AJP - Heart and Circulatory Physiology, Vol 250, Issue 3 443-H452, Copyright © 1986 by American Physiological Society
Vasopressin and renin response to plasma volume loss in spontaneously hypertensive rats
C. D. Sladek, M. L. Blair, Y. H. Chen and R. W. Rockhold
Abnormalities in the vasopressin (VP) and renin-angiotensin systems have
been described in spontaneously hypertensive rats (SHR). Responsiveness of
these systems to a decrease in plasma volume was examined in the SHR at 6,
8, and 18 wk of age and compared with responses in age-matched normotensive
Wistar and Wistar Kyoto rats (WKY). Trunk blood was collected 3 h after
administration of 2 ml/100 g body wt of 0.9% saline, 15 or 30% polyethylene
glycol (PEG), and in one group of conscious 8- and 18-wk-old rats, mean
arterial pressure was monitored following PEG administration. Hematocrit
and serum VP increased significantly in both strains at all ages following
PEG. At 6 and 8 wk of age, the VP response to the PEG injection was
significantly greater in SHR compared with WKY (P less than 0.005), but at
18 wk the response was comparable in the two strains. Serum renin activity
(SRA) also increased in both strains receiving PEG at 6 and 8 wk of age,
but the response was suppressed in the SHR relative to the WKY (P less than
0.001). At 18 wk of age, SRA increased in WKY, but the response was totally
suppressed in SHR. Renal renin content in a separate group of rats was
reduced in 19-wk-old SHR compared with WKY (P less than 0.001) but was not
different in 5- and 8-wk-old rats. Thus there appears to be a
hyperresponsiveness in the VP system in young SHRs that is not present in
the renin-angiotensin system. The divergence in the responsiveness of the
renin and VP systems and the attenuation of responsiveness in the VP system
in 18-wk SHRs indicate a differential effect of the hypertensive process on
the VP and renin systems in the SHR.
