Oestradiol and leptin have separate but additive anorexigenic effects and differentially target fat mass in rats.

We recently showed that male rats exhibit lower hypophagia and body weight loss compared to female rats following central leptin delivery, suggesting a role for oestradiol in leptin responsiveness. Accordingly, we delivered Ob (leptin) or GFP (control) gene into the brain of male rats that were simultaneously treated with oestradiol or vehicle. In a reciprocal approach, we compared oestradiol-deficient (OVX) with intact females (sham) that received leptin or control vector. Changes in food intake), body weight and body composition were examined. In males, oestradiol and leptin resulted in lower cumulative food intake (15%) and endpoint body weight (5%), although rats receiving dual treatment (oestradiol-leptin) ate 28% less and weighed 22% less than vehicle-control. Changes in food intake were unique to each treatment, with a rapid decrease in vehicle-leptin followed by gradual renormalisation. By contrast, hypophagia in oestradiol-control was of lower amplitude and sporadic. Leptin selectively targeted fat mass and endpoint abdominal fat mass was 65%-80% lower compared to their respective control groups. In females, both leptin groups had lower body weight (endpoint values 20% lower than control groups) with the highest extent in sham animals (endpoint value was 28% less in sham-leptin than in sham-control). OVX rats rapidly started regaining their lost body weight reminiscent of the pattern in males. Leptin rapidly and robustly reduced fat mass with endpoint values 30%-35% less than control treated animals. It appears that leptin and oestradiol decreased food intake and body weight via different mechanisms, with the pattern of oestradiol-leptin being reminiscent of that observed in females and the pattern of OVX-leptin reminiscent of that observed in males. Oestrogen status did not influence initial fat mass loss by leptin. It can be concluded that oestradiol modulates the long-term response to central leptin overexpression, although its actions on energy homeostasis are additive and independent of those of leptin.

ACE2 activator diminazene aceturate reduces adiposity but preserves lean mass in young and old rats.

The obesity epidemic is multi-generational and is particularly debilitating in the aging population, necessitating the use of pharmaceutical interventions. Recent evidence suggests that increasing the activity of the angiotensin converting enzyme-2 [ACE2]/angiotensin-(1-7)[Ang-(1-7)]/Mas receptor (MasR) axis in obese animal models leads to significant reductions in body weight. It was hypothesized that activation of ACE2 via diminazene aceturate (DIZE) will significantly reduce body weight of rats fed a high fat diet. Young and old (4 and 23 months, respectively) male Fisher 344 × Brown Norway rats were fed 60% high fat diet for one week, and subsequently given either 15 mg/kg/day DIZE s.c. or vehicle for three weeks. DIZE treatment resulted in a significant reduction of food intake and body weight in both young and old animals. However, that decrease was so dramatic in the older animals that they all nearly stopped eating. Interestingly, the TD-NMR assessments revealed that the weight-loss was primarily a result of decreased body fat percentage, with a relative preservation of lean mass. Tissue weights confirm the significant loss of white adipose tissue (WAT), with no change in muscle weights. Gene expression and serum ACE2 activity analyses implied that increased activation of the ACE2/Ang-(1-7)/MasR axis plays a role in reducing fat mass. Collectively, our results suggest that DIZE may be a useful tool in the study of obesity; however, caution is recommended when using this compound in older animals due to severe anorectic effects, although there is a mechanism by which muscle is preserved.

Limiting feeding to the active phase reduces blood pressure without the necessity of caloric reduction or fat mass loss.

Reducing body weight has been shown to lower blood pressure in obesity-related hypertension. However, success of those lifestyle interventions is limited due to poor long-term compliance. Emerging evidence indicates that feeding schedule plays a role on the regulation of blood pressure. With two studies, we examined the role of feeding schedule on energy homeostasis and blood pressure. In study 1, rats were fed a high-fat diet (HFD) ad libitum for 24 h (Control) or for 12 h during the dark phase (time-restricted feeding, TRF). In study 2, rats fed a HFD were administered a long-acting α-MSH analog at either light onset [melanotan II (MTII) light] or dark onset (MTII dark) or saline (Control). MTII light animals ate most of their calories during the active phase, similar to the TRF group. In study 1, Control and TRF rats consumed the same amount of food and gained the same amount of weight and fat mass. Interestingly, systolic and mean arterial pressure (MAP) was lower in the TRF group. In study 2, food intake was significantly lower in both MTII groups relative to Control. Although timing of injection affected light versus dark phase food consumption, neither body weight nor fat mass differed between MTII groups. Consistent with study 1, rats consuming their calories during the active phase displayed lower MAP. These data indicate that limiting feeding to the active phase reduces blood pressure without the necessity of reducing calories or fat mass, which could be relevant to obesity-related hypertension.

