Chapter 50, Problem 1Q

Summary Introduction

To review:

The changes in blood triglycerides, lactate, and succinate levels due to seasonal variations in relation to the changes in bears metabolism between summer and winter.

Given:

Researchers took brown bears (Ursus arctos) for the study of gut microbiota in food digestion and in many other aspects of nutrition. Brown bears undergo hibernation in the drastic winters. Researchers study whether microbiome of the bear’s gut was different or not, before and after the fasting. For this, the blood along with the fecal sample from 16 free-ranging brown bears has taken during hibernation (February or March) and following hibernation (June) for further study. The fecal samples were analyzed for the presence of different microbe communities, while the blood was tested for triglycerides and other nutrients.

The graphs given below were plotted by the researchers after observing the conditions. Graph1 shows the presence of different composition of microbiome during different seasons. Also, the differences in the blood levels of triglycerides, lactate, and succinate are depicted.

The researchers also examined the effects of these microbiota when introduced into germ-free mice. Germ-free mice, unlike normal mice are devoid of gut microbiota and are unable to gain mass when they are kept on a high-fat diet. Fecal transplants from summer or winter bears were given to the germ-free mice. Graph 2 shows the changes in body mass, fat content, and blood triglyceride levels of the mice after 2 weeks.

Graph 1: The two graphs showing the differences in the gut microbiome of the bear and the content of blood triglycerides, lactate, and succinate during the summers and winters.

Graph 2: The graph showing the differences in the body mass, fat content, and blood triglycerides level of the germ-free mice taken for the experiments and injected with the fecal transplants of bears.

Introduction:

Hibernation may be defined as the behavior of animals in unfavorable winters where they becomes inactive and sleeps for a particular interval of time. The animals do not eat during hibernation, thus, they use the stored fat to meet the energy requirements. Before the onset of hibernation, the animals keep on eating to increase their stored fat content.

Explanation of Solution

It was observed that the levels of blood triglycerides in bears were present in a higher amount in winters than summers. The bears undergo hibernation in winters and during hibernation, energy required by the body is obtained by the lipolysis (breakdown or oxidation of lipids) of the stored fat. Also, the lactate content in the body of bears was observed to be in lesser amounts during winters than in summers and the succinate (for gluconeogenesis) content of the body was higher in the winters.

The given data indicates that bears use mobilization and oxidation of lipids along with reduced glucose utilization and increased gluconeogenesis (generation of new glucose) as a survival strategy during hibernation. These strategies help the bears to cope up with the harsh winter environments.

Conclusion

Thus, it is concluded from the data that in bears, the blood triglycerides and succinate content were present in a higher amount in winters during hibernation as compared to summers while the lactate content was present in lower amounts in the winters. The difference in the content of all three components in summers and winters help the bears to cope up with harsh winters.