TSH and prolactin secretions in Hashimoto's thyroiditis following withdrawal of thyroid hormone therapy

Changes in the pituitary-thyroid axis in patients with Hashimoto's thyroiditis following withdrawal of thyroid suppressive therapy were analyzed. The group of patients with thyroid adenoma served as control (group I). Patients with Hashimoto's thyroiditis were divided into 2 groups on the basis of serum TSH levels 8 weeks after discontinuing the exogenous thyroid hormone (group II, less than 10 microunits/ml; group III, more than 10 microunits/ml). During treatment with L-T4(200 micrograms/day) or L-T3(50 micrograms/day), there was no significant difference in serum T4-I and T3 levels among the three groups. Following L-T4 withdrawal, basal serum TSH levels were higher at 2 to 8 weeks in groups II and III than in group I. Serum TSH response to TRH was greater at 4 to 8 weeks in groups II and III than in group I. Following L-T3 withdrawal, basal serum TSH levels were higher at 1 and 2 weeks in group II than in group I, while those of group III were consistently higher during the study. Higher TSH responses to TRH were observed at 1 to 8 weeks in groups II and III. Neither basal nor TRH-induced prolactin (PRL) secretion differed significantly among the three groups. We have demonstrated that pituitary TSH secretion in patients with Hashimoto's thyroiditis is affected more by withdrawal of thyroid hormone therapy than in patients with thyroid adenoma. In addition, the present findings suggest a difference between the sensitivity of thyrotrophs and lactotrophs in Hashimoto's thyroiditis after prolonged thyroid therapy is discontinued.     

Serum T4, T3 and reverse T3 during treatment with propranolol in hyperthyroidism, L-T4 treated myxedema and in normal man.

Serum concentrations of T4, T3 and reverse T3 were studied in two hyperthyroid groups (n = 13 and 11), in a group of normals (n = 9) and in a group of L-T4 substituted patients (n = 7) with severe pretreatment hypothyroidism. Serum T4 did not change except in one of the hyperthyroid groups change to in which a slight decrease was found. In all groups a significant fall in serum T3 and a significant rise in serum reverse T3 were found. An expected increase in serum TSH in the normal and in the L-T4 substituted groups could not be demonstrated.     

Determination of serum thyroxine enantiomers in patients by liquid chromatography with a chiral mobile phase

A chromatographic method for the separation and determination of D- and L-thyroxine enantiomers (D-, and L-T4) in human serum with a chiral ligand ion-exchange system using a chiral mobile phase additive and a silica column was established. An aqueous eluent containing L-proline (L-pro) sufficiently complexed copper II ions and triethylamine (TEA) was used. It was monitored with a UV detector. The separation was completed in 12 min. The method has acceptable sensitivity, precision and accuracy for analysis. The limit of detection and the limit of quantitation for both D- and L-T4 were 0.1 microg/ml and 0.8 microg/ml, respectively. Calibration curves were linear within 1-100 microg/ml; the mean correlation coefficients were r(D-T4)=0.9986 for D-T4 and r(L-T4)=0.9978 for L-T4. T4 enantiomers were separated on baseline under the optimum condition. L-T4 eluted before D-T4. The concentration of D-T4 and L-T4 in 45 thyroid patients serum (hyperthyroid, hypothyroid, thyroidectomy, goitre or thyroiditis) using HPLC was determined, those results showed that D,L-T4 concentration varied in different thyroid patient. Attention should be paid to this result in treating thyroid disease in the clinic.     

