmonary parameters, including specific airway resistance, over a 4-day period. As well, the usefulness of the setup was confirmed using LTD4 and the LTD4 antagonist MK-571. Aerosols of MK-571 inhibited the bronchoconstriction induced by LTD4 (0.3 μM, 3 min aerosol) with an IC50 value of 65 ± 16 nM. Inhaled neurokinin A (NKA), substance P (SP), [βAla8]NKA(4–10), or [Sar9,Met(O2)11]SP at concentrations up to 10 μM had no bronchoconstrictive effect, unless the guinea pigs were pretreated with the neutral endopeptidase inhibitor thiorphan (0.2 mg/mL, 5 min aerosol). The rank order of bronchoconstriction potency was LTD4 > [βAla8]NKA(4–10) ≈ NKA > [Sar9,Met(O2)11]SP ≈ SP [Formula: see text] histamine. Hyperresponsiveness to NKA-induced bronchoconstriction was evident after 1 day and lasted for 4 days. The response to NKA was not inhibited by mepyramine, indomethacin, or MK-571 but was significantly reduced by atropine and hexamethonium, suggesting the involvement of a cholinergic mechanism. Aerosols of SR-48,968, a selective NK2 antagonist, had potent effects on the bronchoconstriction induced by NKA (1 μM, 3 min aerosol), with an IC50 value of 17 ± 3 nM. SR-48,968 was also active when administered intraperitoneally. The NK1 antagonist CP-99,994 (0.1 μM, 10 min aerosol) inhibited the responses to SP by 70% but had no effect on NKA-induced responses at concentrations up to 10 μM. Interestingly, combination of SR-48,968 (3 nM) and CP-99,994 (100 nM) resulted in more complete inhibition of the NKA-induced bronchoconstriction than was obtained with either antagonist alone. It is concluded that NKA-induced bronchoconstriction in conscious guinea pigs is mediated predominantly by NK2 receptors, with only a minor involvement of NK1 receptors. Although a direct comparison of the potency of SR-48,968 in man and guinea pig is not feasible, our data suggest that it is in the same range in these two species.Key words: neurokinins, NK1 antagonist, NK2 antagonist, conscious guinea pigs, plethysmography.
Evidence for nicotine-induced skin flap ischemic necrosis in the pig
Authors: Forrest Christopher R. , Xu Ning , Pang Cho Y.
Published: April 2011

There is clinical and experimental evidence to indicate that cigarette smoking may increase the risk of skin ischemic necrosis in flap surgery but the pathogenic mechanism remains unclear. The objectives of this project were to investigate the potential deleterious effects and mechanism of action of nicotine, a major by-product of cigarette smoking, in skin flap surgery in the pig. It was observed that 4–5 weeks of intramuscular nicotine injections (4 mg/kg; twice daily) significantly (p < 0.05) decreased the skin flap capillary blood flow and the length and area of skin flap viability in the pig. This nicotine treatment also induced a 1.6-fold increase in skin flap tissue content of norepinephrine compared with the saline-treated control. The estimated mean wet skin tissue content of norepinephrine (5 × 10−7 M) was much higher than the circulating level of norepinephrine (1.8 × 10−9 M) in nicotine-treated pigs. This level of norepinephrine (5 ×10−7 M) was seen to induce a significant vasoconstrictor effect (75% increase over basal perfusion pressure) in isolated perfused pig skin flaps. It was also observed that the vasoconstrictor effect of norepinephrine was significantly (p < 0.05) enhanced in the presence of 10−4 M Nω-monomethyl-L-arginine or NG-nitro-L-arginine, an endothelium-derived relaxing factor – nitric oxide (EDRF/NO) synthesis inhibitor. This vasoconstrictor effect was further enhanced in the presence of NG-nitro-L-arginine and 10−5 M indomethacin, a cyclooxygenase inhibitor. Taken together, these observations indicate that 4–5 weeks of nicotine treatment significantly reduced the skin capillary blood flow and viability in skin flap surgery in the pig and this deleterious effect was likely to be mediated, at least in part, by locally released norepinephrine induced by nicotine treatment. Furthermore, norepinephrine also induced skin flap local release of EDRF/NO and a vasodilating prostanoid that in turn attenuated norepinephrine's vasoconstrictor effect in the skin vasculature. We speculate that skin vasculature with compromised endothelial cell function as a result of trauma or disease is more susceptible to the vasoconstrictor effect of norepinephrine released by nicotine.Key words: chronic nicotine, norepinephrine, skin vasoconstriction, flap surgery.
Occurrence of endothelium-derived relaxing factor – nitric oxide in the lamb ductus arteriosus
Authors: Coceani Flavio , Kelsey Lois , Seidlitz Eric
Published: April 2011

