Possible evidence for endogenous production of a novel galanin-like peptide

Galanin mRNA and peptide are not detectable in normal islets. We studied the effect of galanin antagonists on insulin secretion in the rat beta cell line, RIN5AH, and in perifused rat islets. In RIN cell membranes galanin and its antagonists showed high affinity for 125I-galanin binding sites [Kd: (galanin) 0.03+/-0.01; Ki for galanin antagonists: (C7) 0.12+/- 0.02, (M35) 0.21+/-0.04, and (M40) 0.22+/-0.03 nM, mean+/- SEM, n = 4]. Galanin (1 microM) inhibited glucose-induced insulin release in islets (control 21.2+/-1.5 vs. galanin 4.5+/-0.2 fmol/islet per min, P < 0.001, n = 6) and RIN5AH cells (control 0.26+/-0.01 vs. galanin 0.15+/-0.02 pmol/10(6) cells per h, P < 0.001, n = 9). In RIN5AH cells, all antagonists blocked the inhibitory effects of galanin and stimulated insulin release in the absence of galanin. C7 and M40 (1 microM) alone significantly stimulated glucose-induced insulin secretion. Purified porcine galanin antibody (GAb) enhanced glucose-induced insulin release from islets (control 100+/- 16.3% vs. GAb 806.1+/-10.4%, P < 0.001, n = 6), and RIN5AH cells (control 100+/-9.6% vs. GAb 149+/-6.8%, P < 0. 01, n = 6). Western blotting of dexamethasone-treated islet extracts using GAb showed a specific band of similar molecular weight to porcine galanin not detected using a rat specific galanin antibody. One possible explanation for these results is the presence of an endogenous galanin-like peptide.

Specific adrenomedullin binding sites and hypotension in the rat systemic vascular bed

The potent vasodilator peptide, adrenomedullin, has been shown to be present in plasma, suggesting a physiological role in cardiovascular control. Here we investigated the hypotensive action of adrenomedullin in vivo, using the anaesthetised rat as the bioassay model, and adrenomedullin binding sites using ligand binding assays on rat blood vessel membranes. Rat alpha CGRP and both human and rat adrenomedullins induced dose-dependent, powerful and long-lasting hypotensive effects. At peptide doses used in this study (0.02-2 nmol/kg), the efficacy of both human and rat adrenomedullins was lower than that of rat alpha CGRP. The CGRP1-receptor antagonist, human CGRP(8-37) (200 nmol/kg) was able to completely inhibit the hypotensive effect of rat alpha CGRP (0.2 nmol/kg) but not that of rat adrenomedullin (2 nmol/kg), implying that the adrenomedullin action is independent of CGRP1-receptors. Ligand binding assays confirmed the presence of both CGRP and adrenomedullin binding sites in rat blood vessels. The 125I-rat adrenomedullin binding site has a Kd = 0.32 +/- 0.12 nM (n = 4) for rat adrenomedullin but has a Ki > 10(-6) M for rat alpha CGRP. Chemical cross-linking and SDS-PAGE analysis revealed theadrenomedullin binding protein to have a M(r) of 83000 with a minor band of M(r) = 99000. The results suggest that the hypotensive effect of adrenomedullin may be mediated via specific adrenomedullin binding sites, in vivo.

Pyroglutamyl-phenylalanyl-proline amide attenuates thyrotropin-releasing hormone-stimulated insulin secretion in perifused rat islets and insulin-secreting clonal beta-cell lines

TRH immunoreactivity has been detected in the pancreas of man and rat and localized to the islets of Langerhans. We studied the effect of synthetic TRH and the related tripeptide pyroglutamyl-phenylalanyl-proline amide (EFP) on isolated perifused rat islets and the glucose-responsive clonal cell lines HIT-T15 and RIN5AH. TRH at 10 nM potentiated [0.5 +/- 0.1 (control) vs. 0.8 +/- 0.1 (TRH) pmol/10(6) cells per 120 min; mean +/- SEM; n = 6; P < 0.001; n = 15], whereas EFP from 1 nM upwards suppressed glucose-stimulated insulin secretion [0.8 +/- 0.1 (control) vs. 0.5 +/- 0.1 (EFP) pmol/10(6) cells per 120 min; P < 0.001; n = 12) in the cell lines. Further, EFP reversed TRH-stimulated insulin release. Similar responses were observed in perifused isolated rat islets at the tested dose of 1 microM. Gel permeation chromatography of rat adult and neonatal whole pancreas, isolated islets, and HIT cell extracts demonstrated the elution of total TRH-like immunoreactivity (t-TRH-LI) in the same position as synthetic TRH. Cation exchange analysis of the t-TRH-LI from rat adult pancreas and HIT cell extracts showed that neutral TRH-like peptides corresponding to synthetic EFP were also present. Reverse-phase fast protein liquid chromatographic analysis of t-TRH-LI in the unbound fraction of these extracts subjected to anion exchange columns, also demonstrated peaks corresponding to synthetic EFP. We conclude that TRH potentiates, whereas EFP inhibits, glucose-stimulated insulin release in isolated perifused islets and the cell lines. In addition, EFP reversed the stimulatory effect of TRH. The presence of EFP-LI in rat adult and neonatal pancreas and HIT cell extracts suggests it may contribute in the modulation of pancreatic endocrine function.

Studies on the order and site specificity of GalNAc transfer to MUC1 tandem repeats by UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferase from milk or mammary carcinoma cells

A synthetic peptide [TAP25, (T1aAPPAHGVT9S10APDT14RPAPGS20)T1bAPPA5b] corresponding to one repeat (T1a-S20) and five overlapping amino acids (T1b-A5b) of the MUC1 core protein served as an acceptor substrate for in vitro glycosylation. TAP25 was glycosylated using the detergent-solubilized UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases from the breast carcinoma cell line T47D, the colon carcinoma cell line HT29 and from human premature skim milk. The glycosylated peptides were isolated by ultrafiltration, purified by reverse-phase HPLC and further analysed by liquid secondary ion mass spectrometry (LSIMS). Three different glycosylation species, mono-, di- and triglycosylated peptides were identified. Automated Edman sequencing and LSIMS of proteolytic fragments independently revealed the sites of GalNAc incorporation and confirmed that the threonine residues Thr9 and Thr1b are the preferred sites of glycosylation independent of the enzyme source, while Thr14 remained non-glycosylated even with the enzyme preparation from milk. In addition, evidence was obtained that at least 20% of the glycosylated peptides exhibited GalNAc incorporation at Ser20. On the basis of kinetic studies a preferred sequence of GalNAc addition to the three acceptor sites has been concluded (Thr9-->Thr1b-->Ser20). Although Thr14 within the PDTRP motif of the tandem repeats remained non-glycosylated, the introduction of GalNAc into adjacent positions significantly decreased the immunoreactivity of antibodies SM-3, HMFG-1 and HMFG-2 defining overlapping epitopes of this motif. It is assumed that glycosylation at Thr9, Thr1b and Ser20 distorts the peptide conformation of the binding epitope.

