Galactomannan of the locoweed (<Emphasis Type="Italic">Oxytropis lanata</Emphasis> (Pallas) DC) seeds

Galactomannan with a molecular weight of 1976 kDa was isolated by hot water extraction from the locoweed (Oxytropis lanata (Pallas) DC) seeds (yield, 3.68% of the seed weight); its solutions display high viscosity: [η] = 1697.7 ml/g and optical activity α_D + 76.8°. The polysaccharide consists of mannose and galactose residues at a molar ratio of 1.36: 1. The backbone of galactomannan macromolecule is formed by 1,4-β-D-mannopyranose residues, 73.5% of which are substituted with single α-D-galactopyranose residues at C-6.     

A galactomannan-hydrolysing α-galactosidase from jack fruit (Artocarpus integrifolia) seed: Affinity chromatographic purification and properties

An acid α-galactosidase from the seeds of the jack fruit seed (Artocarpus integrifolia) has been purified to homogeneity by affinity chromatography on a matrix formed by cross-linking the soluble α-galactose-bearing guar seed galactomannan. The 35kDa enzyme was a homotetramer of 9.5kDa subunits. Its carbohydrate part (5.5%) was composed of galactose and arabinose. TheK _m withp-nitrophenyl α-D-galactoside as substrate was 0.35 mM. TheK _i values indicated inhibition by galactose, 1-O-methyl α-galactose and melibiose in the decreasing order. Among α-galactosides, the enzyme liberated galactose from melibiose, but not from raffinose or stachyose at its pH optimum (5.2). The guar seed galactomannan was however efficiently degalactosidated; limited enzyme treatment abolished the precipitability of the polysaccharide by the α-galactose-specific jack fruit seed lectin, and complete hydrolysis yielded insoluble polysaccharide. Though similar in sugar specificity and subunit assembly, α-galactosidase and the lectin coexisting in the jack fruit seed gave no indication of immunological identity.     

Water-Soluble Galactomannan from the Seed of Ground Honeysuckle (Lotus corniculatus L.): Structure and Properties

Galactomannan, a water-soluble heteropolysaccharide, was isolated from the seed of a Far Eastern population of the ground honeysuckle Lotus corniculatus L. (yield, 1.65%). Analysis of this galactomannan showed that it consists of D-mannose and D-galactose residues (molar ratio, 1.22 : 1). Its aqueous solutions were characterized by a specific rotation []_D= +84.1° and intrinsic viscosity [] = 559 ml/g. Analysis of this heteropolysaccharide using chemical and enzymatic procedures, as well as IR and ¹³C NMR spectroscopy, showed that its main chain comprises 1,4--D-mannopyranose residues, 95.5% of which are substituted at C-6 with single residues of -D-galactopyranose.     

Composition and structure of a galactomannan macromolecules from seeds of Astragalus lehmannianus Bunge

The composition and structure of a galactomannan from seeds of Astragalus lehmannianus, an endemic legume species, is reported for the first time. The purified galactomannan (yield, 4.8%) contained 55% D-mannose and 45% D-galactose and had a molecular weight of 997.03 kDa. Its aqueous solutions were optically active and highly viscous (the specific rotation, [alpha]D, equaled +81.3 degrees; the characteristic viscosity, [eta], 868.4 ml/g). Chemical, chromatographic, and spectral (IR and 13C-NMR spectroscopy) methods were used to demonstrate that the main chain of the molecule is formed by residues of 1,4-beta-D-mannopyranose, 78% of which are substituted at position 6 with single alpha-D-galactopyranose. The distribution of galactose along the chain was calculated from NMR spectra: frequencies of occurrence, per pair of neighboring mannose units, of (1) two substituents, (2) one substituent, and (3) no substituents were 65.3, 31.5, and 3.2%, respectively. The specific rotation of galactomannans was shown to correlate with their content of galactose.     

