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Biomedical subjects

R H Buck

Publications and source records attributed to R H Buck.

At least 19 recordsLinked to original sources
PubMed1998

Molecular diagnosis of multiple endocrine neoplasia type 2A.

OBJECTIVE: To identify by means of genetic analyses individuals who are at risk of developing medullary thyroid cancer that is a component of multiple endocrine neoplasia. SUBJECTS: A three-generation kindred with clinically and biochemically diagnosed medullary thyroid cancer. METHOD: Identification of a heterozygote mutation by nucleic acid sequencing and restriction analyses. RESULTS: A heterozygote T-->C (Cys-->Arg) mutation at codon 618 in exon 10 of the RET proto-oncogene was identified in 4 family members who had previously been diagnosed with medullary thyroid cancer. The same mutation was also found in one of the proband's presymptomatic children who subsequently underwent a pre-emptive thyroidectomy. The genetic diagnosis was confirmed by histology. No mutations were detected in any other family members. CONCLUSION: Identification of heterozygote germline mutations in multiple endocrine neoplasia is direct, highly accurate and cost-effective. This study demonstrates that, appropriately used, molecular diagnosis can supersede conventional biochemical methods in the management of patients with inherited cancers.

Adult↗
PubMed1992

The microchemical detection of carbonic anhydrase in corneal epithelia.

Carbonic anhydrase (CA) activity has been detected and quantified in the corneal epithelia of various mammalian species using a microchemical assay. The highest levels were found in the rabbit, followed by man, dog, sheep, and cat. Enzyme levels in the rabbit epithelium were approximately one-third the amount found in the endothelium, perhaps explaining earlier failures to find CA in the epithelium. Selective inactivation of CA-II in tissue homogenates with bromopyruvic acid allowed determination of CA-I/CA-II ratios. The ratios in corneal epithelia from two species (rabbit and dog) approximated that in the erythrocyte. Although CA levels in the epithelium are low they are perhaps functional in the transfer of CO2 across the cornea.

Animals↗
PubMed1992

Influence of ion pairing salts on the transcorneal permeability of ionized sulfonamides.

The effects of cationic ammonium, phosphonium, and arsonium ion pairing salts as well as anionic organic and inorganic salts on the transcorneal permeability of ionized sulfonamide carbonic anhydrase inhibitors have been studied in the excised rabbit cornea. Benzolamide, trichloromethazolamide (TCM), MK-927, and quaternary ammonium sulfonamide (QAS) were examined. The enhancement in the first-order rate constants (k(in)) for the first compound in the presence of pairing salts was as much as 15 times the basal rate, with smaller increases seen with the remaining three drugs. Ion pairing salts may represent a means for enhancing the transcorneal permeability of highly ionized drugs.

Animals↗
PubMed1991

Animal test or chromatography? Validated high-performance liquid chromatographic assay as an alternative to the biological assay for ornipressin.

Ornipressin is a peptide drug which is usually assayed by a test on live rats. In order to reduce the animal experiments an alternative method was developed which uses gradient high-performance liquid chromatography (HPLC) on reversed-phase. The HPLC method was validated and shown to be selective and precise. Correlation studies were performed on samples of different dosage strengths and on thermally degraded samples, showing good correlation with the results obtained by the biological assay. The HPLC method was applied on various batches of ornipressin in bulk and in pharmaceutical preparations. HPLC is a rapid and inexpensive method which can replace the animal assay. A new quality control concept is proposed which uses HPLC for the analysis of ornipressin in bulk and in pharmaceutical preparations. With this concept animal testing can be reduced by 90%.

Amino Acid Sequence↗
PubMed1990

Detection of a small molecular species of human chorionic gonadotropin in the urine of patients with carcinoma of the cervix and cervical intraepithelial neoplasia: comparison with other assays for human chorionic gonadotropin and its fragments.

A low-molecular-weight glycoprotein containing sequences of the beta subunit of human chorionic gonadotropin (hCG) has been found in the urine of patients with carcinoma of the cervix using an immunoradiometric assay. This fragment has chromatographic and immunological identity with hCG beta core. This molecule was present in 52 to 77% of all patients with invasive disease, while between 11 and 27% of patients with cervical intraepithelial neoplasia (CIN) also exhibited significant hCG beta-core immunoactivity. Few patients had either a positive assay for intact hCG or a positive assay directed at an epitope on the beta subunit (beta-hCG radioimmunoassay) in serum. However, between 17 and 40% of patients with invasive disease were positive for free beta-subunit immunoactivity in the blood. The origin of the beta-core immunoactivity in the urine is uncertain; while tumor production cannot be excluded, it is possible that the molecule originates from renal metabolism of small quantities of the beta subunit of hCG. Regardless of the source of the molecule, hCG beta core is a far more sensitive marker of hCG production by tumors than is serum hCG.