Surface plasmon resonance studies of the interaction between factor VII and tissue factor. Demonstration of defective tissue factor binding in a variant FVII molecule (FVII-R79Q)

The blood coagulation cascade is initiated when vessel injury allows factor VII (FVII) to form a complex with tissue factor (TF). Complete deficiency of FVII causes a lethal bleeding diathesis, but individuals with moderately reduced FVII levels are often asymptomatic. Some of these individuals have circulating partially functional FVII, as a result of point missense mutations in critical parts of the molecule. One such mutation has been reported at position 79 in the first epidermal growth factor-like (EGF) domain of FVII, where an arginine residue has been replaced by glutamine. There is controversy as to whether or not this mutation reduces the affinity of the FVII/TF interaction compared to wild-type FVII. To address this problem, we have expressed recombinant FVII-R79Q and subjected it to detailed biochemical analysis. One-stage FVII:C assays show the variant FVII to have reduced activity with respect to the wild type. Rates of autoactivation and activation by FXa to the two-chain molecule were identical for wild-type and variant FVII. The Vmax for FX activation was lower for the mutant as measured using an amidolytic assay for FX activity. In contrast, the Km for FX was lower for the variant than the wild-type molecule. Peptidyl substrate hydrolysis was virtually identical for both variant and normal FVIIa in the presence and absence of TF. The variant has reduced affinity for TF as measured by surface plasmon resonance. FVII-R79Q has an association rate constant (kassoc) one-fifth of that of normal FVII, but a similar kdiss, resulting in a decrease in the affinity of the enzyme for its cofactor.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylin tonally regulates arginine-stimulated insulin secretion in rats

To assess the effect of naturally-present amylin in the control of insulin release we infused a novel amylin antagonist, its 8-37 fragment, or amylin in anaesthetized rats for 60 min, and 30 min after the start arginine was infused for 14 min. Amylin8-37 decreased the blood glucose concentration by 18% whereas the plasma insulin concentration was 90% higher following arginine treatment. In contrast amylin infusion raised both glucose and insulin concentrations. These results suggest that while amylin added at high dose can induce peripheral insulin resistance, naturally present amylin tonally controls insulin secretion.

Synthesis and characterization of wild-type and variant gamma-carboxyglutamic acid-containing domains of factor VII

Synthetic peptides corresponding to portions of the wild-type and variant sequences of the human factor VII gamma-carboxyglutamic acid (Gla)-containing domain have been prepared by direct peptide synthesis using the Fmoc-based protection strategy. Peptides were purified by ion-exchange and reversed-phase chromatography and characterized as the correct products. A peptide comprising residues 1-49 (GP 1-49) inhibited the activation of factor X (FX) by soluble tissue factor (sTF) and recombinant activated factor VII (rFVIIa). In the absence of phospholipid, no inhibition by this peptide was observed. GP 1-49 did not inhibit the hydrolysis of a peptidyl substrate by rFVIIa in the presence of either sTF or relipidated TF apoprotein in the presence or absence of phospholipid. A similar peptide (residues 1-38, GP 1-38) that did not contain the aromatic stack region was also inhibitory. Two variant peptides, one identical to GP 1-49 but lacking the N-terminal alanine residue (GP 2-49) and one identical to GP 1-38 but with an arginine to alanine substitution at position 9 (GP 1-38 R9A), showed substantially reduced inhibitory activity. Kinetic analysis of the inhibition of Xa generation by GP 1-49 revealed a noncompetitive mode of inhibition, probably via a substrate-depletion mechanism. GP 1-49 does not inhibit by preventing FX binding to phospholipid surfaces. This indicates that the N-terminal residues of the FVII Gla domain are important for the structural integrity of the peptide, and implicates the Gla domain per se in a direct interaction with phospholipid-bound FX.

Structural requirements for the interaction between tissue factor and factor VII: characterization of chymotrypsin-derived tissue factor polypeptides

Tissue Factor (TF) is the cellular receptor for coagulation Factor VII/VIIa (FVII/VIIa). TF binds to FVIIa and promotes the rapid activation of the zymogen substrates Factors IX and X (FIX and FX) to the respective serine proteinases. In order to probe structure-function relationships in TF, we have subjected the truncated membrane-bound variant, TF 1-243, to proteolytic digestion in SDS-containing gels. Three major polypeptide fragments were generated by proteolysis of TF 1-243 with chymotrypsin, producing cleavages C-terminal to residues 34, 76 and 103. All three polypeptides, TF 35-243, 77-243 and 104-243, bound biotinylated human FVII in a highly specific ligand blot assay. High-performance electrophoretic chromatography was used to isolated chymotrypsin-derived fragments of TF. These purified fragments bound FVII in ligand blots, and two of the three polypeptides exhibited much reduced, but significant, procoagulant activity in a chromogenic assay for the generation of Factor Xa in the presence of FVIIa and Ca2+. The smallest chymotrypsin-derived TF polypeptide, TF 104-243, showed reduced binding of FVII in ligand blot analyses, inhibited the activity of the full-length molecule, but had no procoagulant activity. These data suggest that a part of the binding site for FVII is contained within the TF sequence 104-243. The sequence TF 1-34 either contains a part of the FVII-binding domain or its removal leads to dysfunctional folding, disrupting binding sites elsewhere in the molecule.

