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Biomedical subjects

R G Downer

Publications and source records attributed to R G Downer.

At least 37 records · Page 2Linked to original sources
PubMed1987

Pharmacological characterisation of the dopamine-sensitive adenylate cyclase in cockroach brain: evidence for a distinct dopamine receptor.

Dopamine increases cyclic AMP production in crude membrane preparations of cockroach brain with plateaus in cyclic AMP production occurring between 1-10 microM and at 10 mM. Maximal production of cyclic AMP is 2.25 fold greater than that of control values. Octopamine also increases cyclic AMP production with a Ka of 1.4 microM and maximal production 3.5 fold greater than that of control. 5-Hydroxytryptamine does not increase cyclic AMP production. The effects of octopamine and dopamine are fully additive. The vertebrate dopamine agonists ADTN and epinine stimulate the dopamine-sensitive adenylate cyclase (AC) with Ka values of 4.5 and 0.6 microM respectively and with maximal effectiveness 1.7 fold greater than that of control. The selective D2-dopamine agonist LY-171555 stimulates cyclic AMP production to a similar extent with a Ka of 50 microM. Other dopamine agonists (apomorphine, SKF-82526, SKF-38393) have no stimulatory effects. The octopamine-sensitive AC is inhibited by a variety of antagonists known to affect octopamine and dopamine receptors, with the following order of potency: mianserin greater than phentolamine greater than cyproheptadine greater than piflutixol greater than cis-flupentixol greater than SCH-23390 greater than (+)-butaclamol greater than SKF-83566 greater than SCH-23388 greater than sulpiride greater than spiperone greater than haloperidol. The dopamine-sensitive AC is inhibited by the same compounds with the following order of potency: piflutixol greater than cis-flupentixol greater than (+)-butaclamol greater than spiperone greater than or equal to SCH-23390 greater than cyproheptadine greater than SKF-83566 greater than SCH 23388 greater than mianserin greater than phentolamine greater than sulpiride greater than haloperidol. With the exception of mianserin, 3H-piflutixol is displaced from brain membranes by dopamine antagonists with an order of potency similar to that observed for the inhibition of dopamine-sensitive AC. The results indicate that the octopamine- and dopamine-sensitive AC in cockroach brain can be distinguished pharmacologically and the dopamine receptors coupled to AC have pharmacological characteristics distinct from vertebrate D1- and D2-dopamine receptors.

Adenylyl Cyclases↗
PubMed1987

Analysis of monoamines and their metabolites by high performance liquid chromatography with coulometric electrochemical detection.

High performance liquid chromatography with coulometric electrochemical detection has been used to achieve simultaneous determination of norepinephrine, epinephrine, 5-hydroxytryptophan, normetanephrine, dopamine, metanephrine, 3,4-dihydroxyphenylacetic acid, N-acetyldopamine, tyramine, tryptophan, 5-hydroxyindoleacetic acid, 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, homovanillic acid, tyrosine, p-octopamine, N-acetyl-p-octopamine, and p-synephrine. The procedure has been applied to study monoamine degradation in the insect brain and to demonstrate that N-acetylation rather than oxidative deamination is the primary route of monoamine catabolism in insects.

Animals↗
PubMed1987

Forskolin-insensitive adenylate cyclase in cultured cells of Choristoneura fumiferana (Insecta).

Adenylate cyclase from a spruce budworm cell line, IBRI-Cfl, is activated by octopamine (Ka = 50 microM), guanine nucleotides and sodium fluoride but not by forskolin. In addition, forskolin does not potentiate the octopamine-sensitive response. To our knowledge, this is the first published report of a hormone-sensitive adenylate cyclase, with a functional guanine nucleotide regulatory protein, that is insensitive to forskolin both in intact cells and washed membrane preparations.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Changes in Amines and Biosynthetic Enzyme Activities in p-Fluorophenylalanine Resistant and Wild Type Tobacco Cell Cultures.

