Glucose Loading & Dehydration in The Camel

Glucose loading and dehydration in the camel

In mammals, insulin stimulates glucose uptake, so no glucose is left in urine unless the critical point is reached where glucose transporters are saturated, and reabsorption rate is exceeded (renal threshold). When dehydrated, camels can implement various physiological mechanisms to prevent gross losses of existing body water supplies. Mechanisms include increasing body temperature, excretion of concentrated urine and CO2 storage. This article encompasses an experiment where five adult female camels were tested under different physiological conditions (dehydration then rehydration) following glucose loading in each case and tracked down for the possible mechanisms which camels put into action to maintain homeostasis. The results of the study showed that camels have higher plasma glucose level during dry season than during green season.• Camels adjust their bodies so that glucose/insulin ratio remains stable (unchanged) in cases of dehydration to maintain blood osmolarity.•Renal handling of glucose is different during water deprivation where latent period before filtration and glomerular filtration rate (GFR) are altered so that water can be retained and minimize any fluid loss.

Camels are mammals with an extraordinary ability to survive extreme cases of dehydration and resources scarce. Article 1 published in 1976 poses many questions about the ability of camels to adapt and the mechanisms they evolved to compensate for instances of water deprivation. The first question this article raises is what happens to the body of camels when a sudden surge of blood glucose occurs in cases of dehydration and hydration? The most part of this article deals with the question. Experimenters administered glucose injections to five adult female camels previously deprived of water for ten days and checked how their bodies dealt with the surge in glucose over a period of three days, and then compared the results to data of camels with hydrated bodies. This study showed that camels adjust their circulatory and excretory systems so that they minimize the loss of fluids, especially through urine, but also strive to maintain blood glucose levels stable so that blood osmolarity does not shift and cause cells to malfunction.

Another question raised by the study is that even in cases of glucose loading while dehydrated, how do camels maintain osmolarity while not excreting any glucose? Further hormonal testing’s, which were the main lead in the 1970’s, showed an increased sensitivity to insulin which enhances the work of glucose transporters causing glucose Tm to increase, and consequently more glucose uptake and storage. However, many questions are yet to be discussed as researchers continue their experiments to uncover the evolutionary puzzle about camels. Article 1 leaves us with questions about the relationship between body temperature of camels and levels of dehydration? Another question of interest, in case of dehydration, any additional solutes ingested are to increase the osmolarity of blood, putting camels at a disadvantage of high osmolarity which impairs many physiological functions and increases urine output to excrete any additional solutes; consequently, additional water is lost, in a case where body strives to preserve water because of dehydration. How do camels compensate for this issue? As we dive into article 2, these questions are studied, and answers are proposed.

Daily regulation of body temperature rhythm in the camel (Camelus dromedarius) exposed to experimental desert conditions. (2014) Rhythmicity is a shared property of all organisms, and of a great importance mainly through pineal gland secretion of melatonin. Circadian clock, located in SCN of hypothalamus, plays an essential role in controlling rhythmic processes and circadian biological rhythms. The aim of the present work was thus to study the nature of daily Tb rhythm in the camel and to determine its relationship with the circadian system under challenging conditions mimicking the desert environment.• Camels are continuously exposed to heat, solar radiation, and water and food deprivation, but they succeed at adapting to this harsh environment through behavioral, anatomical and physiological characteristics that allow them to economize water and regulate their body temperatures. Two experiments were conducted on six healthy female camels designed to define the process of heterothermy in dehydrated camels (exp.1) and investigate the effect of food intake reduction during dehydration (exp.2).•

Observations clearly establish that water deprivation during exposure to daily heat has a significant effect on the amplitude of daily/circadian Tb rhythms in the camel (adaptive heterothermy).• The process of decreasing food intake in dehydrated camels is closely related with heterothermic regulation, and aids in decreasing body metabolic needs, an adaptive mechanism to conserve energy, water, and further regulate body temperatures in harsh environments like deserts. Transition 2:Article 2 focuses on rhythmic and cellular processes. It is important to keep in mind that approximately half a century exists between article 1 published in 1976 and article 2 published in 2014. During that period, science experienced a technological revolution that permitted scientists and researches to discover subcellular processes, functions, and mechanisms that further explains the behavior and anatomy of many organisms. The first question article 2 discusses; what is the relation between camels’ body temperatures (Tb) and heat regulation?

