AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 1 15-R23, Copyright © 1984 by American Physiological Society
Characterization of the renin-angiotensin system in the turtle Pseudemys scripta
M. D. Cipolle and J. E. Zehr
Studies were conducted in freshwater turtles Pseudemys scripta to define
some characteristics of the renin-angiotensin system in this reptile.
Dialyzed acid-treated kidney extract (1 g tissue per ml water) produced a
prolonged pressor response in unanesthetized turtles, which was eliminated
by boiling the extract or by pretreating the turtle with [Sar1,
Ile8]angiotensin II. A rat pressor assay was employed because turtle
angiotensin (ANG) was bound poorly by the anti-[Asp1, Ile5, His9]ANG I used
in our radioimmunoassay. Kidney extract incubated with homologous plasma
(pH 5.5 and 25 degrees C) produced a time-dependent pressor response in
rats. The pressor activity of the product was eliminated by dialysis or by
pretreating the rats with [Sar1, Ile8]ANG II. The pressor response in
anesthetized turtles to ANG I was significantly reduced by captopril,
whereas the ANG II response remained unchanged, thus demonstrating the
presence of ANG-converting enzyme activity in these animals. We determined
the velocity of turtle ANG formation at various dilutions of enzyme (kidney
extract) or substrate (plasma). Turtle kidney extract incubated with
homologous plasma displayed typical Michaelis-Menten kinetics. Finally we
conducted experiments to determine whether a portion of turtle plasma renin
exists in an inactive form. Trypsinization caused a slight increase in
plasma renin activity (PRA), whereas acidification to pH 3.3 yielded a
fourfold increase in PRA.
