Brain Na+,K+-ATPase isozyme activity and protein expression in ouabain-induced hypertension.
In normotensive rats, chronic infusion of exogenous ouabain causes hypertension involving central mechanisms. To determine whether ouabain-induced hypertension is associated with specific changes in brain Na+,K+-ATPase activity and expression, we assessed brain Na+,K+-ATPase isozyme activity and protein expression in rats treated with ouabain (50 microg/day s.c. or 10 microg/day i.c.v. for 14 days). Resting mean arterial pressure (MAP) was higher in s.c.- and i.c.v.-ouabain-treated animals vs. control (124+/-2 vs. 105+/-2 and 130+/-2 vs. 109+/-2, respectively, p<0.01). Ouabain infused s.c. or i.c.v. for 14 days had no effect on Na+,K+-ATPase isozyme activity in hypothalamic, pontine/medullary or cortical microsomes. However, the percent increase in total Na+,K+-ATPase activity produced in vitro by antibody Fab fragments that bind ouabain with high affinity (Digibind) was two-fold greater in s.c.- and i.c.v.-ouabain-treated rats vs. control, but only in hypothalamic microsomes. Thus, ouabain infused s.c. or i.c.v. does appear to directly inhibit Na+,K+-ATPase activity in the hypothalamus. On the other hand, in the hypothalamus, s.c.- and i.c.v.-ouabain infusions tended to increase alpha3 (by 30-44%), but had no effect on alpha1 or alpha2 Na+,K+-ATPase isozyme protein expression. In addition, ouabain was found to partially dissociate from the Na+,K+-ATPase enzyme following sample processing. Thus, the inability to detect a decrease in enzyme activity in the hypothalamus in response to ouabain may be due, in part, to an increase in enzyme expression and the dissociation of ouabain during sample processing.
Kent
Mary-Anne H
MA
Hypertension Unit, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario, Canada K1Y 4W7.
Huang
Bing S
BS
Van Huysse
James W
JW
Leenen
Frans H H
FH
D000818:Animals; D001794:Blood Pressure; D002540:Cerebral Cortex / Q000201:enzymology; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D006973:Hypertension / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology; D007031:Hypothalamus / Q000201:enzymology*; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008526:Medulla Oblongata / Q000201:enzymology; D008861:Microsomes / Q000201:enzymology*; D010042:Ouabain / Q000008:administration & dosage / Q000037:antagonists & inhibitors; D011149:Pons / Q000201:enzymology; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism*
D004791:Enzyme Inhibitors; D007140:Immunoglobulin Fab Fragments; D007527:Isoenzymes; C050199:digoxin antibodies Fab fragments; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase