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

Abstract

Abstracr. The interrelationships among plasma renin activity (PRA, ng AI/ml plasma/hr), aldosterone concentration (ng%), and renal Na+-K+-ATPase activity (pmole P04/mg protein/ hr) 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% sodium) diet. PRA and plasma aldosterone, measured in samples drawn from the ether-anesthetized rat, were higher in weanling SHR ( I 5.2 * 2.0, 37 f 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 k 0.9) and plasma aldosterone (20.0 f 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 (1 37 f 9 weanling SHR, 89 f 7 weanling WKY, 73 f 1 1 adult SHR, 84 f 17 adult WKY). Thus, 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. It was noted, however, that 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. (c 19x4 Societ) for Expcrirnenul Biolog) and Medicine 240

Proximal tubule Na transporter responses are the same during acute and chronic hypertension

“…The density distribution patterns of NHE3 and NaPi2 are very distinct in young vs. adult rats, but very similar between the two strains: in young SHR and SD the apical peak (fractions 4-7) contains more than 70% of the NHE3 and only about 30% of the NaPi, with 70% of the NaPi2 in the intracellular pools (fractions [8][9][10][11][12]. A very recent study of the ontogeny of NaPi2 in the kidney by Traebert et al (34) demonstrates, by confocal immunofluorescence microscopy, that there is, indeed, extensive intracellular staining of NaPi2 in 3-wk-old rats of the Wistar strain, and that this staining decreases with development.…”

“…Sodium retention is also favored by decreased glomerular filtration rate (GFR) due to increased tubuloglomerular feedback sensitivity in young SHR (14,15). With established hypertension in the adult SHR, the differences in transporter activity and GFR between the two strains disappear (8,15,18).…”

Renal Catecholamines and α₂-Adrenergic Receptors in Salt-Related and Genetic Hypertension

“…Our study, however, involved a smaller number of subjects and fewer time points. Young SHR have elevated renal Na-K-ATPase activity [46] and in creased numbers of RotiAR. Interestingly, the SHR exhibited a developmental decline in Ra2AR number which very closely paral lels and age-related decline in renal Na-KATPase activity which has been reported in SIIR [46].…”

“…Young SHR have elevated renal Na-K-ATPase activity [46] and in creased numbers of RotiAR. Interestingly, the SHR exhibited a developmental decline in Ra2AR number which very closely paral lels and age-related decline in renal Na-KATPase activity which has been reported in SIIR [46]. There is also a general age-related decline in Rct2AR number [ 14] and renal Na-K-ATPase also exhibits a decline in activity with age [47], This suggests that perhaps the reported antinatriuretic actions of NE and Ra2AR activation may be related to stimula tion of renal Na-K-ATPase activity.…”

Pathogenesis of the essential hypertensions

“…The stimulation of proximal tubular fluid reabsorption by peritubular angiotensin II was reduced in the 5-week-old rat but not in the 12-week-old rat [13]. Also in weanling rats, Na-K ATPase was more active [14] and renal sympathetic nerve activity was increased [15]. Young SHRs have a reduced glomernlar filtration rate and renal blood flow, and an increased renal vascular resistance; these are genetically linked as shown by cross-breeding studies [16].…”