Biomedical subjects

R D Brown

Publications and source records attributed to R D Brown.

At least 325 records · Page 18Linked to original sources

PubMed1984

Chemical characterization of psoralens used in the National Toxicology Program research projects.

Chemical analyses of 4 psoralen derivatives were performed with the use of various techniques, including thin-layer chromatography, gas chromatography, infrared and nuclear magnetic resonance spectroscopy. 8-Methoxypsoralen, 5-methoxypsoralen, 3-carbethoxypsoralen, and 5-methylisopsoralen were determined to be 99, 93, 97, and 99% pure, respectively. A 7% contaminant in the 5-methoxypsoralen sample was identified as a dimethoxypsoralen isomer. These psoralens are being used in research projects sponsored by the National Toxicology Program.

5-Methoxypsoralen↗

PubMed1983

Nicarbazin complex yields dinitrocarbanilide as ultrafine crystals with improved anticoccidial activity.

Nicarbazin, a drug used to control the protozoal disease coccidiosis in poultry, is a complex of the highly insoluble drug 4,4'-dinitrocarbanilide with 2-hydroxy-4,6-dimethylpyrimidine. The structures of this and other 4,4'-dinitrocarbanilide complexes have not been determined, but an analogous 2:1 complex of 4,4'-dinitrodiphenylamine with 1,4-diacetylpiperazine has been prepared in which the only possible bonds are hydrogen bonds between the amide carbonyls and amino hydrogens. Scanning electron microscopy revealed that micron-size crystals of nicarbazin disintegrate in water to form much smaller dinitrocarbanilide crystals. Similar complex dissolution in the gut of poultry may account for the greater effectiveness of dinitrocarbanilide when administered as complexed rather than uncomplexed drug. Particle size problems associated with other highly insoluble drugs and pesticides may be resolved by the use of nicarbazin-like complexes.

Animals↗

PubMed1983

Stoichiometry of manganese and calcium ion binding to concanavalin A.

Using measurements of solvent nuclear (proton) magnetic relaxation dispersion (NMRD), we have previously shown that concanavalin A (Con A) can exist in two conformational forms and that, in the absence of Ca2+, Mn2+ can bind to both the S1 and S2 sites of each monomer of Con A of at least one conformer [Brown, R.D., III, Brewer, C.F., & Koenig, S.H. (1977) Biochemistry 16, 3883-3896]. Recently other investigators have claimed that the stoichiometry of Mn2+ binding to Con A is only 1:1 for this conformational state, both in the absence and presence of saccharide; the same was claimed for Ca2+ under similar conditions. We now present titration and equilibrium dialysis experiments, both in the absence and presence of saccharide, using NMRD and atomic absorption spectroscopy, to investigate the stoichiometry of Mn2+ and Ca2+ binding to Con A. We have extended the NMRD method to include the determination of the total concentration of Mn2+ in samples of Con A. This, coupled with our previous use of NMRD to measure the concentration of free Mn2+ in protein solutions as well as the distribution of bound Mn2+ among different sites, allows us to measure the stoichiometry of binding with precision. We reconfirm that, at equilibrium in the presence of excess Mn2+, the binding stoichiometry of Mn2+ to Con A is 2:1, both in the absence and presence of saccharide. Addition of Ca2+ to a solution of Mn2+-Con A results in stoichiometric displacement of Mn2+ from the S2 site under the conditions investigated. Under nonequilibrium conditions, Mn2+ forms a metastable binary complex with the protein that persists for days at 5 degrees C. We also report, for the first time, values for all of the dissociation constants of binary and ternary complexes of Mn2+ with both conformations of Con A in solution. Atomic absorption measurements also indicate that Ca2+, in the absence of Mn2+, binds to both S1 and S2 sites in the absence and presence of saccharides.

Calcium↗

PubMed1983

Kinetics of conformational transitions of demetalized Concanavalin A.

