The Relative Merits of Various Techniques for Measuring Radiocalcium Absorption

1980 ◽  
Vol 58 (4) ◽  
pp. 287-293 ◽  
Author(s):  
R. Wootton ◽  
J. Reeve
Keyword(s):  
Calcium Absorption ◽  
Mean Transit Time ◽  
Whole Body ◽  
Physiological Mechanisms ◽  
Systematic Uncertainties ◽  
Body Retention ◽  
Transit Times ◽  
Metabolic Bone ◽  
Absorption Studies

1. One-hundred and ten double-tracer (47Ca/45Ca or 47Ca/85Sr) calcium-absorption studies were performed in patients with a variety of metabolic bone disorders. A computer program was written to fit plasma radioactivity data from both oral and intravenous tracers by spline functions and to deconvolve points interpolated from the fitted curves to obtain the spectrum of *Ca transit times from mouth to plasma. 2. Methodological precision in the estimation of fractional absorption, maximum and mean rates of absorption and mean transit time was not substantially degraded by the normal uncertainties of sample counting. 3. From the results of 35 studies in which 85Sr was given as an additional intravenous tracer, it is concluded that the use of oral 47Ca and intravenous 85Sr is an acceptable alternative to the 47Ca/45Ca combination and offers considerable practical advantages. 4. The single-tracer whole-body retention and faecal collection methods for estimating calcium absorption were found to be sensitive to variations in endogenous excretion and bone accretion of calcium, making these methods unsuitable for some purposes. 5. The single-tracer method of Marshall and Nordin (1969) provided reasonable estimates of absorption rates, but the simplifications inherent in this model give rise to unpredictable systematic uncertainties in the calculation of mean absorption rates. 6. The double-isotope (47Ca oral, 85Sr intravenous) calcium-absorption test, in which blood is sampled serially over 6 h, is the method of choice for the detailed investigation in vivo of the physiological mechanisms of radiocalcium absorption by the undisturbed gut.

DIFFERENTIAL ACTION OF PARATHYROID AND THYROID HORMONES ON EFFECTIVE INTESTINAL ABSORPTION OF CALCIUM

1973 ◽  
Vol 73 (3) ◽  
pp. 489-498 ◽  
Author(s):  
R. Hehrmann ◽  
J. Hagemann ◽  
R. Montz ◽  
E. Jentsch
Keyword(s):  
Thyroid Hormones ◽  
Intestinal Absorption ◽  
Calcium Absorption ◽  
Cyclic Adenosine Monophosphate ◽  
Adenosine Monophosphate ◽  
Whole Body ◽  
Effective Absorption ◽  
Body Retention ◽  
Parathyroid Extract

ABSTRACT The effects of parathyroidectomy (PTX) and radio-thyroidectomy (131I-TX) as well as the actions of parathyroid extract (PTE), dibutyryl cyclic adenosine monophosphate (DBcAMP), calcitonin (CT) and thyroid extract (thyreoidea sicca) on effective intestinal calcium absorption in intact, PTX and 131I-TX rats were evaluated by a new, physiological in vivo method. Ten hours after the administration of 47calcium labelled food the animals were killed and the entire intestine was removed. Whole body retention of 47calcium was measured allowing the calculation of the effective intestinal absorption of calcium (true absorption minus excretion within ten hours). The known actions of PTE and DBcAMP were confirmed by this method. CT did not exert a direct effect in any of the experimental groups. The absence of thyroid hormones (TX rats) remarkably reduced effective calcium absorption. In the presence of endogenous parathyroid hormone (PTH) (TX rats) the administration of minimal amounts of thyroid hormones was sufficient to increase effective calcium absorption, whereas PTE and DBcAMP did not have any effect. In the absence of PTH (TX-PTX rats) thyroid hormones did not enhance effective absorption, indicating, that thyroid hormones alone do not stimulate the effective absorption of calcium. It is concluded, that the thyroid hormones act indirectly, as a permissive agent, enabling PTH to exert its active stimulating effect on the effective intestinal absorption of calcium.

Studies of Calcium Absorption in Man Using a CD-2 Whole-Body Counter

1977 ◽  
Vol 16 (04) ◽  
pp. 163-167
Author(s):  
K. Bakos ◽  
Věra Wernischová
Keyword(s):  
Calcium Absorption ◽  
Whole Body ◽  
Control Group ◽  
Absorption Process ◽  
Whole Body Counter ◽  
Absorption Studies ◽  
Body Counting ◽  
Calcium Load ◽  
Calcium Malabsorption ◽  
Whole Body Counting

SummaryWhole-body counting makes an important contribution of radioisotope techniques to ȁEin vivo“ absorption studies, in comparison with other methods. In a large number of subjects, the method was tested for its usefulness in the diagnosis of calcium malabsorption. The effects of drugs, of the calcium load in the gut and of the whole-body content of calcium on the absorption process were studied in a control group.

Effect of hypophysectomy on calcium transport by rat duodenum.

