[Torsade de pointes in myxedema. Report of a case and review of the literature]

A 57 years old female suffered from recurrent attacks of ventricular tachycardia including one episode of torsade de pointes, she had hypothyroidism with myxedema secondary to Sheehan Syndrome, following thyroid replacement therapy the tachyarrhythmia did not relapse and there was no need to give specific antiarrhythmic therapy.

Treatment of hyperthyroidism with a combination of methimazole and cholestyramine

The entero-hepatic circulation of thyroid hormones is increased in thyrotoxic states. Based on this observation, the use of ionic exchange resins to bind thyroid hormones in the intestine has been tried. The present study evaluates the effectiveness of cholestyramine as an adjunctive therapy in the management of hyperthyroid Graves' disease. Thirty patients with newly diagnosed hyperthyroid Graves' disease were randomly assigned to one of the following treatment groups: methimazole, propranolol and cholestyramine for 4 weeks (group I); methimazole and propranolol for 4 weeks (group II); methimazole, propranolol, and cholestyramine for 2 weeks, followed by 2 weeks of methimazole and propranolol (group III). At the end of the study, total and free T4 as well as T3 levels had decreased more in group I compared with group II: 61%, 78%, 68% in group I compared with 43%, 65%, 50% in group II (P = 0.037 for T4, P = 0.038 for free T4, P = 0.012 for T3). Group III behaved like group I while patients were receiving cholestyramine, but once the drug was discontinued, the rate of decline of thyroid hormones slowed down. We conclude that cholestyramine represents an effective and well-tolerated adjunctive therapy in patients with hyperthyroid Graves' disease, and it produces a more rapid and complete decline in thyroid hormone levels in these patients.

Multifactorial control of the elimination kinetics of unbound (free) growth hormone (GH) in the human: regulation by age, adiposity, renal function, and steady state concentrations of GH in plasma

To evaluate the principal determinants of the MCR and plasma t1/2 of unbound (free) GH in man, we performed steady state infusions of 3 doses of recombinant human GH during pharmacological suppression (iv octreotide) of endogenous GH secretion in 24 healthy adults and 12 patients (6 adults and 6 children) with chronic renal failure (CRF). Free plasma GH was calculated from total plasma GH (measured by immunoradiometric assay) and GH-binding protein activity (radioligand assay). The MCR of free GH was determined from free plasma GH and the rate of recombinant human GH infusion. The t1/2 of free plasma GH, and the concentration and the in vivo dissociation constant (Kd) of GH-binding protein (GHBP) were estimated by dynamic modeling of the postinfusion total plasma GH concentration decay curves. The MCR of free GH decreased and the plasma GH t1/2 increased significantly with increasing plasma GH concentrations. The MCR of free GH over its physiological concentration range was positively correlated with the body mass index as a measure of relative obesity and negatively related to age, but only at supraphysiological GH concentrations. In the adult patients with CRF, the MCR of free GH was decreased at each infusion rate by 25-38%, and the t1/2 was increased by 80-170%. Children with CRF showed a significantly lower MCR and higher t1/2 of plasma free GH than adult patients. Modeling and direct measurements of the off-rate of GH from its high affinity GHBP indicated normal dissociation rate constants but decreased molar concentrations of the GHBP in uremic plasma. We conclude that the rate of elimination of free GH from plasma in man is controlled by 1) plasma total free GH concentrations, 2) relative obesity, and 3) renal function within the physiological GH concentration range, whereas 4) age is a negative predictor of MCR only at supraphysiological GH concentrations.

Growth hormone-binding protein in human lymph

The high affinity GH-binding protein (GHBP) is a soluble circulating ectodomain of the GH receptor (GHR). In humans, it is thought to be released from the plasma membrane-bound GHR by proteolysis at or near the transmembrane domain. GHBP modulates GH action by 1) intravascular complex formation, and 2) competing with the GHR for ligand in tissues (interstitial complex formation). Little is known about the tissue source(s) of GHBP, the local regulation of GHBP generation, or its concentration in the interstitium. To begin addressing these questions, we studied GHBP levels in peripheral lymph, whose composition approximates that of interstitial fluid. Lymph was collected in 13 healthy adult men from cannulated lymphatic vessels in the calf. Venous and arterial blood samples were collected from the femoral vein and radial artery contemporaneously with lymph collection. Potential GHBP production by endothelial or blood cells was assessed by examining conditioned medium from in vitro cell cultures. GHBP activity was measured by standardized GH binding/column chromatography assay. GHBP was consistently and significantly lower in lymph (mean +/- SD, 4.6 +/- 1.2% GH bound/200 microL) than in venous (14.1 +/- 3.0%) or arterial (14.9 +/- 3.6%) plasma. Conditioned medium from endothelial or blood cell cultures did not contain detectable GHBP. We conclude that the level of GHBP in peripheral lymph is substantially lower than that in the peripheral circulation, and that components of the vasculature are not important sources of GHBP. These findings suggests that 1) the main tissue sources of GHBP in man are the central organs (especially liver); and 2) transcapillary diffusion of GHBP into the interstitial space is restricted.