Optimum replacement dose of thyroid hormone assessed by highly sensitive TSH determination in patients with congenital hypothyroidism

Serum thyroid hormone concentrations were measured in 100 samples from 25 patients with congenital hypothyroidism who were clinically well while receiving L-T4 therapy. Thyroxine concentrations were significantly higher than those of controls (p less than 0.01), while triiodothyronine was not significantly different. These samples were divided into four groups according to serum thyroid stimulating hormone concentrations as measured by highly sensitive immunoradiometric assay (IRMA-TSH). Serum thyroid hormone concentrations were compared among groups. The replacement dose of L-T4 and serum thyroid hormone in groups with undetectable IRMA-TSH were significantly higher than those in groups with normal or increased IRMA-TSH. These results show that serum thyroxine concentrations increase in most patients with congenital hypothyroidism on L-T4 therapy. Therefore, thyroxine concentrations above normal are not necessarily of clinical significance if IRMA-TSH is detectable. Undetectable IRMA-TSH might indicate the necessity for a reduction in the L-T4 replacement dose in patients with congenital hypothyroidism.     

Prolactin as a marker of dopaminergic activity at different levels of thyroid function in man

To investigate the hypothesis of an altered dopaminergic activity in hypothyroidism, seven patients without thyroid tissue were studied by means of three consecutive tests: an iv bolus of TRH (200 micrograms); a continuous iv infusion (5 mg during 30 min) of metoclopramide (MCP); and a second, post-MCP, iv bolus of TRH (200 micrograms). The study was performed three times: (A) without treatment; (B) on the 15th day while on L-T4 (150 micrograms i.d.); and (C) on the 30th day with the same treatment. Each time was a different situation of thyroid function; on the basis of basal serum TSH (P less than 0.001, A vs B vs C). The response of PRL to the first (non-primed) TRH, expressed as the sum of increments in ng/ml (mean +/- SE), was significantly higher in A (659 +/- 155) than in C (185 +/- 61). Individual PRL responses correlated with circulating T3 (P less than 0.02), but not with T4. A significant increase of PRL occurred after MCP in the three situations, but there were no differences among them. Likewise, the responses to the second (MCP-primed) TRH showed no differences. Although there was an expected high correlation (P less than 0.001) between basal TSH and circulating thyroid hormones, the maximal response of TSH to both non-primed and MCP-primed TRH was in B. After MCP, no measurable increase of TSH could be demonstrated at any of the three levels of thyroid function. These results do not support the hypothesis of an altered dopaminergic activity in hypothyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Decline of T3 and elevation in reverse T3 induced by hyperglucagonemia: changes in thyroid hormone metabolism, not altered release of thyroid hormones

Recently we reported that hyperglucagonemia induced by glucagon infusion causes a decline in serum Triiodothyronine (T3) and a rise in reverse T3 (rT3) in euthyroid healthy volunteers. These changes in T3 and rT3 levels were attributed to altered T4 metabolism in peripheral tissues. However, the contribution of altered release of thyroid hormones by the thyroid gland could not be excluded. Since the release of thyroid hormones is suppressed by exogenous administration of L-thyroxine (L-T4) in appropriate dosage, we studied thyroid hormone levels for up to 6 hours after intravenous administration of glucagon in euthyroid healthy subjects after administration of L-T4 for 12 weeks. A control study was conducted using normal saline infusion. Plasma glucose rose promptly following glucagon administration demonstrating its physiologic effect. Serum T4, Free T4 and T3 resin uptake were not altered during both studies. Glucagon infusion induced a significant decline in serum T3 (P less than 0.01) and a marked rise in rT3 (P less than 0.01) whereas saline administration caused no alterations in T3 or rT3 levels. Thus the changes in T3 and rT3 were significantly different during glucagon study when compared to saline infusion. (P less than 0.01 for both comparisons). Therefore, this study demonstrates that changes in serum T3 and rT3 caused by hyperglucagonemia may be secondary to altered thyroid hormone metabolism in peripheral tissues and not due to altered release by the thyroid gland, since the release of thyroid hormones is suppressed by exogenous L-T4 administration.     

