Release Of Radioiodine Research Articles

Thyroid activity following intracerebral injection of morphine in the rat.

Injection of microquantities of morphine into two sites in the hypo-thalamus was found to depress the release of radioiodine from the thyroid gland of rats. These sites lay in the supraoptic or the supramammillary region close to the midline. Injection of 0.9 % NaCl into the supraoptic area caused accelerated thyroid activity. These responses to morphine may represent a dual action of the drug: stimulation of neurons in the caudal hypothalamus that inhibit thyroid stimulating hormone release and depression of neurons in the rostral region that normally activate the pituitary-thyroid axis.

Thyroid iodine content and turnover in euthyroid subjects: validity of estimation of thyroid iodine accumulation from short-term clearance studies.

Measurements of thyroidal (k1) and renal (k2) radioiodine clearances, urinary iodine excretion (qe) and fractional thyroidal radioiodine release rate (αk) were conducted in 18 euthyroid young adult subjects in presumed iodine equilibrium, enabling the thyroid iodine accumulation (A) to be calculated. Thyroid iodide content (TI) was also calculated as:

Effects of actinomycin D, cycloheximide and puromycin on thyroid stimulation.

The administration to mice of actinomycin D, cycloheximide or puromycin was found to inhibit the influence of injected thyrotropin in stimulating in vivo the release of thyroid radioiodine. A time lapse of 8 or more hours was required for this inhibitory effect; a similar time was required for the inhibition by actinomycin D of the iodine-releasing action of the long-acting thyroid stimulator. With shorter time intervals there was no inhibition of thyrotropin or the long-acting thyroid stimulator. Major inhibition of incorporation of labeled precursor into protein was found 2 hr after injection of cycloheximide but this was much less evident after 6 hr. Actinomycin D inhibited thyroid incorporation of 3H-uridine into RNA by 21 to 46% when measurement was made in vitro with glands removed 1, 5, 9 and 24 hr after in vivo administration of the antibiotic. While it was concluded that new protein synthesis was not essential for the acute effect of thyrotropin on the release of thyroid hormone, no interpretatio...

A study of the deposition, translocation and excretion of radioiodine inhaled as iodine vapour.

A number of experiments are described in which iodine vapour labelled with 132I was administered to volunteer subjects to provide information of use in the evaluation of the radiological hazard from the accidental release of radioiodine. The experiments showed that the deposition of inhaled iodine vapour is essentially complete at normal breathing rates and that a fall off in deposition is only apparent at respiratory rates well in excess of the normal range. Much of the iodine vapour inhaled by mouth is deposited in the oral pharynx. From this region, iodine is carried down the oesophagus with saliva into the stomach and small intestine, where absorption occurs. Thyroid uptake and urinary excretion patterns are similar to those observed after ingestion of sodium iodide labelled with 132I.

Suppression of Radioiodine Releases from a Radiochemical Separations Plant

In the Purex process used at the Savannah River Plant, the suppression of the release of radioiodine by complexing it with mercury was tested. Suppressing radioiodine release would be desirable if ...

Experimental production of a thyroid-stimulating antithyroid antibody.

ABSTRACT Immunization of rabbits with concentrated homogenate of human thyroid resulted in the appearance in the serum of a thyroid stimulator which caused release of thyroid radioiodine in the suitably prepared assay mouse. The thyroid stimulator was shown not to be thyrotropin (which theoretically might be in enhanced concentration because of thyroiditis) by the following criteria: 1. It was not significantly inhibited by antiserum to thyrotropin. 2. Its concentration in the rabbits' blood was unaffected by thyrotropin-suppressive doses of thyroxine. 3. The activity was retained in purified γ-globulin extracted from the rabbit serum. It was not, however, possible to show conclusively that the activity could be inhibited by antiserum to rabbit γ-globulin; possible explanations for this failure are discussed. Four of the immunized rabbits maintained production of the thyroid stimulator for 9 months and then had thyroid uptake of 131I which was greater than control. While their rate of release of thyroid 1...

Studies on the mechanism of the inhibitory action of excess iodide on the release of radioiodine from the rat thyroid gland.

