Renal cortical and medullary blood flow responses during water
restriction: role of vasopressin.
Franchini, Kleber G., and Allen W. Cowley, Jr.
Heart Institute, University of Sao Paulo, Sao Paulo, Brazil and
Department of Physiology, Medical College of Wisconsin, Milwaukee,
WI
APStracts 3:0009R, 1996.
Experiments were performed in unanesthetized rats to determine
responses to 48 hour water restriction of the renal regional
microcirculation (cortex, outer medulla, and inner medulla) using
implanted optical fibers and laser-Doppler flowmetry. The role of
vasopressin (AVP) as a mediator of renal regional blood flow changes
and its contribution to urinary concentrating ability were assessed
by continuous intramedullary interstitial infusion (r.i.) of specific
V1 receptor antagonist [d(CH2)5[Tyr(Me)2,Ala-NH2]AVP] (2 ng/kg/min).
Inner medullary blood flow decreased 34% at the end of 48 hours of
water restriction while cortical and outer medullary flow did not
change. This fall in inner medullary blood flow was substantially
attenuated (18%) by the continuous r.i. infusion of the antagonist.
Plasma AVP levels increased from control levels of 3.4+/-1.1 to
20.5+/-5.4 pg/ml (p<0.05) by the end of the 48 hour period of
water restriction. Arterial pressure increased slightly but
significantly during water restriction in the control rats. Infusion
of antagonist impaired the maximal urinary concentrating ability, as
demonstrated by the lower urine osmolality in this group than in the
control group (1893+/-49 vs. 2419+/-225 mOsm/kg; p<0.05)
measured during the second day of water restriction. Sodium and urea
concentration decreased 20 and 22%, respectively, indicating that
both contributed to the lower urine osmolality observed in the group
of rats receiving the antagonist. We conclude that water restriction
induces a selective decrease in inner medullary blood flow, which is
mediated almost completely by endogenously released AVP. This
vascular effect of AVP contributes to the maximum concentrating
ability of the kidney.
Received 22 November 1994; accepted in final form 22 December
1995.
APS Manuscript Number R679-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96