Effect of thyroid hormone therapy on plasma insulin-like growth factor I levels in normal subjects, hypothyroid patients and endemic cretins

The effect of thyroid hormone therapy (L-T4 or L-T3) on plasma immunoreactive insulin-like growth factor I (somatomedin C, Sm-C) concentrations was studied in 8 normal controls, 14 primary hypothyroid subjects and in 7 patients with endemic cretinism. In normals basal levels of Sm-C (1.56 +/- 0.77 U/ml) increased to (2.46 +/- 1.0 U/ml; L-T4) and to (2.9 +/- 0.95 U/ml; L-T3). Plasma Sm-C basal levels were significantly lower in primary hypothyroid subjects (0.81 +/- 0.48 U/ml) and increased to 2.54 +/- 1.43 U/ml (L-T4) and to 2.16 +/- 0.83 U/ml (L-T3). A significant and positive correlation (r = 0.56) was found between Sm-C and serum T4 and T3 concentrations. Plasma Sm-C concentrations in endemic cretinism were initially normal in 4 patients, but low in the remaining 3 (mean +/- SD: 1.18 +/- 0.63 U/ml) and did not increase after 12 months (1.34 +/- 0.61 U/ml) or 18 months (1.01 +/- 0.43 U/ml) of L-T4 and L-T3 therapy. Plasma T4 levels and free T4 increased considerably in EC after therapy with a significant decrease in the previously elevated plasma TSH concentrations. The subnormal response of plasma Sm-C during effective thyroid thyroid hormone therapy could be an additional factor involved in growth failure of endemic cretins.     

SMS 201-995 and thyroid function in acromegaly: acute, intermediate and long-term effects.

The acute (TRH-stimulation test), intermediate (0-6 days administration), and long-term (0-30 months administration) effects of SMS 201-995 (octreotide) treatment on thyroid function were studied. Subcutaneous injection of 100 micrograms SMS 201-995 one hour before 200 micrograms TRH intravenously reduced serum TSH response area by more than 50% in 8 healthy volunteers. After 3 days of continuous subcutaneous infusion (CSI) of SMS 201-995 in 9 acromegalic patients (100 micrograms/24 h) a slight but significant decrease in serum total triiodothyronine (TT3) and a concomitant increase in serum TSH were demonstrated, indicating an initial inhibitory effect on peripheral deiodination of thyroxine. After a further 3 days treatment serum T3 and TSH had returned to prevalues. Six of the nine acromegalics were treated with SMS 201-995 (100-1500 micrograms/24 h) and admitted for diurnal hormone profiles on 13 occasions over 30 months. Apart from a barely significant increase in serum TSH, no changes in thyroid function were noted. The study was especially designed to detect minute changes over time in thyroid hormones. The only long-term effect of SMS 201-995 was the barely significant clinically irrelevant increase in serum TSH, possibly caused by a slight inhibition of peripheral deiodination of thyroxine.     

Effects of D- and L-thyroxine on the glucocorticoid binding capacity of adult rat liver

Administration of either D- or L-thyroxine (T4) significantly increased the glucocorticoid binding capacity of cytosol of the livers of adrenalectomized adult rats. Administration of up to 0.5 mg/100 g body wt. of L-T4 was more effective than that of D-T4, but higher doses (0.8-3 mg/100 g body wt.) of D-T4 increased the binding capacity markedly to more than that with L-T4. T4- administration did not alter the apparent dissociation constant of glucocorticoid binding proteins for glucocorticoid binding, or their behavior on DEAE-cellulose chromatography either before or after thermal activation (23 degrees C for 40 min). Thus the increased binding capacity seemed to be due to increase in the level of glucocorticoid receptor in rat liver.     

Treatment of hypothyroidism with L-thyroxin]

To compare an efficacy of the galenic form of desiccated thyroid gland--Thyreoideum "Polfa" with the synthetic L-thyroxine (Eltroxin Glaxo) in the treatment of hypothyroidism 15 patients were investigated. In all 15 cases before and after treatment ECG and the serum concentrations of cholesterol, thyroxine (T4), triiodothyronine (T3) as well as thyrotropin (TSH) in response to TRH were performed. After the treatment with Thyreoideum "Polfa" in doses 0.2 to 0.6 mg/daily there were neither clinical improvement, normalization of ECG, the serum concentrations of cholesterol, T3, T4 nor TSH. However, after the L-thyroxine treatment (Eltroxin Glaxo) in doses 100 to 200 micrograms/daily the clinical signs of hypothyroidism disappeared in all 15 patients. In ECG the statistically significant increase in voltage of the R and T waves after L-thyroxine treatment were observed. Also a significant decrease in the serum concentration of cholesterol and an increase in T4 and T3 were found. The serum concentration of TSH in response to TRH after the L-thyroxine treatment significantly decreased. L-thyroxine appeared to be a very efficacious in the treatment either primary or secondary hypothyroidism.     

