ADRENALINE STIMULATED CYCLIC ADENOSINE-MONOPHOSPHATE RESPONSE IN LEUKOCYTES IS REDUCED AFTER PROLONGED PHYSICAL-ACTIVITY COMBINED WITH SLEEP AND ENERGY DEPRIVATION

The mechanism for adrenergic desensitisation during physical stress wa s studied by measuring [I-125] cyanopindolol ([I-125]CYP) binding site s and the adrenaline stimulated cyclic adenosine monophosphate (cAMP) responses in peripheral blood leucocytes from ten male cadets during a 5-day military training course. The cadets had physical activities ar ound the clock corresponding to a daily energy consumption of about 40 ,000 kJ but with an intake of only 2,000 kJ, and only 1-3 h of sleep i n the 5 days. During the course, the maximal cAMP response to adrenali ne stimulation was reduced to about 45% in granulocytes and to 52% in mononuclear cells, and the half maximal response was obtained only at 5-10 times higher adrenaline concentrations than in the control experi ment. The binding sites for [I-125]-CYP in mononuclear cells increased during the course. However, [I-125]-CYP measured not only surface rec eptors but also intracellular receptors and might even have represente d other binding sites. In conclusion, this study showed that decreased cAMP response to adrenergic stimulation would seem to be one of the m echanisms behind adrenergic desensitisation during stress.