CN Rats Research Articles

Nannochloropsis oceanica as a Microalgal Food Intervention in Diet-Induced Metabolic Syndrome in Rats.

The microalgal genus Nannochloropsis has broad applicability to produce biofuels, animal feed supplements and other value-added products including proteins, carotenoids and lipids. This study investigated a potential role of N. oceanica in the reversal of metabolic syndrome. Male Wistar rats (n = 48) were divided into four groups in a 16-week protocol. Two groups were fed either corn starch or high-carbohydrate, high-fat diets (C and H, respectively) for the full 16 weeks. The other two groups received C and H diets for eight weeks and then received 5% freeze-dried N. oceanica in these diets for the final eight weeks (CN and HN, respectively) of the protocol. The H diet was high in fructose and sucrose, together with increased saturated and trans fats. H rats developed obesity, hypertension, dyslipidaemia, fatty liver disease and left ventricular fibrosis. N. oceanica increased lean mass in CN and HN rats, possibly due to the increased protein intake, and decreased fat mass in HN rats. Intervention with N. oceanica did not change cardiovascular, liver and metabolic parameters or gut structure. The relative abundance of Oxyphotobacteria in the gut microbiota was increased. N. oceanica may be an effective functional food against metabolic syndrome as a sustainable protein source.

Perturbed Vitamin A Status Induced by Iron Deficiency Is Corrected by Iron Repletion in Rats with Pre-Existing Iron Deficiency

Although iron deficiency is known to interrupt vitamin A (VA) metabolism, the ability of iron repletion to restore VA metabolism and kinetics in iron-deficient rats is not well understood. In the present study, we examined the effects of dietary iron repletion on VA status in rats with pre-existing iron deficiency. Weanling Sprague-Dawley rats were fed a VA-marginal diet (0.35mg retinol/kg diet) containing either a normal concentration of iron [35ppm, control group (CN)] or reduced iron (3ppm, iron-deficient group, ID-); after 5 wk, 4 rats/group were killed for baseline measurements. A 3H-labeled retinol emulsion was administered intravenously to the remaining rats (n=6, CN; n=10, ID-) as tracer to initiate the kinetic study. On day 21 after dosing, n=5 ID- rats were switched to the CN diet, generating an iron-repletion group (ID+). Blood samples were collected at 34 time points ≤92 d after dose administration, when all rats were killed and iron and VA status were determined. At baseline, ID- rats had developed iron deficiency, with a reduced plasma VA concentration (0.67compared with 1.20μmol/L in ID- and CN rats, respectively; P <0.01) and a tendency toward higher liver VA (265compared with 187nmol in ID- and CN rats, respectively; P=0.10). On day 92, iron deficiency persisted in ID- rats, accompanied by 2-times higher liver VA (456nmol compared with 190nmol in ID- and CN rats, respectively; P <0.001) but lower plasma VA (0.64compared with 0.94μmol/L in ID- and CN rats, respectively; P=0.05). ID+ rats not only recovered from iron deficiency, but also exhibited less liver VA sequestration (276nmol) and normal plasma VA (0.91μmol/L, not different from CN rats). Our results suggest that iron repletion can remove the inhibitory effect of iron deficiency on hepatic mobilization of VA and restore plasma retinol concentrations in iron-deficient rats, setting the stage for kinetic studies of VA turnover in this setting.

Dietary Iron Repletion Stimulates Hepatic Mobilization of Vitamin A in Previously Iron-Deficient Rats as Determined by Model-Based Compartmental Analysis

