Thanks for all the great questions. I’ll take a stab at a few. We all have different experiences and see things from different vantage points so our answers are not identical in where we place our emphasis. Also, it’s possible that you haven’t quite defined the question for what you want to know. That happens to me a lot.
Pergolide lowers insulin by mediating the effects of PPID, specifically the increase in hormones such as ACTH. These elevated hormone values can result in increased insulin. The only hormone we are able to measure, related to PPID, is ACTH. But there are other hormones which are also affected by PPID. I don’t know which hormone(s) are responsible for increasing insulin because my horse never showed an elevated insulin, even when his ACTH was not particularly well controlled. So, it’s quite possible that Vandy’s insulin would improve dramatically if her PPID were better managed.
There are occasional horses who never show much of an ACTH increase but have good reason to be PPID. I have one and there are others on the group. The point of the TRH stim test is to identify those horses more conclusively. Whether it picks up all of them, I don’t know but you are fortunate in that it did identify Vandy as one of them. I did not do the stim test on my little guy because I wasn’t aware of its existence many years ago when he was first tested.
So, what the test is telling you is that it’s primarily hormones other than ACTH that are being elevated in her PPID. My big guy was on a significant dose of pergolide. He had maintained an ACTH of about 30 but not entirely symptom free. Nice low insulin, fortunately. I switched him to another drug used for PPID and it immediately became obvious that an ACTH reading of 30 had not been telling the whole story. After a very remarkable veil, he began to blossom. At age 31! Even his top line showed improvement in a very short time. When I tested his ACTH, it was higher than I’d ever seen it, at slightly over 100.
To me, there is no question but that Vandy is PPID and quite likely would benefit from considerably more pergolide. In my mind that’s a win because treating the PPID with medicine makes management of IR so much easier. My understanding is that your horse’s breeding, as a Paint, is closely tied to QH? QHs are less likely to be insulin resistant without the provocation of PPID than other horses so that makes it even more likely that your solution is more pergolide.
Martha in Vermont
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