1977 ◽  
Vol 232 (2) ◽  
pp. E229
Author(s):  
E L Krawitt ◽  
A S Kunin ◽  
H W Sampson ◽  
B F Bacon
Keyword(s):  
Calcium Transport ◽  
Calcium Absorption ◽  
Plasma Flux ◽  
Perfusion Technique ◽  
Intestinal Length ◽  
Absorption Studies ◽  
Luminal Perfusion ◽  
Rat Duodenum

To examine the effect of hypophysectomy on intestinal calcium absorption, studies were performed on immature rats 7, 14, and 21 days after hypophysectomy. Duodenal calcium transport was measured in vitro utilizing everted gut sacs and in vivo by a luminal perfusion technique. Hypophysectomy produced no differences in the ability of everted gut sacs to transport calcium. Similarly, when in vivo transport data were expressed on the basis of intestinal length, no significant differences were noted. However, when transport data were expressed on the basis of mucosal weight, increases in absorption and lumen-to-plasma fluxes were apparent in hypophysectomized animals. No differences were seen in plasma-to-lumen fluxes. The results indicate that when the transport data are corrected for mass of intestinal mucosa, the duodenum from hypophysectomized animals absorbs calcium more avidly due to an increase in lumen-to-plasma flux.

scholarly journals Metabolic studies of [75Se]selenocystine and [75Se]selenomethionine in the rat

1975 ◽  
Vol 34 (3) ◽  
pp. 501-509 ◽  
Author(s):  
Christine D. Thomson ◽  
Bridget A. Robinson ◽  
R. D. H. Stewart ◽  
Marion F. Robinson
Keyword(s):  
Oral Dose ◽  
Urinary Excretion ◽  
Tissue Distribution ◽  
Similar Rate ◽  
Whole Body ◽  
Rabbit Kidney ◽  
Body Retention ◽  
Metabolic Pool

1. The long-term fate in rats of an oral dose of [75Se]selenocystine was compared with that of an oral dose of [75Se]selenomethionine.2. Urinary and faecal radioactivities were measured during the 1st week and whole-body radioactivity was determined for 10 weeks. Rats were killed at weekly intervals for 4 weeks and at weeks 6 and 10 for analysis of tissue distribution of 75Se.3. Intestinal absorption of [75Se]selenocystine was 81% of the administered dose; that of [75Se]selenomethionine was 86%. Urinary excretion of absorbed [75Se]selenocystine was 13.9% and that of [75Se]selenomethionine was 5.8%, in the 1st week.4. Whole-body retention of 75Se was greater for [75Se]selenomethionine than for [75Se]-selenocystine but after the 1st week it decreased at a similar rate in both groups. Tissue distribution of retained 75Se was also similar in both groups.5. The initial utilization of [75Se]selenocystine was different from that of [75Se]selenomethionine. However, after the 1st week 75Se from both sources appeared to be metabolized similarly, suggesting that dietary Se of both forms is ultimately incorporated into the same metabolic pool.6. When these findings were compared with those of earlier studies with [75Se]selenite and 75Se incorporated in vivo into rabbit kidney (RK-75Se) (Thomson, Stewart & Robinson, 1975) the metabolism of [75Se]selenocystine resembled that of [75Se]selenite and RK-75Se, rather than that of [75Se]selenomethionine.

scholarly journals Studies on the control of iron uptake by rabbit small intestine

1982 ◽  
Vol 47 (2) ◽  
pp. 251-258 ◽  
Author(s):  
T. M. Cox ◽  
M. W. O'Donnell
Keyword(s):  
Regional Distribution ◽  
Maximum Velocity ◽  
Whole Body ◽  
Fe Deficiency ◽  
Distal Intestine ◽  
Body Retention ◽  
Fe Uptake ◽  
Active Transport Process

1. Whole-body retention in vivo and uptake of 59Fe-labelled ascorbate and nitrilotriacetate chelates by intestinal slices in vitro were determined in groups of normal control rabbits and rabbits with experimentally-induced Fe deficiency.2. Over-all absorption as measured by retention of doses of either chelate was greatly increased in conditions of Fe deficiency.3. Intestinal Fe uptake in vitro was inhibited up to 77% in the presence of 2,4-dinitrophenol and sodium fluoride. Initial rates showed saturation within the concentration range 18–450 μmol/l, suggesting that uptake was brought about by an active transport process.4. When studied at chelate concentrations of 450 μmol/l, significant regional differences in uptake rates were observed. Uptake in duodenal slices was increased when compared with slices from jejunum and ileum.5. Fe uptake from ferric and ferrous chelates was greatly enhanced in Fe deficiency. This was chiefly due to increases in uptake by slices from the duodenum, but uptake into slices of distal intestine was also stimulated.6. Kinetic analysis of Fe uptake by duodenal slices from animals rendered Fe deficient by diet or repeated bleeding indicated in both groups an increased apparent maximum velocity (Vmax) for influx of Fe without significant changes in apparent affinity for Fe.7. The experiments provide further insight into the nature and regional distribution of transport of Fe into the intestine and suggest, in the rabbit, that important control of Fe absorption may be exerted by an active process operating at this initial entry step.

