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Biomedical subjects

A White

Publications and source records attributed to A White.

At least 235 records · Page 13Linked to original sources
PubMed1994

Differential release of proopiomelanocortin-derived peptides from the human pituitary: evidence from a panel of two-site immunoradiometric assays.

In humans, proopiomelanocortin (POMC) and the peptides derived from it have been individually identified in plasma under differing conditions. However, direct quantitative comparison has proved difficult because of the limitations of RIAs. Using a panel of monoclonal antibodies recognizing different regions of POMC, we have developed specific two-site immunoradiometric assays (IRMAs) for the ACTH precursors (POMC and pro-ACTH), ACTH, beta-lipotropin (beta LPH), beta-endorphin (beta EP), and the N-terminal POMC fragment (N-POC). We have quantified these peptides directly in plasma from normal subjects under basal conditions and in response to different regulatory factors. Basal levels of ACTH precursors, 5-40 pmol/L, were greater than or equal to ACTH, less than 0.9-11.3 pmol/L; N-POC, 5.6-16.8 pmol/L; beta LPH, 2.5-6.7 pmol/L; and beta EP less than or equal to 1.7 pmol/L. ACTH, N-POC, beta LPH, and beta EP levels increased in parallel in response to metyrapone (n = 8) and decreased in response to dexamethasone (n = 8), whereas ACTH precursor concentrations did not respond. After human CRH administration, peripheral concentrations of ACTH, N-POC, and beta LPH showed similar increments (median increment, 163%, 145%, and 172%, respectively; n = 6). POMC peptide responses to human CRH were also assessed in inferior petrosal sinuses draining the pituitary in 20 patients with pituitary-dependent Cushing's disease. In these patients, the increment in ACTH after CRH exceeded that in ACTH precursors by 4-fold (median, 459% and 96%). An increase in the ratios of ACTH/N-POC and ACTH/beta LPH was also apparent after CRH stimulation. The increment in beta EP after CRH always exceeded the increments in POMC and beta LPH. In summary, these data suggest that significant concentrations of ACTH precursors are present in the circulation of normal subjects, that ACTH precursors are not regulated in the same way as the processed POMC peptides, and that ACTH and beta EP are preferentially released from the pituitary in response to CRH.

Adrenocorticotropic Hormone↗
PubMed1994

Constitutive synthesis of 1,25-dihydroxyvitamin D3 by a human small cell lung cancer cell line.

One of 16 human small cell lung cancer cell lines examined was shown to synthesize a metabolite resembling 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. The NCI H82 line converted 25-hydroxyvitamin D3 (25OHD3) into a compound indistinguishable from 1,25-(OH)2D3 in 3 different high performance liquid chromatography systems. Electron impact mass spectra for the trimethylsilylethers of the metabolite and authentic 1,25-(OH)2D3 were indistinguishable. Binding to an anti-1,25-(OH)2D3 antibody was identical for the metabolite and authentic 1,25-(OH)2D3, whereas administration to rats in vivo caused equivalent stimulation of calcium transport measured in vitro in duodenal sacs. Activity of the H82 1 alpha-hydroxylase appears to be substrate dependent and is not stimulated by PTH, suggesting that it is similar to the enzyme expressed by activated macrophages and other cell types at extrarenal sites. Inhibition by ketoconazole indicates that, like the renal and extrarenal enzymes, the H82 enzyme is cytochrome P450 dependent. These data indicate that the H82 small cell lung cancer cell line constitutively expresses 25-hydroxyvitamin D3-1 alpha-hydroxylase and can synthesize 1,25-(OH)2D3.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1994

The phosphorylation pattern of insulin-like growth factor-binding protein-1 in normal plasma is different from that in amniotic fluid and changes during pregnancy.

We have determined the phosphorylation pattern of circulating insulin-like growth factor-binding protein-1 (IGFBP-1) in normal subjects and assessed how this changes in pregnancy. Two RIAs employing different monoclonal antibodies (MAbs 6303 or 6305) were used to measure IGFBP-1. In normal subjects, RIA 6303 measured 11-fold higher levels than RIA 6305 (72.8 vs. 6.6 micrograms/L; P < 0.008). However, in amniotic fluid (AF), the two assays gave similar results. Immunoprecipitation of plasma and AF with MAb 6303 and 6305 before nonsodium dodecyl sulfate-electrophoresis and Western ligand blotting revealed different IGFBP-1 isoforms and differential antibody recognition as the cause of this discrepancy. In AF, both MAbs precipitated nonphosphorylated and phosphorylated isoforms, whereas in plasma, only a single highly phosphorylated species, not seen in AF, was observed. This form of IGFBP-1 was precipitated by MAb 6303 only. During pregnancy, the phosphorylation state of IGFBP-1 in the maternal circulation was altered, as nonphosphorylated IGFBP-1 and three lesser phosphoforms were also observed. The appearance of these other variants resulted in a significant increase in IGFBP-1 measured by RIA 6305 (37, 51, and 83 micrograms/L in first, second, and third trimesters, respectively; P < 0.0005 vs. controls). The changes in IGFBP-1 phosphorylation induced by pregnancy may influence the modulatory effects of IGFBP-1 on IGF bioavailability and, hence, fetal growth.

