The Role of Na<SUP>+</SUP>-K<SUP>+</SUP> ATPase Activity on Blood Pressure Regulation and Sodium Metabolism in DOCA-treated Rats

Abstract

In this study, we attempt to clarify the role of sodium-potassium adenosine 5'-triphosphatase (N+-K+ ATPase) on the regulation of systemic blood pressure and renal sodium metabolism. Male Wistar rats (n=20) were divided into four groups: 1) controls (n=5), 2) sodium loading rats (NaCl group, n=5), 3) deoxycorticosterone (DOCA group, n=5) injected rats with intact kidneys (DOCA group, n=5), 4) DOCA and ouabain-injected rats with intact kidneys (ouabain groups) and raised for six weeks. The changes in urine volume and urinary sodium were determined, and urinary excretions of norepinephrine (NE), epinephrine (E) and dopamine were measured in week six. Then blood samples were obtained from the inferior vena cava, and plasma cyclic AMP (cAMP) and cyclic GMP (cGMP) concentration were measured. At the time of sacrifice, systolic blood pressure of the ouabain group (157.3 +/- 24.8 mmHg) was significantly higher than the control group (124.5 +/- 6.9 mmHg) (p less than 0.05), but no significant differences were observed between the control group, NaCl group (123.7 +/- 7.0 mmHg), and DOCA group (128.1 +/- 4.5 mmHg). Urine volume and sodium excretion in the NaCl, DOCA and ouabain groups all increased, but the natriuretic response in the NaCl group was smaller than in either the DOCA and ouabain groups. Urinary NE in the NaCl, DOCA and ouabain groups was 1396 +/- 1025 ng/day, 640 +/- 351 ng/day, 607 +/- 177 ng/day, respectively, and NE excretions in these groups were higher than in the control group (138 +/- 104 ng/day). Urinary E in the NaCl group was higher than in the control group, but there were no significant differences among the control, DOCA and ouabain groups. Urinary dopamine in the NaCl (5723 +/- 2028 ng/day), DOCA (7661 +/- 5992 ng/day) and ouabain (4077 +/- 1984 ng/day) groups was higher than in the control group (2081 +/- 483 ng/day). Plasma cAMP in the DOCA and ouabain groups was slightly higher than in the control group, while no significant differences in plasma cAMP between the control and NaCl groups were observed. Plasma cGMP in the DOCA group was slightly higher than in either of the other three groups. These results suggest that Na+-K+ ATPase may play an important role in the maintenance of blood pressure through sodium efflux and that ouabain, Na+-K+ ATPase inhibitor, may change the renal sodium excretion and vascular responsiveness to endogenous pressor substances, leading to higher blood pressure after the administration of sodium and mineralocorticoid.