Re: Pergolide given in AM?

Eleanor Kellon, VMD

--- In EquineCushings@..., George Browne <gbrowne@...> wrote:

Yes, it would go up. We see it from time to time in advanced PPID/IR horses. Insulin stops climbing and glucose goes up despite a tightly controlled diet.
That must be a real problem to control. Diet certainly, but would the use of insulin injections, as in diabetic humans, be of any use?
Possibly, but the expense and constant monitoring needed make it impractical for most.

Would you consider supplementing L-Tyrosine & phenylalanine useful in horses with PPID?
These amino acids are interconvertible and required for dopamine synthesis. We've actually had a few members try this and there was no effect, likely because the problem is death of the neurons, not amino acid deficiency.

I know haloperidol is used in veterinary applications, though I've not hear of it used in horses. It got me wondering though about not only the sources of oxidative stress but also possible dietary or drug effects on the dopaminergic neurons.
Haloperidol (Haldol) is a heavy duty antipsychotic medication that alters neurotransmitter production, including suppression of dopamine. On the equine end, acepromazine is also a dopamine antagonist, and so is reserpine (sometimes used as a long acting tranquilizer, also an antipsychotic human drug) and domperidone, used to treat fescue toxicosis. Long term treatment with these could lead to a PPID-like state but that would be very unusual.

The suggestion that the MSH test might be more specific for PPID than ACTH because MSH originates in the pars intermedia whereas ACTH comes from the pars distalis is intriguing given the number of horses which test normal for ACTH but benefit from Pergolide, if only during the period of the seasonal rise.

Several years ago UC Davis published preliminary results in their research newsletter on a study that compared MSH, beta-endorphin and ACTH. They concluded that they were equally sensitive and specific in PPID horses. The problem is always with early cases, and even the gold standard of post mortem examination is not clear cut in early cases:

Eleanor in PA
EC Co-owner
Feb 2001

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