Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Metabolic, ventilatory, and hygric physiology of a South American marsupial, the long-furred woolly mouse opossum

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Controle do fornecimento e da utilização de substratos energéticos no encéfalo

Correspondendo a apenas 2% do peso corpóreo, o cérebro apresenta taxa metabólica superior à maioria dos demais órgãos e sistemas. A maior parte do consumo energético encefálico ocorre no transporte iônico para manutenção do potencial de membrana celular. Praticamente desprovido de estoques, os substratos energéticos para o encéfalo são fornecidos necessariamente pela circulação sanguínea.O suprimento desses substratos sofre também a ação seletiva da barreira hemato-encefálica (BHE). O principal substrato, que é a glicose, tem uma demanda de 150 g/dia (0,7 mM/g/min). A metabolização intracelular parece ser controlada pela fosfofrutoquinase. A manose e os produtos intermediários do metabolismo (frutose 1,6 bifosfato, piruvato, lactato e acetato) podem substituir, em parte, a glicose, quando os níveis sangüíneos desta encontram-se elevados. Quando oxidado, o lactato chega a responder por 21% do consumo cerebral de Ov em situações de isquemia e inflamação infecciosa, o tecido cerebral passa de consumidor a produtor de lactato. Os corpos cetônicos também podem reduzir as necessidades cerebrais de glicose desde que oferecidos em quantidades suficientes ao encéfalo. Entretanto, devem ser considerados como um substrato complementar e nunca alternativo da glicose, pois comprometem a produção cerebral de succinil CoA e GTP. Quanto aos demais substratos, embora apresentem condições metabólicas, não existem demonstrações consistentes de que o cérebro produza energia a partir dos ácidos graxos sistêmicos, mesmo em situações de hipoglicemia. de maneira análoga, etanol e glicerol são considerados apenas a nível de experimentação. A utilização dos aminoácidos é dependente da sua captação, limitada tanto pela baixa concentração sangüínea, como pela seletividade da BHE. A maior captação ocorre para os de cadeia ramificada e destes, a valina. A menor captação é a de aminoácidos sintetizados no cérebro (aspartato,gluconato e alanina). Todos podem ser oxidados a CO, e H(2)0. Entretanto, mesmo com o consumo de glicose reduzido a 50%, a contribuição energética dos aminoácidos não ultrapassa 10%. Para manter o suprimento adequado de glicose e oxigênio, o fluxo sangüíneo cerebral é da ordem de 800 ml/min (15% do débito cardíaco). O consumo de O, pelo cérebro é equivalente a 20% do total consumido pelo corpo. Esses mecanismos, descritos como controladores da utilização de substratos energéticos pelo cérebro, sofrem a influência da idade apenas no período perinatal, com a oxidação do lactato na fase pré-latente e dos corpos cetônicos, no início da amamentação.

Role of metabolic control on diabetic nephropathy

OBJETIVO: Os autores relatam a influência do controle metabólico do diabetes, experimentalmente induzido no rato, sobre a nefropatia diabética. Eles observaram o efeito da insulina, da acarbose, um inibidor da glicosidase, e de dois agentes combinados sobre o controle metabólico e o desenvolvimento da expansão mesangial de glomérulos renais, no diabetes induzido pela aloxana no rato. MÉTODOS: Usando 5 grupos de ratos Wistar assim definidos: Normal(N), diabéticos não-tratados (D), diabéticos tratados com acarbose (AD); diabéticos tratados com insulina (ID) e diabéticos tratados com insulina associada à acarbose (IAD) foram avaliados os seguintes parâmetros: peso corporal, ingestão alimentar, ingestão hídrica, diurese, níveis de glicose sanguínea e urinária e as lesões renais: alargamento mesangial e vacuolização de células tubulares, usando contagem semi-quantitativa 1, 3, 6, 9 e 12 meses após a indução do diabetes. RESULTADOS: Houve acentuado aumento da glicemia, dos níveis de glicose na urina, da diurese, da ingestão hídrica e alimentar, e progressiva perda de peso nos ratos diabéticos, enquanto que os ratos diabéticos tratados exibiram melhora significativa destes parâmetros, sendo os ratos tratados com insulina + acarbose os que apresentaram controle metabólico mais satisfatório. Houve um significativo alargamento mesangial nos ratos diabéticos quando comparado ao observado nos ratos normais, desde o 3º até o 12º mês após a indução do diabetes, sendo observada diferença significativa entre os animais tratados com acarbose + insulina e os ratos diabéticos não-tratados. Não houve diferença significativa entre os animais tratados somente com acarbose ou com insulina quando comparados com ratos diabéticos não-tratados. CONCLUSÃO: Os autores discutem os resultados abordando o papel do controle metabólico do diabetes na prevenção da nefropatia diabética.