Adult↗
PubMed1994

Secretion of adrenocorticotrophin (ACTH) and ACTH precursors in ovine anterior pituitary cells: actions of corticotrophin-releasing hormone, arginine vasopressin and glucocorticoids.

Although corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) have been extensively characterized as stimulators, and glucocorticoids as inhibitors of ACTH secretion, far less is known about the control of the secretion of ACTH precursors from the anterior pituitary or about the types of corticotrophs involved. The present study was designed to systematically evaluate the actions of stimulatory and inhibitory factors on the secretion of ACTH and ACTH precursors (pro-opiomelanocortin, M(r) 31,000; pro-ACTH, M(r) 22,000) from dissociated ovine anterior pituitary cells. The cells were stimulated for 3 h with CRH (10 nmol/l) and AVP (100 nmol/l), alone or in combination with the synthetic glucocorticoid dexamethasone. In designated wells, cells were treated with dexamethasone, (100 nmol/l), beginning 16-18 h before and continuing through the 3-h secretion experiments in the presence of CRH and AVP. Secretion of ACTH-like peptides from intact cultures was compared with that from cultures which had been pretreated with a cytotoxic CRH conjugate (cytotoxin) to eliminate CRH-target cells specifically. Immunoreactive (ir)-ACTH was measured by radioimmunoassay (RIA); ACTH(1-39) and ACTH precursors were specifically measured by two-site immunoradiometric assays that discriminate between the two. In intact populations of cells, dexamethasone had no effect on basal ACTH(1-39) secretion, but decreased the secretion of ACTH(1-39) in response to CRH or AVP. Pretreatment of cells in the same experiments with cytotoxin (for 18 h, beginning 3.5 days before secretion studies) also had no significant effect on basal ACTH(1-39) secretion, but eliminated the response to CRH and decreased the response to AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1994

O6-methylguanine-DNA methyltransferase in normal and malignant tissue of the breast.

An important component of high-dose chemotherapy/autologous bone marrow support regimens for adjuvant treatment of breast cancer is carmustine. Preclinical studies have shown that the level of the DNA repair protein O6-methylguanine-DNA methyltransferase is correlated with the resistance of cultured human tumor cells to this drug, but little is known about transferase levels of breast tissue in vivo. We measured the DNA repair activity in 80 tissue samples from 65 patients, including normal, abnormal, benign, and malignant specimens. Wide interindividual variations was observed and average transferase levels were similar in normal and benign tissue. However, transferase levels were significantly elevated in stage I-IV disease. In addition, the frequency of samples with no detectable transferase was greatly reduced in this malignant group, and transferase was positively correlated with the presence of positive nodes, a marker for disease progression. In contrast, transferase levels were not correlated with age or estrogen receptor status, and the levels in normal tissue did not vary between patients with benign or malignant disease. These results suggest that this DNA repair activity may be increased in breast cancer relative to normal tissue and encourage further study of the predictive value of transferase measurements in high-dose chemotherapy/autologous bone marrow transplant for breast cancer.

Adult↗
PubMed1993

A 4.5-megabase yeast artificial chromosome contig from human chromosome 13q14.3 ordering 9 polymorphic microsatellites (22 sequence-tagged sites) tightly linked to the Wilson disease locus.

