Total body sodium in immature spontaneously hypertensive and Wistar Kyoto rats.

Total body sodium of male and female spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats was estimated weekly during the first 8 weeks of life by measuring exchangeable sodium (ENa). Blood pressure and sodium intake was measured from weeks 4 to 8. SHR had significantly higher blood pressure and sodium intake than WKY from 4 to 8 weeks of age. ENa was higher in SHR than WKY throughout the first 8 weeks of life. Relative sodium retention was observed in SHR during weeks 5 to 8 despite a significant rise in SHR blood pressure and fall in sodium intake. These findings suggest a change in the renal pressure/natriuresis relationship at this age in the SHR.