Studies of hormonal regulation of osteocalcin synthesis in cultured fetal rat calvariae.
The synthesis of osteocalcin, the major non-collagenous protein of adult bone, was examined in cultures of 21-day fetal rat calvariae. Osteocalcin was measured by a sensitive and specific radioimmunoassay. Osteocalcin concentration in unincubated calvariae was 14.5 +/- 0.5 ng/calvaria. After incubation, there was a continuous increase in bone and medium osteocalcin, and by 96 h the values were about 100% higher than in unincubated calvariae. 1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) at 10(-11) to 10(-8)M increased osteocalcin synthesis. The effect appeared as early as 6 h after treatment and was primarily observed in the culture medium, and 1,25-(OH)2D3 stimulated osteocalcin up to 9-fold by 96 h. Concomitant with the effect on osteocalcin synthesis, 1,25-(OH)2D3 inhibited collagen synthesis. Cycloheximide markedly decreased osteocalcin concentrations in control and 1,25-(OH)2D3-treated calvariae. The stimulatory effect on osteocalcin synthesis was specific to 1,25-(OH)2D3 since 24,25-dihydroxyvitamin D3, parathyroid hormone, epidermal growth factor, and prostaglandin E2 did not stimulate osteocalcin synthesis, and parathyroid hormone and epidermal growth factor opposed the 1,25-(OH)2D3 stimulatory effect. Insulin did not alter osteocalcin concentration by itself but enhanced the effect of 1,25-(OH)2D3. In conclusion, 1,25-(OH)2D3 stimulates osteocalcin synthesis in cultures of normal calvariae, but this effect is not shared by other hormones known to affect bone metabolism.
D000818:Animals; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D002117:Calcitriol / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000096:biosynthesis*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D005333:Fetus / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D015675:Osteocalcin; D010281:Parathyroid Hormone / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D012886:Skull / Q000378:metabolism
D002135:Calcium-Binding Proteins; D007328:Insulin; D010281:Parathyroid Hormone; D015675:Osteocalcin; D004815:Epidermal Growth Factor; D002117:Calcitriol