We have previously performed a genetic analysis of multiply affected families to map a locus responsible for Wilson disease (WND) to a 0.3-centimorgan (cM) region within chromosome 13q14.3, between D13S31 and D13S59. Here we describe the construction of a contig of approximately 4.5 Mb, which spans this region and extends from D13S25 to D13S59. This contig consists of 28 genomic yeast artificial chromosome (YAC) clones. Five critical crossover events have been defined in this interval in two unaffected (Centre d'Etudes du Polymorphisme Humain) and three WND families. The combination of sequence tagged site content mapping of YACs with both polymorphic and nonpolymorphic markers and recombination breakpoint mapping resulted in the following order of polymorphic markers: centromere-RB1-D13S25-AFM205vh2-D13S31-D13S22 7-D13S228-AFM238vc3-D13S133- AFM084xc5-D13S137-D13S169, D13S155-D13S59-telomere. The recombination/physical distance ratio varies from approximately 3000 kb per cM in the region between D13S31 and D13S25 to 6000 kb per cM in the region between D13S31 and D13S59. Three WND families exhibiting recombination between the disease locus and D13S31 or D13S59 were genotyped for additional markers in this region and further refined the location of the WND gene to between D13S155 and D13S133. Nine of the markers in this region of < 1 cM are polymorphic microsatellites (seven have observed heterozygosities of 70% or above) that will be extremely useful in prenatal and preclinical diagnosis of this disease. This physical map is an essential step in the isolation of the WND gene and is a framework for the identification of candidate genes.

Base Sequence↗
PubMed1993

cGMP mobilizes intracellular Ca2+ in sea urchin eggs by stimulating cyclic ADP-ribose synthesis.

Many hormones or neurotransmitters act at cell surface receptors to increase the intracellular free calcium concentration, triggering a wide range of cellular responses. As the source of this Ca2+ is often internal stores, additional messengers are required to convey the hormonal message from the plasma membrane. Cyclic ADP-ribose (cADPR) has been proposed as the endogenous activator of Ca(2+)-induced Ca2+ release by the ryanodine receptor in sea urchin eggs and in several mammalian cell types. A second messenger role for cADPR requires that its intracellular levels be under the control of extracellular stimuli. Here we demonstrate a novel action of 3',5'-cyclic guanosine monophosphate (cGMP) in stimulating the synthesis of cADPR from beta-NAD+ by activating its synthetic enzyme ADP-ribosyl cyclase in sea urchin eggs and egg homogenates. We suggest that cADPR may transduce signals generated by cell surface receptors or gaseous transmitters linked to cGMP production.

Adenosine Diphosphate Ribose↗
PubMed1993

Amplification potential in preneoplastic and neoplastic Syrian hamster embryo fibroblasts transformed by various carcinogens.

Using a well-defined in vitro model system for neoplastic progression, we have examined two basic characteristics in the acquisition of amplification potential. Since Syrian hamster embryo fibroblasts can be transformed by a variety of methods (spontaneously, chemically, virally, or by transfection with oncogenes), we determined whether the method of transformation affects the capability of a cell to amplify. In addition, since variants can be isolated from cell populations as they progress toward tumorigenicity, we can monitor changes in amplification potential during this multistep process. We find that the capability to amplify is independent of the method of transformation and that the acquisition of this ability occurs in a defined step in the transformation process. In this model system, acquisition of amplification ability occurred concomitantly with the loss of tumor suppression function.

Animals↗
PubMed1993

Association of hormone-replacement therapy with various cardiovascular risk factors in postmenopausal women. The Atherosclerosis Risk in Communities Study Investigators.

BACKGROUND: Most epidemiologic studies of cardiovascular disease in postmenopausal women suggest that estrogen-replacement therapy has a protective effect. The effects of the use of estrogen combined with progestin are less well studied. METHODS: To examine the associations of hormone-replacement therapy with concentrations of plasma lipids and hemostatic factors, fasting serum concentrations of glucose and insulin, and blood pressure, we studied 4958 postmenopausal women participating in a population-based investigation. Using cross-sectional data, we classified the women into four groups according to their use of hormone-replacement therapy: current users of estrogen alone, current users of estrogen with progestin, nonusers who had formerly used these hormones, nonusers who had never used them. RESULTS: Current users had higher mean levels of high-density lipoprotein cholesterol, its subfractions high-density lipoprotein2 and high-density lipoprotein3, and apolipoprotein A-I than nonusers and lower mean levels of low-density lipoprotein cholesterol, apolipoprotein B, lipoprotein(a), fibrinogen, antithrombin III, and fasting serum glucose and insulin. However, current users of estrogen alone had higher triglyceride, factor VII, and protein C levels than either nonusers or current users of estrogen with progestin. After making certain assumptions, we estimated that the findings, if causal, would translate into a reduction of 42 percent in the risk of coronary heart disease in users of hormones as compared with nonusers. Women using estrogen with progestin would have an even greater estimated benefit. CONCLUSIONS: A randomized trial is needed to eliminate possible selection biases in our observational study that are related to the prescription of replacement hormones. Nevertheless, hormone-replacement therapy appears to be associated with a favorable physiologic profile, which probably mediates its protective effects on cardiovascular disease. The use of estrogen combined with progestin appears to be associated with a better profile than the use of estrogen alone.

