Absence of regulatory effects of 1alpha25-dihydroxyvitamin D3 on 25-hydroxyvitamin D metabolism in rats constantly infused with parathyroid hormone.
The regulatory role of 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2-D3] in metabolism of 25-hydroxyvitamin D was studied in sham-operated (sham) or thyroparathyroidectomized (TPTX) vitamin D-deficient rats into which calcium and parathyroid hormone (PTH) were constantly infused. A single dose of 325 or 650 pmol of 1alpha,25-(OH)2-D3 caused significant inhibition of 1alpha,25-(OH)2-D3 synthesis in D-deficient sham rats. This inhibition by 1alpha,25-(OH)2-D3, however, was not observed in D-deficient TPTX rats into which PTH was constantly infused. These results can be explained by supposing that the major regulatory effect of 1alpha,25-(OH) 2-D3 on 1alpha,25-(OH)2-D3 synthesis is realized mostly, if not all, by suppressing endogenous secretion of PTH.
Horiuchi
N
N
Department of Biochemistry, School of Dentistry, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo 113, Japan.
Suda
T
T
Sasaki
S
S
Takahashi
H
H
Shimazawa
E
E
Ogata
E
E
D000818:Animals; D002112:Calcifediol / Q000378:metabolism*; D002117:Calcitriol / Q000378:metabolism* / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D007262:Infusions, Intravenous; D008297:Male; D010281:Parathyroid Hormone / Q000008:administration & dosage* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013965:Thyroidectomy; D014808:Vitamin D Deficiency / Q000097:blood / Q000378:metabolism
D010281:Parathyroid Hormone; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium