Endocrinological aspects of PTH metabolism in the kidney

Various methods for the measurement of intact PTH, PTH fragments and PTH binding to receptors were applied to clarify the role of renal receptors for the bioexpression of PTH. Glomerular receptors may contribute approximately 20% of the renal PTH catabolism. PTH also binds to tubular receptors at the luminal side (brush border membranes) as well as at the antiluminal site (basal-lateral membrane). Scatchard plot analysis of PTH binding to these receptors allows the calculation of an equilibrium dissociation constant and binding capacity, if correction is made for inactivation of bioactive PTH (measured by LAMA). Binding to receptors is--in our systems--invariably associated with degradation of the intact hormone to N-terminal and C-terminal fragments of different molecular weight. Antibodies against basal lateral membranes and against brush border membranes are able to inhibit PTH binding to tubular membranes. Sera of uremic patients with inappropriately high PTH contain a globulin which interferes with PTH binding to the receptor, suggesting that uremia may be another example for a "hormone receptor antibody disease".

Kinetics of PTH metabolism and PTH fragments in chronic renal failure

Distribution and metabolic degradation of bPTH was studied in man after infusion of 400 U bPTH and blood sampling up to 2h. Disappearance rates of intact 1-84 bPTH, carboxyl- and amino-regional peptides were calculated for healthy subjects (n = 12); patients suffering from moderate (GFR 15--30 ml/min, n = 4) and advanced (GFR less than or equal to 10 ml/min, n = 36) chronic renal failure; and bilateral nephrectomized patients (n = 3). Two components with a rapid and a slow disappearance rate can be separated ("distribution", "metabolism"). Half-lives are found to be in the range known from animal experiments with marked differences between intact 1-84 PTH and peptide fragments. Influence of impaired renal function on metabolic turnover rates of PTH is given.

[Coma in myxedema--a rare complication of hypothyroidism. Possible iatrogenic factors should be taken into account]

Myxedema coma is the most severe form of hypothyroidism and is characterized by extreme hypothermia, bradycardia, central hypoventilation and hypoxia. Common causes are intercurrent diseases, interruption of thyroid hormone treatment, or an overdose of sleeping pills or sedatives. The diagnosis is usually readily established on the basis of very high serum TSH and low T4 levels. Consideration must also be given to an extra-thyroidal influence on the hormone levels. Intensive care treatment involving intravenous high-dose L-thyroxine and the reversal of hypoxia improve the prognosis of the serious disease.

[Risk of hyperthyroidism in examinations with contrast media]

Investigations with contrast media inevitably lead to the patient being exposed to large amounts of iodine. Under certain preconditions this gentails danger for the patient by causing either iodine-induced hyperthyroidism, which is difficult to treat, or even a thyrotoxic crisis. Patients with normal thyroid function and size have only minute changes of thyroid hormones and TSH within the normal range and are not at risk. Patients with unknown hyperthyroidism--independent of the etiological form--and patients with functional autonomy are at risk of exacerbation of pre-existing hyperthyroidism or development of iodine-induced hyperthyroidism. This development depends on two factors: a) the volume of autonomous tissue and b) the quantity of iodine exposure. Besides contrast media, other sources of iodine excess are possible, such as iodine-containing disinfectants, secretolytic agents, antiarrhythmics like amiodarone, eye drops and ointments, geriatrics, skin ointments, toothpaste etc. The development of hyperthyroidism can be prevented by combined treatment with antithyroid drugs and perchlorate in the case of preexisting hyperthyroidism or the urgent clinical suspicion of thyrotoxicosis or with perchlorate alone, when the patients is euthyroid and does not have a large nodular goitre.

[Hypocalcemic crisis. Hypoparathyroidism--non-parathyroid origin--the most frequent form: hyperventilation syndrome]

Hypocalcemic crisis presents with the classical symptomatology of tetany plus extrapyramidal symptoms and a disordering of consciousness extending even to coma. It develops when the concentration of ionized serum calcium declines rapidly, and is very rarely found in chronic hypocalcemia. In terms of its etiology, various forms of parathyroid deficiency, and nonparathyrogenic diseases associated with hypocalcemia may be involved. Since in the latter the concentration of albumin is also diminished, and thus ionized calcium decreases to only a small extent, hypocalcemic crisis in these conditions is rare. The most common clinical form is normocalcemic tetany that occurs within the framework of the hyperventilation syndrome. Here, the ionized calcium fraction is temporarily reduced by marked alkalosis. Today, laboratory findings render establishment of the diagnosis simple. Acute therapy takes the form of parenteral calcium administration, and for long-term treatment, vitamin D metabolites, possibly in combination with oral calcium replacement is employed.

