Opioidergic Modulation of Ventilatory Response to Sustained Hypoxia in Obese Zucker Rats

Objective: To determine whether altered central and/or peripheral opioidergic mechanisms contribute to the altered ventilatory response to sustained hypoxia in obese Zucker rats. Research Methods and Procedures: Eight lean (176 ± 8 [SEM] g) and eight obese (225 ± 12 g) Zucker rats were studied at 6 weeks of age. Pulmonary ventilation (V?_E), tidal volume (V_T), and breathing frequency (f) at rest and in response to sustained (30 minutes) hypoxic (10% O₂) challenges were measured on three separate occasions by the barometric method after the randomized, blinded administration of equal volumes of saline (control), naloxone methiodide (N_M; 5 mg/kg, peripheral opioid antagonist), or naloxone hydrochloride (N_HCl; 5 mg/kg, peripheral and central opioid antagonist). Results: Administration of N_M and N_HCl in lean animals had no effect on V?_E either at rest or during 30 minutes of sustained exposure to hypoxia. Similarly, N_M failed to alter V?_E in obese rats. In contrast, N_HCl significantly (p < 0.05) increased V?_E and V_T both at rest and during 2 to 10 minutes of hypoxic exposure in obese rats. After 20 to 30 minutes of hypoxic exposure, V_T remained elevated with N_HCl, but the earlier elevation of V?_E seemed to be attenuated due to a decrease in f at 20 minutes of exposure to hypoxia. Discussion: Thus, endogenous opioids modulate both resting V?_E and the ventilatory response to sustained hypoxia in obese, but not in lean, Zucker rats by acting specifically on opioid receptors located within the central nervous system.     

Regional Fat Pad Growth and Cellularity in Obese Zucker Rats: Modulation by Caloric Restriction

Objective : To investigate, in young obese male Zucker rats, the effects of chronic food restriction and subsequent refeeding on: 1) parameters of nonadipose and adipose growth, 2) regional adipose depot cellularity [fat cell volume (FCV) and number], and 3) circulating leptin levels. Research Methods and Procedures : Obese (fa/fa) and lean (Fa/?) male Zucker rats were studied from age 5 to 19 weeks. After baseline food intake monitoring, 10 obese rats were subjected to 58 days of marked caloric restriction from ad libitum levels [obese‐restricted (OR)], followed by a return to ad libitum feeding for 22 days. Ten lean control rats and 10 obese control rats were fed ad libitum for the entire experiment. All rats were fed using a computer‐driven automated feeding system designed to mimic natural eating patterns. Results : After food restriction, OR rats weighed significantly less than did lean and obese rats and showed a significant diminution in body and adipose growth as compared with obese rats. Relative adiposity was not different between obese and OR rats and was significantly higher than that of lean rats. The limitation in growth of the adipose tissue mass in OR rats was due mostly to suppression of fat cell proliferation because the mean FCV in each of the four depots was not affected. Serum leptin levels of OR and obese rats were not different from each other but were significantly higher than those of lean rats. Discussion : Marked caloric restriction affects obese male Zucker rats in a manner different from that of nongenetic rodent models (i.e., Wistar rats). In comparison with the response to caloric deprivation of Wistar rats, these calorically restricted obese male Zucker rats appeared to defend their relative adiposity and mean FCV at the expense of fat cell number. These findings indicate that genetic and/or tissue‐specific controls override the general consequences of food restriction in this genetic model of obesity.     

Physiological Effects of Dietary PIPS Soybean-Derived Phospholipid in Obese Zucker (fa/fa) Rats

The effects of soybean-derived phospholipid, PIPS NAGASE^TM (PIPS), on obesity-induced diseases were studied in obese rats. Dietary PIPS alleviated hepatomegaly and fatty liver in the rats. These effects were attributable to reduced lipogenesis and enhanced lipolysis in the liver. The results suggest that PIPS can be useful as a dietary component that would reduce the risk of lifestyle-related diseases.     

