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Vitamin D metabolism in the fruit bat (Rousettus aegyptiacus)

A dissertation submitted to the Faculty of Medicine,
University of the Witwatersrand, Johannesburg
for the Degree of Masters of Science. December 1992. / Rouesettus aegyptiacus, the fruit bat is a crepuscular frugivore with no obvious access
to either exogenous or endogenous sources of vitamin D. Therefore this animal's
vitamin D status and endocrine system was investigated.
Both captive and wild populations of fruit bats appear to be naturally in a vitamin D
impoverished state. The serum concentration of the principle circulatory, metabolite
[25(OH)D] is undetectable (< 4 ng/ml), Fruit bats possess the full compliment of
enzymes associated with the vitamin D endocrine system. This was shown when
labelled more polar metabolites were produced after the administration of 3H vitamin
D3 and 3H 2S(OH)D3' Furthermore, a specific vitamin D binding protein (DBP) is
present. After partial purification, it was revealed that this molecule is slightly larger
in molecular mass than that of humans and baboons.
The intraperitoneal administration of 25(OH)D3 revealed enhanced 1a-hydroxylase
activity such that 1.7 times more 1,25(OH)2Ds was produced than 24,25(OH)2D3' The
ratio of these di-hydroxylated metabolites conform with the ratio of these 2 metabolites
in states of vitamin D deficiency and thus confirm the impoverished vitamin D status.
Undetectable serum concentrations of 25(OH)D3 might therefore be explained by a
limited exogenous vitamin D substrate (rotting fruit peels and fungi). Given the elevated
1a hydroxylase activity 1 the small amount'S of 25(OH)D produced would be rapidly
converted to the active metabolite. The low concentration of active hormone appear
adequate for the maintenance of mineral homeostasis as indicated by tightly controlled
serum calcium (2.26 ± 0.17 mrnol/l), magnesium 01.16 + 0.24 mmol/l) and inorganic
phosphorus (2.93 ± 1.01 mmol/I).
Both vitamin D2 and vitamin D3 metabolites were detected in bat serum albeit in very
small amounts, suggesting that fruit bats exploit both exogenous plant sources (skins
of fruit - vitamin 1)2; fungi - vitamin D:3)and might indeed receive some U. V. light
during their crepuscular forays to endogenously produce small amounts of vitamin D3
In conclusion, fruit bats appear to belong to a small group of animals that naturally
have limited access to Vitamin D, yet the vitamin D endocrine system in these animals
is no different to that of other mammals. These animals have adapted their vitamin D
endocrine system to function well at the low hormone concentrations and they exhibit
no pathological problems associated with relative vitamin D depletion. / AC2017
Date January 1992
CreatorsCavaleros, Meropi
Source SetsSouth African National ETD Portal
Detected LanguageEnglish
FormatOnline resource (180 leaves), application/pdf

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