Iron deficiency can result in hyporetinolemia and hepatic vitamin A (VA) sequestration. We used model-based compartmental analysis to determine the impact of iron repletion on VA metabolism and kinetics in iron-deficient rats. At weaning, Sprague-Dawley rats were assigned to either a VA-marginal diet (0.35mg retinol equivalent/kg) with adequate iron (35ppm, control group [CN]) or reduced iron (3ppm, iron-deficient group [ID-]), with an equivalent average body weight for each group. After 5 wk, n=4 rats from each group were euthanized for baseline measurements of VA and iron indices, and the remaining rats (n=6 CN, n=10 ID-) received an intravenous injection of 3H-labeled retinol in an emulsion as tracer to initiate the kinetic study. On day 21 after dosing, half of the ID- rats were switched to the CN diet to initiate iron repletion, referred to as the iron-repletion group (ID+). From the time of dosing, 34 serial blood samples were collected from each rat over a 92-d time course. Plasma tracer and tissue tracee data were fitted to 6- and 4-compartment models, respectively, to analyze the kinetic behavior of VA in all groups. Our mathematical model indicated that ID- rats exhibited a nearly 6-fold decrease in liver VA secretion and >4-fold reduction in whole-body VA utilization, compared with CN rats, whereas these perturbed kinetic behaviors were notably corrected in ID+rats, close to those from the CN group. Iron repletion can remove the inhibitory effect that iron deficiency exerts on hepatic mobilization of VA and restore retinol kinetic parameters to values similar to that of never-deficient CN rats. Together with improvements in iron and VA indices, our results suggest that restoration of an iron-adequate diet is sufficient to improve VA kinetics after a previous state of iron deficiency.

Pregnancy and Lactation Alter Vitamin A Metabolism and Kinetics in Rats under Vitamin A-Adequate Dietary Conditions

Abstract Objectives We investigated the impact of pregnancy and lactation on vitamin A (VA) metabolism and kinetics in rats, hypothesizing that this changed physiological status would perturb whole-body VA kinetics. Such information may be informative for future dietary recommendations. Methods Ten female rats (7 wk of age) and 6 male rats (9 wk of age) were fed an AIN-93 G diet upon arrival. After 1 week of acclimation, female rats received an oral dose of 3H-labeled retinol as the tracer to initiate the kinetic study. On d 21 after dosing (when 3H-retinol was expected to reach a log-linear terminal slope), 6 female rats were mated and checked daily for a vaginal plug to determine the date of pregnancy. On the day of delivery, litter size was adjusted to 10 pups/dam. Serial blood samples were collected from each female rat at 27–28 time points after dose administration until dams and pups were euthanized on d 14 of lactation. Hematocrit was measured, plasma tracer level was determined, and plasma fraction of dose vs. time was plotted. Model-based compartmental analysis will be applied to the plasma tracer data to develop VA kinetic models. Results All mated female rats became pregnant (pregnant group, PG, n = 6). Non-mated female rats were studied as non-pregnant controls (CN, n = 4). No difference was observed in hematocrit between PG and CN rats, suggesting no significant change in plasma volume expansion. Before breeding, plasma tracer response profiles were similar to CN rats. However, a consistent decline in plasma tracer levels was observed in PG rats during the middle of pregnancy, followed by a rise in late pregnancy, whereas such a change did not occur in CN rats. Moreover, during lactation, PG rats exhibited a steeper terminal slope compared to CN rats, indicating a more rapid utilization of VA in these lactating rats. Conclusions Pregnancy and lactation resulted in altered VA metabolism and kinetics in rats. Further analysis using mathematical modeling will explore the changes in kinetic parameters that underlie the perturbations we have observed in VA kinetics. Funding Sources National Institutes of Health.

Salivary Immunoglobulin A Secretion and Polymeric Ig Receptor Expression in the Submandibular Glands Are Enhanced in Heat-Acclimated Rats.

Salivary immunoglobulin A (IgA) plays a critical role in mucosal immunity. Chronic exposure to moderate heat induces heat acclimation, which modifies salivary functions. However, the changes in salivary IgA secretion in heat-acclimated rats are unclear. In this study, we investigated salivary IgA secretion and the expression of polymeric Ig receptor (pIgR), a key mediator of mucosal IgA secretion, in the submandibular glands (SMGs) of heat-acclimated rats. Following maintenance at an ambient temperature (Ta) of 24 ± 0.1 °C for 10 days, male Wistar rats were subjected to Ta of 32 ± 0.2 °C for 5 days (HE group) for heat acclimation or maintained at Ta of 24 ± 0.1°C (CN group). The rats were then anesthetized, pilocarpine (0.5 mg/kg) was intraperitoneally injected, and saliva was collected. Afterward, the SMGs and plasma were sampled. The salivary IgA concentration and IgA flow rate were significantly higher in the HE group than in the CN group. Similarly, SMG pIgR expression was significantly higher in HE rats. The levels of plasma cytokines, including interleukin (IL)-5, IL-6, and interferon-γ, were significantly greater in HE rats than in CN rats. Heat acclimation may enhance oral immunity through salivary IgA secretion and pIgR upregulation in the SMGs.