The levels of free amines and the activities of their biosynthetic enzymes were measured in a p-fluorophenylalanine resistant Nicotiana tabacum L. cv Xanthi cell line (TX4) which accumulates high levels of cinnamoylamides, and a wild type cell line (TX1). Putrescine in TX1 and spermidine in TX1 and TX4 increased 4-fold by day 4 but declined by day 8 of the culture period. Spermine levels were consistently low, while tyramine was not found in TX1 until day 9 when a gradual rise was noted. Ornithine decarboxylase activity in TX1 and TX4 increased slightly through day 2 but declined gradually thereafter. S-Adenosylmethionine decarboxylase activity remained low throughout the culture period, and tyrosine and arginine decarboxylases in TX1 were very low in activity. In contrast, the activities of tyrosine and arginine decarboxylases were elevated in TX4, but a 3-fold increase in tyramine after a subculture was not accompanied by a rise in tyrosine decarboxylase. However, tyrosine decarboxylase activity did increase during a second rise in tyramine levels in aging cells, late in the culture period. Although significant differences exist in amine levels, between TX4 and TX1, it is unclear how altered amine metabolism relates to p-fluorophenylalanine resistance.

Journal Article↗
PubMed1986

Effect of adipokinetic hormone on the structure and properties of lipophorin in locusts.

The reversible association of a low molecular weight hemolymph protein (mol wt 20,000 estimated by SDS-polyacrylamide gel electrophoresis) with lipophorin, following treatment with adipokinetic hormone (AKH), was demonstrated by density gradient ultracentrifugation and by specific precipitation of lipophorin from the hemolymph of resting and AKH-injected locusts. The injection of AKH also stimulated the loading of diacylglycerol from fat body by lipophorin and resulted in a lower density lipophorin ("activated lipophorin"). The activated lipophorin particles (diameter 21.7 +/- 3.0 nm, 15.8 to 33.6 nm) were larger and more heterogeneous in size than those of resting lipophorin (14.5 +/- 1.6 nm, 11.9 to 19.2 nm). A theoretical analysis based on the experimental data (e.g., density gradient profile, electron microscopic observation, and diacylglycerol content) suggests that very large lipophorin particles result from intermolecular fusion of the lipophorin molecules that are activated by AKH. Attempts to demonstrate the effect of AKH on the structure of lipophorin, in vitro, were unsuccessful.

Animals↗
PubMed1984

Influence of octopamine on trehalase activity in muscle and hemolymph of the American cockroach, Periplaneta americana L.

Injection of adult male cockroaches (Periplaneta americana) with 10 microliter 1 microM octopamine causes elevated activity of trehalase (alpha, alpha-trehalose glucohydrolase; EC 3.2.1.28) in hemolymph and muscle but not in gut. Tyramine, dopamine and glutamate, at the same concentration, failed to elicit any effect on trehalase activity. Determination of some kinetic parameters for muscle and hemolymph trehalases reveal that octopamine causes an increase in Vmax without any significant alteration in the Km of the enzyme for trehalose. The results are discussed in terms of the physiological significance of octopamine-mediated activation of tissue trehalases.

Animals↗
PubMed1984

Distribution of 5-hydroxytryptamine and indolealkylamine metabolites in the American cockroach, Periplaneta americana L.

A procedure is described for simultaneous estimation of tryptophan (TP), 5-hydroxytryptophan (5-OHTP), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), N-acetyl 5-hydroxytryptamine (NA5-HT) and N-acetyldopamine (NADA) using high performance liquid chromatography with coulometric electrochemical detection. The procedure has been used to determine the distribution of these compounds in the central nervous system of the American cockroach, Periplaneta americana. The ratio of TP:5-HT is greatest in the cerebral ganglia (6.5) with lesser ratios evident in the thoracic ganglia (15.5-18.9) and abdominal ganglia (9.6-11.2). Relatively low concentrations of 5-OHTP and NA5-HT were observed in the cerebral ganglia whereas 5-HIAA was not detected. Incubation of ganglia resulted in increased concentrations of NA5-HT. Reserpine reduced levels of 5-HT and NADA whereas probenecid caused a marked reduction in TP and slight elevation of NADA levels. No MAO activity was detected in the central nervous system.

5-Hydroxytryptophan↗
PubMed1983

Pharmacology of aminergic receptors mediating an elevation in cyclic AMP and release of hormone from locust neurosecretory cells.