Influence of islet amyloid polypeptide and the 8-37 fragment of islet amyloid polypeptide on insulin release from perifused rat islets

IAPP, or amylin, is a 37-amino acid peptide that is co-secreted with insulin from the pancreatic beta-cells. We have determined the effects of IAPP and the antagonist 8-37 fragment of IAPP on the secretion of insulin from isolated rat islets studied in a perifusion system. Insulin secretion was stimulated by 8 mM glucose and 0.2 microM carbachol. IAPP at 10(-7) M reduced insulin release by 32% from 7.1 (95% Cl 5.8-8.6) to 4.8 (3.0-7.5) fmol.min-1 x islet-1 (P = 0.046, n = 7). IAPP at 1.5 x 10(-6) M reduced insulin release by 62% from 6.5 (3.4-12.3) to 2.5 (1.4-4.4) fmol.min-1 x islet-1 (P = 0.001, n = 6). IAPP at 10(-5) M decreased insulin release by 70% (P < 0.001, n = 6). When IAPP (8-37) at 10(-5) M was added to IAPP at 1.5 x 10(-6) M, there was only a 22% reduction of insulin release (P = 0.06, n = 6) compared with control chambers with no peptide added. This reduction was less (P = 0.002) than observed with IAPP (1.5 x 10(-6) M) alone. IAPP (8-37) at 4 x 10(-5) M in the absence of exogenously added IAPP increased insulin secretion by 48% (P = 0.01, n = 6), but IAPP (8-37) at 10(-5) M did not alter insulin secretion. These findings demonstrate that IAPP decreases insulin secretion from islet beta-cells, an effect that can be antagonized by the 8-37 fragment of IAPP.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterogeneity of circulating TSH-receptor antibodies in thyroid disease demonstrated directly by chromatography

The heterogeneity of circulating TSH-receptor antibodies (TRAb) has been demonstrated directly by affinity chromatography on the dye Remazol Yellow-GGL. The technique resolved these antibodies into discrete peaks within the general serum immunoglobulin background. Peaks were detected initially by a binding (radioreceptor) assay and then characterized by their ability to stimulate the uptake of iodine-125 into FRTL-5 cells. Thirteen subjects with high serum levels of TRAb were studied. The two hypothyroid patients each produced a single peak of TRAb activity with no ability to stimulate uptake of iodine-125 into cultured cells. The remaining 11 patients had Graves' disease; their sera produced a range of elution profiles after chromatography with TRAb activity resolved into as many as five peaks. Considerable differences were seen in the relative abilities of the resolved TRAb components to bind to receptors and to stimulate cellular uptake of iodine-125 both between and within individual samples. No two patients produced components which chromatographed in the same position on the gradients employed for elution from the dye.

IgG heavy-chain subclass restriction of thyrotropin-binding inhibitory immunoglobulins in Graves' disease

The IgG subclass composition of antibodies is an important determinant of their function. Thyrotropin receptor antibodies cause the hyperthyroidism of Graves' disease but their subclass distribution has been incompletely investigated. We have therefore purified IgG subclasses from Graves' sera by passage over affinity columns designed to deplete all but a single subclass, and then assayed those pure subclass fractions for their ability to displace radiolabelled thyrotropin from its solubilized receptor as a measure of thyrotropin receptor antibody activity. Sufficient activity was recovered for analysis in nine of 10 Graves' patients, in five of whom activity was almost completely (97-100%) restricted to the IgG1 subclass; in the remaining four patients the response was predominantly IgG1 and IgG4 with marked under-representation of the IgG2 subclass. This contrasts with the unrestricted subclass response, in the same fractions, for autoantibodies against thyroglobulin and microsomes. These results suggest that there may be a primary defect at the B-cell level in Graves' disease.

The role of thyroid hormone autoantibodies in serum transport

Eleven sera known to contain thyroid hormone autoantibodies were analysed by reverse-flow electrophoresis for the equilibrium distribution of thyroid hormones between these autoantibodies and the three normal binding proteins found in serum. The binding properties of the autoantibodies determined in vitro did not necessarily predict their contribution to transport in serum of T1 and T3. Some could both bind in vitro and transport in serum. Others were able to bind both hormones but transported only one. However, some autoantibodies could be specific, binding and transporting one hormone only. In some sera, the autoantibody was the dominant transport protein having drawn hormone from thyroxine-binding globulin which is normally the most important. The autoantibodies were not saturated even in euthyroid individuals, indicating that they bind hormone reversibly and are a part of an equilibrium system.

Selective autoimmune response to the chicken-specific structures of thyroglobulin in Obese strain chickens

The characteristics of thyroglobulin (Tg) autoantibodies in Obese strain (OS) chickens with thyroiditis have been defined and compared with those of polyclonal antibodies to chicken Tg produced by immunizing normal chickens and a rabbit, and with mouse monoclonal antibodies (MoAb) to chicken Tg. Chicken Tg autoantibodies (aAb), when tested against Tg from 24 species all showed specificity for chicken Tg which ranged from absolute to limited although in most instances cross-reactions with Tgs of other species were either absent or at a low level. Antibodies to chicken Tg produced by immunization showed a similar limited range of cross-reactions. Four of five chTg-MoAbs were specific for chicken Tg and the fifth was almost so. In competitive experiments, the polyclonal rabbit antibody could fully inhibit binding of all chicken Tg-aAb to chicken Tg but not vice versa. It was inferred that polyclonal rabbit Tg antiserum includes antibodies to all the epitopes seen by chicken Tg-aAb and many more besides. In similar experiments with four chicken Tg-MoAbs, the binding of one chicken Tg-aAb was unaffected, and three other patterns of inhibitions were defined. The binding to chicken Tg of a fifth chicken Tg-MoAb was enhanced rather than inhibited by chicken Tg-aAb. Some but not all chicken Tg-aAb preparations could differentiate between Tgs containing different amounts of thyroxine. We conclude that the autoantibodies to Tg in OS chickens are directed in the main against determinants unique to the species. Not all the species-specific determinants are involved in the autoimmune response but the number of epitopes involved is at least four. In these respects the immune response to Tg in OS chickens resembles that in autoimmune thyroid disease in humans. The conformation of chicken Tg may be affected by combination with antibody or by the content of thyroid hormone.

Thyrotrophin (TSH)-binding proteins in bacteria and their cross-reaction with autoantibodies against the human TSH receptor

A screen of a range of bacteria normally found in gut flora identified eight with the ability to bind TSH specifically. These included the previously reported Yersinia enterocolitica, Gram-positive, Gram-negative, pathogenic and commensal organisms. Eleven preparations of TSH-receptor autoantibodies strongly able to displace 125I-labelled TSH from the mammalian TSH receptor differed in their ability to displace the tracer from binding to bacterial extracts. None could displace the tracer from E. coli 06-1, four displaced 125I-labelled TSH from E. coli V21/1 and five displaced the tracer from Y. enterocolitica. Of those immunoglobulin preparations which did react with the bacterial protein, their apparent potency compared with that of TSH in displacing tracer from bacterial binders was an order of magnitude greater than with the mammalian receptor. This is consistent with the autoantibodies having a relatively better fit with the bacterial antigen than with the receptor when compared with TSH. The bacterial-binding activity and mammalian receptor-binding activities in each of two samples co-chromatographed on a Remazol yellow GGL-Sepharose affinity column strongly indicated that the same immunoglobulin species reacts with both antigens. These results are consistent with the proposal that a bacterial protein is the primary immunogen for the TSH-receptor antibodies in at least some patients with Graves' disease.