Apolipoproteins↗
PubMed1993

Cerebrospinal fluid levels of substance P and calcitonin-gene-related peptide: correlation with sural nerve levels and neuropathic signs in sensory diabetic polyneuropathy.

1. Lumbar spinal substance P and calcitonin-gene-related peptide derive from spillage out of the dorsal horns associated with activity of small primary sensory afferents (C- and A delta-fibres). Cerebrospinal fluid and sural nerve levels of substance P and calcitonin-gene-related peptide have been measured in patients with diabetic polyneuropathy to determine whether differences in small primary sensory afferent activity are related to the presence or absence of painful symptoms. 2. Calcitonin-gene-related peptide was undetectable in the cerebrospinal fluid of the majority of diabetic patients (14 out of 22); it was lower overall in diabetic patients as compared with control subjects (P < 0.01), it was lower in those diabetic patients with painless neuropathy (100% undetectable) as compared with those with painful neuropathy (50% undetectable; P < 0.05) and it correlated conversely with warming threshold (r = 0.50; P < 0.01). 3. Substance P showed no overall numerical intergroup differences or correlation with other measured variables, but six diabetic patients as compared with one control subject had undetectable cerebrospinal fluid levels and the proportion of patients with undetectable levels was higher in the group with painless neuropathy than in the group with painful neuropathy (P < 0.05). 4. The levels of each peptide in cerebrospinal fluid correlated with its equivalent in sural nerve (P < 0.01 for calcitonin-gene-related peptide and P < 0.03 for substance P). Calcitonin-gene-related peptide correlated with substance P in the sural nerve (r = 0.84; P < 0.002) and in the cerebrospinal fluid (r = 0.30; P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcitonin Gene-Related Peptide↗
PubMed1993

Effect of cricoid pressure on ease of insertion of the laryngeal mask airway.

We have evaluated the effects of cricoid pressure on laryngeal mask airway (LMA) insertion after an elective rapid sequence induction in 100 patients allocated randomly to two groups. An attempt was made to insert the LMA after application of cricoid pressure in one group and with no pressure in the other. The anaesthetist was blinded to the application of cricoid pressure. Insertion was successful in 45 of 50 patients in the cricoid pressure group and in 49 of 50 patients in the non-cricoid group (P < 0.1) We discuss the implications of these findings for failed intubation in the nonfasted patient.

Adolescent↗
PubMed1993

Comparative myocardial imaging in the baboon with 123I-labelled ortho and para isomers of 15-(iodophenyl)pentadecanoic acid (IPPA).

The use of various animal models for researching radioiodinated fatty acid cardiac metabolism has been proven to be risky. This fact is here confirmed in the higher primate. Six baboons were injected on different occasions with 123I-labelled para and ortho isomers of 15-(iodophenyl) pentadecanoic acid (123I-pPPA and 123I-oPPA, respectively) for dynamic scintigraphy, followed by a Na123I injection at 30 min for blood background correction. Times for maximum myocardial tracer uptake (Tmax), and half-times of clearance (two phases T1/2(1) and T1/2(2)) from biexponential fitting of the time-activity curves proved statistically not different for pPPA and oPPA (P > 0.05). A repeat study at a later stage on the same baboons included pretreatment (2 h pretracer) with a carnitine palmitoyl transferase I inhibitor (Extomoxir; 10 mg kg-1) to block myocardial beta-oxidation. Time-activity curves with Tmax, T1/2(1) and T1/2(2) followed as above and were compared to the initial uninhibited values. Blocking of the carnitine shuttle was demonstrated by significantly increased retention of 123I-pPPA and 123I-oPPA. Thus both the tracers are beta-oxidized in the baboon myocardium, which is different in rat and human studies. In rats both isomers wash out from the myocardium, but 123I-oPPA is not metabolized. In humans the 123I-pPPA is beta-oxidized as with rats, but the 123I-oPPA is retained in the lipid pool of the myocardium. Simultaneous multiple consecutive gated blood pool studies (six of 1 min each) provided encouraging perfusion-related, background corrected images, and corresponding uptake information.

Animals↗
PubMed1993

The cellular and molecular basis of the ectopic ACTH syndrome.