Thyroid release of radioiodine was inhibited by excess iodide in rats receiving small daily dose of propylthiouracil (PTU). This inhibition by excess iodide is not due to the synthesis and release of unlabeled thyroid hormone in amounts adequate to inhibit the release of thyrotropin, for the dilution of 131I within the thyroid by newly formed organic iodine after excess iodide is the same in the groups which received either a small (5 rag) or a large (30 mg) dose of PTU. Furthermore, the amount of plasma PBI newly secreted is negligible at both levels of PTU. Demonstration of the iodide effect in thyroxine and TSH treated animals indicated further that the iodide effect was not due to inhibition of TSH secretion. Administration ofsmall dose of PTU immediately augmented release of radioiodine from the thyroid, increased blood TSH within 24 hr and produced a large goiter after 2 weeks. Large doses of PTU are less effective in these actions. Administration of a small dose of methimazole similarly augments th...

Comparison of early effects of thyrotropin and long-acting thyroid stimulator on thyroid secretion.

LATS and TSH are chemically different thyroid-stimulating agents. To compare their early actions, we examined the effects in mice of LATS and TSH upon 2 thyroidal reresponses related to hormone secretion, namely, intracellular appearance of colloid droplets and release into the blood of preformed colloidstored radioiodine. Intracellular colloid droplets were induced by LATS in a manner qualitatively indistinguishable from the effect of TSH, but with a longer latency. In mice injected with 0.5 mU of TSH, a marked increase in the number of colloid droplets was observed in 10 min and a maximum was reached in 30 min. A dose of LATS which was chosen to match 0.5 mU of TSH in its radioiodine-releasing effect (at 2 hr) caused no increase in colloid droplets in 10 min, a small but significant increase in 30 min, and a maximal increase in 2 hr. When 16 times as much LATS was injected and shorter time intervals were examined, there was a slight increase in colloid droplets at 10 min, but the shape of the time-response curve was still grossly different from that of TSH, whose latency was greater than 4 but less than 7 min. Both LATS and TSH induced discernible release of thyroidal radioiodine only after the colloid droplet response was well established. Again, LATS showed a longer latency than TSH, and this difference in shape of the early part of the time-response curve could be used to distinguish the two agents. It is concluded that the early phase of stimulation of the thyroid by LATS is qualitatively similar to that due to TSH, but has a longer latency, which, among other explanations, might reflect a difference in the initial process of stimulation by the 2 materials. (Endocrinology80: 957, 1967)

Re-evaluation of the effect of estrogen on thyroid activity in the rat and its mechanism.

Estradiol benzoate (EB) was injected sc daily for 14 days into male and female rats. EB, over a wide dose range, produced an increase of thyroid weight and thyroidal radioiodine uptake. The increase in these indices was roughly proportional to the doses of EB used. By similar treatment, thyroidal radioiodine release was increased. In hypophysectomized animals, EB stimulated thyroidal radioiodine uptake slightly, but had no effect on thyroid weight. The EB-induced increase of thyroid weight and thyroidal radioiodine uptake of intact animals decreased progressively with the administration of increasing doses of thyroxine, but, at all levels of thyroxine dosage, thyroid weight and thyroidal radioiodine uptake were greater in EB-treated animals than in the controls. EB caused a statistically significant increase in the uptake of labeled thyroxine from plasma by human red blood cells and rat diaphragm. EB lowered plasma PBI in thyroidectomized, thyroxine-maintained animals. It is concluded that EB augments thy...

Rapeseed Meal Studies: 5. Effects of (±)-5-Vinyl-2-Oxazolidinethione, a Goitrogen in Rapeseed Meal, on the Rate of Growth and Thyroid Function of Chicks

ASTWOOD et al. (1949a, b) and Carroll (1949) isolated goitrin from rapeseed and identified it as L-5-vinyl-2-thiooxazolidone which more recently has been named (–)-5-vinyl-2-oxazolidinethione. Synthesis of (±)-5-vinyl-2-oxazolidinethione has been accomplished by Ettlinger (1950). The work to be reported concerns the effects of synthetic goitrin on the growth rate of chicks and on the structure and function of the thyroid glands of chicks. METHODSApproximately 50 grams of (±) -5-vinyl-2-oxazolidinethione (hereafter referred to as oxazolidinethione) was synthesized by following essentially the procedure outlined by Ettlinger (1950). Unfortunately supplies of one of the starting materials (3,4-epoxy-l, butene) became unavailable shortly after the project was commenced, otherwise a larger quantity of oxazolidinethione would have been prepared.In order to permit study of the effects of feeding oxazolidinethione for varying periods of time on the growth of chicks, the uptake and release of radio-iodine by the thyroid glands of chicks and on thyroid …

