Stimulation of corticotrophin-releasing hormone release by the obese (ob) gene product, leptin, from hypothalamic explants

Recent data have suggested that adipocytes synthesize and secrete a 16 kDa peptide which acts centrally to regulate weight gain by suppressing appetite and activating the sympathetic nervous system. To exert such effects, it may function as an endogenous ligand in the CNS, since specific receptors (OB-R) have been recently reported to be widely distributed in the brain. We have speculated that this peptide, now known as leptin, may act centrally by stimulating the release of corticotrophin-releasing hormone (CRH), a recognized potent inhibitory modulator of appetite. We tested in vitro the effect of murine leptin on CRH secretion in the dose range of 0.1 pM-100 nM. The static rat hypothalamic incubation system used involved fresh hypothalamic explants maintained in EBSS with consecutive 20 min incubations, and estimation of CRH concentrations in the medium by a specific and sensitive radioimmunoassay. The effect of heat-denatured leptin at a dose of 1 nM and 10 nM, was also investigated. Any possible modulation of leptin effects by adrenergic pathways was then explored by coincubating hypothalami with leptin 10 nM and equimolar concentrations of the alpha 1-adrenergic antagonist prazosin or the beta-adrenergic antagonist propranolol. The active leptin, but not the heat-inactivated peptide, caused a dose-dependent stimulation of CRH release in vitro (p < 0.05- < 0.0001 vs control), with a plateau effect at a dose of 10 nM. The addition of either prazosin or propranolol was without effect on leptin-dependent CRH stimulation. These findings are consistent with the reported presence of leptin receptors in the rat brain, and suggest that leptin may act to regulate appetite at least in part by directly modulating the secretion of CRH from the hypothalamus. It would also appear that such effect occurs via a non-adrenergic mechanism.

Virtuous capital: what foundations can learn from venture capitalists

U.S. foundations and nonprofits work diligently on behalf of society's most needy and yet report that progress is slow and social problems persist. How can they learn to be more effective with their limited resources? Foundations should consider expanding their mission from investing only in program innovation to investing in the organizational needs of nonprofit organizations as well. Their overemphasis on program design has meant deteriorating organizational capacity at many nonprofits. If foundations are to help nonprofits be assured of making payroll, paying the rent, or buying a much-needed computer, they must develop hands-on partnering skills. Venture capital firms offer a helpful benchmark. In addition to putting up capital, they closely monitor the companies in which they have invested, provide management support and stay involved long enough to see the company become strong. If foundation officers familiarize themselves with such practices, they can begin to build organizational capacity in the nonprofit sector. Foundations can hire organizational experts to assist grantees; they can lengthen grant terms to allow nonprofits to build up organization strengths; and they can create new classes of grants that allow for organizational effectiveness. Nonprofits in turn should articulate their organizational needs when applying for grants; they should apply to foundations known for longer-term grants; and they should create plans that justify long-term support from foundations.

Pendred syndrome: evidence for genetic homogeneity and further refinement of linkage

Pendred syndrome is the association between congenital sensorineural deafness and goitre. The disorder is characterised by the incomplete discharge of radioiodide from a primed thyroid following perchlorate challenge. However, the molecular basis of the association between hearing loss and a defect in organification of iodide remains unclear. Pendred syndrome is inherited as an autosomal recessive trait and has recently been mapped to 7q31 coincident with the non-syndromic deafness locus DFNB4. To define the critical linkage interval for Pendred syndrome we have studied five kindreds, each with members affected by Pendred syndrome. All families support linkage to the chromosome 7 region, defined by the microsatellite markers D7S501-D7S523. Detailed haplotype analysis refines the Pendred syndrome linkage interval to a region flanked by the marker loci D7S501 and D7S525, separated by a genetic distance estimated to be 2.5 cM. As potential candidate genes have as yet not been mapped to this interval, these data will contribute to a positional cloning approach for the identification of the Pendred syndrome gene.