Synaptic activation of the neurosecretory cells within the glandular lobe of the corpus cardiacum of locusts results in the release of bioassayable adipokinetic hormones and an elevation in cAMP. The effectiveness of several putative aminergic neurotransmitters in mimicking these actions of the natural transmitter, and the effects of aminergic antagonists, have been studied. The receptors mediating the release of adipokinetic hormones exhibited a specificity for the monophenolic amines octopamine and synephrine at 10(-7) M. These two amines were also the most effective, at 5 X 10(-6) M, in elevating cAMP levels. Octopamine induced a dose-dependent elevation in cAMP with half-maximal stimulation occurring at 5 X 10(-6) M. 5-Hydroxytryptamine (5-HT) was also capable of elevating cAMP levels, but, unlike the octopamine response, or the response to the natural transmitter, the response to 5-HT was not blocked by the antagonist phentolamine. Gramine was also an effective antagonist of the octopamine-induced response. The results are consistent with the hypothesis that octopamine is the natural transmitter within this neurosecretory system.

Animals↗
PubMed1983

Rapid estimation of catecholamines, octopamine and 5-hydroxytryptamine in biological tissues using high-performance liquid chromatography with coulometric detection.

A rapid, convenient procedure is described for the simultaneous determination of catecholamines, monohydroxyphenolamines and 5-hydroxytryptamine in biological tissues. The procedure involves homogenization of tissue in perchloric acid, addition of heparin and centrifugation followed by direct injection of the supernatant onto a C18 reversed-phase high-performance liquid chromatographic column. The mobile phase employed sodium dodecyl sulfate as ion pair reagent with 20% acetonitrile and 10-12% methanol as organic modifier. Eluted fractions were detected electrochemically using dual coulometric electrodes operated in screen mode. The procedure has been applied to the analysis of norepinephrine, epinephrine, dopamine, octopamine, tyramine, 5-hydroxytryptamine and tryptophan in a variety of tissues including mammalian heart and brain and insect nerve cord.

Animals↗
PubMed1983

Interaction of formamidines with octopamine-sensitive adenylate cyclase receptor in the nerve cord of Periplaneta americana L.

Chlordimeform (CDM) and demethylchloridimeform (DCDM) mimic the action of octopamine in elevating adenylate cyclase activity in intact nerve cords of the American cockroach, Periplaneta americana. At a concentration of 1 x 10(-5)M, DCDM (13.5x increase within 20 minutes) is a more potent effector of the response than CDM (3x increase within 20 minutes), but both compounds show less efficacy than octopamine (23.5x increase within 15 minutes). DCDM also mimics the stimulatory effect of octopamine on adenylate cyclase activity in nerve cord homogenates whereas CDM has no demonstrable effect on this preparation. The octopamine- and DCDM-induced responses are competitively inhibited by phentolamine (1 x 10(-6)M) and cyproheptadine (1 x 10(-6)M) but not by propranolol (1 x 10(-6)M). DCDM and CDM inhibit the octopamine-induced activation of adenylate cyclase by 33% and 44% respectively. The results are discussed in light of the proposal that DCDM serves as a partial agonist and CDM as an antagonist of the octopamine receptor.

Adenylyl Cyclases↗
PubMed1982

Insect hemolymph lipophorin: a mechanism of lipid transport in insects.

Lipophorin, formerly called the "diacylglycerol-carrying lipoprotein," exists in the hemolymph of many insects including locust, cockroach, and silkworm. A rapid and efficient method has been developed for the purification of lipophorin, which includes a specific precipitation under low ionic concentration and DEAE-cellulose column chromatography. The final preparation of lipophorin is highly homogeneous, as judged by gel electrophoresis, electronmicroscopy, and immunodiffusion. Molecules of lipophorin from the above three insects are almost globular in shape with a diameter of 13-16 nm. Molecular weights are 600,000-700,000, and the lipid content totals 40-50%. The lipids are comprised of diacylglycerol, cholesterol, and phospholipid. Of particular interest is that the locust and cockroach lipophorin contains large amounts of hydrocarbons in addition to the above lipids. Apoprotein of lipophorin consists of two-non-identical subunits, heavy chain (M.W. 250,000) and light chain (M.W. 85,000); carbohydrate (mainly mannose) is covalently associated only with the heavy chain. Tests of the physiological function of insect lipophorin indicate that it has multiple roles as a true carrier and a reusable shuttle in transporting diacylglycerol, cholesterol, and hydrocarbon from sites of storage, absorption, and synthesis to sites where these lipids are utilized as metabolic fuel, precursors of triacylglycerol and phospholipid synthesis, or structural components of cell membrane and cuticle. In view of this functional multiplicity as a true carrier and reusable shuttle, therefore, the insect lipophorin is unique lipoprotein and essentially different from mammalian plasma lipoproteins.

