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Discussion on Levothyroxine and IR
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Member:
gwenyth
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Posted on Monday, Jun 15, 2009 - 4:14 pm:
I came across the following article:
"Insulin sensitivity and insulin resistance in horses have become increasingly important areas of research in equine medicine over the past several years, as evidenced by the timely and popular presentations at this year's American College of Veterinary Internal Medicine (ACVIM) Forum, held June 4-7 in San Antonio, Texas.
Rebecca Carter, a PhD candidate from Virginia Tech, and co-author of the research abstract, "Increased adiposity in horses is associated with decreased insulin sensitivity but unchanged inflammatory cytokine expression in subcutaneous adipose tissue," described their study of obesity, insulin sensitivity, and inflammation in horses.
Researchers fed 12 Arabian geldings 200% of their energy requirements for four months to induce weight gain. Various parameter evaluating adiposity, glucose, and insulin dynamics, and inflammation were assessed before and after weight gain.
At the end of the study, body weight, subcutaneous fat, resting insulin levels, and insulin responses were all significantly increased while insulin sensitivity was significantly decreased. No changes in the expression of the measured markers of inflammation were noted.
Together, these results indicate that overweight horses have decreased insulin sensitivity and experience a compensatory increase in insulin secretion.
In the abstract, "Effects of pretreatment with dexamethasone or levothyroxine on endotoxin-induced insulin resistance in horses," Ferenc Toth, DVM, PhD and colleagues evaluated whether resting insulin sensitivity could affect the degree of insulin resistance caused by endotoxins. Endotoxemia, which is caused by release of toxins produced by gram negative bacteria (such as Escherichia coli), is associated with laminitis and is a life-threatening condition in horses.
Twenty adult mares were included in the study and randomly divided into the control (n=8), dexamethasone pre-treatment (n=4), or the levothyroxine pre-treatment group (n=8). While 14 days of dexamethasone administration exacerbated insulin resistance and potentially decreased insulin sensitivity, 14 days of levothyroxine treatment prevented the endotoxin-induced insulin resistance.
Toth explained that together, these results suggest that insulin resistant horses that develop endotoxemia might experience marked alterations in insulin sensitivity, but vets might be able to reduce these changes with levothyroxine pretreatment.
Research in the field of insulin sensitivity and resistance is ongoing."
SO - I was wondering about my IR horse who is currently on Thyro-L. I understand that he is NOT hypothyroid, in fact, he has always tested "normal", but my veterinarian felt it might help him anyway. However, is the Thyro-L ameliorating the IR symptoms (as suggested by the article above), and should I keep him on it? My gelding has lost about 150# in 5 months, due to diet and exercise, and is on 1/2 of the Thryo-L that he was on in January. However, he is still on pasture for 12 hours a day, though I know that is usually not indicated for IR horses. I was wondering if the Thryo-L would be a "protective mechanism" for him being on grass. He is continuing to lose weight despite the pasture time. He gets no grain.
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Member:
scooter
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Posted on Tuesday, Jun 16, 2009 - 8:07 am:
Hi Nancy, my vet also suggested thro-L for my IR easy keeper. I read the same article and really considered it. I decided tho that if I could control it with diet and exercise I didn't want to add any drugs.
It is possible your horse can tolerate grazing because he has lost weight and not because of Thyro-L.
I JUST had this discussion with my vet again, he said again I should try Thro-L for Hank...not sure why, he is doing wonderful with diet and exercise.
I told my vet the thing I find scary about him recommending this stuff, is owners may think their IR horses are safe from founder and not still continue to manage them properly.
My personal opinion is if it helps with no ill effects I guess it's worth a try, I just don't like adding drugs if it isn't necessary JMHO.
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Moderator:
DrO
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Posted on Tuesday, Jun 16, 2009 - 8:51 am:
Hello nancy,
Thanks for bringing this paper to our attention and I hope to find the whole piece to study. From the information above the above paper does not suggest that the thyroid hormone supplementation ameliorated the effects of insulin resistance (IR) caused by obesity. The paper found pretreatment with thyroid hormone prevented an increase in IR induced by endotoxin administration in obese horses who already had an increased IR. However there is a potential mechanism already studied that suggests that thyroid supplementation may help with the problem of obesity and therefore help with decreasing IR.
Starting early last year we began reporting on the beneficial effects of thyroid supplementation in obese horses. Note that anything which reduces weight reduces IR. However my own experiences were not so positive during years of experience with thyroid supplementation in obese horses predisposed to founder. In contrast to thyroid supplementation I always had good experiences with dietary control though in some horses management was not easy. I am wondering if thyroid supplementation would help make obesity control easier without doing harm. In all other species supplementing thyroid hormone in the euthyroid individual leads to adverse consequences. Studies and experiences in horses suggest they are not as sensitive to oversupplementation.
I continue to watch this issue closely and feel this is a very complicated issue partially because of the ease with which the effects of digestible and nondigestible nonstructural carbohydrates are confused as they always occur together in forages yet may have very different effects with respect to obesity, IR, and the induction of founder.
For more on the recent issues of hormone supplementation see Diseases of Horses » Endocrine System » Hypothyroidism in Adult Equines » Research Summary: Thyroid Supplementation for Weight Control?.