Production, purification and characterization of a constitutive intracellular α-galactosidase from the thermophilic fungus Humicola sp

The thermophilic fungus Humicola sp constitutively produces intracellular α-galactosidase (1.33 U mg⁻¹ protein) within 48 h at 45°C in shaken flasks, when grown in a medium containing 7% wheat bran extract as a carbon source and 0.5% yeast extract as a nitrogen source. The enzyme has been purified to homogeneity by ultrafiltration, ethanol precipitation, DEAE cellulose and Sephacryl S-300 chromatography with a 124-fold increase in specific activity and 29.5% recovery. The molecular weight of the enzyme is 371.5 kDa by gel filtration on Sephacryl S-300 and 87.1 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme has an optimum temperature of 65°C and an optimum pH of 5.0. Humicola α-galactosidase is a glycoprotein with 8.3% carbohydrate content and is acidic in nature with a pI of 4.0. The K _m S for p-nitrophenyl-α-D-galactopyranoside, O-nitrophenyl-α-D-galactopyranoside, raffinose and stachyose are 0.279, 0.40, 1.45 and 1.42 mM respectively. The enzyme activity was strongly inhibited by Ag⁺ and Hg²⁺. D-Galactose inhibited α-galactosidase competitively and the inhibition constant (K _i) for galactose was 11 mM. Received 28 January 1999/ Accepted in revised form 07 April 1999     

Composition and Structure of Galactomannan from the Seed of Gleditsia ferox Desf.

Galactomannan, a heteropolysaccharide with a molecular weight of 1660 kDa, was isolated from the seed of Gleditsia ferox Desf., introduced in Russia, with a yield of 18.9%. Its aqueous solutions were optically active ([]_D = +30.5°) and highly viscous ([] = 1430 ml/g). An analysis of the heteropolysaccharide using chemical, enzymatic, and chromatographic procedures showed that it consists of D-mannopyranose and D-galactopyranose residues (molar ratio, 2.54 : 1). The main chain of this galactomannan consists of 1,4--D-mannopyranose residues, 39.2% of which are substituted at C6 with single residues of -D-galactopyranose. The probability of occurrence of mannobiose units differentially substituted with galactose was determined by ¹³C-NMR data and equaled, respectively, 0.37, 0.47, and 0.16 for non-substituted Man–Man units, monosubstituted Gal(Man–Man) and (Man–Man)Gal units taken together, and for the disubstituted Gal(Man–Man)Gal units.     

Fractional Isolation and Study of the Structure of Galactomannan from Sophora (Styphnolobium japonicum) Seeds

Two fractions (1 and 2) of the galactomannan from seeds of sophora (Styphnolobium japonicum) were isolated using cold and hot aqueous extraction with a total yield of 12.88%. The two fractions differed by the ratio between mannose (Man) and galactose (Gal) residues (4.8 : 1 and 5.3 : 1, respectively) and molecular weight (1190 and 1400 kDa, respectively). Aqueous solutions of these fractions were optically active ([]_D = +4.80° and –3.36°, respectively) and highly viscous ([] 1028.8 and 1211.2 ml/g). ¹³C NMR spectra of both fractions were identical with respect to the number and positions of signals, which indicates that their primary structures were identical. Using chemical and spectroscopic (IR and NMR) methods, it was shown that the galactomannan has a main chain consisting of 1,4--D-mannopyranose, some residues of which (16 and 17% in fractions 1 and 2, respectively) are -galactosylated at the C-6 position. Frequencies of differently substituted mannobiose blocks in the chain, calculated for fraction 1 using NMR spectroscopic data, were 0.13 for the disubstitited blocks Gal(Man–Man)Gal, 0.37 for the sum of monosubstituted blocks Gal(Man–Man) and (Man–Man)Gal, and 0.50 for the unsubstituted block Man–Man.     

