RENAL TUBULAR REABSORPTION OF IODIDE AS COMPARED WITH CHLORIDE

Studies on urinary excretion and variability of dietary iodine in healthy Japanese adults

The daily consumption of iodine in Japan is higher than in most countries, and there are few reports on iodine metabolism and variance of habitual iodine ingestion in an iodine-sufficient area. To elucidate the patterns of short-term urinary iodine excretion (UIE) and long-term variability of habitual iodine intake, the urinary iodine excretion process after a high dietary iodine load of 3 mg was observed in eight Japanese adults under strict supervision with complete urine collections for three days. In addition, estimated UIE and dietary iodine intake (DII) were assessed in 24 university students using repeated spot urine samples of ten consecutive days and a food frequency questionnaire in each of the four seasons. Approximately 50, 75 and 90% of orally ingested iodine was excreted into the urine at 8, 13 and 22 hours after ingestion, respectively. Almost an equal amount of ingested iodine in meals was cleared within 33.5 h after eating with a maximum excretion rate at 3-4 h. There was a high fluctuation in the UIE and DII in the university students. The intra- and inter-individual crude coefficients of variation were 123 or 294.7% for UIE, and 58.3 or 88.7% for DII, respectively, indicating a higher variance of habitual iodine intake than in other countries. The frequency of occurrence for UIE above 3 mg was every 43 days. Rapid renal clearance of iodine and high variability as well as low frequency of dietary iodine intake might prevent people from being exposed to an excess iodine intake over the long term in Japan.

Impact of Moderate Sodium Restriction and Hydrochlorothiazide on Iodine Excretion in Diabetic Kidney Disease: Data from a Randomized Cross-Over Trial

Sodium restriction may potentially reduce iodine intake. This study aimed to determine the effect of sodium restriction (dietary counseling) on 24-h urinary iodine excretion. Diuretics provide an alternative to sodium restriction and are frequently added to sodium restriction, so the effects of hydrochlorothiazide (50 mg daily) and combined therapy were also studied. We performed a post-hoc analysis of a Dutch multi-center, randomized cross-over trial in 45 patients with diabetic kidney disease with a mean age of 65 ± 9 years, mean eGFR of 65 ± 27 mL/min/1.73 m², median albuminuria of 648 [230–2008] mg/24 h and 84% were male. During regular sodium intake with placebo, mean 24 h urinary sodium and iodine excretion were 224 ± 76 mmol/24 h and 252 ± 94 ug/24 h, respectively (r = 0.52, p < 0.001). Mean iodine excretion did not change significantly if sodium restriction and hydrochlorothiazide were applied separately; mean difference −8 ug/day (95% CI −38, 22; p = 0.6) and 14 ug/day (95% CI −24, 52; p = 0.5), respectively. Combined therapy induced a significant decrease in mean iodine excretion (−37 ug/day; 95% CI −67, −7; p = 0.02), yet this was not seen to a clinically meaningful level. The number of patients with an estimated intake below recommended daily allowances did not differ significantly between the four treatment periods (p = 0.3). These findings show that sodium restriction is not a risk factor for iodine deficiency.

Prediction of iodine-131 biokinetics and radiation doses from therapy on the basis of tracer studies: an important question for therapy planning in nuclear medicine

OBJECTIVES

This study aimed to present a comparison of iodine-131 (I) biokinetics and radiation doses to red-marrow (rm) and whole-body (wb), following the administration of tracer and therapeutic activities, as a means of confirming whether I clearance and radiation doses for therapy procedures can be predicted by tracer activities.

METHODS

Eleven differentiated thyroid cancer patients were followed after receiving tracer and therapeutic I activity. Whole-body I clearance was estimated using radiation detectors and OLINDA/EXM software was used to calculate radiation doses to rm and wb.

