AJP - Renal Physiology, Vol 249, Issue 1 169-F173, Copyright © 1985 by American Physiological Society
Tubuloglomerular feedback activity in virgin and 12-day-pregnant rats
C. Baylis and R. C. Blantz
Tubuloglomerular feedback activity was evaluated by micropuncture and
microperfusion techniques in virgin and 12-day-pregnant Munich-Wistar rats.
Plasma volume increases in pregnancy, which could suppress feedback
activity, thus contributing to the rise in glomerular filtration rate
observed in normal midterm pregnancy. Late proximal tubules were
microperfused at 0, 10, 20, and 40 nl/min and the resulting filtration rate
in the same nephron was evaluated. Nephron filtration rate (SNGFR) in
proximal and distal tubules of other nephrons was also measured to assess
the degree of activation of the tubuloglomerular feedback system and the
relation of the spontaneous (normal) late proximal flow rate and SNGFR
(distal tubule collections). SNGFR decreased significantly (from the 0
nl/min perfusion value) when late proximal tubules were perfused at 20 and
40 nl/min in both virgin and 12-day-pregnant rats. Tubuloglomerular
feedback activity was not suppressed in pregnancy, but the relationship
between SNGFR and late proximal tubule perfusion rate was reset for a
higher value for SNGFR. The difference between proximal and distal SNGFR
suggests that the feedback system was more activated in the virgin than in
the pregnant rat. Thus, in spite of the known increases in plasma volume
that occur in pregnancy, the kidney does not sense this volume expansion as
a stimulus to suppress feedback activity.