Overpressure blast injury-induced oxidative stress and neuroinflammation response in rat frontal cortex and cerebellum.

BACKGROUND & AIM: Overpressure blast-wave induced brain injury (OBI) and its long-term neurological outcome pose significant concerns for military personnel. Our aim is to investigate the mechanism of injury due to OBI. METHODS: Rats were divided into 3 groups: (1) Control, (2) OBI (exposed 30psi peak pressure, 2-2.5ms), (3) Repeated OBI (r-OBI) (three exposures over one-week period). Lung and brain (cortex and cerebellum) tissues were collected at 24h post injury. RESULTS: The neurological examination score was worse in OBI and r-OBI (4.2±0.6 and 3.7±0.5, respectively) versus controls (0.7±0.2). A significant positive correlation between lung and brain edema was found. Malondialdehyde (index for lipid peroxidation), significantly increased in OBI and r-OBI groups in cortex (p<0.05) and cerebellum (p<0.01-0.001). The glutathione (endogenous antioxidant) level decreased in cortex (p<0.01) and cerebellum (p<0.05) of r-OBI group when compared with the controls. Myeloperoxidase activity indicating neutrophil infiltration, was significantly (p<0.01-0.05) elevated in r-OBI. Additionally, tissue thromboplastin activity, a coagulation marker, was elevated, indicating a tendency to bleed. NGF and NF-κB proteins along with Iba-1 and GFAP immunoreactivity significantly augmented in the frontal cortex demonstrating microglial activation. Serum biomarkers of injury, NSE, TNF-alpha and leptin, were also elevated. CONCLUSION: OBI triggers both inflammation and oxidative injury in the brain. This data in conjunction with our previous observations suggests that OBI triggers a cascade of events beginning with impaired cerebral vascular function leading to ischemia and chronic neurological consequences.

iBAT sympathetic innervation is not required for body weight loss induced by central leptin delivery.

We evaluated the contribution of brown adipose tissue (BAT) sympathetic innervation on central leptin-mediated weight loss. In a short- and long-term study, F344BN rats were submitted to either a denervation of interscapular BAT (Denervated) or a sham operation (Sham). Animals from each group received the Ob (Leptin) or green fluorescent protein (GFP; Control) gene through a single injection of recombinant adeno-associated virus delivered centrally. Changes in body weight were recorded for 14 or 35 days, after which adipose tissues and skeletal muscles were weighed. In both studies, hypothalamic phosphorylated STAT3 (P-STAT3) was significantly higher in Sham-Leptin and Denervated-Leptin groups compared with their respective Control groups ( P < 0.01), indicating that leptin signaling was enhanced at the end point. We measured uncoupling protein 1 (UCP1), a marker of BAT thermogenic activity, and found a significant induction in Leptin in Sham animals ( P < 0.001) but not in Denervated animals, demonstrating that BAT UCP1 protein was only induced in Sham rats. Both Sham-Leptin and Denervated-Leptin rats lost ~15% of their initial body weight ( P < 0.001) by day 14 and reached a maximum of 18% body weight loss that stabilized over week 3 of treatment, indicating that sympathetic outflow to BAT is not required for leptin-mediated weight loss. In summary, interscapular BAT (iBAT) denervation did not prevent body weight loss following central leptin gene delivery. The present data show that sympathetic innervation of iBAT is not essential for leptin-induced body weight loss.

Activation of the central melanocortin system in rats persistently reduces body and fat mass independently of caloric reduction.