The effects of spiradoline (U-62066E), a kappa-opioid receptor agonist, on neuroendocrine function in man

1. Opioid drugs act on specific receptors which are principally classified into mu, delta and kappa subtypes. Spiradoline (U-62066E) is a kappa-selective agent which has been shown to possess potent anti-nociceptive effects but does not show cross tolerance with morphine. 2. We have assessed the neuroendocrine effects of spiradoline in healthy volunteers with two doses (1.6 and 4.0 micrograms kg-1, i.m.) of the compound. Six male non-smokers aged 19-27 years were studied by use of a randomized, double-blind three-limb placebo-controlled cross-over design. Blood was taken from an in-dwelling venous cannula basally and at 15 min intervals for 2 h for determination of serum cortisol, prolactin, growth hormone (GH) and catecholamines. 3. Psychological function was assessed by the Stanford Sleepiness Scale (SSS) and the Addiction Research Centre Inventory (ARCI) administered before the medication and at 35 min, 1 h 25 min and 2 h afterwards. Cardiovascular variables were recorded at 10 min intervals. Results were analysed by analysis of variance. 4. Spiradoline showed a significant (P < 0.05) dose-dependent increase in free water clearance, as predicted for a kappa-opioid agonist. It also caused a dose-dependent stimulation of prolactin, (increment over baseline for higher dose 214%), GH (433%) and cortisol (215%) release (P < 0.05). There were no significant drug-related changes in plasma catecholamines, blood pressure, pulse or psychological variables. 5. We have therefore confirmed that kappa-opioids increase free-water clearance and may participate in the stimulation of prolactin and GH release. In contrast to mu and delta-opioid agonists, this novel kappa-agonist stimulates cortisol release in man.

Requirement for the transcription factor LSIRF/IRF4 for mature B and T lymphocyte function

Lymphocyte-specific interferon regulatory factor (LSIRF) (now called IRF4) is a transcription factor expressed only in lymphocytes. Mice deficient in IRF4 showed normal distribution of B and T lymphocyes at 4 to 5 weeks of age but developed progressive generalized lymphadenopathy. IRF4-deficient mice exhibited a profound reduction in serum immunoglobulin concentrations and did not mount detectable antibody responses. T lymphocyte function was also impaired in vivo; these mice could not generate cytotoxic or antitumor responses. Thus, IRF4 is essential for the function and homeostasis of both mature B and mature T lymphocytes.

A combined test using desmopressin and corticotropin-releasing hormone in the differential diagnosis of Cushing's syndrome

To assess the ability of desmopressin to differentiate between pituitary and ectopic ACTH-dependent Cushing's syndrome and to determine whether diagnostic accuracy could be improved by administering it together with human sequence CRH, we examined its effects on cortisol and ACTH secretion when given alone or in combination with CRH in patients with Cushing's syndrome of varied etiology and compared these data to the results of a standard CRH test in the same individuals. Each patient was studied on three occasions, in random order, separated by at least 48 h. At 0900 h, via an indwelling forearm cannula, 10 micrograms desmopressin, 100 micrograms CRH, or a combination of the two were given as an iv bolus; thereafter, blood was drawn every 15 min for 2 h. The responses to the individual agents were determined according to the timing and calculation criteria suggested by Nieman et al. (1993). A total of 25 patients with Cushing's syndrome were studied: 17 patients with pituitary-dependent Cushing's syndrome, Cushing's disease (CD); 5 patients with occult ectopic ACTH secretion (EC); and 3 patients with primary adrenal (ACTH-independent) Cushing's syndrome. In this series, the best discrimination among ACTH-dependent patient groups was achieved using the combined test. Using the responses of plasma cortisol, all 17 patients with CD showed a rise greater than any of the 5 patients with EC, whereas 1 patient with CD showed a plasma ACTH response within the range seen in the patients with EC. Plasma cortisol responses to desmopressin alone were seen in 14 of 17 patients with CD and 1 of 5 patients with EC and, after CRH alone, in 15 of 17 patients with CD but in no patient with EC. In contrast, plasma ACTH responses after CRH alone were seen in 14 of 17 patients with CD and 2 of 5 patients with EC and, after desmopressin alone, in 12 of 17 with CD and 3 of 5 with EC, thus indicating overlapping responses between the groups and poorer discrimination. No responses were seen in the ACTH-independent group. These data indicate that desmopressin causes the secretion of ACTH and cortisol in patients with ACTH-dependent Cushing's syndrome, and that in combination with CRH, it may provide an improvement over the standard CRH test in the differential diagnosis of ACTH-dependent Cushing's syndrome. Furthermore, these data suggest that there may be abnormalities in vasopressin receptor function or number in ACTH-secreting tumors.

