Vasopressin in Plasma and Cerebrospinal Fluid of Hydrated and Dehydrated Steers

Publisher Website
Google Scholar
Abstract
Levels of arginine-vasopressin (AVP), the antidiuretic hormone, were concurrently measured by radioimmunoassay (RIA) in plasma (p) and cerebrospinal fluid (CSF) from conscious, unrestrained steers. During 4 days of dehydration, plasma osmolarity (posm) rose progressively from control hydrated levels of 301.3 .+-. 0.632 mosm/l (mean .+-. SE) to 338.5 .+-. 3.00 mosm/l (P < 0.001). Packed cell volume also rose form 39.9 .+-. 0.64% to 44.7 .+-. 1.24% (P < 0.001). Associated with these changes was a progressive increase in pAVP from control levels of 1.3 .+-. 0.19 .mu.U/ml to 16.9 .+-. 1.88 .mu.U/ml (P < 0.001) after 4 days without water. Log pAVP was linearly related to posm (r = 0.82, P < 0.001). Mean level of CSF-AVP in control animals was 5.4 .+-. 0.97 .mu.U/ml. During dehydration, CSF-AVP levels also rose, becoming significantly greater than control levels (P < 0.01) after 3 days without water and further increasing to reach 15.2 .+-. 1.83 .mu.U/ml after 4 days without water (P < 0.001). Log CSF-AVP could also be linearly related to posm (r = 0.62, P < 0.01). Termination of dehydration by restoration of ad libitum water supply was accompanied by return to pAVP and CSF-AVP to predehyration levels. Regression analysis of concurrent levels of pAVP and CSF-AVP indicates that CSF-AVP levels were linearly correlated to pAVP levels in hydrated and dehydrated animals (r = 0.70, P < 0.001). Apparently neurosecretory neurons secreting AVP at sites accessible to CSF respond to similar stimuli during dehydration as those neurons secreting AVP into blood.