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Biomedical subjects

B G Green

Publications and source records attributed to B G Green.

At least 55 records · Page 3Linked to original sources
PubMed1993

Oral astringency: a tactile component of flavor.

The psychophysical, chemical and physiological bases of the oral sensation of astringency are discussed in an effort to clarify the nature of this enigmatic sensation. It is argued that, despite recent data from animal studies that suggest it is a taste sensation mediated by the chorda tympani nerve, astringency arises primarily from increases in friction between mucosal surfaces. Evidence is discussed that supports the view that oral astringency results primarily from the precipitation of salivary mucoproteins, which impairs the natural lubrication of oral surfaces. The ensuing rise in friction induces sensations of dryness and roughness which, although subtle at first, can grow in magnitude over repeated exposures. These changes in the surface texture of the mouth are an important component of the 'flavor' of common foods and beverages such as fruits, nuts, teas and coffee.

Astringents↗
PubMed1992

Specificity, stability, and potency of monocyclic beta-lactam inhibitors of human leucocyte elastase.

Stable, potent, highly specific, time-dependent monocyclic beta-lactam inhibitors of human leucocyte elastase (HLE) are described. The heavily substituted beta-lactams are stable under physiological conditions including in the presence of enzymes of the digestive tract. The beta-lactams were unstable in base. At pH 11.3 and 37 degrees C they were hydrolyzed with half-lives of 1.5-2 h. Hydrolysis produced characteristic products including the substituent originally at C-4 of the lactam ring, a substituted urea, and products resulting from decarboxylation of the acid after ring opening. The most potent beta-lactam displayed only 2-fold less activity versus HLE than alpha 1PI, the natural proteinaceous inhibitor. The compounds were more potent against the human and primate PMN elastases than versus either the dog or rat enzymes. Differences in the structure-activity relationships of the human versus the rat enzymes suggest significant differences between these two functionally similar enzymes. The specificity of these compounds toward HLE versus porcine pancreatic elastase (PPE) is consistent with the differences in substrate specificity reported for these enzymes [Zimmerman & Ashe (1977) Biochim. Biophys. Acta 480, 241-245]. These differences suggest that the alkyl substitutions at C-3 of the lactam ring bind in the S1 specificity pocket of these enzymes. The dependence of the stereochemistry at C-4 suggests additional differences between HLE and PPE. Most of the compounds do not inhibit other esterases or human proteases. Weak, time-dependent inhibition of human cathepsin G and alpha-chymotrypsin by one compound suggested a binding mode to these enzymes that places the N-1 substitution in the S1 pocket.

Animals↗
PubMed1992

Mechanism of inhibition of human leukocyte elastase by two cephalosporin derivatives.

The cephalosporin derivatives L 658758 [1-[[3-(acetoxymethyl)-7 alpha-methoxy-8-oxo-5-thia-1-azabicyclo [4.2.0]oct-2-en-2-yl]carbonyl]proline S,S-dioxide] and L 659286 [1-[[7 alpha-methoxy-8-oxo-3-[[(1,2,5,6-tetrahydro-2-methyl-5,6-dioxo- 1,2,4-triazin-3-yl)thio]methyl]-5-thia-1-aza-(6R)-bicyclo[4.2.0]-o ct-2-en-2-yl]carbonyl]pyrrolidine S,S-dioxide] are mechanism based inhibitors of human leukocyte elastase (HLE). The mechanism involves initial formation of a Michaelis complex followed by acylation of the active site serine. The group on the 3'-methylene is liberated during the course of these reactions, followed by partitioning of an intermediate between hydrolysis to regenerate active enzyme and further modification to produce a stable HLE-inhibitor complex. The partition ratio of 2.0 obtained for the reaction with L 658758 approaches that of an optimal inhibitor. These compounds are functionally irreversible inhibitors as the recovery of activity after inactivation is slow. The half-lives at 37 degrees C of the L 658758 and L 659286 derived HLE-I complexes were 9 and 6.5 h, respectively. The complexes produced by both inhibitors are similar chemically since the thermodynamic parameters for activation to regenerate active enzyme are essentially identical. The free energy of activation for this process is dominated primarily by the enthalpy term. The stability of the final complexes likely arises from Michael addition on the active site histidine to the 3'-methylene.

