Effect of Losartan on Plasma Aldosterone and Renin
Losartan causes plasma aldosterone concentrations to fall while simultaneously increasing plasma renin activity 2-3 fold and plasma angiotensin II levels 2-3 fold. 1
Mechanism of Action
Losartan blocks the AT1 angiotensin II receptor, which directly interrupts aldosterone secretion by the adrenal cortex 1. By removing the negative feedback that angiotensin II normally exerts on renin release, losartan causes a compensatory doubling to tripling of plasma renin activity and a consequent rise in angiotensin II plasma concentrations 1.
Specific Hormonal Changes
Aldosterone Response
- Plasma aldosterone concentrations fall following losartan administration 1
- This decrease occurs despite the rise in angiotensin II levels, because losartan blocks the AT1 receptor through which angiotensin II stimulates aldosterone secretion 2
- The aldosterone reduction is dose-dependent and clinically significant 2, 3
Renin Response
- Plasma renin activity increases 1.7-fold with 100 mg losartan (compared to 2.8-fold with ACE inhibitors like enalapril) 2
- In some studies, renin levels increased up to 100-fold with chronic administration 4
- The renin increase is greater at 2 weeks than at 6 weeks of treatment, suggesting some adaptation over time 2
Angiotensin II Response
- Plasma angiotensin II increases 2.5-fold with 100 mg losartan 2
- This contrasts sharply with ACE inhibitors, which decrease angiotensin II by 77% 2
- The elevated angiotensin II does not counteract the antihypertensive effect because the AT1 receptor remains blocked 2
Clinical Context and Timing
The hormonal effects show distinct temporal patterns:
- Peak effects occur 4-6 hours after dosing, when receptor blockade is maximal 5
- At trough (24 hours post-dose), plasma renin activity remains elevated but angiotensin II and aldosterone changes are less pronounced 5
- After the last dose, plasma renin activity and angiotensin II return to placebo levels by 36 hours 2
Dose-Response Relationship
The effects are dose-dependent 2:
- 25 mg losartan produces modest changes
- 100 mg losartan produces the full hormonal response described above
- Higher doses (150 mg) do not produce substantially greater hormonal changes, though they may improve clinical outcomes 6
Potassium Effects
Despite the fall in aldosterone, losartan causes very little effect on serum potassium 1. This is clinically important because it means losartan does not typically cause the hyperkalemia that might be expected from aldosterone suppression.
Comparison with ACE Inhibitors
The hormonal profile differs from ACE inhibitors 2:
- ACE inhibitors: ↑↑↑ renin, ↓↓↓ angiotensin II, ↓ aldosterone
- Losartan: ↑↑ renin, ↑↑ angiotensin II, ↓ aldosterone
This distinction is mechanistically important but does not translate to major clinical differences in most patients.
Special Populations
In end-stage renal disease, losartan still decreases plasma aldosterone and increases plasma renin activity, with no dosage adjustment required 7. In heart failure patients, the aldosterone suppression occurs in a dose-dependent manner, with compensatory increases in both angiotensin II and renin that are greatest at the highest doses 3.
Implications for Primary Aldosteronism Screening
ARBs like losartan can interfere with primary aldosteronism screening by raising renin levels, potentially causing false-negative aldosterone-to-renin ratio (ARR) results 8, 9, 10. Current guidelines recommend withdrawing ARBs for at least 2-4 weeks before measuring the ARR for diagnostic purposes 8, 9. However, if renin remains undetectable despite ARB treatment, this makes primary aldosteronism strongly suspected 8.