The Regulation of Vitamin D Metabolism

Parathyroidectomy reduces 25-hydroxyvitamin D3-1 alpha-hydroxylase activity in the hypocalcemic vitamin D-deficient chick.

“…Accordingly, Fraser and Kodicek concluded that 25-OHD3-lahydroxylase is regulated and stimulated by circulating PTH (13 (11,13,(16)(17)(18). In light of this fact, the observations of Galante et al (15), and other considerations (10,18,19), DeLuca (11) reported that the activity of 25-OHD3-la-hydroxylase was decreased 24 h after PTX, compared to the activity in sham-operated controls. The reported decrease in the enzyme activity, however, is difficult to interpret since the decrease might reflect a moribund status of the chicks, rather than an effect of the absence of circulating PTH.…”

“…The reported decrease in the enzyme activity, however, is difficult to interpret since the decrease might reflect a moribund status of the chicks, rather than an effect of the absence of circulating PTH. When PTX is performed in the vitamin D-deficient chick or rat that is already hypocalcemic, increasing hypocalcemia, tetany, and moribundity are predictable complications (12,15,20 (1:1) was added to the previously initiated solution in amounts calculated to deliver calcium at the rate of 15-20 mg/kg per h. In the earlier studies chicks were sedated overnight with intravenously administered sodium pentobarbital. With each successive study, the agent was administered at a lesser rate (1.0-0 mg/kg per h).…”

Effects of Dietary Calcium Restriction and Chronic Thyroparathyroidectomy on the Metabolism of [3H]25-Hydroxyvitamin D3 and the Active Transport of Calcium by Rat Intestine

“…Parathyroid hormone (PTH) secreted in response to serum calcium levels, has been proposed as the tropic factor in the modulation of 1,25-(OH)2-D3 synthesis, and lhenice the factor responsible for adaptation of intestinal calcium transport to variations in dietary calcium intake (31)(32)(33). As will be discussed below, however, this view is not universally held (34)(35)(36)(37) (38).…”

Separation of hydroxylated derivatives of vitamin D3 by high speed liquid chromatography (HSLC)

“…In all instances where a comparison has been possible between the UV peak and the radioactivity profile of a vitamin Ds derivative the resultant peaks have had the same width and elution position (see for example ref. [2] ) The ability to repetitively inject samples into an automatic instrument is a great advantage over the preparation and operation of many columns eluted with volatile organic solvents, the need for lengthy runs and the use of many fraction collectors as is necessary with analyses in Sephadex LH-20.…”