Adipose Tissue↗
PubMed1981

Diacylglycerol-carrying lipoprotein of hemolymph of the American cockroach: purification, characterization, and function.

A diacylglycerol-carrying lipoprotein (DGLP) was isolated from the hemolymph of adult male and female American cockroaches, Periplaneta americana. The purification procedure involved dialysis against distilled water, precipitation at low ionic concentration at pH 6.6, and separation by column chromatography on DEAE-cellulose. The final preparation was homogeneous as judged by polyacrylamide gel electrophoresis and electron microscopy. The lipoprotein comprised over 50% of the total hemolymph protein. The DGLP molecule was almost globular in shape with a diameter of approximately 160 A. The molecular weight, determined by a sedimentation-equilibrium method, was approximately 600,000. Apoprotein of DGLP consisted of two subunits, heavy chain (mol wt 250,000) and light chain (mol wt 85,000). The total lipid content of DGLP amounted to about 50%. The lipids comprised diacylglycerol (15% of total lipid), hydrocarbons (28%), cholesterol (5%), and phospholipids (43%). n-Pentacosane, 3-methylpentacosane, and 6,9-heptacosadiene were identified as major hydrocarbons. Mannose(0.9%) and glucosamine (0.3%) were associated with apoprotein of DGLP. The capacity of the purified DGLP to accept diacylglycerol from both fat body and midgut was demonstrated in vitro; thus it was suggested that the same carrier molecule served to transport this lipid from storage site and absorption site. The possible multiple role of cockroach DGLP in transporting such lipids as diacylglycerol, cholesterol, and hydrocarbon from the site of storage, absorption, or synthesis is discussed.

Amino Acids↗
PubMed1980

Conversion of [U-14C] glucose to lipid in the American cockroach, Periplaneta americana L.

The incorporation of D-[U-14C] glucose into fat body acylglycerols was studied in fed and starved adult cockroaches, Periplaneta americana. About 7-10% of injected glucose is incorporated into the triacylglycerol component of fat body within three hours of injection. The capacity for conversion of glucose to triacylglycerol is greater in fed than starved Insects and the differences in lipogenic capacity of fat body from fed and starved cockroaches are retained in vitro. Incubation of fat body in the presence of haemolymph enhances the lipogenic capacity of fat body.

Adipose Tissue↗
PubMed1977

The role of diacylglycerol-carrying lipoprotein I in lipid transport during insect vitellogenesis.

A diacylglycerol-carrying lipoprotein was isolated from mature eggs of the silkworm, Philosamia cynthia and compared, for physiochemical properties, with the major diacylglycerol-carrying lipoprotein I (LP-I) of hemolymph. The two molecules are identical an electrophoretic mobility, structural configuration as revealed by electron microscopy, and amino acid composition. In addition mannose was detected in the lipid-free protein moiety, thus enabling classification of the molecules as glycoproteins. The molecules differ in lipid content with egg-LP-I containing only 3.6% of the diacylglycerol content of hemolymph LP-I and the phospholipid and cholesterol components also showing a marked reduction. Analysis of the LP-I and vitellogenin (another diacylglycerol-carrying lipoprotein; LP-II) concentrations of mature eggs indicates that the amounts of the two glycolipoproteins in eggs are insufficient to account for the total acylglycerol content of the eggs. The results suggest that LP-I functions as a true carrier-protein serving to transport diacylglycerol from the fat body to the ovary. This proposal is supported by the observation that LP-I isolated from the egg retains the physiological capacity of hemolymph-LPi to take up diacylglycerol from fat body. Thus it is suggested that LP-I is the major source of lipid for vitellogenesis, whereas vitellogenin is the primary source of protein.

Amino Acids↗