In vivo mobilization of bone calcium in thyroparathyroidectomized rats by 1 alpha, 25-dihydroxycholecalciferol (calcitriol) and related compounds.
Calcitriol, 0.5 microgram/rat, given subcutaneously (sc), did not mobilize 45Ca from bone in intact, pre-labeled rats, but caused significant elevation of serum radioactivity in thyroparathyroidectomized (TPTX) rats. The response to calcitriol in TPTX rats was dose-dependent with significant activity at sc doses of 40 ng/rat and above when measured at 18 hours after dosing. Parathyroid hormone, 1 alpha-hydroxycholecalciferol, 1 alpha, 24R,25-trihydroxycholecalciferol and 5,6-trans-25-hydroxycholecalciferol were also effective in TPTX rats. The latter two compounds required microgram doses to mobilize 45Ca from bone. Calcitriol, 25-hydroxycholecalciferol and 24R,25-dihydroxycholecalciferol were inactive in TPTX rats even with doses of 40 microgram/rat and measurement of serum radioactivity up to 72 hours after dosing.
D000818:Animals; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002112:Calcifediol; D002117:Calcitriol; D002118:Calcium / Q000378:metabolism*; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D008297:Male; D010280:Parathyroid Glands / Q000502:physiology*; D010281:Parathyroid Hormone / Q000494:pharmacology; D051381:Rats; D013965:Thyroidectomy
D004100:Dihydroxycholecalciferols; D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone; C013721:1,24,25-trihydroxyvitamin D3; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium; C008088:alfacalcidol