Effect of norepinephrine and vasopressin on carotid sinus baroreceptor activity in the anesthetized rabbit

Summary Norepinephrine (NE) 10^–6 M or vasopressin (VP) 12.5 U/ml were injected into the isolated carotid sinus of anesthetized rabbits. The sinus was exposed either to the arterial pressure or to a pressure controlled reservoir. Multifiber and single fiber recordings were made. Both NE and VP increased baroreceptor activity at all sinus pressures but decreased activity in a few fibers. The results are consistent with the drugs having their effects on smooth muscle fibers in the adventitia.Acknowledgments. This work was supported by grants from the Medical Research Council of Canada and the B.C. Heart Foundation. The authors are grateful to J. Sharp and D. Morton for their excellent assistance.     

Storage of irradiated human blood; a source of error in quantitative chromosome analysis

Summary Human whole blood was irradiated with 2.5 Gy of 220 kVp X-rays and stored before culture with 9.7 M BrdU and 19.4 or 38.7 M BrdU for 0, 24, 48 and 72 h. The frequency of dicentrics and ring chromosomes was determined in cells staining as first division (M1) metaphases with the fluorescence plus Giemsa technique. Storage had no influence on the observed aberration yields in 44 h cultures containing 9.7 M BrdU. In 66 h cultures at 19.4 M BrdU the observed yields after 2 and 3 days' storage were significantly lower as compared to cultures from fresh blood. No storage effect was revealed in 66 h cultures containing 38.7 M BrdU. In cases where cytogenetic radiation dosimetry has to be carried out using blood samples which have been in transit for 2–3 days, the findings are of relevance for a correct determination of the chromosome damage in M1 cells.     

Erythrocyte 2,3-diphosphoglycerate in anaemic sheep

Summary Experimental anaemia resulted in an increase of red cell 2,3-DPG from 0.11 M/gHb to 0.99 M in haemoglobin A sheep and from 0.21 M to 1.5 M in haemoglobin B sheep. Production of haemoglobin C as a result of anaemia was confined to haemoglobin A only. The results, therefore, appear to suggest that the rise in 2,3-DPG in the red blood cells of different haemoglobin types is independent of haemoglobin C.This work was supported by grants from the National Health and Medical Research Council, The Clive and Vera Ramaciotti New South Wales Foundations and Helena Rubinstein Foundation, Inc. We wish to thank Mr J. Sheedy for his expert technical assistance, and Professor G. J. Brewer for his constructive criticism.     

Effects of puromycin on rat embryos in vitro

Summary Somite-staged rat embryos were exposed to varying concentrations of puromycin for 48 h in vitro. Medium concentrations below 0.92 M had no significant effects, while concentrations above 1.84 M were lethal. Between these extremes, there were concentration dependent increases in the incidence of malformations in a close relationship to growth retardation.     

Involvement of H1 receptors in the central antinociceptive effect of histamine: Pharmacological dissection by electrophysiological analysis

Intracerebroventricular (i.c.v.) administration of histamine (HA, 0.025–0.1 M/rat) to arthritic rats induces a dose-related inhibition of the neuronal thalamic firing evoked by peripheral noxious stimuli. To characterize the type(s) of HA receptors involved in this depressing activity of the amine we used electrophysiological techniques to examine the effects of i.c.v. administration of H₁ and H₂ agonists and antagonists on the spontaneous and evoked nociceptive firing of the thalamic neurons in rats rendered arthritic by Freund's adjuvant. The H₁ agonist 2-pyridylethylamine (0.4–1.0 M/rat, i.c.v) displayed a dose-dependent antinociceptive effect very similar to that of HA, while the H₂ agonist dimaprit (0.05–0.2 M/rat, i.c.v.) did not modify thalamic firing. Neither mepyramine (H₁ antagonist, 0.1 M/rat, i.c.v.) nor zolantidine (H₂ antagonist, 0.01 M/rat, i.c.v.) modified the evoked firing of rat thalamic neurons. When administered before HA (0.1 M/rat, i.c.v.) mepyramine but not zolantidine was able to inhibit the antinociceptive effect of HA. On the basis of the present electrophysiological results, we suggest that a specific interaction of histamine with H₁ receptors may be important for its antinociceptive effect on afferent peripheral inputs to the thalamus.     