Transit time dispersion in pulmonary and systemic circulation: effects of cardiac output and solute diffusivity

2006 ◽  
Vol 291 (2) ◽  
pp. H861-H870 ◽  
Author(s):  
Michael Weiss ◽  
Tom C. Krejcie ◽  
Michael J. Avram
Keyword(s):  
Cardiac Output ◽  
Systemic Circulation ◽  
Relative Dispersion ◽  
Whole Body ◽  
Body Distribution ◽  
Distribution Kinetics ◽  
Transit Times ◽  
Time Dispersion ◽  
Kinetics Of

We present an in vivo method for analyzing the distribution kinetics of physiological markers into their respective distribution volumes utilizing information provided by the relative dispersion of transit times. Arterial concentration-time curves of markers of the vascular space [indocyanine green (ICG)], extracellular fluid (inulin), and total body water (antipyrine) measured in awake dogs under control conditions and during phenylephrine or isoproterenol infusion were analyzed by a recirculatory model to estimate the relative dispersions of transit times across the systemic and pulmonary circulation. The transit time dispersion in the systemic circulation was used to calculate the whole body distribution clearance, and an interpretation is given in terms of a lumped organ model of blood-tissue exchange. As predicted by theory, this relative dispersion increased linearly with cardiac output, with a slope that was inversely related to solute diffusivity. The relative dispersion of the flow-limited indicator antipyrine exceeded that of ICG (as a measure of intravascular mixing) only slightly and was consistent with a diffusional equilibration time in the extravascular space of ∼10 min, except during phenylephrine infusion, which led to an anomalously high relative dispersion. A change in cardiac output did not alter the heterogeneity of capillary transit times of ICG. The results support the view that the relative dispersions of transit times in the systemic and pulmonary circulation estimated from solute disposition data in vivo are useful measures of whole body distribution kinetics of indicators and endogenous substances. This is the first model that explains the effect of flow and capillary permeability on whole body distribution of solutes without assuming well-mixed compartments.

Distribution Of Indium-111 In Labeled Human Platelets: Implications In Platelet Survival And Dosimetry

1981 ◽  
Author(s):  
M K Dewanjee ◽  
S A Rao ◽  
P Didisheim
Keyword(s):  
Binding Sites ◽  
Human Platelets ◽  
Whole Body ◽  
Freezing And Thawing ◽  
Platelet Protein ◽  
Body Retention ◽  
Repeated Freezing ◽  
Indium 111 ◽  
Ultimate Fate

Subcellular distribution of In-111 in In-111-labeled platelets (In-P1) determines the biodistribution and dosimetry of In-111 after the in vivo lysis of In-P1. Human platelets were labeled with In-111-oxine (In-Ox) and In- 111-troPolone (In-TPL) in ACD/saline (A/S) and plasma (P). In-P1 was lysed after 6 repeated freezing and thawing procedures. A fraction of In-P1-lysate (In-P1-LS) was filtered (0.22 ym) and passed through a calibrated Sephadex G-100 column for estimation of molecular weight (Mol. wt.) of In-bound Pl-protein. The In-P1-LS was injected in 15 rabbits and biodistribution (% I.D.) performed at 24 hours after I.V. administration. Results are tabulated below: 80 ± 11% and 70 ± 10% of In was bound to soluble platelet protein when platelets were labeled in plasma and A/S respectively. Mol. wt. of In-bound platelet protein was estimated as 52,000 ± 5,000 daltons. Biodistribution shows that In-PI-LS labeled in A/S localizes more in RES than plasma; whole body retention is also longer. These studies shed further light on the binding sites of In in platelets labeled in A/S or plasma media and their ultimate fate after administration

Modulation of uptake of heme by rat small intestinal mucosa in iron deficiency

1993 ◽  
Vol 265 (4) ◽  
pp. G712-G718 ◽  
Author(s):  
S. K. Roberts ◽  
R. W. Henderson ◽  
G. P. Young
Keyword(s):  
Iron Deficiency ◽  
Specific Binding ◽  
Iron Status ◽  
Significant Rise ◽  
Whole Body ◽  
Small Intestinal Mucosa ◽  
Body Retention ◽  
Iron Deficient ◽  
Mucosal Uptake

Although body iron status modulates whole body retention of heme derived iron, it is not known with certainty whether modulation occurs by regulation of mucosal uptake of heme. In vivo uptake from perfused intestine of heme labeled with 14C in the porphyrin ring was studied in groups of rats of differing iron status ranging from fully replete to markedly iron deficient. Heme extraction from infusate and mucosal heme uptake were significantly different between test groups (P < 0.005 and 0.001, respectively). Marked iron deficiency induced a 4.8-fold rise in heme extraction relative to iron-replete animals; rats with latent iron deficiency showed a smaller but still significant rise. Heme extraction correlated negatively with indicators of iron status: hemoglobin (r = -0.76, P < 0.001) and serum iron (r = -0.56, P < 0.05). The specific binding of [14C]heme to purified brush borders from iron-replete and iron-deficient rats was 1.4-fold higher in deficient rats when expressed per milligram of protein (P = 0.046) and 3.3-fold higher when expressed relative to alkaline phosphatase activity (P = 0.014). Thus mucosal uptake of heme in iron deficiency is increased because of an increase in its binding to the brush border.

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