Angiotensin ii and the maturation of renal cortical na+/h+
exchanger activity during fetal life in sheep.
Guillery, Edward N., Michael S. Mathews, John Orlowski, Jean E.
Robillard.
Department of Pediatrics, The University of Iowa, Iowa City, IA
52242; Department of Pediatrics, The University of Wisconsin,
Madison, WI 53792; Department of Physiology, McGill University,
Montreal, Quebec, H3G1Y6, Canada
APStracts 3:0206R, 1996.
The postnatal rise in renal Na+ reabsorption is associated with an
increase in proximal tubule apical membrane Na+/H+ exchanger (NHE)
activity in sheep. As circulating angiotensin II (AII) levels
increase immediately after birth and AII is known to upregulate NHE
activity in the adult proximal tubule, we postulated that AII plays a
role in mediating maturational changes in NHE activity. We therefore
studied the effects of AII infusion (10 ng/h) for 24 h on renal
cortical NHE activity in chronically-instrumented, twin ovine fetuses
(129+/-2 d gestation, term is 145 d, n=10 pairs); one twin of each
pair served as a control. After 24 h, the fetuses were sacrificed and
brush border membrane vesicles (BBMV) were prepared from the renal
cortices. Post-infusion plasma AII levels were significantly higher
and plasma renin activities were significantly lower in treated
fetuses when compared to controls. Kinetic analysis revealed an
increase in NHE activity following AII treatment, however the
difference was not statistically significant: Vmax (in nmol/sec/mg
protein), control 1.65+/-0.50, treated, 2.31+/-0.66 (P=0.11, n=9
pairs); KM, control 8.29+/-1.17 mM, treated 9.84+/-1.26 mM (P=0.11).
Northern blots of total RNA from the cortices of these animals were
hybridized to a D-[32P]UTP labeled antisense RNA probe, prepared from
a 1.3 kb rat NHE-3 cDNA fragment. There were no differences between
the groups in NHE-3 mRNA levels (32P counts were: control 413+/-54,
treated 340+/-46). AII does not appear to play an important role in
the regulation of NHE activity in the proximal tubule of the near
-term sheep fetus.
Received 21 September 1995; accepted in final form 21 May 1996.
APS Manuscript Number R591-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96