A growth hormone/prolactin-binding protein in human milk

In the course of studies of the distribution of GH-binding proteins (GHBP) in biological fluids, we identified a human (h) GH/hPRL-binding component in human milk. To characterize its nature, 16 human milk samples were analyzed by molecular exclusion chromatography after incubation with monomeric [125I]hGH. All samples showed a peak indicative of a hGH-containing complex with a mol wt of 52 kilodaltons (kDa)--considerably smaller than the high affinity GH-binding protein complex in plasma (80-85 kDa). Binding of [125I]hGH was inhibited in a dose-dependent fashion by unlabeled hGH and to a lesser extent by hPRL, but not by oGH. Scatchard analysis yielded a Ka of 2.1 x 10(8) M-1 and a maximum binding capacity of 5.1 micrograms/L for hGH, and a Ka of 0.5 x 10(8) M-1 for hPRL. The derived molecular size of the milk GH/PRL-binding protein (BP) is 30 kDa, assuming 1:1 binding stoichiometry. The milk BP was not immunoprecipitable with any of 4 monoclonal antibodies directed against the hGH receptor or with a polyclonal antiserum directed against the hPRL receptor. The milk BP bound to hGH affinity columns, but unlike the GHBP in human plasma, did not bind to wheat germ lectin columns, suggesting different or no glycosylation. We conclude that human milk contains a high affinity GH/PRLBP that differs from the serum GHBP in its ligand specificity (binding both hGH and hPRL), molecular size, immunological, and glycosylation characteristics. Based on its immunochemical and ligand-binding characteristics, it does not appear to be a truncated GH receptor such as the plasma GHBP. Its lack of immunoreactivity with the one available antiserum also does not support its identity with a truncated PRL receptor. However, it cannot be excluded that the milk BP may represent a proteolytically or otherwise altered truncated form of the PRL receptor (or, less likely, the GH receptor) that maintains some binding activity, but has its immunological epitope(s) disabled. The precise nature and function of this protein remain to be defined.

Assay systems for the growth hormone-binding protein

The first method used for detection of growth hormone-binding protein (GHBP) in biological fluids was based on the incubation of the sample with radiolabeled GH followed by separation of bound and free GH by gel exclusion chromatography. Recently, other methods have been developed which are faster and easier to use. These methods include variants of the original binding/column assay (e.g., separation of bound and free GH is obtained by immunoprecipitation, charcoal adsorption, ion exchange chromatography, or HPLC), and a ligand-mediated immunofunctional assay (LIFA), in which a monoclonal antibody is used to capture the GHBP on a microtiter plate; all binding sites are saturated with GH and an anti-GH antibody is used to detect the amount of GH (endogenous and exogenous) bound to the GHBP. To permit comparison of results obtained by different methods we have cross-validated the LIFA with two different binding assays: (i) the original long column assay (column assay), and (ii) an assay based on immunoprecipitation (RIPA) of the GH/GHBP complex with an anti-GHBP antibody.

The stoichiometry of growth hormone-binding protein complexes in human plasma: comparison with cell surface receptors