RESULTS AND DISCUSSION

Tracer I activity of 86 (±14) MBq and therapeutic activity of 8.04 (±1.18) GBq were administered to patients, thereby producing an average wb I effective half-time and residence time of, respectively, 13.51 (±4.05) and 23.13 (±5.98) h for tracer activities and 13.32 (±3.38) and 19.63 (±4.77) h for therapy. Radiation doses to rm and wb were, respectively, 0.0467 (±0.0208) and 0.0589 (±0.0207) mGy/MBq in tracer studies and 0.0396 (±0.0169) and 0.0500 (±0.0163) mGy/MBq in therapy. Although the differences were not considered statistically significant between averages, those between the values of effective half-times (P=0.906), residence times (P=0.145), and radiation doses to rm (P=0.393) and to wb (P=0.272), from tracer and therapy procedures, large differences of up to 80% in wb I clearance, and up to 50% in radiation doses were observed when patients were analyzed individually, thus impacting on the total amount of I activity calculated to be safe for application in individual therapy.

CONCLUSION

I biokinetics and radiation doses to rm and wb in therapy procedures are well predicted by diagnostic activities when average values of a group of patients are compared. Nonetheless, when patients are analyzed individually, significant differences may be encountered, thus implying that nuclear medicine therapy-planning requires due consideration of changes in individual patient-body status from initial tracer to final therapy procedures to thus provide appropriate adjustments in therapeutic activities.

Breastfed infants metabolize perchlorate

Bifidobacteria are the dominant intestinal bacteria in breastfed infants. It is known that they can reduce nitrate. Although no direct experiments have been conducted until now, inferred pathways for Bifidobacterium bifidum include perchlorate reduction via perchlorate reductase. We show that when commercially available strains of bifidobacteria are cultured in milk, spiked with perchlorate, perchlorate is consumed. We studied 13 breastfed infant-mother pairs who provided 43 milk samples and 39 infant urine samples, and 5 formula-fed infant-mother pairs who provided 21 formula samples and 21 infant urine samples. Using iodine as a conservative tracer, we determined the average urinary iodine (UI) to milk iodine (MI) concentration ratio to be 2.87 for the breastfed infants. For the same samples, the corresponding perchlorate concentration ratio was 1.37 (difference significant, p < 0.001), indicating that perchlorate is lost. For the formula fed infant group the same ratios were 1.20 and 1.58; the difference was not significant (p = 0.68). However, the small number of subjects in the latter group makes it more difficult to conclude definitively whether perchlorate reduction does or does not occur.

Higher urine volume results in additional renal iodine loss

BACKGROUND

For some endocrine and nutritional biomarkers, for example, cortisol and vitamin B(12), significant associations between 24-hour renal analyte excretion and the respective 24-hour urine volume (U-Vol) have been reported. Therefore, our objective was to investigate whether 24-hour U-Vol (a marker of fluid intake) is also a relevant influencing factor of absolute daily iodine excretion.

METHODS

Urinary iodine excretion rates were measured in repeatedly collected 24-hour urine samples of (i) 9 healthy women participating in a controlled diet experiment with constant iodine intake and (ii) 204 healthy free-living adolescents (aged 13-18 years) who performed the respective urine collection during 2003-2008. Associations between U-Vol (L) and renal iodine excretion (μg/24 h) were investigated cross sectionally (multiple linear regression model, PROC GLM) and longitudinally (repeated-measures regression models, PROC MIXED). The major iodine sources in the adolescent's diet (iodized salt, milk, fish, eggs, and meat) were controlled for.

RESULTS

Urinary iodine excretion was significantly associated with 24-hour U-Vol in all performed fully adjusted regression models. A 1-L increase of U-Vol predicted an additional 15.0 μg/day (adolescents, 95% confidence interval: [9.8, 20.0], p < 0.0001) and 16.5 μg/day (women, 95% confidence interval: [9.2, 23.7], p = 0.0002) increase in iodine excretion. The longitudinal analysis in adolescents revealed a stronger relation of iodine excretion with U-Vol in girls than in boys (β = 17.1 vs. β = 10.5).

CONCLUSION

A high fluid consumption, and thus a high U-Vol, could lead to an additional renal iodine loss that obviously cannot be compensated by the iodine contents of non-milk-based beverages, reported to amount to ∼4 μg/L, on average. For specific research questions using the biomarker 24-hour urinary iodine excretion, U-Vol should therefore be considered as a potential confounder.

Urinary iodide concentration in hyperthyroid cats

OBJECTIVE

To compare concentrations of urinary iodide (UI) in euthyroid and untreated hyperthyroid cats.