Transforming growth factor-β1 modulates the effect of 1α,25-dihydroxyvitamin D3 on leukemic cells

Summary The human leukemic cells HL-60, U937, KG-1 and THP-1 incubated with transforming growth factor-β1 (TGF-β1) were studied by examining cell surface antigens and macrophage-specific activities. The addition of 0.5 ng/ml (20 pM) of TGF-β1 with 1α,25-dihydroxyvitamin D₃ [1α, 25(OH)₂D₃] induced more Leu-M3 (CD14)-positive cells (approximately 80%) than 5×10⁻⁸ M 1α,25(OH)₂D₃ alone did (30 to 50%), although original HL-60 cells did not express any Leu-M3 antigen at all. Tumor necrosis factor-α (TNF-α) with TGF-β1 and 1α,25(OH)₂D₃ was found to potentiate the expression of these surface antigens. Furthermore, the phagocytic activity was also induced strongly. The expression of CR3 (CD11b) antigen was also increased, and all Leu-M3-positive cells were found CR3-positive when HL-60, U937, and THP-1 cells were treated with these stimulants. In contrast, CR3 but not Leu-M3 was induced in KG-1 cells after the same treatment. This may indicate that the responsiveness of leukemic cells to TGF-β1 and 1α,25(OH)₂D₃ might vary depending on a differentiation stage of the target cells. Furthermore, K562 cells originated from a more undifferentiated precursor, were not able to respond to these two inducers. These results suggested that some of TGF-β superfamily proteins might represent potent modulators in hematopoiesis, especially in the development of monocytes-macrophages or their precursors.     

Galactomannan from the seeds of chinese honey locust (Gleditsia sinensis Lam.)

By the hot water extraction method, galactomannan was extracted (4.5% yield of the seed mass) from the seeds of Chinese honey locust (Gleditsia sinensis Lam). It had a molecular weight of 1230 kDa, and its solutions had a high viscosity [η] of 1064 ml/g and optical activity [α]_D of +21.4°. The polysaccharide consists of mannose and galactose residues in the molar ratio 2.69: 1. In the galactomannan macromolecule the backbone is formed by 1,4-β-D-mannopyranose residues, 37% of which are substituted by α-D-galactopyranose at C6. By ¹³C-NMR-spectroscopy, fragments of differently galactose-substituted mannobiose units were found to be in the galactomannan being studied: Man-Man, (Gal)Man-Man, and Man-Man(Gal) in the ratio of 0.23: 0.47: 0.30.     

N- and O-linked oligosaccharides completely lack galactose residues in the gms1och1 mutant of Schizosaccharomyces pombe

Unlike their counterparts in budding yeast Saccharomyces cerevisiae, the glycoproteins of Schizosaccharomyces pombe contain, in addition to α-d-mannose (Man), a large number of α-d-galactose (Gal) residues. In both yeasts, large outer chains are attached to the oligosaccharide cores of glycoproteins during export via Golgi. Formation of the yeast-specific large outer chain is initiated by α-1,6-mannosylatransferase encoded by the och1 ⁺ gene, the disruption of which blocked outer chain elongation. We previously reported that N-linked oligosaccharide structures of S. pombe och1Δ mutant consisted of Gal_2–6Man₉GlcNAc₂ with α-linked Gal residues attached to the core oligosaccharide moiety. The disruption of gms1 ⁺, a gene encoding the UDP-galactose transporter required for the synthesis of galactomannan, abolished cell surface galactosylation in S. pombe. In this study, we constructed a gms1Δoch1Δ double mutant and determined the N- and O-linked oligosaccharide structures present on the cell surface. Oligosaccharides were liberated from glycoproteins by hydrazinolysis and labeled with the fluorophore, 2-aminopyridine. The pyridylaminated N-linked oligosaccharides were analyzed by high-performance liquid chromatography in combination with α1,2-mannosidase digestion and partial acetolysis. These analyses revealed that the N-linked oligosaccharides of gms1Δoch1Δ cells consisted of α1,2-linked Man-extended core oligosaccharides (Man_8–12GlcNAc₂) from which the fission yeast-specific α-linked Gal residues were completely absent.     

