AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 4 644-R657, Copyright © 1986 by American Physiological Society
Osmotic and volemic regulation of plasma arginine vasotocin in conscious domestic fowl
J. N. Stallone and E. J. Braun
Recently developed radioimmunoassay methods were utilized to quantitatively
characterize secretion of the avian antidiuretic hormone [arginine
vasotocin (AVT)] by the hypothalamo-neurohypophyseal system (HNS) of the
conscious domestic fowl. The functional characteristics of the
osmoreceptor-HNS were evaluated during independent experimental
manipulations of extracellular osmolality or volume. Simultaneous
measurements of plasma AVT (PAVT) and either plasma osmolality (Posm) or
blood volume (BV) in these experiments permitted determination of
osmoreceptor sensitivity to independent osmotic or volemic stimuli and set
point of the AVT secretory system under conditions of normal hydration. In
normally hydrated birds, PAVT and Posm averaged 2.7 +/- 0.2 microU/ml (12.9
+/- 1.0 pg/ml) and 308.1 +/- 0.6 mosmol/kg H2O, respectively (means +/-
SE). Characterization of AVT secretion revealed that Posm is a primary
determinant of AVT secretion by the HNS of the domestic fowl. Highly
correlated and significant relationships between Posm and PAVT exist both
above and below the observed basal Posm of normally hydrated birds, with an
apparent osmotic threshold for AVT secretion at a Posm of 288.8 mosmol/kg
H2O. Analysis of the data also suggested that the HNS is insensitive to
changes in BV less than or equal to 10%, because neither isotonic expansion
nor reduction of BV altered PAVT. Comparison of past and present avian data
with that of the mammalian HNS indicates that 1) the osmotic regulation of
antidiuretic hormone secretion is qualitatively and quantitatively similar
in birds and mammals, and 2) the volemic regulation of antidiuretic hormone
secretion is substantially more important in mammals than in birds.