Recent evidence indicate that melanotan II (MTII) reduces body mass independently of caloric reduction. Because MTII induces a transient hypophagia, caloric reduction is still considered a primary mechanism for MTII-mediated body mass loss. To examine the contribution of caloric reduction to long-term body mass loss in response to MTII, we centrally infused MTII or vehicle in ad libitum fed (MTII and Control) animals in comparison with a group of animals that were pair-fed (PF) to the MTII group. Food intake and body mass were recorded daily, and body composition was assessed biweekly. The present study demonstrates that central MTII-mediated body mass loss is only partially mediated by caloric restriction, and the long-term body mass loss is independent of the initial hypophagia. More importantly, central MTII administration induced a rapid but sustained fat mass loss, independently of caloric reduction. MTII-treated animals preserved their lean/fat mass ratio throughout the study, whereas PF animals underwent a transient reduction of lean/fat mass ratio that was only normalized when food intake returned to Control level. In summary, it can be concluded that activation of the central melanocortin system in rats persistently reduces body and fat mass independently of caloric reduction.

A Proteomic Evaluation of Sympathetic Activity Biomarkers of the Hypothalamus-Pituitary-Adrenal Axis by Western Blotting Technique Following Experimental Traumatic Brain Injury.

Endocrine disorders and autonomic dysfunction are common paradigms following traumatic brain injury (TBI). Alterations in the hypothalamus-pituitary-adrenal (HPA) axis following TBI may result in impaired vasopressor response, energy imbalance, fatigue, depression, or neurological disorders. Autonomic dysfunction is a common disorder following TBI. The sympathetic activity markers on HPA axis can be measured by Western blot protein analysis. Tyrosine hydroxylase, dopamine beta hydroxylase are the key enzymes for the synthesis of norepinephrine; and neuropeptide Y (NPY) is the peptide that is co-stored and co-released with norepinephrine. Thus, the present chapter reviews the experimental protocols for Western blot protein analysis for the measurement of biomarkers that indicate sympathetic activity in brain regions (hypothalamus, pituitary, cerebral cortex, and cerebellum) following TBI.

Effect of High-Salt Diet on Age-Related High Blood Pressure and Hypothalamic Redox Signaling.

AIM: The aim of this study was to investigate the effect of a high salt (HS) diet on age-related changes in blood pressure (BP) and the possible role played by regulatory central mechanisms. METHODS: Young (5 months) and old (27 months) male Fischer 344 × Brown Norway (F344/BN) rats were fed standard chow or 8% HS diet for 12 days. BP and heart rate (HR) were measured by telemetry. RESULTS: Mean arterial BP (MAP) was significantly elevated in old rats during the day and night when compared with young animals. The HS diet further elevated MAP in both age groups, and the increase was more pronounced in the old animals, while HR was not altered by age or HS diet. In addition, cardiovascular responses to restraint stress were diminished in the old when compared with the young and were unchanged with HS diet in either age group. Both age and the HS diet elevated the adrenomedullary mRNA levels of tyrosine hydroxylase, an indicator for sympathoexcitation. HS diet enhanced intracerebroventricular angiotensin II (AngII)-induced BP and HR elevations in both age groups. AngII type 1 receptor mRNA increased significantly in the hypothalamus with age and HS diet. Furthermore, hypothalamic p22phox mRNA and gp91phox protein, subunits of NADPH oxidase, as well as NADPH oxidase activity increased with the HS diet in the old animals, whereas antioxidant enzymes that decreased with age yet remained unaltered with the HS diet. CONCLUSION: Our findings indicate that sensitivity of BP to HS diet increases with age, and that central AngII-induced pressor responses are diminished in old rats compared with the young both under control conditions and during HS diet treatment. These changes are paralleled by increases in the expression and NADPH oxidase activity in the hypothalamus, possibly leading to central oxidative stress-mediated sympathoexcitation and high BP.

Intracerebroventricular tempol administration in older rats reduces oxidative stress in the hypothalamus but does not change STAT3 signalling or SIRT1/AMPK pathway.

Hypothalamic inflammation and increased oxidative stress are believed to be mechanisms that contribute to obesity. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol), a free radical scavenger, has been shown to reduce inflammation and oxidative stress. We hypothesized that brain infusion of tempol would reduce oxidative stress, and thus would reduce food intake and body weight and improve body composition in rats with age-related obesity and known elevated oxidative stress. Furthermore, we predicted an associated increase in markers of leptin signalling, including the silent mating type information regulator 2 homolog 1 (SIRT1)/5'AMP-activated protein kinase (AMPK) pathway and the signal transducer and activator of transcription 3 (STAT3) pathway. For this purpose, osmotic minipumps were placed in the intracerebroventricular region of young (3 months) and aged (23 months) male Fischer 344 x Brown Norway rats for the continuous infusion of tempol or vehicle for 2 weeks. Tempol significantly decreased (p < 0.01) nicotinamide adenine dinucleotide phosphate oxidase activity in the hypothalamus but failed to reduce food intake or weight gain and did not alter body composition. SIRT1 activity and Acetyl p53 were decreased and phosphorylation of AMPK was increased with age, but they were unchanged with tempol. Basal phosphorylation of STAT3 was unchanged with age or tempol. These results indicate that tempol decreases oxidative stress but fails to alter feeding behaviour, body weight, or body composition. Moreover, tempol does not modulate the SIRT1/AMPK/p53 pathway and does not change leptin signalling. Thus, a reduction in hypothalamic oxidative stress is not sufficient to reverse age-related obesity.