Effects of Intracerebroventricular Infusion of Leptin in Obese Zucker Rats

AL-BARAZANJI, KAMAL A, ROBIN E BUCKINGHAM, JONATHAN RS ARCH, ANDREA HAYNES, DANUTA E MOSSAKOWSKA, DIANE L McBAY, STEPHEN D HOLMES, MARK T McHALE, XIN-MIN WANG, ISRAEL S GLOGER. Effects of intracerebro-ventricular infusion of leptin in obese Zucker rats. The obese Zucker rat (OZR) exhibits a missense mutation in the cDNA for the leptin receptor, producing a single amino acid substitution in the extracellular domain of the receptor. A mutation in the leptin receptor gene of the db/db mouse prevents the synthesis of the long splice variant of the receptor. The possibility that the OZR, like the db/db mouse, is refractory to the actions of murine leptin was tested by infusing the protein intracerebroventricularly via a minipump for 7 days. Lean Zucker rats (LZR) infused with leptin acted as positive controls, and other groups of OZR and LZR were infused with vehicle. In LZR, leptin reduced body-weight and food intake and increased brown adipose tissue (BAT) temperature. Plasma corticosterone increased (61%) in these rats, and plasma triglycerides fell (78%). Leptin treatment improved tolerance to an oral glucose load (16% reduction in the area under the blood glucose curve) while lowering plasma insulin. In OZR, the actions of leptin were blunted. Food intake was slightly, but not significantly, reduced. Although there was a reduction in the rate of increase in body mass, the effect of leptin was about half that seen in LZR. BAT temperature and glucose tolerance were unchanged. In contrast to the elevated plasma corticosterone seen in LZR, leptin reduced the level of this hormone (27%) in OZR. In OZR and LZR treated with leptin, the plasma leptin levels were increased 24-fold and 47-fold, respectively. The results suggest that leptin retains some efficacy in OZR, although these rats are less responsive than LZR.     

Increased A‐ring Reduction of Glucocorticoids in Obese Zucker Rats: Effects of Insulin Sensitization

Objective: Obesity is associated with altered glucocorticoid metabolism, which may impact on hypothalamic‐pituitary‐adrenal axis activity. Here we characterize hepatic 5α‐ and 5β‐reductase in obese rats and their responses to insulin sensitization. Research Methods and Procedures: Hepatic A‐ring reductase protein and mRNA were assessed in lean and obese Zucker rats after insulin sensitization with metformin or rosiglitazone (n = 7 to 8/group). Results: Hepatic 5α‐reductase 1 and 5β‐reductase mRNA and protein (p < 0.01) were increased in obese rats. Insulin sensitization ameliorated increased 5α‐reductase 1 mRNA in obese rats (p < 0.01) and partially reversed increased 5β‐reductase activity. Discussion: Hepatic clearance of glucocorticoids by 5α‐ and 5β‐reductase is increased in obese Zucker rats, and this increase in clearance is attenuated by insulin sensitization. This increased hepatic clearance may underpin compensatory activation of the hypothalamic‐pituitary‐adrenal axis in obesity.     

Effects of Irbesartan on the Growth and Differentiation of Adipocytes in Obese Zucker Rats

Objective: The aim of this study was to evaluate the effects of the selective angiotensin receptor 1 antagonist irbesartan on the growth and differentiation of the adipocytes in obese Zucker fa/fa rats. Research Methods and Procedures: Obese Zucker fa/fa rats were treated by oral route for 3 weeks with irbesartan at doses of 3–10‐30 mg/kg per day. The adipocyte differentiation was evaluated by analyzing tissue samples of white (retroperitoneal) or brown (interscapular) adipose tissue for the presence of peroxisome proliferator activated receptor γ, leptin, and the activity of glycerol‐3‐phosphate dehydrogenase. Results: This study showed that the treatment of obese Zucker fa/fa with irbesartan effectively reduced the differentiation of adipocytes within brown (interscapular) and white (retroperitoneal) adipose tissue. In fact, irbesartan significantly (p < 0.01) and dose‐dependently reduced the tissue levels of leptin, peroxisome proliferator activated receptor γ, and the activity of the enzyme glycerol‐3‐phoshate dehydrogenase accepted markers of adipocyte differentiation. None of the tested doses of irbesartan affected these markers in non‐obese rats. Discussion: The antagonism of the angiotensin receptor 1 receptors with irbesartan reduces the adipogenic activity of angiotensin II in obese Zucker rats, with the endpoint being reduction of the growth and differentiation of the adipocytes within the adipose tissue.     

