EFFECTS OF ARGININE-VASOPRESSIN ON REGIONAL BLOOD-VOLUME DISTRIBUTIONIN SUPINE HUMANS

In healthy humans, the increase in arterial blood pressure seen in pat ients with autonomic dysfunction in response to exogenous vasopressin (AVP) is abolished. We tested the hypothesis that redistribution of bl ood from the intra- to the extrathoracic vascular compartment might co ntribute to this buffer response. Regional distribution of Tc-99m labe led autologous red cells was assessed in healthy supine volunteers (n = 7) during arginine-vasopressin administration (1 ng . kg-1 bolus i.v . followed by a 14-min infusion of 3 ng . kg-1 . min-1), along with ar terial and central venous pressures, and heart rate. Exogenous vasopre ssin increased plasma vasopressin concentration from 4.0 +/- 1.4 SEM t o 91 pg . ml-1 +/- 12. Thoracic counts increased slightly but signific antly by 2.2 % +/- 0.9, while global abdominal counts remained unchang ed. Most surprisingly, counts in the liver markedly increased (+8.1 % +/- 1.8, p = 0.02), but significantly decreased in the spleen (-3.1 % +/- 1.4). Intestinal (-2.5 % +/- 2.4) and limb counts did not change s ignificantly. Consistent with the increase in thoracic counts central venous pressure increased from 3.6 mm Hg +/- 1 to 4.7 +/- 1 (p = 0.02) , while arterial pressure and heart rate did not change. All changes r eversed towards baseline when vasopressin administration ceased. Thus, in humans with an intact autonomic system, vasopressin, at concentrat ions observed during hypotension, increases liver and, albeit to a sma ll extent, also thoracic blood volume, but decreases splenic blood con tent. These results 1) are incompatible with the hypothesis that AVP i nduces a shift of blood from intra- to extrathoracic capacitance vesse ls, and 2) show that AVP increases rather than decreases central blood volume.