Altered potassium ATP channel signaling in mesenteric arteries of old high salt-fed rats.

PURPOSE: Both aging and the consumption of a high salt diet are associated with clear changes in the vascular system that can lead to the development of cardiovascular disease; however the mechanisms are not clearly understood. Therefore, we examined whether aging and the consumption of excess salt alters the function of potassium ATP-dependent channel signaling in mesenteric arteries. METHODS: Young (7 months) and old (29 months) Fischer 344 x Brown Norway rats were fed a control or a high salt diet (8% NaCl) for 12 days and mesenteric arteries were utilized for vascular reactivity measurements. RESULTS: Acetylcholine-induced endothelium relaxation was significantly reduced in old arteries (81 ± 4%) when compared with young arteries (92 ± 2%). Pretreatment with the potassium-ATP channel blocker glibenclamide reduced relaxation to acetylcholine in young arteries but did not alter dilation in old arteries. On a high salt diet, endothelium dilation to acetylcholine was significantly reduced in old salt arteries (60 ± 3%) when compared with old control arteries (81 ± 4%). Glibenclamide reduced acetylcholine-induced dilation in young salt arteries but had no effect on old salt arteries. Dilation to cromakalim, a potassium-ATP channel opener, was reduced in old salt arteries when compared with old control arteries. CONCLUSION: These findings demonstrate that aging impairs endothelium-dependent relaxation in mesenteric arteries. Furthermore, a high salt diet alters the function of potassium-ATP-dependent channel signaling in old isolated mesenteric arteries and affects the mediation of relaxation stimuli.

Age Impaired endothelium-dependent vasodilation is improved by resveratrol in rat mesenteric arteries.

PURPOSE: To determine whether resveratrol improves the adverse effects age on vascular function in mesenteric arteries (MAs), and diminishes the hyperactivity in adrenal gland with age. METHODS: Male F344 x Brown Norway rats were assigned to 6-month control (YC), 6-month resveratrol (YR), 24-month control (OC) and 24-month resveratrol (OR). Resveratrol (15 mg/kg) was provided to resveratrol groups in drinking water for 14 days. RESULTS: Concentration response curves to phenylephrine (PE, 10(-9)-10(-5)M), acetylcholine (Ach, 10(-9)-10(-5)M) and resveratrol (10(-8)-10(-4)M) were evaluated in pressurized isolated MAs. The Ach concentration-response curve was right shifted with maximal response diminished in OC compared with YC rats. These effects were reversed by resveratrol treatment. The resveratrol-mediated relaxant responses were unchanged with age or resveratrol suggesting an endothelium-independent mechanism. Resveratrol tended to increase endothelial nitric oxide synthase; caused no effect on copper-zinc superoxide dismutase; and normalized the age-related elevatation in DßH and NPY levels in adrenal medulla, two indicators of sympathetic activity. CONCLUSION: These data indicate that resveratrol reverses age-related dysfunction in endothelium-dependent vasodilation in MAs and partially reverses hyperactivity of adrenomedullary function with age. This treatment may have a therapeuticpotential in the treatment of cardiovascular diseases or hypertension in the elderly.

Anorexic response to rapamycin does not appear to involve a central mechanism.