Experiment 1 proved that camels keep their temperatures within a strict scale of 12L/12D (light and dark cycle) despite the great fluctuation of temperatures in deserts during the day-night cycle and the day to day switches. It was established that dehydration and heat stress have a great impact on the circadian cycle, which permitted camels, who conferred an evolutionary advantage, to embrace adaptive heterothermy characterized by a double switch to adapt to prolonged periods of water deprivation and heat. This has been referred to as thermoregulatory plasticity. The other question at hand deals with food intake, heat stress and dehydration. Experiment 2 results proved that when camels are dehydrated, they decrease the amount of food they intake to control their metabolic processes and regulate their body temperatures. This was proved as the weight of camels in this experiment decreased gradually over the course of dehydration.

The conclusion drawn links metabolic processes with energy storage and food intake. Metabolic processes under heat stress result in additional heat that camels struggle to lose especially in extremely hot environments. This causes them to lose more energy for thermal regulation rather than storing it. Also, with the changes of blood osmolarity as discussed before, additional effort is spent to maintain homeostasis and prevent any further water loss. All that puts dehydrated camels at a disadvantage; consequently, camels reduce their daily intake so that neither waste heat energy is lost, nor they are deprived of food. As we move on in time, article 3 which was published in 2017, argues the genetic code that encodes different enzymes and proteins that allow camels to rapidly adapt to the harsh environment of the desert. Knowing that many plants that inhabit the deserts are toxic or high in salt. The question is then how do camels process this food without being hurt? Also, Cytochrome P450, which was isolated from camels and showed a fast rate of evolution, what is its function? What advantage does its evolution confer?

Diversity and distribution of CYP gene family in Bactrian camel. (2017)• Deserts are mainly inhabited by toxic/salty plants that camels continuously eat and survive on. How are camels not harmed by these plants?• Genomic studies showed that camels’ genome evolved much faster than cows or humans, and most of these mutations were in the metabolic pathway.• Cytochrome P450 is a large family of mixed functional enzymes that participate in the digestion and processing of the food camels eat, most of which are toxic and carcinogenic inducing plants.• Sampling and DNA extractions, sequencing and establishing databases, contig splicing, gene predictions and functional annotation and analysis of the CYP genome of camels where all methods used to test for the CYP genes of camels. These genes were mainly associated with metabolic pathway, an observation that suggests that camels have evolved these genes as a method to adapt to living in deserts and the few resources it offers.• The main evolved genes included insulin pathways, mTOR pathway, and many other metabolic pathways, all of which are associated with glucose homeostasis in camels and contributed to increased glucose and insulin tolerance in these organisms.• It was concluded that many of these CYP genes duplicated and mutated which made it possible for camels to be toxin and glucose tolerant, able to feed and survive of the very few resources that the harsh environment of the desert has to offer.

References:

1. Yagil, R. & Berlyne, G.M. (1976, October 1). Glucose loading and dehydration in the camel. Retrieved from https://www-physiology-org.proxy.lib.wayne.edu/doi/pdf/10.1152/jappl.1977.42.5.690
2. Bouaouda, H. et al. (2014, August 12). Daily regulation of body temperature rhythm in the camel (Camelus dromedarius) exposed to experimental desert conditions. Retrieved from https://physoc.onlinelibrary.wiley.com/doi/epdf/10.14814/phy2.12151
3. Hasi, S. et al. (2017, September 12). Diversity and distribution of CYP gene family in Bactrian camel. Retrieved from https://link-springer-com.proxy.lib.wayne.edu/article/10.1007%2Fs10142-017-0571