The Role of Gluconeogenesis in Regulating Naturally High Plasma Glucose Concentrations in Mourning Doves

Description

Birds have been found to possess naturally high blood glucose levels compared to other mammals of similar sizes (Braun and Sweazea, 2008). Additionally, birds utilize lipids as their primary source of fuel yet continue to have high resting blood glucose…

Birds have been found to possess naturally high blood glucose levels compared to other mammals of similar sizes (Braun and Sweazea, 2008). Additionally, birds utilize lipids as their primary source of fuel yet continue to have high resting blood glucose levels (Landys et al., 2005). It has been hypothesized that the underlying cause of this is a preference to oxidize fatty acids rather than carbohydrates, which results in the production of glycerol (a precursor to gluconeogenesis). Thus, the role of gluconeogenesis in blood glucose regulation in birds was examined in this study. We captured seven mourning doves (Zenaida macroura) in Tempe, Arizona, and allowed them to acclimate to their new environment for two weeks. One bird was released prior to experimentation due to poor acclimation. Over a course of six weeks following this acclimation period, birds were administered either metformin (an inhibitor of gluconeogenesis that is commonly used in type 2 diabetes patients) at 150 mg/kg or 300 mg/kg, a compound called DAB (1,4-dideoxy-1,4-imino-D-arabinitol) at a dose of 2.5 mg/kg that acts to inhibit glycogenolysis (a potential compensatory mechanism that elevates blood sugar), or a control (water). Blood draws were conducted at 0, 5, and 15 minutes following each treatment. In this crossover design study, each bird received one treatment each week. In the first phase of this study, Kreisler et al. found that 150 mg/kg metformin significantly increased blood glucose whereas 300 mg/kg metformin did not increase over two hours. These observations held true in the current acute study as well. Additionally, Kreisler et al. observed no effect of METDAB (150 mg/kg metformin and 2.5 mg/kg DAB) on blood glucose compared to the control, indicating that DAB effectively inhibited glycogenolysis induced by metformin. Contrary to this, the current study observed a significant increase (p<0.05) in blood glucose over 15 minutes after administration of METDAB, suggesting that DAB does not act within a shorter period of time. While metformin increases blood glucose within only 5 minutes, the longer timeframe with which DAB acts was not sufficient to prevent the increase. Additionally, when administered alone, DAB had no effect on blood glucose concentrations over a 2-hour period. This suggests that glycogenolysis is most likely not activated in healthy mourning doves under fed conditions and that gluconeogenesis plausibly plays a much larger role.

Date Created
2023-05
Agent

Effects of an Urban Diet on Glucose, Sodium, and Osmolality in the Mourning Dove, Zenaida macroura

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Description
Prior studies of Mourning Doves have observed no changed in glucose in response to either a high fat “chow” diet or a white bread diet. In the current feeding study, we fed doves an urban diet, high in carbohydrates, fat,…

Prior studies of Mourning Doves have observed no changed in glucose in response to either a high fat “chow” diet or a white bread diet. In the current feeding study, we fed doves an urban diet, high in carbohydrates, fat, and sodium, which is representative of typical American nutrition accessible to the avian population in an urbanized environment. Based on studies of other avian species that examined the effects of an urban diet on physiology, I hypothesized that doves fed an urban diet would have increased plasma glucose and sodium, which would promote an increase in plasma osmolality. This hypothesis was based on preliminary data that found birds fed an urban diet developed impaired vasodilation compared to seed diet control birds. Therefore, differences in plasma glucose, sodium, and osmolality were examined as increases may contribute to the impairment. Adult doves of both sexes were captured on the Arizona State University, Tempe campus. Doves were placed in two dietary groups: an urban diet consisting of a 50/50 ratio of French fries and nutritionally-balanced bird seed (n=7) and a control group of only the seed diet (n=6). Following the four-week diets, birds were euthanized, and cardiac plasma samples were collected from birds to measure glucose, sodium, and osmolality. There were no significant differences between the two study groups in plasma glucose concentration (p=0.445), sodium concentration (p=0.731), or osmolality (p=0.692). Sodium concentrations were signficantly more variable in birds consuming a seed diet than those that were provided the mixed French fry and seed diet (p=0.014). These results suggest that glucose, sodium, and osmolality likely do not contribute to the altered vasodilation of doves fed an urban diet and that such a diet may not be as detrimental to the doves health given their phenotypic flexibility.
Date Created
2020-05
Agent

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

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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.
Date Created
2020-05
Agent

Impact of Sumac on Lowering Oxidative stress as it pertains to Dementia

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Description
Background: To determine the effect of sumac on vasodilation and oxidative stress in vascular tissue. This study hypothesized that sumac would increase vasodilation and reduce vascular damage in vascular tissue taken from rats to improve symptoms and risk of vascular…

Background: To determine the effect of sumac on vasodilation and oxidative stress in vascular tissue. This study hypothesized that sumac would increase vasodilation and reduce vascular damage in vascular tissue taken from rats to improve symptoms and risk of vascular dementia.
Methods: Male Sprague-Dawley rats were fed a chow diet or a high fat diet (HFD) for ten weeks. Endothelium-dependent vasodilation was measured in isolated mesenteric arterioles that were treated with or without 80 µg/ml sumac in the superfusate throughout the experiment.
Results: Sumac did not improve vasodilation or in ex vivo arteries from rats fed a high fat diet. There were trends of improved vasodilation in sumac treated vessels from high fat diet rats, but sumac did not significantly improve vasodilation. In rats fed a chow diet, sumac prevented phenylephrine (PE) constriction in the vascular tissue. The most likely cause for this is the presence of Gallic acid in sumac. Another possible explanation is the presence of nitrates in sumac which may have prevented PE vasoconstriction.
Conclusions: Sumac did not significantly improve vasodilation in isolated arteries from rats fed a high fat diet. The results are inconclusive for the improvement of symptoms or risk of vascular dementia. In vivo treatment with sumac should be tested as results may differ.
Date Created
2018-05
Agent
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