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R C Milton

Publications and source records attributed to R C Milton.

17 recordsLinked to original sources
PubMed1992

Total solid-phase synthesis and prolactin-inhibiting activity of the gonadotropin-releasing hormone precursor protein and the gonadotropin-releasing hormone associated peptide.

The human gonadotropin-releasing hormone precursor protein, pHGnRH (Met-23-Ile69) (preproGnRH), and three of its fragment peptides, pHGnRH (Asp14-Ile69) (gonadotropin-releasing hormone associated peptide--GAP), pHGnRH (Phe38-Ile69), and pHGnRH (Ser47-Ile69), were assembled in a stepwise solid-phase cosynthesis employing Boc/Bzl tactics and an optimized acylation schedule which included recoupling steps with hexafluoro-2-propanol to help overcome the aggregation of the pendant peptide chains of the peptidoresin during difficult couplings. Reversed-phase high-performance liquid chromatography (HPLC) purification yielded products which were characterized by analytical reversed-phase HPLC, ion-exchange chromatography, capillary zone electrophoresis, SDS-polyacrylamide gel electrophoresis, and ion-spray mass spectrometry to reveal a high degree of homogeneity. Biological characterization demonstrated that only GAP stimulated luteinizing hormone and follicle-stimulating hormone release from primary cultures of rat anterior pituitary cells, while GAP, pHGnRH (Phe38-Ile69), and preproGnRH all inhibited prolactin release, with the latter being the most potent at concentrations comparable to bromocryptine. However, only GAP and pHGnRH (Phe38-Ile69) were able to displace a labeled gonadotropin-releasing hormone agonist from binding to rat pituitary membrane preparations. This first demonstration of significant biological activity with a precursor protein also suggests that the gonadotropin-releasing and prolactin release-inhibiting functions of GAP are not mediated through the same pituitary receptors.

Amino Acid Sequence↗
PubMed1992

Total chemical synthesis of a D-enzyme: the enantiomers of HIV-1 protease show reciprocal chiral substrate specificity [corrected].

The D and L forms of the enzyme HIV-1 protease have been prepared by total chemical synthesis. The two proteins had identical covalent structures. However, the folded protein-enzyme enantiomers showed reciprocal chiral specificity on peptide substrates. That is, each enzyme enantiomer cut only the corresponding substrate enantiomer. Reciprocal chiral specificity was also evident in the effect of enantiomeric inhibitors. These data imply that the folded forms of the chemically synthesized D- and L-enzyme molecules are mirror images of one another in all elements of the three-dimensional structure. Enantiomeric proteins are expected to display reciprocal chiral specificity in all aspects of their biochemical interactions.

Amino Acid Sequence↗
PubMed1992

Activity of vertebrate gonadotropin-releasing hormones and analogs with variant amino acid residues in positions 5, 7 and 8 in the goldfish pituitary.

All non-mammalian vertebrates as well as marsupial mammals have two or more forms of gonadotropin-releasing hormone (GnRH) in the brain. Goldfish brain and pituitary contains two molecular forms of GnRH, salmon GnRH ([Trp7, Leu8]m-GnRH; s-GnRH) and chicken GnRH-II ([His5, Trp7, Tyr8]m-GnRH; cII-GnRH). Both sGnRH and cII-GnRH stimulate gonadotropin (GtH) as well as growth hormone (GH) release from the goldfish pituitary. The purpose of the present study was to study the activity of the five known forms of GnRHs as well as analogs of mammalian GnRH (m-GnRH) with variant amino acid residues in positions 5, 7 and 8 in terms of binding to GnRH receptors, and release of GTH and GH from the perifused fragments of goldfish pituitary in vitro. All five vertebrate GnRH peptides stimulated both GtH and GH release in a dose-dependent manner, although their potencies were very different. cII-GnRH was somewhat more active than s-GnRH in releasing GtH, whereas s-GnRH tended to have a greater potency than cII-GnRH in terms of GH release. Both chicken GnRH-I (cI-GnRH) and lamprey GnRH (l-GnRH) were significantly less potent than mGnRH, s-GnRH and cII-GnRH in releasing GtH and GH. cII-GnRH binds with higher affinity for the high affinity binding sites compared to all other native peptides. The activity of [Trp7]-GnRH was similar to both s-GnRH and cII-GnRH in releasing GtH and GH. Substitution of His5 resulted in a significant decrease in GtH releasing potencies compared to mGnRH, sGnRH and cII-GnRH. [His5]-GnRH also had lower GH releasing potency than mGnRH and sGnRH. Tyr8, His8 and Leu8 substitutions caused significant decreases in GtH releasing potencies compared to mGnRH, s-GnRH and cII-GnRH, but did not cause a significant change in GH releasing potency. The combination of [His5, Trp7]-GnRH had GtH and GH releasing activities similar to m-GnRH, s-GnRH and cII-GnRH.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1991

Diarrhea, respiratory infections, and growth are not affected by a weekly low-dose vitamin A supplement: a masked, controlled field trial in children in southern India.

