Regulation of vitamin D metabolism and function.

A Radioimmunoassay for Measurement of 3,3′, 5′-Triiodothyronine (Reverse T3)

“…These workers have made a fascinating discovery of two parallel enzyme systems in the kidney which lead to the conversion of 25-hydroxyvitamin D3 (25-OH-D3) to either biologically more active 1,25(OH)2-D3 or to a relatively biologically inert 24,25-(OH)2-D3. Generally, when 1,25-(OH)2-Ds production is diminished, 24,25-(OH)2-D3 production is increased (44)(45)(46). In this respect, the findings of the present study, i.e., that serum rT3 is markedly elevated in the newborn whose serum T3 is markedly low, are similar.…”

“…These considerations lead one to suspect that rT3 may not be just an inactivation product of T4, but that it may be involved in physiological regulation of metabolism and biological action of T4. Additionally, it is tempting to consider that conversion of T4 to T3 and/or to rT3 may be physiologically regulated phenomena, similar to those proposed recently by DeLuca, Omdahl, and Tanaka for vitamin Ds (44)(45)(46). These workers have made a fascinating discovery of two parallel enzyme systems in the kidney which lead to the conversion of 25-hydroxyvitamin D3 (25-OH-D3) to either biologically more active 1,25(OH)2-D3 or to a relatively biologically inert 24,25-(OH)2-D3.…”

Prostaglandin-stimulated bone resorption by rheumatoid synovia. A possible mechanism for bone destruction in rheumatoid arthritis.

“…The vitamin D metabolite 1,25-dihydroxycholecalciferol has potent BRS activity and is soluble in organic solvents (17). However, since the site of synthesis of this compound is thought to be limited to the kidney (18), it seems unlikely that it would be released in significant concentrations from synovial tissues.…”

Kinetic analysis of 25-hydroxyvitamin D3 metabolism in strontium-induced rickets in the chick.

“…The function of vitamin D to enhance intestinal calcium absorption, bone mineral mobilization, and calcification is well appreciated (1,2). However, to effect such actions vitamin D must be metabolically activated, initially in the liver (25-hydroxylation) (3,4) and subsequently in the kidney (la-hydroxylation) (5,6), resulting in the synthesis of la,25-dihydroxyReceived for publication I July 1976 and in revised form 17 June 1977. vitamin DI (la,25-(OH)2D)2 (7,8).…”