vitamin A vs carotenoids

[fluxlizard]

Recently I was re-reading "The Panther Chameleon- Color Variation, Natural History, Conservation, and Captive Management" by Ferguson, Murphy, Ramanamanjato and Raselimanana and came across the following bits-

page 14-

"Substituting carotenoids (pre-vitamin A) for preformed vitamin A has been proposed to be a preferable way to satisfy vitamin A requirements. ... Although this may be true for some species, including humans, there is mounting evidence that panther chameleons can not utilise carotenoids for the required minimum levels of preformed vitamin A. Eggs from wild-caught gravid females contain substantial levels of both vitamin A and carotenoids..."

page 78-

after discussing a recommendation for gutloading crickets 70 IU/g of vitamin A resulting in about 10 IU/g being delivered to the chameleon-

"A diet containing carotenoids but not vitamin A does not seem to be effective at preventing vitamin A deficiency symptoms in panther chameleons."

So, my question is, have their been studies since this book was published in 2004 that show that carotenoids are effectively converted to enough vitamin A in chameleons to prevent vitamin A deficiency?

 

[ChamOh]

good stuff. in for responses.

 

[kinyonga]

This quote "Eggs from wild-caught gravid females contain substantial levels of both vitamin A and carotenoids" is what has always made me wonder why its being said that they can't convert beta carotene (a carotenoid) into vitamin A. At the very least is it not saying that the female must have had carotenoids that she passed on to the egg??? I would like someone to explain it to me if my thinking is incorrect.

 

[fluxlizard]

Well, we are moving beyond my complete understanding a little, but it doesn't necessarily follow that the carotenoids found in the egg are only beta carotene. Maybe we are incorrectly assuming those are the carotenoids referred to by the reference to vit.a in the same sentence? maybe?

Also the function of beta cerotene and other carotenoids is not limited to vitamin A conversion? There are hundreds of kinds of carotenoids and most carotenoids do not convert to vitamin A?

 

[fluxlizard]

It does seem kind of weird though if the author brought carotenoids up in that way without clarifying unless he did mean beta carotene. It probably is what he was referring to.

Yet they were unable to get chams to convert enough beta carotene to vitamin A in the labratory.

Their method seemed to involve delivery only by gutloading though. Vit A amount delivered to the chameleon in this way was 1/7th the amount fed to the crickets- makes me wonder how effective gutloading would have been as a method for delivering beta cerotene. It could be like delivering 1/7th the amount of beta cerotene that dusting could deliver, (or more or less- who knows?). I wonder how many units of beta cerotene would be needed to convert to 1 unit of vitamin A to begin with even before potentially most could be lost to gutloading?

So, all these questions, I am wondering if anyone else has done a study?

 

[kinyonga]

All of these were measured in the eggs..."α- and β-carotene, cryptoxanthin, lutein/zeaxanthin, and lycopene"...and these comments were then made..."Measurable concentrations of retinol at all stages of egg development in the chameleons suggests effective conversion from carotenoid precursors, with concentrations similar to those measured in other lizard eggs"...and...."β-carotene concentrations were of the same magnitude as reported in grazing tortoises"...and..."β-Carotene and β-cryptoxanthin were the predominant carotenoids in yolk and embryos, comprising about 95% of total carotenoids detected"...
http://onlinelibrary.wiley.com/doi/10.1002/zoo.10039/abstract

 

[fluxlizard]

Ah, just what I was looking for.

Thank you!



Now if only I could download the pdf.


That gutloading for delivery thing bothered me.

I'll bet that's why he failed.

 

[fluxlizard]

It occurred to me while I was out feeding my insects this evening that my last statement sounded like I might not believe in gutloading.

LOL

I believe feeding the insects a good diet throughout their life is very important for the benefit of the lizards eating them.

To clarify- It bothered me that he concluded that beta-carotene could not be converted to vitamin a when he apparently only tried providing the beta carotene via gutload and never directly to the lizard.

Thanks again Kinyongia- amazing how you keep up on all the published papers. It's like having a research librarian for the forums.

I learned some stuff today trying to understand this.

 

[kinyonga]

There are still too many papers out there that I need to read. Its a never-ending story.