Fat mobilization and plasma hormone levels in fasted dogs

Phospholipid Fatty Acid Profiles of Plasma and Erythrocyte Membranes in Dogs Fed with Commercial Granulated Food

Intake of long-chain n-3 polyunsaturated fatty acids (PUFA) benefits human and animal health. Our study aimed to analyze the long-chain n-3 PUFA content of two types of food and their effect on plasma and erythrocyte phospholipids of Belgian Shepherd dogs. A total of 10 dogs were fed commercial granulated food (Food 1), and another 10 were provided commercial Premium granulated food of high quality (Food 2). All the analyses were performed using gas-liquid chromatography. Our results showed that Food 1 contained more n-3 PUFA than Food 2, which was reflected in higher n-3 PUFA in plasma and erythrocyte phospholipids. Because long-chain n-3 PUFA in phospholipids are precursors for antioxidative molecules, further studies should investigate the effects of the analyzed commercial granulated food rich in n-3 on oxidative stress parameters in dogs.

Macronutrient Proportions and Fat Type Impact Ketogenicity and Shape the Circulating Lipidome in Dogs

Many physiological processes including ketogenesis are similar in dogs and humans, but there is little information available on the effect of carbohydrate restriction in dogs. Here, the ketogenicity and serum metabolic profiles of dogs were assessed after they had consumed high carbohydrate (HiCHO); high protein, low carbohydrate (PROT_LoCHO); or high fat, low carbohydrate (FAT_LoCHO) foods. Thirty-six dogs were fed HiCHO for 4 weeks, then randomized to PROT_LoCHO or FAT_LoCHO for 5 weeks. Dogs then crossed over to the other food for an additional 5 weeks. Generally, reduction of dietary carbohydrate by replacement with either protein or fat increased the energy required to maintain body weight, and fat had a greater effect. Postabsorptive energy availability derived mainly from glucose and triglycerides with HiCHO, from gluconeogenic amino acids and fatty acids with PROT_LoCHO, and from fatty acids and β-hydroxybutyrate with FAT_LoCHO. This study demonstrated that the reduction of carbohydrate in canine foods is potentially beneficial to dogs based on improvements in metabolism and supports the use of low-carbohydrate foods as safe and effective for healthy adult dogs.

Nutrients, Cognitive Function, and Brain Aging: What We Have Learned from Dogs

Due to a difference in genetics, environmental factors, and nutrition, just like in people, dogs age at different rates. Brain aging in people and dogs share similar morphological changes including irreversible cortical atrophy, cerebral amyloid angiopathy, and ventricular enlargement. Due to severe and irreversible brain atrophy, some aging dogs develop cognitive dysfunction syndrome (CDS), which is equivalent to dementia or Alzheimer’s disease (AD) in people. The risk factors and causes of CDS in dogs have not been fully investigated, but age, gender, oxidative stress, and deficiency of sex hormones appears to be associated with increased risk of accelerated brain aging and CDS in dogs. Both AD and CDS are incurable diseases at this moment, therefore more efforts should be focused on preventing or reducing brain atrophy and minimizing the risk of AD in people and CDS in dogs. Since brain atrophy leads to irreversible cognitive decline and dementia, an optimal nutritional solution should be able to not only enhance cognitive function during aging but also reduce irreversible brain atrophy. Up to now, only one nutritional intervention has demonstrated both cognition-enhancing benefits and atrophy-reducing benefits.

Immunohistochemical Markers of Apoptotic and Hypoxic Damage Facilitate Evidence-Based Assessment in Pups with Neurological Disorders

Seizures in puppies often present a diagnostic challenge in terms of identifying and treating the underlying cause. Dog breeds with mutations of the MDR1-gene are known to show adverse reactions to certain drugs, yet metabolic imbalance exacerbated by physiologically immature organs and other contributing pathologies require consideration before arriving at a diagnosis. This study analysed the brains of two male, 5-week-old Australian Shepherd siblings that died after displaying severe neurological symptoms upon administration of MilproVet® to treat severe intestinal helminth infection. Despite the initial symptoms being similar, their case histories varied in terms of the symptom duration, access to supportive therapy and post-mortem interval. Histopathology and immunohistochemistry were used to obtain more information about the phase of the pathological processes in the brain, employing protein markers associated with acute hypoxic damage (β-amyloid precursor protein/APP) and apoptosis (diacylglycerolkinase-ζ/DGK-ζ, apoptotic protease activating factor 1/Apaf1, and B-cell lymphoma related protein 2/Bcl-2). The results seem to reflect the course of the animals' clinical deterioration, implicating that the hypoxic damage to the brains was incompatible with life, and suggesting the usefulness of the mentioned immunohistochemical markers in clarifying the cause of death in animals with acute neurological deficits.

