Biomedical Engineering Reference
In-Depth Information
Deficiency
Signs of vitamin A deficiency have been characterized in
rhesus macaques and capuchin monkeys, with weakness,
loss of appetite, poor growth, and diarrhea among the early
signs (
National Research Council, 2003
). Chronic defi-
ciency is associated with eye pathology. Deficiency can
take many months and even years to manifest due to the
ability to store significant amounts of vitamin in body
stores.
to distribute them uniformly in dry diets; therefore water
soluble compounds such as menadione dimethylpyr-
imidinol bisulfate (MPB), menadione sodium bisulfite
(MSB), and menadione sodium bisulfite complex (MSBC)
are commonly used.
Vitamin D, Calcium, and Phosphorus
These nutrients are strongly linked in their function, regu-
lation, and thus requirements. Calcium and phosphorus are
the two most common minerals in vertebrate bodies
because of the large depots in bone and teeth. Most phos-
phorus in the body is in the form of phosphate. Although
they are linked in bone formation processes and also in
absorption and excretion mechanisms (via vitamin D),
calcium and phosphate have separate, independent func-
tions as well. Calcium is a major inter- and intracellular
signaling ion, and phosphate is a component of the basic
metabolic molecules of life (e.g. ATP). Because bone
contains large amounts of potentially available calcium and
phosphate, dietary deficiency does not exhibit quickly and
may not be detected until there are significant changes to
bone. Because of the shared regulatory mechanisms via
vitamin D, it is appropriate to consider these two minerals
in concert when evaluating a diet. The recommended ratio
of calcium to phosphorus in a diet is between 1:1 and 2:1.
Vitamin D is a canonical example of the effects of
captivity on nutrient requirements. Under natural condi-
tions, vitamin D is not a required nutrient for primates.
Rather, vitamin D is produced through a photosynthetic
reaction in skin that converts 7-hydrocholesterol to provi-
tamin D, which is then thermally converted to vitamin D.
Vitamin D itself has relatively low biological activity;
however, there are several important vitamin Dmetabolites.
The vitamin D metabolite with the greatest biological
activity is 1,25 dihydroxyvitamin D (calcitriol), which is
formed by two hydroxylation events catalyzed by two
separate enzymes. Vitamin D is first converted to 25
hydroxyvitamin D (calcidiol) in the liver by 25 hydroxy-
lase. This reaction is unregulated and 25 hydroxyvitamin D
is the primary circulating vitamin D metabolite. Its circu-
lating concentration is considered the best measure of
vitamin D status (
National Research Council, 2003
). It
serves as the substrate for production of 1,25 dihydroxy-
vitamin D via a tightly regulated system in the kidney. The
parathyroid gland contains an ionized calcium (Ca) sensor,
which regulates the secretion of parathyroid hormone
(PTH). Low ionized serum Ca results in increased secretion
of PTH, which acts on the kidney to increase 1
Toxicity
There has been some concern expressed recently that many
captive primates are routinely overdosed with vitamin A,
leading to chronic vitamin A overnutrition that may have
negative consequences over time (
Dever and Tanumi-
hardjo, 2009
). In addition, vitamin A interacts with vitamin
D. High levels of preformed vitamin A in the animal can
interfere with vitamin D function (
Rohde and Deluca,
2005
).These authors suggest that
-carotene may be a safer
source of dietary vitamin A than preformed vitamin A
because its conversion to vitamin A is regulated in primates
by vitamin A status.
b
Vitamin E
Vitamin E, like vitamin A, is a collective term for
compounds that have specific biological activity;
for
vitamin E the reference compound is
-tocopherol. Vitamin
E serves as an antioxidant but appears to have other func-
tions as well, such as modulating the activity of some
enzymes important in fatty acid metabolism.
a
Deficiency
Vitamin E deficiency is associated with anemia, muscular
dystrophy, lethargy, weakness, jaundice, and splenomegaly.
The amount of polyunsaturated fatty acids (PUFAs) in the
diet modulate the susceptibility to vitamin E deficiency;
diets that are moderate to high in PUFAs hastened or
exacerbated the development of vitamin E deficiency in
cebus monkeys (
Ausman and Hayes, 1974
), common
marmosets (
McIntosh et al., 1987
), vervet monkeys (
Parks
et al., 1990
), and cynomologus macaques (
Ausman and
Hayes, 1974
).
Vitamin K
Vitamin K is required for blood clotting and is important in
bone formation. Phylloquinone is the plant form of vitamin
K and menaquinones are the vitamin K compounds
produced by bacteria. It is not known the extent to which
gut bacteria can contribute to vitamin K status in nonhuman
primates. Menadione is a synthetic provitamin that is
metabolized in the liver to form menaquinone-4. All these
forms of vitamin K are fat soluble, which makes it difficult
hydrox-
ylase, the enzyme that converts 25 hydroxyvitamin D to
1,25 dihydroxyvitamin D.
The most biologically active form of vitamin D (1,25
dihydroxyvitamin D) is a steroid hormone. It binds to the
vitamin D receptor and stimulates production of peptide
a