Cloning of human lymphocyte-specific interferon regulatory factor (hLSIRF/hIRF4) and mapping of the gene to 6p23-p25

The interferon regulatory factor (IRF) genes encode a family of transcription factors involved in the transcriptional regulation of interferon and the interferon stimulated genes through recognition of the interferon stimulated response element. We previously reported the cloning of a murine lymphocyte-specific IRF (mLSIRF), which was rapidly induced following B- or T-cell receptor crosslinking. To study the role of LSIRF in human lymphocyte development, we have cloned the complete 5.3-kb cDNA for the human homolog (hLSIRF). hLSIRF is a protein of 450 amino acids with a predicted molecular weight of 51.6 kDa and possesses 92% identity at the amino acid level to mLSIRF, including near identity in the DNA-binding domain. In Northern blot analysis, a single transcript of approximately 5 kb was highly expressed in spleen and peripheral blood lymphocyte. hLSIRF mRNA was rapidly induced in peripheral T cells after crosslinking the T-cell receptor. Analysis of tumor cell lines showed that hLSIRF mRNA was basally expressed in most B- but not T-cell lines. Surprisingly hLSIRF mRNA was also found in the melanoma line G361 and is expressed in normal melanocytes as well. Sequence from a genomic clone for hLSIRF was compared to that from mouse and revealed an identical exon-intron structure and a conserved PU-1-binding motif in the promoter. By FISH analysis, hLSIRF was mapped to 6p23-p25.

Sulfur availability and the SAC1 gene control adenosine triphosphate sulfurylase gene expression in Chlamydomonas reinhardtii

A Chlamydomonas reinhardtii adenosine triphosphate (ATP) sulfurylase cDNA clone (pATS1) was selected by complementing a mutation in the ATP sulfurylase gene (cysD) of Escherichia coli. E. coli cysD strains harboring pATS1 grow on medium containing sulfate as the sole sulfur source and exhibit ATP sulfurylase activity. The amino acid sequence of the C. reinhardtii ATP sulfurylase, derived from the nucleotide sequence of the complementing gene (ATS1), is 25 to 40% identical to that of ATP sulfurylases in other eukaryotic organisms and has a putative transit peptide at its amino terminus. ATP sulfurylase mRNA was present when cells were grown in sulfur-replete medium, but accumulated to higher levels when the cells were exposed to sulfur-limiting conditions. Furthermore, sulfur-stress-induced accumulation of the ATS1 transcript was reduced in a strain defective in SAC1, a gene that is critical for acclimation to sulfur-limited growth.

The acute cardiovascular actions of intravenous thyrotrophin releasing hormone (TRH) in man are mediated by non-catecholaminergic mechanisms

1. Intravenous bolus doses of thyrotrophin releasing hormone (TRH, 50-1000 micrograms) caused statistically significant, non-dose dependent and transient rises in blood pressure, heart rate and plasma catecholamines in healthy young males. 2. Mean peak incremental rises in systolic blood pressure (mean +/- s.e. mean) following 50, 200 and 500 micrograms TRH were 14.3 +/- 2.9 mmHg, 15.7 +/- 3.2 mmHg and 17.1 +/- 3.9 mmHg respectively (all P < 0.05 vs placebo). Mean incremental rises in heart rate for the three doses of TRH were 8.2 +/- 2.2 beats min-1, 7.1 +/- 1.8 beats min-1, and 10.7 +/- 2.9 beats min-1 respectively (all P < 0.05 vs placebo). 3. Following the 50 micrograms and 1000 micrograms doses of TRH, plasma noradrenaline and adrenaline rose significantly (P < 0.05) between 4 and 8 min. Mean +/- s.e. mean incremental plasma noradrenaline rise following 50, 200 and 100 micrograms TRH were 0.4 +/- 0.13 nmol 1(-1), 0.37 +/- 0.21 nmol 1(-1) and 0.41 +/- 0.18 nmol 1(-1) respectively. Mean +/- s.e. mean incremental rise in adrenaline for the 50, 200 and 1000 micrograms dose were 0.13 +/- 0.04 nmol 1(-), 0.08 +/- 0.03 nmol 1(-1), and 0.11 +/- 0.05 nmol 1(-1) respectively. 4. Following administration of the ganglion blocking drug pentolinium (5 mg) the incremental systolic blood pressure and heart rate rises following 500 micrograms TRH alone 16.6 +/- 2.8 mmHg and 10.4 + 3.1 beats min-1 respectively. 5. The rises in plasma noradrenaline and adrenaline following TRH were attenuated by prior ganglion blockade. 6. alpha-Adrenoceptor blockade with thymoxamine (0.3 mg kg-1 bolus + 0.3 mg kg-1 h-1 infusion), singly and combined with intravenous propranolol (10 mg i.v. over 10 min), did not alter the pressor or tachycardic effects of 500 micrograms TRH. 7. In conclusion, although plasma noradrenaline rises following i.v. TRH, suggesting activation of the sympathetic nervous system, this effect is not responsible for the pressor response to TRH, which appears to be due to either a direct vasoconstrictive effect on the peripheral resistance vessels or a direct inotropic/chronotropic effect on the heart.

