Renal Na+-K+-ATPase in Weanling and Adult Spontaneously Hypertensive Rats

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Abstract
The interrelationships among plasma renin activity (PRA, ng AI/ml plasma/h), aldosterone concentration (ng%), and renal Na+-K+-ATPase activity (.mu.mol PO4/mg protein/h) were studied in 9 weanling normotensive spontaneously hypertensive rats (SHR), 9 adult hypertensive SHR, and 9 weanling and 9 adult normotensive Wistar-Kyoto rats (WKY). All groups were placed on a normal (0.4% Na) diet. PRA and plasma aldosterone, measured in samples drawn from the ether-anesthetized rat, were higher in weanling SHR (15.2 .+-. 2.0, 37 .+-. 4.2) than in WKY. PRA measured in samples collected from a separate group of unanesthetized weanling SHR was also greater than in age-matched WKY. In adult SHR, PRA (6.1 .+-. 0.9) and plasma aldosterone (20.0 .+-. 2.7) were decreased. During the weanling period Na+-K+-ATPase activity in SHR was not only greater than in age-matched WKY but was also increased compared to adult normotensive and hypertensive rats (137 .+-. 9 weanling SHR, 89 .+-. 7 weanling WKY, 73 .+-. 11 adult SHR, 84 .+-. 17 adult WKY). During the weanling period the renin-angiotensin-aldosterone (R-A-A) system and renal Na+-K+-ATPase activity are activated in SHR. The elevation of Na+-K+-ATPase activity may be due to increased aldosterone levels. Plasma aldosterone was similar in adult WKY and weanling SHR, while Na+-K+-ATPase activity was higher in SHR. These findings involving R-A-A and renal Na+-K+-ATPase activity prior to the elevation of blood pressure suggest that the kidneys may play a role in the initiation of hypertension in SHR.