AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 4 1353-R1358, Copyright © 1994 by American Physiological Society
Levels of active and inactive reninlike enzymes in plasma and reproductive tract of the pregnant wallaby
E. R. Lumbers, R. I. Menzies, K. J. Gibson and C. H. Tyndale-Biscoe
School of Physiology and Pharmacology, University of New South Wales, Sydney, Australia.
Active and total (acid-activated) levels of a reninlike enzyme (hereafter
called renin) were measured in plasma, tissues, and yolk sac fluid of
pregnant and postpartum wallabies. Plasma active renin generated
angiotensin I (ANG I) from sheep angiotensinogen at 14 +/- 1.3 (SE)
ng.ml-1.h-1, whereas acid-activated renin generated ANG I at 33.3 +/- 2.5
ng.ml-1.h-1, i.e., 44.2 +/- 3.7% of renin in plasma was active, and 58 +/-
3.7% was inactive. Inactive renin levels were highest in pregnant animals
(P = 0.05). Uterine renin was mainly inactive (95%); levels were 5.1 +/-
1.1 times plasma levels. The levels of renin in nonpregnant uteri were the
same as those in pregnant uteri from the same animals. Uterine renin levels
did not change with gestation. Pooled acid-activated yolk sac fluid
generated ANG I at low rates (0.7 and 1.6 ng.ml-1.h-1); the acid-activated
supernatant of a homogenate of pooled fetal membranes generated ANG I at 15
ng.g wet wt-1.h-1. Yolk sac fluid was strikingly different in electrolyte
composition from maternal plasma. Its lower osmolality suggests that the
membranes separating it from maternal plasma have a low permeability to
water. Thus, although eutherian and marsupial mammals diverged 136-164
million years ago, the wallaby, like many eutherian mammals, has inactive
renin in blood, in the female reproductive tract, and in fetal membranes.