Thyroxine-binding globulin deficiency re-examined

Seven sera, previously categorised as completely deficient in thyroxine-binding globulin (TBG) by an immunoelectrophoretic technique, were re-examined with a sensitive ELISA method. Only one of the sera was confirmed completely deficient by ELISA. The remaining six contained 0.08-0.19 mg/l. The protein was immunologically identical with 'normal' TBG, could bind to thyroxine and had the correct mobility in reverse-flow electrophoresis. Complete TBG deficiency may therefore be rare.

Critical role of iodination for T cell recognition of thyroglobulin in experimental murine thyroid autoimmunity

We have used two clonotypically distinct thyroglobulin (Tg)-specific, I-Ak restricted monoclonal T cell populations to investigate the role of thyroid peroxidase-catalyzed iodination in Tg recognition by autoreactive T cells. The results showed that these T cells could recognize Tg only it it was sufficiently iodinated. Unlike normal mouse Tg, noniodinated mouse Tg was unable to induce significant thyroid lesions but could trigger the production of Tg autoantibodies. In these experiments, the importance of T cell recognition of iodination-related epitopes was emphasized by the inability of serum antibodies to distinguish Tg on the basis of iodine content, whether they were induced with normal or noniodinated Tg. Therefore, thyroid peroxidase-dependent modification of Tg would appear to be central to its recognition by autoreactive T cells and hence its capacity to induce autoimmune thyroid lesions.

Critical role of iodination for T cell recognition of thyroglobulin in experimental murine thyroid autoimmunity

We have used two clonotypically distinct thyroglobulin (Tg)-specific, I-Ak restricted monoclonal T cell populations to investigate the role of thyroid peroxidase-catalyzed iodination in Tg recognition by autoreactive T cells. The results showed that these T cells could recognize Tg only it it was sufficiently iodinated. Unlike normal mouse Tg, noniodinated mouse Tg was unable to induce significant thyroid lesions but could trigger the production of Tg autoantibodies. In these experiments, the importance of T cell recognition of iodination-related epitopes was emphasized by the inability of serum antibodies to distinguish Tg on the basis of iodine content, whether they were induced with normal or noniodinated Tg. Therefore, thyroid peroxidase-dependent modification of Tg would appear to be central to its recognition by autoreactive T cells and hence its capacity to induce autoimmune thyroid lesions.

Recognition of thyroglobulin autoantigenic epitopes by murine T and B cells

We have used a large panel of thyroglobulins (Tg) prepared from a wide range of mammalian species to study the Tg autoantigenic epitopes recognized by populations of monoclonal and polyclonal murine T and B cells. This approach showed the existence of at least six different epitopes; three recognized by T cells (in association with I-Ak on antigen-presenting cells) and three by B cells (monoclonal antibodies). The majority of serum and monoclonal autoantibodies were found to be highly specific for mouse Tg, with some cross-reactive binding to rat Tg. In contrast, T-cell lines/clones and hybridomas recognized cross-reactive epitopes on Tg that were highly conserved throughout most of the mammalian orders. Moreover, two hybrid clones, which showed similar patterns of cross-reactivity, differed in their responsiveness to tryptic digests of human Tg. Thus, autoreactive T and B cells recognize distinct areas of the Tg molecule.

Human autoantibodies to thyroglobulin are directed towards a restricted number of human specific epitopes

Significant binding of thyroglobulin (Tg) autoantibodies was restricted to primate Tg, although some sera showed weak cross-reactivities with other species at high concentrations. In contrast rabbit anti-human Tg bound to all other animals' Tg in addition to human and this was not due to crossreactions with the thyroxyl residues. Mouse antihuman Tg monoclonal antibodies (MoAb) showed at least three different patterns of cross-reactivities. Group 1 MoAb, like Tg autoantibodies, were primate specific; two out of six MoAb bound only human Tg. Group 2 MoAb also bound a few other animals' Tg in addition to human. Of the three MoAb in group 3, two reacted with most or all of eight animal Tg tested while the other bound to all eight. However the binding of thirteen out of the fourteen MoAb against human Tg including all of the primate Tg specific group 1 MoAb was not inhibited by any of the nine Tg autoantibodies. Reactions of MoAb with heat-treated human Tg varied. Examples of decreased, increased or no change in reactivity could be demonstrated. On this basis at least five or possibly six separate human-specific epitopes could be defined by group 1 MoAb. Monoclonal antibody 1D6 (group 2) was inhibited by six out of nine Tg autoantibodies at high concentrations. This MoAb, similarly to the eight Tg autosera tested, had reduced reactivity with heat treated Tg. These studies demonstrated that human Tg has immunogenic structures conserved in the Tg of many species. The protein also has, however, primate and human-specific antigenic sites but at least five or possibly six of these are not related to autoantibody binding.

Human monoclonal antibodies to thyroid antigens derived by hybridization of lymphocytes from a diabetic patient

Human monoclonal antibodies to human endocrine cells have been obtained following the generation of immunoglobulin-secreting interspecies lymphocyte hybridomas. Peripheral blood lymphocytes from an adult patient presenting with acute onset, Type I, diabetes mellitus were fused in vitro with mouse myeloma cells of the NS1 cell line. Initial selection of resulting hybridomas was made by their ability to proliferate in HAT medium. Those hybridomas secreting human immunoglobulins were identified by radioimmunoassay and, thereafter, cloned at frequent intervals to ensure continued antibody production. Human monoclonal antibodies selected in this manner are being employed to identify those epitopes which are common antigenic targets during initial stages of autoimmune-mediated diabetes mellitus and associated multiple endocrinopathies. Of these antibodies, one (HML 3.22) recognizes an epitope present on the human TSH receptor and a second (HML 3.21) identifies a component of thyroglobulin. The potential value of human monoclonal antibodies as probes for analyzing autoimmune-mediated endocrine diseases is discussed.