Incidence, duration, and severity of diarrhea and respiratory symptoms were monitored weekly for 1 y in 15,419 children 6-60 mo of age in a randomized, placebo-controlled, masked clinical trial conducted in southern India. Half the children received weekly doses of 8.7 mumol (2500 microgram) vitamin A and 46 mumol (20 mg) vitamin E (treated) and the other half, 46 mumol vitamin E (control). Medical and ocular examinations and anthropometric measurements were obtained before and after 52 wk of intervention. Ocular examinations also were obtained after 26 wk. Supplements were delivered weekly from calibrated dispenser bottles by community health volunteers who also recorded each mother's recall of daily morbidity of her child during the previous week. Baseline characteristics of treated and control subjects were similar and documented a prevalence of 11% xerophthalmia and 72% undernutrition. Weekly treatment with the low-dose vitamin A supplement did not influence the incidence, severity, or duration of diarrhea or respiratory infections and did not influence linear or ponderal growth.

Child Development↗
PubMed1990

Reduced mortality among children in southern India receiving a small weekly dose of vitamin A.

BACKGROUND: Clinical vitamin A deficiency affects millions of children worldwide, and subclinical deficiency is even more common. Supplemental vitamin A has been reported to reduce mortality among these children, but the results have been questioned. METHODS: We conducted a randomized, controlled, masked clinical trial for one year in southern India involving 15,419 preschool-age children who received either 8.7 mumol (8333 IU) of vitamin A and 46 mumol (20 mg) of vitamin E (the treated group) or vitamin E alone (the control group). Vitamin supplements were delivered weekly by community health volunteers who also recorded mortality and morbidity. Weekly contact was made with at least 88 percent of the children in both study groups. The base-line characteristics of the children were similar and documented a high prevalence of vitamin A deficiency and undernutrition. RESULTS: One hundred twenty-five deaths occurred, of which 117 were not accidental. The risk of death in the group treated with vitamin A was less than half that in the control group (relative risk, 0.46; 95 percent confidence interval, 0.30 to 0.71). The risk was most reduced among children under 3 years of age (6 to 11 months--relative risk, 0.28; 95 percent confidence interval, 0.09 to 0.85; 12 to 35 months--relative risk, 0.46; 95 percent confidence interval, 0.26 to 0.81) and among those who were chronically undernourished, as manifested by stunting (relative risk, 0.11; 95 percent confidence interval, 0.03 to 0.36). The symptom-specific risk of mortality was significantly associated with diarrhea, convulsions, and other infection-related symptoms. CONCLUSIONS: The regular provision of a supplement of vitamin A to children, at a level potentially obtainable from foods, in an area where vitamin A deficiency and under-nutrition are documented public health problems contributed substantially to children's survival; mortality was reduced on average by 54 percent.

Adolescent↗
PubMed1990

Selective FSH-releasing activity of [D-Trp9]GAP1-13: comparison with gonadotropin-releasing abilities of analogs of GAP and natural LHRHs.

We had previously shown that fragments of human gonadotropin-releasing hormone associated peptide (GAP) stimulated FSH and LH release in vivo. In particular, GAP1-13 had a preferential FSH-releasing activity. To decrease enzymatic degradation, analogs of GAP1-13 with D-amino acid substitutions were synthesized. The activities were tested in ovariectomized, estrogen-progesterone primed (OEP) rats and compared with those of GAP1-13, mammalian (m), chicken II (cII), and lamprey (1) LHRH. The peptides were injected (IV) into conscious, OEP rats and blood samples were obtained via the jugular catheter. [D-Trp9 )GAP1-13 selectively stimulated FSH release at a dose of 1 microgram. Multiple injections of this analog (10 micrograms every 30 min for 5 injections) induced a marked elevation of plasma FSH values which peaked (p less than 0.001) after the third injection. By contrast, [D-Trp9]GAP1-13 had no effect on LH and prolactin (PRL) release after either single or multiple injections. These doses of [D-Ala4]GAP1-13 had no effect on the release of FSH, LH or PRL. Both human GAP1-13 and its [D-Trp9] analog exerted a selective FSH-releasing effect at a dose of 10 micrograms, however, the [D-Trp9] analog was more potent than GAP1-13 on FSH release. The potency of [D-Trp9]GAP1-13 in releasing FSH was approximately 1/100th that of mLHRH. Chicken II LHRH had slightly selective FSH-releasing activity with a potency 1/10th that of mLHRH. Lamprey LHRH had a preferential LH-releasing activity and a potency 1000 times less than mLHRH. In conclusion. [D-Trp9]GAP1-13 is a selective FSH-releasing peptide of potential clinical value.

