Plasma arginine vasopressin and atrial natriuretic peptide concentration in patients with hyponatremia at diagnosis and following treatment

BackgroundMuch evidence for arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) in the pathogenesis of hyponatremia in humans is based on single measurements. To study the roles of AVP and ANP in the pathogenesis and recovery of hyponatremia, sequential measurements of ANP and AVP were taken during treatment in a group of hyponatremic patients with different etiologies.MethodsConsecutive adult patients with hyponatremia (serum Na < 130 mmol/l) and healthy controls were studied. Volume status was determined by clinical and laboratory criteria. Plasma AVP and ANP, fractional sodium excretion, and urine osmolality were determined daily until serum Na was above 135 mmol/l or for at most 7 days.ResultsA total of 16 controls and 40 hyponatremic patients (12 normovolemic, 9 hypervolemic, and 19 hypovolemic) were studied. Patients' plasma AVP on the first day [1.0 (0.3–2.3) ng/l] and on the last day [1.1 (0.3–2.5) ng/l] of the study did not differ from that of controls [0.7 (0.5–1.0) ng/l]. Serum sodium concentration increased significantly in patients between the first and the last day. Patients had significantly lower ANP concentrations, both on the first day [25 (15–46) ng/l] and on the last day [29 (17–46) ng/l], than controls [41 (28–51) ng/l]. Plasma AVP was elevated relative to serum osmolality on the first day and to a lesser extent on the last day of the study.ConclusionsAVP is inappropriately high in a majority of hyponatremic patients. Plasma AVP and ANP concentrations do not change during treatment in hyponatremic patients despite a significant increase in serum osmolality. A low ANP concentration in clinically normovolemic and hypovolemic patients indicates volume depletion, which may lead to baroreceptor-stimulated AVP secretion.