Hyperthyroxinemia due to the coexistence of two raised affinity thyroxine-binding proteins (albumin and prealbumin) in one family

The T4-binding proteins of a euthyroid subject with persistent hyperthyroxinemia (T4, greater than 20 micrograms/dl) were present in normal concentrations. Abnormal transport of both T4 and rT3 was demonstrated by reverse flow paper electrophoresis; excess T4 was bound to albumin and prealbumin, while increased binding of rT3 was confined to prealbumin. The three T4-binding proteins in the serum of the subject were isolated by affinity chromatography and characterized. Equilibrium dialysis experiments demonstrated a 20-fold increase in affinity of the albumin for T4 (Ka, 5.1 X 10(6) M-1) and a 4-fold increase in affinity of prealbumin for T4 (Ka, 3.0 X 10(8) M-1); T4-binding globulin affinity was normal. Nine other members of the family were also studied. Two sisters of the propositus have both the abnormal albumin and the variant prealbumin, while a brother has normal T4-binding proteins. The mother has the abnormal albumin alone. The father, his sister, and one of his three brothers have the variant prealbumin only. Despite the presence of the variant prealbumin in some of the paternal relatives of the propositus, their total iodothyronine concentrations were within the normal ranges; the condition may, therefore, often go undetected. The characteristics of the albumin found in the affected members of this kindred are those we have defined for familial dysalbuminemic hyperthyroxinemia type I, which is inherited as an autosomal dominant trait. The pattern of inheritance of the variant prealbumin is also consistent with a dominant mode with strong penetrance. The presence of two separately inherited abnormal T4 transport proteins in the same family suggests that both conditions may be more common than has been thought.

Novel separation method for serum immunoglobulins. Application to thyroid related antibodies

A dye-based affinity chromatographic system using Remazol yellow GGL-Sepharose is described for the fractionation of serum immunoglobulins. Immunoglobulins are sequentially eluted from the gel columns using gradients of pH and salt with greater than 88% recovery. Specific immunoglobulin activities were identified as discrete peaks and antibodies raised against the same antigen were separated. Biological properties of antibodies were retained following chromatography. The method is applicable to both human and animal immunoglobulins.

Structural differences around hormonogenic sites on thyroglobulins from different species detected by monoclonal antibodies

Thyroxine remains attached to its synthetic site in thyroglobulin until it is released by proteolysis. Strong homology in the primary sequence surrounding thyroxine-forming residues in thyroglobulins from various species suggests a unique three-dimensional structure at hormonogenic sites. To examine this, two thyroxine-binding mouse anti-(chicken thyroglobulin) monoclonal antibodies, 1A10 and 5F6, were used as probes for this region in an enzyme-linked immunosorbent inhibition assay. The thyroxine content of thyroglobulins had a marked positive influence on the monoclonal antibody binding: when the thyroxine content of human thyroglobulin rose by 6.6-fold, cross-reactivities rose 25-fold for the 1A10 monoclonal antibody and 17.6-fold for the 5F6 monoclonal antibody. However, interspecies comparison of thyroglobulin preparations with similar thyroxine content showed lower than expected cross-reactivities for human, pig and sheep thyroglobulins when compared with chicken thyroglobulin. Only when the thyroxine content of heterologous thyroglobulin preparations was two or three times higher did the cross-reactivities equal or surpass that of chicken thyroglobulin. It is concluded that in thyroglobulin there are structural differences in the different animal species near the thyroxine-forming sites bound by these monoclonal antibodies. The known primary sequence similarity does not seem to result, therefore, in identical three-dimensional structures about this site. These differences may reflect species-specific variations in distant regions brought close as a result of chain folding to form the hormonogenic site, such as those around the donor diiodotyrosine residue or in polysaccharide structures. These monoclonal antibodies provide information about the structure of thyroglobulin, which cannot be obtained from knowledge of the amino acid sequence alone.

Iodothyronine kinetics in the rabbit: an experimental model

Turnover studies of thyroxine (T4), 3,5,3'-tri-iodothyronine (T3) and 3,3',5'-tri-iodothyronine (rT3) have been performed in the rabbit. A novel modification of a conventional radioimmunoassay has been used to measure specific 125I-labelled iodothyronines in small volumes of plasma in the presence of other 125I-labelled metabolites. Kinetic analysis of plasma disappearance of tracer was performed by a new theoretical approach. For T4 the mean (+/- S.D.) plasma concentration, clearance and production rates were 34 +/- 12 nmol/l, 109 +/- 19 ml/kg per day and 3.7 +/- 1.4 nmol/kg per day respectively (n = 9). For T3 the corresponding values were 2.04 +/- 0.42 nmol/l, 1.52 +/- 0.29 litres/kg per day and 3.07 +/- 0.76 nmol/kg per day (n = 8), and for rT3 0.12 +/- 0.04 nmol/l, 5.7 +/- 1.7 litres/kg per day and 0.69 +/- 0.23 nmol/kg per day (n = 8). The combination of these two new methodologies affords a simple and convenient means of studying iodothyronine metabolism under normal and abnormal conditions. The techniques employed may be generally applied to turnover studies of other compounds of physiological interest which can be measured by radioimmunoassay.

Structural basis for the reaction of 3,5,3'-tri-iodothyronine-specific antibodies with thyroxine-containing thyroglobulin

A series of human autoantibodies against thyroglobulin (Tg) which exhibit different specificities for iodothyronines were studied. The ability of a thyroxine (T4)-containing peptide (T4P) isolated from human thyroglobulin (Tg) to displace [125I]T3 from human T3-specific autoantisera was 11-50 times greater than that of T4 alone. These antisera therefore strongly recognize amino acids adjacent to T4 in the Tg structure. This was confirmed when a Tg preparation (Tg[0.05]) containing an average of only 0.05 of a T4 residue/molecule and much less T3 had good cross-reactivities with these antisera. Cross-reactivities of other Tg preparations with different T4 contents increased only slowly with increase of T4 content up to a mean of 6.6 residues/molecule and were not proportional to T3 content. In contrast, cross-reactivities with a human T4-specific autoantiserum were strongly dependent on T4 content. Tg[0.05] was 500 times less reactive than T4P and 615 times less than T4. Cross-reactivities rose rapidly as the T4 content of Tg preparations increased from a mean of 0.05 to approx. 1-2 residues/molecule. Thyroxine is therefore a dominant feature of the antigenic site for this antiserum. There was little further increase in cross-reactivities for those Tg preparations containing up to an average of 6.6 residues T4 per molecule, confirming previous conclusions that all T4-containing sites are not immunologically identical and that autoantibodies exhibit a preference for particular sites on Tg. Similar conclusions were reached for a non-specific iodothyronine-binding antiserum. These results indicate that iodothyronine specificity in human autoantisera is not necessarily determined by the iodothyronine present in the immunogenic area, but by the precise site selected by the immune response. T4- or non-specific antibodies have thyroxine as a dominant feature of the antigenic site. T3- specific antibodies have the thyroxine residue as a peripheral feature of the binding site, and it is not necessary to postulate that T3 was part of the immunogen or is required in the epitope. These antisera may have value in mapping the hormonogenic regions in Tg from human and other species.