Animals↗
PubMed1989

Chimeric analogues of vertebrate gonadotropin-releasing hormones comprising substitutions of the variant amino acids in positions 5, 7, and 8. Characterization of requirements for receptor binding and gonadotropin release in mammalian and avian pituitary gonadotropes.

Variant forms of mammalian gonadotropin-releasing hormone (GnRH) (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly.NH2) are present in chicken ([Gln8] GnRH and [His5, Trp7, Tyr8]GnRH), salmon ([Trp7, Leu8]GnRH), and lamprey ([Tyr3, Leu5, Glu6, Trp7, Lys8] GnRH). To delineate the functional importance of the variant amino acids in positions 5, 7, and 8, the natural peptides and chimeric analogues were tested for gonadotropin-releasing activity and receptor-binding activity in rat, sheep, and chicken pituitaries. The results demonstrate that (i) the mammalian receptor has a high fidelity for Arg8 while the chicken receptor is less discriminatory and accepts basic or neutral amino acids in this position. Arg8 may contribute to conformational stabilization, and conformational constraint with D-Trp6 restored activity to analogues lacking Arg8 in the mammalian systems. D-Trp6 incorporation did not generally enhance activity in the chicken pituitary. (ii) His5 accompanying Arg8 in analogues markedly diminished activity in the chicken while gonadotropin-releasing activity was retained in the sheep pituitary. Receptor-binding activity was increased in the sheep indicating an uncoupling of receptor occupancy and activation. (iii) Substitution in position 7 is tolerated by the mammalian and chicken receptor. With Trp7-substituted analogues receptor-binding activity was relatively lower than gonadotropin-releasing activity in the sheep pituitary, suggesting an enhanced receptor activation by these analogues or the existence of different GnRH receptors.

Amino Acid Sequence↗
PubMed1989

Age-related cataract in the Tibet Eye Study.

The Tibet Eye Study was designed to estimate the prevalence of age-related cataract in Duilong-Deqing County, west of Lhasa, China (altitude, 4000 m). Previous reports have suggested an unusually high prevalence of age-related cataract in Tibet. A two-stage probability sample of persons aged 20 years or older from the 35 townships of the county targeted 2884 persons for inclusion in the study; 2665 (92.4%) were examined. Age-related cataract was diagnosed when (1) visual acuity was worse than 6/12 (20/40) because of nuclear or cortical (including posterior subcapsular) opacities, or (2) aphakia associated with a history of age-related cataract was present in either eye. The prevalence of age-related cataract among persons aged 20 to 39 years was 0.2%; among persons 40 years old or older, the prevalence was 11.8%. Cortical cataracts were by far the most common type of cataract diagnosed. Age- and sex-adjusted prevalence in Tibet was 60% higher than the prevalence in a similar, previously conducted study of 6951 person in Shunyi County, northeast of Beijing (altitude, 50 m). A second, independent slit-lamp classification of lens status was conducted in the Tibet Eye Study using standard photographs previously described. Age-specific cataract prevalence was similar with the two examination techniques. Results from the Tibet Eye Study support previous suggestions of a high prevalence of age-related cataract in Tibet.

Adult↗
PubMed1989

India-US case-control study of age-related cataracts. India-US Case-Control Study Group.

In a hospital-based case-control study of 1441 patients with age-related cataracts and 549 controls, we studied associations between types of cataract--nuclear, cortical, posterior subcapsular, and mixed--and a number of physiologic, behavioral, environmental, and biochemical variables. Using polychotomous logistic regression analysis, we found an increased risk of cataract with lower educational achievement (all types of cataract), decreased cloud cover at place of residence (all types), use of aspirin less than once a month (posterior subcapsular and mixed), diets low in selected nutrients (posterior subcapsular, nuclear, and mixed), higher blood pressure (nuclear and mixed), lower body mass index (nuclear and mixed), use of cheaper cooking fuels (cortical, nuclear, and mixed), and lower levels of an antioxidant index based on red blood cell levels of glutathione peroxidase and glucose-6-phosphate dehydrogenase and plasma levels of ascorbic acid and vitamin E (posterior subcapsular and mixed). All risks cited were significantly different from those for the other cataract types, a finding that emphasizes the need to investigate the epidemiology of specific types of cataract.