[Hypercalcemic crisis. Exacerbation of an existing hypercalcemia syndrome]

Acute hypercalcemic crisis is the life-threatening exacerbation of an existing hypercalcemia syndrome, which is characterized by additional cerebral symptoms such as clouding of consciousness, somnolence and coma as well as rapid deterioration of renal function. Possible causes are diseases associated with severe hypercalcemia, such as malignant diseases, primary and tertiary hyperparathyroidism, vitamin D poisoning and treatment with calcium, vitamin D and calcium-containing ion exchangers in renal insufficiency. Nowadays the specific diagnosis can usually be established quickly and simply, since only in primary and tertiary hyperparathyroidism are calcium and the intact parathormone elevated. The aim of treatment is to bring about an effective reduction in serum calcium by inhibiting bone resorption and increasing calcium excretion in the urine. Today, the substances calcitonin, biphosphonate, mithramycin (plicamycin) and glucocorticoids, each with a different mode of action, are available. In patients with underlying malignant diseases these substances are used to supplement the treatment of the malignancy, while in hyperparathyroidism they are administered prior to operative parathyroidectomy.

[Thyrotoxic crisis. Pitfalls in diagnosis--intensive therapy]

Thyroid storm--a dramatic exacerbation of existing hyperthyroidism of sudden onset associated with hyperthermia, tachycardia and CNS symptomatology--remains a life-threatening disease. On account of an overlapping of the symptoms of precipitating conditions, and complications, e.g. thromboembolism, the clinical diagnosis is not easy, and is often established "too late'. Since an additional role is often played by exposure to iodine, treatment is also rendered more difficult, for antithyroid drugs inhibit only de novo synthesis, but not the secretion of stored thyroxin. Treatment requires the use of thyroid-specific and numerous adjuvant measures, and the patient must be admitted to an intensive care unit with relevant experience.

[Recurrent hematemesis and hemobilia in ruptured hepatic artery aneurysm--differential diagnostic aspects of acute, upper gastrointestinal hemorrhage]

Aneurysms of the hepatic artery are mostly localized extra hepatic (80%). Today atherosclerosis is the most prevalent etiology (32%), followed by trauma (22%) and inflammatory lesions (10%). Rupture or perforation of the aneurysm is the initial clinical manifestation (60-80%), and occurs with nearly equal frequency into the peritoneal cavity and into the hepatobiliary tract. Rupture into bile ducts is often responsible for characteristic findings of upper gastrointestinal bleedings with hematemesis. The case of a 38 year-old man is presented and the clinical manifestation, the diagnostic and therapeutic procedures are demonstrated.

Parathyroid hormone in coronary artery disease--results of a prospective study

Parathyroid hormone (PTH) influences the calcium metabolism of many different mammalian cell types; indeed, hypertension due to changes in muscle tone is a frequent symptom of hypercalcemic hyperparathyroidism. In a blind study of 81 patients with various forms of heart disease undergoing coronary angiography, the plasma concentrations of the midcarboxyl regional PTH immunoreactivity were determined. PTH concentrations were elevated in 26 of the 56 patients exhibiting organic coronary artery disease (CAD). The plasma PTH levels were highest in those patients with CAD affecting three vessels and in patients with evidence of myocardial infarction. PTH levels were not influenced by previous drug treatments, and did not correlate to stress hormone levels. We propose that increased PTH levels may be a marker for initiation or potentiation of calcium-dependent changes in vascular smooth muscle behavior inducing coronary functional and anatomic lesions typical of CAD.

Androgen and estrogen response to adrenal and gonadal stimulation in idiopathic hemochromatosis: evidence for decreased estrogen formation

