Sticky Acromegaly-- The Basics

Discussion in 'Acromegaly / IAA / Cushings Cats' started by Carolynn FletcherGA & RobbieGA, Dec 30, 2009.

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  1. Carolynn FletcherGA & RobbieGA

    Carolynn FletcherGA & RobbieGA Member

    Dec 28, 2009
    Posted by: Beth & Pickles (Tam GA) (IP Logged)
    Date: August 31, 2008 03:45AM

    With more new owners joining the Acrocat group I think it's important to make sure that everyone understands what Acromegaly actually is. Why we see the things we see in the cats, what's going on to produce the outward signs and thus the reason why we do some things. I've written this as simply as I could so that hopefully everyone can understand. I'm not suggesting that people are unable to understand biology but I'm aware that we all have our strengths and biology might not be one of them!

    Acromegaly is caused by prolonged overproduction of Growth Hormone (GH) by a pituitary gland tumour. The pituitary is a small gland at the base of the brain that produces several important hormones to control body functions such as growth and development, reproduction, and metabolism. An adenoma (tumour) in the pituitary gland at the base of the brain causes the excess production of growth hormone. These tumours are usually benign and grow slowly, gradually producing more and more GH. Most pituitary tumors arise spontaneously and are not genetically inherited. Many pituitary tumors arise from a genetic alteration in a single pituitary cell which leads to increased cell division and tumor formation. This genetic change permanently switches on the signal that tells the cells to divide and secrete growth hormone. In some instances, the tumor can be present in another organ of the cat's body, such as the pancreas or liver.

    Growth Hormone has several functions including the stimulation of production of insulin-like growth factor 1 (IGF-1) which is mainly made by the liver. Almost every cell in the human body is affected by IGF-1, especially cells in muscle, cartilage, bone, liver, kidney, nerves, skin, and lungs. IGF-1 also regulates cell growth and development, especially in nerve cells. IGF-1 attatches itself to a cell and says "Grow".

    As it's name suggests, IGF-1 is very similar in structure to insulin and in excess quantities (like in an acrocat) it competes with the cat's own insulin to fill the insulin receptor sites on the cell surfaces. However, IGF-1 doesn't do the same job as insulin (helping get the glucose into the cells) so an acrocat has high blood suagrs and needs huge amounts of insulin to out-compete the IGF-1 at the receptor sites. Think of the hormones (IGF-1 & insulin) as keys and the receptors on the cells as locks. You need the right key to put in the lock to open the door to the cell to get the job done. So with IGF-1 in an insulin receptor it's a bit like putting the wrong key into a lock - it doesn't open the door but it also prevents the right key from being used. In acrocats the pancreas still works just fine. It puts out insulin when there is glucose in the blood needing to be taken to the cells for fuel. The problem is that the pancreas can't kick out enough insulin to out compete the IGF-1 so we have to help by providing 'extra' insulin so there are more of the right kind of keys to make it into the locks.

    Once IGF-1 levels get to a certain level in the body, signals are sent back to the pituitary gland to reduce growth hormone out put. As the growth hormone levels drop so too does the IGF-1 levels. However, in an acrocat the tumour isn't listening. The pituitary tumour ignores the signal to turn things down & continues to make growth hormone. As a result the level of IGF-1 continues to rise to abnormally high levels.

    Prolonged high IGF-1 levels lead to the insulin resistance, organ and soft tissue growth (pot belly, narrowed airways) and changes in bone structures (big jaws, paws, longer limbs). It also means that even though the cat has uncontrolled diabetes and is not being able to effectively get all the nutrition it gets from it's food an acrocat often doesn't loose weight and might even gain weight.

    The Pituitary Gland naturally fluctuates the amount of hormones it gives out hour to hour, day to day, week to week. This is a normal process which sometimes can influence the tumour cells. This means that in some cats the tumour cells do not give out a constant flow of GH. The tumour cells are not so sensitive as the proper Pituitary Cells so the changes in the amount of unwanted GH are not necessarily obvious or predictable. However, it does mean that just how 'diabetic' an acrocat is on any given day can change. Several acrocats can go for several days (or weeks in some cases) with normal BGs because the amount of GH coming from the tumour has dropped, which drops the IGF-1 levels. Lower IGF-1 levels means the cat's own insulin 'keys' are sufficient to cope with the blood glucose levels (they're not being out numbered by too many IGF-1 keys in the insulin locks). That means the amount of insulin we need to give to help out is reduced.

    There is nothing we can do about the damaging effects of the excess IGF-1 (apart from considering raidiation therapy) so we try to decrease the damage done by high BGs for as long as possible. Also by limiting the damage of high BGs to the pancreas we are trying to make sure it's not damaged so that it can continue to help.

    There are three main tools (weapons?!) that we have to fight acromegaly in our cats:
    1. Appropriate diet
    2. Hometesting the BGs
    3. Appropriate Insulins & dosing schedules

    Beth & Pickles (GA)
    Norwich, UK
    Dx with Diabetes Mar 2005. Dx with Acromegaly Oct 2006
    Died: 11th July 2007 - Pancreatic cancer.
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