Re: electrolyte supplementation

[Susan Evans Garlinghouse <suendavid@worldnet.att.net>]

Debby, I agree with Heidi, I think you're thinking of
calcitonin---calcitriol is one of the terms for the active form of
vitamin D3, aka 1,25-dihydroxycholecalciferol (see why the easier name
of calcitriol)?  It does have a hand in calcium metabolism, but not in
the way you're describing, that's calcitonon and, as Heidi explained,
it's effects on parathyroid hormone and hence effects of plasma calcium
during exercise.

PTH is what they call an "inducible hormone", meaning that it's levels
are dependent on the changing needs for it (as opposed to other hormones
which stay constant no matter what).  You could induce increases in PTH
before an event, but in doing so by witholding one feed or another,
whatever benefits you're getting by stimulating PTH levels are probably
going to be lost in the general upset you're causing by changing the
ration and putting microbial populations into an uproar.  Both are
pretty subtle effects, but there nonetheless.

Rather than trying to stimulate PTH before an event, you're alot better
off feeding a ration that is adequate, but not excessive, in calcium and
letting the homeostatic systems adjust themselves accordingly---you'll
have a MUCH better response during exercise than by witholding calcium
feeds before a ride.:-D

Susan Garlinghouse

> In a message dated 98-04-19 00:36:04 EDT, Debbyly@aol.com writes:
> 
> <<
>  At the AERC convention several years ago there was a lecture about the
>  mechanisms for utilizing calcium during an endurance ride.  It had to do with
>  a form of calcitriol (sp?) that, according to this theory, would be produced
>  in greater quantities if the horse was stressed with calcium depletion a few
>  days before the ride.
> 
> Debby, are you talking about calcitonin?  That is a hormone which regulates
> calcium.  If there is always a lot of calcium available, the parathyroid gland
> does not produce large quantities of the hormone, so that if a great need for
> calcium arises (such as an endurance ride, or lactation, etc.) the body is not
> able to mobilize calcium and gets into trouble.  However, I think the time
> frame is more than just a few days, if I remember my endocrinology correctly.
> At any rate, the upshot is that feeding too much calcium can actually cause a
> serious drop in calcium at these crucial times since the body's ability to
> mobilize it is not up to par.
> 
> Heidi