Gonadal function in idiopathic hemochromatosis (IHC) was evaluated by comparing clinical features and levels of sex hormones in 10 male patients with IHC (cirrhosis, 4; fibrosis, 6), 6 male patients with alcoholic cirrhosis (AC) and 10 healthy, age-matched controls. Impotence was present in 9 IHC and all AC patients and was associated with decreased plasma testosterone levels. However, gynecomastia, a feature in all patients with AC, was not present in IHC, and plasma sex hormone binding globulin was normal. Patients with IHC showed significantly lower basal estradiol levels (17.7 +/- 6.3 pg per ml) than did controls (28.5 +/- 8.5 pg per ml), and low LH levels (p less than 0.01), which were insufficiently stimulated by luteinizing hormone releasing hormone (n = 8) as well as a decrease in prolactin concentration (2.9 +/- 1.4 vs. 5.9 +/- 1.9 ng per ml in the controls) suggesting pituitary failure. Synthesizing capacity of sex hormones was determined by adrenocorticotropic hormone and human chorionic gonadotropin administration. Basal and stimulated levels of androstenedione and cortisol indicated normal function of the adrenals in IHC. However after adrenocorticotropic hormone, estrone levels increased to only 16.2 +/- 8.4 pg per ml (controls, 27.3 +/- 4.7 pg per ml; p less than 0.01). Increments of estrone (12.5 +/- 9.2 pg per ml) and estradiol (17.9 +/- 11.6 pg per ml) were also lower in IHC following human chorionic gonadotropin administration than in controls (26.0 +/- 7.2 and 37.5 +/- 11.4 pg per ml, respectively). In contrast, plasma human chorionic gonadotropin raised testosterone levels 3.3-fold in IHC and 2.2-fold in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

[No effect of digitalis on sex and adrenal hormones in healthy subjects and in patients with congestive heart failure]

Digoxin was studied to see whether it impairs adrenal function and feminizes male subjects by changing plasma sexual hormones; both have been reported on previously. In eight healthy male subjects neither estrone (38.7 +/- 7.7 vs 35.4 +/- 3.2 pg/ml) nor estradiol (35.8 +/- 6.4 vs 32.2 +/- 3.9 pg/ml) nor testosterone (6.32 +/- 0.74 vs 6.45 +/- 0.73 ng/ml) were found to be altered by digoxin administration (plasma levels 1.55 +/0- 0.27 ng/ml) lasting 35 days. The same was true of free testosterone (147 +/- 24 vs 142 +/- 19 pg/ml) and free estradiol (657 +/- 77 vs 615 +/- 78 fg/ml). Even maximal stimulation of the adrenal and gonadal glands by adrenocorticotropic hormone (ACTH) and human chorionic gonadotropin (hCG) did not exhibit any digoxin-induced alterations in the synthesizing capacity of steroid hormones, as shown by plasma cortisol (increase from 128 +/- 18 to 389 +/- 18 ng/ml) and testosterone (from 5.96 +/- 0.90 to 10.33 +/- 1.19 ng/ml). Furthermore, seven subjects on digoxin were observed over a period of 150-210 days; they did not show any increase of estrogens. This was also found in three subjects when estrogen levels were elevated initially due to extreme obesity. Also, 35 patients who took beta-methyldigoxin (n = 8), beta-acetyldigoxin (n = 20) and digitoxin (n = 7) from 1 to 9 (mean: 1.9) years demonstrated normal plasma concentrations of gonadal and adrenal steroids, irrespective of duration of application or the digitalis compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Homologous radioimmunoassay for human mid-regional parathyroid hormone

A radioimmunoassay, selective for the clinically important mid region of human parathyroid hormone (hPTH), is reported. The synthetic 44-68 amino acid sequence (h44-68PTH) was used as both the standard and tracer material. This eliminated many of the undesirable characteristics associated with PTH assays the employ hormone of biological origin. These components allowed the detection of mid regional fragments present in both intact and fragmented hPTH, with a working range between 50 and 2500 pg/ml h44-68PTH. There was no interference from serum proteins and no significant cross reactivity to a range of N-terminal, C-terminal and other mid regional hPTH peptides. The assay proved to be rapid (total time 24 h) and was extremely reproducible, with an intraassay and interassay variation of 2.8% and 5.6% respectively (expressed as percentage SE in mean). The plasma concentration of normal subjects was established as 129 +/- 6 pg/ml (h44-68PTH) with a range of 50-300 pg/ml (n = 42). This assay, using fully synthetic hPTH peptides, was able to distinguish between euparathyroid and hyperparathyroid subjects, which suggests that the assay is of diagnostic value.

