AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 6 1045-R1049, Copyright © 1993 by American Physiological Society
Characterization of organic osmolytes in avian renal medulla: a nonurea osmotic gradient system
Y. H. Lien, M. M. Pacelli and E. J. Braun
Department of Internal Medicine, College of Medicine, University of Arizona, Tucson 85724.
We measured the organic osmolytes present in the renal cortex and medullary
cones of adult female domestic fowl before and after 48 h of water
deprivation. Urine osmolality increased from 198 +/- 82 to 569 +/- 42
mosmol/kgH2O after water deprivation. In water-deprived birds, the major
organic osmolytes, myoinositol, betaine, and taurine, in the medullary
cones increased by 40, 100, and 24%, respectively, compared with control
birds. No sorbitol was detected, and glycerophosphorylcholine (GPC) content
was not affected by water deprivation. In the renal cortex, only betaine
content increased significantly (4.8 +/- 0.6 vs. 3.1 +/- 0.3 mmol/kg wet
wt) after water deprivation. In this study, we demonstrated that birds,
like mammals, accumulate organic osmolytes in response to the increased
interstitial osmolality that occurs during antidiuresis. Because urea is
nearly absent in the avian medullary interstitium, our observation that GPC
is not osmoregulated in the avian kidney supports the idea that GPC is the
"counteracting osmolyte" for urea in the mammalian kidney. Furthermore, the
organic osmolytes present in avian medullary cones are remarkably similar
to those of the mammalian outer medulla. This similarity may be relevant to
the morphological analogy of the two regions.