Catalysis↗
PubMed1992

Electroejaculation in combination with in vitro fertilization and gamete micromanipulation for treatment of anejaculatory male infertility.

OBJECTIVE: Failure to ejaculate may be overcome by use of electroejaculation. However, such semen samples are often unsuitable for therapies like intrauterine insemination. The combination of electroejaculation with in vitro fertilization, including gamete micromanipulation, should improve chances of fertilization and pregnancy in such cases. STUDY DESIGN: Within a private infertility clinic electroejaculation in combination with intrauterine insemination was carried out in 18 cycles (10 couples). Four couples went on to receive therapy by electroejaculation plus in vitro fertilization, along with six other couples (15 cycles total) with semen too poor for intrauterine insemination. RESULTS: One term pregnancy arose in the electroejaculation-intrauterine insemination group, and one term pregnancy plus one continuing pregnancy arose from two couples (three cycles) who underwent in vitro fertilization with conventional insemination after electroejaculation. Six couples (nine cycles) had embryos arising only from gamete micromanipulation transferred, and this yielded two term pregnancies, one spontaneous abortion, and a biochemical pregnancy. Two couples (three cycles) failed to achieve fertilization even with micromanipulation; however, donor-inseminated eggs gave rise to two term pregnancies and one continuing pregnancy in these patients. CONCLUSIONS: This report confirms the feasibility of in vitro fertilization in conjunction with electroejaculation and extends the therapy to incorporate gamete micromanipulation.

Adult↗
PubMed1992

The value of urodynamics and bladder management in predicting upper urinary tract complications in male spinal cord injury patients.

A review of 160 male patients admitted to the Shepherd Spinal Center was completed to determine the influence of urodynamic findings and choice of bladder management program on the risk of developing upper urinary tract distress following acute spinal injury. Within the context of this investigation, upper urinary tract distress was defined as presence of hydronephrosis, febrile urinary tract infection, urolithasis or vesicoureteral reflux. Three groups were identified according to the urodynamic findings and the bladder management program. Thirty-four subjects with preservation of detrusor function managed their bladders by spontaneous voiding. Seventy patients with detrusor areflexia managed their bladders via intermittent catheterization; and 56 males who had detrusor hyperreflexia on urodynamics were managed by a reflex voiding program with condom drainage. None of the subjects with preservation of spontaneous voiding function experienced upper tract distress. Seven percent of those on intermittent catheterization and 32% of those managed by a reflex voiding program experienced upper tract distress. The presence of detrusor hyperreflexia with or without vesicosphincter dyssynergia influenced the likelihood that subjects would experience upper urinary tract distress following spinal injury. While traditional urodynamics failed to distinguish patients managed by a reflex voiding program who experienced upper tract distress from those who did not, calculation of a new urodynamic variable, the urethral pressure gradient, was found to assist in this prediction.

Adult↗
PubMed1992

Potency of antileukoprotease and alpha 1-antitrypsin to inhibit degradation of fibrinogen by adherent polymorphonuclear leukocytes from normal subjects and patients with chronic granulomatous disease.

