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Biomedical subjects

D McMahon

Publications and source records attributed to D McMahon.

69 records · Page 4Linked to original sources
PubMed1975

Cycloheximide is not a specific inhibitor of protein synthesis in vivo.

Cycloheximide is frequently presumed to inhibit specifically the cytoplasmic protein synthesis of eukaryotes. Although previous investigators have shown that it had other effects on the cells of a variety of organisms, these results were frequently presumed to be secondary effects of the inhibition of protein synthesis. This paper shows that a wide range of deleterious effects are produced by cycloheximide on a single organism, Chlamydomonas reinhardi Dangeard. If, protein synthesis is inhibited by nonpermissive conditions in temperature-sensitive mutants or with other treatments these "secondary" effects are not produced. Instead, cycloheximide appears to have two or three independent inhibitory effects on the cell. Moreover, in contrast to a number of previous investigations, these results show that protein synthesis is not required for RNA synthesis. Instead the rate of RNA synthesis is actually increased by interference with protein synthesis.

Journal Article↗
PubMed1974

Chemical messengers in development: a hypothesis.

The hypothesis that physiological and developmental regulatory mechanisms are similar has been presented. Well-known developmental systems chosen illustrate the capability of the model to suggest a simple mechanism underlying the effects on development of a diverse group of chemicals. This hypothesis might be applied to other systems including the induction of the lens, limb regeneration, and the induction of the head of hydra (124). I have proposed this hypothesis not only because it permits consideration of a complex and varied array of experimental observations as reflections of a simple basic biochemical mechanism, but because recent technical advances in instrumentation and methods allow it to be directly tested. The fluorescent antibody method for the cytochemical measurement of cyclic nucleotides provides a means for investigating changes in the concentrations of cyclic nucleotides in developing cells and could also be used to detect neurotransmitters in developing cells. Similarly, the scanning electron microscope in the emitted x-ray mode provides a method for measuring changes in the content and distribution of cations within developing cells. The hypothesis presented here suggests pleasing asceticism on the part of eukaryotes. It suggests that simple derivatives of metabolites, including neurotransmitters and cyclic nucleotides, are linked together as regulatory molecules throughout the eukaryotes. The neurotransmitters are suggested to have a more general role in information transmission in eukaryotes than is generally accepted. They are hypothesized to have progressed during evolution from being intracellular messengers to a role as intercellular messengers for the relatively slow communication of developmental informatbn; and, finally, this process has culminated with their participation in the rapid intercellular communication mediated by nerves. The thought that the complex pictures of physiological regulation and of the construction of a complex multicellular organism like man might be painted with so few colors is quite satisfying.

Adenylyl Cyclases↗
PubMed1973

A cell-contact model for cellular position determination in development.

The fate of a cell in a developing organism is a function of its position within the organism. The molecular mechanism that cells use to determine their position and to convert positional information into a form that can be used to regulate the expression of genes is not understood. This paper presents a model in which contacts between complementary molecules on plasma membranes of adjacent cells regulate the concentration of a morphogenetic substance and transmit positional information. This model is described by four equations that, when solved with realistic parameters, demonstrated that this mechanism will produce discrete populations of cells within a few hours from an initially undifferentiated array of cells. The model suggests an explanation for several phenomena that have been observed and suggests experiments to test it and to clearly differentiate it from other models for position determination.

Amoeba↗
PubMed1968

Inhibition of the formation of photosynthetic enzymes by inhibitors of photosynthesis.

It has been shown previously that an increase in ribulose diphosphate carboxylase activity occurs upon brief illumination of leaves of dark-grown Zea mays plants; an increase in ribose 5-phosphate isomerase occurs after prolonged illumination. Both of these responses to illumination are inhibited by chloramphenicol.The administration of p-chlorophenyldimethylurea, an inhibitor of photosynthesis, to etiolated maize does not affect the normal early rise in ribulose diphosphate carboxylase activity when the leaves are illuminated but does block the increase in ribose 5-phosphate isomerase. This pattern of response suggests that photosynthetic activity is required for the increase in isomerase-perhaps products of photosynthesis induce isomerase synthesis-but that the level of ribulose diphosphate carboxylase is controlled by other processes. Chlorophyll formation (as has been shown by others) is slightly suppressed by the inhibitor; levels of total soluble leaf protein appear to be unaffected.Salicylaldoxime, which is a more general inhibitor of metabolism than p-chlorophenyldimethylurea, arrests the normally observed increases of ribulose diphosphate carboxylase, ribose 5-phosphate isomerase, and chlorophyll during illumination of dark-grown maize. The level of soluble leaf protein is also lower in leaves treated with this compound.

Journal Article↗
PubMed1967

Early effects of illumination on the activity of some photosynthetic enzymes.

Leaves of dark-grown corn (Zea mays) were illuminated for periods ranging from 3 minutes to 12 hours. The changes in the activities of ribose-5-phosphate isomerase, ribulose-5-phosphate kinase, and ribulose-1,5-diphosphate carboxylase were followed.The activity of ribose-5-phosphate isomerase did not change significantly until between 12 and 24 hours of illumination. An increase in ribulose-5-phosphate kinase activity occurred after a lag of about 6 hours. The increase in carboxylase activity began after 3 minutes of illumination and increased until after 3 to 6 hours in the light, after which it began to decline. The increases in these enzymes appear to be the result of protein synthesis.

Journal Article↗
PubMedDate not supplied

The role of nursing in a support group for heart transplantation recipients and their families.

Heart transplantation, an increasingly accepted intervention to prolong life, involves specific nursing interventions, not only in the area of patient physical care but also in areas of health teaching and psychosocial assessment. This study discusses data collected from a support group created in September 1984 for heart transplant recipients and their families. The major concerns of patients and families were identified and translated into implications for nursing care. Fourteen sessions were voice-recorded and analyzed, identifying common, recurring topics. A total of 24 potential candidates for transplantation and recipients, ranging in age from 19 to 52 years, and eight wives participated in at least one of the weekly sessions. The average attendance per session was eight patients and three wives. The major areas of concern related to; health maintenance, role-relationships, self perception/self concept, values/beliefs regarding health, and coping/stress tolerance. Preoperative patients had greater concern for health maintenance, whereas patients in the post-transplant period were more concerned about role-relationships, sexual function and activity-exercise patterns. Nursing implications in these areas included in-depth health teaching about procedures, medications and their side effects, self-care regarding signs and symptoms of infection or rejection, and dietary requirements and limitations. Other aspects involved psychosocial adjustments following discharge from the hospital.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Psychological↗
PubMedDate not supplied

The diagnosis of dementia associated with alcoholism: a preliminary report of a new approach.

The historical, clinical, neurological and neuropsychological features of 13 subjects with independently diagnosed dementia associated with alcoholism (AlcD) were compared to 13 subjects with probable Alzheimer's disease (AD), matched for age and severity of dementia. Neurological abnormalities were present in all the subjects with AlcD even though the diagnosis of Wernicke-Korsakoff was recorded in only one of these subjects. Only one subject with probable AD demonstrated any neurological abnormality. There was no difference between the AD and AlcD subjects in either the total scores of the Mini-Mental State Examination (MMSE) or in any of the subscores. The presence of neurological signs does appear to be a useful method to assist in the diagnosis of AlcD.

Aged↗