Specificity of transaminase activities in the prediction of drug-induced hepatotoxicity

The activities of the transaminases (aminotransferases) alanine aminotransferase and aspartate aminotransferase in the blood (serum or plasma) are widely used as sensitive markers of possible tissue damage and, in particular for liver toxicity. On the other hand, an increase in transaminase activities is not always accompanied by findings suggestive of hepatotoxicity. Transaminases are some of the key enzymes in the gluconeogenesis and glycolysis pathways and exist in many organs and tissues which have high activities of the gluconeogenesis and glycolysis. The activities of transaminases are altered not only in the liver but also in other organs by modification of gluconeogenesis by nutritional or hormonal factors and this phenomenon leads to alteration of transaminase activity in the blood. Drugs, which are considered to directly or secondarily modify gluconeogenesis through lowering blood glucose levels or activating lipid metabolism, such as α-glucosidase inhibitors and fibrates, slightly increase transaminase activities in the blood but there is little evidence that the phenomenon is related to drug-induced liver injury (DILI). This type of elevations can be called pharmacology-related elevation. The pharmacology-related elevation of transaminase activities sometimes makes it difficult to assess precisely the potential hepatotoxicity of new investigational drugs. Considering the characteristic of transaminases, concomitant use of new biomarkers more specific to hepatic injury is needed in the assessment of DILI both in non-clinical and clinical studies. In this review, we will discuss the specificity of transaminases to DILI and future perspectives for transaminases in the estimation of risk of DILI.

Lipid Catabolism in Starved Yak Is Inhibited by Intravenous Infusion of β-Hydroxybutyrate

Simple Summary

Yak, which is the predominant and semi-domesticated livestock on the Qinghai-Tibet Plateau, suffers severe starvation and body weight reduction in the cold season because of the harsh highland environment. Lipids are important energy sources to starvation animals. β-hydroxybutyrate (BHBA) that is derived from lipid decomposition as the primary ketone body is with the function not only to provide energy for animals as energy materials, but also regulate lipid metabolism as signaling molecular. However, the effects of starvation and BHBA on lipid metabolism and its mechanism are still unclear for ruminant animals. Herein, we investigated the effects of starvation and intravenous infusion of BHBA solution on Yak growth, serum biochemistry, hormones, subcutaneous adipocyte morphology, fatty acid composition, activity of enzymes related to lipid metabolism, and signal pathway. The results showed that starvation promoted lipid catabolism and BHBA infusion up-regulated the mRNA expression of receptor GPR109A in subcutaneous adipose tissue, inhibited the Cyclic adenosine monophosphate(cAMP)/Protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) signaling pathway, and inhibited lipolysis. Our study was beneficial for enriching the nutrition regulation theory of yaks and improving their growth potential.

Abstract

Lipid is the chief energy source for starved animals. β-hydroxybutyrate (BHBA) is the main ketone body produced by lipid decomposition. In Chinese hamster ovary (CHO) cell experiment, it was found that BHBA could be used not only as an energy substance, but also as a ligand of GPR109A for regulating lipid metabolism. However, whether BHBA can regulate lipid metabolism of yaks, and its effective concentration and signal pathway are not clear. This study investigated the effects and mechanism of starvation and BHBA on the lipid metabolism of yak. Eighteen male Jiulong yaks were selected and then randomly divided into three groups: normal feeding group (NG), starvation group (SG), and starvation with BHBA infusion group (SBG). The yaks in the NG group were freely fed during the trial, while the yaks in the SG and SBG groups fasted; from 7th to 9th days of the experiment, the NG and SG were infused continuous with 0.9% normal saline and SBG was infused 1.7 mmol/L BHBA solution respectively. The blood samples were collected on the 0th, 1st, 3rd, 5th, 7th, and 9th day of experiment. The subcutaneous adipose tissue of all the yaks in this study were taken from live bodies after infusion. Serum glucose, lipid metabolites, hormone concentrations, and mRNA and protein expressions of key factors of lipid metabolism and signaling pathway in subcutaneous adipose tissue were measured. The results showed that, as compared with NG, starvation significantly reduced the body weight of yak in SG, and significantly increased the concentration of BHBA in serum and the mRNA expression of PKA and CREB1 in subcutaneous adipose tissue, while the mRNA expression of MEK, PKC, ERK1/2, the area of adipocytes, and the proportion of saturated fatty acid were decreased. Whereas, further increase of BHBA concentration through infusion promoted the mRNA expression of GPR109A receptor in the subcutaneous adipose tissue of SBG, inhibited the mRNA expression of AC and PKA, and decreased the phosphorylation protein abundance of CREB1, and significantly increased the diameter and area of adipocytes. These findings suggest that starvation led to enhanced lipid catabolism in yaks. An increasing BHBA concentration could increase the mRNA expression of GPR109A receptor in subcutaneous adipose tissue and inhibit the cAMP/PKA/CREB signaling pathway and lipid decomposition.

Endocrinologic Adaptations to Wintertime Fasting in the Male American Mink (Mustela vison)

The aim of this study was to investigate the endocrine response to wintertime starvation in the male American mink (Mustela vison) fasted for 16 hrs, 2 days, 3 days, 5 days, or 7 days (n–10 per group). After 2 days of fasting, the plasma leptin concentrations decreased, along with the triiodothyronine, testosterone, and progesterone levels, and the blood monocyte counts. Leptin also seems to trigger the response to fasting in mustelids by inducing immunosuppression and downregulation of the reproductive and thyroid axes. The dramatic increase in the peptide YY concentrations after 3 days of fasting may be required to suppress gastrointestinal processes during food scarcity. The plasma insulin levels decreased, and those of glucagon increased after 5 days of fasting in association with efficient glucose sparing and lipid mobilization. Body energy stores cannot be wasted for growth during nutritional scarcity and, thus, the growth hormone levels of the minks decreased after 5 days of fasting. The plasma noradrenaline and cortisol concentrations also decreased after 3 and 7 days without food, respectively. The plasma ghrelin, adiponectin, resistin, thyroxine, adrenaline, or estradiol levels did not respond to fasting. The endocrine response to food deprivation is remarkably similar in divergent mammalian orders, indicating that the hormonal signals enhancing survival during nutritional scarcity must be evolutionarily old and well conserved.