Effect of sodium valproate on luteinizing hormone secretion in pre- and postmenopausal women and its modulation by naloxone infusion

The synchronized activity of the GnRH neurons can be modulated through both excitatory and inhibitory circuits: one such inhibitory modulator is gamma-aminobutyric acid (GABA), but this has been little studied in humans. The aim of this study was to examine whether acute or chronic modulation of the GABA-ergic system with the drug sodium valproate (VPA) affects gonadotropin secretory frequency and/or amplitude in a steroid-dependent manner, and whether any such modulation might interact with endogenous opioids. Sixty postmenopausal women (age range 50-60 yr, group I), 50 postmenopausal women who had been on estrogen replacement therapy (group II), and 30 women in the luteal phase of their regular menstrual cycle (age range 25-40 yr, group III) were studied. VPA was administered acutely using doses of 300, 600, and 1200 mg orally. Samples for serum gonadotropins were taken at intervals over 24 h. Each dose of VPA caused significant LH suppression in group I. The maximum degree of suppressibility was the same with the three doses of VPA (14-20%). However, no dose had any effect on gonadotropin levels in group II. In group III, the single high dose of 1200 mg VPA significantly suppressed serum LH levels. The efficacy of chronic VPA administration in the three groups studied was assessed by measuring LH pulsatility (10-min samples) over 6 h, before and after 1 month's treatment with VPA. No change in either mean basal LH or in the LH pulsatility parameters was found. Naloxone infusion (1.6 mg/h for 6 h) had no effect on LH pulsatility in group I. When 1200 mg of VPA was administered before naloxone infusion, the level of LH suppression was 18% and was associated with a significant decrease in LH pulse frequency (P < 0.01). Naloxone infusion alone significantly increased mean serum LH and LH pulse frequency in group II patients (P < 0.01), and this elevation was antagonized by VPA pretreatment. Naloxone infusion alone significantly increased mean LH levels and LH pulse frequency in patients in group III, and this was also blocked by VPA pretreatment. These results suggest that an acute increase in GABA-ergic tone may inhibit gonadotropin secretion in the estrogen-deprived state, or when endogenous opioid inhibition is blocked in postmenopausal women on estrogens, as well as during the luteal phase of the menstrual cycle. It is possible that GABA-ergic pathways interact with opioids in the inhibitory modulation of gonadotropins in the human female.

Longitudinal study of adrenal steroids in a cohort of HIV-infected patients with hemophilia

The objective of the study was to relate plasma dehydroepiandrosterone sulfate (DHEA-S) concentrations to the progression of HIV infection in individual HIV-infected men with hemophilia and to obtain information on the cause of DH EA-S alterations. Blood samples were obtained from 16 men with hemophilia; in 9 men serial samples were available for up to 11 years after HIV-1 infection. Control samples were obtained from men of comparable ages without hemophilia or HIV infection. Measurements were made of CD4+ cell counts, plasma adrenocorticotropic hormone (ACTH), cortisol, DHEA, DHEA-S, and prolactin. Before HIV infection, men with hemophilia had significantly lower plasma levels of DHEA-S than control men. After infection, 3 of 9 subjects studied serially had little or no change in plasma DHEA-S levels or in CD4+ cell counts over 11 years. Four of the 9 i n whom AIDS developed had progressive decreases in plasma DHEA-S concentrations that, in some cases, preceded a precipitous fall in CD4+ cell counts. Major decreases in plasma DHEA-S levels before falls in CD4+ counts were observed in 2 ot her subjects who had other severe illnesses. None of the decreases in DHEA-S levels were associated with decreased concentrations of plasma cortisol, ACTH, or prolactin. We conclude that plasma DHEA-S is an indicator of general health rather than a specific indicator for progression of HIV. The decrease in plasma DHEA-S is not related to ACTH stimulation of the adrenal gland or to cortisol secretion, but it may be related to cytokines that can inhibit 17-hydroxylation of DH EA-S precursors.

