Re: trying to rule out pre-cushings with IR pony
Eleanor Kellon, VMD
It really is confusing!
IR only causes increased urination when blood sugar is elevated (typically has to be close to 200 to have this effect). Are you able to accurately keep track of how much water he drinks? Studies are divided on whether or not there is a seasonal change in insulin sensitivity.
Intolerance to heat can be a weight issue, especially if he is sweating well. It's also difficult to sort out respiratory distress from heat distress and breathing is much more difficult in hot and humid weather. Any one of the other signs could just be an individual thing but taken together I agree they point to PPID and TRH stimulation test is the way to go. Also important to note there are some PPID horses whose hormonal profile doesn't include obviously elevated ACTH. In fact, this group founder's mare was like that! It probably shouldn't be surprising when you consider that of all the hormones put out by the pituitary in PPID, ACTH is by far at the lowest concentration. We're way past the time to switch to testing POMCs across the board or alpha-MSH instead.
McFarlane's study on ACTH and pergolide in PPID horses found that by 10 days after the last dose there is no detectable pergolide in any horse. At five days, half the horses still had low levels of pergolide but 2/3 were showing ACTH on the rise. At 2 days after the last dose, ACTH had increased by 50% in half the horses and there was a significant rise in all the horses by 14 days after stopping pergolide and this continued to rise to the 21 day mark.
As an aside, do you see any pattern to his insulins, weight or crest when he's getting Lung EQ?
Eleanor in PA