Perturbed Whole-body Vitamin a Kinetics Induced by Iron Deficiency Is Corrected by Dietary Iron Repletion in Rats (OR05-03-19)

ObjectivesWe investigated the impact of iron repletion on vitamin A (VA) metabolism and kinetics in iron-deficient rats, hypothesizing that iron repletion can remove the inhibitory effect of iron deficiency on hepatic mobilization of VA and improve the hyporetinolemia of iron deficiency. MethodsAt weaning, rats were divided into two groups and fed either a VA-marginal diet (control group, CN) with normal levels of iron (37 ppm) or the same diet with reduced iron (5 ppm, iron deficient group, ID-). After 5 weeks, n = 4 rats from each group were euthanized for baseline measurements, and the remaining rats (n = 6 CN, n = 10 ID-) received an i.v. dose of 3H-labeled retinol in an emulsion as tracer to initiate the kinetic study. On day 21 after dosing, half of the ID- rats were switched to the CN diet, thus creating an iron repletion group (ID+). Serial blood samples were collected from each rat at 34 preselected time points after dosing. On day 92, all rats were euthanized. Iron and VA status were determined, and model-based compartmental analysis was applied to the plasma tracer data to develop VA kinetic models for rats from all groups. ResultsRats fed the iron-deficient diet developed iron deficiency, and exhibited reduced plasma retinol (0.67 vs. 1.19 μmol/L), with higher liver VA (265 vs. 187 nmol) at the start of the kinetic study, suggesting impaired hepatic VA mobilization. At the study conclusion, ID+ rats had recovered from iron deficiency, as indicated by hematological indices including hemoglobin, hematocrit, and serum iron. While liver VA storage was more than doubled in ID- rats (456 nmol) vs. CN rats (190 nmol), hyporetinolemia was maintained in ID- rats. In contrast, VA in the liver of ID+ rats was mobilized, reflected by the reduced liver VA mass (276 nmol) and increased hepatic output of VA into plasma based on predictions of the compartmental model, and plasma retinol in ID + rats returned to normal. ConclusionsIron repletion restored plasma retinol concentrations and increased liver vitamin A mobilization in iron deficient rats. Funding SourcesNational Institutes of Health.

Theobromine Improves Working Memory by Activating the CaMKII/CREB/BDNF Pathway in Rats.

Theobromine (TB) is a primary methylxanthine found in cacao beans. cAMP-response element-binding protein (CREB) is a transcription factor, which is involved in different brain processes that bring about cellular changes in response to discrete sets of instructions, including the induction of brain-derived neurotropic factor (BDNF). Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been strongly implicated in the memory formation of different species as a key regulator of gene expression. Here we investigated whether TB acts on the CaMKII/CREB/BDNF pathway in a way that might improve the cognitive and learning function in rats. Male Wistar rats (5 weeks old) were divided into two groups. For 73 days, the control rats (CN rats) were fed a normal diet, while the TB-fed rats (TB rats) received the same food, but with a 0.05% TB supplement. To assess the effects of TB on cognitive and learning ability in rats: The radial arm maze task, novel object recognition test, and Y-maze test were used. Then, the brain was removed and the medial prefrontal cortex (mPFC) was isolated for Western Blot, real-time PCR and enzyme-linked immunosorbent assay. Phosphorylated CaMKII (p-CaMKII), phosphorylated CREB (p-CREB), and BDNF level in the mPFC were measured. In all the behavior tests, working memory seemed to be improved by TB ingestion. In addition, p-CaMKII and p-CREB levels were significantly elevated in the mPFC of TB rats in comparison to those of CN rats. We also found that cortical BDNF protein and mRNA levels in TB rats were significantly greater than those in CN rats. These results suggest that orally supplemented TB upregulates the CaMKII/CREB/BDNF pathway in the mPFC, which may then improve working memory in rats.

Chronic administration of theobromine inhibits mTOR signal in rats.