Biological evaluation of a series of 2-acetamido-2-deoxy-D-glucose analogs towards cellular glycosaminoglycan and protein synthesis in vitro

Using primary hepatocytes in culture, various 2-acetamido-2-deoxy-D-glucose (GlcNAc) analogs were examined for their effects on the incorporation of D-[³H]glucosamine, [³⁵S]sulfate, and L-[¹⁴C]leucine into cellular glycoconjugates. A series of acetylated GlcNAc analogs, namely methyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-(3) and β-D-glucopyranoside (4) and 2-acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-D-glucopyranose (5), exhibited a concentration-dependent reduction of D-[³H]glucosamine, but not of [³⁵S]sulfate incorporation into isolated glycosaminoglycans (GAGs), without affecting L-[¹⁴C]leucine incorporation into total protein synthesis. These results suggest that analogs 3–5 exhibit an inhibitory effect on D-[³H]glucosamine incorporation into isolated GAGs by diluting the specific activity of cellular D-[³H]glucosamine and by competing for the same metabolic pathways. In the case of the corresponding series of 4-deoxy-GlcNAc analogs, namely methyl 2-acetamido-3,6-di-O-acetyl-2,4-dideoxy-α-(6) and β-D-xylo-hexopyranoside (7) and 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-D-xylo-hexopyranose (8), compound 8 at 1.0 mM exhibited the greatest reduction of D-[³H]glucosamine and [³⁵S]sulfate incorporation into isolated GAGs, namely to ∼7% of controls, and a moderate inhibition of total protein synthesis, namely to 60% of controls. Exogenous uridine was able to restore the inhibition of total protein synthesis by compound 8 at 1.0 mM. Isolated GAGs from cultures treated with compound 8 were shown to be smaller in size (∼40 kDa) than for control cultures (∼77 kDa). These results suggest that the inhibitory effects of compound 8 on cellular GAG synthesis may be mediated by the incorporation of a 4-deoxy moiety into GAGs resulting in premature chain termination and/or by its serving as an enzymatic inhibitor of the normal sugar metabolites. The inhibition of total protein synthesis from cultures treated with compound 8 suggests a uridine trapping mechanism which would result in the depletion of UTP pools and cause the inhibition of total protein synthesis. A 1-deoxy-GlcNAc analog, namely 2-acetamido-3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-glucitol (9), also exhibited a reduction in both D -[³H]glucosamine and [³⁵S]sulfate incorporation into isolated GAGs by 19 and 57%, of the control cells, respectively, at 1.0 mM without affecting total protein synthesis. The inability of compound 9 to form a UDP-sugar and, hence, be incorporated into GAGs presents another metabolic route for the inhibition of cellular GAG synthesis. Potential metabolic routes for each analog's effects are presented.     

Marine Bacterial Sulfated Fucoglucuronomannan (SFGM) Lyase Digests Brown Algal SFGM into Trisaccharides

Abstract Three kinds of trisaccharides were prepared by digesting fucoidan from the brown alga Kjellmaniella crassifolia, with the extracellular enzymes of the marine bacterium Fucobacter marina. Their structures were determined as Δ^4,5GlcpUA1-2(L-Fucp(3-O-sulfate)α1-3)D-Manp, Δ^4,5GlcpUA1-2(L-Fucp(3-O-sulfate)α1-3)D-Manp(6-O-sulfate), and Δ^4,5GlcpUA1-2(L-Fucp(2,4-O-disulfate)α1-3)D-Manp(6-O-sulfate), which indicated the existence of a novel polysaccharide in the fucoidan and a novel glycosidase in the extracellular enzymes. In order to determine the complete structure of the polysaccharide and the reaction mechanism of the glycosidase, the fucoidan was partially hydrolyzed to obtain glucuronomannan, which is the putative backbone of the polysaccharide, and its sugar sequence was determined as (-4-D-GlcpUAβ1-2D-Manpα1-)_n, which disclosed that the main structure of the polysaccharide is (-4-D-GlcpUAβ1-2(L-Fucp(3-O-sulfate)α1-3)D-Manpα1-)_n. Consequently, the glycosidase was deduced to be an endo-α-D-mannosidase that eliminatively cleaves the α-D-mannosyl linkage between D-Manp and D-GlcpUA residues in the polysaccharide and produces the above trisaccharides. The novel polysaccharide and glycosidase were tentatively named as sulfated fucoglucuronomannan (SFGM) and SFGM lyase, respectively.     

