AJP - Endocrinology and Metabolism, Vol 249, Issue 6 568-E576, Copyright © 1985 by American Physiological Society
Effects of parathyroid hormone on puppies during development of Ca and vitamin D deficiency
K. M. Wong, L. Klein and B. Hollis
The acute effects of parathyroid extract (PTE) were studied repeatedly in
young dogs (prelabeled with 45Ca and [3H]tetracycline) during the
development of calcium (Ca) and vitamin D deficiency. Blood Ca and
radioactivity changes were monitored sequentially after subcutaneous PTE,
injected seven times over 63 days. In control dogs, all sequential
responses to acute PTE challenges were constant in both magnitude of
increase and time at which maximum response occurred over the entire
experiment. Under chronic Ca and D deficiency, plasma 25-hydroxyvitamin D
in experimental dogs decreased continuously to very low levels at 63 days,
whereas 1,25-dihydroxyvitamin D initially increased to a maximum at 32 days
and thereafter decreased. In response to an acute challenge of PTE, dogs on
the deficient diet for 3 and 10 days showed a greater response of blood Ca
and 45Ca than the controls but subsequently showed a smaller response than
controls after 49 and 63 days on the deficient diet. Compared with control
dogs, the time of maximal response of blood Ca and 45Ca to PTE occurred
much earlier in dogs that were on the deficient diet for 35-63 days. The
blood [3H]tetracycline response (index of bone resorption) to exogenous PTE
in the deficient dogs, however, was constant and similar to that of the
control dogs during the entire period. The data suggest that the bone
resorption response to PTE was normal in Ca- and D-deficient puppies with
hypocalcemia.(ABSTRACT TRUNCATED AT 250 WORDS)