[Plasma thyroid hormones and TSH during the early stage of acute myocardial infarction (author's transl)]

In 21 males (age 50-78 yrs) without endocrine diseases, plasma thyroxine, triiodothyronine, reverse-triiodothyronine and TSH were determined by specific RIAs in the early stage of an acute myocardial infarction. Blood was taken every 4 hours up to 43 hours after admission. The patients were separated in 2 groups, depending on the severity of the infarction (group A with 11 patients = severe infarction; group B with 10 patients = not severe infarction). 25 healthy men served as an aged-matched control group (age 56-83 yrs). Thyroxine in all patients (group A and B together) did not show essential fluctuations during the 43 hours of observation. The mean values were elevated, the individual values were predominantly in the normal range. There were no significant differences between the groups A and B. As well in the total-patients group as in the groups A and B already on admission, T3 was diminished and went on falling during the 43 hours. From 35 hours after admission, T3 was significantly decreased in group A compared to group B. On admission, rT3 was elevated in both the total-patients group and group A and B; it reached its maximum after 19 hours. Group A showed from 7 hours after admission a tendency more increased levels compared to group B. In all cases (total-patients group, group A and B) TSH levels were constant within the normal range during the whole time. The results suggest that in the early stage of myocardial infarction an important alteration in the thyroxine metabolism with enhancement of the inactive reverse-triiodothyronine production occurs very quickly. Moreover, the results show that this alteration may depend on the severity of myocardial infarction. Hypothyreoidism can be excluded because of the normal or elevated thyroxine values and the normal TSH levels.

Preliminary results on the use of an antiserum to human parathyrin in a homologous radioimmunoassay

A new antiserum (Ab Giselle) raised in sheep against extracted human parathyrin was evaluated and compared with an established antiserum (Ab S-478 VI) under several test conditions. The assay system contained an extracted 1--84 human parathyrin standard and a 1--84 bovine parathyrin tracer. The total assay time was 24 h and the main assay characteristics as follows: B0/T 0.28 +/- 0.02 and 50% intercept 553 +/- 47 U . 1(-1). The corresponding data for Ab S-478 VI were: B0/T 0.23 +/- 0.02 and 50% intercept 890 +/- 142 U . 1(-1). The normal range in 152 normocalcaemic volunteers (age range 16--67 years) was 10.6--423 U . 1(-1) (where 1 vial MRC reference preparation 75/549 for human parathyrin = 25 U), compared with 0--300 U . 1(-1) for Ab S-478 VI. With the new antiserum, differentiation between hypoparathyroid patients and those with normal function was often possible, and differentiation between normal and elevated levels, as in hyperparathyrinaemia, was very good. Correlation between Ab Giselle and Ab S-478 VI in 80 normal volunteers was positive (r = 0.450, p = 0.01) although the regression line showed that the antisera had different specificities (data for the regression line y = a + bx, a = 0.13, b = 0.55). Under the assay conditions, the association constant for Ab Giselle was 0.41 +/- 10(14) l . mol-1 in contrast to Ab S-478 VI which had a Ka for 0.53 x 10(10) l . mol-1 under identical conditions. Assays using Ab Giselle could be performed at room temperature, whereas those using Ab S-478 VI performed best at 0 degrees C. Preliminary results suggest that Ab Giselle is better for the routine assay of human parathyrin in serum than Ab S-478 VI, especially in the case of hypoparathyroid patients.

[The child's skeleton following renal transplant. A correlation of the radiographic findings to the amount of parathormone (author's transl)]

The skeletal X-rays (magnification radiography of hand, pelvis, knee and shoulder joint) of 20 children before and after successful kidney transplantation were compared with the parathormone concentrations measured in the interval closest to the roentgenological examination. In 19 children, renal osteodystrophy existed before kidney transplantation, which was diagnosed based on the following radiographic findings of varying frequency: rarefaction and fuzziness of the spongiosa, fraying of metaphysical ends, widening of the growth plates, subperiosteal resorption and acroosteolysis. The parathormone concentrations were definitely increased before kidney transplantation. After kidney transplantation the abnormal radiographic findings receded corresponding to normalisation of the parathormone concentrations. Nevertheless, in 14 out of 19 children a rarefaction of the spongiosa remained, the cause of which is presumed to be steroid therapy.

Acute hyperparathyroidism. Clinical, laboratory and ultrastructural findings in a variant of primary hyperparathyroidism

In a series of 6 patients out of 47 cases with extrarenal hyperparathyroidism we investigated the clinical, laboratory and ultrastructural peculiarities of acute hyperparathyroidism. It was found that there are characteristic differences between both entities which, however, are fluid. Clinically more severe were neuromuscular psychiatric and mental signs. In the laboratory parameters PTH determined by radioimmunoassay and calcium were higher whereas hemoglobin was lower. The weights of the adenomas did not differ in both groups and this was also true for light microscopy findings. Electron microscopy revealed accelerated hormone extrusion and autodigestion of retrived membrane material in the cases of acute hyperparathyroidism similar to characteristics of parathyroid cells stimulated by hypocalcemia in tissue culture.

