AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 4 631-G638, Copyright © 1990 by American Physiological Society
Vitamin D-independent intestinal calcium and phosphorus absorption during reproduction
R. Brommage, D. C. Baxter and L. W. Gierke
Department of Physiology, Chicago College of Osteopathic Medicine, Downers Grove, Illinois 60515.
A special metabolic cage system was employed to measure the intestinal,
renal, and mammary gland fluxes of Ca, P, and Mg in vitamin D-deficient
rats during late pregnancy and lactation. Dietary Ca, P, and Mg levels were
0.78, 0.34, and 0.083%, respectively; this diet minimizes the reduction in
milk production observed during vitamin D deficiency. Compared with
identically treated virgin rats, lactating rats were slightly hypocalcemic
and severely hypophosphatemic. Hypertrophy of the small intestine, as
indicated by increased intestinal length and villus height, occurred during
lactation. Net fractional intestinal absorption of Ca and P, but not Mg,
was elevated twofold during late pregnancy and throughout lactation.
Despite this elevated intestinal absorption, lactating rats were in
negative Ca and P balance and lost bone mass. The transfer rates of Ca, P,
and Mg into milk were approximately 77% of values previously observed in
vitamin D-replete rats. Lactating rats conserved P by dramatically reducing
renal P excretion. Pup retention of ingested Ca was virtually complete.
These results, together with previous observations using everted duodenal
gut sacs, indicate that there is a vitamin D-independent stimulation of
intestinal Ca and P absorption during pregnancy and lactation. Because
fractional Mg absorption was not similarly enhanced, this stimulation shows
some specificity.