Skeletal muscle tissue transcriptome differences in lean and obese female beagle dogs

Skeletal muscle is a large and insulin-sensitive tissue that is an important contributor to metabolic homeostasis and energy expenditure. Many metabolic processes are altered with obesity, but the contribution of muscle tissue in this regard is unclear. A limited number of studies have compared skeletal muscle gene expression of lean and obese dogs. Using microarray technology, our objective was to identify genes and functional classes differentially expressed in skeletal muscle of obese (14.6 kg; 8.2 body condition score; 44.5% body fat) vs. lean (8.6 kg; 4.1 body condition score; 22.9% body fat) female beagle adult dogs. Alterations in 77 transcripts was observed in genes pertaining to the functional classes of signaling, transport, protein catabolism and proteolysis, protein modification, development, transcription and apoptosis, cell cycle and differentiation. Genes differentially expressed in obese vs. lean dog skeletal muscle indicate oxidative stress and altered skeletal muscle cell differentiation. Many genes traditionally associated with lipid, protein and carbohydrate metabolism were not altered in obese vs. lean dogs, but genes pertaining to endocannabinoid metabolism, insulin signaling, type II diabetes mellitus and carnitine transport were differentially expressed. The relatively small response of skeletal muscle could indicate that changes are occurring at a post-transcriptional level, that other tissues (e.g., adipose tissue) were buffering skeletal muscle from metabolic dysfunction or that obesity-induced changes in skeletal muscle require a longer period of time and that the length of our study was not sufficient to detect them. Although only a limited number of differentially expressed genes were detected, these results highlight genes and functional classes that may be important in determining the etiology of obesity-induced derangement of skeletal muscle function.

Hormonal responses to extreme fasting in subantarctic fur seal (Arctocephalus tropicalis) pups

Surviving prolonged fasting implies closely regulated alterations in fuel provisioning to meet metabolic requirements, while preserving homeostasis. Little is known, however, of the endocrine regulations governing such metabolic adaptations in naturally fasting free-ranging animals. The hormonal responses to natural prolonged fasting and how they correlate to the metabolic adaptations observed, were investigated in subantarctic fur seal ( Arctocephalus tropicalis ) pups, which, because of the intermittent pattern of maternal attendance, repeatedly endure exceptionally long fasting episodes throughout their development (1–3 mo). Phase I fasting was characterized by a dramatic decrease in plasma insulin, glucagon, leptin, and total l-thyroxine (T4) associated with reductions in mass-specific resting metabolic rate (RMR), plasma triglycerides, glycerol, and urea-to-creatine ratio, while nonesterified fatty acids (NEFA) and β-OHB increased. In contrast, the metabolic steady-state of phase II fasting reached within 6 days was associated with minimal concentrations of insulin, glucagon, and leptin; unchanged cortisol and triiodothyronine (T3); and moderately increased T4. The early fall in insulin and leptin may mediate the shift to the strategy of energy conservation, protein sparing, and primary reliance on body lipids observed in response to the cessation of feeding. In contrast to the typical mammalian starvation response, nonelevated cortisol and minimal glucagon levels may contribute to body protein preservation and downregulation of catabolic pathways, in general. Furthermore, thyroid hormones may be involved in a process of energy conservation, independent of pups' nutritional state. These original hormonal settings might reflect an adaptation to the otariid repeated fasting pattern and emphasize the crucial importance of a tight physiological control over metabolism to survive extreme energetic constraints.

Enhancing brain functions in senior dogs: a new nutritional approach

Aging induces many morphological and metabolic changes in the brain, which may eventually lead to cognitive impairment and dementia called cognitive dysfunction syndrome in senior dogs. Cognitive impairment and dementia can adversely affect the quality of life in both dogs and their owners. Progress has been made over the past years to understand how aging affects brain and its functions in humans and animals including dogs. Existing data indicate that aging-induced changes in the brain are gradual and irreversible. Therefore, it is too late to effectively manage dogs with cognitive impairment and cognitive dysfunction syndrome. The best option to manage brain aging successfully is to reduce or prevent aging-induced changes in the brain by correcting early metabolic changes and eliminating risk factors associated with brain aging and dementia. This article reviews behavioral, morphological, and metabolic changes in the brain induced by aging and discusses a novel nutritional solution for the aging-induced metabolic changes in the brain.

Dietary supplementation with medium-chain TAG has long-lasting cognition-enhancing effects in aged dogs

The present study focused on the hypothesis that dietary supplementation with medium-chain TAG (MCT) will improve cognitive function in aged dogs by providing the brain with energy in the form of ketones. Aged Beagle dogs were subjected to a baseline battery of cognitive tests, which were used to establish cognitively equivalent control or treatment groups. The dogs in the treatment group were maintained on a diet supplemented with 5.5 % MCT. After an initial wash-in period, all the dogs were tested with a battery of cognitive test protocols, which assessed sequentially landmark discrimination learning ability, egocentric visuospatial function and attention. The groups were maintained on the diets for 8 months. The MCT-supplemented group showed significantly better performance in most of the test protocols than the control group. The group differences also varied as a function of task difficulty, with the more difficult task showing greater supplementation effects than the easier tasks. The group given the MCT supplement showed significantly elevated levels of beta-hydroxybutyrate, a ketone body. These results indicate, first, that long-term supplementation with MCT can have cognition-improving effects, and second, that MCT supplementation increases circulating levels of ketones. The results support the hypothesis that brain function of aged dogs can be improved by MCT supplementation, which provides the brain with an alternative energy source.