Sac1, a putative regulator that is critical for survival of Chlamydomonas reinhardtii during sulfur deprivation

The sac1 mutant of Chlamydomonas reinhardtii is aberrant in most of the normal responses to sulfur limitation; it cannot synthesize arylsulfatase, does not take up sulfate as rapidly as wild-type cells, and does not synthesize periplasmic proteins that normally accumulate during sulfur-limited growth. Here, we show that the sac1 mutant dies much more rapidly than wild-type cells during sulfur deprivation; this emphasizes the vital role of the acclimation process. The loss of viability of the sac1 mutant during sulfur deprivation is only observed in the light and is mostly inhibited by DCMU. During sulfur-stress, wild-type cells, but not the sac1 mutant, downregulate photosynthesis. Thus, death of the sac1 mutant during sulfur deprivation is probably a consequence of its inability to downregulate photosynthesis. Furthermore, since SAC1 is necessary for the downregulation of photosynthesis, the process must be highly controlled and not simply the result of a general decrease in protein synthesis due to sulfur limitation. Genomic and cDNA copies of the SAC1 gene have been cloned. The deduced amino acid sequence of Sac1 is similar to an Escherichia coli gene that may involved in the response of E.coli to nutrient deprivation.

Thyroid peroxidase: evidence for disease gene exclusion in Pendred's syndrome

OBJECTIVE

Pendred's syndrome is an association between congenital neurosensory deafness and goitre with abnormal discharge of iodide following perchlorate challenge, indicating a defect of iodide organification. Although Pendred's syndrome may cause up to 7.5% of all cases of congenital deafness, the molecular basis of the association between the hearing loss and the thyroid organification defect remains unknown. We chose to investigate the role of the thyroid peroxidase (TPO) gene as the genetic defect in Pendred's syndrome.

DESIGN

A highly informative variable number tandem repeat (VNTR), located 1.5 kb downstream of exon 10 of the TPO gene, was used to search for genetic linkage in multiple sibships affected by Pendred's syndrome.

PATIENTS

Seven kindreds were recruited from the UK, each with at least two affected members. We have also examined a large inbred Israeli family with two affected offspring and five unaffected children.

MEASUREMENTS

Individuals were assigned affected status based on the characteristic clinical features of Pendred's syndrome, namely the presence of congenital sensorineural hearing loss and the appearance in early life of a goitre. Additionally, at least one affected member from each sibship had a characteristic positive perchlorate discharge test (Morgans & Trotter, 1958). PCR amplification of genomic DNA at the TPO VNTR allowed assignment of genotypes to each individual and the calculation of a two-point LOD score.

RESULTS

In six of the nine sibships analysed we found obligatory recombination between TPO and Pendred's syndrome. Non-complementation observed in affected parents with an affected offspring excluded TPO in an affected sibship with genotype sharing and supports a hypothesis of genetic homogeneity for Pendred's syndrome. In two sibships, mutation of the TPO gene as the cause of Pendred's syndrome could not be excluded.

CONCLUSIONS

These data suggest that defects at the thyroid peroxidase locus on chromosome 2 are not the major cause of Pendred's syndrome.

Pendred syndrome (goitre and sensorineural hearing loss) maps to chromosome 7 in the region containing the nonsyndromic deafness gene DFNB4

Inherited causes account for about 50% of individuals presenting with childhood (prelingual) hearing loss, of which 70% are due to mutation in numerous single genes which impair auditory function alone (non-syndromic). The remainder are associated with other developmental anomalies termed syndromic deafness. Genes responsible for syndromic forms of hearing loss include the COL4A5 gene in Alport syndrome and the PAX3 and MITF genes in Waardenburg syndrome. Pendred syndrome is an autosomal recessive disorder associated with developmental abnormalities of the cochlea, sensorineural hearing loss and diffuse thyroid enlargement (goitre). Pendred syndrome is the most common syndromal form of deafness, yet the primary defect remains unknown. We have established a panel of 12 families with two or more affected individuals and used them to search for the location of the Pendred gene by linkage analysis. We excluded localization to four previously mapped nonsyndromic deafness loci but obtained conclusive evidence for linkage of the Pendred syndrome gene to microsatellite markers on chromosome 7q31 (D7S495 Zmax 7.32, Qmax = 0). This region contains a gene, DFNBL, for autosomal recessive non-syndromic sensorineural hearing loss. Multipoint analysis indicates that DFNB4 and Pendred syndrome co-localize to the same 5.5 centiMorgan (cM) interval flanked by D7S501 and D7S523. These data raise the possibility that Pendred syndrome is either allelic with DFNB4 or may represent an inherited contiguous gene disorder, not clinically manifest in the heterozygote.