Muscarinic cholinoceptor agonists and antagonists are modulators of the activity of α<Subscript>1</Subscript>-adrenoceptors in the membranes of rat cerebral cortex

The effects of activation and inhibition of muscarinic cholinoceptors by carbachol and atropine on the binding of specific nonselective α₁-antagonist [³H]prazosine in synaptosomal membranes of rat cerebral cortex have been studied. It has been shown that the ligand-receptor interaction of α₁-adrenoceptors corresponds to the model suggesting the presence of a single receptor pool and the binding of two ligand molecules to the receptor. The parameters of [³H]prazosine binding to α₁-adrenoceptors were as follows: K _d = 1.56 ± 0.17 nM, B _max = 30.25 ± 1.78 fmol/mg protein, n = 2. Upon inhibition of muscarinic cholinoceptors by atropine or their activation by carbachol, the radiolabelled ligand is bound to α₁-adrenoceptors according to the same model but at n = 1. In the presence of atropine, the sensitivity of α₁-adrenoceptors to [³H]prazosine decreases more than twofold (K _d = 3.52 ± 0.36 nM) and the concentration of the active receptors is 36% lower (B _max = 19.45 ± 1.46 fmol/mg protein). Carbachol does not reduce the affinity of adrenoceptors to the ligand, while the concentration of active receptors decreases like in the case of atropine. It is supposed that α₁-adrenoceptors in the membranes of rat cerebral cortex exist as dimers. The modulating effects of atropine and carbachol on the binding of specific antagonist by α₁-adrenoceptors are exhibited as changes in the general character of binding (monomerization of α₁-adrenoceptors) and as inhibitory effect on the [³H]prazosine binding parameters.     

Alkali-soluble polysaccharides of <Emphasis Type="Italic">Laetiporus Sulphureus</Emphasis> (Bull.: Fr.) Murr fruit bodies

Alkali-soluble polysaccharides have been extracted from Laetiporus Sulphureus (Bull.: Fr.) Murr fruit bodies with a yield of 42.7%. The structure of the dominant polymer (16.05% of fruit bodies’ mass), named latiglucan I, has been determined. It is linear β-1,3-glucan (molecular weight 1.8 × 10⁵ Da, [α]_D-17°).     

The effects of 1α,25-dihydroxyvitamin D3 on matrix metalloproteinase and prostaglandin E2 production by cells of the rheumatoid lesion

The biologically active metabolite of vitamin D₃, 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃], acts through vitamin D receptors, which were found in rheumatoid tissues in the present study. IL-1β-activated rheumatoid synovial fibroblasts and human articular chondrocytes were shown to respond differently to exposure to 1α,25(OH)₂D₃, which has different effects on the regulatory pathways of specific matrix metalloproteinases and prostaglandin E₂.     

Galactomannan from the seeds of Ural licorice (<Emphasis Type="Italic">Glycyrrhiza uralensis</Emphasis> Fisch.)

Galactomannans from the seeds of Ural licorice (Glycyrrhiza uralensis Fisch.) obtained by hot water extraction of freshly ripened (GGu-1) and overwintered (GGu-2) seeds were studied. GGu-1 and GGu-2 (yield, 1.98 and 1.99% of the seed weight) had molecular weights of 1379 and 877 kDa, respectively; their solutions were characterized by high viscosity ([η 1193.1 and 765.8 mg/g, respectively) and optical activity ([α_D, +64.8 and +65.6 deg, respectively). Their galactose-to-mannose ratio was 1: 1.52 and 1: 1.50, respectively. According to IR and ¹³C NMR spectroscopic data and methylation analysis, the polymeric chains of GGu-1 and GGu-2 are comprised of 1,4-β-D-mannopyranose residues substituted at C-6 with single α-D-galactopyranose residues. The content of mannobiose units Man-Man, (Gal)Man-Man/Man-Man(Gal), and (Gal)Man-Man(Gal) differentially substituted with galactose in macromolecules GGu-1 and GGu-2 was 25.2, 18.4 and 55.9% for GGu-1 and 26.5, 32.5, and 41.0% for GGu-2.     

