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Biomedical subjects

J Hamlin

Publications and source records attributed to J Hamlin.

10 recordsLinked to original sources
PubMed1995

Vaccination levels in Los Angeles public health centers: the contribution of missed opportunities to vaccinate and other factors.

We abstracted 752 randomly selected records of 2-year-old children at 5 public health centers in Los Angeles. Only 27% of the children were up-to-date in their vaccinations by 2 years of age. Being up-to-date was strongly associated with the number of missed opportunities to vaccinate and number of well child visits. Missed opportunities to vaccinate occurred during 52% of all visits and were associated with minor illness diagnoses and inaccurate immunization status assessment by nurses. Frequent missed opportunities to vaccinate and inadequate numbers of well child visits may result in low immunization levels among children attending public health clinics.

Child, Preschool↗
PubMed1987

Insulin-mimetic actions of wheat germ agglutinin and concanavalin A on specific mRNA levels.

Insulin has pleiotropic effects on sensitive cells, including the regulation of specific mRNA accumulation initiated by the binding of insulin to its plasma membrane receptor. Lectins, such as wheat germ agglutinin (WGA) and concanavalin A (Con A), are known to be insulin mimetic. It is thought that WGA and Con A interact with the insulin receptor or associated membrane glycoproteins which, when activated, lead to insulin-mimetic responses. We attempted to determine whether WGA and Con A could induce the accumulation of a specific messenger RNA (p33-mRNA). Insulin treatment of H4IIE (H4) hepatoma cells increased the concentration of p33-mRNA within 30 min after addition, with a maximum effect of 10- to 15-fold. WGA and Con A also exhibited time- and dose-dependent stimulatory effects on p33-mRNA accumulation with maximal effects of 30- to 40-fold. The effect of insulin was maximal by 1 h and plateaued thereafter, whereas lectins had maximal effects at 2 h after addition to cell cultures. Insulin, WGA, and Con A did not significantly alter the stability (half-life) of p33-mRNA. The addition of RNA synthesis inhibitors blocked the ability of insulin, WGA, and Con A to induce the amount of p33-mRNA. These data suggest that lectins, as well as insulin, induce the synthesis of p33-mRNA in acutely treated H4 hepatoma cells.

Animals↗
PubMed1987

Nerve fiber layer photography. A comparative study.

Observation of the retinal nerve fiber layer with red-free light is an important means of evaluating optic nerve integrity. Many investigators have attempted to increase the usefulness of the technique by improving photographic procedures. Most reports comparing various parameters neither indicate the method of comparison nor give quantitative measure of the improvement gained with different films, filters, cameras, or processing procedures. We have compared in a masked fashion the parameters most recently recommended in the literature. Twelve trained observers compared 12 masked pairs of nerve fiber layer photos taken from the same eye in the same manner on two cameras and preferred those taken with a Canon CF-60Z camera 69% of the time and those taken with a Zeiss FF-111 17% of the time (this difference was statistically significant, P less than 0.01). Fourteen observers compared 14 pairs of photographs and judged Panatomic-X film to be superior to Plus-X film 51% of the time and both films to be of the same quality 25% of the time (this difference was also significant P less than 0.05). Fifteen observers compared 12 pairs and preferred the Standard SE-40 blue filter 2:1 over the green Spectrotech 540 filter. This difference was not statistically significant, and the preference was found to be dependent on fundus pigmentation and clarity of the media. The blue filter gave better contrast for the nerve fiber layer in patients with lightly pigmented fundi, and use of the green filter resulted in less light scatter in patients with ocular media opacities.

Evaluation Studies as Topic↗
PubMed1987

Positive interaction between insulin and phorbol esters on the regulation of a specific messenger ribonucleic acid in rat hepatoma cells.

With Northern blot analysis, we demonstrate that phorbol 12-myristate 13-acetate (PMA) stimulated P-33 messenger RNA (mRNA)-accumulation in rat hepatoma cells in a time- and concentration-dependent manner similar to insulin and plant lectins. No effect of PMA on P-33 mRNA half-life was detected when mRNA synthesis was inhibited with either actinomycin D or 5.6-dichloro-1-beta-D-ribofuranosyl benzimidazole. The effects of insulin and PMA were additive at submaximal concentrations and no additivity was observed under these conditions at maximal concentrations. Thus PMA has a marked insulin-like effect on the accumulation of P-33 mRNA in rat hepatoma cells.

