Vasopressin and renin response to plasma volume loss in spontaneously hypertensive rats

Abstract

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 < 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 < 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 < 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.