The authors have previously demonstrated that a low and intermittent peripheral dose of rapamycin (1 mg/kg three times/week) to rats inhibited mTORC1 signalling, but avoided the hyperlipidemia and diabetes-like syndrome associated with higher doses of rapamycin. The dosing regimen reduced food intake, body weight, adiposity, serum leptin and triglycerides. mTORC1 signalling was inhibited in both liver and hypothalamus, suggesting some of the actions, in particular the decrease in food intake, may be the results of a central mechanism. To test this hypothesis, rapamycin (30 µg/day for 4 weeks) was infused into 23-25-month-old F344xBN rats by intracerebroventricular (icv) mini pumps. Our results demonstrated that central infusion did not alter food intake or body weight, although there was a tendency for a decrease in body weight towards the end of the study. mTORC1 signalling, evidenced by decreased phosphorylation of S6 protein at end of 4 weeks, was not activated in liver, hypothalamus or hindbrain. Fat and lean mass, sum of white adipose tissues, brown adipose tissue, serum glucose, insulin and leptin levels remained unchanged. Thus, these data suggest that the anorexic and body weight responses evident with peripheral rapamycin are not the result of direct central action. The tendency for decreased body weight towards the end of study, suggests that there is either a slow transport of centrally administered rapamycin into the periphery, or that there is delayed action of rapamycin at sites in the brain.

Protective effects of resveratrol on aging-induced cognitive impairment in rats.

Resveratrol, a polyphenol phytoalexine, has been shown to play a neuroprotective role in the neurodegenerative process in Alzheimer's disease (AD) and improve memory function in dementia. However, the in vivo effect of resveratrol in normal aging models of learning and memory has not yet been evaluated. Therefore, the present neurobehavioral study was undertaken to evaluate the effect of resveratrol on cognitive impairment induced by aging in passive avoidance and Morris water maze (MWM) tests. Male Wistar albino rats were divided into four groups: young control (4month), young resveratrol (4month+RESV), old control (24month) and old resveratrol (24month+RESV). Resveratrol (50mg/kg/day) was given to the 4month+RESV and 24month+RESV groups orally for 12weeks. There was no significant difference between the groups for the first day of latency, while in aged rats, the second day of latency was significantly shortened compared to the young group in the passive avoidance test (p<0.05). Additionally, in the MWM test, the results showed a decrease in the time spent in the escape platform's quadrant in the probe test in aged rats (p<0.05). The administration of resveratrol at 50mg/kg/day increased the retention scores in the passive avoidance test and the time spent in the escape platform's quadrant in the MWM task (p<0.05). Furthermore resveratrol attenuated the protein levels of TNFα and IL1ß in the 24-month group. These findings indicate that aging impairs emotional and spatial learning-memory and resveratrol reverses the effect of age-related learning and memory impairment. The results of this study suggest that resveratrol is effective in preventing cognitive deficit in aged rats by inhibiting the production of inflammatory cytokines.

Onset of leptin resistance shows temporal differences related to dose or pulsed treatment.

Leptin administration results in leptin resistance presenting a significant barrier to therapeutic use of leptin. Consequently, we examined two hypotheses. The first examined the relationship between leptin dose and development of physiological and biochemical signs of leptin resistance. We hypothesized lower doses of leptin would produce proportional reductions in body weight without the adverse leptin-induced leptin resistance. The second compared pulsed central leptin infusion to continuous leptin infusion. We hypothesized that pulsed infusion at specific times of the day would evoke favorable body weight reductions while tempering the development of leptin-induced leptin resistance. The first experiment examined leptin responsiveness, including food intake, body weight and hypothalamic STAT3 phosphorylation to increasing doses of viral gene delivery of leptin. Varying the dose proved inconsequential with respect to long-term therapy and demonstrated proportional development of leptin resistance. The second experiment examined leptin responsiveness to pulsed central leptin infusion, comparing pulsed versus constant infusion of 3µg/day leptin or a 2h morning versus a 2h evening pulsed leptin infusion. Pulsed delivery of the supramaximal dose of 3µg/day was not different than constant delivery. Morning pulsed infusion of the submaximal dose of 0.25µg reduces food intake only over subsequent immediate meal period and was associated with body weight reductions, but results in cellular leptin resistance. Evening pulsed infusion did not decrease food intake but reduces body weight and maintains full leptin signaling. The positive benefit for pulsed delivery remains speculative, yet potentially may provide an alternative mode of leptin therapy.

Fructose consumption does not worsen bone deficits resulting from high-fat feeding in young male rats.

