Angiotensin i converting enzyme activity in tubular fluid along the
rat nephron..
Casarini, D. E., Boim, M. A., Stella, R. C. R., Krieger-Azzolini M.
H., Krieger J. E. and Schor, N.
Disciplina de Nefrologia and Departamento de Bioqumica,
Universidade Federal de So Paulo, Escola Paulista de Medicina, S[pi]o
Paulo, SP, CEP 04023-062, Brazil, and Laborat
APStracts 3:0215F, 1996.
The activity of angiotensin I converting enzyme (ACE) was determined
in tubular fluid collected from several portions of the rat nephron
and urine, and in total and efferent arteriolar blood using hippuryl
-L-His-Leu as substrate. ACE activity decreased 30% from the pre- to
the postglomerular arterioles (p<0.001), suggesting a role of the
glomerulus in ACE clearance. The enzyme activity was found to be
present throughout the rat nephron. However, the highest activities
were found in the proximal tubule and urine ( 0.692(0.007 and
1.05(0.015 pmol.(l-1.min-1, respectively). When compared with other
segments, ACE activity decreased from the initial portion of the
proximal tubule to the distal nephron, and increased again in the
urine. Along the proximal tubule, ACE is secreted and degraded and/or
reabsorbed and then secreted again into the collecting duct since no
ACE activity was found in the late distal tubule but a high level was
detected in the urine, indicating a potential physiological role in
the inactivation of the kinins formed by kallikrein beyond the
connecting tubules. Moreover, the possible role of mesangial cells
(MC) in the decrease of intraglomerular ACE was also evaluated. The
analysis of ACE gene showed that MC in culture are able to express
ACE mRNA. Moreover, ACE is produced as an ectoenzyme and as a
secreted form of the enzyme, indicating a potential effect of local
angiotensin II production on MC function.
Received 20 February 1996; accepted in final form 12 November
1996.
APS Manuscript Number F53-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996