Adult↗
PubMed1989

Grading of images in a clinical trial.

We developed a computer model to compare the power in clinical trials that use either of two grading schemes for objectively recorded dependent variables. The example we use is an eye lens photo. The first grading system consists of side by side comparison of the before and after treatment photos; the second involves separate grading of the two photos. This modelling experience suggests that separate grading may often yield more power than side by side comparison, and offers other advantages as well. For applications in which grading error is considerably smaller in the side by side method, power may be markedly better. Most importantly, strong prejudice in favour of one or the other approach in all situations seems unwarranted.

Cataract↗
PubMed1989

Impaired vision and hip fracture. The Framingham Study.

Falls affect a large proportion of the elderly and can result in a variety of injuries, including hip fractures. Several studies have suggested that visual impairment contributes to falls, but studies have not used standardized definitions of visual impairment and have not examined injurious falls or fractures. We looked at the risk of hip fracture associated with visual impairment in those members of the Framingham Study Cohort who took part in the Framingham Eye Study in 1973-75. Of 2,633 subjects followed for 10 years after the eye exam, 110 sustained hip fractures. The fracture rates in those with moderately impaired (20/30 to 20/80) vision (8.5%) and poor (20/100 or worse) vision (11.3%) were higher than in those with good (20/25 or better) vision (3.0%). After adjustment for age, sex, weight, alcohol consumption, and (in women) estrogen use, the relative risk of fracture in those with moderate impairment was 1.54 (95% CI = 0.95-2.49), while for those with poor vision, the relative risk was 2.17 (95% CI = 1.24-3.80). Of note, those with moderately impaired vision in one eye and good vision in the other had a higher risk of fracture (relative risk = 1.94) than those with a similar degree of binocular impairment (relative risk = 1.11). Poor vision in one or both eyes was linked to an elevated fracture risk. This suggests that good stereoscopic vision may be necessary to prevent falls. The risk of fracture with poor and moderately impaired vision combined was increased in women (relative risk = 1.96, 95% CI = 1.23-3.11) but not in men (relative risk = 0.79, 95% CI = 0.23-2.72).(ABSTRACT TRUNCATED AT 250 WORDS)

Accidental Falls↗
PubMed1979

Statistical computing in the United States.

Recent history and developments related to the increase in statistical computing activities in the United States and by U.S. participants in international efforts are reviewed, with emphasis on important events, organizations, references, and products which contribute to informed selection and use of statistical programs. Three features matrices for major statistical packages are included as potential aids to Japanese statisticians in assessing the utility of these packages in biostatistical applications.

Biometry↗
PubMed1978

Plasma cofactors of platelet function: correlation with diabetic retinopathy and hemoglobins Ala-c.

We studied 29 diabetic patients (eight without and 21 with retinopathy) and 29 matched control subjects for hemoglobins Ala-c and plasma levels of fibrinogen, von Willebrand factor, and factor VIII/von Willebrand factor antigen. Hemoglobins Ala-c were elevated in all diabetic patients, regardless of retinopathy (P less than 0.001); fibrinogen was elevated only in those with retinopathy (P less than 0.001); and plasma von Willebrand factor was clearly elevated in those with proliferative retinopathy and minimally, if at all, elevated in those with background or no retinopathy. Plasma from five diabetic patients with proliferative retinopathy and five control subjects was tested for its ability to enhance the ADP-induced platelet aggregation of normal or von Willebrand platelet-rich plasma; no differences were found. We conclude that elevated levels of fibrinogen and von Willebrand factor, both recognized plasma cofactors of platelet function, are associated with proliferative diabetic retinopathy. A plasma factor that enhances ADP-induced platelet aggregation could not be found in diabetic plasma, and we doubt that increased von Willebrand factor is responsible for its finding by others.

Adenosine Diphosphate↗
PubMed1977

Variability in grading diabetic retinopathy from stereo fundus photographs: comparison of physician and lay readers.

Two physicians and two lay readers were trained according to a detailed protocol in the grading of 17 lesions found in diabetic retinopathy by evaluation of stereo fundus photographs according to a modified Airlie House classification. Intraobserver and interobserver variability of these readers was assessed by two methods: weighted kappa, and frequency of agreement within one grade. In general, physician readers were found to be less variable on replicate readings than were lay leaders, and had slightly better agreement with each other than with the lay readers. The physiological significance of the direction and magnitude of the difference between physician and lay reader variability for individual lesions was often uncertain. Assessment of contribution to disagreement by individual readers was possible and permits future training directed at reducing disagreement to acceptable values.

Analysis of Variance↗