Effects of fasting on the blood chemistry of the rattlesnake, Crotalus atrox

Glucosensing and glucose homeostasis: from fish to mammals

This review is focused on two topics related to glucose in vertebrates. In a first section devoted to glucose homeostasis we describe how glucose levels fluctuate and are regulated in different classes of vertebrates. The detection of these fluctuations is essential for homeostasis and for other physiological processes such as regulation of food intake. The capacity of that detection is known as glucosensing, and the different mechanisms through which it occurs are known as glucosensors. Different glucosensor mechanisms have been demonstrated in different tissues and organs of rodents and humans whereas the information obtained for other vertebrates is scarce. In the second section of the review we describe the present knowledge regarding glucosensor mechanisms in different groups of vertebrates, with special emphasis in fish.

Starvation physiology: reviewing the different strategies animals use to survive a common challenge

All animals face the possibility of limitations in food resources that could ultimately lead to starvation-induced mortality. The primary goal of this review is to characterize the various physiological strategies that allow different animals to survive starvation. The ancillary goals of this work are to identify areas in which investigations of starvation can be improved and to discuss recent advances and emerging directions in starvation research. The ubiquity of food limitation among animals, inconsistent terminology associated with starvation and fasting, and rationale for scientific investigations into starvation are discussed. Similarities and differences with regard to carbohydrate, lipid, and protein metabolism during starvation are also examined in a comparative context. Examples from the literature are used to underscore areas in which reporting and statistical practices, particularly those involved with starvation-induced changes in body composition and starvation-induced hypometabolism can be improved. The review concludes by highlighting several recent advances and promising research directions in starvation physiology. Because the hundreds of studies reviewed here vary so widely in their experimental designs and treatments, formal comparisons of starvation responses among studies and taxa are generally precluded; nevertheless, it is my aim to provide a starting point from which we may develop novel approaches, tools, and hypotheses to facilitate meaningful investigations into the physiology of starvation in animals.

A seasonally dependent change in the distribution and physiological condition of Caiman crocodilus yacare in the Paraguay River Basin

The distribution and physiological condition of 116 Caiman crocodilus yacare was assessed over one year in the Southern Pantanal. Body mass and intermediary plasma metabolites were measured at three different time periods, representing large differences in the abundance of surface water. During the wet season the study site was completely submerged under water and C.c. yacare were distributed evenly throughout. High levels of [glucose] and [triglyceride] in the plasma indicated regular feeding. As the dry season progressed C.c. yacare became increasingly crowded around the remaining ponds. They showed a reduction in plasma [glucose] and [triglyceride], and an increase in plasma [β-hydroxy-butyrate], signifying that they were feeding less and utilising fat reserves. At this sampling period, ~40% of the male C. c. yacare that were >10 years old inhabited dry grassland and did not have access to water. These animals were significantly lighter than males of a similar length that had immediate water access, and plasma [uric acid] indicated that they had not fed for a long time and were metabolising tissue proteins. Essentially, the adult male C.c. yacare that inhabited dry grassland were in a state of energy deficiency. This was so severe in some animals that recovery seemed unlikely. The study suggests that fluctuations in the abundance of surface ground water may influence the size and structure of the C. c. yacare population in the Pantanal.

Snakes survive starvation by employing supply- and demand-side economic strategies

Animals vary widely in their abilities to tolerate extended periods of food limitation. Although some snakes are known for their unique ability to survive periods of inanition that last up to 2 years, very little is known about the biological mechanisms that allow them to do this. Consequently, the present study examined physiological, compositional, and morphological responses to 168 days of starvation among three distantly related snake species (i.e., ball python, Python regius; ratsnake, Elaphe obsoleta; and western diamondback rattlesnake, Crotalus atrox). Results revealed that each of these species was able to successfully tolerate starvation by adaptively utilizing supply- and demand-side regulatory strategies. Effective demand-side strategies included the ability of snakes to depress their resting metabolic demands by up to 72%. Moreover, supply-side regulation of resources was evidenced by the ability of snakes to spare their structurally critical protein stores at the expense of lipid catabolism. Such physiological strategies for minimizing endogenous mass and energy flux during periods of resource limitation might help explain the evolutionary persistence of snakes over the past 100 million years, as well as the repeated radiation of snake lineages into relatively low-energy environments. The final section of this study outlines a novel modeling approach developed to characterize material and chemical flux through animals during complete inanition. This approach was used to make comparisons about the efficacy of various supply- and demand-side starvation strategies among the three species examined, but could also be used to make similar comparisons among other types of animals.

Western Diamondback Rattlesnakes Demonstrate Physiological and Biochemical Strategies for Tolerating Prolonged Starvation

Because of the uncertainty in food resources in nature, all animals face the possibility of imposed periods of fasting (i.e., starvation) at some point in their lives. I investigated physiological and biochemical responses to starvation that occur in a species of rattlesnake known to tolerate successfully prolonged periods of starvation in the wild. Sixteen subadult Crotalus atrox were fasted for up to 24 wk under controlled conditions simulating their active season. Snakes exhibited significant reductions in plasma glucose but increased circulating ketone bodies. Fasting snakes lost mass at a linear rate and increased their relative moisture content during the experiment. The bodies of fasting snakes demonstrated an increase in their fatty acid (FA) unsaturation index and were apparently able to "spare" essential FAs effectively from beta -oxidation. Endogenous essential and nonessential amino acids were used indiscriminately to fuel energetic requirements, suggesting that essential amino acids are not preferentially spared during starvation. The (15)N signature of excreted nitrogenous waste increased significantly, presumably as a result of shifting amino acid source pools during starvation. Because our comparative knowledge of starvation physiology contains large taxonomic gaps, particularly with respect to amphibians and reptiles, an understanding of the biological responses exhibited by these animals may offer insight into the evolution of physiological strategies animals employ to cope with the pressures of starvation.

Effect of age, starvation and circadian rhythm on the ascorbic acid content and succinic dehydrogenase activity of the kidney of male garden lizard, Calotes versicolor

Both ascorbic acid content and SDH activity of kidney reached peak levels during sexual maturity and then declined. Starvation stress (21 days) induced low levels of ascorbic acid content and SDH activity of the kidney. Nocturnal levels of ascorbic acid content and SDH activity were significantly lower than the diurnal values.

Anticoagulants for avian and reptilian blood: heparin and EDTA

The effectiveness of EDTA (dipotassium and disodium salts) and heparin as anticoagulants for the blood of puffadders and pigeons has been investigated. In the case of the snakes all three substances produced haemolysis after variable time intervals, and increases in cell volume were observed. In the case of the pigeons, samples stored at 4 degrees C showed lower haematocrit values and haemolysed sooner than samples stored at room temperature.