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(Hypertension. 1996;27:90-95.)
© 1996 American Heart Association, Inc.

Articles

Blood Pressure and Its Regulation in Spontaneously Hypertensive Rats Bred on the Lowest Sodium Diet for Normal Growth

Shuichi Takishita; Koshiro Fukiyama; Tanenao Eto; Nobuyuki Kawazoe; Yorio Kimura; Yuji Tomita; Tatsumi Tsumagari; Kenichi Onishi

From the Third Department of Internal Medicine (S.T., K.F., N.K., Y.K.), University of the Ryukyus School of Medicine, Okinawa; the First Department of Internal Medicine (T.E.), Miyazaki Medical College, Miyazaki; the Second Department of Internal Medicine (Y.T.), Faculty of Medicine, Kyushu University, Fukuoka; the Research Laboratory (T.T.), Yoshitomi Pharmaceutical Industries, Ltd, Fukuoka; Seiwa Experimental Animals, Ltd (K.O.), Fukuoka; and the National Cardiovascular Center (S.T.), Osaka, Japan.

Correspondence to Shuichi Takishita, MD, Division of Hypertension and Nephrology, National Cardiovascular Center, 5-7-1 Fujishirodai, Suita, Osaka 565, Japan.

Abstract To investigate the effects of dietary sodium restriction from conception to adulthood on blood pressure and its regulatory mechanisms, male offspring were derived from inbreeding in spontaneously hypertensive rats fed a diet containing sodium of 175 µmol/g food (control) or 22 µmol/g (low sodium), which is the least sodium content for normal growth. While urinary sodium excretion was markedly less, the low sodium diet did not inhibit body growth and failed to blunt the development of hypertension. Neither plasma catecholamine concentration nor depressor response to hexamethonium was different between the two groups at any age examined (8, 12, and 20 weeks). Plasma renin concentration was not elevated, whereas urinary excretion of aldosterone was increased at any age in the low sodium group compared with that in the control group. Other sets of rats were fed a diet containing sodium of 175 µmol/g plus mefruside (a diuretic) of 0.001% in the same manner as in the other two groups. Urinary sodium excretion per creatinine was higher than in the other groups. The diuretic treatment inhibited body growth and suppressed adult blood pressure. While the sympathetic function was not affected, both plasma renin concentration and urinary excretion of aldosterone were elevated. These results indicate that dietary sodium restriction with the least sodium for normal growth from conception cannot blunt either the sympathetic nervous function or the development of hypertension in spontaneously hypertensive rats. Aldosterone appears to play an important role in maintaining sodium homeostasis under the dietary sodium restriction.

Key Words: aldosterone • catecholamines • diuretics • rats, inbred SHR • renin-angiotensin system • sodium, dietary

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