Animals↗
PubMed1986

Effect of gamma rays at the dihydrofolate reductase locus: deletions and inversions.

A series 11 gamma-ray-induced mutants at the dihydrofolate reductase (dhfr) locus in Chinese hamster ovary cells has been examined for the types of DNA sequence change brought about by this form of ionizing radiation. All 11 mutants were found to have suffered major structural changes affecting the dhfr gene. In eight of the mutants, all or part of the dhfr gene has been deleted. The extent of these deletions was examined in seven of these mutants and, for comparison, in two deletion mutants that were induced by UV irradiation. For this purpose, probes from an overlapping set of cosmids that span 210 kb of DNA in this region were used. Three of seven gamma-ray-induced mutants and one UV-induced mutant were shown to have deleted the entire 210-kb region. In the remaining mutants, endpoints ranging from within the dhfr gene to 100 kb downstream were observed. No upstream endpoints were detected, so that an upper limit on the size of these large deletions could not be assigned. Three of the 11 gamma-ray-induced mutants contained an interruption in the dhfr gene without any detectable loss of sequence. Restriction analysis of these interrupted mutants showed that at least 8-14 kb of "foreign" DNA sequence became joined to the gene at the point of disruption. Cytogenetic analysis of these mutants showed that in two cases an inversion of the banding pattern on chromosome Z-2 had taken place. The inverted dhfr mutants contain very low amounts of dhfr RNA sequences, and the 5' end of an inversion mutant gene exhibits the same pattern of DNA methylation and DNase I-hypersensitivity as the wild-type gene. Our results suggest that ionizing radiation causes primarily, if not exclusively, large deletions and inversions in mammalian cells.

Animals↗
PubMed1985

The effects of insulin and concanavalin A on the accumulation of a specific mRNA in rat hepatoma cells.

One of insulin's effects is to stimulate specific mRNA synthesis. Treatment of H4IIE hepatoma cells with 0.01-1.0 nM insulin results in a maximum 10-15 fold increase in the accumulation of a specific mRNA (p33-mRNA) as measured with a cloned cDNA. Concanavalin A, a lectin known to mimic many of insulin's effects, also stimulates the accumulation of p33-mRNA. The effects of both insulin and Con A were blocked by the addition of two RNA synthesis inhibitors, actinomycin D or 5,6 dichloro-1-beta-D-ribofuranosyl-benzimidazole. We therefore suggest that insulin and concanavalin A act to stimulate p33-mRNA synthesis.

Animals↗
PubMed1985

Effects of insulin alone on the accumulation of a specific mRNA in rat hepatoma cells.

Experiments were conducted to investigate the action of insulin alone on the induction of a specific mRNA referred to as p33. In 24-h serum-deprived rat liver hepatoma cells (H4) grown in monolayer cultures, insulin induced a 3-fold increase in the levels of p33 mRNA within 30 min, and a maximum 10-fold increase was observed by 1 h. The effects of insulin were evident at concentrations as low as 10(-12) M and were maximal at 0.5-1 X 10(-8) M. The effect of insulin was specific, since the level of mRNA for the histocompatibility complex, H2d, was unaffected by insulin. The increase in p33 mRNA was not due to an effect of insulin on the stabilization of mRNA, since insulin did not alter the half-life of this message. In addition, two different RNA synthesis inhibitors blocked the stimulation of p33 mRNA production by insulin. These data suggest that insulin may specifically stimulate the synthesis of p33 mRNA which results in an increased accumulation of total cellular p33 mRNA.

Animals↗
PubMed1972

-Galactosidase: immunological activity of ribosome-bound, growing polypeptide chains.

Ribosomes carrying nascent chains of beta-galactosidase were prepared by disruption of Escherichia coli in detergent-free buffer of high salt concentration, followed by purification on a discontinuous sucrose gradient. Assay by the method of immune hemolysis inhibition with anti-beta-galactosidase indicated that considerable amounts of antibody were bound by the growing chains. Much of the crossreacting material could be released from the ribosomes by treatment with puromycin. The ability to bind anti-beta-galactosidase was completely destroyed when ribosomes were heated at 60 degrees C. At very early times after induction, well before the appearance of active enzyme, crossreacting material could be demonstrated on ribosomes; this finding correlated with the appearance of an amino-terminal fragment of beta-galactosidase. Thus, growing chains of beta-galactosidase must begin to fold before their release from the ribosome.

Animals↗