Further Studies on Inhibitory Effect of Excess Iodide on Thyroidal Hormone Release in the Rat

To determine whether a decrease of thyroidal radioiodine release produced by excess iodide in animals receiving small daily doses of PTU reflects a change in the secretion rate of thyroid hormone, several mechanisms were investigated in the rat. In agreement with the previous study (Yaraada et al., Endocrinology 72: 83, 1963), the present data indicated that thyroidal radioiodine release was inhibited by 50 or 200 μg KI in animals receiving small daily doses of PTU. Excess iodide apparently does inhibit the secretion of thyroid hormone. Furthermore, a decrease of plasma PBI in KI-treated animals was suggested by the measurements of muscle and resin sponge uptake of labeled thyroxine, processes which indicate indirectly the concentration of stable hormone in the blood. The inhibitory effect of excess iodide on thyroid hormone release was completely abolished by prior administration of KC1O4. The blocked thyroid failed to respond to exogenous TSH. In animals receiving large daily doses of PTU or in animals ...

Effects of novobiocin on pituitary-thyroid axis in the rat and its mechanism

Graded doses (20 to 60 mg.) of novobiocin were injected subcutaneously daily for varying periods of time, and effects of those injections on thyroid weight, thyroidal radioiodine uptake, organic binding of iodine, thyroidal radioiodine release, blood PBI and thyroxine-plasma protein interaction were studied in the rat. Administration of 20 or 40 mg. novobiocin for 7 days produced a low blood PBI without affecting thyroid weight, thyroidal radioiodine uptake and organic binding of iodine. However, thyroidal radioiodine uptake was suppressed at the beginning of the drug administration but it returned to normal by 2 days. In contrast, large doses of novobiocin for 7 days suppressed thyroidal radioiodine uptake and blood PBI. Since the novobiocin-suppressed thyroidal radioiodine release could be accelerated by the administration of exogenous TSH, and since novobiocin did not suppress adrenocortical and gonadal activity, those transitory and continuous inhibitions of thyroid activity might be produced by a decrease of TSH secretion. Muscle uptake of labeled thyroxine was high in the presence of plasma obtained from novobiocin-treated animals or in the presence of plasma with added novobiocin in vitro. Novobiocin was without effect on muscle uptake of thyroxine in the absence of plasma. Electrophoretic study indicated that novobiocin displaced thyroxine from albumin in vitro. It is suggested that novobiocin produced a low blood PBI by displacing thyroxine from albumin. The transitory inhibition of thyroid activity produced by small doses of novobiocin suggests the pattern reaching a new equilibrium in which thyroxine-plasma protein interaction is impaired. A new equilibrium may not be established by 7 days when large doses of novobiocin are administered in the rat.

Thyroidal 131-I turnover in hypothyroidism: correlation with thyrotropin responsiveness.

Turnover of thyroidal radioiodine was determined in 24 hypothyroid subjects by counting over the gland on 7 consecutive days after administration of a tracer. Upon completion of this procedure, all subjects received 3 injections of TSH and a second tracer to evaluate responsiveness of thyroid uptake. In 15 patients there was a rapid release of radioiodine, and in each instance this was shown to be associated with refractoriness to TSH. In the remaining 9 subjects, the turnover of thyroidal radioiodine was negligible and in these individuals there was normal responsiveness to TSH. These observations suggest that the turnover rate of thyroidal radioiodine may serve to differentiate primary from secondary hypothyroidism. A rapid release suggests primary thyroid pathology, whereas a slow release supports pituitary pathology as the cause of the thyroid insufficiency.

DIFFERENTIAL EFFECTS OF HYPOTHALAMIC LESIONS ON PITUITARY-THYROID ACTIVITY IN THE RAT.