Tannic acid inhibits insulin-stimulated lipogenesis in rat adipose tissue and insulin receptor function in vitro

Tannins occur naturally in relatively abundant amounts in fruits, herbal medicines and common beverages. Thus an understanding of how these polyphenols affect peptide hormone action is of importance. We report here that tannic acid (a hydrolysable tannin) inhibits insulin-stimulated lipogenesis in rat adipose tissue in vitro, with an IC₅₀ estimated to be about 350 M. However, its monomer, gallic acid, did not show a similar inhibitory effect at concentrations up to 1 mM. The inhibition by tannic acid was less evident with higher concentrations of bovine serum albumin in the incubation buffer. This was attributed to the formation of a tannin-protein complex between bovine serum albumin and tannic acid. In a binding assay, it was observed that the specific binding of insulin to its receptor was not inhibited by tannic acid in the concentration range 0–200 M. However, insulin-stimulated autophosphorylation of the insulin receptor, and receptor-associated tyrosine kinase phosphorylation of RR-SRC peptide, were inhibited by tannic acid at concentrations as low as 25 M. Our data do not support the current speculation that tannins affect the activity of peptide hormones by binding to them. Therefore, our finding opens up a new perspective in the understanding of the mode of action of tannins on such hormones.     

‘Binding’ of glycine andγ-aminobutyric acid to synaptosomal fractions of 6 regions of the feline brain; effects of strychnine

Summary GABA (6×10^–6 M) binding to synaptosome-enriched fractions of cat CNS exhibited a clear rostro-caudal gradient, whereas glycine (6×10^–6 M) binding was greatest to particles of cerebellar cortex, and this was followed by medulla caudate nucleus cerebral cortex pons > corona radiata. Strychnine-SO₄ (10^–3 or 10^–4 M) inhibited the binding of GABA and glycine in all brain regions studied; at 10^–5 M this drug inhibited the binding of both GABA and glycine only to particles of the cerebral cortex.This study was supported by Centro Nacional Ramón y Cajal and Fundación Juan March. P. M. was a summer student from Eastern Nazarene College, Wollaston, Mass., USA.     

Patch and whole-cell voltage clamp of single mammalian visceral and vascular smooth muscle cells

Summary Dispersal of the constituent cells of mammalian visceral and vascular smooth muscles has permitted recordings both of membrane currents under whole-cell voltage clamp, and of currents through single ionic channels using the patch-clamp technique. A rectangular depolarizing step applied to a single cell under voltage clamp yielded a net inward current followed by a net outward current in normal physiological solution. In isolated, inside-out patches of cell membrane a calcium- and potential-sensitive K channel (100 pS conductance) and a calcium-insensitive, potential-sensitive K⁺ channel (50 pS conductance) with slow kinetics have so far been identified and characterized.     

Evidence against a role of (Na++K+-ATPase in the alpha-adrenoceptor mediated positive inotropic effect of phenylephrine

Summary Phenylephrine (0.1–100 M) in the presence of 1 M propranolol increased the force of contraction in electrically driven papillary muscles from cats. This presumably alpha-adrenoceptor mediated positive inotropic effect of phenylephrine occurred without any influence on (Na⁺+K⁺-ATPase activity.This work was supported by the Deutsche Forschungsgemeinschaft.     

Effects of cortisone and thyroxine on intestinal trehalase activity in infant mouse

Summary Cortisone acetate (25 g/g b.wt/day) administration to 8-day-old suckling mice induces a premature increase of trehalase activity along the entire small intestine. On the other hand, thyroxine (1 g/g b.wt/day) is unable to provoke a precocious increase of trehalase activity. Trehalase appears to be the only brush border membrane disaccharidase controlled solely by glucocorticoid hormones during the postnatal maturation of the intestine.Supported by grant MA-5969 from the Medical Research Council of Canada to D.M. C.M. is a recipient of a studentship from MRC of Canada.     

Disruption of mitochondrial function as the basis of the trypanocidal effect of trifluoperazine onTrypanosoma cruzi

Summary The tricyclic anti-calmodulin drug trifluoperazine (TFP) inhibited growth and motility of epimastigotes ofTrypanosoma cruzi, at concentrations lower than 100 M, and motility and infectivity of the bloodstream trypomastigote form at 200 M. Electron microscopy of TFP-treated epimastigotes showed that the major effect was at the mitochondrial level, with gross swelling and disorganization. The oligomycin-sensitive, mitochondrial ATPase was completely inhibited by 20 M TFP, and the same drug concentration caused a 60% decrease in intracellular ATP content. The results suggest that the trypanocidal effect of TFP may be related more to mitochondrial damage than to the well-known anticalmodulin effect of the drug.     

