Interaction between sodium and angiotensin II: role of dose and duration of treatment

Diuretic and Enhanced Sodium Restriction Results in Improved Antiproteinuric Response to RAS Blocking Agents

Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and diuretics may exert synergistic antiproteinuric effects. Eighteen patients with a proteinuria >1 g/24 h after 6 mo of treatment with ramipril at 5 mg/d were assigned to receive in random order ramipril at 10 mg/d, valsartan at 160 mg/d, or combined ramipril at 5 mg/d and valsartan at 80 mg/d in addition to their antihypertensive treatment. The treatment periods lasted 4 wk and were separated by a 4-wk washout with ramipril at 5 mg/d. At the end of this crossover sequence, patients received combined ramipril at 5 mg/d, valsartan at 80 mg/d, and an increased furosemide dosage for an additional 4-wk period. The primary end point was the urinary protein/creatinine ratio for two 24-h urine collections at the end of each treatment period. No significant differences were noted between the study end points of the ramipril 10, valsartan 160, and combined ramipril 5 and valsartan 80 treatment groups. However, the urinary protein/creatinine ratio was lower with combined ramipril 5 and valsartan 80-increased furosemide dosage than with valsartan 160 and combined ramipril 5 and valsartan 80, with a similar tendency compared with ramipril 10. Combined ramipril 5 and valsartan 80-increased furosemide dosage decreased systolic home BP and increased serum creatinine but did not significantly increase the number of symptomatic hypotension cases compared with the other three treatments. Thus, in patients with severe proteinuria and hypertension, a cautious increase in diuretic dosage in addition to combined angiotensin-converting enzyme inhibitors and angiotensin receptor blockers decreases proteinuria and BP but may expose the patient to prerenal failure.

Pathogenesis of structural vascular changes in hypertension

The pathogenic role of angiotensin II (ANG II), dietary sodium chloride, sympathetic activation, obesity and aldosterone in the development of structural vascular changes (SVCs) in hypertension is considered from three perspectives (criteria): their utility in predicting hypertension and its complications (predictability); the effect of their inhibition or removal on the reversal of SVCs (reversibility); and their ability to induce SVCs in experimental animals (reproducibility). Only ANG II meets all three criteria. Importantly, ANG II increases preglomerular vascular resistance by inducing structural changes in renal cortical resistance arteries and arterioles. High salt intake, by dilating and thereby stiffening some arteries, may play a role in the development of systolic hypertension with aging, but does not produce structural changes in renal cortical resistance vessels. While high circulating levels of norepinephrine are associated with SVCs, the experimental evidence for the role of sympathetic nerve stimulation in the development of SVCs is inconclusive. Obesity is associated with hypertension, but is not known to be associated with SVCs. Salt-loading is required for aldosterone to produce SVCs, but vascular pathology in this experimental model differs from that in benign essential hypertension. The findings of this review indicate that SVCs in extra-renal sites by themselves do not lead to hypertension; structural changes in renal cortical arteries and arterioles that increase preglomerular vascular resistance are needed. Progressive trophic stimulation of preglomerular resistance vessels by itself may lead to hypertension. ANG II is prime candidate for such stimulus.

Role of angiotensin II, sympathetic stimulation and salt in the development of structural vascular changes in rat kidney

1. Functional and structural vasoconstriction of renal cortical arteries is the earliest change leading to hypertension. In the present study, the interaction of a subpressor dose of angiotensin (Ang) II, a 2% NaCl diet and sympathetic stimulation in the form of overnight cold exposure was investigated in the development of renal structural vascular changes in male Sprague-Dawley rats. 2. Morphometric measurements of renal cortical resistance arteries and volume density measurements of renal cortical components were performed in eight groups of rats after 12 weeks of treatment: AngII; 2% NaCl diet; cold exposure (5 degrees C); AngII plus 2% NaCl diet; AngII plus cold exposure; cold exposure plus 2% NaCl diet; ANG II plus 2% NaCl diet plus cold exposure; and sham operation and treatment (control). 3. The average weekly systolic blood pressure of AngII-treated plus salt-fed rats was increased, whereas that of cold-stressed plus salt-fed rats at room temperature decreased compared with controls. The blood pressure rise of the former group was accompanied by an increased wall-to-lumen ratio (WLR) of cortical resistance arteries and decreased glomerular volume, whereas the reduction in blood pressure in the latter group was accompanied by a decreased WLR of cortical resistance arteries and increased volume density of cortical renal tubules. There were no changes in either the blood pressure or renal structure of the other groups. 4. There is a parallel relationship between changes in preglomerular structural vascular resistance and changes in blood pressure in rats. It remains to be determined whether renal cortical structural changes are the cause of, or are compensatory for, chronic changes in blood pressure.

Altered structure and reduced distensibility of arteries in Dahl salt-sensitive rats

OBJECTIVES

The role of salt sensitivity in arterial stiffening and the structural basis of reduced arterial distensibility were investigated in Dahl salt-sensitive (DS) rats.

METHODS

Three-month-old male DS rats received a normal (0.7% NaCl) or a high-sodium (2% NaCl) diet for 3 months. Dahl salt-resistant (DR) rats were controls. Pressure-volume (distensibility) relationships were measured in in-vitro-perfused segments of right carotid and iliac arteries, in the presence and absence of extracellular calcium. The left carotid and iliac arteries were perfusion-fixed at 100 mmHg for morphometric measurements.

RESULTS

The average monthly tail systolic blood pressure (SBP) of DS rats on normal and high-sodium diets were increased compared to that of DR rats. Compared to controls, carotid and iliac artery pressure-volume curves of DS rats on normal and high-sodium diets were shifted toward the pressure axis, without a change in elastic moduli. In DS rats, reduced distensibility of the carotid artery was accompanied by increased lumen diameter and increased thickness of media and elastic lamellae, the wall to lumen ratio being unchanged; wall thickness was increased and lumen diameter unchanged in the iliac artery. The high-sodium diet had no effect on either distensibility or dimensions of carotid and iliac arteries in DS or DR rats.

CONCLUSION

Geometry (increased or unchanged lumen and increased wall thickness), rather than increased stiffness of wall components, appears to be the cause of reduced distensibility of arteries in DS rats. Structural and functional adaptation to salt sensitivity may occur on what is considered a 'normal' sodium diet.