Nutritional therapies to improve health: lessons from companion animals

Companion animals represent an under-utilised resource. The present paper is designed to encourage collaborative studies. Dogs and cats are out-bred animals that are willing to consume a consistent diet for long periods, so are ideal candidates for prospective studies of naturally-occurring disease. In some studies the effect of diet on survival has been substantial. Food restriction, for example, slows the development of osteoarthritis and increases the lifespan of Labrador retrievers by 2 years, protein and P restriction more than doubles the median survival time of dogs and cats with chronic kidney disease and addingn-3 fats and arginine to the diet of dogs with stage 3 lymphoma improves median survival time by one-quarter. Obesity is also very common in both dogs and cats and is also associated with disease as in human subjects. When interpreting these results, however, it is essential to take into account pathophysiological differences among species. Dogs and cats do not display all the characteristics of metabolic disease in human subjects, they metabolise fat well and atherosclerosis and cardiac infarction are uncommon. Such differences should not, however, preclude further study because differences among species often clarify knowledge. Monitoring of disease in companion animals may also provide a surveillance system for the safety of the food supply, as illustrated by recent outbreaks of acute renal failure and liver failure in cats and dogs in the USA caused respectively by melamine and mycotoxin contamination of pet foods.

Adaptations to fasting in a terrestrial mustelid, the sable (Martes zibellina)

The aim of this study was to investigate whether the actively wintering Palearctic sable Martes zibellina has evolved physiological adaptations to tolerate nutritional scarcity. Sixteen farm-bred male sables were divided into a fed control group and an experimental group fasted for 4 days. The rate of weight loss in the sable was similar to other medium-sized mustelids. Fasting led to hypoglycaemia and to a decreased lymphocyte percentage. The sable derived metabolic energy from both subcutaneous and intraabdominal white adipose tissues and the relative decrease in fat mass was the largest for the retroperitoneal and subcutaneous depots. Metabolic energy derived partly from body proteins indicated by the increased plasma levels of urea, uric acid and total essential amino acids. Triacylglycerols accumulated in the livers of the fasted sables and the increased plasma aminotransferase activities suggested hepatic dysfunction. The decreased plasma insulin concentrations and the elevated cortisol levels probably contributed to stimulated lipolysis and protein catabolism. Moreover, fasting increased the plasma ghrelin concentrations of the sables and down-regulated the thyroid activity.

Physiological adaptations to fasting in an actively wintering canid, the Arctic blue fox (Alopex lagopus)

This study investigated the physiological adaptations to fasting using the farmed blue fox (Alopex lagopus) as a model for the endangered wild arctic fox. Sixteen blue foxes were fed throughout the winter and 32 blue foxes were fasted for 22 d in Nov-Dec 2002. Half of the fasted blue foxes were food-deprived again for 22 d in Jan-Feb 2003. The farmed blue fox lost weight at a slower rate (0.97-1.02% body mass d(-1)) than observed previously in the arctic fox, possibly due to its higher initial body fat content. The animals experienced occasional fasting-induced hypoglycaemia, but their locomotor activity was not affected. The plasma triacylglycerol and glycerol concentrations were elevated during phase II of fasting indicating stimulated lipolysis, probably induced by the high growth hormone concentrations. The total cholesterol, HDL- and LDL-cholesterol, urea, uric acid and total protein levels and the urea:creatinine ratio decreased during fasting. Although the plasma levels of some essential amino acids increased, the blue foxes did not enter phase III of starvation characterized by stimulated proteolysis during either of the 22-d fasting procedures. Instead of excessive protein catabolism, it is liver dysfunction, indicated by the increased plasma bilirubin levels and alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase activities, that may limit the duration of fasting in the species.

Effects of fasting and exogenous melatonin on annual rhythms in the blue fox (Alopex lagopus)

The arctic fox (Alopex lagopus) is a winter-active inhabitant of the high arctic with extreme fluctuations in photoperiod and food availability. The blue fox is a semi-domesticated variant of the wild arctic fox reared for the fur industry. In this study, 48 blue foxes were followed for a year in order to determine the effects of exogenous melatonin and wintertime food deprivation on their reproductive and thyroid axes. Half of the animals were treated with continuous-release melatonin capsules in July 2002, and in November-January, the animals were divided into three groups and either fed continuously or fasted for one or two 22-day periods. Food deprivation decreased the plasma triiodothyronine and thyroxine concentrations probably in order to preserve energy due to a decreased metabolic rate. The same was observed in the plasma testosterone levels of the males but not in the plasma estradiol concentrations of the females. Exogenous melatonin advanced the autumn moult and seasonal changes in the voluntary food intake. It also advanced the onset of the testosterone peak in the males. The plasma estradiol levels of the females were unaffected, but the progesterone levels peaked more steeply in the sham-operated females. Melatonin exerted a strong influence not only on the reproductive axis of the males but also on the seasonal food intake. The species seemed quite resistant to periodic involuntary food deprivation.