Demetalized Concanavalin A exists in two conformational states, known as locked (PL) and unlocked (P) [Brown et al., Biochemistry 16, 3883 (1977)]. The equilibrium ratio [PL]/[P] is 0.14 +/- 0.01 at 25 degrees C, pH 6.4 [Brown et al., Biochemistry 21, 465 (1982)]. We now report values of the rate constants for the P in equilibrium; k1 = (33 +/- 4 h)-1 and k-1 = (4.6 +/- 0.6 h)-1 for the P leads to PL and PL leads to P transitions, respectively, at 25 degrees C, pH 6.4. The experiments utilize the fact that saccharide binds to PL [Koenig et al., Biochemistry 17, 4251 (1978)], producing a time-dependent increase in the total concentration of locked forms at equilibrium, and use a new technique for measuring this concentration.

Chemical Phenomena↗

PubMed1983

Kinetic analysis of bacterial clearance in mice using the ESTRIPc and KINET microcomputer programs.

Two BASIC microcomputer programs, ESTRIPc and KINET, were used to analyze the kinetics of bacterial clearance from the blood and mesenteric lymph nodes of mice. Because of the similarities between the clearance of bacteria and the clearance of drugs from tissue, blood pharmacokinetic techniques were applied to the analysis of bacterial clearance data. The ESTRIPc program, developed for pharmacokinetic analysis and modified for the study of bacterial clearance, was employed to fit the experimental data of bacterial survival versus time to a polyexponential equation with 1, 2, or 3 terms. The KINET program, written specifically for kinetic analysis of bacterial clearance, uses the biexponential equation constants derived with ESTRIPc to calculate half-life values, rate constants, and other useful kinetic parameters. The combined use of these programs permits precise comparisons of the clearance rates of different bacterial species from the blood or tissues of experimental animals.

Animals↗

PubMed1983

The use of peripheral blood feeder layers as a source of GM-CSF for human bone marrow cultures.

The use of peripheral blood feeder layers as a source of stimulus for colony formation by human granulocytic progenitor cells in semi-solid agar cell cultures was examined. Comparison with various conditioned media demonstrated that cultures stimulated by peripheral blood feeder layers produced the greatest number and largest colonies. The cell concentration in the feeder layers was more important than the total cell number. Feeder layer plates containing 2 X 10(5) cells at a concentration of 1 X 10(6) cells/ml proved to be just potent as the conventional feeder layer plates containing 1 x 10(6) cells/ml in 1 ml. Thus feeder layer plates can be more economical in terms of cell numbers than has previously been reported. By using a known panel of donors for the leukocytes, the number of sub-optimal batches of feeder layers was reduced. Addition of 1 microM adenosine 3':5'-cyclic-monophosphate or 10 micrograms/ml Li2CO3 to poor feeder layers enhanced their colony-stimulating ability.

Bone Marrow Cells↗

PubMed1983

Aging and aldosterone.

We measured urinary and plasma aldosterone in normal subjects, aged 20 to 59 years, during a period of unrestricted sodium intake and after sodium depletion, using furosemide or a 20 meq sodium diet. Before and after sodium depletion, the mean and the upper limit of the range of urinary aldosterone excretion were considerably lower in subjects over 50 years compared with subjects under 30 years. Aging had no effect on plasma aldosterone concentration when the subjects were on an unrestricted sodium diet and blood was sampled while they were recumbent. In contrast, when the subjects were upright, both before and after sodium depletion, the mean and the upper limit of the range of plasma aldosterone concentration were lower in the subjects over 50 years compared with those under 30 years. The metabolic clearance of aldosterone was the same in the younger and the older subjects. Of eight patients over 40 years of age with aldosterone-producing adenoma, four had normal aldosterone excretion rates when the normal range was not age adjusted, but with age adjustment, all of the patients had clearly elevated excretion rates. Similarly, six of seven patients over 40 years of age had normal upright plasma aldosterone concentrations if the normal range of plasma aldosterone concentration was not age adjusted. We conclude that aldosterone secretion declines with advancing age. The effect of age on aldosterone secretion is an important consideration when evaluating older hypertensive patients for primary aldosteronism.

