THE ROLE OF RENAL METABOLISM IN HYPERTENSION AND UREMIA

Renal Epithelial Mitochondria: Implications for Hypertensive Kidney Disease

According to the Centers for Disease Control and Prevention, 1 in 2 U.S. adults have hypertension, and more than 1 in 7 chronic kidney disease. In fact, hypertension is the second leading cause of kidney failure in the United States; it is a complex disease characterized by, leading to, and caused by renal dysfunction. It is well-established that hypertensive renal damage is accompanied by mitochondrial damage and oxidative stress, which are differentially regulated and manifested along the nephron due to the diverse structure and functions of renal cells. This article provides a summary of the relevant knowledge of mitochondrial bioenergetics and metabolism, focuses on renal mitochondrial function, and discusses the evidence that has been accumulated regarding the role of epithelial mitochondrial bioenergetics in the development of renal tissue dysfunction in hypertension. © 2024 American Physiological Society. Compr Physiol 14:5225-5242, 2024.

RENAL HYPERTENSION PRODUCED BY AN AMINO ACID

Acute renal hypertension is produced by the injection of the amino acid dopa (l-dihydroxyphenylalanine) into the partially or completely ischemic kidney of the cat. Evidence is presented suggesting that the rise in blood pressure following the injection of dopa is caused by its conversion into hydroxytyramine, a pressor amine. Kidneys with normal blood flow fail to transform dopa into a pressor substance.

NUTRITIONAL DEFICIENCIES AS A CAUSE OF ELEVATED BLOOD PRESSURE IN RATS (WITH ESPECIAL REFERENCE TO THE VITAMIN B(2) COMPLEX)

The effects of dietary deficiencies on the blood pressure of rats were studied, with especial reference to vitamin B deficiencies. A deficiency of the entire vitamin B complex was followed by a slight fall in blood pressure. A deficiency of only thse heat-stable fractions was followed by a significant and persistent rise in pressure, which could be reversed by restoring these factors to the diet. Partial deficiencies were followed by a higher rise of blood pressure than were complete deficiencies, perhaps because of the debilitating effects of the latter. Even an excessive intake of the heat-stable fractions of the vitamin B complex did not prevent entirely a rise of pressure if the diet was otherwise deficient. Under the latter conditions, the rise in pressure was slower and less marked than in those animals with a deficiency of the vitamin B₂ complex only. It therefore appears that, while a deficiency of the vitamin B₂ complex plays a dominant rôle in causing a rise of blood pressure in rats, other dietary factors as yet undefined are also involved. From analogy with other deficiency states, it is possible that thsese undefined nutritional factors cause their effects by interfering with absorption and utilization of the vitamin B₂ complex.

The pathogenesis of hypertension induced by renal constriction

Blood pressures were determined on forty-two young male albino rats and a basal level established. The rats were then divided into four groups and subjected to one of the following operations: (a) unilateral nephrectomy with exposure and handling of the opposite kidney; (b) unilateral nephrectomy and constriction of the remaining kidney with a silk figure-of-eight ligature; (c) unilateral renal constriction with a silk figure-of-eight ligature, the other kidney being left intact after exposure and handling; (d) unilateral nephrectomy and removal of the poles of the contralateral kidney (three-quarters nephrectomy). The animals were followed for 50 days, during which blood pressures were measured on twenty occasions, then killed by exsanguination under ether anesthesia. The organs were weighed according to a standardized procedure and studied histologically. Individual determinations of serum creatinine and of the hematocrit levels were made. Mean lines and frequency distributions of blood pressure were subjected to statistical analysis. A definitely significant increase in blood pressure developed in the group subjected to operation (b) within 4 days postoperative. In none of the other groups did hypertension develop. Analysis of the individual renal weights and creatinine levels indicates the independence of the development of hypertension from the total mass of functioning renal tissue. Nor is it dependent on the prevention of renal hypertrophy or the presence of fibrous perinephritis. The effect is probably due to the production of a disturbance of hemodynamics or tissue tension with the liberation of a pressor substance by the injured kidney.

THE EFFECT OF HIGH PROTEIN DIETS ON EXPERIMENTAL RENAL HYPERTENSION

The effect of high and low protein diets were studied on fourteen dogs in twenty-four different experiments. In only two of these animals, both with moderate renal excretory failure, was a reversible rise in blood pressure elicited by a high protein diet. The possible mechanisms involved in meeting an increased excretory load are discussed.