Differential Short-Term Distribution of Estrone and Oleoyl-Estrone Administered in Liposomes to Lean and Obese Zucker Rats

Thirteen-week-old female Zucker lean (Fa/Fa) and obese (fa/fa) rats were injected through a cannula inserted in the left jugular vein with 1 mL/kg of ³H-labeled oleoyl-estrone in liposomes (Merlin-2) (i.e., 670 fmol, 84 kBq). The rats were killed 10 minutes later and dissected. The presence of intact or hydrolyzed oleoyl-estrone was later determined in all samples. The pattern of distribution of estrone was quite different from that of oleoyl-estrone both in rats that were lean and in those that were obese. Estrone was better retained by white adipose tissue than oleoyl-estrone. Liver, spleen, and lungs accumulated more oleoyl-estrone and split part of it, from 4.7% (lung, obese) to 27% (liver, lean). The overall high retention of estrone by the rat tissues results in its very low circulating levels. The fast splitting of liposome-carried oleoyl-estrone by most tissues (up to more than 67% by intestine and skin of lean rats) may help explain the rise in blood free estrone. The differences between lean and obese Zucker rats are mainly quantitative in the case of estrone, the main differences being found in blood and adipose tissues. However, when we compare the data for oleoyl-estrone, the differences cannot be dismissed simply as due to differences in body size or the extent of fat deposits. A large portion of the label remained in the blood of the rats that were obese but not in those that were lean, the tissues of which took up more label. Brown adipose tissue shows a fair affinity for oleoyl-estrone in the rats that were lean but practically does not retain label in the rats that were obese, suggesting that oleoyl-estrone may have a direct effect on brown adipose tissue. The decreased uptake of oleoyl-estrone in rats that were obese shows that the mechanism regulating the turnover or disposal of this signal is altered in this type of genetic obesity.     

Modulation of adenosine A1 and A2A receptors in C6 glioma cells during hypoxia: involvement of endogenous adenosine

During hypoxia, extracellular adenosine levels are increased to prevent cell damage, playing a neuroprotective role mainly through adenosine A₁ receptors. The aim of the present study was to analyze the effect of hypoxia in both adenosine A₁ and A_2A receptors endogenously expressed in C6 glioma cells. Two hours of hypoxia (5% O₂) caused a significant decrease in adenosine A₁ receptors. The same effect was observed at 6 h and 24 h of hypoxia. However, adenosine A_2A receptors were significantly increased at the same times. These effects were not due to hypoxia-induced alterations in cells number or viability. Changes in receptor density were not associated with variations in the rate of gene expression. Furthermore, hypoxia did not alter HIF-1α expression in C6 cells. However, HIF-3α, CREB and CREM were decreased. Adenosine A₁ and A_2A receptor density in normoxic C6 cells treated with adenosine for 2, 6 and 24 h was similar to that observed in cells after oxygen deprivation. When C6 cells were subjected to hypoxia in the presence of adenosine deaminase, the density of receptors was not significantly modulated. Moreover, DPCPX, an A₁ receptor antagonist, blocked the effects of hypoxia on these receptors, while ZM241385, an A_2A receptor antagonist, was unable to prevent these changes. These results suggest that moderate hypoxia modulates adenosine receptors and cAMP response elements in glial cells, through a mechanism in which endogenous adenosine and tonic A₁ receptor activation is involved.     

Modulation of cardiac A1-adenosine receptors in rats following treatment with agents affecting heart rate

Effects of chronic treatment affecting heart rate on A₁ adenosine receptor levels and their functions were studied. Treatment of rats with isoproterenol for 10 days accelerated heart rate and increased the level of adenosine receptors, in both the atria and ventricles. Negative dromotropic response of isolated heart to adenosine was enhanced in isoproterenol-treated rats. Similar results were obtained following treatment with atropine sulfate, or swimming training but not after treatment with thyroxine. On the other hand, treatment with amiodarone, which normally causes a decrease in heart rate, also increased the level of adenosine receptors in both atria and ventricles. The sensitivity of the isolated heart to the negative dromotropic and chronotropic effects of adenosine was not enhanced in the amiodarone treated rats. Similar results were obtained following treatment with propranolol, while treatment with PTU (6-n-propyl-2-thiouracil) increased adenosine sensitivity in the isolated heart. It was concluded that the levels of A₁ adenosine receptors in the heart correspond to heart rate, and to cardiac efficiency. While an increase in heart rate was followed by up-regulation of A₁ adenosine receptors, a decrease in heart rate caused a moderate elevation of these receptors.     

