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An Urban Diet Impairs Tibial Vasodilation in Mourning Doves (Zenaida macroura)

Description

Birds maintain resting plasma glucose concentrations (pGlu) nearly twice that of comparably sized mammals. Despite this, birds do not incur much of the oxidative tissue damage that might be expected from a high pGlu. Their ability to stave off oxidative

Birds maintain resting plasma glucose concentrations (pGlu) nearly twice that of comparably sized mammals. Despite this, birds do not incur much of the oxidative tissue damage that might be expected from a high pGlu. Their ability to stave off oxidative damage allows birds to serve as a negative model of hyperglycemia-related complications, making them ideal for the development of new diabetes treatments with the potential for human application. Previous studies conducted by the Sweazea Lab at Arizona State University aimed to use diet as a means to raise blood glucose in mourning doves (Zenaida macroura) in order to better understand the mechanisms they utilize to stave off oxidative damage. These protocols used dietary interventions—a 60% high fat (HF) “chow” diet, and a high carbohydrate (HC) white bread diet—but were unsuccessful in inducing pathologies. Based on this research, we hypothesized that a model of an urban diet (high in fat, refined carbohydrates, and sodium) might impair vasodilation, as the effect of this diet on birds is currently unknown. We found that tibial vasodilation was significantly impaired in birds fed an urban diet compared to those fed a seed diet. Unexpectedly, vasodilation in the urban diet group was comparable to data of wild-caught birds from previous research, possibly indicating that the birds had already been eating a diet similar to this study’s urban diet before they were caught. This may constitute evidence that the seed diet improved vasodilation while the urban diet more closely mimicked the diet of the birds before the trial, suggesting that the model of the urban diet acted as the control diet in this context. This study is the first step in elucidating avian mechanisms for dealing with diabetogenic diets and has potential to aid in the development of treatments for humans with metabolic syndrome.

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Date Created
2020-05

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The Role of Lipolysis in Regulating Plasma Glucose Concentrations in Mourning Doves

Description

Birds have unusually high plasma glucose concentrations compared to mammals of similar size despite their high metabolic rate. While birds use lipids as their main source of energy, it is still unclear how and why they maintain high plasma glucose

Birds have unusually high plasma glucose concentrations compared to mammals of similar size despite their high metabolic rate. While birds use lipids as their main source of energy, it is still unclear how and why they maintain high plasma glucose concentrations. To investigate a potential underlying mechanism, this study looks at the role of lipolysis in glucose homeostasis. The purpose of this study is to examine the effects of decreased glycerol availability (through inhibition of lipolysis) on plasma glucose concentrations in mourning doves. The hypothesis is that decreased availability of glycerol will result in decreased production of glucose through gluconeogenesis leading to reduced plasma glucose concentrations. In the morning of each experiment, mourning doves were collected at the Arizona State University Tempe campus, and randomized into either a control group (0.9% saline) or experimental group (acipimox, 50mg/kg BM). Blood samples were collected prior to treatment, and at 1, 2, and 3 hours post-treatment. At 3 hours, doves were euthanized, and tissue samples were collected for analysis. Acipimox treatment resulted in significant increases in blood glucose concentrations at 1 and 2 hours post- treatment as well as renal triglyceride concentrations at 3 hours post-treatment. Change in plasma free glycerol between 0h and 3h followed an increasing trend for the acipimox treated animals, and a decreasing trend in the saline treated animals. These results do not support the hypothesis that inhibition of lipolysis should decrease blood glycerol and blood glucose levels. Rather, the effects of acipimox in glucose homeostasis appear to differ significantly between birds and mammals suggesting differing mechanisms for glucose homeostasis.

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2015-05

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The Effect of Glucocorticoids on Insulin Resistance in Rat Skeletal Muscle via TXNIP

Description

Glucocorticoids are a class of corticosteroids that bind to glucocorticoid receptors
within cells that result in changes in the metabolism of carbohydrates and immune functions.
Ingesting glucocorticoids has also been linked to insulin resistance, a main feature of

Glucocorticoids are a class of corticosteroids that bind to glucocorticoid receptors
within cells that result in changes in the metabolism of carbohydrates and immune functions.
Ingesting glucocorticoids has also been linked to insulin resistance, a main feature of Type 2
diabetes. Experiments including polymerase chain reaction, western blotting, and glycogen
synthase analysis were conducted to determine if exposure to higher doses of dexamethasone, a
glucocorticoid, induces insulin resistance in cultured rat skeletal muscle via interaction with
thioredoxin-interacting protein (TXNIP). Treatment with dexamethasone was shown to cause
mild increases in TXNIP while a definitive increase or decrease in insulin signaling was unable
to be determined.

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Date Created
2020-05

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The Impact of Different Normalization Methods on Western Blot Results

Description

Reducing the amount of error and introduced data variability increases the accuracy of Western blot results. In this study, different methods of normalization for loading differences and data alignment were explored with respect to their impact on Western blot results.

