Differential responses of plasma oxytocin and vasopressin to dehydration in non-stressed sheep

Group housed, castrated rams (N = 10) were studied over a 2 day period. Water was available ad libitum during day 1 (control) but was withheld throughout day 2 (experimental). On both days, blood was collected by jugular venepuncture at 10.30 h, and then again 2, 4, 6 and 24 h later. Plasma samples were analysed by radioimmunoassay for arginine vasopressin (AVP), oxytocin and cortisol content and measurements were also made of the haematocrit and plasma osmolality and electrolyte (Na+, Cl-) concentrations. After 24 h water deprivation there was a significant increase in plasma AVP levels but no changes in oxytocin or cortisol concentrations. Dehydration also significantly depressed the haematocrit and increased plasma osmolality and electrolyte concentrations.