AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 5 1107-R1112, Copyright © 1995 by American Physiological Society
Effect of acute manipulation of blood volume and osmolality on plasma [AVT] in seawater flounder
J. M. Warne and R. J. Balment
School of Biological Sciences, University of Manchester, United Kingdom.
Chronically cannulated seawater (SW)-adapted flounder (Platichthys flesus)
were used unanesthetized and unrestrained in an experimental series that
acutely manipulated blood volume and plasma osmolality to determine their
influence on plasma arginine vasotocin (AVT) concentrations. Immunoreactive
AVT was measured using a radioimmunoassay validated for flounder and other
teleosts. After hemorrhage-induced hypovolemia or hypervolemia produced by
saline infusion, no major changes in plasma AVT concentrations were
detected. Raising plasma osmolality by intraperitoneal injection of 1 M
NaCl compared with control 150 mM NaCl-injected fish (329.4 +/- 3.4 vs.
320.4 +/- 3.0 mosmol/kgH2O, P < 0.05) produced an increase in plasma AVT
concentration (6.7 +/- 1.2 vs. 4.2 +/- 0.2 fmol/ml, P < 0.05). In a
separate study, plasma composition in a large number of uncannulated
SW-adapted flounder was determined. This demonstrated a positive linear
relationship between the natural variation in plasma AVT concentrations and
plasma osmolality and Na+ and Cl- concentrations observed between fish.
These data indicate that AVT secretion in SW-adapted flounder is closely
related and perhaps directly sensitive to changes in plasma tonicity.