In recent years the techniques of molecular and cellular biology have made it possible to begin to dissect the origins and behaviour of the ACTH-secreting tumour cell. It is becoming apparent that these tumours represent undifferentiated neuroendocrine cells, and it may be that their peptide-secreting properties may have no more sinister oncological significance. However, an autocrine role for beta-endorphin may confer a selective growth advantage on the POMC-expressing cell. It is still not clear why glucocorticoids fail to inhibit the POMC gene in these extra-pituitary tumours despite the presence of glucocorticoid receptors. This may not be resolved until the mechanism for inhibition of POMC by glucocorticoids in the normal pituitary is understood, although it is tempting to speculate that a mutation in the glucocorticoid receptor or a tissue specific interaction is responsible for the resistance of POMC observed in the ectopic ACTH syndrome. In studying the peptides secreted by the extra-pituitary tumours responsible for the ectopic ACTH syndrome it would appear that direct measurement of ACTH precursors and comparison with the circulating concentrations of ACTH can give valuable information on the percentage of tumours which do not effectively process the ACTH precursors. However, far more data have to be collected on patients with occult tumours in order to identify whether this type of processing is tissue specific. Nevertheless, these studies provide useful insights into the mechanisms of intracellular signalling and regulation in such tumours which may identify unique pharmacological tools to inhibit ACTH secretion or more importantly tumour growth.

ACTH Syndrome, Ectopic↗
PubMed1993

Adrenocorticotrophin and cortisol secretion in children after low dose cranial irradiation.

OBJECTIVE: We investigated the effect of low dose cranial irradiation (18-24 Gy) on spontaneous ACTH and cortisol secretion in children. DESIGN: We analysed 24-hour plasma ACTH and cortisol profiles sampled at 20-minute intervals. PATIENTS: Twenty long-term survivors of acute lymphoblastic leukaemia were studied and results compared with those in 14 normal children. MEASUREMENTS: ACTH and cortisol profiles were analysed by Fourier transformation and spectral analysis of stationarized data, autocorrelation and coherency analysis. RESULTS: The normal circadian rhythms of ACTH and cortisol were preserved in the children after cranial irradiation. The median 0900 h and midnight values were 1.50(0.8-6.4)pmol/l and 1.0(0.6-3.7)pmol/l respectively for ACTH and 282(48-1913)nmol/l and 57.5(44-637)nmol/l respectively for cortisol, and were not significantly different from those in the normal group. Fourier transformation revealed dominant periodicities for ACTH at 0.7-1.1 h, equivalent to 22-34 ACTH secretory bursts per 24 hours, and for cortisol at 0.7-1.1 h and 2-4.8 h. Similar results were found in the normal group. Coherency analysis indicated a significant shared periodicity of 0.7-1.2 h in nine children, corresponding to 20-34 related secretory bursts in 24 hours for ACTH and cortisol. After pooling the coherency spectra in the cranially irradiated group, comparison with the pooled data from the normal group revealed no significant difference between the two groups in the relationship between the two hormones. CONCLUSION: No significant disruption of spontaneous ACTH or cortisol secretion, either in the amount or pattern of hormones secreted, was found in children after low dose cranial irradiation (18-24 Gy).

Adolescent↗
PubMed1993

Isolated congenital ACTH deficiency: a cleavage enzyme defect?

The pro-opiomelanocortin (POMC) gene encodes adrenocorticotrophin (ACTH) which is derived from precursors by proteolytic cleavage. Congenital, isolated ACTH deficiency is rare but may be familial and fatal. The aetiology is unknown though defects at both hypothalamus and adenohypophysis have been postulated. We have studied a female presenting with hypoglycaemia in the neonatal period. When studied at 6 weeks of age, ACTH was unmeasurable even after injection of corticotrophin releasing hormone (CRH1-41). ACTH precursors, quantitated by two-site immunoradiometric assay, were clearly measurable prior to treatment and were stimulated by CRH1-41 and suppressed by glucocorticoid administration. Concentrations of POMC, N-terminal pro-opiocortin (N-POC) and beta-endorphin (beta-EP) were within the normal adult range during glucocorticoid replacement therapy; ACTH and beta-lipotrophin remained undetectable. The secretion of glucagon, measured by radioimmunoassay, in response to hypoglycaemia was normal. By sequencing polymerase chain reaction products from the patient's genomic DNA, the entire coding region of the POMC gene was established to be normal. The results are compatible with a cleavage enzyme defect.

Adrenal Cortex↗