Intestinal Absorption of Phosphate in the Chick: Effect of Vitamin D3 and Other Parameters

Abstract

Listen

Translate article

The effect of various parameters, including vitamin Ds, on the intestinal absorption of T-phosphate in the chick was investigated. Translocation was determined by the in situ ligated loop technique and measurements were made of radionuclide leav ing the intestinal lumen (absorption), accumulation by scraped mucosa (in gut tissue) and that entering the blood (transferred to body). It was observed, initially, that 1ZP was rapidly translocated across all segments of the small intestine (duodenum, jejunum, ileum) and vitamin D3 positively affected the total process in each segment. Because of the ease of showing a responsiveness to vitamin D3 by the ileum, the subsequently de scribed results were obtained with this segment. In a time course experiment, it was noted that 32Paccumulation by mucosa proceeded at a more rapid rate than the release of radionuclide to blood, indicating that the latter was the limiting step. The absorptive process was saturable as shown by a study in which increasing levels of stable phosphate were present in the absorption fluid. An effect of vitamin D3 on the transfer of 32Pfrom mucosa to body was evident, as well as an effect on the uptake phase. Arsenate, EHDP and L-phenylalanine inhibited 32Ptranslocation, but primarily in the vitamin Ds-repleted chicks. This suggested, as did the study of the effect of various levels of stable phosphate, that 32Pinteracts with some intestinal component in the transport path. Since NaEGTA (a Ca-chelator) and thorough washing of the ileal lumen did not alter 32Pabsorption and mucosal uptake, it was evident that Pi was not absorbed as a coion to calcium. A direct relationship between serum Ca levels and the degree of S2Pabsorption became evident, although this correlation (r = 0.82) might be fortuitous. Vitamin D3, when given to rachitic chicks, elicited an enhanced 32Pabsorption at 16 hours; the appearance of vitamin D-dependent CaBP was evident at 12 hours. Studies on the nature of 3AP in mucosal tissue after absorption indicated that the radionuclide was largely indistinguish able from ortho-phosphate, and that only a small fraction was present as phospholipid-HP. No phosphate binder in mucosal supernatant fluid, analogous to CaBP, was detected under the specific conditions employed. J. Nutr. 103: 586-599, 1973.