To determine whether the ductus arteriosus can form endothelium-derived relaxing factor – nitric oxide, we used isolated ductal strips from near-term fetal lamb and examined their response to bradykinin (a nitric oxide stimulator), L-arginine (a nitric oxide precursor), and agents interfering with the synthesis (Nω-nitro-L-arginine) and action (methylene blue) of nitric oxide. Bradykinin relaxed the indomethacin-contracted ductus dose dependently from a threshold of about 10−10 M, and peak relaxation was greater at high (176–210 mmHg; 1 mmHg = 133.3 Pa) than low (15–25 mmHg) [Formula: see text]. Bradykinin relaxation was nearly completely or completely abolished in endothelium-denuded preparations and, in its place, there was often a small contraction. Pretreatment with nitric oxide inhibitors also prevented, in part (methylene blue, 1 μM) or in full (Nω-nitro-L-arginine, 100 μM), the relaxant effect of bradykinin. Paradoxically, L-arginine (10 μM) had an inhibiting rather than an enhancing effect on the bradykinin relaxation. Nω-Nitro-L-arginine (100 μM) and methylene blue (1–100 μM) contracted by themselves the untreated ductus, and their action persisted after removal of the endothelium. These findings indicate the presence in the ductus arteriosus of a nitric oxide based relaxing mechanism, which may supplement prostaglandin E2 in keeping the vessel patent in the fetus. This mechanism may, on one hand, afford protection against nonsteroidal antiinflammatory drugs in utero and may, on the other hand, complicate the management of prematures with persistent ductus and account for failures of the indomethacin therapy.Key words: ductus arteriosus patency and closure, endothelium-derived relaxing factor – nitric oxide, prostaglandin.
Hormonal dose–response to an adenosine receptor agonist
Authors: LeBlanc Jacques , Soucy Julie
Published: April 2011

The effect of various doses of i.p. injection of the adenosine receptor agonist (R)-phenylisopropyladenosine (R-PIA), ranging from nanomolar to micromolar concentrations, on plasma levels of free fatty acids, glucose, insulin, glucagon, ACTH, and corticosterone was examined in 200-g male rats. At the lowest dose of R-PIA (0.005 μmol/kg), a marked decrease in plasma insulin and free fatty acids was observed. This effect on free fatty acids persisted up to the highest concentration of R-PIA (50 μmol/kg). The insulin response showed a similar pattern except at the highest concentration, when the plasma levels were within normal ranges. A 100% increase in plasma glucose was found, but only with doses of 0.5 μmol/kg and above, suggesting an A2 receptor influence, possibly related to the elevation of plasma glucagon observed with the same doses of R-PIA. It has been shown that caffeine, an antagonist of adenosine, stimulates the pituitary–adrenal axis. Surprisingly, it was shown that R-PIA produces the same effect, as evidenced by the marked elevation of both plasma ACTH and corticosterone at concentrations of 0.5 μmol/kg and higher. It is suggested that this centrally mediated effect is due to a primary peripheral action.Key words: adenosine, glucose, free fatty acids, insulin, glucagon, ACTH, corticosterone.
Kynurenic acid distribution into brain and peripheral tissues of mice
Authors: Lou G. L. , Pinsky C. , Sitar D. S.
Published: April 2011

Kynurenic acid (KYN), an antagonist of excitatory amino acid receptors, is a putative antidote against neuroexcitatory amino acid toxicity. We studied various doses (0.05–3.17 mmol/kg, i.p.) and the effects of probenecid coadministration (0.70 mmol/kg, i.p.) on tissue distribution of KYN in male and female Swiss–Webster mice. After injection of [3H]KYN, samples of brain, heart, liver, kidney, skeletal muscle, and gut were collected at selected times and assayed for KYN by liquid scintillation counting. The substance was absorbed rapidly and distributed into all tissues. Its content (nmol/g, mean ± SE) at 60 min was 0.26 ± 0.05, 1.80 ± 0.05, and 40.4 ± 8.1 in brain (for 0.05, 0.53, and 3.17 mmol/kg), 1.43 ± 0.11, 14.3 ± 3.7, and 212 ± 32 in heart, 1.16 ± 0.21, 10.6 ± 2.6, and 254 ± 21 in liver, and 7.41 ± 2.65, 180 ± 63, and 1899 ± 254 in kidney. Net accumulation of KYN in brain was much lower than in other tissues. Probenecid increased KYN concentration in brain 2.5-fold. Peak brain:blood concentration ratio occurred between 60 and 180 min, was inversely associated with dose, and was not affected by probenecid. Although brain content was similar, female mice had an earlier peak brain:blood ratio (120 min) than males (180 min) for the 0.05 mmol/kg dose. Our results suggest the presence of a restricted transfer process for KYN with delayed egress from brain.Key words: kynurenic acid, brain, tissue distribution.
Influence of vascular and luminal hexoses on rat intestinal basolateral glucose transport
Authors: Tsang Raymond , Ao Ziliang , Cheeseman Chris
Published: April 2011

