Acute effects of parathyroid extract on renal vitamin D hydroxylases in Japanese quail.

The dose- and the time-response relationships of parathyroid hormone's modulation of in vitro 1,25-(OH)2D3 and 24,25-(OH)2D3 production in Japanese quail were investigated. 4-week-old female Japanese quail were injected intramuscularly with three different doses (30, 90 and 270 USP units/kg) of parathyroid extract (PTH). 4, 12 and 24 h after the in vivo administration of PTH, kidney homogenates were incubated with tritiated 25-(OH)D3. All three doses of PTH stimulated 1,25-(OH)2D3 and inhibited 24,25-(OH)2D3 production at 12 h relative to the vehicle-treated control group. The responses of the vitamin D hydroxylases were not detectable at 4 h and had returned to control levels by 24 h. Plasma calcium rose significantly at 4 h with the two higher doese of PTH (90 and 270 USP units/mg) but not with the lowest dose. By 12 h the plasma calcium had returned to control levels except at the highest dose of PTH. By 24 h all of the plasma calcium levels had returned to control values. Plasma inorganic phosphate levels were depressed at 4 h by all three PTH doses; they remained depressed at 12 h and returned to control levels by 24 h. It is concluded that the pharmacological effects of PTH on the renal vitamin D hydroxylases are slower in onset and shorter in duration when compared with those of estradiol.