Glucose metabolism in the erythrocytes of the buffalo (Bubalus bubalis)

(CO2)-C-14 production from [1-C-14] glucose, the rate of glycolysis measured by the value of lactate production and the activities of various enzymes were determined in buffalo erythrocytes. Buffalo red cell glycolytic metabolites were estimated and used for the calculation of the mass action ratios of reactions catalyzed by the glycolytic enzymes of Bubalus bubalis. A comparison of the values of the mass action ratios with the equilibrium constants of the various glycolytic reactions indicate that hexokinase, phosphofructokinase, phosphoglycerate kinase and pyruvate kinase reactions are displaced from equilibrium, suggesting a regulatory role for each of these enzymes in buffalo erythrocyte glycolysis. (C) 1997 Elsevier B.V.

Protein malnutrition does not impair glucose metabolism adaptations to exercise-training

Malnutrition is a common health problem in developing countries and is associated with alterations in glucose metabolism. In the present study we examine the effects of chronic aerobic exercise on some aspects of glucose metabolism in protein-deficient rats. Two groups of adult rats (90 days old) were used: Normal protein group (17%P)- kept on a normal protein diet during intra-uterine and postnatal life and Low protein group (6%P)- kept on a low protein diet during intrauterine and post natal life. After weaning (21 days old), half of the 17%P and 6%P rats were assigned to a Sedentary (Sed) or an Exercise-trained (Exerc = swimming, 1 hr/day, 5 days/week, supporting an overload of 5% of body weight) subgroup. The area under blood glucose concentration curve (Delta G) after an oral glucose load was higher in 17%P Sed rats (20%) than in other rats and lower in 6%P Exerc (11%) in relation to 6% Sed rats. The post-glucose increase in blood insulin (Delta I) was also higher in 17%P Sed (9%) than in other rats. on the other hand, the glucose disappearance rate after exogenous subcutaneous insulin administration (Kitt) was lower in 17%P Sed rats (66%) than in other rats. Glucose uptake by soleus muscle was higher in Exerc rats (30%) than in Sed rats. Soleus muscle glycogen synthesis was reduced in 6%P Sed rats (41%) compared to 17%P Sed rats but was restored in 6%P Exerc rats. Glycogen concentration was elevated in Exerc (32%) rats in comparison to Sed rats. The present results indicate that glucose-induced insulin release is reduced in rats fed low protein diet. This defect is counteracted by an increase in the sensitivity of the target tissues to insulin and glucose homeostasis is maintained. This adaptation allows protein deficient rats to preserve the ability to appropriately adapt to aerobic physical exercise training. (C) 2000 Elsevier B.V.

Protein deficiency during pregnancy and lactation impairs glucose-induced insulin secretion but increases the sensitivity to insulin in weaned rats

We studied glucose homeostasis in rat pups from darns fed on a normal-protein (170 g/kg) (NP) diet or a diet containing 60 g protein/kg (LP) during fetal life and the suckling period. At birth, total serum protein, serum albumin and serum insulin levels were similar in both groups. However, body weight and serum glucose levels in LP rats were lower than those in NP rats. At the end of the suckling period (28 d of age), total serum protein, serum albumin and serum insulin were significantly lower and the liver glycogen and serum free fatty acid levels were significantly higher in LP rats compared with NP rats. Although the fasting serum glucose level was similar in both groups, the area under the blood glucose concentration curve after a glucose load was higher for NP rats (859 (SEM 58) mmol/l per 120 min for NP rats v. 607 (SEM 52) mmol/l per 120 min for LP rats; P < 0.005). The mean post-glucose increase in insulin was higher for NP rats (30 (SEM 4.7) nmol/l per 120 min for NP rats v. 17 (SEM 3.9) nnol/l per 120 min for LP rats; P < 0.05). The glucose disappearance rate for NP rats(0.7 (SEM 0.1) %/min) was lower than that for LP rats (1.6 (SEM 0.2) %/min; P < 0.001). Insulin secretion from isolated islets (1 h incubation) in response to 16.7 mmol glucose/l was augmented 14-fold in NP rats but only 2.6-fold in LP rats compared with the respective basal secretion (2.8 mmol/l; P <0.001). These results indicate that in vivo as well as in vitro insulin secretion in pups from dams maintained on a LP diet is reduced. This defect may be counteracted by an increase in the sensitivity of target tissues to insulin.