The influence of luminal and vascular hexoses in rats on glucose transport across the jejunal basolateral membrane (BLM) was measured using isolated membrane vesicles prepared from infused animals. In vivo vascular infusions of glucose produced an increase in glucose transport across BLM vesicles. Sucrose, mannose, galactose, and fructose had no significant effect. Plasma glucose concentrations were unaffected by galactose and sucrose vascular infusions, while mannose and fructose produced a modest rise, and glucose increased plasma glucose to 20 mM. Insulin release was significantly increased by vascular infusion of glucose and fructose, while mannose produced only a small sustained rise. Sucrose and galactose had no effect. Perfusion through the lumen of the rat jejunum in vivo, for up to 4 h, with glucose, fructose, sucrose, or lactate (100 or 25 mM) produced a significant increase in the maximal rate of glucose transport (up to 4- to 5-fold) across BLMs. Galactose and mannose had no effect. Luminal glucose perfusion produced a small nonsignificant increase in glucose inhibitable cytochalasin B binding to BLM vesicles, and no change was seen in the microsomal pool of binding sites. The abundance of GLUT2 in the jejunal BLM, as determined by Western blotting, was unaffected by luminal perfusion of 100 mM glucose for 4 h. Fructose almost completely inhibited the carrier-mediated uptake of glucose in control and upregulated jejunal BLM vesicles. These results are discussed in relation to the physiological role of the upregulation of GLUT2 activity by luminal and vascular hexoses.Key words: intestinal transport, basolateral membrane, glucose transport, intestinal adaptation.
Digestion and absorption of food: usefulness and limitations of in vitro models
Authors: Savoie L.
Published: April 2011

The digestion and absorption of food is a spatiotemporal and dynamic process involving complex enzymatic and transport reactions, and it is illusive to try to reproduce in a single model all these biochemical and physiological events. A more practical and realistic approach is to separately evaluate the specific contributions of oral and gastric digestion, intestinal digestion by pancreatic enzymes, brush-border hydrolysis, and eventually intestinal absorption and enterocyte metabolism. The models proposed must be versatile enough to be able to modify their conditions of operation according to physiological adaptation to food. Enzymatic preparations must be kept close to physiological conditions in regard to their nature and their mode of operation. A digestion cell and a peptidase bioreactor were developed for this purpose. The challenge is to find a way to integrate all these data. This can be partially achieved by selecting techniques that allow the collection and isolation of reaction products from one step for use as substrates for the next event. Various models are presented to illustrate this concept as applied to food protein.Key words: digestion, proteolysis, in vitro models, amino acid release, kinetics of digestion.
Uterine β-adrenergic receptors in allogeneic and syngeneic pregnancy
Authors: Sales Maria Elena , Borda Enri S.
Published: April 2011

Two different mechanisms of regulation in uterine β-adrenergic receptors in allogeneic pregnancy (AP) and syngeneic pregnancy (SP) are described in this work. Firstly we noted changes in β-adrenergic sensitivity to isoproterenol in AP, while in SP differences in uterine reactivity to isoproterenol were found. In binding assays with the β-antagonist [3H]dihydroalprenolol, changes in β-receptor affinity were seen in AP, while in SP the maximal number of binding sites is altered. In addition, there are differences in uterine concentrations of cyclic AMP in both types of pregnancies as well as in the nucleotide response to isoproterenol. The differences in the reactivity and expression of uterine β-adrenoceptors in both types of pregnancies may be due to a distinctive immunological role of the semiallogeneic fetus in AP.Key words: β-adrenoceptors, cyclic AMP production, uterus, contractility, binding assay, syngeneic pregnancy, allogeneic pregnancy.
Grasp stability during manipulative actions
Authors: Johansson Roland S. , Cole Kelly J.
Published: April 2011