Structural analysis of galactomannans by NMR spectroscopy

The structure of naturally occurring galactomannans was characterized by high resolution NMR spectroscopy involving two-dimensional (2D) NMR measurements of the field gradient DQF-COSY, HMQC, HMBC, and ROESY experiments. Four galactomannans with different proportions of galactose (G) and mannose (M), from fenugreek gum (FG), guar gum (GG), tara gum (TG), and locust bean gum (LG), were investigated. Because these galactomannans had very high molecular weights, hydrolysis by dilute H₂SO₄ was carried out to give the corresponding low molecular weight galactomannans, the structural identities of which were established by comparison of the specific rotations, shape of the GPC profiles, and NMR spectra with those of higher molecular weight galactomannans. The correlation signals GH1-GC4, -GC5, and -MC6 in HMBC and GH1-GH6 in ROESY spectra of FG showed that more than two galactopyranose units with the 1 → 4 linkage were connected at C6 of the mannopyranose main chain. The coupling constant (J_H1,2) of galactose was 3.4 Hz, indicating that galactose has an α-linkage. The main chain mannose was found to connect through the 1 → 4 linkage, because of the appearance of the correlation signals MH1-MC4, and MC1-MH4 in the HMBC spectrum due to the long-range correlation signals between two neighboring mannopyranose residues through the M4-O-M1 bond. Although the main chain mannose J_H1,2 was not observed, probably because of the high molecular weight, the specific rotation of LG with a higher proportion of mannose was low, [α]_D²⁵ = +10.8°, compared with that of FG with a lower proportion of mannose, [α]_D²⁵ = +90.5°, suggesting that the mannose in the main chain had a α-linkage. These results suggest that the galactomannans comprise a (1 → 4)-β-mannopyranosidic main chain connected with more than two (1 → 4)-α-galactopyranosidic side chains, in addition to the single galactopyranose side chain, at C6 of the mannopyranose main chain.     

Coupling of D1 and D5 dopamine receptors to multiple G proteins

Dopamine receptors are a subclass of the super family of G protein-coupled receptors, that transduce their effects by coupling to specific G proteins. Within the dopamine receptor family, the adenylyl cyclase stimulatory receptors include the D₁ and D₅ subtypes. The D₁ and D₅ dopamine receptors are genetically distinct, sharing >80% sequence homology within the highly conserved seven transmembrane spanning domains, but displaying only 50% overall homology at the amino acid level. When expressed in transfected GH₄C₁ rat pituitary cells, both D₁ and D₅ receptors stimulate adenylyl cyclase and have identical affinities toward dopaminergic agonists and antagonists. In order to analyze specific signaling pathways mediated by activation of either D₁ or D₅ receptors, we have identified the G proteins that are coupled to these receptors. Through functional analyses and competition binding studies, and from immunoprecipitation techniques, using antisera against the various α subunits of G proteins, we have established that both D₁ and D₅ receptors couple to G_sα. In addition, D₁ receptors are also coupled to G_oα. Since G_oα has been implicated in the regulation of Ca²⁺, K⁺, and Na⁺ channels, this finding would suggest that D₁ receptors can mediate the functional activity of these ion channels. There is also evidence to indicate that D₅ receptors couple to G_zα, a novel G protein abundantly expressed in neurons. Thus, despite similar pharmacological properties, such differential coupling of D₁ and D₅ receptors to G proteins other than G_sα, indicates that dopamine can transduce varied signaling responses upon the simultaneous stimulation of both these receptors.     