Adenoma↗

PubMed1983

Thyroxine levels and antler growth in white-tailed deer.

1. Five normal male, 5 female, and 3 castrated fawns and 5 adult male white-tailed deer were housed in individual pens for one year to compare the relationships between thyroxine (T4) and other blood parameters and the antler cycle. 2. Biweekly serum samples were examined for T4 titers and levels of serum calcium (Ca), inorganic phosphorus (P), and alkaline phosphatase activity (AP). 3. Seasonal T4 changes were found in all deer groups, with elevated titers in the fall. Female fawns had overall lowered T4 levels. In male fawns and adult bucks, T4 seemed to play a synergistic role in antler initiation and growth. 4. Serum Ca levels remained constant throughout the year, but with lower levels in the female fawns. 5. Serum P levels were also constant seasonally, but with higher levels in the female fawns. There was no age effect on either Ca or P. 6. An age effect was evident on plasma alkaline phosphatase with lower activity in adult bucks. There was no sex effect on AP activity. 7. T4 might have an indirect association with the enzyme AP in Ca and P transport system in white-tailed deer.

Alkaline Phosphatase↗

PubMed1983

Hormone levels and antler development in white-tailed and sika fawns.

Overall mean values of testosterone (T), androstenedione (A), thyroxine (T4), calcium (Ca), phosphorus (P), and alkaline phosphatase (AP) were (T) 2.56 +/- 2.44 ng/ml, (A) 3.16 +/- 2.58 ng/ml, (T4) 8.22 +/- 4.18 micrograms/dl, (Ca), 10.88 +/- 0.65 mg%, (P) 8.03 +/- 0.68 mg%, and (AP) 81.89 +/- 19.45 IU/l in white-tailed fawns and (T) 3.69 +/- 2.76 ng/ml, (A) 18.26 +/- 17.58 ng/ml, (T4) 4.41 +/- 1.59 micrograms/dl, (Ca) 10.08 +/- 0.80 mg%, (P) 9.42 +/- 1.69 mg% and (AP) 95.35 +/- 22.65 IU/l in sika fawns. High T titers correlated with antler button growth, and A titers peaked as buttons hardened in both groups. Higher T4 levels in late fall and early winter may have had a synergistic role for button growth in both groups. Generally higher P levels in sika fawns and relatively higher Ca levels in white-tailed fawns might be species dependent. However, relatively constant Ca and P in both groups represented mineral homeostasis. The mineralization role of AP activity was evident in both groups.

Alkaline Phosphatase↗

PubMed1983

Water exchange at the active site of carbonic anhydrase. A synthesis of the OH- and H2O-models.

We have measured the paramagnetic contribution to the magnetic relaxation rate of solvent protons in highly purified, buffer- and salt-free solutions of Co(2+)-substituted human carbonic anhydrase B (HCAB), as a function of pH in the range 5.5-10 and as a function of magnetic field. We have also measured the optical absorption at 640 nm to characterize the enzyme. The relaxation rates vary with pH much as does the CO(2) hydration activity, increasing with increasing pH. We find that the relaxation rates at all intermediate values of pH can be described as linear combinations of the rates obtained at the extremes of pH used, indicating the existence of low- and high-pH forms of the enzyme with pH-dependent concentrations. The optical data can be similarly represented. The fraction of high-pH form present, determined from either the relaxation or optical data, has a pK(a) of approximately 7.6 when approximated by a single ionization. The data are very similar to that for HCAB in the presence of buffer, in contrast to the bovine enzyme for which the pK(a) is affected substantially by the presence of sulfate. Previous analysis of the high relaxation rates at high pH indicated rapid exchange of Co(2+)-liganded protons, possible only if these exchanging protons were conveyed by water molecules. On the other hand, the present demonstration of the existence of two forms of HCAB in highly purified solutions, coupled with other data, argues strongly for ionization of a water molecule ligand of the metal ion at the active site, with OH(-) as the solvent-donated ligand at high pH. We propose a mechanism of ligand exchange at high pH that reconciles these ostensibly conflicting requirements by invoking a pentacoordinate intermediate having both OH(-) and H(2)O as ligands. Proton exchange can be rapid between these ligands because charge transfer without net ionization can occur, so that the leaving water can carry away the initial OH(-). The low-pH form is a thermal mixture of tetra- and pentacoordinate species, the latter having low relaxation rates by analogy with inhibitor derivatives of the enzyme and model systems. The proposed associative ligand-exchange mechanism reconciles the distinctions between the OH- and H(2)O-models of carbonic anhydrase by merging them, providing the first model is consistent with the observed pH dependence of hydration activity, optical absorption, and solvent magnetic relaxation.

