AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 5 688-R692, Copyright © 1984 by American Physiological Society
Circadian variations in contributions of bone and intestine to plasma calcium in dogs
K. M. Wong and L. Klein
Young euparathyroid dogs, prelabeled with radiocalcium and fed a
normal-calcium diet exhibited circadian variations in the amount of bone
calcium contributed to the plasma calcium pool, as evaluated by changes in
plasma calcium-45 radioactivity. When these dogs were fed a low-calcium
diet or fasted, the contribution of bone calcium to plasma calcium rose to
the point where bone constituted nearly the sole source of plasma calcium,
and plasma calcium-45 no longer varied. In thyroparathyroidectomized (TPTX)
dogs fed a normal diet, the fraction of plasma calcium due to bone
contribution was reduced and plasma calcium-45 did not vary. When dietary
calcium in TPTX dogs was increased by supplementation with calcium lactate
pills, total plasma calcium rose, but the contribution of bone calcium to
the plasma calcium pool remained unchanged. Thus the ability of normal
young dogs to modulate bone calcium mobilization in response to dietary
calcium intake appears to be hormonally regulated in a circadian manner.