Changes in rat erythrocyte membrane induced byΔ 1-tetrahydrocannabinol,scanning electron microscope study

Summary Although some biochemical dose-dependent effects are revealed in erythrocytes exposed to ¹ (THC) already at concentrations well below 10 M, marked morphological changes of the erythrocyte membrane become evident, by scanning electron microscopy, only at THC concentrations beyound 15 M. These observations provide evidence additional to previous chemical and physical studies, in which 15 M is found to be a critical concentration with respect to the effects of TCH on erythrocyte membrane.Acknowledgments. The authors are indebted to Prof. R. Mechoulam from the School of Pharmacy, The Hebrew University, Jerusalem, for providing the THC. The excellent technical assistance of Mrs R. Mordechai and of Miss L. Motola is gratefully acknowledged.     

Lack of effect of cortisone,thyroxine and insulin on the developmental pattern of mouse intestinal glucose-6-phosphatase activity

Summary Daily administration for 3 days of cortisone (25 g/g b.wt), thyroxine (1 g/g b.wt) or insulin (12.5 mU/g b.wt) to 8-day-old suckling mice does not induce a premature decrease of the phosphohydrolase activity of intestinal glucose-6-phosphatase.Supported by grant MA-5969 from the Medical Research Council of Canada (D.M.). C.M. is a recipient of a studentship from MRC of Canada. D.M. is a chercheur-boursier du Conseil de la recherche en santé du Québec.     

Inhibition of hepatic Na+, K+-adenosinetriphosphatase in taurolithocholate-induced cholestasis in the rat

Summary Na⁺, K⁺-adenosinetriphosphatase (Na⁺, K⁺-ATPase) activity was decreased in liver plasma membranes from rats in which cholestasis had been induced by i.v. administration of sodium taurolithocholate (5 moles/100 g b. wt). Incubation of liver plasma membranes with taurolithocholate (10–1300 M) caused significant and dose dependent reductions of Na⁺, K⁺-ATPase activity at taurolithocholate concentrations above 100 M. These findings lend support to the hypothesis that cholestasis induced by monohydroxy bile acids is at least partially the result of an inhibition of hepatic Na⁺, K⁺-ATPase activity.This work was supported by the Swiss National Science Foundation.The authors thank Mr H. Sägesser and Miss B. Schütz for technical assistance.     

Studies on muscle fibre splitting in skeletal muscle

Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner.     

Studio farmacologico di un nuovo coleretico derivato dall'acidoα-cicloesil butirrico

Summary -(1-Hydroxy-4-phenyl-cyclohexyl)butyric acid (M. G. 4833) and-(1-hydroxy-3-phenyl-cyclohexyl) butyric acid (M. G. 4834) have been synthesized; both substances were endowed with choleretic activity.M. G. 4833 is the more active; it acts at lower doses and for a longer time than sodium dehydrocholate on rats, rabbits and dogs submitted to temporary fistulization of the bile-duct.     

Enhanced enzyme activity in concentrated salt solutions

Summary The enzyme activity of thrombin, -factor Xa-E and trypsin was enhanced in 1.0 M sodium citrate solution. Thrombin activated factor X. Synthetic substrate S-2222, designed for factor Xa, was hydrolyzed more rapidly with factor Xa or with thrombin in 1.0 M sodium citrate solution than in dilute salt solutions.Recipient of a Fogarty International Research Fellowship (TW-02743-02).     

Effect of dipyridamole on glomerular mesangial cell ecto-5′-nucleotidase expression

Although dipyridamole has been extensively studied as an anti-aggregating agent, its mechanism of action has not been elucidated. Cultured mesangial cells were treated with dipyridamole 1–100 M from 6–72 h. Ecto-5-nucleotidase activity approximately doubled (from 115±11 to 226±14 nmol/min/mg) after treatment with 100 M dipyridamole for 72 h. This effect was concentration- and time-dependent. Cycloheximide, an inhibitor of protein synthesis, did not alter basal 5-nucleotidase activity. However, it prevented stimulation by 5 M dipyridamole. Adenosine availability at the receptor sites was increased by dipyridamole and S-(p-nitrobenzyl)-6-thioinosine (NBTI), which inhibit adenosine uptake into the cell. Addition of dipyridamole or NBTI to the adenosine-treated mesagial cells produced an additive increase in ecto-5-nucleotidase activity. Dipyridamole, through its effect on extracellular adenosine and ecto-5-nucleotidase, may have an influence upon regulation of the glomerular microcirculation.     

An approach for the in vitro screening of drugs for activity against leprosy

Summary Slow growing strains of mycobacteria isolated from leprous tissues present a characteristic resistance pattern to antibacterial agents that is comparable to drug sensitivity ofM. leprae in man.The Hansen Chair of Research is a foundation of Le Secours aux Lépreux (Canada) Inc..