Gender‐dependent regulation of G‐protein‐gated inwardly rectifying potassium current in dorsal raphe neurons in knock‐out mice devoid of the 5‐hydroxytryptamine transporter

Agonists at G‐protein‐coupled receptors in neurons of the dorsal raphe nucleus (DRN) of knock‐out mice devoid of the serotonin transporter (5‐HTT^?/?) exhibit lower efficacy to inhibit cellular discharge than in wild‐type counterparts. Using patch‐clamp whole‐cell recordings, we found that a G‐protein‐gated inwardly rectifying potassium (GIRK) current is involved in the inhibition of spike discharge induced by 5‐HT_1A agonists (5‐carboxamidotryptamine (5‐CT) and (±)‐2‐dipropylamino‐8‐hydroxy‐1,2,3,4‐tetrahydronaphthalene hydrobromide (8‐OH‐DPAT); 50 nM–30 μM) in both wild‐type and 5‐HTT^?/? female and male mice. These effects were mimicked by 5′‐guanylyl‐imido‐diphosphate (Gpp(NH)p; 400 μM) dialysis into cells with differences between genders. The 5‐HTT^?/? knock‐out mutation reduced the current density induced by Gpp(NH)p in females but not in males. These data suggest that the decreased response of 5‐HT_1A receptors to agonists in 5‐HTT^?/? mutants reflects notably alteration in the coupling between G‐proteins and GIRK channels in females but not in males. Accordingly, gender differences in central 5‐HT neurotransmission appear to depend—at least in part—on sex‐related variations in corresponding receptor‐G protein signaling mechanisms. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

细菌应激反应中(p)ppGpp代谢的调控

(p)ppGpp是介导细菌细胞对环境胁迫产生应激反应的重要胞内信号,通过控制一系列重要的细胞活动使细菌得以生存。通过对蓝细菌中(p)ppGpp代谢的研究,对(p)ppGpp作用机制、控制(p)ppGpp代谢的酶系统、环境胁迫信号传递、细胞中(p)ppGpp水平的调控及其多样性进行了总结。     

The Insulin Tolerance Test in Morbidly Obese Patients Undergoing Bariatric Surgery

Objective: To assess the effect of massive weight loss in relation to insulin resistance and its correlation to changes in glycemic homeostasis and lipid profile in severely obese patients. Research Methods and Procedures: A prospective clinical intervention study was carried out with 31 morbidly obese women (body mass index: 54.2 ± 8.8 kg/m²) divided into three groups according to their glucose tolerance test: 14 normal, 8 impaired glucose tolerance, and 9 type 2 diabetes. All subjects underwent an insulin tolerance test with intravenous bolus of 0.1 U insulin/kg body weight before silastic ring vertical gastroplasty Roux‐en‐Y gastric bypass surgery, and again at 2, 4, 6, and 12 months postoperatively. Fasting plasma glucose, hemoglobin A1c, and lipid profile were also evaluated. Results: A reduction of 68 ± 15% in initial excess body weight was evident within 1 year. Along with weight loss, the following statistically significant changes were found: an increase in the insulin‐sensitivity index (Kitt) and a decrease in fasting plasma glucose and hemoglobin A1c, most notably in the type 2 diabetes group. An overall improvement in lipid profile was observed in all three groups. Discussion: Bariatric surgery was an effective therapeutic approach for these obese patients because it reduced both weight and insulin resistance, along with improving metabolic parameters. Significant correlations were found between insulin resistance and metabolic improvements. Weight loss after bariatric surgery induced an improvement in metabolic fitness, related to the reduction in insulin resistance over a range of glucose tolerance statuses from normal to diabetic.     

