A relationship between manganese and
abnormal carbohydrate metabolism was
first suggested by Rubenstein and co-workers
in 1962 (5). They reported the case of a
diabetic patient, resistant to insulin therapy,
who responded to oral doses of manganese
chloride with a consistent drop in blood
glucose levels. Manganese supplementation
was tried because of the ineffectiveness of
high doses of insulin in maintaining normal
blood glucose and the patient's statement
that his diabetic condition could be con
trolled to some extent by an extract of lucerne
(alfalfa, Medicago sativa). Analysis of the
alfalfa extract revealed a high concentration
of manganese In contrast to the effective
ness of manganese, oral supplements of zinc,
magnesium, cobalt or iron had no effect on
the patient's blood sugar levels, indicating a
specific role for manganese in insulin release
or action.
A similar observation was reported by
Shani et al. (6). They found that the sand
rat, whose natural diet is high in manganese,
developed an insulin-resistant diabetes when
fed a commercial rat feed containing rela
tively low levels of manganese. The diabetic
condition was reversed after reintroduction
of the manganese-rich natural diet.
Everson and Shrader (7) reported that
guinea pigs, born to manganese-deficient
dams and fed manganese-deficient diets
from birth to 60 days of age, had abnormal
glucose tolerance curves. Histological exami
nation of the pancreas from these animals
indicated that the deficient animals had
hypertrophied pancreatic islet tissue with
degranulated beta-cells and an increased pro
portion of alpha-cells(8). All of these signs o
manganese deficiency were reversed follow
ing dietary manganese supplementation fo
2 months.
Based on the latter observations, we formulated
the hypothesis that manganese deficiency
might result in altered insulin secretion.
Such an abnormality could explain, at
least partially, the altered glucose metabolism
observed in manganese-deficient animals.
The specific effect of manganese on insulin
metabolism might occur at several
levels, including reduced synthesis and/or
secretion of insulin (in addition to reduced
peripheral insulin sensitivity). In this study,
we have examined the relationship of manganese
deficiency and pancreatic function in rats.
Edited by rwac, 28 September 2009 - 03:02 AM.