A new and distinctive albumin variant with increased affinities for both triiodothyronines and causing hyperthyroxinaemia

A new variant albumin with increased affinities for iodothyronines has been identified. A euthyroid woman had raised total serum concentrations of T4 (155 nmol/l), T3 (3.0 nmol/l) and rT3 (700 pmol/l) but normal levels of all three iodothyronine-binding proteins. The affinity constant for T3 binding to the albumin was substantially raised (2.2 x 10(5) l/mole; normal immeasurable), that for rT3 (1.4 x 10(6) l/mole) was increased three-fold. This new albumin binds the analogues of T4 and T3 used in Amerlex free-hormone assays more strongly than does normal albumin, resulting in erroneously elevated estimates of serum free-T4 and free-T3 by this method. The new variant albumin was indistinguishable from normal albumin in molecular size and by electrophoretic and immunological techniques. Three distinct variant albumins exhibiting differential binding of iodothyronines have now been defined: Type I causes a raised total serum T4 only; Type II produces increased total T4 and rT3; Type III (the present example) results in elevated total T4, rT3 and T3. All three variants have normal free-T4 by dialysis but spuriously raised results by the Amerlex free-T4 method. Type III also causes an artificial increase in Amerlex free-T3. The pattern of thyroid function test results in Type III can readily be confused with both hyperthyroidism and with partial peripheral resistance to thyroid hormones.

Familial abnormalities of thyroxine binding proteins: some problems of recognition and interpretation

A three generation family study was carried out after inappropriate treatment with radioactive iodine of a 50 year old woman with a raised serum total thyroxine concentration and free thyroxine index. Subsequent investigations showed that she and five members of her family had raised thyroxine binding globulin concentrations. Free thyroxine and free triiodothyronine concentrations were normal. Problems encountered in the recognition of this thyroxine binding protein disorder are discussed. Clinicians and clinical biochemists should be aware of these pitfalls and thus avoid further incorrect treatment on the basis of biochemical findings, even though free hormone estimations are now becoming readily available.

Inhibition of human alkaline phosphatase isoenzymes by the affinity reagent reactive yellow 13

The dye Reactive Yellow 13, an affinity reagent for intestinal alkaline phosphatase, inhibits intestinal and other human alkaline phosphatases in solution. The inhibition depends markedly on the presence of a phosphate acceptor such as diethanolamine. The dye is an uncompetitive inhibitor with respect to both substrate and phosphate acceptor in the case of non-intestinal phosphatases. However, in the case of intestinal alkaline phosphatase, the inhibition is noncompetitive with respect to the substrate and competitive with respect to the phosphate acceptor. These observations account for the specific binding of intestinal phosphatase when the dye is used as a ligand in affinity chromatography.

A prealbumin variant with an increased affinity for T4 and reverse-T3

A euthyroid adult female (LC) was found to have persistently raised concentrations of total T4 (159 nmol/l) and rT3 (500 pmol/l) in her serum in association with a normal T3 (2.1 nmol/l). Serum concentrations of all three T4-binding proteins were within normal limits. A variant prealbumin with an increased affinity for T4 was found to be responsible for the raised serum level of T4. Unlike normal prealbumin, the variant also bound appreciable amounts of rT3. The affinity constant for T4 binding to prealbumin LC was 5.5 X 10(8) l/mole which is sevenfold higher than that obtained for normal prealbumin (8.5 X 10(7) l/mole). The affinity constant for the binding of rT3 to prealbumin LC was 2.0 X 10(6) l/mole while that for the normal protein was unmeasurable by our method. The T4-binding capacity of prealbumin LC in serum was within the normal range indicating that there is no new additional T4-binding site on the protein. Prealbumin LC has the same molecular size as the normal protein, hence it is likely that the tetrameric structure has been preserved. The electrophoretic mobility of prealbumin LC was normal indicating no alteration in charge. It is postulated that the increased affinity for T4 (and presumably for rT3) results from a hydrophobic amino-acid substitution in the prealbumin monomer.

Subfractionation of human immunoglobulin G with dye-Sepharose adsorbents

Seventeen reactive dyes were separately covalently attached to Sepharose-4B and examined for their ability to subfractionate the immunoglobulin G found in human serum. Each dye-Sepharose-4B adsorbent appeared to bind a characteristic proportion of the protein when tested with "pure" preparations. It is suggested that this is due to stereospecific interactions between each dye and various interaction sites on the immunoglobulin G molecules. These sites of interaction are not those which define the four major subclasses of the H-chain nor those which distinguish the kappa and lambda light chains. The adsorption may be influenced by the presence of other proteins when serum samples are tested due to competition for binding to the immobilised ligands but sequential use of the adsorbents can progressively enrich a particular immunological activity in human serum. This method offers a convenient and gentle way to subfractionate immunoglobulin G especially when the antigen is not known or unavailable for conventional affinity chromatography.

Binding of amiodarone by serum proteins and the effects of drugs, hormones and other interacting ligands

Amiodarone is chiefly bound to albumin (62.1%) and much of the remainder (33.5%) is carried on a high molecular weight protein, probably beta-lipoprotein. Analysis of data for amiodarone binding to albumin revealed a high affinity primary binding site (Ka 5.6 X 10(6) litre mol-1) with about four secondary sites (average Ka 1.9 X 10(5) litre mol-1). Studies of the binding of amiodarone in serum revealed one type of binding site only with an affinity constant (Ka 4.2 X 10(6) litre mol-1) similar to that of the primary site on albumin. The secondary albumin binding sites do not seem therefore to be utilized in whole serum and the affinity of the lipoprotein must be similar to that of the primary amiodarone binding site on albumin. The effects of a wide range of compounds on albumin binding of amiodarone were examined by equilibrium dialysis. Quinidine, amitriptyline, cephazolin and palmitate decreased albumin-bound [125I]amiodarone. Neither warfarin nor digoxin affected the binding of amiodarone by albumin, thus of the three drugs known to be potentiated by concomitant amiodarone administration, only potentiation of quinidine could be explained by displacement from serum albumin. Rifampicin, frusemide, phenytoin, (-)-adrenaline, bromocresol green, (-)-noradrenaline and bromocresol purple were found to increase binding of [125I]amiodarone by albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of thyroxine residues in human thyroglobulin. Two-site binding studies