The recent demonstration of two independent receptor-binding sites (sites 1 and 2) on human GH (hGH) raises the question of the stoichiometry of circulating GH-binding protein (GH-BP) complexes in human plasma (i.e. is it one hGH per one GHBP or one hGH per two GHBPs?). Previous studies have all assumed 1:1 binding in plasma, based on gel exclusion chromatography and cross-linking data. To address this issue, human plasma was incubated with radioiodinated hGH as well as hGH mutants that had either a Tyr103-->Ala or a Gly120-->Arg substitution in the region of binding site 2. The former mutant retains normal site 2 binding activity even when iodinated; the latter has binding site 2 inactivated. Bound and free hGH were then separated on a Sephadex G-100 column according to a standard protocol for measuring GHBP. In all three cases, more than 90% of the high affinity GH-BP complex eluting from the column was consistent with 1:1 binding. Similar results were obtained when a physiological amount of recombinant or purified natural GHBP was substituted for plasma. However, at supraphysiological concentrations of GHBP, an additional component corresponding to the 2:1 complex eluted from the column; the relative proportions of the 2:1 and 1:1 complexes were dependent on the GHBP concentration. These data suggest that at physiological GHBP levels in plasma, the 1:1 complex predominates, and that small amounts of the 2:1 complex may be difficult to detect because of partial peak overlap with the 1:1 complex, dissociation, and, in whole plasma, coelution with the low affinity GHBP complex. Calculation of the theoretical partition of hGH between 1:1 and 2:1 complexes indicated that at concentrations of GHBP prevailing in plasma (approximately 1 nmol/L), the 1:1 complex predominates, but that at the high receptor concentrations prevailing at the cell surface (60 nmol/L to 6.7 mumol/L, depending on the cell type), virtually all hGH is captured in a 2:1 complex. These findings are consistent with the present and previous experimental data on the size of the circulating high affinity GH-BP complex, as well as with those indicating the importance of GH-induced receptor dimerization for GH action. A functional consequence of the large concentration difference between GHBP in plasma and GH receptors at the cell surface is that the circulating GHBP can serve as a dynamic buffer, modulating bound and free GH and prolonging its half-life, whereas the receptor acts as a dominant force in unidirectional capture of GH.(ABSTRACT TRUNCATED AT 400 WORDS)

Heterogeneity of circulating growth hormone

Human growth hormone (GH) represents a family of related proteins arising from two genes, alternative mRNA splicing, and several post-translational modifications. In addition, post-secretory events occur when GH enters the circulation. The full scale of GH heterogeneity is only beginning to be appreciated, and new GH forms or related proteins may be discovered in the future. GH measurements are affected by GH heterogeneity. Immunoassays are influenced by the mixture of GH variants, but are not sensitive to GH binding proteins (GHBPs). In contrast, radioreceptor assays are sensitive to both GH variant mixtures and to the high affinity GHBP. It is hoped that in the future, these problems can be minimized by rigorous characterization of existing antibodies with respect to epitope recognition on various GH forms, and ultimately, by production of GH variant-specific antibodies that permit direct and individual assessment of the circulating members of the GH family.

Distribution of growth hormone receptor messenger ribonucleic acid containing and lacking exon 3 in human tissues

The extent of expression of the GH receptor (GHR) in human tissues is largely unknown. In some cell lines and placenta, the GHR gene generates two different mRNAs by alternative splicing of exon 3, one coding for a full-length receptor (GHR + 3) and the other for a receptor isoform that lacks exon 3 (GHR-3), with deletion of amino acid residues 7-28. To determine the distribution of the GHR and the relative abundance of its two isoforms in man, we studied a variety of tissues obtained at autopsy by reverse transcription and polymerase chain reaction (PCR) amplification, using isoform-specific primers. The nature of the PCR products was verified by restriction analysis and DNA sequencing. The relative proportions of the two GHR isoforms were determined by competitive PCR using a 32P-labeled anti-sense primer and a mixture of both isoform-specific sense primers in equimolar amounts. Electrophoretic bands corresponding to the amplification products were excised and counted, or quantitated by laser densitometry. Restriction analysis and sequencing of the amplified products were consistent with their predicted sequence. Both GHR transcripts were found in all 19 tissues tested, but their relative proportions varied depending on the tissue and, to a lesser extent, between subjects. They ranged from a preponderance of GHR-3 (kidney, bladder, adrenal, and brain stem) to a predominance of GHR + 3 (skeletal muscle and liver). We conclude that the GHR gene is widely expressed in human tissues. Both GHR + 3 and GHR-3 transcripts are present, but their relative proportions depend on the tissue and, possibly, the metabolic status. The physiological significance of the existence of two human GHR forms remains to be elucidated.