We have studied the relative efficacy of antileukoprotease (ALP) and alpha 1-antitrypsin (alpha 1AT) to inhibit the degradation of substrate by polymorphonuclear leukocytes (PMN) attached onto a fibrinogen matrix. PMN elastase activity was assayed by radioimmunoassay of a specific 21-residue cleavage product from the amino terminus of the A alpha chain, A alpha (1-21), of fibrinogen. The adherence of PMN (1.0 x 10(6)) to a fibrinogen matrix was facilitated by incubation with recombinant tumor necrosis factor-alpha (1 nM). Subsequently, the cells were exposed to inhibitors before stimulation with cytochalasin B and formylmethionyl-leucylphenylalanine. Under these conditions, ALP inhibited A alpha (1-21) formation with an IC50 of 85 +/- 30 nM and alpha 1AT gave an IC50 of 220 +/- 98 nM (mean +/- SD). The effect of oxidant production on A alpha (1-21) formation was evaluated by comparing the effect of PMN from normal subjects with PMN from subjects with X-linked NADPH oxidase deficiency. Stimulation of PMN from the latter subjects in a similar fashion as described above resulted in the formation of 40 +/- 4 pmol/ml A alpha (1-21), or approximately twice the amount seen with cells from normal subjects. Preincubation with ALP or alpha 1AT in a concentration range between 10 to 900 nM resulted in an IC50 of 50 +/- 13 nM for ALP compared with 150 +/- 21 nM for alpha 1AT. Both inhibitors are more effective to prevent fibrinogen degradation caused by chronic granulomatous disease (CGD) PMN than by normal PMN despite the fact that CGD PMN generated more A alpha (1-21) than did normal PMN.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochalasin B↗
PubMed1992

The sensory effects of l-menthol on human skin.

Psychophysical measurements were made of the sensory effects of l-menthol applied topically to the forearm under controlled thermal conditions. In the first experiment, subjects judged the intensity and quality of sensations produced by warming or cooling the skin in the presence of menthol or the vehicle. During cooling, menthol intensified cutaneous sensations and increased reports of burning. During warming, menthol intensified sensations transiently at low temperatures and weakened them lastingly at higher temperatures; the frequency of reports of burning varied with intensity. A second experiment tested the hypothesis that menthol would lower the threshold for warmth and raise the threshold for heat pain. No change in either threshold was observed. The primary sensory effects of l-menthol on hairy skin are therefore to heighten the perception of cooling and to attenuate the perception of moderate warming. In contrast with other common chemical irritants, menthol's pungent qualities appear to be enhanced by cooling and suppressed by warming; this suggests that its sensory irritancy may be attributable to the stimulation of a population of high-threshold cold fibers or cold-sensitive nociceptors.

Adult↗
PubMed1991

PMN elastases: a comparison of the specificity of human isozymes and the enzyme from other species toward substrates and inhibitors.

The human elastases isolated from polymorphonuclear neutrophils (PMN) and purulent sputum displayed identical kinetic constants toward substrates and inhibitors. The elastases from the two sources yield identical N-terminal sequences and were recognized by antiserum prepared against human sputum elastase (HSE) isozyme-4 (I-4). The data support the proposal put forth by Twumasi and Liener (1977, J. Biol. Chem. 252, 1917-1926) that the human elastase from sputum is of PMN origin. PMN elastases from other species displayed kinetic constants toward both substrates and inhibitors significantly different from the human enzyme. Therefore, extrapolation of inhibitor profiles from these elastases to the human source should be avoided. Four groups of isozymes were resolved from HSE by FPLC. Only the most basic isozyme (I-4) was obtained as a single species. The isozymes displayed identical macroscopic kinetic constants toward several substrates and two classes of inhibitors. The similar partition ratios observed with a cephalosporin-derived inhibitor suggest that the microscopic rate constants are also identical. The data support the proposal suggested by Baugh and Travis (1976, Biochemistry 15, 836-841) that HLE isozymes differ only in carbohydrate content. Whatever the source of human PMN elastase heterogeneity, it does not result in heterogeneous catalytic properties. In addition, a new protein was identified in elastase preparations derived from human sputum. This protein displayed homology to serine proteases and properties suggesting that it is identical to azurocidin.

Amino Acid Sequence↗
PubMed1991

Temporal characteristics of capsaicin sensitization and desensitization on the tongue.