Seasonal physiology of the wild raccoon dog (Nyctereutes procyonoides)

The raccoon dog (Nyctereutes procyonoides) is a canid omnivore with autumnal fattening and winter sleep. Farmraised raccoon dogs have elevated plasma leptin and growth hormone levels in the winter and depressed plasma cortisol and insulin concentrations during wintertime food deprivation. However, these parameters were not previously tested in the wild population. In the present study 37 wild raccoon dogs were sampled at different seasons and diverse biochemical variables were determined. The results mostly confirmed previous observations on farmraised raccoon dogs. The liver glycogen stores increased during the autumnal fattening period but were low in the winter. The liver glycogen phosphorylase activity decreased but lipase activity increased in the winter indicating the use of fat as the principal metabolic fuel. The plasma insulin concentrations were low in the winter allowing the release of fatty acids from adipose tissue. Low wintertime cortisol and thyroid hormone levels could contribute to protein sparing. Unlike on farms, wild raccoon dogs did not show seasonal fluctuations in their plasma ghrelin or growth hormone levels. The observed physiological phenomena emphasise the adaptation of the species to long periods of food scarcity in the winter.

A pilot study of protein sparing in healthy dogs using peripheral parenteral nutrition

Total parenteral nutrition is the standard nutritional support of dogs when the enteral route is contraindicated, but it can be difficult because of cost, technical difficulties, and potential complications. Peripheral parenteral nutrition (PPN) may be a feasible option for short-term support in some cases. The objectives of this study were to determine the effect of PPN on nitrogen balance (as an indicator of the effect on protein sparing), serum folate concentrations and serum insulin-like growth factor-I (IGF - I) concentrations in fasting dogs. The effect of PPN on these parameters has not previously been reported in dogs. Using a cross-over design, three healthy adult fasting dogs were randomly assigned to three treatments: 5 per cent amino acid solution, 5 per cent glucose solution, and a control electrolyte solution. The solutions were administered into a peripheral vein at 60 ml kg(-1)per day for 4 days. The amino acid infusion resulted in a positive nitrogen balance and the glucose infusion produced less nitrogen loss than the control. Amino acid, but not glucose or electrolyte infusions, decreased serum folate concentrations. Amino acid and glucose infusions resulted in higher serum IGF -I concentrations than electrolyte infusions, although the differences were small and IGF -I decreased in all cases. In conclusion, these findings suggest that PPN increases nitrogen balance in healthy dogs undergoing short-term fasting.

Hormones and metabolites of arctic foxes (Alopex lagopus) in response to season, starvation and re-feeding

Svalbard's arctic foxes experience large seasonal variations in light, temperature and food supply throughout the year, which may result in periods of starvation. The aim of this work is to investigate if there are seasonal variations in post-absorptive plasma thyroid hormones (free thyroxin (fT(4)), free triiodothyronine (fT(3)) and reverse triiodothyronine (rT(3))) and metabolites (free fatty-acids (FFA) and beta-hydroxybutyrate (beta-OHB)) with season and their response to starvation and re-feeding. The concentrations of post-absorptive free triiodothyronine were significantly higher in November than May, while those of thyroxin, reverse triiodothyronine, free fatty-acids and beta-hydroxybutyrate remained unchanged. Possible explanations for the seasonal variations in free triiodothyronine are discussed. There were no significant changes from post-absorptive concentrations of thyroxin and reverse triiodothyronine in starved and re-fed foxes. However, free triiodothyronine concentrations decreased during starvation and increased again with re-feeding both in May and November. Starvation induced high levels of free fatty acids in both May and November, indicating increased lipolysis. There was a significant increase in beta-hydroxybutyrate in November only, indicating that arctic foxes are capable of protein conservation during starvation.

Idiopathic epilepsy in dogs

Idiopathic epilepsy is a chronic condition characterized by recurrent seizures for which there is no identifiable cause. It is the most common neurologic disorder in the dog. This article discusses the diagnostic evaluation and rational treatment of dogs with recurrent seizures. Types of seizures, client education, choice of therapy, use of specific drugs, therapeutic monitoring, and nondrug treatments are reviewed.

Thyroid hormone loss and replacement during resuscitation from cardiac arrest in dogs

Circulating concentrations of thyroxine (T4), triiodothyronine (T3), and reverse triiodothyronine (rT3) were followed in dogs subjected to 9 min of normothermic ventricular fibrillation. Significant decreases were detected 12 h post-arrest when compared to pre-arrest levels in total T4 (P < 0.0005), free T4 (P < 0.0005), total T3 (P < 0.003), and free T3 (P < 0.003), and levels of reverse T3 were significantly elevated (P = 0.0001). Similar changes occurred with only 30 s of arrest. Post-arrest replacement therapy with 7.5 micrograms/kg per h (Rx-7.5) and 15 micrograms/kg per h (Rx-15) levothyroxine sodium (L-T4) increased total T4, free T4, and total T3 (P < 0.01). Free T3 decreased in the Rx-7.5 group (P < 0.01) and did not fall in the Rx-15 group (P = 0.16). Reverse T3 increased with either treatment (P < 0.005). Both treatment groups had higher levels of all five hormones than non-treated animals (P < 0.001). Neurologic function, assessed with a standardized scoring system, showed significant improvement in the treated groups by 6 h (P < 0.05, compared to non-treated group) and remained significant through 24 h post-arrest (P < 0.05). The documentation of rapid and dramatic changes in thyroid hormones immediately following cardiac arrest and resuscitation indicates a significant acute hypothyroid state that may potentially benefit from replacement therapy.

