The effects of an active versus an inactive lifestyle on the renal function during exercise and dehydration

The renal perfusion in rest is approximately 20-25% of the cardiac output and
it is of great importance for a normal functioning of the human body. An
important function of the kidneys is maintaining of the water and salt
homeostasis. Dehydration is the reduction of the body mass (>2%) by excessive
fluid loss. Next to the negative consequences of dehydration on exercise
performance, dehydration also increase the risk to develop heat-related
illnesses, fatigue/exhaustion, loss of coordination and loss of consciousness.
During exercise and dehydration the renal function will change. For example
there is a decrease in renal perfusion, which results in a lower renal
clearance of wast products. Furthermore, two mechanisms to maintain the water
and salt balance will be activated. First of all, there is an increased
secretion of the arginin vasopressin (AVP), which stimulates the reabsorption
of water by the kidneys. Second, the renin angiotensin aldosteron pathway
become activated, resulting in a higher reabsorption of water and salt in the
renal tubules. However, it is unknown if the responses to exercise and
dehydration are different between healthy active males and inactive males. If
the adaptaptional ability of the kidneys are different, this will give us the
important new insight that exercise is good for maintaining the osmo- and fluid
balance, which indicates that the renal function have benefits from exercise. A
better adaptational ability of the kidneys may possibly be an advantage in
other (clinical) situations and/or disturbances.

The primary objective of this study is to examine if the respones of the
kidneys to exercise and dehydration are different between healthy active and
inactive males.

Observational study

During the study the subjects are exposed to two exercise test, including one
maximal exercise test. Maximal exercise testing is safe and not associated with
health risks. Moreover, subjects are medically screened prior to the exercise
and the test location is provided with an AED and an emergency box with
emergency medications. This emergency box is compiled and checked by the
pharmachy of the Radboudumc. During the proposed study a blood sample will be
taken four times using a vena punction. The blood sample will be used to
determine the osmolarity, creatinine concentration, plasma copeptide
concentration and plasma renine activity. The collection of a blood sample with
a vena punction is a frequently used medical intervention without any risks, in
particular because the vena punction will be performed by an experienced
employee.A potential negative effect of the vena punction could be the
development of a small haemorrhage. However, the incidence is low (5%),
completely reversibel and not a limiting factor in daily life. Next to the
blood samples, a urine sample will be collected three times during the study.
The total load of these provisions, both physically and in time, are minimal
provide important information necessary for answering the main question