Originally Posted by zip2play
2. Is there a feedback system that tries HARDER to raise BP when we try to force it down.
Yes, it's called renin. Your kidneys produce this in response to a low sodium or low volume (i.e. low BP) situation. Renin is an enzyme that converts angiotensinogen to angiotensin I. And, we all know that ACE then converts I -> II. Which in turn causes BP to go up.
So, if you eat lots of salt, you are screwed. No renin. But, your BP goes up naturally from the volume. If you cut the salt, you're screwed because your kidneys are giving a feedback that ultimately causes vasoconstriction.
In some folks (high renin), this feedback can actually cause BP to be higher in a low sodium/low volume situation. That's why diuretics don't work for everybody. However, if this feedback mechanism is blocked (ACEI or ARB), then diuretics can give better results.
In others (salt sensitive folks), little renin is produced. Therefore, little feedback response. Diuretics work great for these people.