[Plasma parathyroid hormone after kidney transplantation. A sensitive parameter for the estimation of graft function (author's transl)]

Patients after kidney transplantation were investigated for parameters for kidney function and calcium metabolism including a definitively characterized parathyroid hormone (PTH) radioimmunoassay, of which quality criteria have been documented. In 72 transplanted patients 3 months to 7 years after operation a close correlation between graft function and plasma PTH concentrations was found. Patients with clearly elevated PTH revealed definitively decreased graft function. Three patients with normal GFR and clearly elevated PTH showed - at least transiently - all criteria of an autonomous hyperparathyroidism including hypercalcaemia and hypophosphataemia. Borderline PTH elevations associated with normal GFR can be explained by corticosteroid treatment. In 100 patients, which were investigated before and during the first 10 days after transplantation, again a close correlation was documented between the development of PTH concentrations and the function of the transplanted kidney. PTH concentrations are not only a very sensitive parameter of graft function; in various situations plasma PTH concentrations additionally allow an estimate of graft prognosis. This is particularly true in primary graft failure and in early rejection episodes.

[Reciprocal changes of triiodothyronine and reverse triiodothyronine in the early stage of myocardial infarction (author's transl)]

The changes of thyroid hormones and TSH in plasma of males in the early stage of myocardial infarction are described. Already on admission T3 was diminished and went on falling. On admission rT3 was elevated and reached its maximum after 19 hours. T4 and TSH did not show essential alterations. The results suggest that in the early stage of myocardial infarction a rapid shift of the monodeiodination of T4 to rT3 occurs instead of T3 with a quick decrease of T3 and increase of rT3 in the blood.

Human parathyroid hormone: antibody characterization

PTH antibodies were raised in two sheep (S 469 and S 478) by immunizing with porcine and bovine parathyroid extracts. Both antisera were characterized with various PTH preparations and fragments. Both antisera cross react with human, bovine and porcine PTH, one antiserum also binds rat PTH. Region specificity could be attributed to the mid region of the PTH molecule with particularly high affinities of both antisera for the fragment 44-68 hPTH. S 478 has similarly high affinity for intact hormone (affinity constants 0.6 x 10(13) l/mol), while S 469 has much higher affinity for the 44-68 fragment (affinity constant 0.84 x 10(13) l/mol) than for intact hormone. The antibodies are useful not only for clinical radioimmunoassay, but also for experimental work. They have been distributed to many laboratories.

Regulatory hyperparathyroidism in a pig breed with vitamin D dependency rickets

A radioimmunoassay for porcine parathyroid hormone has been developed and applied to measure immunoreactive parathyroid hormone (PTH) in plasma of pigs with hereditary vitamin D dependency rickets (VDDR) (pseudovitamin D deficiency rickets). Levels of 25-hydroxycholecalciferol (25-(OH)-D3) in plasma were measured by a protein binding assay. Both plasma concentrations of PTH and 25-(OH)-D3 showed an approximately 4-fold increase compared to normal pigs. PTH levels increased with duration of the disease. Daily dosing of the animals with 1--4 micrograms of 1,25-dihydroxycholecalciferol (1,25-(OH)2-D3) reduced PTH concentrations and resulted in clinical healing. Iv administration of 10 micrograms of 25-(OH)-D3/day did not alter PTH concentrations nor the clinical symptoms. The results suggest that these animals suffer from regulatory hyperparathyroidism. The metabolic defect could be due to a failure of the kidney to convert 25-(OH)-D3 to 1,25-(OH)2-D3.

[Kinetics of whole-body water and bromide space in patients with liver cirrhosis (author's transl)]

The kinetics of extracellular water (82Br) and total body water (THO) in controls and patients with liver cirrhosis are studied. Analysis of the plasma activity of the radionuclides as a function of time shows that distribution volumes and kinetics can be described by a linear open three-compartment model and that the volumes are of about equal size. Measuring is carried out in the central compartment in which the radionuclides are injected as a bolus. In cirrhotic patients equilibration into a third compartment is attained about four times slower than in controls. Elimination is reduced by about the same factor. Reduced diffusion and effective blood flow in the cirrhotic patients are discussed as possible reasons for the differences.

[Primary hyperparathyroidism as differential diagnosis of severe skeletal destructions (author's transl)]

The case of a 45-year old female patient with primary hyperparathyroidism is described to show that this disease can occur under the principal sign of a destruction of the cervical vertebral column. The roentgenological changes associated with primary hyperparathyroidism are discussed and their differential diagnostic significance is emphasised. The radially located subperiostal absorptions are the first roentgenological changes seen in PHPT and represent signs which make it highly probably that this disease is present.