Growth hormone-binding proteins in plasma

Two growth hormone-binding proteins (GHBPs), one with high and the other with low affinity, have recently been described in the blood of humans and several other species. The high-affinity GHBP represents a circulating fragment of the GH receptor, encompassing its extracellular domain. The molecular nature of the low-affinity GHBP is not known in detail. GHBPs form complexes with circulating GH, prolong its biological half-life, restrict its distribution in the body, and modulate the binding of GH to receptors in tissues. Their net effect in vivo is to enhance GH action. The level of high-affinity GHBP in plasma probably reflects receptor concentrations in tissues. The level/activity of GHBP is linked to GH action, and several congenital or acquired conditions with altered GHBP levels are characterized by parallel changes in GH action (Laron-type dwarfism, pygmy dwarfism, malnutrition, obesity, insulin-dependent diabetes mellitus, liver cirrhosis, renal insufficiency). The GHBP/receptor level is nutritionally regulated, with levels low in undernutrition and high in overnutrition. Regulation of lean body mass anabolism/catabolism at the level of the GHBP/receptor provides a rational explanation for the derangements in the GH axis and their biological consequences (retarded or accelerated somatic growth) observed in nutrition disorders.

Effect of growth hormone administration frequency on 24-hour growth hormone profiles and levels of other growth related parameters in girls with Turner's syndrome. Dutch Working Group on Growth Hormone

OBJECTIVE

The optimal dose and frequency of GH administration in Turner's syndrome is unknown. There is some evidence that a schedule which mimics normal pulsatile GH secretion may be more effective than a single daily dose. We therefore wished to study the influence of the frequency of GH administration on 24-hour GH profiles and levels of other growth-related factors in Turner's syndrome.

DESIGN

Four weeks after initiation of 0.05 microgram/kg/day ethinyl oestradiol, we compared twice daily (b.i.d.-fractionated dose) with once daily (o.d.) s.c. injections of 6 IU GH/m2/day in a 2-week cross-over design with a 2-week washout interval. Each treatment period was concluded with 24-hour GH profile tests. Pretreatment plasma/serum levels of GH, IGF-I, binding proteins for GH (GHBP) and IGF-I (IGFBP-3) were used as a basis for comparison of the levels found after each regimen. A one-compartment open model was used for estimation of pharmacokinetic parameters.

SUBJECTS

Ten previously untreated girls with Turner's syndrome aged > or = 11 years.

MEASUREMENTS

Plasma levels of GHBP by standardized binding assay; GH, IGF-I, and IGFBP-3 serum/plasma levels by radioimmunoassay.

RESULTS

There were significantly higher maximum GH levels and a greater area under the curve with o.d. than with b.i.d. GH, while GH clearance was greater with b.i.d. The pharmacokinetic values with o.d. injections were in conformity with values for healthy and GH-deficient children. Pretreatment GHBP levels tended to be high compared with values in healthy prepubertal children. These levels decreased with GH therapy, significantly so with b.i.d. GH only. There was a significant increase in levels of IGF-I and IGFBP-3, irrespective of regimen. The IGF-I to IGFBP-3 ratio, a possible indicator of the growth response, rose significantly and comparably with both regimens. There was no consistent diurnal variation with either regimen in GHBP, IGF-I or IGFBP-3 levels. Four-hourly levels of GH, GHBP, IGF-I and IGFBP-3 were not correlated.

CONCLUSIONS

Although the 24-hour profiles differed during once or twice daily administration of the same total growth hormone dose, the diurnal pattern and mean levels of factors involved in the biological effects of GH are comparable for both regimens.

Growth hormone-binding protein determination in plasma: a comparison of immunofunctional and growth hormone-binding assays

The recent development of an immunofunctional assay for GH-binding protein (GHBP) facilitates measurement of GHBP in biological fluids. Previous methods employed GH binding followed by size exclusion chromatography to determine GHBP levels (GH binding assay), and a considerable body of information exists based on data obtained with that type of assay. To cross-validate the two methods and permit comparison of results obtained in the two assays, we measured GHBP by both methods in 61 plasma samples from normal adults (aged 19-69), 10 patients with acromegaly, 2 patients with Laron dwarfism, and in a normal adult plasma pool. The results show a good overall correlation between the two methods (r = 0.669). However, for individual observations, the coefficient of determination was not high enough to permit interconversion of data with high precision. There is both biological and methodological variation in GHBP levels, rendering the interpretation of a single observation difficult except in the extreme range. The range of values was wider in the immunoassay (56-1187 pmol/L) than in the GH-binding assay (12.1-36.1% GH bound/400 microL). There was no significant sex difference in plasma GHBP levels, nor was there an age-dependent trend in adult subjects as assessed by both assays. Patients with acromegaly had significantly decreased GHBP levels in both assays, but the majority of the values were within the low normal range. The two patients with Laron dwarfism had undetectable GHBP in both assays. The previously defined unit of GHBP (i.e. the amount contained in 1 ml pooled adult plasma) corresponds to 256 fmol GHBP as determined by immunofunctional assay.