Importance of basal glucagon in maintaining hepatic glucose production during a prolonged fast in conscious dogs

We undertook studies in conscious dogs to assess the role of basal glucagon in stimulating glucose production after a 7-day fast. Two protocols consisting of a 40-min basal period (-40 to 0 min), and a 180-min test period (0-180 min) were used. During the test period of the first protocol (hormone replacement; n = 4), somatostatin was infused (0.8 micrograms.kg-1.min-1) along with basal intraportal replacement amounts of insulin and glucagon, whereas in the second protocol (glucagon deficiency; n = 5), somatostatin plus insulin alone were infused. Glucose production and gluconeogenesis were measured using tracer and arteriovenous difference techniques. Plasma insulin levels were similar during the test period in both protocols (6 +/- 1 microU/ml). The plasma immunoreactive glucagon level in the control protocol averaged 50 +/- 8 pg/ml, whereas in the glucagon-deficiency protocol the level fell from 50 +/- 8 to 29 +/- 8 pg/ml (P less than 0.05). The plasma glucose level and the rate of glucose production were unchanged during bihormonal replacement. During glucagon deficiency the plasma glucose level was held constant at 100 +/- 4 mg/dl by glucose infusion. Tracer-determined endogenous glucose production fell from 1.8 +/- 0.1 to 1.0 +/- 0.1 mg.kg-1.min-1 by 30 min (P less than 0.05). After 3 h of glucagon deficiency, gluconeogenic conversion of alanine to glucagon was reduced 40% and the hepatic fractional extraction of alanine was reduced by 45%. The efficiency of the gluconeogenic process within the liver was not altered by glucagon deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental induction of fasting hypoglycaemia and fatty liver syndrome in three Yorkshire terrier pups

Eight hours fasting in Yorkshire terrier pups resulted in marked variation of blood glucose, showing both hypo- en hyperglycaemia. Prolonged fasting in three Yorkshire terrier pups resulted in hypoglycaemia with concomitant ketosis and steatosis of the liver. The hypoglycaemia was associated with decreasing insulin and increasing glucagon and cortisol levels. This is in contrast to fasting adult dogs, which maintain glucohomeostasis and show only slightly decreased insulin levels, normal glucagon levels and a moderate increase of plasma ketone bodies. The reaction to an eight hour fasting period in the Yorkshire terrier pups is thought to be related to inadequate gluconeogenesis and diminished insulin production and/or release. The different reaction to prolonged fasting, compared to adult dogs and pups of larger breeds, seems related to inadequate gluconeogenesis and results in hypoglycaemia, a ketogenic hormonal setting and steatosis of the liver. Frequent feeding of a high-energy, protein-rich diet to both mother and pups may prevent toy-breed pups from developing hypoglycaemia and may help them to overcome periods with a decreased intake of energy.

Role of insulin and branched-chain amino acids in regulating protein metabolism during fasting

This study examines the independent effects of insulin and amino acids on protein metabolism after a 12-h and 4-day fast in healthy volunteers. Leucine (Leu) kinetics were examined during sequential insulin infusions of 0 (group I) or 0.0125 (groups II and III), 1.2, and 10 mU.kg-1.min-1. Plasma Leu was maintained at 12-h fasted levels in groups I and II and at 84-h fasted levels in group III. Four-day fast (vs. 1 day, P less than 0.01) was associated with a 79% drop in plasma insulin and elevations in plasma Leu (122%), Leu rates of appearance (Ra) (21%), and Leu oxidation (56%), and no change in nonoxidative rates of disappearance (Rd). Insulin resulted in a dose-dependent suppression of endogenous Leu Ra with group III = I greater than II. Leu oxidation rose 1.7-fold in group III at the highest insulin dose but remained stable in the two other groups. In conclusion, 4-day fasting is associated with enhanced proteolysis and Leu oxidation with no change in nonoxidative Rd (protein synthesis). Elevated branched-chain (and other) amino acids were required to restore tissue sensitivity and specificity to the effects of insulin on protein metabolism after 4 days of fasting.

Effect of hyperglucagonemia on hepatic glycogenolysis and gluconeogenesis after a prolonged fast

The aim of this study was to determine if glucagon can stimulate hepatic glucose production in prolonged fasted (7 days) animals. Two protocols were used; in one ("hormone replacement"; n = 4), intraportal basal replacement amounts of insulin and glucagon were given during a somatostatin infusion, whereas, in the other ("glucagon excess"; n = 5) basal insulin was given along with somatostatin and excess glucagon. Plasma insulin levels were similar and constant throughout both protocols (6 +/- 1 microU/ml). The plasma glucagon was basal in the hormone-replacement protocol (49 +/- 9 pg/ml) but rose from 46 +/- 7 to 448 +/- 35 pg/ml (P less than 0.05) in the other protocol. Plasma glucose levels and the rates of glucose production were unchanged during hormone replacement but rose from 100 +/- 5 to 199 +/- 28 mg/dl and from 1.5 +/- 0.1 to a peak of 5.6 +/- 0.2 mg.kg-1.min-1 at 15 min (P less than 0.05) and an eventual plateau of 2.7 +/- 0.2 mg.kg-1.min-1 (P less than 0.05) in response to glucagon excess. Because of the sluggish increase in gluconeogenic parameters, the early marked rise in glucose production was attributable to increased glycogenolysis. Eventually, however, the gluconeogenic rate rose, with net hepatic uptake of alanine increasing 50% and fractional alanine extraction doubling. Gluconeogenic efficiency and conversion increased in response to glucagon excess by 0.30 +/- 0.05 and 159 +/- 48%, respectively, although it should be noted that these parameters rose 0.15 +/- 0.06 and 150 +/- 49% in the hormone-replacement protocol. In conclusion, even after a prolonged fast physiological glucagon can cause hyperglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipomobilizing effects of procaterol and yohimbine in the conscious dog: comparison of endocrinological, metabolic and cardiovascular effects

