Lapis ISSN 2398-2969

Hypervitaminosis A

Synonym(s): Vitamin A toxicity

Introduction

  • Vitamin A   Vitamin A  is a generaly term for a large number of related compounds.
  • Retinol + retinal together are preformed vitamin A, which becomes retinoic acid in animal tissues.
  • Carotenoids are pigments formed by plants (beta-carotene being the most important); these compounds are converted to retinol within mucous membranes once eaten.
  • Retinol is stored in the liver bound to proteins (retinol binding proteins or RBPs) from where it is delivered to cells according to need.
  • Vitamin A is essential for bone development, maintaining epithelial integrity, reporduction and mounting an immune response.
  • Cause: excess vitamin A intake, possible iatrogenic overdose.
  • Signs: squamous metaplasia, kertainization of mucous membranes, pain/tenderness of bones/joints.
  • Diagnosis: hematology, biochemical evaluation, liver/kidney function tests, radiography.
  • Treatment: no specific treatment or antidote available. Stop access to feed containing vitamin A and vitamin A supplementation, rehydration, use of diuretics if hypercalcemic. Empirical treatment of seizures may be required. Vitamin E supplementation may be helpful.
  • Prognosis: long-term skeletal changes possible.

Presenting signs

  • Similar to those of deficiency and include squamous metaplasia and keratinization of mucous membranes.
  • Pain and tenderness of long bones and joints.
  • Cervical ventroflexion reported in other species.

Acute presentation

  • Significant acute overdose is very unlikely and has not been reported in the rabbit specifically; the potential for this to occur iatrogenically should be noted.
  • Extrapolating from other species expected signs might include malaise, anorexia, weakness, possibly progressing to tremors, covulsions, paralysis and death.

Age predisposition

  • The effects of overdose are worse in young animals as their ability to store vitamin A is less.

Cost considerations

  • Potentially significant, especially in breeding colonies.

Special risks, eg anesthetic

  • Vitamin A maintains the integrity of mucous membranes; therefore any organ system reliant on these will be functionally impaired in cases of overdose.
  • This includes the lungs, making anesthesia an increased risk, and the kidneys therefore concomitant drug use should be approached with caution.
  • Vitamin A is often called the anti-infection vitamin and therefore individuals suffering from overdose may be at increased risk of infection.

Pathogenesis

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Diagnosis

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Treatment

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Prevention

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Sequelae

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Castellini C, Mourvaki E, Dal Bosco A et al (2007) Vitamin E biochemistry and function: A case study in a male rabbit. Reprod Dom Anim 42 (3), 248-256 PubMed.
  • Czarnecki W & Zimmer L (2006) Pharmacokinetics and bioavailability of alpha-tocopherol in rabbits. Annales Universitatis Mariae Curie-Skladowska Lublin-Polonia 19 (2, 22), 153-160.
  • Schneider C (2005) Chemistry and biology of vitamin E. Mol Nutr Food Res 49 (1), 7-30 PubMed.
  • Axford-Gatley R A & Wilson G J (1990) Reduction of experimental myocardial infarct size by oral administration of alpha-tocopherol. Cardiovasc Res 25 (2), 89-92 PubMed.
  • Godfried S L, Combs G F Jr., Saroka J M et al (1989) Potentiation of atherosclerotic lesions in rabbits by a high dietary level of vitamin E. Br J Nutr 61 (3), 607-617 PubMed.
  • Bardosi A & Dickmann U (1987) Necrotizing myopathy with paracrystalline inclusion bodies in hypervitaminosis E. Acta Neuropathol 75 (2), 166-172 PubMed.
  • Jack Yang N Y & Desai I D (1976) Effect of high levels of dietary vitamin E on hematological indices and biochemical parameters in rats. J Nutr 107 (8), 1410-1417 PubMed.

Other sources of information

  • Higdon J, Drake V J & Traber M G (2008) Vitamin E. Oregon State University, Linus Pauling Institute, Micronutrient Information Center. Website:http://lpi.oregonstate.edu/infocenter/vitamins/vitaminE. Last accessed 16th September 2010.
  • Higdon J, Drake V J & Russell R M (2007) Vitamin A. Oregon State University, Linus Pauling Institute, Micronutrient Information Center. Website:http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA. Last accessed 16th September 2010.
  • Harcourt-Brown F (2002) Textbook of Rabbit Medicine. Butterworth Heinemann.
  • McDonald P, Edwards R A, Greenhalgh J F D & Morgan C A (1996) Animal Nutrition. 5th edn. Longman.
  • Cheeke P R (1994) Nutrition and Nutritional diseases. In: Biology of the Laboratory Rabbit. 2nd edn. Eds: Manning P J, Ringler D H & Newcomer C E. Academic Press. pp 321-333.
  • Hunt C E & Harrington D D (1974) Nutrition and Nutritional diseases of the Rabbit. In: Biology of the Laboratory Rabbit. 1st edn. Eds: Manning P J, Ringler D H & Newcomer C E. Academic Press. pp 403-428.


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