Fasting for 21days leads to changes in adipose tissue and liver physiology in juvenile checkered garter snakes (Thamnophis marcianus)

Ultrasonographic evaluation of the liver and gallbladder and hepatic histogram of non-venomous snakes

This study aimed to describe sonographic features of the liver, gallbladder and hepatic histogram from grey-scale ultrasound in three species of healthy non-venomous snakes. Twenty-eight adult snakes were enrolled in the study, including 10 common boas (Boa constrictor), eight black-tailed pythons (Python molurus) and 10 rainbow boas (Epicrates crassus). The snakes fasted for 30 days and were manually restrained while conscious. For B. constrictor and P. molurus the liver and gallbladder were best visualized in ventral recumbency, and E. crassus in dorsal recumbency. A single elongated hepatic lobe was identified in all snakes. The gallbladder was positioned caudal and separated from the liver, with an oval shape and homogeneous anechoic content in the lumen, and thin and regular walls. A region of interest by pixel number was chosen for the liver, fat bodies, left kidney, and splenopancreas. The mean grey level (G) of the organs had significant differences within each species. Standard deviation of grey levels (SG ) had significant differences within B. constrictor and E. crassus. P. molurus had no significant difference among organs. The comparison among snakes showed that E. crassus had G of liver and splenopancreas lower than B. constrictor and P. molurus. The SG of the liver in E. crassus was lowest compared to B. constrictor and P. molurus. P. molurus showed the highest values in mean of G and SG . In conclusion, despite the liver and gallbladder having similar sonographic features, the grey-level histogram showed that liver echotexture and echogenicity differ among species.

The physiology of lipid storage and use in reptiles

Lipid metabolism is central to understanding whole-animal energetics. Reptiles store most excess energy in lipid form, mobilise those lipids when needed to meet energetic demands, and invest lipids in eggs to provide the primary source of energy to developing embryos. Here, I review the mechanisms by which non-avian reptiles store, transport, and use lipids. Many aspects of lipid absorption, transport, and storage appear to be similar to birds, including the hepatic synthesis of lipids from glucose substrates, the transport of triglycerides in lipoproteins, and the storage of lipids in adipose tissue, although adipose tissue in non-avian reptiles is usually concentrated in abdominal fat bodies or the tail. Seasonal changes in fat stores suggest that lipid storage is primarily for reproduction in most species, rather than for maintenance during aphagic periods. The effects of fasting on plasma lipid metabolites can differ from mammals and birds due to the ability of non-avian reptiles to reduce their metabolism drastically during extended fasts. The effect of fasting on levels of plasma ketones is species specific: β-hydroxybutyrate concentration may rise or fall during fasting. I also describe the process by which the bulk of lipids are deposited into oocytes during vitellogenesis. Although this process is sometimes ascribed to vitellogenin-based transport in reptiles, the majority of lipid deposition occurs via triglycerides packaged in very-low-density lipoproteins (VLDLs), based on physiological, histological, biochemical, comparative, and genomic evidence. I also discuss the evidence for non-avian reptiles using 'yolk-targeted' VLDLs during vitellogenesis. The major physiological states - feeding, fasting, and vitellogenesis - have different effects on plasma lipid metabolites, and I discuss the possibilities and potential problems of using plasma metabolites to diagnose feeding condition in non-avian reptiles.