Tablet Levothyroxine (L-T4) Malabsorption Induced by Proton Pump Inhibitor; A Problem that was Solved by Switching to L-T4 in Soft Gel Capsule

ObjectiveTo report a patient in whom the impaired absorption of tablet levothyroxine (L-T4) due to a proton pump inhibitor (PPI) use was corrected by switching the patient to the soft gel capsule.MethodsA woman with Hashimoto’s thyroiditis-associated hypothyroidism (serum thyroid-stimulating hormone [TSH] 6.8-9.6 mU/L) had been treated with tablet L-T4 (100 μg/day). Because she used to take pantoprazole just before L-T4 in the morning, TSH failed to normalize (4.4-6.5 mU/L). Thus, the daily dose had been progressively increased to 125 and 150 μg/day, with serum TSH levels of 2.4 and 0.6 mU/L, respectively.ResultsWhile maintaining pantoprazole, we switched the tablet L-T4 (150 g/day) to a soft gel capsule (125 μg/ day; Tirosint® capsule, IBSA, Lugano, Switzerland) and after 2 months, to 100 μg/day. Serum TSH was lower than under the equivalent regimens with the tablet: 0.5 versus 2.4 mU/L (125 μg/day) and 2.4 versus 4.4 to 6.5 mU/L (100 μg/day). Upon switching back to the tablet (100 μg/day), serum TSH increased to 3.2 and 4.7 mU/L and then dropped to 2.7-3.0 mU/L when the dose was increased to 125 μg/day. We also acutely evaluated the intestinal absorption of L-T4 by administering 600 μg LT4 as a tablet or soft gel capsule while maintaining pantoprazole. Pharmacokinetic indices showed better and faster absorption for the soft gel capsule versus tablet (area under the curve [AUC]_0-4h = 16,240 vs. 10,960 nmol/L × 4 hours, maximum absorption [C_max] = 108 vs. 73 nmol/L, and time of maximum absorption [T_max] = 120 minutes vs. 180 minutes).ConclusionConfirming in vitro studies conducted by other authors, the soft gel capsule L-T4 is negligibly affected by changes in gastric pH compared to tablet L-T4. (Endocr Pract. 2014;20:e38-e41)     

Nuclear thyroxine and triiodothyronine binding in mononuclear cells in dependence of age

Nuclear binding of thyroxine (T4) and triiodothyronine (T3) in mononuclear blood cells was investigated in 12 young (age 16-30 years) healthy subjects (group A), in 12 middle-aged (age 31-60 years) healthy subjects (group B) and in 12 elderly (61-90 years) healthy subjects. Serum free T3 was depressed in group C as compared to the younger age groups, whereas serum free T4 and TSH did not differ between the groups. Maximal specific nuclear binding capacity for both T4 and T3 decreased with increasing age, T4 group A: 1.2 fmol T4/100 micrograms DNA, group B: 1.2 fmol T4/100 micrograms DNA, group C: 0.7 fmol T4/100 micrograms DNA; T3 group A: 1.7 fmol T3/100 micrograms DNA, group B: 1.0 fmol T3/100 micrograms DNA, group C: 0.9 fmol T3/100 micrograms DNA. The equilibrium association constant (Ka) for T4 increased with age, group A: Ka = 3.3 X 10(9) l/mol, group B: Ka = 3.2 X 10(9) l/mol, group C: Ka = 6.4 X 10(9) l/mol, whereas Ka for nuclear binding of T3 decreased with age group A: Ka = 3.9 X 10(9) l/mol, group B: Ka = 5.9 X 10(9) l/mol, group C: Ka = 1.8 X 10(9) l/mol. We conclude that, whereas the opposite variations of nuclear capacity and binding affinity for T4 tend to preserve the nuclear T4 concentration, the nuclear T3 concentration definitely decreases with age. The unaltered serum levels of TSH suggest that the decrease of both serum levels of free T3 and the nuclear T3 concentration might represent physiologically changes in old age.     

