Acute effects of calcitriol and phosphate salts on mineral metabolism in children with hypophosphatemic rickets.
We investigated the acute effects of oral administration of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and phosphate on the major mineral metabolism indexes in six children with vitamin D-resistant rickets treated with a long-term regimen of phosphate and calcitriol. Two acute tests were performed in which plasma calcium, phosphate, immunoreactive parathyroid hormone (iPTH) (intact molecule), 25-hydroxyvitamin D (25-OHD), and 1,25-(OH)2D levels were measured: the first after an oral phosphate load (20 mg/kg) was administered after calcitriol had been discontinued for 10 days, and the second after a calcitriol load (0.03 microgram/kg) plus the same phosphate load but with the children receiving the usual combination treatment. There were no significant differences in basal levels of calcium, phosphate, iPTH, 25-OHD, or 1,25-(OH)2D between the two tests, nor were delta percent calcium and 25-OHD values significantly different. The delta percent plasma phosphate concentration at 60 minutes was significantly higher during test 2 than during test 1 (p less than 0.01) and delta percent iPTH concentration at 60 minutes was significantly higher during test 1 than during test 2 (p less than 0.01). In test 2 the iPTH level returned to baseline at 180 minutes. Higher delta percent 1,25-(OH)2D values at 60 minutes were observed in test 2 than in test 1 (p less than 0.01). Furthermore, the delta percent 1,25-(OH)2D levels were still higher at 180 minutes in test 2 than during test 1 (p less than 0.01). Our study indicates that oral calcitriol has an inhibitory effect on iPTH secretion in the hours immediately after oral phosphate administration in children with vitamin D-resistant rickets.
Bettinelli
A
A
Istituto di Clinica Pediatrica II e Clinica Medica I, Università di Milano, Italy.
Bianchi
M L
ML
Mazzucchi
E
E
Gandolini
G
G
Appiani
A C
AC
D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D000284:Administration, Oral; D000293:Adolescent; D001798:Blood Proteins / Q000032:analysis; D002117:Calcitriol / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D002118:Calcium / Q000097:blood; D002648:Child; D002675:Child, Preschool; D003404:Creatinine / Q000097:blood; D006801:Humans; D007015:Hypophosphatemia, Familial / Q000097:blood*; D008903:Minerals / Q000097:blood*; D010281:Parathyroid Hormone / Q000097:blood*; D010710:Phosphates / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D001798:Blood Proteins; D008903:Minerals; D010281:Parathyroid Hormone; D010710:Phosphates; D015652:25-Hydroxyvitamin D 2; D003404:Creatinine; D002117:Calcitriol; D002118:Calcium