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Instituto de Biologia Unicamp






ABSTRACTA IB (2) - 1999


P030-99 Stress-induced alteration in the lipolytic response to b -adrenoceptor agonists in rat white adipocytes

Farias-Silva E, Grassi-Kassisse DM, Wolf-Nunes V, Spadari-Bratfisch RC*

The sensitivity to b -adrenoceptor agonists was analyzed in epididymal adipose cells from rats submitted to a stress protocol previously reported to induce alterations in sensitivity to catecholamines in cardiac tissue from rats. Food intake and body weight were lower, whereas adipocytes basal lipolysis was higher in stressed compared to control rats. The response to isoprenaline, adrenaline, and salbutamol were sensitized, and the lipolytic response to norepinephrine, and to BRL37344 were desensitized. Responses to the higher used concentration (100 m M) of isoprenaline, epinephrine, salbutamol, and d-butytyl-cAMP were significantly enhanced in adipocytes from stressed rats. pD2 or maximum response to CGP12177 were not altered. Supersensitivity to isoprenaline was abolished by 50 nM ICI118,551 but was not modified by 100 nM metoprolol. However, subsensitivity to norepinephrine and to BRL37344 was abolished by 100 nM metoprolol. The results suggest that in epididymal adipocytes from stressed rats there is a desensitization of the response to adrenoceptor agonists mediated by b 1-adrenoceptors together with a sensitization of the response mediated by b 2-adrenoceptors. b 3-adrenoceptors may be resistant to the stress effect. Journal of Lipid Research 40: 1719-1727, 1999 IF= 3.764

P031-99 Pharmacological evidence for beta(2)-adrenoceptor in right atria from stressed female rats

Spadari-Bratfisch RC*, Santos IN, Vanderlei LCM, Marcondes FK

A physiological response to TA2005, a potent b 2-adrenoceptors (b 2-AR) selective agonist, was studied in right atria isolated from stressed female rats under the influence of the estrous cycle. Concentration-response curves to the agonist were obtained in presence and in absence of selective antagonists in right atria isolated from female rats submitted to three daily footshock sessions and sacrificed at estrus or diestrus. The pD2 values of TA2005 were not influenced by estrous cycle phase or foot-shock stress. However, in right atria from stressed rats sacrificed during diestrus, the concentration-response curve to TA2005 was biphasic with a response being obtained at concentrations of 0.1 nM, whereas during estrus no response was observed at doses lower than 3 nM. Concentration-response curves to TA2005 in presence of ICI118,551 were best fitted by a one site model equation. The b 1-AR antagonist, CGP20712A, shifted to the right only the second part of the concentration-response curves to the agonist, unmasking the putative b 2-AR mediated response to the agonist in tissues isolated from stressed rats at diestrus. Under this condition, concentration-response curves to the agonist were best fitted by a two-site model equation. pD2 and maximum response of TA2005 interaction with b 1 and putative b 2-adrenoceptor components were calculated. pKB values for ICI118,551 could not be obtained in stressed rats sacrificed at diestrus since Schild plot slope were lower than 1.0. In right atria from control rats, ICI118,551 pKB values were similar to reported values for the interaction of the antagonist with b 1-AR. These results confirm a heterogenous b -AR population mediating the chronotropic response to catecholamines in right atria from foot-shock stressed female rats sacrificed at diestrus. The stress-induced response seems may be mediated by the b 2-AR subtype. Right atria from rats sacrificed during estrus are protected against stress-induced alterations on the homogeneity of b -AR population. Canadian Journal of Physiology and Pharmacology 77: 432-440, 1999 IF= 1.275

P032-99 Lysine degradation through the saccharopine pathway in mammals: involvement of both bifunctional and monofunctional lysine-degrading enzymes in mouse

Papes F, Kemper EL, Cord-Neto G, Langone F*, Arruda P

Lysine-oxoglutarate reductase and saccharopine dehydrogenase catalyse the first two steps of lysine degradation through the saccharopine pathway in upper eukaryotes. Here we describe the isolation and characterization of a cDNA clone encoding a bifunctional enzyme bearing domains corresponding to these two enzymic activities. These activities were partly purified for mouse liver. Both a bifunctional lysine-oxoglutarate reductase/saccharopine dehydrogenase and a monofunctional saccharopine dehydrogenase were shown for the first time to be probably present in this organ. Northern analyses indicate the existence of two mRNA species in liver and kidney. The longest molecule, 3.4 kb in size, corresponds to the isolated cDNA and encodes the bifunctional enzyme while the 2.4 kb short transcript probably codes for the monofunctional dehydrogenase. Sequence analyses show that the bifunctional enzyme is likely to be a mitochondrial protein. Enzymic and expression analyses suggest that lysine-oxoglutarate reductase/saccharopine dehydrogenase levels increase in livers of mice under starvation. Biochemical Journal 344(Pt 2): 555-563, 1999 IF= 3.579

P033-99 Remodeling of HDL by CETP in vivo and by CETP and hepatic lipase in vitro results in enhanced uptake of HDL CE by cells expressing scavenger receptor B-I

Collet X, Tall AR, Serajuddin H, Guendouzi K, Royer L, Oliveira H*, Barbaras R, Jiang XC, Francone OL

The transport of HDL cholesteryl esters (CE) from plasma to the liver involves a direct uptake pathway, mediated by hepatic scavenger receptor B-I (SR-BI), and an indirect pathway, involving the exchange of HDL CE for triglycerides (TG) of TG-rich lipoproteins cholesteryl ester transfer protein (CETP). HDL CE turnover studies were performed in mice expressing human CETP and/or human lecithin:cholesterol acyltransferase (LCAT) transgenes on a background of human apoA-I expression. The fractional clearance of HDL CE by the liver was delayed by LCAT transgene, while the CETP transgene increased it. No incremental transfer of HDL CE radioactivity to the TG-rich lipoprotein fraction in mice expressing CETP, suggesting increased direct removal of HDL CE in the liver. HDL isolated from mice expressing CETP showed a 2- to 4-fold increase in SR-BI-mediated HDL CE uptake, compared to HDL from mice lacking CETP. The addition of pure CETP to HDL in cell culture did not lead to increased selective uptake of HDL CE by cells. However, when human HDL was enriched with TG by incubation with TG-rich lipoproteins in the presence of CETP, and treated with hepatic lipase, there was a significant enhancement of HDL CE uptake. Thus, the remodeling of human HDL by CETP, involving CE;-TG interchange, followed by the action of hepatic lipase (HL), leads to the enhanced uptake of HDL CE by cellular SR-BI. The observations suggest that in humans in which both the selective uptake and CETP pathways are active, the two pathways could operate in a synergistic fashion to enhance reverse cholesterol transport. Journal of Lipid Research 40:1185-1193, 1999 IF= 3.764

034-99 Diurnal variations in insulin secretion and K+ permeability in isolated rat islets

Delattre E, Cipolla-Neto J, Boschero AC*

The effects of glucose on insulin secretion and 86Rb efflux from isolated rat islets were studied at six different times during a 24 h period. In the absence of glucose and in the presence of substimulatory concentrations (2.8 mM) of the sugar, insulin secretion did not vary with the time of day. At a glucose concentration of 5.6 mM the stimulated insulin secretion was greater than basal levels only at 20 h. At a sugar concentration of 8.3 mM the increase in insulin secretion and the reduction in 86Rb efflux rate were more marked during the dark period. No effect of the time of day on insulin secretion was observed at glucose concentrations above 8.3 mM (except in 27.7 mM). Thus, the time of day appears to affect insulin secretion mainly at glucose concentrations close to physiological values, which is in agreement with the ability of physiological amounts of glucose to alter the 86Rb-permeability of pancreatic B-cells at the same time intervals. Clinical and Experimental Pharmacology and Physiology 26: 505-510, 1999 IF= 0.938

P035-99 Reduced insulin secretion in response to nutrients in islets from malnourished young rats is associated with a diminished calcium uptake

