Atrial natriuretic peptide in plasma after prolonged physical strain, energy deficiency and sleep deprivation

Plasma concentrations of atrial natriuretic peptide (ANP) were investigated daily in 16 male cadets during a 6-day military training course with continuous heavy physical activities, sleep and energy deficiency (course I). At the end of another similar course (course II) 15 cadets were studied during 30-min cycle exercise at 50% maximal oxygen uptake with and without glucose infusion. A small, but not significant increase was found in the plasma concentrations of ANP during course I from 9.6 (SEM 1.1) pmol.l-1 in the control experiment to 11.1 (SEM 0.5) pmol.l-1 on day 5. During course II a small but significant increase was found from 7.8 (SEM 0.5) pmol.l-1 in the control experiment to 9.1 (SEM 0.5) pmol.l-1 at the end of the course. Plasma osmolality and chloride concentration decreased during the course. During the exercise test a significant increase was seen in ANP concentration from 8.2 (SEM 0.8) to 13.1 (SEM 2.0) pmol.l-1 in the control experiment and from 9.4 (SEM 0.7) to 13.5 (SEM 1.2) pmol.l-1 during the course. This response was attenuated by glucose infusion, an effect which may have been due to an exercise induced increase in plasma chloride concentration being abolished. In contrast, the potassium concentration response to exercise was increased during the course but unaffected by glucose infusion. In conclusion, the large increases in endogenous plasma catecholamine concentration shown to take place during previous courses were not reflected in the plasma concentrations of ANP, indicating only a moderate cardiac stress or no cardiac work overload during such courses.