Energy Expenditure and Oxygen Consumption as Novel Biomarkers of Obesity-induced Cardiac Disease in Rats

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Protein Deficiency Attenuates the Effects of Alloxan on Insulin Secretion and Glucose Homeostasis in Rats

We have investigated the effect of alloxan on insulin secretion and glucose homeostasis in rats maintained on a 17% protein (normal protein, NP) or 6% protein (low protein, LP) diet from weaning (21 days old) to adulthood (90 days old). The incidence of alloxan diabetes was higher in the NP (3.5 times) than in the LP group. During an oral glucose tolerance test, the area under serum glucose curve was lower in LP (57%) than in NP rats while there were no differences between the two groups in the area under serum insulin curve. The serum glucose disappearance rate (Kitt) after exogenous insulin administration was higher in LP (50%) than in NP rats. In pancreatic islets isolated from rats not injected with alloxan, acute exposure to alloxan (0.05 mmol/L) reduced the glucose- or arginine-stimulated insulin secretion of NP islets by 78% and 56%, respectively, whereas for islets from LP rats, the reduction was 47% and 17% in the presence of glucose and arginine, respectively. Alloxan treatment reduced the glucose oxidation in islets from LP rats to a lesser extent than in NP islets (23% vs. 56%). In conclusion, alloxan was less effective in producing hyperglycemia in rats fed a low protein diet than in normal diet rats. This effect is attributable to an increased peripheral sensivity to insulin in addition to a better preservation of glucose oxidation and insulin secretion in islets from rats fed a low protein diet.

Glucose homeostasis in pregnant rats submitted to dietary protein restriction

In the present work, we examined the effects of feeding a low protein diet during pregnancy on glucose-induced insulin secretion and glucose homeostasis in rats. Young (60 days), pregnant (P) or non-pregnant (NP) rats were fed during pregnancy or for 21 days (the NP) a normal (17%) or a low (6%) protein diet. Serum glucose and insulin levels and pancreas insulin content in the fed state; total area under serum glucose curve (AG) after a glucose load and serum glucose disappearance rate (Kitt) after insulin administration; as well as 86Rb outflow, 45Ca uptake and insulin secretion by isolated pancreatic islets in response to glucose were evaluated. Serum glucose was lower in 17%-P (12%) and 6%-P (27%) than in corresponding NP-rats. Serum insulin was higher in 17%- P (153%) and 6%-P (77%) compared to the corresponding NP-rats. Pancreatic insulin was higher in 6%-rats (55%) than in 17%-rats. No differences were found in AG among the groups whereas Kitt was lower in 6%-NP and higher in 6%-P than in the equivalent 17% rats. Increasing glucose concentration from 2.8 to 16.7 mmol/l, reduced 86Rb outflow from isolated islets from all groups. Increasing glucose concentration from 2.8 to 16.7 mmol/l elevated 45Ca uptake by 17%-NP (47%), 17%-P (40%) and 6%-P (214%) islets but not by 6%-NP ones. The increase in 45Ca uptake was followed by an increase in insulin release by the 17%-NP (2767%), 17%-P (2850%) and 6%-P (1200%) islets. In conclusion, 6%-P rats show impaired glucose induced insulin secretion related to reduced calcium uptake by pancreatic islets. However, the poor insulin secretion did not fully compensate the high peripheral sensitivity to the hormone, resulting in hypoglycemia.