Dietary-induced obesity (DIO) resulting from high-fat (HF) or high-sugar diets produces a host of deleterious metabolic consequences including adverse bone development. We compared the effects of feeding standard rodent chow (Control), a 30% moderately HF (starch-based/sugar-free) diet, or a combined 30%/40% HF/high-fructose (HF/F) diet for 12weeks on cancellous/cortical bone development in male Sprague-Dawley rats aged 8weeks. Both HF feeding regimens reduced the lean/fat mass ratio, elevated circulating leptin, and reduced serum total antioxidant capacity (tAOC) when compared with Controls. Distal femur cancellous bone mineral density (BMD) was 23-34% lower in both HF groups (p<0.001) and was characterized by lower cancellous bone volume (BV/TV, p<0.01), lower trabecular number (Tb.N, p<0.001), and increased trabecular separation versus Controls (p<0.001). Cancellous BMD, BV/TV, and Tb.N were negatively associated with leptin and positively associated with tAOC at the distal femur. Similar cancellous bone deficits were observed at the proximal tibia, along with increased bone marrow adipocyte density (p<0.05), which was negatively associated with BV/TV and Tb.N. HF/F animals also exhibited lower osteoblast surface and reduced circulating osteocalcin (p<0.05). Cortical thickness (p<0.01) and tissue mineral density (p<0.05) were higher in both HF-fed groups versus Controls, while whole bone biomechanical characteristics were not different among groups. These results demonstrate that "westernized" HF diets worsen cancellous, but not cortical, bone parameters in skeletally-immature male rats and that fructose incorporation into HF diets does not exacerbate bone loss. In addition, they suggest that leptin and/or oxidative stress may influence DIO-induced alterations in adolescent bone development.

Rapamycin Normalizes Serum Leptin by Alleviating Obesity and Reducing Leptin Synthesis in Aged Rats.

This investigation examines whether a low intermittent dose of rapamycin will avoid the hyperlipidemia and diabetes-like syndrome associated with rapamycin while still decreasing body weight and adiposity in aged obese rats. Furthermore, we examined if the rapamycin-mediated decrease in serum leptin was a reflection of decreased adiposity, diminished leptin synthesis, or both. To these ends, rapamycin (1mg/kg) was administered three times a week to 3 and 24-month old rats. Body weight, food intake, body composition, mTORC1 signaling, markers of metabolism, as well as serum leptin levels and leptin synthesis in adipose tissue were examined and compared to that following a central infusion of rapamycin. Our data suggest that the dosing schedule of rapamycin acts on peripheral targets to inhibit mTORC1 signaling, preferentially reducing adiposity and sparing lean mass in an aged model of obesity resulting in favorable outcomes on blood triglycerides, increasing lean/fat ratio, and normalizing elevated serum leptin with age. The initial mechanism underlying the rapamycin responses appears to have a peripheral action and not central. The peripheral rapamycin responses may communicate an excessive nutrients signal to the hypothalamus that triggers an anorexic response to reduce food consumption. This coupled with potential peripheral mechanism serves to decrease adiposity and synthesis of leptin.

Rapamycin Versus Intermittent Feeding: Dissociable Effects on Physiological and Behavioral Outcomes When Initiated Early and Late in Life.

Rapamycin, an inhibitor of the mammalian target of rapamycin pathway, has been shown to increase mammalian life span; less is known concerning its effect on healthspan. The primary aim of this study was to examine rapamycin's role in the alteration of several physiological and behavioral outcomes compared with the healthspan-inducing effects of intermittent feeding (IF), another life-span-enhancing intervention. Male Fisher 344 × Brown Norway rats (6 and 25 months of age) were treated with rapamycin or IF for 5 weeks. IF and rapamycin reduced food consumption and body weight. Rapamycin increased relative lean mass and decreased fat mass. IF failed to alter fat mass but lowered relative lean mass. Behaviorally, rapamycin resulted in high activity levels in old animals, IF increased levels of "anxiety" for both ages, and grip strength was not significantly altered by either treatment. Rapamycin, not IF, decreased circulating leptin in older animals to the level of young animals. Glucose levels were unchanged with age or treatment. Hypothalamic AMPK and pAMPK levels decreased in both older treated groups. This pattern of results suggests that rapamycin has more selective and healthspan-inducing effects when initiated late in life.

AT1 receptor blocker losartan protects against mechanical ventilation-induced diaphragmatic dysfunction.

