AJP - Renal Physiology, Vol 249, Issue 6 842-F850, Copyright © 1985 by American Physiological Society
Contributions of glomerular and tubular mechanisms to antidiuresis in conscious domestic fowl
J. N. Stallone and E. J. Braun
Recently developed radioimmunoassay (RIA) techniques were employed in a
quantitative investigation of the renal actions of the avian antidiuretic
hormone arginine vasotocin (AVT) in the conscious domestic fowl. Constant
intravenous infusion of AVT at doses of 0.125-1.00 ng X kg-1 X min-1 was
used to produce plasma AVT (PAVT) concentrations (verified by RIA) over the
entire range of physiological PAVT levels in the domestic fowl. Comparison
of the dose-response relationships between PAVT and glomerular and tubular
mechanisms of antidiuresis revealed that tubular mechanisms are of primary
importance and glomerular mechanisms of secondary importance in the
conservation of water by the avian kidney. The greatest proportion of the
total AVT-induced reduction in renal water excretion occurred at low
physiological PAVT levels (less than 5 microU/ml), prior to any significant
reduction in glomerular filtration rate (GFR), and appeared to be the
exclusive result of tubular mechanisms of antidiuresis. At high PAVT levels
(5-16 microU/ml), glomerular and tubular mechanisms overlapped, and their
effects on water conservation could not be separated. Although GFR was
reduced by nearly 30% at the highest dose of AVT, only minor additional
amounts of water were conserved by the combined actions of glomerular and
tubular mechanisms. Thus glomerular mechanisms appear to have only a minor
secondary effect on water-conserving ability of the avian kidney.