Metabolic, ventilatory, and hygric physiology of the gracile mouse opossum (Gracilinanus agilis)

We present the first complete study of basic laboratory-measured physiological variables (metabolism, thermoregulation, evaporative water loss, and ventilation) for a South American marsupial, the gracile mouse opossum (Gracilinanus agilis). Body temperature (Tb) was thermolabile below thermoneutrality (Tb = 33.5°C), but a substantial gradient between Tb and ambient temperature (Ta) was sustained even at Ta = 12°C (Tb = 30.6°C). Basal metabolic rate of 1.00 mL O2 g-1 h-1 at Ta = 30°C conformed to the general allometric relationship for marsupials, as did wet thermal conductance (5.7 mL O2 g-1 h-1 °C-1). Respiratory rate, tidal volume, and minute volume at thermoneutrality matched metabolic demand such that O2 extraction was 12.4%, and ventilation increased in proportion to metabolic rate at low T a. Ventilatory accommodation of increased metabolic rate at low Ta was by an increase in respiratory rate rather than by tidal volume or O2 extraction. Evaporative water loss at the lower limit of thermoneutrality conformed to that of other marsupials. Relative water economy was negative at thermoneutrality but positive below Ta = 12°C. Interestingly, the Neotropical gracile mouse opossums have a more positive water economy at low Ta than an Australian arid-zone marsupial, perhaps reflecting seasonal variation in water availability for the mouse opossum. Torpor occurred at low Ta, with spontaneous arousal when . T b > 20°C. Torpor resulted in absolute energy and water savings but lower relative water economy. We found no evidence that gracile mouse opossums differ physiologically from other marsupials, despite their Neotropical distribution, sympatry with placental mammals, and long period of separation from Australian marsupials. © 2009 by The University of Chicago. All rights reserved.

Meal size effects on the postprandial metabolic response of Bothrops alternatus (Serpentes: Viperidae)

We examined the effects of meal size on the postprandial metabolic response of the lancehead Bothrops alternatus (Duméril, Bibron & Duméril, 1894), fed mice equaling to 5, 10, 20, and 40% of the snake's body mass. The maximum O2 consumption rates measured during digestion increased with meal size, reaching levels up to 2.8-7.8-fold higher than the metabolic rate measured during fasting. Specific Dynamic Action (SDA) duration also increased with meal size, lasting from 54 to 212 hours to complete. Under our experimental conditions, 30°C, the majority of our snakes failed to completely digest prey with a relative size of 40%. The SDA coefficient ranged from 17 to 27% of the energy content of the meal and was not affected by meal size. © 2013 Sociedade Brasileira de Zoologia All rights reserved.

Exercício físico na prevenção e no tratamento da síndrome metabólica: um modelo experimental com ratos

Pós-graduação em Ciências da Motricidade - IBRC

Loss of the Ability to Control Right-to-Left Shunt Does Not Influence the Metabolic Responses to Temperature Change or Long-Term Fasting in the South American Rattlesnake Crotalus durissus

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estresse oxidativo, alterações metabólicas e renais decorrentes da elevada ingestão de sacarose: efeito protetor da N-acetilcisteína (NAC)

Oxidative stress is related with physiopathology of diabetes mellitus type II and with its secondary complications, such as diabetic nephropathy. Thus, the purpose of this study was to examine the effects of n-acetylcysteine NAC, an antioxidant from Allium cepa, on oxidative stress, morphometrical and nutritional parameters and basal metabolism and energetic substrate utilization, serum glucose and oral glucose tolerance test (OGTT), and renal function of high-sucrose intake rats. Animals were initially divided into three groups. Rats in the control group (C; n=10) were given free access to a standard chow and water; (S; n=10) group received standard chow and 30% sucrose in its drinking water; (SN; n=5) group received standard chow and 2g/L NAC and 30% sucrose in its drinking water. After 25 days of treatments, rats were submitted to indirect calorimetry in fasted and feed states. After 30 days of treatments, rats from C and S groups were divided into four groups of five rats each. The (CC) and (SS) groups were given an intra-gastric dose 0,6mL saline (0,9%NaCl) and the (CNAC) and (SNAC) groups were treated with a intra-gastric dose of 0,6mL NAC (160g/day), and then everybody received a intra-gastric dose of glucose solution (20%) for the OGTT. Animals of S and SN groups have higher liquid consumption and lower food consumption than C group. Calorimetric analyses confirm that despite of the final body weight had not statistical difference among groups, S group have lower resting metabolic rate when compared to C and SN animals. Besides, S group has higher respiratory quotient, higher carbohydrate oxidation and lower lipid oxidation, both in fasted and feed states, than C and SN groups, evidencing the beneficial effect of NAC. Fasting plasma glucose is increased in SS and SNAC animals when compared to CC and CNAC, however SN group has glicemic level at 30 min before OGTT decreased when ...(Complete abstract click electronic access below)