The Effect of Hemorrhage and Hypertonic Saline upon Plasma Oxytocin and Arginine Vasopressin in Conscious Dogs*

Abstract

Sensitive and highly specific RIAs for arginine vasopressin (AVP) and oxytocin (OT) were utilized to assess the specificity of neurohypophyseal hormone release after hemorrhage or infusion of hypertonic saline to trained conscious dogs. Phlebotomy of 12.5 and 25 ml/kg produced increases in plasma AVP from 1.0 ± 0.2 to 7.8 ± 2.1 and 41.6 ± 9.7 (SEM) μU/ml respectively, and both responses differed significantly from values in control experiments (P < 0.01 after the first phlebotomy and P < 0.001 after the second phlebotomy). Plasma OT concentrations rose from baseline values of 1.1 ± 0.4 to 3.3 ± 0.6 and 8.3 ± 1.7 μU/ml (P < 0.005 and P < 0.001 compared to controls); plasma osmolality and sodium concentrations were unchanged. Both log AVP and log OT were highly correlated with the quantity of blood removed (r = -0.92 and -0.82, each P < 0.001). Infusion of hypertonic (20g/dl) NaCl (3.4 meq/kg) over 20 min caused plasma osmolality and sodium to rise from 304 ± 1.0 mosm/kg and 143 ± 3.0 meq/liter to 316 ± 1.0 mosm/kg and 150 ± 3.0 meq/liter (each P < 0.001). Plasma AVP rose from 1.5 ± 0.2 to 2.4 ± 0.2 µU/ml (P < 0.0025) and OT rose from 1.2 ± 0.5 to 2.6 ± 0.7 µU/ml (P < 0.005). The stimulus response ratios (change in log hormone concentration divided by the rise in plasma osmolality) were comparable for both hormones (0.024 ± 0.006 for AVP and 0.031 ± 0.008 for OT; P > 0.4). The data indicate that hemorrhage or hypertonic saline stimulate release of both AVP and OT. After hemorrhage, there is greater stimulation of AVP than OT, whereas there is comparable stimulation of both peptides after hypertonic saline.