1. Lipid mobilization during a hypocaloric diet may be enhanced by a pharmacological approach using beta 2-adrenoceptor agonists or alpha 2-adrenoceptor antagonists. Studies were undertaken in the dog, an animal model presenting fat cell antilipolytic alpha 2- and lipolytic beta-adrenoceptors, in order, firstly, to demonstrate the presence of beta 2 subtype adrenoceptors on adipocytes and, secondly, to compare the effects of procaterol (beta 2-adrenoceptor agonist) and of yohimbine (alpha 2-adrenoceptor antagonist) on metabolic, endocrinological and cardiovascular parameters. 2. Procaterol strongly stimulates lipolysis in dog adipocytes in vitro. The utilisation of selective beta 1- and beta 2-adrenoceptor antagonists (bisoprolol and ICI 118,551) in both lipolysis and binding studies (displacement of [3H]-dihydroalprenolol binding) demonstrated the presence of the two beta-adrenoceptor subtypes in dog fat cells. 3. Infusion of either yohimbine or procaterol (10 and 0.4 nmol min-1 kg-1, respectively for 30 min), provoked an equivalent increase in plasma non-esterified fatty acids (+100%). Procaterol, but not yohimbine, induced hyperglycaemia (+120%). Plasma insulin was weakly enhanced by yohimbine (+120%) as compared to the increase given by procaterol (+500%). 4. Both drugs stimulated sympathetic nervous system activity, as indicated by the increased plasma noradrenaline concentration, but only yohimbine increased the plasma adrenaline level. 5. Cardiovascular measurements indicated that procaterol strongly enhances heart rate and transiently decreases mean blood pressure. Yohimbine exhibits a weaker effect on heart rate and slightly increases mean blood pressure. 6. The present work clearly indicates that lipid mobilization is enhanced during fasting in the dog by selective beta 2-adrenoceptor stimulation or by alpha 2-adrenoceptor blockade. This enhanced lipolytic effect may result either from a direct action of the drugs on the adrenoceptors of fat cells or from an activation of the sympathetic nervous system. Procaterol suffers major limitations since it strongly increases heart rate, immunoreactive insulin and glycaemia. On the other hand, yohimbine induces only minor modifications both in cardiovascular and endocrinological parameters.

Effect of somatostatin on glucose homeostasis in conscious long-fasted dogs

The effects of somatostatin plus intraportal insulin and glucagon replacement (pancreatic clamp) on carbohydrate metabolism were studied in conscious dogs fasted for 7 days so that gluconeogenesis was a major contributor to total glucose production. By use of [3-3H]glucose, glucose production (Ra) and utilization (Rd) and glucose clearance were assessed before and after implementation of the pancreatic clamp. After an initial control period, somatostatin (0.8 microgram . kg-1 . min-1) was infused with intraportal replacement amounts of glucagon (0.42 ng . kg-1 . min-1) and insulin. The insulin infusion rate was varied to maintain euglycemia and then kept constant (68 +/- 16 microU . kg-1 . min-1) for 250 min. Plasma glucagon was similar (84 +/- 14 and 89 +/- 19 pg/ml) before and during somatostatin infusion, while plasma insulin was lower (9.3 +/- 0.9 and 6.6 +/- 0.5 microU/ml, P less than 0.05). Plasma glucose levels remained similar (89 +/- 2 and 96 +/- 9 mg/dl), while Ra and Rd and the ratio of glucose clearance to plasma insulin were significantly (P less than 0.05) increased (from 2.18 +/- 0.12 to 3.21 +/- 0.35 and 2.30 +/- 0.09 to 3.26 +/- 0.38 mg . kg-1 . min-1, and 0.30 +/- 0.03 to 0.59 +/- 0.11, respectively). Net hepatic lactate uptake and [14C]alanine plus [14C]lactate conversion to [14C]glucose increased (P greater than 0.05) (from 9.32 +/- 0.47 to 16.54 +/- 2.97 mumol . kg-1 . min-1 and 100 to 263 +/- 37%, respectively). In conclusion, somatostatin alters glucose clearance in 7-day fasted dogs, resulting in changes in several indices of carbohydrate metabolism.