Adrenal incidentaloma: subclinical Cushing's syndrome

Adrenal incidentalomas present a significant differential diagnostic challenge. All patients with an incidentally discovered adrenal lesion should be carefully considered and re-evaluated to exclude extra-adrenal malignancy. Tumours with hypersecretory syndromes require excision, whilst those tumours more than 6 cm in size, particularly if they exhibit other features of malignancy on computed tomography (CT), magnetic resonance imaging (MRI) or scintigraphy, should also be excised. In all cases screening for phaeochromocytomas should be performed, and in the context of hypertension and spontaneous hypokalaemia, a primary aldosterone-secreting tumour requires exclusion. However, the natural history and treatment regimens for those individuals demonstrating 'subclinical Cushing's syndrome' is far from clear. Size, as determined by CT or MR scanning, does not in itself reliably distinguish benign from malignant disease. Scintigraphy may be a useful adjunct, with discordant patterns suggesting malignant disease. Fine needle aspiration should not routinely be used but may be useful in cases of doubt about other extra adrenal malignancy.

Diurnal variation in the effect of melatonin on neurohypophysial hormone release from the rat hypothalamus

Secretion of neurohypophysial hormones can show a diurnal variation. This has been investigated further in rats maintained on 14 h light:10 h dark using a previously validated in vitro technique employing hypothalami obtained at three different times, 2-3 h after lights on (group A), 13-14 h after lights on (group B), and at 4-5 h after lights off (group C). Hormone release under basal conditions and following stimulation with 40 mM KCl was monitored with or without added melatonin in the concentration range 4.3-43 nM. Basal release of hormone was not influenced by the time of day when the animals were taken, although stimulated release was elevated at midnight. In groups A and B both doses of melatonin significantly reduced basal and stimulated release of vasopressin and basal release of oxytocin (p < 0.01), although no effect was seen in group C animals. Inhibition of stimulated oxytocin release was only produced in group B. These findings suggest that the inhibitory effect of melatonin depends on the time of day and are consistent with the suggestion that melatonin secretion during the dark period may acutely downregulate binding sites in the brain.

A single sleeping midnight cortisol has 100% sensitivity for the diagnosis of Cushing's syndrome

OBJECTIVE

The diagnosis of Cushing's syndrome remains a major challenge in clinical endocrinology. Various screening tests are commonly used to support a biochemical diagnosis in the context of clinical suspicion. The aim of this study was to compare the sensitivity in the diagnosis of Cushing's syndrome of a single in-patient sleeping midnight cortisol to a standard 48-hour in-patient low-dose dexamethasone suppression test (LDDST) during the same admission.

DESIGN

A retrospective analysis was performed on 150 patients investigated in our department between the years 1970 and 1994 with a confirmed diagnosis of Cushing's syndrome.

PATIENTS

One hundred and fifty patients with a diagnosis of Cushing's syndrome were analysed: 110 with Cushing's disease; 12 with tumours with ectopic ACTH secretion; 8 with ACTH dependent Cushing's syndrome of so far undetermined origin; 17 with cortisol secreting adrenal tumours; 3 with adrenocortical nodular hyperplasia. Twenty normal volunteers and nine patients with non-endocrine conditions were also investigated as controls.

MEASUREMENTS

Plasma cortisol was measured by radioimmunoassay (RIA) in the 122 patients presenting after 1980, and by fluorimetry prior to this date.

RESULTS

In all the control subjects the sleeping midnight cortisol was < 50 nmol/l, below the lowest standard of the routine in-house RIA. In every patient with Cushing's syndrome the sleeping midnight cortisol was detectable with a value greater than 50 nmol/l, with a range of 70-2000 nmol/l. In contrast, in three cases, all of whom had proven Cushing's disease on histology, there was uncharacteristic complete suppression of plasma cortisol to < 50 nmol/l following the LDDST.