Carcinoma↗
PubMed1990

A validated HPLC assay for salmon calcitonin analysis. Comparison of HPLC and biological assay.

A high-performance liquid chromatographic (HPLC) method is described for the assay of salmon calcitonin. The method uses a 5-microns octadecasilyl silica column (100 x 4.6 mm) at 50 degrees C and an initial mobile phase (flow rate 1 ml min-1) comprising 35% of B (1 M tetramethylammonium hydroxide-water-acetonitrile, 8:392:600) and 65% of A (1 M tetramethylammonium hydroxide-water-acetonitrile, 20:880:100) with linear gradient elution over 21 min to a final mobile phase of 57% B; solutions A and B are adjusted to pH 2.5 with phosphoric acid. Detection was by UV spectrophotometry at 210 nm. The method has been shown to be selective, precise and rapid and, in a collaborative study to give excellent correlation with the results obtained by using the biological assay method of the European Pharmacopoeia. The method, which has been applied successfully to the assay of different batches of salmon calcitonin in bulk drug and in formulated products, is recommended for adoption as the pharmacopoeial assay method.

Amino Acid Sequence↗
PubMed1990

Measurement of human chorionic gonadotrophin (hCG): indications and techniques for the clinical laboratory.

The structure of human chorionic gonadotrophin (hCG) is so similar to that of luteinizing hormone (LH) that a variety of assay techniques have been devised to differentiate between these two hormones. The principal indications for measurement of hCG using these methods have not changed greatly over the past decade but the improvements in the sensitivity, specificity and the development of assays for free subunits and metabolic fragments have expanded the use of hCG assays. The review discusses the use of hCG measurement in a routine clinical immunoassay laboratory and emphasizes different requirements for clinical situations.

Amino Acid Sequence↗
PubMed1990

Isolation of (4R)-4-[(E)-2-butenyl]-4-methyl-L-threonine, the characteristic structural element of cyclosporins, from a blocked mutant of Tolypocladium inflatum.

By mutagenic treatment of a strain of Tolypocladium inflatum, a cyclosporin non-producing mutant was obtained which accumulated the characteristic building unit of cyclosporins, (4R)-4-[(E)-2-butenyl]-4-methyl-L-threonine (abbreviation Bmt; systematic name: (2S,3R,4R,6E)-2-amino-3-hydroxy-4-methyl-6-octenoic acid) in free form. The isolation from a culture filtrate was performed by extraction, chromatographic separation and final crystallization from methanol - water. The structure and stereochemistry of this amino acid was determined by chemical transformation and correlation to dihydro-MeBmt, with known chirality [(2S,3R,4R)-3-hydroxy-4-methyl-2-methylamino-octanoic acid], obtained by hydrolysis of dihydrocyclosporin A.

Chemical Phenomena↗
PubMed1990

The incidence of hyponatremia during prolonged ultraendurance exercise.

Recent studies have shown that potentially fatal hyponatremia can develop during prolonged exercise. To determine the incidence of hyponatremia in athletes competing in ultradistance events, we measured serum sodium levels in 315 of 626 (50%) runners who were treated for collapse after two 90 km ultramarathon footraces (total starters 20,335; total finishers 18,031) and in 101 of 147 (69%) finishers in a 186 km ultratriathlon. In both races the athletes drank fluids with low sodium chloride content (less than 6.8 mmol.l-1). Hyponatremia (serum sodium level less than 130 mmol.l-1) was identified in 27 of 315 (9%) collapsed runners in the 90 km races and in none of the triathletes. In response to diuretic therapy, the runner with the most severe hyponatremia (serum sodium level = 112 mmol.l-1) excreted in excess of 7.5 l dilute urine during the first 17 h of hospitalization. These data suggest that, although symptomatic hyponatremia occurs in less than 0.3% of competitors during prolonged exercise even when they ingest little sodium chloride, it is found in a significant proportion (9%) of collapsed runners. A regulated contraction of the extracellular fluid volume would explain why the majority of athletes maintain normal serum sodium levels even though they develop a significant sodium chloride deficit during prolonged exercise. Alternatively, sodium chloride losses during prolonged exercise may be substantially less than are currently believed. Physicians treating collapsed ultradistance athletes need to be aware that as many as 10% or more of such patients may be hyponatremic.