Increased follistatin (activin-binding protein) gene expression in rat anterior pituitary tissue after ovariectomy may be mediated by pituitary activin

For lack of evidence to the contrary, it is now believed that the FSH-suppressing actions of follistatin are due to its ability to bind endogenous pituitary activin. Recent data have demonstrated a role for pituitary activin-B in mediating FSH hypersecretion after ovariectomy (OVX) and during the secondary FSH surge on estrus. Therefore, given that follistatin is produced within anterior pituitary tissue, and considering the potentially important function of follistatin to modulate activin bioactivity, we sought to gain insights into the regulation of follistatin gene expression in the anterior pituitary gland of adult female rats. At the termination of all in vivo investigations, rats were killed, trunk blood was collected for determination of serum LH and FSH levels by RIA, and pituitary tissue was collected, pooled (two or three glands per pool), and processed for determination of follistatin messenger RNA (mRNA) levels by a solution-hybridization RNase protection assay. In the first experiment, pituitary follistatin mRNA levels were significantly (P < 0.01) increased 3 weeks after OVX. Treatment of long-term ovariectomized rats with a Nal-Glu LHRH antagonist restored serum LH levels to precastration levels and suppressed serum FSH concentrations by 70%, but follistatin message levels were not altered. In contrast, treatment of castrated rats with recombinant human follistatin-288 selectively suppressed serum FSH levels (50%) and completely abolished OVX-induced increases in follistatin mRNA levels. Subsequent experiments revealed that OVX-induced increases in follistatin gene expression could be observed in pituitary tissue grafted underneath the kidney capsule of hypophysectomized rats. Furthermore, follistatin mRNA levels were significantly (P < 0.05) higher in pituitary glands taken from estrous rats during the secondary FSH surge (0200 h) than in glands obtained from rats on proestrous morning when serum FSH levels were basal. Because increased steady state follistatin mRNA levels in the latter two instances were associated with selective FSH hypersecretion, and such hypersecretion was previously shown to be dependent to a significant degree on pituitary activin, we next tested the hypothesis that increased pituitary follistatin gene expression is mediated by activin. Using cultures of dispersed pituitary cells, addition of recombinant human activin-A for 72 h increased follistatin mRNA levels 3-fold while enhancing only FSH secretion. Collectively, the present results demonstrate a coupling of follistatin gene expression in the anterior pituitary gland with changes in pituitary FSH secretion under conditions where LH secretion is unaltered. Viewed in the context of previous work, the data also suggest that changes in follistatin mRNA levels may be linked to activin signaling.

Effects of estrous cycle stage and pregnancy on follistatin gene expression and immunoreactivity in rat reproductive tissues: progesterone is implicated in regulating uterine gene expression

Follistatin, a monomeric protein originally isolated from ovarian follicular fluid, is now believed to be a major local regulator of the multifaceted actions of activin by virtue of its activin-binding properties. In view of the ability of follistatin to stimulate progesterone production from granulosa cells and its presence in newly formed corpora lutea, the following study was conducted to determine the effects of cycle stage and pregnancy on follistatin gene expression and immunoreactivity in the rat ovary and uterus with the intent of gaining additional insights into the regulation of follistatin in these tissues. Decidua and placentas were also examined on days 15, 18, and 21 of pregnancy. Follistatin messenger RNA (mRNA) levels were quantified using a sensitive solution hybridization-RNase protection assay and values normalized to the amount of cyclophilin mRNA present in each sample. Levels of follistatin-like immunoreactivity (FLI) in serum and tissues were estimated using a homologous porcine follistatin RIA. Follistatin message levels in the ovary increased between proestrus and estrus with a return to proestrous values on both days of diestrus. In the nonpregnant uterus, mRNA levels on proestrus were similar to levels measured in uteri taken from hypophysectomized or ovariectomized rats. Interestingly, follistatin gene expression increased almost 3-fold between proestrus and estrus. An additional experiment demonstrated that this increase could be abated by treatment of proestrous rats with pentobarbital which blocks preovulatory rises in serum progesterone levels and could be restored by administration of progesterone to pentobarbital-treated proestrous rats. In pregnant rats, ovarian follistatin message levels on days 3 and 6 of pregnancy were identical to levels observed on day 2 of diestrus. However, an abrupt 4-fold increase in ovarian mRNA levels occurred between days 6 and 9 with a further 58% increase occurring by day 12. This marked increase in message levels was unaccompanied by changes in ovarian FLI levels. A precipitous decrease in transcript levels accompanied by a decline in FLI levels then followed with ovarian gene expression on days 15 through 21 being slightly higher than expression during the initial stages of gestation. Expression of the gene in the decidua and placenta did not vary between days 15 and 21 of pregnancy. Levels of FLI in serum also were invariant during the cycle and pregnancy.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of the high-affinity growth hormone (GH)-binding protein on plasma profiles of free and bound GH and on the apparent half-life of GH. Modeling analysis and clinical applications