CONCLUSION

In this series of 150 cases, a single in-patient sleeping midnight cortisol above 50 nmol/l had a 100% sensitivity for the diagnosis of Cushing's syndrome, clearly different from normal subjects. In contrast, the low-dose dexamethasone suppression test had a sensitivity of 98% even when the drug was administered as an in-patient. We recommend that a low-dose dexamethasone suppression test should not be used alone for confirmation of Cushing's syndrome since it may miss 2% of cases.

Low circulating IGF-I levels in hyperthyroidism are associated with decreased GH response to GH-releasing hormone

OBJECTIVE

Several abnormalities in the GH response to pharmacological stimuli have been described in hyperthyroidism. Both normal and high serum IGF-I levels have been reported, as well as a decrease in IGF-I bioactivity. We have evaluated the GH response to GH-releasing hormone (GHRH) in hyperthyroid patients and the effects of hyperthyroidism on serum IGF-I levels. The possible relations between nutritional status, thyroid hormones and IGF-I levels were also investigated. We also studied the influence of long-term beta-adrenoceptor blockade on the GH response to GHRH in these patients.

DESIGN

In 18 hyperthyroid patients and in 12 control subjects, GHRH (100 micrograms) was administered as an i.v. bolus injection. Eight hyperthyroid patients and 8 control subjects received 50 micrograms GHRH i.v. Seven hyperthyroid patients were reevaluated after beta-adrenoceptor blockade. IGF-I and albumin levels were measured initially in all hyperthyroid patients and control subjects. Body composition was determined in 11 hyperthyroid patients and in a group of 33 matched normal controls.

PATIENTS

Hyperthyroid patients were compared to control subjects.

MEASUREMENTS

GH, TSH and free T4 were measured by immunofluorometric assay. IGF-I, total T3 and total T4 were measured by radioimmunoassay. Body composition was determined using a dual-energy X-ray absorptiometer.

RESULTS

The GH response to 100 micrograms GHRH in hyperthyroid patients was blunted compared to control subjects. The mean peak GH levels and the area under the curve were significantly lower in hyperthyroid patients compared to control subjects (11 +/- 1 vs 27 +/- 5 micrograms/l and 820 +/- 113 vs 1879 +/- 355 micrograms/l 120 min, respectively; P < 0.01). IGF-I levels were significantly reduced in hyperthyroid patients compared to controls (131 +/- 10 vs 201 +/- 16 micrograms/l, respectively; P < 0.01). Ideal body weight, serum albumin levels and the lean body mass were also reduced in hyperthyroid patients. After beta-adrenoceptor blockade there were no changes in the blunted GH response to GHRH in hyperthyroid patients.

CONCLUSION

Our data suggest that the blunted GH response to GHRH in hyperthyroidism is apparently not related to circulating IGF-I levels. It is possible that nutritional factors could play a role in the reduced circulating IGF-I levels found in these patients.

Molecular cloning of LSIRF, a lymphoid-specific member of the interferon regulatory factor family that binds the interferon-stimulated response element (ISRE)

Interferon regulatory factor (IRF) genes encode a family of DNA-binding proteins that are involved in the transcriptional regulation of type-I interferon and/or interferon-inducible genes. We report here the characterization of LSIRF, a new member of the IRF gene family cloned from mouse spleen by the polymerase chain reaction using degenerate primers. LSIRF was found to encode a 51 kDa protein that shares a high degree of amino acid sequence homology in the DNA-binding domain with other IRF family members. LSIRF expression was detectable only in lymphoid cells. In contrast to other IRF genes, LSIRF expression was not induced by interferons, but rather by antigen-receptor mediated stimuli such as plant lectins, CD3 or IgM crosslinking. In in vitro DNA binding studies, LSIRF was able to bind to the interferon-stimulated response element (ISRE) of the MHC class I promoter. The expression pattern and DNA binding activities suggest that LSIRF plays a role in ISRE-targeted signal transduction mechanisms specific to lymphoid cells.

Are activating mutations of the adrenocorticotropin receptor involved in adrenal cortical neoplasia?

The objective of this study was to investigate the presence of activating mutations of the ACTH receptor gene in benign and malignant adrenocortical tumours. Genomic DNA was extracted from a variety of adrenocortical neoplasms from 16 patients and the entire ACTH receptor gene was then amplified by the polymerase chain reaction and sequenced. No mutations were detected within the coding region of the ACTH receptor gene in the 16 adrenocortical tumours studied. It is likely that mutations of the coding region of the ACTH receptor gene do not play a major role in adrenocortical tumourigenesis.