Theobromine is a caffeine derivative and the primary methylxanthine in Theobroma cacao. We have shown previously that theobromine inhibits the Akt-mammalian target of rapamycin (mTOR) signal in vitro. In this study, we investigated whether orally administered theobromine could inhibit mTOR activity in rats. mTOR is phosphorylated by Akt. Thus, the level of phosphorylated mTOR was used as an index of mTOR activity. Male Wistar rats were divided into two groups. The control group (CN) was fed a normal diet, while the theobromine group (TB) was fed a diet supplemented with 0.05% theobromine for 40days. We measured body-weights and tissue weights, food and water intake, blood count, concentrations of theobromine in the plasma, liver and brain, and the levels of phosphorylated mTOR in the liver and brain. Orally administered theobromine did not affect the body-weights and tissue weights, food and water intake, and blood count as determined by comparison with levels in rats that were fed standard chow. Theobromine was detected in the plasma, liver and brain obtained from TB rats, but was not detected in tissues obtained from CN rats. The phosphorylated mTOR levels in the liver and brain were significantly lower in TB rats than in CN rats. The results suggest that oral theobromine inhibits mTOR signalling in vivo.

Stress exposure alters brain mRNA expression of the genes involved in insulin signalling, an effect modified by a high fat/high fructose diet and cinnamon supplement.

In occidental societies, high fat and high sugar diets often coincide with episodes of stress. The association is likely to modify brain energy control. Brain insulin signalling is rarely studied in stressed individuals consuming high fat diets. Furthermore the effects of cinnamon supplement are not known in these conditions. Therefore, we exposed rats, over a 12-week period, to a control (C) or a high fat/high fructose (HF/HFr) diet that induces peripheral insulin resistance. A cinnamon supplement (C+CN and HF/HFr +CN) was added or not. After diet exposure, one group of rats was exposed to a 30-min restraint followed by a 10-min open-field test, their combination featuring a moderate stressor, the other rats staying unstressed in their home cages. The insulin signalling in hippocampus and frontal cortex was studied through the mRNA expression of the following genes: insulin receptor (Ir), insulin receptor substrate (Irs1), glucose transporters (Glut1 and Glut3), glycogen synthase (Gys1) and their modulators, Akt1 and Pten. In C rats, stress enhanced the expression of Ir, Irs1, Glut1, Gys1 and Akt1 mRNA. In C+CN rats, stress induced an increase in Pten but a decrease in Gys1 mRNA expression. In HF/HFr rats, stress was associated with an increase in Pten mRNA expression. In HF/HFr+CN rats, stress increased Pten mRNA expression but also decreased Gys1 mRNA expression. This suggests that a single moderate stress favours energy refilling mechanisms, an effect blunted by a previous HF/HFr diet and cinnamon supplement.

Effects of Nori- and Wakame-enriched meats with or without supplementary cholesterol on arylesterase activity, lipaemia and lipoproteinaemia in growing Wistar rats

Some seaweeds exert antioxidant and hypocholesterolaemic properties. The effects of diets including restructured meats (RM) containing Wakame (W) or Nori (N) algae on arylesterase (AE) activity and lipoprotein concentration and composition were tested. In the present study, six groups of ten male growing Wistar rats each were fed a mix of 85% AIN-93M diet and 15% freeze-dried RM for 35d. The control group (C) consumed control RM, the W and N groups consumed RM with 5% W and 5% N, respectively. The cholesterol-enriched C (CC), W (CW) and N (CN) groups consumed their corresponding basal diets with supplementary cholesterol (2·43%) and cholic acid (0·49%). Cholesterol in the diet induced lower (P<0·001) growth ratios. Both W and N diets significantly increased AE activity. VLDL-cholesterol values were lower in N rats than in W rats. AE activity increased (P<0·001) in CC and CW rats but not in CN rats compared with their corresponding counterparts. AE was lower (P<0·05) in the CN group than in the CC and CW groups. The CN diet partially blocked (P<0·001) the hypercholesterolaemic induction observed in CC and CW diets and reduced TAG levels (at least P<0·05) with respect to those of CC rats. Although dietary cholesterol supplementation increased total cholesterol, VLDL-cholesterol and (intermediate-density lipoprotein+LDL)-cholesterol (all P<0·001) in all rats, the CN diet moderately improved the lipoprotein profile of hypercholesterolaemic rats. Changes in AE activity and plasma cholesterol in CN rats but not in CW rats suggest a possible relationship between the two parameters. It is concluded that inclusion of RM enriched with N may be used in hypercholesterolaemic diets to improve lipoprotein metabolism.

