Regulation of ADH: Adh Secretion

by Carlo Raj, MD

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    00:00 and 3, three major actions of ADH. Beautiful table here for us to truly understand.

    00:03 Do you remember those wheels of life? And by that I mean, we took a look at two circles, one circle was dealing with tonicity and the other circle was dealing with volume. Do you remember that? And I told you at that time with the circles that you wanted to pay attention to the tonicity first because that becomes of upmost priority and importance within our body on a day-to-day breath-by-breath moment, With that said, tonicity, what was the hormone that was responsible for properly monitoring or regulating your tonicity? I believe it is ADH. That is correct.

    00:43 And osmoreceptors, remember all of that also plays a role as we discussed in the very beginning of this lecture. Let us take all this into consideration. I want to set up this graph. You see it first and then we are going to walk through the verbiage, not vice versa. I want you to see it first, then we will walk to the words. Otherwise, I am wasting your time. On the X-axis is your percentage change. On your Y-axis, actually says plasma ADH. So as you move up the Y-axis, you are increasing your plasma ADH and the X-axis represents the percentage change that is occurring. Now, that is just the parameters. Let us now make sense of all this, what I really need to also pay attention to is the actual terminology here, that yellow golden lines solid and linear fashion that you are seeing there is your isotonic osmotic increase. I would like for us to work on that first, please. That linear relationship that you see on the golden line there represents for every percentage increase in tonicity.

    01:53 You find a linear increase of your ADH. So even a little bit of increase of your osmolarity tells your osmoreceptors and signals the release of ADH. That is how important as I said plasma osmolarity is to you and how important it is to regulate that. Okay. If that is the case and that is your osmotic line, what is the green curve that we are seeing? Well go up to the key and in the key, you'll noticed that this is isotonic volume depletion.

    02:28 Do you see as to how I emphasize depletion? So the percentage change here on your X-axis is representing volume loss percentage. What is that magic number? Do you remember when you had a crossover? What crossover? What does that even mean? Dr. Raj, I don't remember anything that you are saying. Yes, you do. The wheels, the tonicity was one wheel and that was dealing with ADH and the other wheel in the circle that I showed you was dealing with aldosterone and volume and then I told you that tonicity is measured and regulated all of the time, volumes when need be with aldosterone. At some point in time, when you have enough volume loss of ten percent of the effective circulating volume, you will then have a crossover effect of one circle to another. In other words, you will have the angiotensin II from the wheel of the volume, which is then going to trigger the release of ADH, which is then going to do what? Now keep in mind what the heck is going on here clinically? You have lost greater than ten percent of volume. Do you understand the significance of that? Let us back up, big picture. Your patient just lost greater than ten percent volume. What does that mean? Massive hemorrhage. So what do you think is the most important thing to do in your body? It is to replenish what? The volume, isn't it? So, therefore, the osmolarity will then be sacrificed for the replenishment of the volume. That is a lot of information for you to interpret in this graph and all of it is here, but the only way that you make sense of it is by listening to my previous discussions that we have had about regulation.

    04:11 And if you weren’t paying attention there, that is okay, there's a lot of information.

    04:14 Go back and review those wheels real quick for me. Take a look at that crossover effect. You pay attention to that ten percent that I refer to there and you will notice that here. Take a look at the red box now. That red box as you move from zero on the X-axis, 0, 5, 10.

    04:31 That's ten percent. Now for volume, that means that you have lost up to or greater than ten percent. I want you to move up now, the Y-axis you will notice. Please notice between 0 and 10 percent was there much of a change on your Y-axis? Look. Once again between 0 and 10 were there much of a change on your Y-axis? No there wasn't. It was pretty flat. It means the ADH remained at a relatively constant level maybe it increased a little bit, but my goodness you go beyond 10 percent loss of your volume, you almost find not just a linear, but hyperbole type curve in which you have a massive release in ADH because the volume must be replenished because your patient is in severe hypovolemic shock. With all that said, let us now walk you through the verbiage that we see here. They're controlled by the hypothalamic osmoreceptors. Who is? ADH secretion. That is the theme of this slide.

    05:36 ADH secretion stimulated by plasma osmolarity. Plasma hypovolemia. Stop there. That is the big deal now, isn't it? When do you have hypovolemia that finally releases ADH? That is the big point.

    05:53 That is the green line. That is the green curve. It is only when you lose greater than 10 percent in which plasma hypovolemia will release ADH. Apart from that, on a homeostatic control mechanism in which everything is normal, it is plasma osmolarity that truly regulates your ADH, as I said on a minute-to-minute basis. This crossover effect meaning who is it that comes from the volume circle that then is going to release ADH to then control or should I say release your ADH? And that is going to be angiotensin II. Remember the angiotensin II was on the wheel of your volume and that was dealing with sodium and company. You only have that crossover effect with angiotensin II. So, therefore, that also becomes extremely important. Let us move on ADH inhibition. So if hyperosmolarity within the plasma, therefore, released ADH, you will notice you have hypo-osmolality. In other words, your plasma is diluted thus you are going to inhibit ADH and plasma hypervolemia, the opposite. They are also though, would be, well we will take a look at a graph in a little bit where 10 percent becomes interesting.

    07:12 So at this point though, your focus should be on volume loss and only after you have understood everything that I have said, you will go into hypervolemia, but not before that, please. Now, overall physiologic range of effective circulating volume, what that represents is from 0 to 10 percent X-axis and you don't have much of a change in ADH with volume. In general, only volume depletion now here is the point. Take a look at where now we have had a blank from 0 to 10. The 10 has now been boldened and look at the verbiage. The words are saying here depletion of greater than 10 percent has a severe stimulation of ADH release and hence you find that the green curve is now taking a drastic increase on your Y-axis. What happen here? Hypervolemic

    About the Lecture

    The lecture Regulation of ADH: Adh Secretion by Carlo Raj, MD is from the course SIADH.

    Included Quiz Questions

    1. Plasma hyper-osmolality
    2. Plasma hypovolemia
    3. Plasma hypervolemia
    4. Plasma hypo-osmolality
    5. Plasma renin activity
    1. Angiotensin II induced ADH release
    2. Activation of osmoreceptors in the hypothalamus
    3. Plasma hypervolemia
    4. Increased systolic blood pressure
    5. Increased activation of systemic baroreceptors
    1. ADH secretion is inhibited by plasma hypo-osmolality.
    2. Plasma volume is tightly regulated by ADH release.
    3. ADH is released from the anterior hypothalamus in response to decreased plasma osmolality.
    4. Under normal conditions, angiotensin-II is the most important regulator of ADH release.
    5. ADH release is triggered by activation of osmoreceptors in the anterior pituitary.
    1. Thirst
    2. Urine osmolarity
    3. V1 receptor activation
    4. Urine volume
    5. Plasma osmolarity

    Author of lecture Regulation of ADH: Adh Secretion

     Carlo Raj, MD

    Carlo Raj, MD

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