Latorraca MQ, Carneiro EM, Mello MAR, Boschero AC*

Changes in 45 Ca uptake and insulin secretion in response to glucose, leucine, and arginine were measured in isolated islets derived from four weeks old rats born from mothers maintained with normal (NP-17%) or low protein (LP-6%) diet during pregnancy and lactation. Glucose provoked a dose-dependent stimulation of insulin secretion in both groups of islets with basal and maximal release significantly reduced in LP as compared to NP islets. In LP group the concentration-response curve to glucose was shifted to the right compared to NP group, with the half-maximal response occurring at 16.9 and 13.3 mmol/L glucose, respectively. In LP islets, glucose-induced first and second phases of insulin secretions was drastically reduced. In addition, insulin response to individual amino-acids, or in association with glucose was also significantly reduced in LP group as compared to NP islets. In LP islets the 45Ca uptake after 5 min or 90 min incubation (reflecting mainly the entry of Ca2+, and the Ca2+ retention, respectively), was lower than NP islets. These results indicate that both initial and sustained phases of insulin secretion in response to glucose were reduced in malnourished rats.
Journal of Nutritional Biochemistry 10: 37-43, 1999 IF= 1.337

P036-99 Insulin-induced tyrosine phosphorylation of SHC in liver, muscle and adipose tissue of insulin resistant rats

Páez-Espinosa V, Rocha EM, Velloso LA, Boschero AC*, Saad MJA

Insulin stimulates rapid tyrosine phosphorylation of the protein Shc, which subsequently binds to Grb2, resulting in the activation of a complex mitogen network. We examined the levels of p52Shc protein, its phosphorylation state and Shc-Grb2 association in liver, muscle and adipose tissue before and after insulin administration in three animal models of insulin resistance (chronic dexamethasone treatment, 72 h-starvation, and aging). No differences in Shc protein expression between tissues from controls and insulin resistant animals were found. In fasted rats, which presented hypoinsulinemia, there was a decrease in Shc phosphorylation levels in liver and in adipose tissue after insulin infusion. On the other hand, a significant increase in Shc phosphorylation was observed in tissues from hyperinsulinemic animals. Alterations in Shc phosphorylation correlated well with the Shc-Grb2 binding capacity. These findings indicate that Shc tyrosil phosphorylation and Shc-Grb2 association are regulated differently by the different modalities of insulin resistance, which is probably related to the animal plasma insulin levels. The Shc-Grb2 association may be directly related to the insulin-induced tyrosil phosphorylation of p52Shc.
Molecular and Cellular Endocrinology 156:121-129, 1999 IF= 2.064

P037-99 Biochemical characterization of two crotamine isoforms isolated by a single step RP HPLC from Crotalus durissus terrificus (South American rattlesnake) venom and their action on insulin secretion by pancreatic islets

Toyama MH, Carneiro EM, Marangoni S, Barbosa RL,Corso G, Boschero AC*

Crotamine, a neurotoxin present in the venom of the South American rattlesnake Crotalus durrisus terrificus exists as several polymorphic variants, as demonstrated by recombinant DNA technology. We have isolated native crotamine by chromatography and have purified two crotamine isoforms (F2 and F3) by a single step of RP-HPLC. Native crotamine and RP-HPLC fractions F2 and F3 produced skeletal muscle spasms and spastic paralysis in mice. At low glucose concentrations, none of the crotamines altered the insulin secretion by rat isolated islets. In the presence of 16.7 mmol glucose/L, F2 (5 m g/ml), but not F3, increased insulin secretion two-fold, whereas native crotamine (1.5, 5 and 16.5 m g/ml) potentiated the secretion dose-dependently. The mode of action of the F2 and F3 isoforms in b -cells is thus different from that in muscle cells, which may be related to the binding affinity of each isoform for the Na+ channels located in the b -cell membrane. We concluded that crotamine isoforms may be valuable tools for studying the involvement of Na+ channels in the mechanism of insulin secretion.
Biochimica et Biophysica Acta 24957: 1-6, 1999 IF= 2.411

P038-99 Ocorrência natural de parasitóides de Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae)

Souza CEP, Amaral Filho BF*

Anais da Sociedade de Entomologia do Brasil 28:741-743, 1999


P039-99 Nova planta hospedeira de Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae)

Souza CEP, Amaral Filho BF*

Anais da Sociedade de Entomologia do Brasil 28: 745-748, 1999


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