1. Intestinal phosphate absorption was measured in normal subjects, in patients with chronic renal failure, and in post-transplant patients, by a double isotope technique involving oral administration of 32P and simultaneous intravenous injection of 33P with subsequent deconvolution analysis. 2. By this technique intestinal phosphate absorption has been shown to have two components: an initial rapid phase, which is completed by 3 h, and a slower more prolonged phase, which continues beyond 7 1/2 h. 3. Phosphate malabsorption has been demonstrated in chronic renal failure and transplant patients, which is accounted for by impairment of the initial rapid phase of absorption. 4. Results obtained by deconvolution analysis have been compared with other estimates of phosphate absorption obtained from analysis of 32P radioactivity curves alone. 5. The fractional hourly rate of absorption and the plasma 32P radioactivity at 60 min corrected for extracellular fluid volume provided the best approximations to the result obtained by deconvolution analysis, with respect to both the maximal rate of phosphate absorption and cumulative percentage phosphate absorption.

Number of references: 40Number of words in Abstract: 250 Number of words in Introduction: 640Number of words in Discussion: 1214 Abbreviations (alphabetical order):5' UTR, 5' untranslated region; ABCG2, ATP-binding cassette subfamily G member 2; AF, allele frequency; ARE, antioxidant response element; AHR, aryl hydrocarbon receptor; BCRP, breast cancer resistance protein; CYP, cytochrome P450; DRE, dioxin response element; EGFR, epidermal growth factor receptor; ERα, estrogen receptor alpha; ERβ, estrogen receptor beta; ERE, estrogen response element; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HIF1α, hypoxia inducible factor 1 alpha; HRE, hypoxia response element; NRF2, nuclear factor erythroid 2-related factor 2; PPARγ, peroxisome proliferator-activated receptor gamma; PPRE, peroxisome proliferator response element; PBS/T, PBS with 0.5% Tween-20; PR, progesterone receptor; RPL13A, ribosomal protein L13A; SNP, single nucleotide polymorphism; SP1, SP1 transcription factor; SP3, SP3 transcription factor; TSS, transcriptional start site contribute to our understanding of the interindividual regulation of BCRP expression in term placentas and may help to identify infants at risk for increased fetal exposure to chemicals due to low expression of this efflux protein.