ARGININE VASOPRESSIN RESPONSE TO HYPERTONICITY IN HYPERTENSION STUDIED BY ARGININE VASOPRESSIN ASSAY IN UNEXTRACTED PLASMA

Objective: To investigate whether plasma osmolality (P(osm))-plasma arginine vasopressin (P(AVP)) response relationships with particular characteristics of sensitivity, gain or response pattern (linear/non-linear) occur more frequently in hypertensive than normotensive subjects. Design: Analysis of P(osm)-P(AVP) curves observed in individual normotensive and hypertensive subjects rather than whole groups was considered appropriate for the described objective. Methods. A sensitive and precise radioimmunoassay of P(AVP) in unextracted plasma was developed. P(osm) was raised in 11 normotensive and 19 hypertensive subjects by infusion of NaCl solution (0.86 mol/l, i.v.), and P(AVP) assayed at intervals. Best-fitting linear and non-linear equations for the P(osm)-P(AVP) relationship were established by computer. Results: The mean rise in osmolality, blood pressure and blood volume was similar in the two groups. Hypertensive subjects showed a tendency towards higher rates of response (pmol AVP/l per mosm per kg) at P(osm) > 290 mosm/kg, leading to a non-linear response pattern compared with the normotensive subjects. Conclusions: The enhanced P(AVP) responses found in the hypertensive subjects at P(osm) > 290 mosm/kg may reinforce vascular and central nervous pathogenetic mechanisms.