DrO
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Member:
gwenyth
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Posted on Tuesday, Jun 16, 2009 - 3:40 pm:
DrO - my gelding has been on Thyro-L for 4 years as my vet was not sure why he was so fat. It did help his obesity initially (as is suggested above), but as time went on, it had less effect and I increased the dosage as recommended by my vet. He was diagnosed with IR (lab test) in January 2009, and when I found your website I followed the diet/exercise recommendations, and the weight came off.
I have cut back his Thyro-L as you recommend. However, my question is - since he has been on Thyro-L for 4 years, and is 18 years old, will his thyroid "take over" as I cut back on the supplement, or must I keep him on it? I have cut him back from 3t to 1 1/2 t daily.
That is why the article I quoted above was interesting to me - It suggested that there may be a link between IR, obesity, and Thyroid supplementation, still to be determined.
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Moderator:
DrO
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Posted on Wednesday, Jun 17, 2009 - 8:19 am:
Thanks for the background nancy, I had your experience dozens of times when I first starting practicing and your post somewhat reaffirming for me.
I go to these conferences and read these papers where positive effects of L-T4 supplementation are presented and wonder what planet they are conducting experiments on. I often think the devil may be in the details but I do try to keep an open mind just in case I am, for lack of a better expression, full of it on this issue.
If I had some uncontrolled horses in the practice I might be tempted to try it again just as an experiment but then I get back to the fact that I am making some very basic changes in the horse's metabolic regulatory system that is not clearly indicated. I continue to have a problem with that.
DrO
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Member:
gwenyth
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Posted on Wednesday, Jun 17, 2009 - 3:14 pm:
DrO, glad I could give you confirmation - I am quite positive that testing my horse for IR and getting him on the diet and exercise program has given him a "new lease on life" and I truly thank you for it!! My veterinarian is astonished, and I think it is safe to say that she would follow these guidelines with other obese horses in her practice.
However - my question - would you remove a horse COMPLETELY from Thyro-L after 4 years of treatment on the drug or does the drug cause the thyroid gland to atrophy/quit working permanently? I want to remove him from it, but my veterinarian is concerned that his thyroid gland will no longer work properly after 4 years of supplementation. I have DrOpped the dosage by 1/2t daily every 30 days, so it has been a very gradual process.
Thanks so much for your advice.
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Moderator:
DrO
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Posted on Thursday, Jun 18, 2009 - 7:43 am:
I have not seen any evidence that the drug causes permanent damage and have gradually removed horses that have been on Thyro-L for longer than 4 years without complications.
DrO
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Member:
gwenyth
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Posted on Thursday, Jun 18, 2009 - 7:50 am:
Excellent - then I will continue to reduce it gradually as I have been doing.
Thanks for your advice!!!
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Member:
kathleen
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Posted on Sunday, Jun 21, 2009 - 4:58 pm:
DrO
According to my vet, Nat Messer has been presenting seminars about his research (combined with the research of others) regarding Thryo-L (levothyroxine) supplementation for EMS horses. In the words of my vet, he is the "guru" on this subject. What is your opinion of Messer's research?
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Moderator:
DrO
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Posted on Monday, Jun 22, 2009 - 7:59 am:
Kathleen can you be more specific, what in particular about Dr. Messers seminars/research you want a comment on? I do see where Dr Messer has published a review paper several years ago in the Equine Clinics series but have not seen his seminar but do not see any research into this subject in particular.
I personally think Dr. Frank and the group out of Uni of Tenn as being on the cutting edge of published research on levothyroxin use in euthyroid obese horse. I outline their findings along with my own thoughts on this above and in the subtopic on this in the article on EMS.
DrO
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Member:
kathleen
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Posted on Tuesday, Jun 23, 2009 - 9:09 pm:
I'm sorry, I guess I was not clear about my question. Dr Messer has been giving 'seminars' (for lack of a better word) regarding Thyro-L supplementation for EMS horses. As you mentioned in your answer, it is about 'euthyroid obese horses'. I wanted to know if you knew about his latest research (ie as a paper or as presented at one of the annual conferences that you vets have - maybe one of those that you mention above  ). I assume from your answer that you are not familiar, so thank you very much for your time and I'll continue my journey for info on this subject.
Kathleen
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Member:
gwenyth
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Posted on Tuesday, Jun 23, 2009 - 9:46 pm:
Kathleen, I seem to remember something in "The Horse" magazine about this research, You can go to their website and search for articles online. Good luck!
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Moderator:
DrO
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Posted on Wednesday, Jun 24, 2009 - 7:27 am:
Kathleen, no I have not heard Nat Messer speak so do not know what information he may be presenting on Thyro-L and IR so don't know if I am familiar or not. However the latest published research is presented in our articles and includes Dr Messer's research on adipokines. I would hope his opinion reflects this research.
I did attend Dr Frank's presentation at the AAEP meeting 6 months ago on Endocrinopathic Laminitis, Obesity-Associated Laminitis, and Pasture- Associated Laminitis. Do to his extensive peer reviewed published research on this subject, I believe Dr Frank's should be considered the cutting edge and his work is reflected in our article on EMS, IR, and laminitis and their respective pathophysiology and treatment.
DrO
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