Temporal and mechanistic dissociation of ATP and adenosine release during ischaemia in the mammalian hippocampus

Adenosine is well known to be released during cerebral metabolic stress and is believed to be neuroprotective. ATP release under similar circumstances has been much less studied. We have now used biosensors to measure and compare in real time the release of ATP and adenosine during in vitro ischaemia in hippocampal slices. ATP release only occurred following the anoxic depolarisation, whereas adenosine release was apparent almost immediately after the onset of ischaemia. ATP release required extracellular Ca2+. By contrast adenosine release was enhanced by removal of extracellular Ca2+, whilst TTX had no effect on either ATP release or adenosine release. Blockade of ionotropic glutamate receptors substantially enhanced ATP release, but had only a modest effect on adenosine release. Carbenoxolone, an inhibitor of gap junction hemichannels, also greatly enhanced ischaemic ATP release, but had little effect on adenosine release. The ecto-ATPase inhibitor ARL 67156, whilst modestly enhancing the ATP signal detected during ischaemia, had no effect on adenosine release. Adenosine release during ischaemia was reduced by pretreatment with homosysteine thiolactone suggesting an intracellular origin. Adenosine transport inhibitors did not inhibit adenosine release, but instead they caused a twofold increase of release. Our data suggest that ATP and adenosine release during ischaemia are for the most part independent processes with distinct underlying mechanisms. These two purines will consequently confer temporally distinct influences on neuronal and glial function in the ischaemic brain.     

Miglitol (BAY m 1099) Treatment of Diabetic Hypothalamic-Dietary Obese Rats Improves Islet Response to Glucose

AXEN, KATHLEEN V., XUE LI, AND ANTHONY SCLAFANI. Miglitol (BAY m 1099) treatment of diabetic hypothalamic-dietary obese rats improves islet response to glucose. Obes Res. 1999;7:83–89. Objective : The well-absorbed α-glucosidase inhibitor, miglitol (BAY m 1099), was included in the diets of hypothalamic-dietary obese diabetic rats to investigate its ability to improve glycemia and thereby reverse glucotoxic effects on islet secretory response. Research Methods and Procedures : Female rats received bilateral electrolytic lesions of the ventromedial hypothalamus and were fed high-fat, sucrosesupplemented diets until hyperinsulinemia and hyperglycemia were observed after 3 hours of food deprivation (nonfed). Diabetic animals were assigned to miglitol-treated (40 mg/17 g of diet) or untreated groups for 3 weeks; pancreatic islets were isolated for incubation experiments. Results : No differences in food intake, body weights, or nonfed plasma glucose or insulin levels were seen between treated and untreated diabetic rats. Islets isolated from untreated diabetic rats showed elevated basal insulin release and no insulin secretory response to an elevation in glucose concentration. In contrast, islets obtained from miglitol-treated rats showed more normal basal release and a significant insulin secretory response to glucose. Incubation of islets, obtained from normal control rats or untreated diabetic rats, in media containing miglitol at levels estimated to exist in plasma of treated rats had no effect on islet insulin secretory responses to glucose. Discussion : Islet secretory response was improved despite continued hyperglycemia and severe insulin resistance. Miglitol treatment may improve islet sensitivity to glucose either through effects on islet metabolism requiring prolonged exposure or by improvement in postmeal glycemia, despite persistent hyperglycemia.     

Rice PCR1 influences grain weight and Zn accumulation in grains

Proteins containing a placenta‐specific 8 domain (PLAC8) function as major organ size regulators in Solanum lycopersicum and Zea may, and putative metal ion transporters in Arabidopsis thaliana, Oryza sativa and Brassica juncea. However, it is unknown how PLAC8 domain‐containing proteins fulfill such diverse roles. Here, we found that plant cadmium resistance 1 (PCR1) influences both zinc (Zn) accumulation and grain weight in rice. OsPCR1 knockout and knockdown lines produced lighter grains than the wild type, while OsPCR1 overexpression lines produced heavier grains. Furthermore, the grains of OsPCR1 knockdown lines exhibited substantially higher Zn and lower cadmium (Cd) concentrations than the control, as did yeast heterologously expressing OsPCR1. Through sequence analysis, we showed that the amino acid sequence of japonica‐type PCR1 was distinct from that of indica‐type and wild rice accessions. This difference was correlated with distinct Zn‐related phenotypes. Japonica‐type PCR1 had a shorter N‐terminus than did PCR1 in the other rice types, and yeast heterologously expressing japonica‐type PCR1 was more sensitive to Zn than was yeast expressing indica‐type PCR1. Furthermore, japonica‐type grains accumulated less Zn than did indica‐type grains. Our study suggests that rice PCR1 maintains metal ion homeostasis and grain weight and might have been selected for during domestication.     