ABSTRACT In order to determine more precisely the areas and possible neural pathways involved in pituitary-thyroid activity, lesions were made in a variety of locations within the hypothalamus by means of stereotaxy and high frequency coagulation. Lesions were either single midline lesions or double bilaterally placed lesions. Single midline lesions which destroyed the area between the fornix bundles at the level of the paraventricular nuclei (PVN), resulted in a reduction in the rate of thyroidal radioiodine release in rats maintained at room temperature and such lesions also blocked the thyroidal response to cold (4° C). A comparison was made between the effects of these lesions and of similar lesions located immediately anterior, posterior, superior, inferior and lateral to the PVN site. Single midline lesions just inferior to the PVN caused inhibition of the thyroid response to cold but at room temperature they appeared to be less effective than midline lesions at the level of the PVN. When lesions were made anterior to the PVN, the cold response was partially blocked, but there was no effect on thyroid activity at room temperature. In contrast, complete absence of any effects on thyroid activity was observed, following coagulation of midline structures either superior or posterior to the PVN site. Bilaterally placed lesions, located laterally to the PVN were also ineffective provided the region immediately adjacent to the midline was left intact. When animals with lesions of the PVN site were placed on a diet containing 0.3 % methylthiouracil (MTU), goitre development was retarded at 2 and at 4 weeks, but thyroid weight equalled that of the control animals after 40 days of MTU treatment. After still longer periods on MTU, goitres seemed to regress again to some extent in the lesioned rats. Thyroxine administration to rats bearing identical lesions resulted in inhibition of the radioiodine release rate. However, injection of 2 μg of thyroxine daily was insufficient to cause inhibition of iodine release in the lesioned rats, although such a dose was effective in the control animals.

RADIOIODINE RELEASE INCIDENT AT THE SAVANNAH RIVER PLANT.

Abstract—A release of 153 c of radioiodine from a Purex fuel processing facility, most of which occurred May 30 through June 3, 1961, temporarily increased the level of I131 in the environment of the Savannah River Plant (SRP). Prevailing southwest winds and atmospheric inversions dispersed the radioiodine mainly to the northeast of the Plant. Theoretical dispersion equations were verified by measurements of I131 in air at distances up to 25 miles from the Plant. I131 on vegetation decayed with an apparent half-life of 5 days, as compared to the physical half-life of 8 days. This is attributed to dilution of the activity by new vegetative growth. The reduction of radioiodine in milk closely followed the apparent half-life in grass. Laboratory tests with iodine-contaminated vegetation showed that rainfall removed little or no iodine. Consumption of milk in the area of highest deposition could have resulted in a thyroid dose up to 1.2 rems for a child. Empirical relationships relating the transfer of radioiodine from air to grass and then to milk are compared with those determined earlier at SRP and elsewhere.

THE CONCENTRATION OF RADIOACTIVE IODINE IN THE THYROID LYMPH, THYROID VENOUS BLOOD AND PERIPHERAL BLOOD OF PRIMATES.

Attempts were made to find out to what extent iodinated compounds are present in lyraph draining from the thyroid gland of the primate, by using baboons, Papio papio, which were injected with 50 to 200 μC 131I 2 to 7 days before collection of lymph. Radioiodine was released from the thyroid gland of the baboon into the lymphatic vessels which drain the gland, as well as into the thyroid venous blood. A high proportion, 90% or more, of the 131I appeared in the thyroid lymph in organically combined form. The concentration of 131I in the thyroid lymph was very much higher (10 to 100-fold) than that in the thyroid venous blood or in the peripheral blood. The administration of thyroidstimulating hormone (TSH) raised the concentration of radioactivity in the thyroid lymph as well as in the thyroid venous blood and these separate effects of TSH appeared to be closely related processes. lt is known that physical or radiation damage to the thyroid gland may lead to the appearance of iodoprotein in the peripheral blood; however, it was possible to exclude the factor of physical damage by collecting lynaph at a distance from the gland. To avoid radiation damage, the dosesmore » of 131I used were lower than those generally used in experiments on the release of radioiodine from the thyroid gland. It was shown that if 125I was used instead of 131I, the radiation dose rate to the thyroid gland of a small animal can be reduced by a factor of about 25, and a preliminary study, in which125I was used in the monkey, suggested that a similar release of radioiodine, in organic form, takes place into the thyroid lymph. It seems unlikely that such a very low radiation dose could damage the thyroid gland. Therefore, it was concluded that the release of iodinated compounds into the lymphatics of the thyroid is a physiological phenomenon and that it is not due to damage to the gland.« less

THYROXINE SECRETION RATE DURING INFANCY: EFFECT OF ESTROGEN.