The discovery of a specific high-affinity growth hormone (GH) binding protein (GH-BP) in plasma adds complexity to the dynamics of GH secretion and clearance. Intuitive predictions are that such a protein would damp sharp oscillations in GH concentrations otherwise caused by bursts of GH secretion into the blood volume, prolong the apparent half-life of circulating GH, and contribute a reservoir function. To test these implicit considerations, we formulated an explicit mathematical model of pulsatile GH secretion and clearance in the presence of absence of a specific high-affinity GH-BP. Simulation experiments revealed that the pulsatile mode of physiological GH secretion creates a highly dynamic (nonequilibrium) system, in which the half-life of free GH, its instantaneous secretion rate, and the GH-BP affinity and capacity all contribute to defining momentary levels of free, bound, and total GH, the percentage of GH bound to protein, and the percentage occupancy of GH-BP [corrected]. In contrast, the amount of free GH at equilibrium is specified only by the GH distribution volume and secretion rate and the half-life of free hormone. We conclude that the in vivo dynamics of GH secretion, trapping, and clearance from the circulation offer a variety of regulatory loci at which the time structure of free, bound, and total GH delivery to target tissues can be controlled physiologically.

Low plasma growth hormone binding protein in IDDM

Poorly controlled insulin-dependent diabetes mellitus (IDDM) is associated with elevated basal plasma growth hormone (GH), disproportionally low insulin-like growth factor I (IGF-I) levels, and impaired somatic growth. These derangements in the GH-IGF axis imply a state of GH resistance. The mechanism of GH resistance is unknown; it may involve a defect at the level of the GH receptor, unresponsiveness due to a postreceptor defect in GH action, or both. To investigate a potential receptor involvement, we measured plasma high-affinity GH-binding protein (GHBP), which represents a truncated GH receptor and may reflect GH receptor levels in tissues, in patients with IDDM, patients with non-insulin-dependent diabetes (NIDDM), and nondiabetic control subjects. Patients with IDDM had significantly lower plasma GHBP levels than either patients with NIDDM or nondiabetic control subjects (mean value 18.2 vs. 24.6 and 23.8% GH bound/ml plasma, respectively, P less than 0.001). This difference persisted when only lean patients (less than 115% ideal body wt) were included in the analysis. Basal plasma GH levels were significantly elevated in IDDM compared with either patients with NIDDM or nondiabetic control subjects (mean 6.9 vs. 2.1 and 2.0 micrograms/L, respectively, P less than 0.001), whereas IFG-I levels were not significantly different in IDDM and NIDDM. No correlations were found between levels of GHBP and HbA1, duration of diabetes, or plasma GH. GHBP and IGF-I levels were significantly correlated in NIDDM but not in IDDM. We conclude that IDDM is associated with low GHBP levels and that GH resistance found in this disorder may be mediated, at least in part, by a decrease in GH receptor levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Successful treatment of steroid-resistant double-lung allograft rejection with Orthoclone OKT3

An 18-yr-old woman with cystic fibrosis who received a double-lung transplant developed a severe episode of acute lung rejection. Bronchoalveolar lavage and transbronchial biopsy were used to establish the diagnosis. The rejection was refractory to administration of high-dose pulse steroids. OKT3 therapy was successfully used to reverse this episode. This is the first case report of a steroid-resistant double-lung allograft rejection successfully treated with OKT3.

Complementary DNA structure of the high molecular weight rat insulin-like growth factor binding protein (IGF-BP3) and tissue distribution of its mRNA

Insulin-like growth factors (IGFs) found in extracellular fluids are bound to specific binding proteins. Recently a high molecular weight IGF-binding protein (IGF-BP3) has been isolated from porcine ovarian follicular fluid based on its inhibition of follicle stimulating hormone-stimulated estradiol production in rat granulosa cells. The complete primary structure of the porcine IGF-BP3 was deduced by molecular cloning. Using the porcine cDNA as a probe, we have now isolated and characterized cDNAs encoding rat IGF-BP3 from a pregnant mare serum gonadotropin-stimulated ovarian library. The predicted amino acid sequence revealed a mature polypeptide consisting of 265 amino acids with 18 cysteines and 4 potential Asn-linked glycosylation sites. Northern analysis of the IGF-BP3 mRNA in rat tissues showed a single 2.6 kb band in liver, kidney, stomach, heart, adrenal, ovary, testis, spleen, lung, small and large intestine in varying amounts, but the message is below the limit of detection in hypothalamus and brain cortex.

