AJP - Heart and Circulatory Physiology, Vol 255, Issue 1 94-100, Copyright © 1988 by American Physiological Society
Parathyroid hormone effects on skeletal exchangeable calcium and bone blood flow
G. W. Brindley, E. A. Williams, J. T. Bronk, T. H. Meadows, R. J. Montgomery, S. R. Smith and P. J. Kelly
Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905.
The effects of alterations in serum calcium levels on the volume of
distribution of a calcium tracer in bone and on bone blood flow were
investigated in dogs by manipulation of parathyroid status. The volume of
distribution increases with increasing serum calcium. This implies that
there is a concentration-dependent binding mechanism in the extravascular
space of bone, which is not saturated at the levels of serum calcium
achieved in these experiments. The skeletal exchangeable calcium was
increased in hypercalcemic dogs and decreased in hypocalcemic dogs.
Cancellous bone contains proportionately more exchangeable calcium than
cortical bone. Bone blood flow was decreased by 50% 15 min after injection
of a bolus of parathyroid hormone (PTH) but returned to control values by
240 min. Fifty-two hours after the induction of hypercalcemia with repeated
doses of PTH, there was no difference in blood flow over control animals.
