Water conservation in camels aided by cholesterol!

Komal Bavaskar, Mumbai university

Camels are large animals with long legs, a large nose, and a humped back. They are divided into two types: dromedary camels with one hump and Bactrian camels with two humps. Arabian camels are also called dromedary camels are found in the Middle East & North Africa. The scientific name Camelus dromedarius was given in 1758 by Swedish naturalist Carl Linnaeus, who was only familiar with the domestic type.

The humps allow camels to survive an extremely long up to 2 weeks without food. Because camels typically live in the desert where food can be scarce for a very long stretch. Camel water consumption is 5 gallons per day. Camel may lose 25 liters of water from its body tissue without harm. That indicates the camel’s body tissues have already stored all of the water the camel requires.

Camels are very adept at saving water. Camel can withstand huge body temperature fluctuations, which helps them preserve water. They may begin the day with a body temperature of 320C and increase to a maximum of 400C. Only at the extreme temperature range, it needs to sweat to avoid overheating.

Role of the hump in fighting water deficiency:

Camels’ humps are made up of fat that has been stored and might be metabolized when food and water are limited. The camel’s humps also assist in regulating its body temperature, which is crucial within the desert, where temperatures could also be extremely hot during the day and significantly lower at night. Due to fatty tissue in the hump, they are ready to reduce heat insulation throughout their body, in the day when the temperature increases, body temperature also increases. Then night, the excess heat is then dissipated throughout the camel’s body at night, ensuring that their body temperature does not drop too low as the temperature drops.

Although the humps do not retain water, camels are highly efficient in terms of the quantity of water they utilize per day, which is why they can go nearly a week without drinking. This is because camel blood cells are oval, enabling them to absorb a huge amount of water (up to 30 liters in one go). After all, the cells are more elastic and can alter shape more quickly.

Other adaptations for water conservation:

In dromedaries, the kidney produces concentrated urine and hence conserves water. The camel kidney is smooth, bean-shaped, multi-lobe, and uni-papillary, with complete fusion of renal papillae producing renal papilla or crest that channels urine into a central renal pelvis. The renal pelvis is known to influence urine concentration by recycling urea to enhance medullary osmotic concentration, which favors the counter-current mechanism. The renal pelvis of the camel contains a major crescentic cavity that follows the kidney’s long axis and curvature. The crescentic main cavity of the pelvis divides into 20–24 three-dimensional radiating collateral recesses that contain the medullary pyramids. The renal pelvis is directly connected to the renal medulla. This wide pelvic-medullary interface is bordered by simple low cuboidal epithelium& also due to the tight connection of the renal pelvis and medulla, there is a high surface area for water & urea recycling from the pelvic urine into the medulla and contributes directly to urine concentration. This means there are more solutes and less water in urine.

Hence, during dehydration camels can preserve the water. Because of lower solute loads, plasma loads and tubular loads in the kidney resulted in the trapping of components in the plasma to store more water. Therefore, producing concentrated urine to store water is an essential factor in camels.

Another feature is cholesterol level is related to water conservation in camels. Hundreds of genes and proteins are altered in both the renal cortex and medulla of dehydrated & rehydrated animals. During chronic dehydration, the majority of genes and proteins involved in the synthesized cholesterol pathway were downregulated in the dromedary’s kidney. Hence, cholesterol may play a role in water conservation during dehydration. Also, several ion and water transporters are well known to be influenced directly or indirectly by cholesterol levels in the cell. As cholesterol in the plasma membrane was found to be lower in dehydrated dromedary’s kidney. The suppression of the cholesterol synthesis process and the resultant reduction in membrane cholesterol may enhance ion & water transport in the kidney of dehydrated camels. Cholesterol depletion increases the activity of ion&water transport, across the renal nephron, facilitating water reabsorption.

Responses of dromedary camels to dehydration: –

Camels can alter the production of hormones that affect sodium and water balance. The hormone system serves to retain water or sodium and maintain circulatory and renal activity. A liver receptor study was carried out by inhibiting angiotensin II type AT1 with losartan and this administration has affected body weight, serum creatinine, and urea response to dehydration. Dehydration increased serum urea and creatinine levels, indicating a significant decrease in glomerular filtration rate. Dehydration caused significant increases in serum sodium, urea, and creatinine and also a significant decrease in body weight, activation of the renin-angiotensin system, and increased circulating levels of AVP. The plasma level of aldosterone changes as the sodium level rises. Hence, the renin-angiotensin system most likely helps to maintain circulatory homeostasis and kidney function in the camel during dehydration.

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References:                                                           

1. Alvira-Iraizoz, F., Gillard, B. T., Lin, P., Paterson, A., Pauža, A. G., Ali, M. A., Alabsi, A. H., Burger, P. A., Hamadi, N., Adem, A., Murphy, D., & Greenwood, M. P. (2021). Multiomic analysis of the Arabian camel (Camelus dromedarius) kidney reveals a role for cholesterol in water conservation. Communications Biology, 4(1), 779. https://doi.org/10.1038/s42003-021-02327-3

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