Prostaglandin E1 Increases in vivo and in vitro calcitriol biosynthesis in rabbits

IntroductionProstaglandins have an anabolic effect on bone. Possible mediation of this effect is via calcitriol. This study determines in vivo and in vitro effects of PGE1 on calcitriol synthesis.MethodologyIn vivo: rabbits received intravenous vehicle or prostaglandin E1 (50 μg/day) for 20 days before measurements of serum total and ionic calcium, magnesium and phosphorus levels, total and bone-specific alkaline phosphatases, 25(OH)D3, calcitriol, parathyroid hormone and calcitonin.In vitro: rabbit proximal renal tubules were incubated with 25(OH)D3 (8 μM) together with PGE1 (2.82×10−6 M) and the prostaglandin receptor inhibitor AH6809 (10−4 M) in selected samples. After 5 or 30 min incubation, calcitriol production was measured by radioimmunoassay and data analysed statistically.ResultsIn vivo, in groups receiving PGE1, levels of total Ca, Mg and calcitriol increased significantly and 25 dihydroxyvitamin D3, parathyroid hormone and calcitonin remained unchanged. In vitro, PGE1 increased calcitriol biosynthesis and the prostaglandin inhibitor AH6809 reduced calcitriol levels significantly after prolonged incubation.ConclusionsIn vivo and in vitro results demonstrate that PGE1 stimulates calcitriol synthesis. This study represent a major advancement in knowledge of bone metabolism.