Role of acidosis in regulating hepatic nitrogen metabolism during fasting in conscious dog

This study was designed to investigate the role that acidosis plays in the metabolic responses to fasting. Eighteen conscious dogs with surgically implanted catheters in the femoral artery and in the hepatic, portal, and renal veins were studied. Six were fasted for 24 h and 12 were fasted for 4 days (96 h). On the day of the study, six 4-day fasted dogs were infused intravenously with NaHCO3 (10 mumol X kg-1 X min-1) for 3 h, while the rest received saline and acted as controls. Splanchnic balances of glutamine, alanine, blood urea nitrogen, ammonia, lactate, beta-hydroxybutyrate, and acetoacetate were estimated using the Fick principle. Blood flow to the splanchnic and renal beds were estimated using indocyanine green and p-aminohippurate extraction methods, respectively. The infusion of NaHCO3 nearly abolished the base deficit associated with fasting and normalized arterial bicarbonate levels but did not alter blood pH. It suppressed but did not abolish hepatic glutamine output by 60%. This was associated with a shift in cytoplasmic and mitochondrial redox potentials of the hepatocyte as evident by a decrease in hepatic production of beta-hydroxybutyrate and an increase in hepatic production of acetoacetate and a decrease in hepatic lactate utilization. Concomitantly, renal glutamine uptake decreased. Glutamine release of skeletal muscle was unchanged. The data suggest that hepatic glutamine synthesis and release seen with 4-day fasting has two components: a bicarbonate-dependent component that is influenced by the redox potential of the hepatocyte and a bicarbonate-independent component, the nature of which is not yet clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver glycogen and plasma insulin and glucagon levels in food- and water-deprived black-tailed prairie dogs (Cynomys ludovicianus)

1. Liver glycogen levels and plasma levels of insulin and glucagon were measured in fed and in food- and water-deprived prairie dogs. 2. Liver glycogen values decreased from 45.5 to 12.4 mg/g (73%) after 21 days of food and water deprivation, while a 24-hr fast resulted in a liver glycogen value of 47.5 mg/g. 3. Rat liver glycogen values decreased from 45.6 to 2.3 mg/g (95%) after a 24-hr fast. 4. Prairie dog plasma insulin values were 69.2, 15.8 and 25.4 microU/ml in fed, and in 24-hr and 32-day food- and water-deprived animals, respectively. 5. Prairie dog plasma glucagon levels were 57.0 and 38.4 microU/ml in fed and in 32-day food- and water-deprived animals. 6. Plasma values for glucose, urea nitrogen, acetone and triglyceride agreed with previously published results. 7. We conclude that it is possible that the maintenance of liver glycogen levels in food- and water-deprived prairie dogs may be correlated with a smaller decrease in plasma insulin levels, relative to other species, and with a decrease in plasma glucagon levels.

The effect of long-term fasting on ketone body metabolism in the dog

Ketone-body metabolism was studied in overnight-fasted and in 10-days fasted dogs by a ketone-body tolerance test and by infusing [14C]ketone bodies. Clearance of ketone bodies from the blood was significantly decreased after 10 days of fasting. The utilization of ketone bodies was, however, significantly higher in the fasted animals due to the increase in blood ketone-body concentrations. It is concluded that the low level of ketone bodies, which is characteristic for fasting dogs, results from an efficient peripheral utilization. The contribution of ketone bodies to the daily energy requirement of the dog has been tentatively estimated to increase from 7% in the overnight-fasted state to 13% after 10 days of starvation.

Propylthiouracil, ipodate, dexamethasone and periods of fasting induce different variations in serum rT3 in dogs

Fasting or administration of propylthiouracil (PTU), ipodate, or dexamethasone are all known to induce a pattern of low serum triiodothyronine (T3) concentrations and high serum reverse T3 (rT3) concentrations in humans. In the present study it was found that this is not a universal phenomenon. In normal dogs exposed to fasting or these various pharmacologic agents, the serum T3 level was always depressed as in humans. However, different variations in serum rT3 levels were observed. Fasting and PTU administration were accompanied by slight decreases in the serum rT3 concentration. A single dose of ipodate did not alter serum rT3 levels, but serum thyroxine (T4) levels increased by more than 50%. Dexamethasone induced a considerable increase in serum rT3 levels, while serum T4 levels were unaltered. The results suggest that the high serum rT3 level nearly always seen in "the low T3 syndrome" in humans is merely a coincidental character of the human species, and that it has little importance for in vivo homeostasis.

Ketogenesis in mitochondria isolated from liver biopsies of normal and starved dogs: comparison with rat-liver mitochondria

Fatty acid oxidation and ketogenesis were studied in isolated dog-liver mitochondria in order to investigate whether the absence of hyperketonemia in fasting dogs results from a low capacity of hepatic ketogenesis. Isolated rat-liver mitochondria were used as reference. The results indicate that: (a) Dog-liver mitochondria oxidize long-chain fatty acids and produce ketone bodies at about equal rates as rat-liver mitochondria. No differences were detected in the regulation of ketogenesis. (b) Rates of oxidation of medium-chain fatty acids are significantly lower in dog-liver mitochondria than in rat-liver mitochondria. (c) Fasting does not influence the capacity of liver mitochondria for fatty acid oxidation but their ketogenic capacity is slightly enhanced in both species. The regulation of the energy metabolism in the fasting dog is discussed and compared with that in other mammalian species.

Glycogenolysis in the fasting dog

Glycogen concentrations were determined in liver-biopsy specimens which were taken from four dogs during five consecutive days of fasting. It was found that maximal depletion of liver glycogen occurred between the second and the third day. Starvation-induced glycogenolysis was much slower in the dog than in men and rats. Fuel fluxes are discussed and it is tentatively concluded that in the fasting dog larger amounts of glycerol are available for gluconeogenesis than in other species.