Radioimmunoassay of Arginine Vasopressin in Rhesus Monkey Plasma

Abstract

Using a new antiserum, an enzymatic radioiodination of arginine vasopressin (AVP), and the methodology of Robertson et al. (1, 2), we have developed a sensitive and specific radioimmunoassay for plasma AVP in the monkey. The sensitivity of the assay is 0.5 μU/ml, the cross reaction with oxytocin (OT), minimal. We used this assay to study the effects that variations in blood osmolality have in regulating AVP secretion in unanesthetized, chair-restrained, chamber-isolated, adult female rhesus monkeys. Under water ad lib conditions, plasma AVP and osmolality were relatively constant, averaging 1.7 ± 0.6 (SD) μxU/ml and 298 ± 3 mosmol/kg, respectively. Water loading decreased plasma AVP and osmolality to 0.6 ± 0.2 μU/ml and 282 ± 6 mosmol/kg, respectively. When fluid restriction increased osmolality, plasma AVP rose progressively to twice the baseline after 1 day, and to 6 times the baseline after 3 days. The rise in plasma AVP was linearly correlated with the rise in osmolality (r = 0.93; P < 0.001). Intravenous infusions of hypertonic saline produced significant rises in plasma osmolality and plasma AVP. There was a dose-related rise in plasma AVP that declined later at the expected rate with the infusion of physiological amounts of synthetic AVP. © 1976 by The Endocrine Society.