Rabbit myocardial membrane Ca2+-adenosine triphosphatase activity: stimulation in vitro by thyroid hormone

The in vitro stimulation of human and rabbit erythrocyte membrane Ca2+-ATPase activity by physiological concentrations of thyroid hormone has recently been described. To extend these observations to a nucleated cell model, Ca2+-ATPase activity in a membrane preparation obtained from rabbit myocardium has been studied. Activity of 5'-nucleotidase in the preparation was increased 26-fold over that of myocardial homogenate, consistent with enrichment by sarcolemma. Mean basal enzyme activity in membranes from nine animals was 20.8 +/- 3.3 mumol Pi mg membrane protein-1 90 min-1, approximately 20-fold the activity described in rabbit red cell membranes. Exposure of heart membranes in vitro to L-thyroxine (T4) (10(-10)M) increased Ca2+-ATPase activity to 29.2 +/- 3.8 mumol Pi (P less than 0.001). Dose-response studies conducted with T4 showed that maximal stimulatory response was obtained at 10(-10) M). Hormonal stimulation was comparable for L-T4 and triiodo-L-thyronine (T3) (10(-10) M). Tetraiodothyroacetic acid was without biological activity, whereas triiodothyroacetic acid and D-T4, each at 10(-10) M, significantly decreased enzyme activity compared to control (basal) levels. The action of L-T4 on myocardial membrane Ca2+-ATPase activity was inhibited by trifluoperazine (100 microM) and the naphthalenesulfonamide W-7 (50-100 microM), compounds that block actions of calmodulin, the protein activator of membrane-associated Ca2+-ATPase. Radioimmunoassay revealed the presence of calmodulin (1.4 micrograms/mg membrane protein-1) in the myocardial membrane fraction and 0.35 micrograms/mg-1 in cytosol. Myocardial Ca2+-ATPase activity, apparently of sarcolemmal origin, is thus thyroid hormone stimulable. The hormonal responsiveness of this calcium pump-associated enzyme requires calmodulin.     

Galactorrhea in subclinical hypothyroidism

Galactorrhea was found in 5 patients with subclinical hypothyroidism. The galactorrhea consisted of the discharge of a few drops of milk only under pressure. Serum T4 was in the lower level of the normal range, but serum T3 was normal (T4: 6.3 +/- 1.2 micrograms/dl, T3: 113 +/- 7 ng/dl). Basal serum TSH and PRL were slightly increased only in 2 and 1 cases, respectively. The PRL responses to TRH stimulation were exaggerated in all cases, although the basal levels were normal. An enlarged pituitary gland was observed in 1 patient by means of CT scanning. All patients were treated by T4 replacement. In serial TRH tests during the T4 replacement therapy, the PRL response was still increased even when the TSH response was normalized. Galactorrhea disappeared when the patients were treated with an increased dose of T4 (150-200 micrograms/day). Recurrence of galactorrhea was not observed even though replacement dose of T4 was later decreased to 100 micrograms/day in 4 cases. In patients with galactorrhea of unknown origin, subclinical hypothyroidism should not be ruled out even when their serum T4, T3, TSH and PRL are in the normal range. The TRH stimulation test is necessary to detect an exaggerated PRL response, as the cause of the galactorrhea. To differentiate this from pituitary microadenoma, observation of the effects of T4 replacement therapy on galactorrhea is essential.     

