Effect of potassium administration on peripheral vascular reactivity and blood pressure of the potassium-deficient rat

Effect of potassium depletion on two-kidney, one-clip renovascular hypertension in the rat

There is considerable controversy about the hemodynamic effect of potassium in hypertension. To determine if K depletion could alter the control of blood pressure, studies were performed in rats with 2-kidney, 1-clip renovascular hypertension (RVH) after 3 to 6 wks of severe and moderate K depletion. After application of a 0.23 mm clip to the left renal artery, rats were placed on a K-replete (KR) (240 mEq/kg), a moderately K-depleted (KDM) (59 mEq/kg), or a severely K-depleted (KDS) (5 mEq/kg) diet. After 3 wks, mean arterial pressure (MAP) reached 154 +/- 3 in KR but only 121 +/- 2 in KDM (P less than 0.01) and 106 +/- 4 mm Hg in KDS (P less than 0.001). After 6 wks, MAP was 160 +/- 8 in KR, but only 132 +/- 5 in KDM (P less than 0.01) and 129 +/- mm Hg in KDS (P less than 0.01). Plasma K at 3 wks was 4.1 +/- .1 in KR, but only 3.5 +/- .1 in KDM (P less than 0.05) and 2.3 +/- .1 mEq/liter in KDS (P less than 0.001). This was associated with an 8% decrease in muscle K in KDM and a 16% decrease in muscle K in KDS. Although KDS animals did not grow during the 6 wks of study, KDM rats gained 60% as much weight at 3 wks, and, by 6 wks, weight gain was comparable in KDM (101 +/- 9) and KR (110 +/- 9 g) animals (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Mineralocorticoid-induced hypertension in patients with orthostatic hypotension

The mechanism of recumbent hypertension induced by fludrocortisone was studied in seven patients with orthostatic hypotension. All showed increases in blood pressure in the recumbent and standing positions, and hypertensive levels were achieved on recumbency in four of them. Hypertensive retinopathy developed in two patients and cardiomegaly in one. Initial blood-pressure elevations were associated with sodium retention and plasma-volume expansion. However, with long-term treatment, plasma volume decreased to control levels despite further blood-pressure increases. Treatment did not affect plasma levels of catecholamines but did enhance pressor responsiveness to infused norepinephrine in some subjects. Hemodynamic studies indicated that hypertension in the recumbent position was related to increases in total peripheral-vascular resistance and not to changes in cardiac output. Clinically, hypertension in the recumbent position is an important risk of fludrocortisone treatment in patients with orthostatic hypotension. This unusual model of chronic mineralocorticoid-induced hypertension is not volume dependent but is related to increased peripheral-vascular resistance.

Potassium deficiency and cardiac catecholamine metabolism in the rat

Norepinephrine metabolism, arterial blood pressure, and electrolytes were studied in rats maintained on either potassium-deficient or control diets. After 3 weeks on the test diets, the arterial blood pressure was significantly lower and the ratio of [Na] to [K] in cardiac tissue was significantly higher in potassium-deficient rats as compared to controls. Ten minutes after intravenous injection of 3 H-norepinephrine the specific activity of cardiac norepinephrine was similar in the control and potassium-deficient groups despite a significant increase in endogenous norepinephrine concentration in the potassium-deficient hearts. But 24 hours after injection, there was a significant increase in 3 H-norepinephrine specific activity, concentration, and content in the potassium-deficient group. Cardiac tissue monoamine oxidase activity was similar in both groups. The increased 3 H-norepinephrine retention and concentration and the decreased arterial blood pressure of the potassium-deficient rate suggest an impairment in norepinephrine release by the sympathetic neurons.

Abnormalities of renal function and circulatory reflexes in primary aldosteronism

The renal response to intravenous administration of isotonic saline solution and circulatory reflex reactivity was studied in nine patients with primary aldosteronism before and after surgical removal of an adrenal adenoma. In preoperative tests, infusion of saline was followed by abnormally rapid renal excretion of sodium and water, such as occurs in patients with autonomic insufficiency. Circulatory reflex function was also abnormal in all patients; the most severe impairment was shown by two patients with hypokalemia and weakness of long duration. Postoperatively, both renal and circulatory reflex responses returned to normal or near normal. In preoperative tests on three patients, potassium repletion effected a similar correction of both renal and circulatory reflex abnormalities. The cause of these abnormalities in patients with primary aldosteronism is not known. Potassium depletion may be a factor, although a general disturbance of autonomic cardiovascular function cannot be excluded.

Correlation of Serum Potassium Concentrations with the Blood Pressure in Rats Fed a Potassium-Deficient Ration

Rats which develop low blood pressures as a result of low potassium diet are shown to have lowered serum potassium levels. When the blood pressure is restored to normal by injection and 24 hour feeding of potassium, serum potassium levels also return to normal.