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1 Departments of Physiology and Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109; 2 Department of Pathology, University of North Carolina, Chapel Hill, North Carolina 27599; 3 Guilford Medical Associates, Greensboro, North Carolina 27405; and 4 National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892
In these experiments, we used a strain of angiotensin converting
enzyme (ACE) germline null mutant mice, generated by J. H. Krege and
co-workers (J. H. Krege, S. W. M. John, L. L. Langenbach, J. B. Hodgin, J. R. Hagaman, E. S. Bachman, J. C. Jennette, D. A. O'Brien, and O. Smithies. Nature 375:
146-148, 1995), to examine the effect of chronic ACE deficiency on
the magnitude of tubuloglomerular feedback (TGF) responses. The
genotype was determined by PCR on DNA extracted from the tail and was
verified after each experiment by assessment of the blood pressure
response to an injection of ANG I. To assess TGF responsiveness, we
determined the change in stop-flow pressure
(PSF) caused by increasing NaCl
concentration at the macula densa by using micropuncture techniques.
When loop of Henle flow rate was increased from 0 to 40 nl/min,
PSF fell from a mean of 42.3 ± 1.95 to 33.6 ± 2.09 mmHg (n = 6, P = 0.005) in wild-type mice (+/+),
fell from 40.6 ± 2.35 to 38.6 ± 1.93 mmHg in heterozygous
(+/
) mice (n = 7, P = 0.014), and did not change in
homozygous ACE (
/
) mice [36.7 ± 2.02 mmHg vs.
36.4 ± 2.01 mmHg; n = 4, P = not significant (NS)].
During an infusion of ANG II at a dose that did not significantly
elevate blood pressure (70 ng · kg
1 · min
1),
TGF response magnitude
(PSF 0
PSF 40) increased from 6.5 ± 1.4 to 9.8 ± 1.19 mmHg in +/+
(P = 0.006), from 1.14 ± 0.42 to
4.6 ± 1.3 mmHg in +/
(P = 0.016), and from 0.42 ± 0.25 to 4.02 ± 1.06 in
/
mice
(P = 0.05). Absence of TGF responses
in ACE null mutant mice and restoration of near-normal responses during
an acute infusion of ANG II supports previous conclusions that ANG II
is an essential component in the signal transmission pathway that links
the macula densa with the glomerular vascular pole.
transgenic mouse; gene knockout; micropuncture; angiotensin converting enzyme; stop-flow pressure
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