Human thyroglobulin (Tg) could be adsorbed through one of its thyroxine (T4) residues by either of two T4-binding antibodies which had been covalently attached to Sepharose- CL4B . The antibodies used were (i) a purified human autoantibody specific for a T4-containing epitope in human Tg, or (ii) a rabbit antibody raised against T4 conjugated to bovine albumin side chains. Tg adsorbed by either immobilized antibody could then itself adsorb either type of antibody free in solution on to a further T4 residue. At least two T4 residues in human Tg are therefore sufficiently exposed to interact with T4-binding antibodies. Furthermore, these T4 residues are sufficiently far apart to allow the binding of two immunoglobulin molecules simultaneously. Previous observations of a marked preference by human autoantibodies for one of the T4-containing epitopes in Tg therefore reflect a higher binding energy with that epitope rather than an inability to interact with others. The T4-containing epitope which preferentially reacts with human Tg autoantibodies must therefore have a distinctive topography.

Free thyroid hormone concentrations in subjects with various abnormalities of binding proteins: experience with amerlex free-T4 and free-T3 assays

Free thyroid hormone concentrations measured by Amerlex assays were studied in subjects with inherited disorders of thyroxine-binding globulin (TBG) synthesis, variant albumins with a high avidity for T4, and iodothyronine-binding autoantibodies. Free T4 (fT4) and free T3 (fT3) levels were normal in euthyroid subjects with TBG deficiency and excess. Free T3 concentration was in the low normal range in subjects having a variant albumin but fT4 (Amerlex) was erroneously elevated because of the enhanced affinity of the 125I-T4 analogue employed in the assay for the abnormal albumin. The 125I-T3 analogue used in the fT3 assay does not bind more strongly to this variant albumin than to normal albumin. Amerlex assays for fT4 and fT3 in patients with iodothyronine-binding autoantibodies to thyroglobulin give variable results according to the specificity of the autoantibodies: non-specific antibodies cause extraordinarily high values even in hypothyroid patients; fT3 measurements may be appropriate in patients with T4-specific antibodies and even in some with T3-specific antibodies. The presence of such antibodies should be suspected if the results of Amerlex assays for fT4 and fT3 are discordant or are inconsistent with the clinical picture or TSH levels.

Increased serum concentration of T4-binding globulin in patients with hypogammaglobulinaemia

Patients with hypogammaglobulinaemia have been regularly found to have abnormal conventional thyroid function test results. The abnormality is due to an increased plasma concentration of T4-binding globulin (TBG). As the prevalence of autoimmune thyroid disease is probably increased in hypogammaglobulinaemia this further abnormality in the plasma proteins may lead to diagnostic confusion. Administration of gammaglobulin by infusion causes a rapid but transient fall in plasma concentrations of TBG and T4 which is probably due to a temporary redistribution of the plasma proteins.

Studies on the antigenicity of human thyroglobulin

Human iodothyronine-binding auto-antisera were used to define a thyroxyl containing antigenic site on thyroglobulin. The peptide sequences flanking the thyroxyl residue are important antigenic determinants of this region and only one such thyroxyl seems to be exposed on the thyroglobulin molecule. Apparent specificity for binding of free thyroxine or triiodothyronine by these auto-antibodies does not necessarily imply the presence of either one or the other in the immunogen.

Hyperthyroxinaemia: abnormal binding of T4 by an inherited albumin variant

Two euthyroid subjects with high total concentrations of T4 in their sera have been studied (J.D.: T4, 170; T3, 1.90; rT3, 0.54 nmol/l. E.T.: T4, 185; T3, 1.63; rT3, 0.37 nmol/l). Concentrations of all three T4-binding proteins were within normal limits in both cases. However, on reverse-flow electrophoresis an abnormally large amount of thyroxine was found to travel with albumin. The three T4-binding proteins in the sera of both patients were separated from each other by a novel affinity chromatographic method using dye-Sepharose conjugates. Affinity constants for T4 binding to TBG and to prealbumin from both patients were normal. The albumin preparations were further purified and shown by physical and immunochemical techniques to be uncontaminated by other proteins. Scatchard plots of the binding of T4 to each of these pure albumins revealed two components, one having a normal affinity constant (J.D., 1.8 x 10(5) lmol-1 and E.T., 2.3 x 10(5) lmol-1), the other having a raised affinity constant (J.D., 5.4 x 10(6) lmol-1 and E.T., 5.8 x 10(6) lmol-1). Extrapolation of the plots showed that the high affinity components comprised 66% (J.D.) and 54% (E.T.) of the total purified albumin. The raised affinity and high concentrations of the variants thus account for the raised total T4 concentrations in the patients. The presumed amino acid substitution in the albumins may be different in the two patients since the affinities for rT3 differ. Some methods for the estimation of free T4 levels give misleading results in the presence of these albumin variants. In the course of two episodes of illness, patient J.D. manifested large falls in serum T4 levels which could only be accounted for by reduced carriage of T4 by the abnormal and conventional binding proteins. Many cases reported in the literature as partial peripheral resistance to thyroid hormone may be examples of similar albumin variants.

Restricted antigenicity of thyroxyls in human thyroglobulin

Interactions between two human iodothyronine-binding autoantisera and three preparations of human thyroglobulin (Tg) were not proportional to the latter's thyroxyl residue content. Probably only one of the several thyroxyl-containing sites in Tg reacted with the immunoglobulins from both antisera. In the case of one of the antisera, which was thyroxine (T4)-specific, the thyroxyl residue was the immunodominant feature of the antigenic site. The other antiserum, which had a specificity for 3,5,3'-tri-iodothyronine (T3), recognized different determinants around the same thyroxyl residue, but this residue was not itself an important element of the binding site. Thus, despite the specificity for T3 free in solution, the presence of T4 in the complete antigenic site was tolerated, since other structures supplied the bulk of the binding energy. 'Specificity' of this antiserum for T3 in solution is therefore coincidental and need not be ascribed to the presence of T3 in the original immunogen. Some results obtained in these studies may be interpreted as supporting the possibility that a modified Tg was the immunogen for the generation of these naturally occurring human antisera.