Brain stem heme oxygenase 1 (HO‐1) mRNA expression in inbred rat strains after severe hemorrhage

Previously Klemcke et al. showed 8‐fold difference in survival time among inbred rat strains after severe hemorrhage (Shock 29:748, 2008). For Brown Norway (BN/Mcwi) rats we also found a 2.7‐fold increase in cardiac HO‐1 mRNA expression in catheterized plus hemorrhaged rats (Bled) compared to unmanipulated controls (CN; FASEB J. 23:801.2, 2009). To further examine HO‐1 as a possible intermediary of cellular responses to hemorrhage, in the same study we measured HO‐1 mRNA expression in brain stem of DA, Fawn Hooded Hypertensive (FHH), and BN/Mcwi strains. Using real time PCR, the relative quantity (RQ) of HO‐1 mRNA was measured with multiple housekeeping genes (Genome Biology 8:R19, 2007). Across all treatments (CN, catheterized only, and Bled) RQs were greater (P&lt;0.05) in BN/Mcwi (0.47 ± 0.02; mean ± SEM) and FHH (0.48 ± 0.02) than in DA rats (0.41 ± 0.02). When considering all strains, HO‐1 mRNA RQ increased 12% (P&lt;.05) in Bled rats compared with CN. Within strains and treatments, BN/Mcwi CN rats had greater (P&lt;.05) RQs (0.46 ± 0.01) than did DA control rats (0.38 ± 0.03). The data imply that rat brain stem has minor strain‐dependent differences in HO‐1 mRNA expression, and that basal expression is modestly increased after the combined stressors of catheterization and hemorrhage.

Persistent neurochemical and behavioral abnormalities in adulthood despite early iron supplementation for perinatal iron deficiency anemia in rats

Background Iron deficiency anemia (IDA) has been associated with altered cognitive, motor, and social-emotional outcomes in human infants. We recently reported that rats with chronic perinatal IDA, had altered regional brain iron, monoamines, and sensorimotor skill emergence during early development. Objective To examine the long-term consequences of chronic perinatal IDA on behavior, brain iron and monoamine systems after dietary iron treatment in rats. Methods Sixty dams were randomly assigned to iron-sufficient (CN) or low-iron (EID) diets during gestation and lactation. Thereafter, all offspring were fed the iron-sufficient diet, assessed for hematology and behavior after weaning and into adulthood and for brain measures as adults (regional brain iron, monoamines, dopamine and serotonin transporters, and dopamine receptor). Behavioral assessments included sensorimotor function, general activity, response to novelty, spatial alternation, and spatial water maze performance. Results Hematology and growth were similar for EID and CN rats by postnatal day 35. In adulthood, EID thalamic iron content was lower. Monoamines, dopamine transporter, and dopamine receptor concentrations did not differ from CN. EID serotonin transporter concentration was reduced in striatum and related regions. EID rats had persisting sensorimotor deficits (delayed vibrissae-evoked forelimb placing, longer sticker removal time, and more imperfect grooming chains), were more hesitant in novel settings, and had poorer spatial water maze performance than CN. General activity and spatial alternation were similar for EID and CN. Conclusion Rats that had chronic perinatal IDA showed behavioral impairments that suggest persistent striatal dopamine and hippocampal dysfunction despite normalization of hematology, growth and most brain measures.

Iron deficiency affects acoustic startle response and latency, but not prepulse inhibition in young adult rats

Iron deficiency is associated with alterations in dopamine and serotonin transporters as well as changes in dopamine receptor (DR) density, monoamine concentrations, and in vivo extracellular contents of monoamines in terminal fields. Human infants with iron deficiency have both delayed maturation as well as lengthened central conduction times in auditory evoked potential studies. The current study utilizes the magnitude of the acoustic startle response (ASR), prepulse inhibition (PPI), and mean latency to maximum startle response ( T max), to examine the functional integrity of response to environmental cues. Male and female rats consumed iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. ID rats of both sexes had 20–60% reductions in ASR when compared to CN rats but there was no effect on PPI. T max was significantly longer by 10–20% in females, but not males. Dopamine transporter density was significantly lower in putamen, nucleus accumbens, and olfactory tubercle in males, but not female rats while the serotonin transporter was significantly different from control animal density in five of 14 brain regions. Norepinephrine transporter density was lower in the locus ceruleus of ID male rats but was unaffected in ID female rats. Regression modeling of ASR with brain monoamine transporters and receptors showed hematocrit, norepinephrine transporter (NET) in dentate gyrus, and D 1R in the nucleus accumbens account for nearly 49% of the variance in ASR. T max was not significantly associated with any of the independent variables. We conclude that iron deficiency affects the startle response, but not the inhibitory circuits involved in prepulse inhibition. Importantly, sex also strongly influenced these behavioral responses. Future studies, perhaps pharmacologic in nature, are necessary to ascertain whether iron deficiency modifies the contribution of monoaminergic systems to responses to environmental stimuli.

