Nonosmotic influences on osmotic stimulation of vasopressin in humans

To study the influence of cardiopulmonary baroreceptor loading and unloading on the osmotic stimulation of arginine vasopressin (AVP) in normal humans, we gave 105-min 5% saline infusions (0.06 ml X kg-1 X min-1) to three groups of subjects under different cardiopulmonary baroreceptor loading conditions. Group A received only the infusion, with a consequent increase in central venous pressure (CVP) of 2.6 +/- 1.7 mmHg; group B had CVP held constant by continuous lower body negative pressure; and group C had CVP decreased by -3.3 +/- 1.4 mmHg, also with lower body negative pressure, for the duration of the infusion. Mean arterial pressure increased in group A by 6.6 +/- 3.7 mmHg, but did not change in groups B and C. On average, osmolality increased by the same amount in each of the three groups (11.6 +/- 3.3, 13.7 +/- 3.2, and 10.9 +/- 2.5 mosmol/kg, P = NS). The changes in AVP in the three groups were 3.6 +/- 2.0, 2.7 +/- 1.9, and 6.2 +/- 3.5 pg/ml, P less than 0.03, with group C different from group B and groups A and B not different by individual pairs testing. An independent effect of prolonged CVP reduction on AVP levels in group C was made unlikely by studies in four additional subjects in whom AVP did not change at constant osmolality during 105 min of CVP reduction comparable with that in group C. Thus modest loading of both cardiopulmonary and sinoaortic baroreceptors does not alter the osmotic stimulation of AVP in normal humans.(ABSTRACT TRUNCATED AT 250 WORDS)