Plasma inorganic iodine

In summary, as compared to the era of pre-iodization, in the post-iodization period there has been an increase in urinary iodine excretion (three—five-fold), plasma inorganic iodine (ten-fold), and absolute iodine intake (fivefold), while there has been a decrease in the percentage of thyroid uptake of iodine ingested (by 60%) and thyroid iodine clearance (three-fold). These changes are very... 

Study (year) Urinary Iodine excretion Plasma Inorganic Iodine (yg/d ) Thyroid Iodine clearance (ml/mln) Absolute Iodine clearance (yg/h)... 

Higher urinary iodine No change in plasma inorganic iodine Increased thyroid iodine clearance Increased absolute iodine uptake by the thyroid Increased thyroid organic pool of iodine... 

Notes. The percentage decrease in the serum thyroid hormone levels in Graves patient treated with carbimazoie with respect to plasma inorganic iodine levels does not show a strong relationship. Values are expressed in mean (standard deviation). T3 triiodothyronine, T4 thyroxine. 

After iodization, there has been an increase in urinary iodine concentration, an increase in plasma inorganic iodine level and a decrease in thyroid iodine clearance and radioiodine uptake by the thyroid gland in normal subjects. 

As a result of the low iodine intake, the plasma inorganic iodine averages 0.14 0.05 pg/dl in euthyroid normal adults and 0.064 0.038 Jig/dl in the euthyroid goitrous patients. Accordingly, the inorganic iodine pool is respectively 35 and 15 ig in euthyroid nongoitrous and goitrous subjects. 

PI 1= Plasma Inorganic Iodine, Ul= Urinary Iodine, (calc)= Ul calculated by multiplying the PI I x 48 (48 l/d is the average renal iodide... 

Most of the transport phenomena are descrihed by linear processes, but, for example, the uptake of inorganic iodine by the thyroid from the blood plasma is primarily a zero-order process, and several enzyme kinetic reactions and bindings are second-order processes. 

TRANSPORT OF THYROID HORMONES IN THE BLOOD Iodine circulates as both organic iodine (95%) and inorganic iodide (5%). Most organic iodine is in T (90-95%), while Tj contains approximately 5%. Both T and T are transported in the blood in strong but noncovalent association with plasma proteins. 

The earliest and potentially most damaging result of iodine deficiency is neonatal hypothyroidism and cretinism. The wide prevalence of cretinism in the Himalayan and sub-Himalayan belt has been shown by several authors, starting from the turn of the last century. Studies of iodine metabolism in the Himalayan goiter zones of India and Nepal (Karmarkar et ai, 1974) showed (a) markedly increased avidity of the thyroid to radioiodine (b) reduced excretion of stable iodine in urine (c) extremely low levels of iodine in the drinking water (d) normal or reduced protein-bound iodine in plasma and (e) low inorganic iodide concentration in plasma. These findings are compatible with the hypothesis that environmental deficiency of iodine is the primary factor responsible for endemic goiter in these areas. 

The inorganic form of iodine represents about 0.5 % of the total plasma iodine. The rest occurs in bound form with specific plasma protein (protein - boimd iodine, FBI) which has gained wide use as an indicator of thyroid activity in humans. It has been reported that the total plasma iodine concentration in healthy subjects is between 40 and 80 pg/l. According to Allain s studies when plasma iodine concentrations are below 40 pg/l, hypothyroidism is highly likely, when they are between 80 and 250 pg/1, hyperthyroidism, particularly Graves disease is probable. Above 250 pg/1 - iodine overload is almost certainly indicated (Allain et al., 1993). 

In discussing iodide metabolism, we need only be concerned with the fate of inorganic iodides because organic iodides (tyrosine derivatives) are absorbed and enter the normal plasma pool of organic iodides produced by the thyroid. The site and the mechanism of absorption of organic iodides in the intestine are not exactly known, but somehow the dietary iodine is transported from the intestinal lumen into the blood. 

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