ANIMALS

118 euthyroid and 88 hyperthyroid client-owned cats from 2 nonreferral veterinary practices.

PROCEDURES

Iodide concentration was measured in 5 urine samples collected every 3 to 12 months from selected cats, and variability of results between euthyroid cats and hyperthyroid cats prior to the diagnosis of hyperthyroidism was evaluated via 1-way ANOVA, after logarithmic transformation of UI concentrations (logUIs). The UI concentration in hyperthyroid cats was measured at diagnosis and 2 to 6 weeks and 3 to 6 months after treatment for hyperthyroidism. The pretreatment logUI in hyperthyroid cats was compared with that in euthyroid cats, taking into account the effects of renal function on UI concentration. Iodine intake was estimated in euthyroid cats following calculation of the volume of daily urine output, with a fixed value for iodine concentration in feces.

RESULTS

The variability of UI concentrations did not differ significantly between hyperthyroid (n = 10) and euthyroid (8) cats. The logUI increased 2 to 6 weeks after initiation of treatment in hyperthyroid cats (n = 80) and was lower in azotemic versus nonazotemic cats. Hyperthyroid cats had a lower logUI than euthyroid cats, and there was no evidence of deficient iodine intake in euthyroid cats.

CONCLUSIONS AND CLINICAL RELEVANCE

The logUI was lower in cats with azotemia and with untreated hyperthyroidism, compared with that in euthyroid cats from the same population. Additional studies are needed to determine whether iodine intake plays a role in the development of hyperthyroidism in cats.

Role of pendrin in iodide balance: going with the flow

Pendrin is expressed in the apical regions of type B and non-A, non-B intercalated cells, where it mediates Cl(-) absorption and HCO3(-) secretion through apical Cl(-)/HCO3(-) exchange. Since pendrin is a robust I(-) transporter, we asked whether pendrin is upregulated with dietary I(-) restriction and whether it modulates I(-) balance. Thus I(-) balance was determined in pendrin null and in wild-type mice. Pendrin abundance was evaluated with immunoblots, immunohistochemistry, and immunogold cytochemistry with morphometric analysis. While pendrin abundance was unchanged when dietary I(-) intake was varied over the physiological range, I(-) balance differed in pendrin null and in wild-type mice. Serum I(-) was lower, while I(-) excretion was higher in pendrin null relative to wild-type mice, consistent with a role of pendrin in renal I(-) absorption. Increased H2O intake enhanced differences between wild-type and pendrin null mice in I(-) balance, suggesting that H2O intake modulates pendrin abundance. Raising water intake from approximately 4 to approximately 11 ml/day increased the ratio of B cell apical plasma membrane to cytoplasm pendrin label by 75%, although circulating renin, aldosterone, and serum osmolality were unchanged. Further studies asked whether H2O intake modulates pendrin through the action of AVP. We observed that H2O intake modulated pendrin abundance even when circulating vasopressin levels were clamped. We conclude that H2O intake modulates pendrin abundance, although not likely through a direct, type 2 vasopressin receptor-dependent mechanism. As water intake rises, pendrin becomes increasingly critical in the maintenance of Cl(-) and I(-) balance.

Comparison of the transfer of 125I, 82Br, and 26Cl into the growing oocytes of the Japanese quail

Laying Japanese quail were doubly-labeled with either 125I and 36Cl or 82Br and 36Cl. Eighteen-hour accumulations, expressed as percent of tracer doses, were: growing oocytes, 125I 48.2 vs. 36Cl 2.07, 82Br 4.01 vs. 36Cl 1.99; thyroids, 125I 10.6 vs. 36Cl .030, 82Br .027 vs. 36Cl .020. Concentrations (expressed as percent per gram) of the radionuclides in the growing oocytes and the thyroids as compared with concentrations in the plasma were: for oocytes, the mean 125I concentration was 199 times the mean plasma concentration, 82Br was .34 x and 36Cl was .13 x; for thyroids, 125I was 13,500 x, 82Br was .48 x, and 36Cl was .41 x the mean plasma concentration. Eight day totals for yolks of eggs laid were 125I 29% vs. 36Cl 3.7%.