Previous work has demonstrated that repeated applications of capsaicin can sensitize the tongue to subsequent exposures to capsaicin. However, if stimulation is interrupted for a period of minutes, the contrasting phenomenon of desensitization occurs. The purpose of the present study was to investigate the effect of interstimulus interval (ISI) on the development of both sensitization and desensitization to sequential capsaicin stimuli. It was determined in the first experiment that the rate of sensitization varied inversely with ISI for intervals briefer than 3.5 min; when ISI was lengthened to 5.5 min, sensitization was replaced by a trend toward desensitization. A second experiment established that increasing ISI from 9.5 min to 14.5 min tended to reduce rather than to enhance desensitization. It was therefore concluded that the sensitization process can be optimized by decreasing the time between successive stimuli (ISIs less than 3.5 min), whereas the trend toward desensitization appears to be optimal when stimuli are separated by at least 5.5 min but by less than 14.5 min.

Adult↗
PubMed1991

Interactions between chemical and thermal cutaneous stimuli: inhibition (counterirritation) and integration.

Methyl salicylate, a commonly used chemical counterirritant, was applied topically to the forearm to determine whether a nonpainful chemical irritation could inhibit the perception of another (weaker) chemical irritation. In the first experiment, sensations of irritation (burning and stinging) produced by a 10% solution of methyl salicylate were significantly attenuated when a 15% solution of the same chemical was applied to the opposite forearm. In the second experiment, neither the perception of warmth nor the heat pain threshold was affected by application of 10% or 15% methyl salicylate to a site 10 cm from the thermal stimulus. Inhibition did, however, occur in the opposite direction: Chemical irritation was reduced after the thermal stimulus reached a painful level. In the third experiment, a 15% solution of methyl salicylate was applied immediately adjacent to the thermal stimulus, with the result that ratings of warmth intensity increased rather than decreased, and perceived irritation was again attenuated following a painful heat stimulus. Overall, the results indicate that (1) chemical counterirritation can occur at nonpainful levels; (2) the resulting inhibition is confined to the nociceptive system; and (3) when the nociceptive and warmth system are activated together, the tendency is toward integration rather than inhibition.

Adult↗
PubMed1990

Sensory characteristics of camphor.

The perceptual effects of camphor on hairy skin were measured in a psychophysical experiment. Subjects rated the intensity and quality of sensations produced when a solution of 20% camphor (in a vehicle of ethanol and deionized H2O) was applied topically to the volar forearm. Under conditions in which skin temperature was varied either from 33-43 degrees C or from 33-18 degrees C, it was found that camphor increased the perceived intensity of the cutaneous sensations produced during heating and cooling. Although camphor's effect appeared to be greater during warming, neither effect was large. Camphor also produced a significant increase in the frequency of reports of "burning." It is concluded that camphor is a relatively weak sensory irritant that may have a modest excitatory effect on thermosensitive (and perhaps nociceptive) cutaneous fibers.

Adult↗
PubMed1990

Identification of the insulin-like growth factor I (IGF I) epitopes recognized by monoclonal and polyclonal antibodies to IGF I.

We have characterized the binding epitopes of human insulin-like growth factor I (IGF I) for a polyclonal (UB286) and a monoclonal (SM 1.2) antibody using IGF analogs obtained by site-directed mutagenesis. The polyclonal antibody, UB286, which was obtained from the National Hormone and Pituitary Program, recognizes determinants surrounding residues 15 and 16 in the B-region and residues 49-51, 55 and 56 in the A-region. These residues are predicted to be within helical segments which are accessible for surface binding. The monoclonal antibody SM 1.2 selectively recognizes the region surrounding residues 15 and 16. Antibodies UB286 and SM 1.2 are both neutralizing antibodies as judged by their ability to inhibit binding of 125I-IGF I to type 1 receptors on human placental membranes. In addition, SM 1.2 inhibits the ability of IGF I and IGF analogs for which it has high affinity to stimulate DNA synthesis in murine fibroblasts. In contrast, analogs with substitutions at residues 15 and 16, which have poor affinity for SM 1.2, stimulate DNA synthesis with equal potency in the presence and absence of SM 1.2. These antibodies bind normally to analogs which we have previously shown have drastically reduced binding to type 1 IGF receptors, indicating that the antibodies and the receptors recognize distinct domains of IGF I.