Effect of Gastric Banding on Aminoterminal Pro‐brain Natriuretic Peptide in the Morbidly Obese

Objective: Aminoterminal pro‐brain natriuretic peptide (NT‐proBNP), like brain natriuretic peptide, might have diagnostic utility in detecting left ventricular hypertrophy and/or left ventricular dysfunction. The aim of the study was to investigate the relationship between morbid obesity and NT‐proBNP and the effect of weight reduction on this parameter. Research Methods and Procedures: A total of 34 morbidly obese patients underwent laparoscopic adjustable gastric banding (LAGB). NT‐proBNP levels were measured before and 12 months after the surgery. Results: Metabolic features and systolic and diastolic blood pressure were significantly decreased (p < 0.00001 for both) after a cumulative weight loss of 19.55 kg 1 year after LAGB. NT‐proBNP concentration was significantly higher in morbidly obese patients before LAGB than in normal‐weight control subjects (341.15 ± 127.78 fmol/mL vs. 161.68 ± 75.78 fmol/mL; p < 0.00001). After bariatric surgery, NT‐proBNP concentration decreased significantly from 341.15 ± 127.78 fmol/mL to 204.87 ± 59.84 fmol/mL (p < 0.00, 001) and remained statistically significantly elevated (204.88 ± 59.84 fmol/mL vs. 161.68 ± 75.78 fmol/mL; p = 0.04) compared with normal‐weight subjects. Discussion: This investigation demonstrates higher levels of NT‐proBNP in morbidly obese subjects and a significant decrease during weight loss after laparoscopic adjustable gastric banding. In obesity, NT‐proBNP might be useful as a routine screening method for identifying left ventricular hypertrophy and/or left ventricular dysfunction.     

Topoisomerase-II-inhibitory principles from the stems of Spatholobus suberectus

Bioassay-guided fractionation of the stems of Spatholobus suberectus led to the isolation of procyanidin B4 (= (+)-catechin-(4-->8)-(-)-epicatechin) (1) and (+)-catechin-(4-->8)-(+)-catechin-(4-->8)-(-)-epicatechin (2). These compounds, isolated before from other sources, were found to be highly potent inhibitors of DNA-topoisomerase-II (Topo-II)-mediated KDNA decatenation, with IC50 values of 22.5+/-2.3 and 21.9+/-2.2 nM, resp.     

Modulation of photosynthesis and respiration in guard and mesophyll cell protoplasts by oxygen concentration

Stomatal movement is an energetic oxygen-requiring process. In the present study, the effect of oxygen concentration on mitochondrial respiratory activity and red-light-dependent photosynthetic oxygen evolution by Vicia faba and Brassica napus guard cell protoplasts was examined. Comparative measurements were made with mesophyll cell protoplasts isolated from the same species. At air saturated levels of dissolved oxygen in the protoplast suspension media, respiration rates by mesophyll protoplasts ranged from 6 to 10μmoles O₂ mg^?1 chl h^?1, while guard cell protoplasts respired at rates of 200–300 μmoles O₂ mg chl^?1 h^?1, depending on the species. Lowering the oxygen concentration below 50–60 mmol m^?3 resulted in a decrease in guard cell respiration rates, while rates by mesophyll cell protoplasts were reduced only at much lower concentrations of dissolved oxygen. Rates of photosynthesis in mesophyll cell protoplasts isolated from both species showed only a minor reduction in activity at low oxygen concentrations. In contrast, photosynthesis by guard cell protoplasts isolated from V. faba and B. napus decreased concomitantly with respiration. Oligomycin, an inhibitor of oxidative phos-phorylation, reduced photosynthesis in mesophyll cell protoplasts by 27–46% and in guard cell protoplasts by 51–58%. The reduction in both guard cell photosynthesis and respiration following exposure to low oxygen concentrations suggest close metabolic coupling between the two activities, possibly mediated by the availability of substrate for respiration associated with photosynthetic electron transport activity and subsequent export of redox equivalents.