The control of adequate contact forces between the skin and an object (grasp stability) is examined for two classes of prehensile actions that employ a precision grip: lifting objects that are "passive" (subject only to inertial forces and gravity) and preventing "active" objects from moving. For manipulating either passive or active objects the relevant fingertip forces are determined by at least two control processes. "Anticipatory parameter control" is a feedforward controller that specifies the values for motor command parameters on the basis of predictions of critical characteristics, such as object weight and skin–object friction, and initial condition information. Through vision, for instance, common objects can be identified in terms of the fingertip forces necessary for a successful lift according to previous experiences. After contact with the object, sensory information representing discrete mechanical events at the fingertips can (i) automatically modify the motor commands, (ii) update sensorimotor memories supporting the anticipatory parameter control policy, (iii) inform the central nervous system about completion of the goal for each action phase, and (iv) trigger commands for the task's sequential phases. Hence, the central nervous system monitors specific, more or less expected peripheral sensory events to produce control signals that are appropriate for the task at its current phase. The control is based on neural modelling of the entire dynamics of the control process that predicts the appropriate output for several steps ahead. This "discrete-event, sensor-driven control" is distinguished from feedback or other continuous regulation. Using these two control processes, slips are avoided at each digit by independent control mechanisms that specify commands and process sensory information on a local, digit-specific basis. This scheme obviates explicit coordination of the digits and is employed when independent nervous systems lift objects. The force coordination across digits is an emergent property of the local control mechanisms operating over the same time span.Key words: precision grip, hand, grasp stability, grasp force, tactile afferents.
In vitro effect of D-myo-inositol 1,2,6-trisphosphate (PP-56) on aggregation of platelets from normal and diabetic rats: relationship to malondialdehyde release and phosphoinositide pathway
Authors: Ruf J. C. , Ciavatti M. , Gustafsson T. , Renaud S.
Published: April 2011

In the present study, we investigated the in vitro effects of D-myo-inositol 1,2,6-trisphosphate (PP-56) on platelets from normal and streptozotocin-induced diabetic rats. PP-56 markedly inhibited aggregation, in a dose-related manner, when added in vitro, more efficiently with thrombin- than with ADP-induced aggregation and, after 90 min incubation, more in diabetic than in normal platelets. The PP-56 platelet inhibitory effect seems to be related to its phosphate content. PP-56 blocked the release of malondialdehyde from erythrocytes, but to the same extent in normal and diabetic rats. PP-56, after 20 min incubation, restored the platelet phosphoinositide turnover, which was significantly modified in diabetic rats. This last observation could explain at least part of the specificity of PP-56 for normalizing platelet aggregation in diabetic animals after long-term administration in vivo.Key words: inositol phosphates, platelet aggregation, streptozotocin-induced diabetic rats.
Iron chelators of the pyridoxal isonicotinoyl hydrazone class. Relationship of the lipophilicity of the apochelator to its ability to mobilise iron from reticulocytes in vitro
Authors: Ponka P. , Richardson D. R. , Edward J. T. , Chubb F. L.
Published: April 2011

Analogues of the iron (III) chelator, pyridoxal isonicotinoyl hydrazone (PIH) show high potential as orally active agents for the treatment of iron-overload diseases, such as thalassemia. In the present study, the n-octanol–water partition coefficients of 30 analogues of PIH were measured by thin-layer chromatography and also calculated using the additive schemes of Rekker. The purpose was to examine the relationship between lipophilicity of the apochelator and its ability to promote the release of 59Fe from reticulocytes loaded with nonheme 59Fe. Interestingly, maximum activity occurred when the partition coefficient of the apochelator was approximately 1 (log P = 0). Considering the results in the context of the design and synthesis of more active analogues of PIH, it can be suggested that before initiating synthesis, a useful indication of biological activity can be determined by examining the lipophilicity of the molecule, using the schemes of Rekker to calculate the partition coefficient. By using this strategy, analogues of PIH with inappropriate lipophilicity can be excluded before initiating the expensive process of screening in biological models.Key words: iron chelation, iron mobilisation, iron overload, pyridoxal isonicotinoyl hydrazone.
Effects of some naturally occurring prostanoids and some cyclooxygenase inhibitors on the contractility of the human lower uterine segment in vitro
Authors: Crankshaw D. J. , Dyal R.
Published: April 2011

The contractility of strips of human lower segment myometrium obtained from elective cesarean section performed at term of pregnancy was studied in vitro. The effects of indomethacin and tiaprofen upon spontaneous contractile activity were examined. Concentration–effect curves for PGD2, PGE2, PGF2α, 6-keto-PGE1, and 6-keto-PGF1α, were constructed in the presence of indomethacin. Neither indomethacin nor tiaprofen in concentrations up to 100 μmol/L had any effect upon spontaneous activity. Contractions were induced by the prostanoids with the following mean EC50 values: PGE2, 13 nM; PGF2α, 250 nM; PGD2, 790 nM; both 6-keto-PGF1α and 6-keto-PGE1 were without effect in concentrations up to 30 μmol/L. In some tissues PGE2 inhibited spontaneous activity with a mean IC50 of 100 nM. No other prostanoid tested caused inhibition under any circumstance. The marked potency differences between the natural prostanoids is an important parameter to consider when assessing their relative contributions to the process of parturition and the design of new therapeutic agents for the management of preterm labour.Key words: prostaglandins, indomethacin, myometrium, human, uterine contraction.