Radioimmunoassay for parathyrin. Characterization of six different antigens and antisera

We studied six different antisera to bovine or porcine parathyrin (parathyroid hormone, PTH), produced in rabbit, guinea pigs, sheep or goat, two of which are commercially available. The antisera were characterized with regard to species specificity, affinity and their ability to identify patients with primary hyperparathyroidism. In this heterologous radioimmunoassay system in which [125I]parathyrin is used as a tracer, some cross-reactivity of the antisera to the hormone or hormone fragments present in human serum was demonstrated. However, there is some overlap of serum immunoreactive parathyrin in patients with or without primary hyperparathyroidism. The results of this and other studies illustrate the necessity for a homologous radioimmunoassay for human parathyrin.

Studies on circadian variations of plasma TSH, thyroxine and triiodothyronine in man

To evaluate the existence of circadian variations in thyroid hormone and TSH levels, blood was drawn every 20 min for 24 h in four and for 14 h in one volunteer. Hormones were measured by sensitive radioimmunoassays. TSH: A diurnal rhythmicity could be demonstrated with peaks from 8 p.m. to 2 a.m and a nadir from 7 a.m. to 2 p.m. Superimposed on the diurnal rhythm multiple shortlived fluctuations were observed. Thyroxine: Pooled data showed peak values from 8 a.m. to 12 a.m. and lowest levels from 11 p.m. to 3 a.m. Again, shortlived fluctuations were superimposed on the diurnal rhythm in all instances. Triiodothyronine: Hormone levels were highest from 7 a.m. to 1 p.m. and lowest from 11 p.m. to 3 a.m. Fluctuations in T3 levels were less marked than those of T4. Diurnal variations in hormone levels can be demonstrated in most, but not in all instances. Fluctuations are minor and do not exceed the normal range. Therefore these changes are of no relevance in routine testing of these hormones.

[A highly sensitive C-terminal specific radioimmunoassay for human parathormone as a routine method (author's transl)]

The basis for the radioimmunoassay of parathormone (PTH) as a routine method is a new sheep antiserum and a labelled PTH stabilised by a modification of the purification technique. The antiserum is obtained by immunisation with pig and cattle parathormone, it is C-terminal specific and is used in the assay in a final dilution of 1:35000. The affinity to human PTH is markedly greater than of the antisera used up to now. Two purification steps of 125J labelled bovine PTH lead to a tracer with a nonspecific binding of approximately 5% which increases to approximately 10% within 6 weeks. All normal sera investigated so far were measurable quantitatively (normal range 0.7 to 2.5 mul/equiv.). The lower sensitivity range was at 0.3 mul/equiv. All patients with chronic renal insufficiency and dialysis patients have an increased PTH concentration (3.9 to greater than 20 mul/equiv.). This also applies to patients with primary hyperparathyroidism (2.9 to greater than 20 mul/equiv.).

Radioimmunoassay of thyroxine-binding globulin in human plasma

A highly specific and precise radioimmunoassay for thyroxine-binding globulin (TBG) has been developed. Crossreactivity with albumin and prealbumin was excluded. The normal range in young adults was 0.97 mg/100 ml. In childhood TBG was elevated (1.34 mg/100 ml) also in old age (1.28 mg/100 ml). In normals and in childhood there was a good correlation of TBG with thyroxine (T4). T4 did not correlate with TBG with regard to age. Triiodothyroxine (T3) did not correlate with TBG in any group. T4 and T3 exhibited a progressive decrease with age. No correlation between age and TBG was found. In mild thyrotoxicosis (T3 : 4.5 ng/ml, with normal T4 and negative TRH-test) TBG was slightly increased (1.20 mg/100 ml), whereas in more severe hyperthyroidism (T3 : 6.4 ng/ml, T4 : 16.3 mug/100 ml) TBG concentration was not significantly different from normals. In hypothyroidism TBG was elevated (1.26 mg/100 ml). The conclusion from these data is that TBG does not follow the progressive decrease of T4 and T3 with age. Thus, age-dependent euthyroid ranges for thyroid hormone concentration, including TBG concentration, must be established for better clinical discrimination of thyroid function. Possible dependence of TBG on the nature of thyroid hormone concentration must be considered in the production and peripheral kinetics of thyroid hormones.

Differential action of parathyroid and thyroid hormones on effective intestinal absorption of calcium. In vivo studies with 47calcium in rats

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.