Mechanical ventilation is a life-saving intervention for patients in respiratory failure. Unfortunately, prolonged ventilator support results in diaphragmatic atrophy and contractile dysfunction leading to diaphragm weakness, which is predicted to contribute to problems in weaning patients from the ventilator. While it is established that ventilator-induced oxidative stress is required for the development of ventilator-induced diaphragm weakness, the signaling pathway(s) that trigger oxidant production remain unknown. However, recent evidence reveals that increased plasma levels of angiotensin II (ANG II) result in oxidative stress and atrophy in limb skeletal muscles. Using a well-established animal model of mechanical ventilation, we tested the hypothesis that increased circulating levels of ANG II are required for both ventilator-induced diaphragmatic oxidative stress and diaphragm weakness. Cause and effect was determined by administering an angiotensin-converting enzyme inhibitor (enalapril) to prevent ventilator-induced increases in plasma ANG II levels, and the ANG II type 1 receptor antagonist (losartan) was provided to prevent the activation of ANG II type 1 receptors. Enalapril prevented the increase in plasma ANG II levels but did not protect against ventilator-induced diaphragmatic oxidative stress or diaphragm weakness. In contrast, losartan attenuated both ventilator-induced oxidative stress and diaphragm weakness. These findings indicate that circulating ANG II is not essential for the development of ventilator-induced diaphragm weakness but that activation of ANG II type 1 receptors appears to be a requirement for ventilator-induced diaphragm weakness. Importantly, these experiments provide the first evidence that the Food and Drug Administration-approved drug losartan may have clinical benefits to protect against ventilator-induced diaphragm weakness in humans.

The functional and structural changes in the basilar artery due to overpressure blast injury.

Overpressure blast-wave induced brain injury (OBI) leads to progressive pathophysiologic changes resulting in a reduction in brain blood flow, blood brain barrier breakdown, edema, and cerebral ischemia. The aim of this study was to evaluate cerebral vascular function after single and repeated OBI. Male Sprague-Dawley rats were divided into three groups: Control (Naive), single OBI (30 psi peak pressure, 1 to 2 msec duration), and repeated (days 1, 4, and 7) OBI (r-OBI). Rats were killed 24 hours after injury and the basilar artery was isolated, cannulated, and pressurized (90 cm H2O). Vascular responses to potassium chloride (KCl) (30 to 100 mmol/L), endothelin-1 (10(-12) to 10(-7) mol/L), acetylcholine (ACh) (10(-10) to 10(-4) mol/L) and diethylamine-NONO-ate (DEA-NONO-ate) (10(-10) to 10(-4) mol/L) were evaluated. The OBI resulted in an increase in the contractile responses to endothelin and a decrease in the relaxant responses to ACh in both single and r-OBI groups. However, impaired DEA-NONO-ate-induced vasodilation and increased wall thickness to lumen ratio were observed only in the r-OBI group. The endothelin-1 type A (ET(A)) receptor and endothelial nitric oxide synthase (eNOS) immunoreactivity were significantly enhanced by OBI. These findings indicate that both single and r-OBI impairs cerebral vascular endothelium-dependent dilation, potentially a consequence of endothelial dysfunction and/or vascular remodelling in basilar arteries after OBI.

The effects of aging on the functional and structural properties of the rat basilar artery.

Aging leads to progressive pathophysiological changes in blood vessels of the brain and periphery. The aim of this study was to evaluate the effects of aging on cerebral vascular function and structure. Basilar arteries were isolated from male Fischer 344 cross Brown Norway (F344xBN) rats at 3, 8, and 24 months of age. The basilar arteries were cannulated in the pressurized system (90 cm H2O). Contractile responses to KCl (30-120 mmol/L) and endothelin-1 (10(-11)-10(-7) mol/L) were evaluated. Responses to acetylcholine (ACh) (10(-10)-10(-4) mol/L), diethylamine (DEA)-NONO-ate (10(-10)-10(-4) mol/L), and papaverin (10(-10)-10(-4) mol/L) were assessed to determine both endothelium-dependent and endothelium-independent responsiveness. Advanced aging (24 months) decreased responses of the basilar artery to both the contractile and relaxing agents; whereas, DEA-induced dilation was significantly higher in the 8-month-old group compared with the younger and older groups. The arterial wall-to-lumen ratio was significantly increased in 24-month-old rats. Smooth muscle cell count was also decreased in old rats. These findings indicate that aging produces dysfunction of both the endothelium and the vascular smooth muscle in the basilar artery. Aging also alters wall structure of the basilar artery, possibly through decreases in smooth muscle cell number and concomitant hypertrophy.