Comparative effects of desiccated thyroid gland and sodium salt of L-thyroxine in the treatment of hypothyroidism

The studies comparing the actions of dried thyroid gland (Thyroideum-Polfa) with L-thyroxine sodium (L-T4) were carried out in 20 female patients with hypothyroidism, including 19 patients with the primary hypothyroidism and 1 patient with hypothyroidism secondary to pituitary deficiency. Administration of the dried thyroid gland did not normalize blood serum T4 an TSH in any patient. Normal serum T4 or even slightly increased was achieved in all patients treated with L-T4. Serum TSH was normalized in 17 patients with the primary hypothyroidism. The following conclusions have been drawn: 1. Dried thyroid gland (Thyroideum-Polfa) is ineffective in the treatment of hypothyroidism. 2. Serum TSH remains elevated despite normal serum T3 in cases of the primary hypothyroidism with decreased serum T4 levels. 3. Sodium salt of L-thyroxine should be used for the treatment of hypothyroidism. 1-Triiodothyronine sodium may be used as an adjuvant therapy.     

3,5-T2 stimulates oxygen consumption, but not glucose uptake in human mononuclear blood cells.

L-thyroxine (T4), L-triiodothyronine (T3) and 3,5-di-iodothyronine (T2) rapidly (within 30 min) stimulated oxygen consumption in human mononuclear blood cells, whereas the D isomers of T4 and T3 and Triac had no stimulatory effect. Oxygen consumption was stimulated by the same magnitude by equimolar concentrations (5-500 nmol/l) of L-T4, L-T3 and 3,5-T2 reaching a plateau at 100 nmol/l of 0.025 umol/mg DNA x h. The stimulatory effects of T4 and T3, but not of T2 were inhibited by PTU. Glucose uptake was stimulated only by L-T4 and L-T3, whereas 3,5-T2, Triac and the D-isomers of T4 and T3 had no effect. The dose response curve reached an apparent maximum at 100 nmol/l of 0.30 mmol/l x mg DNA x h and PTU had no effect on iodothyronine stimulated glucose uptake. We conclude that 3,5-T2 is a significant intracellular stimulator of oxygen consumption, whereas T3 and T4 stimulate glucose uptake.     

Effect of acute intravenous administration of thyroliberin on circulating reverse-T3

Some of the Authors previously demonstrated a significant precocious serum T3 increase after 200 micrograms TRH acute intravenous administration (TRH test). Reverse-T3 (rT3) is now known to interfere with T4 conversion to T3. We therefore compared spontaneously occurring to TRH test-induced changes in T3 and rT3 serum levels within a group of four healthy women in fertile age. Maximum rT3 increase during TRH test did not differ significantly from the maximum spontaneous variation at the same time of the day. Maximum T3 increase, on the contrary, was significantly higher than observed maximum spontaneous variation (0,81 ng/ml versus 0,39 ng/ml increase, p less than 0,01). Possible implications are discussed in the text.     

Growth hormone stimulates the peripheral conversion of thyroxine into triiodothyronine by increasing the liver 5'-monodeiodinase activity in the fasted and normal fed chicken

Normal fed and 2 days fasted Warren chickens were injected intravenously with 100 micrograms of ovine growth hormone (GH) and ovine prolactin and plasma concentrations of thyroid hormones were assayed prior and up to 2 h after injection. Fasting alone decreases T3, but increases T4. An injection of GH resulted in increases of plasma T3 concentrations in two fasting experiments by 40% (after 3/4 h) and 104% (after 1 h). In normal fed animals no increase is observed in the first experiment, whereas a 35% increase occurs in the second one. An injection of 100 micrograms prolactin does not influence T3 in normal fed or fasting animals. Both GH and prolactin, however, may decrease plasma concentrations of T4. In a separate experiment 50 micrograms and 200 micrograms of GH raised the decreased T3 levels after fasting by 39% and 60% respectively 1 h after injection and by 24 and 61% respectively in normal fed chicken, whereas prolactin was ineffective in this regard. Using Hisex chickens, the influence of an injection of 100 micrograms GH on plasma concentrations of thyroid hormones could be confirmed. At the same time GH increases the liver 5'-monodeiodinase activity by 330% after 1 h and by 147% after 2 h. The peroxidase activity is not influenced in normal fed chickens, but GH decreases this activity in food deprived animals after 1 h and 2 h. It is concluded that ovine GH, but not prolactin, stimulates the peripheral conversion of T4 into T3 in both normal fed and food deprived chicken and that this effect is dose dependent.     

