AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 1 14-G18, Copyright © 1986 by American Physiological Society
Calcium absorption in rat large intestine in vivo: availability of dietary calcium
P. Ammann, R. Rizzoli and H. Fleisch
Calcium absorption in the large intestine of the rat was investigated in
vivo. After a single injection of 45CaCl2 into the cecum, 26.0 +/- 2.5%
(mean +/- SE, n = 9) of the 45CaCl2 injected disappeared. This absorption
was modulated by 1,25-dihydroxyvitamin D3, increased to 64.0 +/- 4.2% under
a low-Ca diet, and increased under low-Pi diet. In contrast, when the
difference of nonradioactive Ca in the cecal content and the feces was
measured, only 4.1 +/- 4.6% (not significant) was absorbed. Secretion of
intravenously injected 45Ca into the lumen was small and not altered by any
of the conditions tested. When cecum contents were placed into duodenal
tied loops, 14 +/- 6.2% were absorbed in situ when 45Ca was given orally,
whereas when 45Ca was directly added to the content 35.6 +/- 4.6% were
absorbed (P less than 0.02). These results indicate that the large
intestine has an important vitamin D-dependent Ca absorptive system
detectable if 45Ca is injected into the cecum. However, it is not effective
in vivo because the Ca arriving in the large intestine appears to be no
longer in an absorbable form.