Prenatal ultrasonographic diagnosis of thoracopagus conjoined twins

Conjoined twins are a rare obstetric event occurring 1/50,000 to 1/60,000 deliveries as a result of incomplete fission of the embryonic disc before the third week of pregnancy. They belong to the monochorionic-monoamniotic type of monozygotic twins and are classified according to the area of union, the most common site being the chest and upper abdomen (thoracopagus). Reported are two cases of thoracopagus twins in which the diagnosis was made prenatally by ultrasound in the second trimester of pregnancy. The most significant ultrasound findings included the demonstration of a single cardiac activity, the inability to separate the fetal bodies at their ventral portion, and a face-to-face fetal position. The pregnancies were allowed to continue until term with no significant prenatal complications, and an elective cesarean section was performed to avoid a traumatic delivery. In both cases the infants died during the first week of life because of cardiorespiratory insufficiency. The ultrasound criteria for the antenatal diagnosis of conjoined twins are reviewed, concluding that the careful ultrasound examination of all identified sets of twins, specially in those cases in which no separating membrane is demonstrated, is the cornerstone in making the prenatal diagnosis. In addition, ultrasound plays a crucial role not only in the diagnosis, but also in establishing the degree of conjoining, which is essential for planning an appropriate obstetrical and perinatal management.

Complementary DNA cloning and sequencing of rat ovarian basic fibroblast growth factor and tissue distribution study of its mRNA

Three cDNA clones encoding rat basic fibroblast growth factor (FGF) were isolated from 10(6) independent clones prepared from a pregnant mare serum gonadotropin (PMSG)-stimulated rat ovarian cDNA library. One of the cDNA clones contained the entire coding sequence for basic FGF. The other two possessed the sequence coding the carboxy terminal 61 amino acids of rat basic FGF, the putative upstream intron sequence, and a 3'-noncoding region. The cDNAs encoding rat basic FGF predict a molecule consisting of 154 amino acid residues, which is one amino acid shorter than the human and bovine basic FGF. Otherwise, there are only 5 conservative amino acid substitutions between the rat and the human/bovine sequences. Poly A+ RNA from brain cortex and hypothalamus show a single 6.0 kb band that hybridizes to the cloned cDNA probe by Northern analyses. The observation that basic FGF mRNA is below the limits of detection in adrenal, spleen, heart, lung, kidney, liver, stomach, small intestine, large intestine, testis, and ovary support the notion that the that the high levels of the protein found in these tissues is due to storage of the mitogen in the extracellular matrix and not continuous gene expression. The significance of the abundance of mRNA in tissues which are not undergoing either active angiogenesis or cell proliferation (hypothalamus and brain cortex) is unclear but emphasizes the potential neuronotrophic function of basic FGF.

Primary structure of the human follistatin precursor and its genomic organization

Follistatin is a single-chain gonadal protein that specifically inhibits follicle-stimulating hormone release. By use of the recently characterized porcine follistatin cDNA as a probe to screen a human testis cDNA library and a genomic library, the structure of the complete human follistatin precursor as well as its genomic organization have been determined. Three of eight cDNA clones that were sequenced predicted a precursor with 344 amino acids, whereas the remaining five cDNA clones encoded a 317 amino acid precursor, resulting from alternative splicing of the precursor mRNA. Mature follistatins contain four contiguous domains that are encoded by precisely separated exons; three of the domains are highly similar to each other, as well as to human epidermal growth factor and human pancreatic secretory trypsin inhibitor. The genomic organization of the human follistatin is similar to that of the human epidermal growth factor gene and thus supports the notion of exon shuffling during evolution.