β-Adrenoreceptor agonists and antagonists modulate the activity of α<Subscript>2</Subscript>-adrenoreceptors in rat cortex cerebral membranes

The influence of isoprenaline- and propranolole-induced activation and inhibition of β-adrenoreceptors on the specific nonselective α₂-antagonist [³H]RX821002 binding was studied on rat cerebral cortex subcellular membrane fractions. It was shown that the ligand-receptor interaction for α₂-adrenoreceptors corresponded to the model that assumed the presence of one receptor pool and binding of two ligand molecules to a receptor dimer. The following parameters were determined for [³H]RX821002 binding to α₂-adrenoreceptors: K _d1 = 1.57 ± 0.27 nM, B _max = 7.24 ± 1.63 fmol/mg of protein, n = 2. In the case of isoprenaline-induced activation of β-adrenoreceptors the binding of radiolabeled ligand to α₂-adrenoreceptors was described by the same model. The affinity of α₂-adrenoreceptors for [³H]RX821002 decreased more than twofold (K _d = 3.55 ± 0.02 nM) and the quantity of active receptors increased by 69% (B _max = 12.24 ± 0.06 fmol/mg of protein). Propranolole changed the model of ligand binding, and two pools of receptors were detected with the following parameters: K _d1 = 0.61 ± 0.02 nM, K _d2 = 3.41 ± 0.13 nM, B _ml = 1.88 ± 0.028 fmol/mg of protein, B _m2 = 9.27 ± 0.08 fmol/mg of protein, n = 2. The data suggest that α₂-adrenoreceptors in subcellular membrane fractions from rat cerebral cortex exist in dimeric form. Isoprenaline and propranolole exhibit modulating effect on the specific antagonist binding to α₂-adrenoreceptors, which results in the inhibition and alteration of [³H]RX821002 binding parameters.     

Exercise-induced oxyhemoglobin desaturation and pulmonary diffusing capacity during high-intensity exercise

The purpose of this investigation was to examine if exercise-induced arterial oxyhemoglobin desaturation selectively observed in highly trained endurance athletes could be related to differences in the pulmonary diffusing capacity (D _L) measured during exercise. The D _L of 24 male endurance athletes was measured using a 3-s breath-hold carbon monoxide procedure (to give D _LCO) at rest as well as during cycling at 60% and 90% of these previously determined O_2max. Oxyhemoglobin saturation (S _aO₂%) was monitored throughout both exercise protocols using an Ohmeda Biox II oximeter. Exercise-induced oxyhemoglobin desaturation (DS) (S _aO₂% < 91% at O_2max) was observed in 13 subjects [88.2 (0.6)%] but not in the other 11 nondesaturation subjects [NDS: 92.9 (0.4)%] (P ≤ 0.05), although O_2max was not significantly different between the groups [DS: 4.34 (0.65) l / min vs NDS: 4.1 (0.49) l / min]. At rest, no differences in either D _LCO [m1 CO · mmHg⁻¹ · min⁻¹: 41.7 (1.7) (DS) vs 41.1 (1.8) (NDS)], D _LCO / _A [8.2 (0.4) (DS) vs 7.3 (0.9) (NDS)], MVV [l / min: 196.0 (10.4) (DS) vs 182.0 (9.9) (NDS)] or FEV₁/FVC [86.3 (2.2) (DS) vs 82.9 (4.7) (NDS)] were found between groups (P ≥ 0.05). However, _E /O₂ at O_2max was lower in the DS group [33.0 (1.1)] compared to the NDS group [36.8 (1.5)] (P ≤ 0.05). Exercise D _LCO (m1 CO · mmHg⁻¹ · min⁻¹) was not different between groups at either 60% O_2max [DS: 55.1 (1.4) vs NDS: 57.2 (2.1)] or at 90% O_2max [DS: 61.0 (1.8) vs NDS: 61.4 (2.9)]. A significant relationship (r = 0.698) was calculated to occur between S _aO₂% and _E /O₂ during maximal exercise. The present findings indicate that the exercise-induced oxyhemoglobin desaturation seen during submaximal and near-maximal exercise is not related to differences in D _L, although during maximal exercise S _aO₂ may be limited by a relatively lower exercise ventilation. Accepted: 25 September 1996