Exercise↗
PubMed1989

Comparison of human chorionic gonadotrophin concentrations in the sera of patients with normal and abnormal pregnancy measured by radio-immunoassay and immunoradiometric assay.

Human chorionic gonadotrophin (HCG) concentrations were measured in the serum of 40 patients with normal pregnancy, 18 with ectopic pregnancy, 36 with incomplete abortions and 24 patients with gestational trophoblastic disease using a radio-immunoassay (RIA) and immunoradiometric assay (IRMA). There were no significant differences in HCG concentrations measured by the two assays with regard to the first three groups but the patients with gestational trophoblastic disease had consistently higher results on RIA, probably reflecting increased circulating free beta-subunit of HCG. It was concluded that measurement of HCG using IRMA for the intact molecule gives equivalent results to RIA in patients with normal and ectopic pregnancy as well as after abortion. However, monitoring of patients with choriocarcinoma and hydatidiform mole requires an assay that detects free beta-HCG.

Chorionic Gonadotropin↗
PubMed1988

Serum progesterone in the diagnosis of ectopic pregnancy: a valuable diagnostic test?

The value of a single serum progesterone (P) assay in the diagnostic work-up of suspected ectopic pregnancy was investigated in 89 patients with ectopic pregnancy and 27 patients with incomplete abortion. Reference values for P in the blood were obtained from 77 patients with normal intrauterine pregnancies in the first trimester. With the use of a discriminatory level of 63 nmol/l (20 ng/ml), sensitivity of 92%, specificity of 84%, positive predictive index of 90%, and negative predictive index of 87% were achieved. Addition of pelvic ultrasound further improved the diagnostic accuracy. It is concluded that serum P measurement offers a valuable adjunct to existing methods of diagnosis of ectopic pregnancy.

Biomarkers↗
PubMed1988

Impaired corpus luteum function in ectopic pregnancy cannot be explained by altered human chorionic gonadotropin.

We studied the cause of the low serum progesterone, 17 beta-estradiol, and 17-hydroxyprogesterone levels that occur in women with an ectopic pregnancy. Only women who had been amenorrheic for less than 8 weeks were studied in order to assess corpus luteum rather than placental biosynthesis of these steroids; each woman with an ectopic pregnancy was matched to a woman with a normal intrauterine pregnancy on the basis of serum intact hCG levels within 10% of one another to obviate the influence of different levels of this luteotropic hormone. Every woman with an ectopic pregnancy had lower serum progesterone, estradiol, and 17-hydroxyprogesterone levels than her matched normal pregnant pairmate (median values: progesterone, 27.9 vs. 83.5 mmol/L; estradiol, 0.36 vs. 1.79 nmol/L; 17-hydroxyprogesterone, 4.95 vs. 22.1 nmol/L, respectively; all P less than 0.002). The ratios of intact hCG, measured by immunoradiometric assay, to hCG, measured by a hCG beta-specific RIA, were similar in the two groups. Serum hCG bioactivity was assayed by measuring the ability of serum to stimulate testosterone secretion from mouse Leydig cells. The mean biological to intact immunological hCG ratios were 2.06 +/- 1.39 (+/- SD) for ectopic pregnancy and 1.91 +/- 0.81 for normal pregnancy (P greater than 0.05). The biological hCG to immunoreactive hCG beta ratios were 1.98 +/- 0.75 and 2.02 +/- 0.82, respectively. Serum hCG from both groups of women stimulated cAMP generation by testicular cells similarly. We conclude that the lower serum steroid levels in women with ectopic pregnancy cannot be explained by altered hCG bioactivity. The lower steroid levels may thus reflect a primary defect of the corpus luteum, absence of another stimulator of ovarian steroid biosynthesis, or more subtle alterations in hCG glycosylation which are important in vivo but not assessed by the in vitro bioassay.

Animals↗
PubMed1988

Blood or urine measurement of human chorionic gonadotropin for detection of ectopic pregnancy? A comparative study of quantitative and qualitative methods in both fluids.