Dietary L-Carnitine Enhances the Lymphatic Absorption of Fat and α-Tocopherol in Ovariectomized Rats

This study was conducted to determine whether the feeding of dietary L-carnitine (CN) improves the intestinal absorption of fat and α-tocopherol (αTOH) in ovariectomized (OX) rats. OX adult rats were weight-matched and assigned to 2 groups fed a modified AIN-93G diet containing αTOH-stripped soybean oil without (−CN) or with (+CN) supplemental CN at 150 mg/kg diet. At 5 wk, each rat with a lymph cannula was infused intraduodenally at 3.0 mL/h with a lipid emulsion consisting of 565 μmol triolein labeled with 14C (14C-OA), 3.6 μmol αTOH, and 396 μmol sodium taurocholate in 24 mL PBS buffer. Lymph was collected hourly for 8 h and analyzed for lipids. The lymphatic absorption of αTOH for 8 h in +CN rats (899 ± 201 nmol) was higher (P < 0.05) than in −CN rats (587 ± 92 nmol). The absorption of 14C-OA in +CN rats (53.5 ± 4.0% dose/8 h) also was increased (P < 0.05) compared with −CN rats (47.6 ± 5.0% dose/8 h). Lymph flow did not differ between the groups. When bile was diverted but with infusion of sodium taurocholate, the lymphatic absorption of lipids did not differ. The present study provides evidence that dietary CN enhances the rates and amounts of lymphatic absorption of αTOH and fat in OX rats. Our findings suggest that dietary CN may influence the process of lipid packaging and absorption by the enterocyte in OX rats, and may explain in part the increased status of αTOH in CN-fed animals.

Role of gut flora on intestinal group II phospholipase A2 activity and intestinal injury in shock.

We previously showed that group II phospholipase A2 (PLA2-II), a secretory, bactericidal, and proinflammatory protein in intestinal crypts, is upregulated after lipopolysaccharide (LPS) and platelet-activating factor (PAF) challenge. Here we examined whether germ-free environment (GF) or antibiotic treatment (ABX) affects the pathophysiological responses and intestinal PLA2-II activity after PAF (1.5 microg/kg) or LPS (8 mg/kg) injection. We found that LPS and PAF induced hypotension and mild intestinal injury in conventionally fed (CN) rats; these changes were milder in ABX rats, whereas GF rats showed no intestinal injury. PLA2-II enzyme activity was detected in normal rat small intestine; the basal level was not diminished in ABX or GF rats. PAF and LPS caused an increase in PLA2-II activity, which was abrogated in GF and ABX rats. Recolonization of GF rats by enteral contamination restituted their PLA2-II response to PAF and LPS and susceptibility to bowel injury. We conclude that PAF- and LPS-induced increases in PLA2-II activity are dependent on gut bacteria, and ABX and GF rats are less susceptible to LPS-induced injury than CN rats.

Simulated microgravity enhances vasoconstrictor responsiveness of rat basilar artery.