Binding Sites↗

PubMed1983

Antihypertensive and metabolic effects of a new converting enzyme inhibitor, enalapril.

Thirty-one men with mild, uncomplicated essential hypertension were studied for 18 wk in a double-blind, placebo-controlled, randomized clinical trial. Those whose supine diastolic pressure was 90 to 104 mm Hg after 4 wk of placebo were randomly assigned to three groups. Group I (11 subjects) initially received one 10-mg enalapril capsule in the morning and one placebo capsule in the evening. Group II (10 subjects) received one 5-mg enalapril capsule twice daily. Group III (10 subjects) received one placebo capsule twice daily. Drug dosages were doubled and then quadrupled in all groups at wk 8 and 12. Metabolic, ophthalmologic, and audiometric studies were done on all subjects at wk 2, 4, 8, 12, and 16. Enalapril lowered diastolic pressure in the supine and upright positions in single and divided doses. Its antihypertensive effect was dose dependent, and it was greater in white patients than in black patients. The drug was well tolerated by all subjects and did not cause clinical or metabolic complications. It is concluded that enalapril is effective in lowering the arterial pressure in single and divided daily doses; its effect is dose dependent and is greater on the diastolic arterial pressure than on the systolic pressure; and it is well tolerated.

Adult↗

PubMed1983

Metal ion binding and conformational transitions in concanavalin A: a structure-function study.

The affinity of the lectin Concanavalin A (Con A) for saccharides, and its requirement for metal ions such as Mn2+ and Ca2+, have been known for about 50 years. However the relationship between metal ion binding and the saccharide binding activity of Con A has only recently been examined in detail. Brown et al. (Biochemistry 16, 3883 (1977)) showed that Con A exists as a mixture of two conformational states: a "locked" form and an "unlocked" form. The unlocked form of the protein weakly binds metal ions and saccharide, and is the predominate conformation of demetallized Con A (apo-Con A) at equilibrium. The locked form binds two metal ions per monomer with the resulting complex(es) possessing full saccharide binding activity. Brown and coworkers measured the kinetics of the transition of the unlocked form to the fully metallized locked conformation containing Mn2+ and Ca2+. They also demonstrated that Mn2+ alone could form a locked ternary complex with Con A, and that rapid removal of the ions resulted in a metastable form of apo-Con A in the locked conformation which slowly (hours at 25 degrees C) reverted back to (predominantly) the unlocked conformation. The ability to form either conformation in the absence or presence of metal ions has thus allowed us to explore the relationship between metal ion binding and conformational transitions in Con A as determinants of the saccharide binding activity of the lectin. Based on the kinetics of the transition of unlocked apo-Con A to fully metallized locked Con A, and X-ray crystallographic data, it appears that the transition between the two conformations of Con A involves a cis-trans isomerization of an Ala-Asp peptide bond in the backbone of the protein, near one of the two metal ion binding sites. The relatively large activation energy for the transition (approximately 22 kcal M-1) results in relatively slow interconversions between the conformations (from minutes to days), whereas the equilibria with metal ions and saccharide are rapid. Thus, many metastable complexes can be formed and a variety of transition pathways between the two conformations studied. We have identified and characterized binary, ternary, and quaternary complexes of both conformations of Con A containing Mn2+ and saccharide, and have determined both metal ion and saccharide dissociation constants for all of them, as well as equilibrium and kinetic values for the conformational transitions between them.(ABSTRACT TRUNCATED AT 400 WORDS)

Carbohydrates↗

PubMed1983

In vitro clonogenic assays in selective neutropenia.