Reducing the amount of error and introduced data variability increases the accuracy of Western blot results. In this study, different methods of normalization for loading differences and data alignment were explored with respect to their impact on Western blot results. GAPDH was compared to the LI-COR Revert total protein stain as a loading control. The impact of normalizing data to a control condition, which is commonly done to align Western blot data distributed over several immunoblots, was also investigated. Specifically, this study addressed whether normalization to a small subset of distinct controls on each immunoblot increases pooled data variability compared to a larger set of controls. Protein expression data for NOX-2 and SOD-2 from a study investigating the protective role of the bradykinin type 1 receptor in angiotensin-II induced left ventricle remodeling were used to address these questions but are also discussed in the context of the original study. The comparison of GAPDH and Revert total protein stain as a loading control was done by assessing their correlation and comparing how they affected protein expression results. Additionally, the impact of treatment on GAPDH was investigated. To assess how normalization to different combinations of controls influences data variability, protein data were normalized to the average of 5 controls, the average of 2 controls, or an average vehicle and the results by treatment were compared. The results of this study demonstrated that GAPDH expression is not affected by angiotensin-II or bradykinin type 1 receptor antagonist R-954 and is a less sensitive loading control compared to Revert total protein stain. Normalization to the average of 5 controls tended to reduce pooled data variability compared to 2 controls. Lastly, the results of this study provided preliminary evidence that R-954 does not alter the expression of NOX-2 or SOD-2 to an expression profile that would be expected to explain the protection it confers against Ang-II induced left ventricle remodeling.

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2021-05

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Investigating the influence of food on reproductive physiology and gonad growth: urbanization as a natural experiment

Description

For animals that experience annual cycles of gonad development, the seasonal timing (phenology) of gonad growth is a major adaptation to local environmental conditions. To optimally time seasonal gonad growth, animals use environmental cues that forecast future conditions. The availability

For animals that experience annual cycles of gonad development, the seasonal timing (phenology) of gonad growth is a major adaptation to local environmental conditions. To optimally time seasonal gonad growth, animals use environmental cues that forecast future conditions. The availability of food is one such environmental cue. Although the importance of food availability has been appreciated for decades, the physiological mechanisms underlying the modulation of seasonal gonad growth by this environmental factor remain poorly understood.

Urbanization is characterized by profound environmental changes, and urban animals must adjust to an environment vastly different from that of their non-urban conspecifics. Evidence suggests that birds adjust to urban areas by advancing the timing of seasonal breeding and gonad development, compared to their non-urban conspecifics. A leading hypothesis to account for this phenomenon is that food availability is elevated in urban areas, which improves the energetic status of urban birds and enables them to initiate gonad development earlier than their non-urban conspecifics. However, this hypothesis remains largely untested.

My dissertation dovetailed comparative studies and experimental approaches conducted in field and captive settings to examine the physiological mechanisms by which food availability modulates gonad growth and to investigate whether elevated food availability in urban areas advances the phenology of gonad growth in urban birds. My captive study demonstrated that energetic status modulates reproductive hormone secretion, but not gonad growth. By contrast, free-ranging urban and non-urban birds did not differ in energetic status or plasma levels of reproductive hormones either in years in which urban birds had advanced phenology of gonad growth or in a year that had no habitat-related disparity in seasonal gonad growth. Therefore, my dissertation provides no support for the hypothesis that urban birds begin seasonal gonad growth because they are in better energetic status and increase the secretion of reproductive hormones earlier than non-urban birds. My studies do suggest, however, that the phenology of key food items and the endocrine responsiveness of the reproductive system may contribute to habitat-related disparities in the phenology of gonad growth.

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Date Created
2014

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Consequences of Negative Energy Balance on Avian Reproductive Physiology: Endocrine and Metabolic Mediators

Description

Reproduction is energetically costly and seasonal breeding has evolved to capitalize on predictable increases in food availability. The synchronization of breeding with periods of peak food availability is especially important for small birds, most of which do not store an

Reproduction is energetically costly and seasonal breeding has evolved to capitalize on predictable increases in food availability. The synchronization of breeding with periods of peak food availability is especially important for small birds, most of which do not store an extensive amount of energy. The annual change in photoperiod is the primary environmental cue regulating reproductive development, but must be integrated with supplementary cues relating to local energetic conditions. Photoperiodic regulation of the reproductive neuroendocrine system is well described in seasonally breeding birds, but the mechanisms that these animals use to integrate supplementary cues remain unclear. I hypothesized that (a) environmental cues that negatively affect energy balance inhibit reproductive development by acting at multiple levels along the reproductive endocrine axis including the hypothalamus (b) that the availability of metabolic fuels conveys alterations in energy balance to the reproductive system. I investigated these hypotheses in male house finches, Haemorhous mexicanus, caught in the wild and brought into captivity. I first experimentally reduced body condition through food restriction and found that gonadal development and function are inhibited and these changes are associated with changes in hypothalamic gonadotropin-releasing hormone (GnRH). I then investigated this neuroendocrine integration and found that finches maintain reproductive flexibility through modifying the release of accumulated GnRH stores in response to energetic conditions. Lastly, I investigated the role of metabolic fuels in coordinating reproductive responses under two different models of negative energy balance, decreased energy intake (food restriction) and increased energy expenditure (high temperatures). Exposure to high temperatures lowered body condition and reduced food intake. Reproductive development was inhibited under both energy challenges, and occurred with decreased gonadal gene expression of enzymes involved in steroid synthesis. Minor changes in fuel utilization occurred under food restriction but not high temperatures. My results support the hypothesis that negative energy balance inhibits reproductive development through multilevel effects on the hypothalamus and gonads. These studies are among the first to demonstrate a negative effect of high temperatures on reproductive development in a wild bird. Overall, the above findings provide important foundations for investigations into adaptive responses of breeding in energetically variable environments.

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Date Created
2018