Recently, hypertrophy and increased myogenic tone of brain vessels have been observed in rats after simulated microgravity. It is expected that simulated microgravity may also induce hyperreactivity of brain vessels. To test this hypothesis, Sprague-Dawley rats were subjected to a 4-wk tail-suspended hindlimb unloading (TS) to simulate the cardiovascular deconditioning effect of microgravity. After 4 wk, the vasoreactivity of isolated basilar arterial rings from TS rats to both receptor- and non-receptor-mediated vasoconstrictors, such as KCl, arginine vasopressin, or 5-hydroxytryptamine (5-HT), and vasodilators such as ACh, thrombin, adenosine, or sodium nitroprusside were examined and compared with those from simultaneous control (Cn) rats. In the first part of this study, it was found that the maximal isometric contractile responsiveness evoked by vasoconstrictors such as KCl, arginine vasopressin, or 5-HT was enhanced in basilar arterial rings from TS rats, whereas vasodilatory responsiveness to vasodilators showed no significant difference between TS and Cn rats. In the second part of this study, it was found that removal of the endothelium had no effects on the contractile responsiveness to 5-HT in basilar arterial rings from TS rats but enhanced markedly the responsiveness in basilar arterial rings from Cn rats to an extent comparable with that of TS rats. Application of tetraethylammonium also had no effects on the contractile response to 5-HT in basilar arterial rings from TS but significantly increased the responsiveness of basilar arterial rings from Cn rats with endothelium intact. These results showed that 4-wk simulated microgravity enhanced the vascular contractile responsiveness of basilar arterial rings to both receptor- and non-receptor-mediated vasoconstrictors, and the enhancement of 5-HT-induced contraction in TS rat basilar arteries was due to an impairment of endothelium-dependent mechanism. These results suggest that endothelium-derived hyperpolarizing factors are responsible for this endothelium-dependent attenuating modulatory mechanism in contractile responsiveness of rat basilar arteries to 5-HT.

Beta-cell mass dynamics in Zucker diabetic fatty rats. Rosiglitazone prevents the rise in net cell death.

The evolution of diabetes in the male leptin receptor-deficient (fa/fa) Zucker diabetic fatty (ZDF) rat is associated with disruption of normal islet architecture, beta-cell degranulation, and increased beta-cell death. It is unknown whether these changes precede or develop as a result of the increasing plasma glucose, or whether the increased beta-cell death can be prevented. Early intervention with thiazolidinediones prevents disruption of the islet architecture. To determine the specific effects of rosiglitazone (RSG) on beta-cell mass dynamics, male fa/fa (obese) and +/fa or +/+ (lean) rats age 6 weeks were fed either chow (control group [CN]) or chow mixed with rosiglitazone (RSG group) at a dosage of 10 micromol. kg(-1) body wt.day(-1). Rats were killed after 0, 2, 4, 6, or 10 weeks of treatment (at age 6, 8, 10, 12, or 16 weeks). Plasma glucose increased from 8.9 +/- 0.4 mmol/l at 0 weeks to 34.2 +/- 1.8 mmol/l (P = 0.0001) at 6 weeks of treatment in obese CN rats and fell from 8.0 +/- 0.3 to 6.3 +/- 0.4 mmol/l in obese RSG rats (P = 0.02). beta-cell mass fell by 51% from 2 to 6 weeks of treatment (ages 8-12 weeks) in obese CN rats (6.9 +/- 0.9 to 3.4 +/- 0.5 mg; P < 0.05), whereas beta-cell mass was unchanged in obese RSG rats. At 10 weeks of treatment (age 16 weeks), beta-cell mass in obese CN rats was only 56% of that of obese RSG rats (4.4 +/- 0.4 vs. 7.8 +/- 0.3 mg, respectively; P = 0.0001). The beta-cell replication rate fell from a baseline value of 0.95 +/- 0.12% in lean rats and 0.94 +/- 0.07% in obese rats (at 0 weeks) to approximately 0.3-0.5% in all groups by 6 weeks of treatment (age 12 weeks). After 10 weeks of treatment, beta-cell replication was higher in obese RSG rats than in CN rats (0.59 +/- 0.14 vs. 0.28 +/- 0.05%, respectively; P < 0.02). Application of our mass balance model of beta-cell turnover indicated that net beta-cell death was fivefold higher in obese CN rats as compared with RSG rats after 6 weeks of treatment (age 12 weeks). The increase in beta-cell death in obese CN rats during the 6-week observation period was well correlated with the increase in plasma glucose (r2 = 0.90, P < 0.0001). These results suggest that the development of hyperglycemia in ZDF rats is concomitant with increasing net beta-cell death. beta-cell proliferation compensates for the increased beta-cell loss at a time when plasma glucose is moderately elevated, but compensation ultimately fails and the plasma glucose levels increase beyond approximately 20 mmol/l. Treatment with rosiglitazone, previously shown to reduce insulin resistance, prevents the loss of beta-cell mass in obese ZDF rats by maintaining beta-cell proliferation and preventing increased net beta-cell death.

Chronic intrathecal cannulation enhances nociceptive responses in rats.

