Binding protein for vitamin D and its metabolites in rat mesenteric lymph

Abstract

A protein with high affinity for vitamin D3 and 25-hydroxyvitamin D3 in rat mesenteric lymph has been studied. Mesenteric lymph was collected after duodenal instillation of radiolabeled vitamin D3 and 25-hydroxyvitamin D3. As previously described, approximately 10% of vitamin D3 (S. Dueland, J.I. Pedersen, P. Helgerud, and C.A. Drevon, J. Biol. Chem. 257: 146-150, 1982) and 95% of 25-hydroxyvitamin D3 (S. Dueland, J.I. Pedersen, P. Helgerud, and C.A. Drevon, Am. J. Physiol. 245 (Endocrinol. Metab. 8): E463-E467, 1983) recovered in mesenteric lymph were associated with the alpha-globulin fractions. The radioactive vitamin D3 recovered in the lymph fraction with d greater than 1.006 (free of chylomicrons) coeluted with purified rat serum binding protein for vitamin D and its metabolites (DBP) from an antirat DBP column. The results obtained by immunoblotting after sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that this protein in mesenteric lymph had molecular weight and immunological properties identical with purified serum DBP. Purified serum DBP labeled with 125I was injected intravenously and mesenteric lymph was collected. in lymph, suggesting that DBP may be transferred from blood to mesenteric lymph and that plasma and lymph DBP may have a similar origin.

Uptake and degradation of vitamin D binding protein and vitamin D binding protein–actin complex in vivo in the rat

“…Plasma clearance of the proteins labelled with this method was similar to the clearance obtained when the proteins were labelled by a traditional labelling technique [12]. We have previously reported a ti, for 1251I-labelled rat DBP in the rat of about 8 h [11]. This result has been confirmed by Harper et al [18], who calculated the t1 in the rat to be 7 h. In both of these studies, rat DBP was labelled with 125I by traditional labelling techniques.…”

“…Rat DBP was prepared as described previously [11] and applied to a chromatofocusing column (1.8 cm x 30 cm) with 0.025 M-histidine, pH 6.2, as starting buffer. The protein was eluted with Polybuffer 74 (diluted 1:10), pH 4.0.…”

“…Rat albumin was isolated by an anti-(rat albumin) column as described for DBP [11], except that albumin was eluted from the column by 3.5 M-ammonium thiocyanate.…”

Vitamin D Binding Protein: A Historic Overview

“…Vitamin D from dietary origin is absorbed in the intestine with about 70% efficacy in normal subjects. Although this process was for a long time considered to be a passive transport of a lipophilic molecule to access the lipid layer of the intestinal cells (82), more recent data suggest that vitamin D absorption and secretion from and into the lumen of the gut is medicated by carrier proteins that are also involved in cholesterol transport in the intestine (83). To what extent vitamin D esters are first digested and then absorbed or lost in the feces is still a point of discussion [see Solanum malacoxylon being a 1,25(OH) 2 D-glucuronide causing severe generalized calcinosis in grazing cattle in Argentina (84,85)].…”

“…To what extent vitamin D esters are first digested and then absorbed or lost in the feces is still a point of discussion [see Solanum malacoxylon being a 1,25(OH) 2 D-glucuronide causing severe generalized calcinosis in grazing cattle in Argentina (84,85)]. After passage thought the intestinal cell, vitamin D is transported by chylomicrons and thus uses the lymph pathway before it arrives in the general blood circulation (82). In that circulation, chylomicrons (including vitamin D) are mainly taken up by fat cells or by the liver, but there is also a gradual shift of vitamin D from chylomicrons to DBP.…”