Autoantibodies to thyroglobulin cross reacting with iodothyronines

Serum thyroxine was consistently unmeasurable by radioimmunoassay in an elderly patient with myxoedema after successful treatment with oral thyroxine. Abnormal binding of thyroxine was suspected and shown to be due to the presence in serum of antibodies of the IgG variety. The characteristics of these antibodies with respect to their binding of thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and human thyroglobulin (Tg) were systematically studied. Three preparations of Tg, and t4, T3 and rT3 were examined for their ability to compete with 125I-Tg, 125I-T4, 125I-T3 and 125I-rT3 for binding to the antibodies. For each tracer used the order of competitive efficiency was Tg greater than T4 greater than T3 greater than rT3. This provides for the first time direct evidence that iodothyronine reacting antibodies occurring in man are generated against Tg. All three iodothyronines were able to inhibit tracer binding of labelled iodothyronines completely, the order of effectiveness being T4 greater than T3 greater than rT3, suggesting antibodies with one type of binding site and that these were probably raised against a Tg sequence incorporating T4, although there was some evidence for the existence of a minor subpopulation of antibodies with higher specificity for T3. Complete displacement of labelled Tg by cold iodothyronines, however, was not possible. The experimental evidence suggests two classes of Tg antibodies, 70% of which were directed towards the T4 containing region, and 30% directed against other part(s) of the Tg molecule. Despite the presence of such Tg antibodies conventional haemagglutination tests of the patient's serum for Tg antibodies were negative.

A comparative study of the binding of Graves' immunoglobulins by the patients own and other thyroid membranes

Thyroid membrane preparations from six patients with active Graves' disease were tested in an assay which detects the thyroid interactive immunoglobulins of Graves' disease by their inhibition of binding of [125I]-thyroid stimulating hormone (TSH). With all preparations inhibition of binding of 125I-TSH by excess TSH could be demonstrated (specific binding). The patients' own immunoglobulins were assayed against their own thyroid membranes and against each other's under exactly comparable conditions. Inhibition of binding by IgGs from the patients varied between membrane preparations: with one preparation 5/6 IgGs were inhibitory but with another none were effective. Of the six patients, their own IgG inhibited binding of 125I-TSH to their own thyroid membrane preparation in only four instances, and when interaction did occur this did not reliably predict that the membrane preparation would interact with IgGs from other patients with Graves' disease. The selection of a membrane preparation for this assay cannot be made solely on ability to specifically bind TSH but the measure of the specific interaction with a Graves' IgG of proven potency must also be considered. Moreover, because of the variability between different membrane preparations, sequential clinical studies on individual patients, of the changes in concentration of Graves' IgG, must be performed using the same selected thyroid membrane preparation. We infer from these observations that the membrane structure in the vicinity of the TSH binding site is an important determinant of the interaction of Graves' IgGs with the TSH receptor, and that the configuration of this area is variable between individuals of the same species. The distinction between 'human-specific' and 'non-species-specific' thyroid stimulating antibodies is therefore probably not valid. The observation that the patient's own IgG was not often the most potent IgG inhibitor of binding of TSH also suggests that the Graves' IgG binding site is not identical or restricted to the TSH binding site; alternative explanations are discussed.

Changes in thyroid hormones in obese women following jejuno-ileal bypass surgery

The serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3'5'-triiodothyronine (reverse T3) in 10 massively obese women were studied before and at intervals for one year after jejuno-ileal bypass operation. A significant rise in T3 (P less than 0.01) over the immediately preoperative value, a significant fall in rT3 (P less than 0.01) but no significant change in T4 was found during the post-recovery follow-up period. It is concluded that maintaining a relatively high T3 level following jejuno-ileal bypass surgery may contribute to the substantial weight reduction achieved by patients after this operation.

Different measurements of thyroid function in hypothyroid infants diagnosed by screening

Different measurements of thyroid function including I123 thyroid scanning were performed in 16 hypothyroid infants diagnosed by a TSH screening project. These results were then related to the clinical presentation and the bone age. Although T3 levels were preferentially maintained, it was the best single measure of the severity of hypothyroidism. Thyroglobulin may have a role in the diagnosis of athyrosis. Scanning showed that athyrosis was uncommon (12.5%) but an ectopic gland occurred in 40%, and accounts for many of the less severly affected cases found on screening. Some of these measurements may have prognostic significance.

Interrelation of the pituitary-thyroid system at birth in man

Samples of cord blood derived from 105 normal babies after uncomplicated deliveries were assayed for thyroxine (T4), tri-iodothyronine (T3), reverse tri-iodothyronine (rT3), thyroxine-binding globulin (TBG) and thyrotrophin (TSH). The values for T3, rT3 and TSH were log-normally distributed (geometric means 0.62 nmol/l, 3.28 nmol/l and 10.9 mu./l respectively) and those for T4 and TBG were normally distributed (means 126 nmol/l and 13.7 mg/l), The data were systematically analysed and no evidence was obtained to suggest that the concentration of TSH, which varied widely, was regulated by any of the thyroid hormones alone or in combination. There was a direct relation between the concentrations of T4 and T3 in the cord blood at birth but not between either of these and rT3. There is thus no evidence of a functional interdependence of the hypothalamic-pituitary-thyroid system in man at birth.

Reverse triiodothyronine, thyroid hormone, and thyrotrophin concentrations in placental cord blood

Reverse triiodothyronine (rT3), triiodothyronine (T3), thyroxine (T4), thyroxine binding globulin (TBG), and thyrotrophin (TSH) were measured in sera from placental cord blood in an unselected series of 272 deliveries. In this series the concentrations of rT3 (mean 3.33 nmol/l, 95% confidence limits 1.6--7.0 nmol/l), were log normally distributed and did not overlap the adult normal range (0.11--0.44 nmol/l). There were no correlations between the cord blood concentrations of rT3, T3, T4, and TSH. The cord serum rT3 concentration was not influenced by maturity, birth-weight, or neonatal risk factors, whereas these factors did affect the concentrations of T3, T4, AND TBG. There is no arteriovenous rT3 concentration difference across the placenta, therefore the cord rT3 reflects the systemic rT3 concentration in the baby at birth. As rT3 in the neonate largely, if not entirely, derives from thyroxine from the fetal thyroid, measurement of the cord rT3 concentration may be a good immediate screening test for neonatal hypothyroidism.

Radioaffinity assay, a new approach to binding assays applied to the measurement of serum albumin

The affinity adsorbent Cibacron Blue F3GA-Sepharose 4-B has been used to develop a binding assay for human serum albumin. The method is simple, accurate and precise. It agrees well with the 'rocket' immunoelectrophoretic method and is proposed as an alternative technique for the re-estimation of albumin levels in the low range (less than 30 g/l) where the bromocresol green dye-binding method overestimates. Bilirubin, several drugs, gammaglobulin, haemoglobin and heparin do not interfere with the estimations.