Monocytes and platelets share the glycoproteins IIb and IIIa that are absent from both cells in Glanzmann''s thrombasthenia type I.

The possibility that thyroxine (T4) itself exerts the hormonal effect in vivo on the rat liver nuclear receptor was studied with the aid of iopanoic acid (IOP), an inhibitor of the conversion of T4 into tri-iodothyronine (T3). After administration of 2.4 micrograms of T4/100 g body weight to hypothyroid rats for 7 days, T4 and T3 concentrations in serum and in the liver nuclear non-histone protein (NHP) were all increased to the hyperthyroid range. Hepatic mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) activity and DNA content increased significantly. The equilibrium association constant (Ka) of the nuclear T3 receptor was unchanged and the maximal binding capacity (Cmax.) increased 1.4-fold. Simultaneous administration of IOP (5 mg/100 g body weight) to the rats given 2.4 micrograms of T4/100 g body weight completely blocked the conversion into T3. The serum T4 was even more increased, whereas the serum T3 decreased to the hypothyroid range. Although the NHP-bound T4 was at a concentration comparable with the rats given T4 alone, no NHP-bound T3 was detected. Yet the alpha-GPD activity was elevated 2.8-fold and the DNA content increased to the same extent as observed in the rats given T4 alone. The Ka and Cmax. of the nuclear receptor were significantly decreased. After administration of 48 or 480 micrograms of T4/100 g body weight for 3 days, serum T4 and T3 were markedly increased. The NHP-bound T3 was also increased, but no NHP-bound T4 was detected. The alpha-GPD activity was markedly elevated, but the DNA content was unchanged. The Cmax. per g of liver was increased, whereas the Ka remained unchanged. Simultaneous administration of IOP to these animals could not completely block the T4 conversion. The observed hormonal effects in the absence of nuclear T3 indicate that T4 possesses the intrinsic hormonal activities on the rat liver. T4 is less potent in induction of alpha-GPD activity but as potent in increment of hepatic DNA as T3. Although the binding site for T4 is not fully characterized, it appears to be acidic NHP. T4 is an active hormone, yet is also a prohormone of T3, offering the closest analogy with testosterone.     

Enantioselective resolution of thyroxine hormone by high-performance liquid chromatography utilizing a highly fluorescent chiral tagging reagent

A highly fluorescent chiral tagging reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole, [R(-)-DBD-PyNCS], was employed to develop an indirect resolution method for efficient separation of thyroxine enantiomers,D-T(4) and L-T(4). The reaction of R(-)-DBD-PyNCS with the thyroxine enantiomers proceeds effectively at 40 degrees C for 20 min in the presence of basic medium to produce the corresponding pair of diastereomers. No racemization occurs during the tagging reaction under the optimized conditions. Various experimental parameters for derivatization reaction including the species of catalyst, the concentration of tagging reagent and reaction temperatures, have been examined to get a highest yield for T(4) derivatives. The structure of T(4) derivatives was identified based on ESI-MS/MS measurements in negative mode. The efficient separation of D-, L-T(4) derivatives was achieved by isocratic elution with water-acetonitrile mobile phase containing 1% AcOH on a reversed phase column utilizing a conventional fluorescence detector. The resolution (Rs) value of the diastereomers derived from thyroxine was 5.1. The calibration curves of both the D-T(4) and L-T(4) were linear over the concentration range of 0.1-20 microg/ml. The limits of detection (S/N = 3) for both D-T(4) and L-T(4) were 0.2 ng per injection. The proposed method was applied to the determination of D-T(4) and L-T(4) in pharmaceutical formulations and human serum samples.