Granulocyte-monocyte colony forming cell (GM-CFC) concentration and the proportion of GM-CFC in DNA synthesis (S) were determined in 43 patients with varying degrees of selective neutropenia, including 5 patients who were normal extremes (2.0-2.5 x 10(9) neutrophils/1), to study the diagnostic and prognostic significance of clonogenic assays and to determine the response of the committed myeloid stem cell to neutropenia. The proportion of GM-CFC in S proved to be a more useful parameter than the GM-CFC concentration. 75% of the patients with greater than 60% GM-CFC in S returned to normal within 1 month. Patients with less than 20% GM-CFC in S had at least a 10 times greater incidence of developing a malignant or autoimmune disease than the other 28 patients. The 11 patients with 41-51% in GM-CFC in S had greater than 1 x 10(9) neutrophils/1 and no significant clinical problems but all have remained mildly neutropenic for a long period. An indirect relationship existed between the degree of neutropenia and the proportion of GM-CFC in S (r = -0.70).

Adult↗

PubMed1983

Single dose captopril as a diagnostic test for primary aldosteronism.

Most diagnostic tests for primary aldosteronism use maneuvers to expand the extracellular fluid volume, thereby suppressing the renin-angiotensin system. This results in a decline in plasma aldosterone concentrations in normal subjects and essential hypertension (EH) patients, but not in patients with primary aldosteronism. Captopril blocks angiotensin II synthesis and might be used as a diagnostic test for primary aldosteronism. We have measured plasma aldosterone concentrations 2 h after the administration of 25 mg captopril in 9 normotensive subjects, 10 patients with EH, and 12 patients with primary aldosteronism while they were ingesting an unrestricted diet. The plasma aldosterone concentration decreased to less than 15 ng/dl in all normotensive subjects and in 9 of 10 patients with EH, but remained greater than 15 ng/dl in 4 of 5 patients with idiopathic hyperaldosteronism and in all patients with an aldosterone-producing adenoma. The aldosterone to renin ratio was greater than 50 in 4 of 5 patients with idiopathic hyperaldosteronism and in all adenoma patients, but less than 50 in all normotensive subjects and EH patients. A nomogram comparing the plasma aldosterone concentration with the aldosterone to renin ratio clearly separated primary aldosteronism patients from EH patients.

Adenoma↗

PubMed1983

The protein-bound carbohydrates of seromucoid from normal human serum.

The neutral sugars and hexosamines in the seromucoid fraction of normal human serum were identified and determined simultaneously by gas-liquid chromatography of their aldononitrile acetates. Besides the sialic acid, normal seromucoid contained fucose, arabinose, mannose, glucose, galactose, glucosamine and galactosamine. The presence of arabinose and glucose, not previously reported in seromucoid, as well as the other known carbohydrate components determined by GLC were confirmed from their fragmentation patterns in the electron impact mass spectra and chemical ionization spectra.

Adult↗

PubMed1983

The endocrine control of the initiation and growth of antlers in white-tailed deer.