Porcine follistatin gene structure supports two forms of mature follistatin produced by alternative splicing

Follistatin (FS), a novel gonadal protein which inhibits specifically the secretion of pituitary follicle stimulating hormone (FSH), has recently been isolated from porcine follicular fluid. cDNA cloning of the porcine ovarian FS precursor revealed two populations of cDNAs which differed at the 3'-region of the open reading frames; one population encodes a precursor of 317 amino acids while the other encodes another precursor having the same 317 amino acids, but with an additional 27 amino acids at the carboxy-terminal. Herein, we report the cloning of the porcine FS gene whose DNA structure reveals that the two populations of mRNA are generated by alternative splicing. In addition, restriction endonuclease mapping and DNA sequencing show that the FS gene is approximately 6 Kb long and consists of six exons separated by five introns. The first exon encodes the putative signal sequence, followed by four exons which encode the four domains of FS, three of which are highly homologous to each other. The last exon encodes the extra 27-amino acid carboxy-terminal domain of the 344-residued precursor.

Thyroid function in very preterm infants

Indices of thyroid function were measured in 108 infants born at 23-31 weeks gestation, after birth, at 24 and 72 h, and at 1, 3, 4, 5 and 6 weeks of age. This group was characterised by low serum thyroxine (T4), normal thyroid stimulating hormone (TSH), low-normal thyroid binding globulin (TBG), low free thyroxine index (FTI) and low triiodothyronine (T3). The incidence of hypothyroxinaemia defined as a serum T4 value of less than 65 nmol/l was 58% after birth, increasing to 84% at 1 week, after which there was progressive reduction to 36% by 6 weeks of age. Mean T4 values were inversely proportional to gestational age during this study period. Infants of 23-28 weeks gestation had significantly lower T4, TBG, FTI and T3 values compared to those of 29-31 weeks gestation. Infants who had hyaline membrane disease (HMD) had significantly lower T4 and FTI values compared to those without HMD for up to 3 weeks of age. Similar differences were found between deaths and survivors in the first week after birth. This study suggests that there is increasing delay in maturation of the hypothalamic-pituitary-thyroid axis control with increasing prematurity. In addition, the data suggest that infants who were extremely preterm or those with HMD had worse and more persistent abnormalities of thyroid function secondary to their illness and metabolic stress. The significance of our findings, in particular that of prolonged hypothyroxinaemia, is uncertain. The role of thyroid replacement therapy in these very preterm infants therefore need to be assessed with a randomised clinical trial.

Structural characterization of follistatin: a novel follicle-stimulating hormone release-inhibiting polypeptide from the gonad

Follistatin, a novel, single chain, glycosylated polypeptide bearing no homology with previously characterized inhibins but exhibiting potent and specific pituitary FSH-release inhibition has been structurally characterized by protein microsequencing, cDNA cloning, and DNA sequencing. Two populations of clones differing in their 3'-untranslated sequences were found to encode a 344 amino acid precursor protein and an identical but carboxyl terminal truncated 317 amino acid precursor, respectively. Additionally, one clone, FS18, contained two introns and probably resulted from reverse transcription of heterogeneous nuclear RNA during cDNA library construction. Follistatin is unusually cysteine-rich, containing 36 cysteines in the mature coding sequence of 315 amino acids and an extremely acidic carboxyl terminal region, FS(292-304), comprised of Glu-Asp-Thr-Glu-Glu-Glu-Glu-Glu-Asp-Glu-Asp-Gln-Asp which probably resides outside a tightly cross-linked protein sphere. The heparin-binding ability of follistatin can probably be ascribed to the basic region specified by FS(75-86), Lys-Lys-Cys-Arg-Met-Asn-Lys-Lys-Asn-Lys. Overall, follistatin is organized into three homologous domains, FS(66-135), FS(139-210), and FS(216-287) containing 70, 72, and 72 amino acids, respectively, which show a 52% homology among themselves and a 57% homology with the 56 amino acid human pancreatic secretory trypsin inhibitor protein when aligned for maximum homology.

Symptomatic hypothyroxinemia with normal TSH levels in preterm infants

The authors report eight preterm infants with hypothyroxinemia who developed clinical features similar to those described in congenital hypothyroidism: prolonged jaundice, hypoactivity, lethargy, constipation, edema, and hoarse cry. All had low serum thyroxine, normal thyroid stimulating hormone, and normal thyroid binding globulin levels. After exclusion of other causes for the symptoms, thyroid replacement therapy was started, resulting in rapid resolution of symptoms and return to euthyroid status. Follow-up of these infants after cessation of therapy revealed normal growth and development and normal thyroid function. The authors therefore recommend a prospective study to investigate the incidence of hypothyroxinemia, frequency of associated clinical features, and the benefits of thyroid replacement therapy based on a randomized controlled trial.