Amino Acid Sequence↗
PubMed1990

Spatial summation of chemical irritation and itch produced by topical application of capsaicin.

The effect of increasing the total area of stimulation on the sensations of irritation produced by topical application of capsaicin was studied in two experiments. In the first experiment, stimulus area was varied by changing the size of filter paper disks on which capsaicin was delivered to the skin of the forearm. Subjects rated the intensity and quality of the cutaneous sensations over a 15-min period. Increasing stimulus area by a factor of 15 resulted in a relatively modest increase in the peak perceived intensity of irritation, a shortening of the latency to the onset of irritation, and shifts in the frequency of reports of sensations of itching and stinging/pricking. However, itch was the most frequently reported sensation regardless of stimulus size. In Experiment 2, stimulus area was manipulated by varying the number of stimuli applied to the skin. Despite a smaller difference in total stimulus areas (9-fold vs. 15-fold), the difference in perceived irritation was more pronounced than it was in Experiment 1 and reached statistical significance. It is therefore concluded that spatial summation does occur in the afferent system or systems responsible for the perception of capsaicin on the skin. This result is consistent with previous reports of summation at the threshold for heat pain and constitutes new information about the spatial integration of pruritic stimulation.

Adult↗
PubMed1989

Capsaicin sensitization and desensitization on the tongue produced by brief exposures to a low concentration.

The intensity of sensations of burning and stinging produced by repeated exposures to capsaicin (at a nominal concentration of 3 ppm) was measured on a localized area of the tongue as a function of both the number of exposures and the time between them. It was discovered in the initial experiment that stimulation at the rate of 1/min (for up to 25 min) resulted in a monotonic increase in the intensity of burning sensations in a manner consistent with the phenomenon of sensitization. However, the insertion of a 15-min delay in stimulation resulted in a reduction in the intensity of the sensations produced by further stimulation, i.e., desensitization occurred. Desensitization was statistically significant even after exposure to as few as 5 stimuli prior to the delay. A subsequent experiment established that the minimum delay necessary to produce desensitization was between 2.5 and 5 min. Hence, paradoxically, the sensory response to capsaicin on the tongue increased as stimulation continued, then decreased after stimulation had ceased.

Adult↗
PubMed1989

The C region of human insulin-like growth factor (IGF) I is required for high affinity binding to the type 1 IGF receptor.

We have produced and characterized the binding properties of three structural analogs of human insulin-like growth factor I (hIGF-I). These analogs are [1-62]hIGF-I, an analog lacking the carboxyl-terminal 8-amino acid D region of hIGF-I; [1-27, Gly4, 38-70]hIGF-I, an analog in which residues 28-37 of the C region of hIGF-I are replaced by a 4-reside glycine bridge; and [1-27,Gly4,38-62]hIGF-I, an analog with the C region glycine replacement and a D region deletion. The removal of the D region of hIGF-I has little effect on binding to the type 1 and type 2 insulin-like growth factor (IGF) receptors. [1-62]hIGF-I has 2-fold higher affinity for the insulin receptor and 4-fold higher affinity for IGF serum-binding proteins. The replacement of the C region of hIGF-I with a four-glycine span results in a 30-fold loss of affinity for the type 1 IGF receptor. However this analog has near normal affinity for the type 2 IGF receptor, the insulin receptor, and IGF serum-binding proteins. Incorporating the C region glycine replacement and the D region deletion into one analog does not affect binding to either the type 2 receptor or to IGF serum-binding proteins. As predicted from the single deletion analogs [1-27,Gly4,38-62]hIGF-I has reduced affinity for the type 1 IGF receptor (approximately 40-fold) and increased affinity for the insulin receptor (5-fold). These data indicate that determinants in the C region of hIGF-I are involved in maintaining high affinity binding to the type 1 IGF receptor and that neither the C region nor the D region are required for high affinity binding to the type 2 IGF receptor or to IGF serum-binding proteins.