Five fawn and 5 adult white-tailed deer (Odocoileus virginianus) were maintained in individual pens, fed a complete diet, and bled bi-weekly for one year. Blood serum was analyzed for testosterone (T), androstenedione (A), thyroxine (T4), calcium (Ca), phosphorus (P) and alkaline phosphatase (AP). Adults grew velvet antlers from mid-April and shed their velvet in mid-September. Hardened antlers were cast in March. Fawns grew velvet antler buttons which hardened in February and cast in March, prior to the growth of the first antlers. Adults had higher (P less than 0.05) titres of T and A over the year. Fawns had higher T4 levels and AP activity (P less than 0.05), while Ca and P levels were not different between the groups (P greater than 0.05). In the adults, T peaked in December and April and was correlated with the periods of hard antlers and the initiation of antler growth. In the fawns, T peaked in November and April and was correlated with hardened buttons and the initiation of the first antlers. Adult A peaked in June but hit nadirs in May and July and generally was not correlated with the antler cycle. In the fawns, A was similar to the T cycle. Thyroxine was relatively constant over the year in adults, but was elevated in the winter in fawns during the period of hardened buttons. Calcium and P levels were relatively constant throughout the year in both groups. AP activity was elevated over winter in adults and then decreased sharply when antlers were cast. Activity increased gradually again as new antlers grew. AP activity in fawns was elevated over the winter and spring and gradually declined as the first antlers developed.

Age Factors↗

PubMed1983

Immunoradiometric assay of plasma lactoferrin.

The concentration of lactoferrin, a non-heme iron binding glycoprotein, was determined in more than 1500 EDTA plasma samples by a 2-site solid phase immunoradiometric assay to assess the significance of lactoferrin in plasma and to investigate applications for this assay. The use of commercially available antibody and antigen and a relatively short assay time make this assay more suitable for use in routine clinical laboratories than previous methods. A normal range of 250-750 micrograms/l was established. There was a correlation between plasma lactoferrin concentration and the circulating blood neutrophil count in most patients except those with splenomegaly, post-splenectomy and undergoing intensive chemotherapy. Patients with gross splenomegaly usually had an increased and post-splenectomy patients a decreased lactoferrin/neutrophil ratio indicating a respective increase and decrease in the marginated pool. In patients with acute leukemia after chemotherapy or transplantation plasma lactoferrin levels increased 1 to 5 d before blood neutrophil counts rose. As plasma lactoferrin seems to be derived from neutrophils, its concentration is probably related to the size of the total blood granulocyte pool. Calculation of the lactoferrin/neutrophil ratio demonstrated variations in the size of the bone marrow reserve and the marginated neutrophil pool.

Humans↗

PubMed1983

Effects of dietary carbohydrate and of intestinal microflora on excretion of endogenous amino acids by poultry.

The effects of dietary carbohydrate and of intestinal microflora on excretion of endogenous amino acids by poultry were investigated. Excretion of endogenous amino acids was compared among fasted roosters, intact roosters fed low- or high-fiber, N-free diets, and surgically-modified (SM) roosters fed a low-fiber, N-free diet. The low-fiber diet contained 50% corn starch, 45% glucose, and 5% cellulose, whereas the high-fiber diet contained 25% each of corn starch, glucose, and raw potato starch, 17.5% cellulose, and 7.5% pectin. Digesta were obtained from the terminal ileum of SM roosters to eliminate effects of the microflora in the large intestine and ceca. The roosters were force-fed 60 g of the appropriate diet (30 g at the initiation of the trial followed by an additional 30 g 6 hours later). Excreta or digesta and urine were collected quantitatively for 48 hr after the first force-feeding. Roosters fed the high-fiber diet excreted substantially more (P less than .05) amino acids than did fasted roosters or roosters fed a low-fiber diet. Excreta from roosters fed the high-fiber diet contained higher (P less than .05) levels of alanine and aspartic acid than excreta from fasted or digesta from SM roosters, indicating substantial microbial synthesis of amino acids in the gut. In contrast, amino acid composition of excreta from fasted and intact roosters fed the low-fiber diet was similar to that of digesta from SM roosters, suggesting less microbial influence. Excretion of glucosamine plus galactosamine by SM roosters was approximately twice that of intact roosters fed the same diet. Glycine was the most abundant amino acid in digesta of SM roosters. Results of this study indicate that dietary carbohydrate substantially affects excretion of endogenous amino acids by poultry and that fasted birds may not provide an accurate estimate of endogenous amino acid excretion for birds fed high-fiber feedstuffs in amino acid digestibility trials.

Amino Acids↗