Intestinal calcium uptake follows both a saturable and a non-saturable
uptake route. The saturable route is energy-dependent. Ca2+-Mg2+-ATPa
se is mainly responsible for extrusion of calcium from the intestinal
enterocyte. Saturable intestinal calcium uptake declines significantly
in the rat from 42 days of age until 84 days of age. Similar changes
in Ca2+-Mg2+-ATPase activity have not yet been reported. Male Sprague
Dawley rats (n=32) were used and the total duodenal calcium uptake and
Ca2+-Mg2+-ATPase activity were measured at 28 (n=8), 35 (n=8), 42 (n=
8) and 84 (n=8) +/- 2 days respectively. There was a close relationshi
p between total duodenal calcium uptake and Ca2+-Mg2+-ATPase activity
during the period 28 to 84 days of age. We conclude that Ca2+-Mg2+-ATP
ase activity may also act as a rate-limiting step in intestinal calciu
m uptake.