The influence of a chronically implanted spinal cannula on the nociceptive response induced by mechanical, chemical or thermal stimuli was evaluated. The hyperalgesia in response to mechanical stimulation induced by carrageenin or prostaglandin E2 (PGE2) was significantly increased in cannulated (Cn) rats, compared with naive (Nv) or sham-operated (Sh) rats. Only Cn animals presented an enhanced nociceptive response in the first phase of the formalin test when low doses were used (0.3 and 1%). The withdrawal latency to thermal stimulation of a paw inflamed by carrageenin was significantly reduced in Cn rats but not in Nv or Sh rats. In contrast to Nv and Sh rats, injection in Cn animals of a standard non-steroid anti-inflammatory drug, indomethacin, either intraperitoneally or into the spinal cord via an implanted cannula or by direct puncture of the intrathecal space significantly blocked the intensity of the hyperalgesia induced by PGE2. Cannulated animals treated with indomethacin also showed a significant inhibition of second phase formalin-induced paw flinches. Histopathological analysis of the spinal cord showed an increased frequency of mononuclear inflammatory cells in the Cn groups. Thus, the presence of a chronically implanted cannula seems to cause nociceptive spinal sensitization to mechanical, chemical and thermal stimulation, which can be blocked by indomethacin, thus suggesting that it may result from the spinal release of prostaglandins due to an ongoing mild inflammation.

Resistance Exercise Increases the Capacity of Heme Biosynthesis More Than Aerobic Exercise in Rats.

To evaluate the effects of voluntary resistance exercise and aerobic exercise on iron status in rats fed an iron-deficient diet (5mg Fe/kg, ID) or rats fed a control diet (35mg Fe/kg, CN), we trained female Wistar rats for 3 weeks to climb a wire-mesh tower (∅20cm×200cm, CLIMB) and to swim in a plastic pool (∅50cm×50cm, SWIM). These animals were compared with sedentary (SED) rats. After the experimental period, the blood hemoglobin concentration, hematocrit, plasma iron, and transferrin saturation were significantly lower (p<0.05) in the ID rats than in the CN rats; as was the content in the liver, spleen, heart, kidney, skeletal muscles, and carcass (p<0.05). The activity of δ-aminolevulinic acid dehydratase, the marker enzyme for heme biosynthesis, in bone marrow was significantly higher (p<0.05) in the CLIMB group than in the SWIM group. These results suggest that resistance exercise increases heme biosynthesis more than aerobic exercise but that neither exercise improved severe iron deficiencies.

Effect of exercise and tepary bean type diet on body composition and fat accretion in obese Zucker rats.

The effectiveness of a tepary bean high fat type diet, compared to a purified type high fat diet and exercise, on body composition in fatty Zucker rats was determined. Approximately 6-week-old female fa/fa Zucker rats were divided into four groups of 10 rats each: TE, fed the tepary bean type diet and exercised; TN, fed the tepary bean type diet and not exercised; CE, fed the purified type control diet and exercised; CN, fed the purified type control diet and not exercised. The exercise modality was treadmill running and the experiment lasted 13 weeks. Body weight, cumulative food intake, body composition, weights of adipose tissues and liver, heart and gastrocnemius muscle. At the end of the 13 week experiment, TE rats weighed 511 +/- 22 g and were significantly lighter than TN, 588 +/- 15 g; CE, 606 +/- 22 g; and CN, 660 +/- 27 g. All are means +/- s.e.m. The carcass of CN rats had 58, 20 and 13% more fat than TE, TN and CE rats, respectively; P < 0.01. Lean body mass was the same for all the groups of rats and ranged from means of 216-228 g. However, TE rats had significantly more fat free dry mass (FFDM) than CN rats; 68 +/- 4 vs 58 +/- 2 (means +/- s.e.m.) and tended to have more FFDM than TN and CE rats. Inguinal fat depots weighed 20-30% less in T than in C rats (diet comparisons) and also 20-30% less in E than in N rats (exercise comparisons). Perirenal/retroperitoneal fat depots weighed 25% less in TN than in CN rats and 38% less in TE than in CE rats. Exercise did not reduce perirenal/retroperitoneal fat depot weights. Parametrial fat depot weights were not influenced by diet or exercise. In diets which provided 37% of the energy from fat, the incorporation of tepary beans attenuated weight gain, and subcutaneous and visceral fat gain compared to a purified type diet. Exercised rats gained less weight and subcutaneous, but not visceral fat, than non-exercised rats.