Measurements of thyroxine secretion rate have been conducted by the thyroid I131 blockage method in 17 premature infants. The infants were 24–65 days of age at the beginning of the study; normal thyroid function was indicated by normal initial radioiodine uptake studies. Mean daily thyroxine secretion rate in 13 infants determined by calculation of the regression line of daily thyroidal radioiodine release on increasing doses of thyroxine was 18.6 μg thyroxine/kg/day. The regression lines were not significantly different with and without perchlorate administration, indicating that recycling of radioiodine does not produce significant error. The thyroxine secretion rate of 18.6 μg/kg/day is considerably higher than adult human values by the serum specific activity method. In 5 infants given estradiol benzoate with a concomitant thyroid blocking dose of sodium l-thyroxine, stimulation of radioiodine released occurred. This stimulation was associated with increasing BEI values, suggesting an increase in TBG levels. Mean triiodothyronine I131 resin uptake values, however, increased during the therapy period, indicating endogenous thyroid hormone secretion predominating over the increase in TBG and progressively saturating available protein binding sites. The increased thyroidal radioiodine release rate, which occurred in spite of increasing triiodothyronine I131 resin uptake values, suggests a direct stimulation of hypothalamic-pituitary TSH release by estradiol benzoate.

Inhibitory effect of excess iodide on thyroidal radioiodine release in the rat.

The inhibitory effect of excess iodide on thyroidal radioiodine release was studied in more than 300 rats. In animals receiving 30 mg of PTU daily, excess iodide had no effect on thyroidal radioiodine release. However, excess iodide (50 or 200 μg KI) did suppress significantly the release of thyroidal radioiodine in all animals receiving small doses (0.1–5 mg) of PTU. Although the inhibition continued for more than 40 hr after a single injection of excess KI, this inhibition eventually was followed by resumption of normal thyroidal radioiodine release even after repeated injections of KI. Five μg injections of KI were without effect under the same experimental conditions. The possibility that appreciable quantities of the newly administered I127 were synthesized into thyroid hormone under the influence of small doses of PTU and that the decrease of specific activity resulted in the slowing down of thyroidal radioiodine release is not supported for the following 4 reasons: 1) Small doses of PTU were as eff...

Further studies on the inhibitory effect of diazo dyes on thyroid function in the rat.

In an attempt to determine the mode of action of diazo dyes in suppressing thyroid function, several of the possible pathways were investigated in the rat. Five days after the injections of trypan red and trypan blue, thyroid weight, thyroidal radioiodine uptake and thyroidal radioiodine release had decreased markedly. However, the inhibitory effect of trypan red was much less than that of trypan blue. By injecting graded doses of ACTH, significant increases in adrenal weight were produced, similar to those caused by diazo dye treatment, but no significant changes were found in thyroid weight, thyroidal radioiodine uptake or thyroid hormone synthesis, indicating that the hyperfunctioning pituitary-adrenal system has no causative role in hypofunction of the thyroid. It was found that trypan blue blocked the synthesis of thyroxine but not of DIT, an effect very similar to that produced by hypophysectomy. The uptake of I131 T4 by red blood cells was augmented significantly by both trypan red and trypan blue,...

Further observations on the occurrence of the thyrotropin inhibitor in urine.

ABSTRACT The investigation of factors affecting thyrotropin inhibitor (TSH-I) in urine of patients and euthyroid individuals has been continued. A modified procedure for chick thyroidal radioiodine release for the bio-assay of TSH and a benzoic acid concentration procedure of TSH-I of urine is described. TSH-I preparations from 5-day urine collections revealed minimal presence of TSH-I only in 3 of 10 untreated hypothyroid patients, while the administration of Na-L- or Na-D-thyroxine to euthyroid subjects, hypothyroid and hyperthyroid patients, or radioiodine treatment in hyperthyroid patients invariably resulted in increasing titers of TSH-I. The rise in TSH-I could be correlated with elevation of serum proteinbound iodine levels and reduction of serum cholesterol levels, usually occurring during the first 3 weeks following increase of the medication dose. The increased TSH-I titer reached a peak, followed by a period of adjustment and, in most cases, by a decrease of TSH-I thereafter.