Acute Effects of Parathyroid Extract on Renal Vitamin D Hydroxylases in Japanese Quail

Abstract

The dose- and time-response relationships of parathyroid hormone''s modulation of in vitro 1,25-(OH)2D3 [1,25-dihydroxy vitamin D3] and 24,25-(OH)2D3 [24,25-dihydroxy vitamin D3] production in Japanese quail were studied. Female Japanese quail, 4 wk old, were injected i.m. with 3 different doses (30, 90 and 270 USP units/kg) of parathyroid extract (PTH). After the in vivo administration of PTH (4, 12 and 24 h) kidney homogenates were incubated with 3H 25-(OH)D3. All 3 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 Ca rose significantly at 4 h with the 2 higher doses of PTH (90 and 270 USP units/mg) but not with the lowest dose. By 12 h the plasma Ca levels had returned to control levels except at the highest dose of PTH. By 24 h all of the plasma Ca levels had returned to control values. Plasma Pi levels were depressed at 4 h by all 3 PTH doses; they remained depressed at 12 h and returned to control levels by 24 h. Apparently 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.