How do diuretics lower blood pressure?

How do diuretics lower blood pressure?
Brief Review
Diuretics lower blood pressure by lowering the intravascular volume and sodium content.1 It is mentioned that thiazide diuretics reduce the extracellular volume by about two litres and plasma volume by three hundred milliliters by about two days of usage. But some of these effects on volume contraction get compensated on long term usage due to compensatory mechanisms. Moreover, if volume loss was the main reason for lowering blood pressure with diuretics, loop diuretics which produce more of volume loss should have been more powerful anti hypertensives than thiazide diuretics. But the fact is the reverse, except in situations of volume overload where loop diuretics have a better effect on lowering blood pressure.
Lower sodium content may also reduce the vascular tone. It has been shown that total peripheral resistance falls with long term diuretic treatment.2 This lowering of total peripheral resistance occurs only on long term usage and in the acute state, thiazide diuretics increase the total peripheral resistance by reflex sympathetic activity in response to volume depletion.3
It is interesting to note that while diuretics lower an elevated blood pressure, they seldom reduce blood pressure in normotensives.4 Another notable factor is that the antihypertensive effect of thiazide diuretics is persistent while their plasma half life is relatively short.5
A direct vasodilator effect of thiazides have also been shown in smal...

Source: Cardiophile MD - December 22, 2014 Category: Cardiology Authors: Prof. Dr. Johnson Francis, MD, DM, FACC, FRCP Edin, FRCP London Tags: General Cardiology Source Type: blogs