Vitamin D3 and avian bone in vitro: specificity of effect on Japanese quail calvaria

Calcitriol (1,25(OH)2D3) has been shown, under certain conditions, to elicit an in vitro response in adult avian calvarium which may be interpreted as calcium uptake by the bone. The present investigation was undertaken to study the specificity of this response. Calvaria were removed from 6-week-old female Japanese quail and cultured for periods of up to 96 hours at 37 degrees C in 5% CO2/95% air. 1,25(OH)2D3 induced a fall in the medium total and ionic calcium concentrations at both 48 hours and 96 hours of incubation; these responses were not blocked by the presence of 10(-4) M acetazolamide. Bovine parathyroid hormone (bPTH(1-34] at 10(-7) M, and dibutyryl cyclic AMP (DBcAMP) at 10(-4) M, had no effect on the medium calcium. In contrast, forskolin at 10(-4) M induced a marked fall in medium calcium concentrations, particularly at 48 hours. The specificity was also studied with respect to vitamin D3 and its two major metabolites. 1,25(OH)2D3 exhibited a bell-shaped dose-response relationship with the maximal effect at 10(-7) M. In contrast, the other two compounds elicited no effects at 10(-7) M or 10(-6) M; significant responses were observed at 10(-5) M with both agents. In general, 25-dihydroxyvitamin D3 (25OHD3) was more potent than vitamin D3. These findings suggest that the medium calcium response to 1,25(OH)2D3, interpreted as calcium uptake by the cultured adult avian bone, is relatively specific among calcemic agents; the response was elicited by forskolin but not by bPTH(1-34) or DBcAMP.(ABSTRACT TRUNCATED AT 250 WORDS)