ABSTRACT
We tested the response of plasma atrial natriuretic peptide (ANP) levels to the following physiological stimuli: postural changes; head-out water immersion; and physical exercise. Plasma ANP (p-ANP) levels were assessed by a specific, sensitive radio-immunoassay. Plasma ANP rose significantly when posture shifted from upright to recumbent for 1 h, but fell again to basal values after 10 min standing. Circadian variations did not affect the posture study. Head-out water immersion produced a prompt and remarkable (sevenfold) increase in p-ANP, with a plateau reached after 1 h and held until the end of the experiment (2 h). Plasma ANP levels were measured in 10 normal subjects performing supine treadmill exercise at 50% of maximum aerobic capacity for 30 min. Plasma ANP rose from baseline supine values after 15 min exercise, and remained elevated during the following 15 min exercise. During the recovery phase ANP showed a trend towards baseline values, with a 38% decrease attained after 30 min. We propose that the above tests could be used as ANP-stimulating manoeuvres in physiological and clinical conditions in man.
