Correlation of plasma norepinephrine and plasma atrial natriuretic factor during lower body negative pressure

Plasma atrial natriuretic factor (ANF) is released in proportion to intra-atrial pressures. Plasma norepinephrine (NE) levels are considered to be an indirect reflection of sympathetic tone. These two mediators were studied during human regulation of intravascular volume in the course of exposure to fluid shifts associated with a model of gravitational stress, lower body negative pressure (LBNP.) Blood was drawn from 10 normal subjects before and after exposure to 2 min of a graduated increase in LBNP to a level of 55 mmHg followed by 5 min at 55 mmHg. Plasma ANF was measured by RIA and catecholamines by HPLC-ECD. NE increased from 358 +/- 44 (S.E.M) pg/ml to 511 +/- 48 pg/ml (p = 0.03.) Although ANF only decreased from 27.3 +/- 2.4 pg/ml to 23.5 +/- 2.9 pg/ml (p = 0.33,) a statistically significant negative correlation was observed (r = -0.70, p = 0.02) between the changes in NE and ANF induced by LBNP. The modelling of physiologic responses to gravitational stress in this experiment revealed a negative correlation between changes in sympathetic tone (as reflected by plasma NE) and ANF levels.