Ah, the renal tubule: the convoluted master of filtration, reabsorption, and secretion. Some parts of the renal tubule have so many receptors and ion channels that they start having really crazy names. This is a great way to nerd out when you are otherwise procrastinating, but for the sake of time, there must be an easier way! This is when we enter the realm of the target.
The renal tubule has four major drug targets:
1. The proximal convoluted tubule
2. The ascending Loop of Henle
3. The distal convoluted tubule
4. The collecting duct
The drugs that target the nephron are usually diuretics. So, they target the tubules in such a way as to make more urine and release more fluid from your body. Other drugs have the opposite effect to help you with, for example, an underactive antidiuretic hormone. Now would be a good time to review renal physiology if you are feeling a little rusty!
There is a great adage thrown around in physiology that really helps when you are looking at diuretics: Where salt goes, water follows. You see, it’s easy to get water out when you can just push out the salt. But what if you need some of that salt (not to mention potassium and magnesium!)? Ah, this is why we have different targets for diuretics!
To have a diuretic affect, drugs have to either promote or block receptors for a certain purpose. Therefore, drugs that target the tubules for diuretic purposes…
1. Block reabsorption, or…
2. Enhance secretion, or…
3. Block antidiuretic hormone (ADH)
So, if you are pushing out more fluid using these mechanisms, you will reduce blood volume, resulting in lowered blood pressure, lessened cardiac workload, and reduced edema!