Amino Acid Sequence↗
PubMed1989

Structural analogs of human insulin-like growth factor (IGF) I with altered affinity for type 2 IGF receptors.

We have used site-directed mutagenesis of a synthetic gene for insulin-like growth factor (IGF) I to prepare three analogs in which specific residues in the A region are replaced with the corresponding residues in the A chain of insulin. The analogs are [Ile41, Glu45, Gln46, Thr49, Ser50, Ile51, Ser53, Tyr55, Gln56]IGF I (A chain mutant), in which residue 41 is changed from threonine to isoleucine and residues 42 to 56 of the A region are replaced, [Thr49, Ser50, Ile51]IGF I, and [Tyr55, Gln56]IGF I. These analogs are all equipotent to IGF I at the type 1 IGF receptor in human placental membranes, and in stimulating the incorporation of [3H]thymidine into DNA in the rat vascular smooth muscle cell line A10. However, the A chain mutant and [Thr49, Ser50, Ile51]IGF I have greater than 20-fold lower relative affinity for the type 2 IGF receptor of rat liver membranes, respectively. In contrast, [Tyr55, Gln56]IGF I has 7-fold higher affinity than IGF I for the type 2 IGF receptor. Residues 49, 50, and 51 in IGF I are Phe-Arg-Ser and are strictly conserved in IGF II. Residues 55 and 56 of IGF I and the corresponding residues in IGF II are Arg-Arg and Ala-Leu, respectively. Thus, the presence of the charged residues at these positions in IGF I appears to be responsible, in part, for the lower affinity of IGF I for the type 2 IGF receptor. In addition to the alterations in affinity for the type 2 IGF receptor, the A chain mutant has a 7-fold increase in affinity for insulin receptors, and [Thr49, Ser50, Ile51]IGF I has a 4-fold lower affinity for acid-stable human serum binding protein. These data strongly suggest that specific determinants in the A region of IGF I are important for maintaining binding to the type 2 IGF receptor, and that these determinants are different from those required for maintaining high affinity for the type 1 IGF receptor.

Amino Acid Sequence↗
PubMed1989

Impaired insulin-like growth factor I-mediated stimulation of glucose incorporation into glycogen in vivo in the ob/ob mouse.

The ability of insulin to modulate glucose metabolism is impaired in insulin resistant ob/ob mice. It has been shown that insulin-like growth factor I stimulates the uptake and metabolism of glucose in muscle through the insulin-like growth factor receptor not the insulin receptor. Thus, we have compared the abilities of insulin-like growth factor I and insulin to stimulate the in vivo incorporation of [14C]-glucose into glycogen in the diaphragm of ob/ob mice and their lean littermates. The animals used in these studies were 12-14 weeks old and the serum insulin levels of the ob/ob mice were 16-fold higher than in their lean littermates. There were no differences in the serum levels of glucose or insulin-like growth factor I. Both insulin and insulin-like growth factor I stimulate the incorporation of [14C]-glucose into glycogen in lean mice. Significant stimulation occurs at doses as low as 1 micrograms/kg of either peptide. The effective doses of insulin and insulin-like growth factor I are quite similar, which indicates that the effect of insulin-like growth factor I is mediated by the insulin-like growth factor receptor and not the insulin receptor. In contrast, greater than 100 micrograms/kg of insulin-like growth factor I is required to stimulate [14C]-glucose incorporation into glycogen in the diaphragm of ob/ob mice. Thus, ob/ob mice are resistant to the action of both insulin and insulin-like growth factor I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