One hundred seventy-five patients with features of ectopic pregnancy were studied, of whom 95 were subsequently shown to have an ectopic pregnancy. Paired blood and urine samples were assayed for human chorionic gonadotropin (hCG) by two radioimmunoassays, one immunoradiometric assay for intact hCG and an immunoradiometric assay for free beta subunit that also detects the "beta core" of hCG in urine. Qualitative testing was also performed using the Tandem Icon method of immunoconcentration on a membrane. The quantitative results for intact hCG showed an approximately unitary relationship between concentrations in both fluids, with a close correlation (r = 0.84, gradient = 1.01). The qualitative tests for hCG in both serum and urine were positive in all patients with ectopic pregnancy. The Tandem Icon is equally useful in blood and urine, whereas quantitative assays are more reliable in the blood. Quantitation of urinary hCG is not recommended because of the variable dilution of the glycoprotein in this fluid.

Abortion, Incomplete↗
PubMed1987

High-performance liquid chromatographic determination of enantiomeric amino acids and amino alcohols after derivatization with o-phthaldialdehyde and various chiral mercaptans. Application to peptide hydrolysates.

o-Phthaldialdehyde in combination with a chiral mercaptan is a powerful chiral reagent for the pre-column derivatization of many enantiomeric compounds bearing primary amino groups. The diastereoisomers formed can efficiently be resolved on conventional reversed-phase columns. Simultaneous determination of the enantiomers of various amino acids, amino alcohols and biogenic amines was achieved by gradient elution and fluorescence detection. The resolution was optimized by varying the chiral mercaptan in the reagent, Boc-L-cysteine, N-acetyl-L-cysteine and N-acetyl-D-penicillamine being used for this purpose. The resolutions were calculated. Most of the enantiomers showed good resolution with each of the three chiral mercaptans, whereas some enantiomers were only separable by one or two of them. The method was applied to the analysis of peptide hydrolysates. The composition of peptides bearing L- and D-amino acids and an amino alcohol was determined.

Amino Acids↗
PubMed1987

Detection of urinary human chorionic gonadotropin by rapid immunoconcentration method is the first-line test for suspected ectopic pregnancy.

Nine hundred nine patients with suspected ectopic pregnancy were tested for human chorionic gonadotropin (hCG) using two qualitative assays: the Tandem Icon urine assay (Hybritech, San Diego, CA) and a serum radioimmunoassay (RIA) employing a positive cut-off of 25 IU/l. Pregnancy status was determined by clinical or histologic examination, or detection of hCG or its metabolites in four quantitative immunoassays: two RIAs and two immunoradiometric assays (IRMAs). Both the Tandem Icon and the qualitative RIA detected all 71 patients with ectopic pregnancy. The predictive indices of the Icon were 100% for a positive result and 99.6% for a negative result, and those of the RIA were 96.7 and 99.6%, respectively. The Tandem Icon thus fulfils the need for a simple, rapid, and sensitive method for hCG in the detection of patients with suspected ectopic pregnancy.

Chorionic Gonadotropin↗
PubMed1987

Bedside application of an ultrasensitive urine test for HCG in patients with suspected ectopic pregnancy.

One hundred and seven patients with suspected ectopic pregnancy were tested for HCG at the bedside using the Tandem Icon. The test was performed by ward doctors with no formal laboratory experience. The patients were managed conservatively or by surgery as dictated by the clinical picture and the Icon test result. Retrospective categorisation of the 107 patients by laboratory analysis and clinical outcome showed that 21 were pregnant (17 ectopic, 4 intrauterine) and 86 non-pregnant. At the bedside the Icon was reported as negative in one pregnant patient and three patients who were not pregnant were found to give Icon-positive results. In the laboratory the Icon correctly categorised all patients. Three of the four discrepant results were found to be a direct result of the operator's inexperience in analytical procedure and interpretation. The Tandem Icon HCG urine assay can reliably be used at the bedside of patients with suspected ectopic pregnancy provided that the operator has had sufficient experience in its use.

Chorionic Gonadotropin↗
PubMed1987

Relationship between blood and urine concentrations of intact human chorionic gonadotropin and its free subunits in early pregnancy.

Paired blood and urine samples were obtained from patients between the sixth and 14th weeks of normal pregnancy. The levels of intact human chorionic gonadotropin (hCG), and of the free alpha and beta subunits, were measured by specific immunoassays. There was a close association between blood and urine levels of intact hCG and of the alpha subunit of hCG, but no relation between the levels of beta subunit in these sites. These findings suggest that the use of "beta subunit" assays may give discrepant results according to the fluid examined. By contrast, measurement of intact hCG appears to give similar results in blood and urine.

Chorionic Gonadotropin↗