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Biomedical subjects

L Stern

Publications and source records attributed to L Stern.

At least 73 records · Page 4Linked to original sources
PubMed1983

Gene expression during mammalian spermatogenesis. II. Evidence for stage-specific differences in mRNA populations.

Gene expression during murine spermatogenesis has been studied using highly enriched populations of cells obtained by velocity sedimentation at unit gravity and further purified by density gradient centrifugation through Percoll. Polypeptides whose synthesis was directed by total cytoplasmic RNA from round spermatids, pachytene spermatocytes, primitive type A spermatogonia, and Sertoli cells in cell-free translation systems have been compared by two-dimensional polyacrylamide gel electrophoresis, followed by fluorography. At the level of detection provided by the electrophoretic methods used, each population of cells contained mRNAs encoding over 200 polypeptides, many of which were present in high abundance in all four cell types. However, for each cell type examined, a minimum of 5-10% of these polypeptides appear to be either specific to or greatly enriched within a particular cell type. Analysis of the polysomal and nonpolysomal cell fractions from pachytene spermatocytes and round spermatids revealed that the two compartments share many identical mRNAs but specific mRNAs are selectively compartmentalized between the cell fractions and between the two cell types. Movement between compartments was seen; e.g., some polypeptides encoded by mRNA found primarily in the nonpolysomal fraction of pachytene cells were later seen in the polysomal fraction from round spermatids. Virtually every other combination was also observed. These results suggest that the control of gene expression at the level of selective production of mRNA and selective utilization of mRNA are among the mechanisms involved in regulation of spermatogenic cell differentiation.

Animals↗
PubMed1983

Gene expression during mammalian spermatogenesis. III. Changes in populations of mRNA during spermiogenesis.

Round spermatids and elongating spermatids were purified from a suspension of mouse testicular cells by sedimentation at unit gravity coupled with density gradient centrifugation through Percoll. Following separation, the two cell types were fractionated into polysomal and non-polysomal compartments. By comparison with round spermatids, elongating spermatids contain about one-half as much cytoplasmic RNA per cell, one sixth as much poly(A)+ RNA per cell and one-half the concentration of poly (A)+ mRNA in their cytoplasm. About two-thirds of the poly(A)+ messenger RNA (mRNA) was in the non-polysomal fraction in both cell types. Polypeptides whose synthesis was directed by cell-free translation of purified mRNA from each cell fraction were analyzed by two-dimensional gel electrophoresis. At the level of detection provided by the electrophoretic methods used, the majority of peptides from the polysomal and non-polysomal compartments for each cell type were similar. However, between the two cell types, approx. 5-10% of the polypeptides in the polysomal and non-polysomal fractions differed markedly in abundance. When the polypeptides encoded by the polysomal and non-polysomal mRNA from round spermatids were compared to the polypeptides encoded in the equivalent fractions from elongating spermatids, a significant reduction in number of polypeptides from elongating spermatids was seen. The presence of specific mRNAs in the non-polysomal fraction of round spermatids and in the polysomal fraction of elongating spermatids suggests that storage of mRNA in the cytoplasm and subsequent utilization provides a source of mRNA for proteins expressed at a time during spermiogenesis when transcription has terminated.

Animals↗
PubMed1983

The pathogenesis of Dupuytren's contracture: contractile mechanisms of the myofibroblasts.

The role of myofibroblasts in the pathogenesis of Dupuytren's contracture was investigated by light and electron microscopic histochemical methods. Dupuytren's myofibroblasts contain an intracellular contractile mechanism that is driven by the dephosphorylation of adenosine triphosphate. Our study of calcium adenosinetriphosphatase (ATPase) activities verifies that the site of this energy system is on the myofilaments of the myofibroblasts. The degree of ATPase activity, as determined by cell counts, appeared to correlate with the residual contracture as predicted by the Legge and McFarlane Outcome Standard Formula. Further, alcian blue staining on the ultrastructural level indicates that the myofibroblasts are associated with each other and with surrounding collagen by a glycosaminoglycan matrix 300 to 1000 A thick. Collagen fibrils are attached by a similar matrix comprised of 100 A thick fibrils. The dynamic cellular architecture of the multiple adjacent myofibroblasts with their connections to surrounding collagen may be partially responsible for the residual clinical deformities seen in this disease.

Adult↗
PubMed1983

Opportunity and health care: criticisms and suggestions.

orman Daniels' proposal to distribute health care on the basis of fair equality of opportunity, is, in this writer's opinion, unworkable. His concepts of species-typical activity and normal opportunity range are unclear; so is the relationship between them. His view that justice accords disease a better claim on the health dollar than other causes of death, pain, and disability, commits him unknowingly to indefensible positions on particular sorts of health care, such as the care of the aging and of pregnant women. Daniels' concept of opportunity is so inclusive, his notion of balancing opportunities so vague, that his theory loses systematic power. I offer a different account from Daniels' concerning why health care needs are objective and of special importance. I also argue for a voucher system which levels out class inequalities and which finances current medical practices more or less uncritically, but allows for change through a diversity of insurance plans available to consumers. This system is just, and more practical than rating health care needs by impact on opportunity.

Aging↗
PubMed1983

Gene expression during mammalian spermatogenesis. I. Evidence for stage-specific synthesis of polypeptides in vivo.

Following intratesticular injection of [35S]methionine or [3H]leucine, four testicular cell types (pachytene spermatocytes, round spermatids, elongating spermatids and residual bodies) were purified from mouse testicular cell suspensions by unit gravity sedimentation and equilibrium density gradient centrifugation through Percoll. Measurement of the amount of radiolabeled amino acid incorporated into protein in the testicular cells revealed that for a constant number of cells, pachytene spermatocytes incorporated 5.4 times more isotope than round spermatids, which incorporated 2.4 times more isotope than elongating spermatids. Analysis by two-dimensional gel electrophoresis of the polypeptides synthesized in vivo in the four testicular cell types demonstrated qualitative and quantitative changes in protein synthesis during spermatogenesis. At the level of detection provided by the electrophoretic methods used, pachytene spermatocytes and round spermatids synthesized approximately equivalent numbers of polypeptides while the number of polypeptides synthesized in elongating spermatids and residual bodies was decreased. Quantitative changes for polypeptides ranging in molecular weight from 16,500 to 82,000 were detected during spermatogenesis. For each cell type examined, a minimum of 5% of the polypeptides appear to be either unique or greatly enriched. These studies indicate that the expression of a sizable number of polypeptides is specific to certain stages of spermatogenesis.

Animals↗
PubMed1983

Uptake, storage and secretion of 5-hydroxytryptamine and its amino acid precursor by dispersed rat pancreas acinar cells.

Rat pancreas acinar cells contain 5-hydroxytryptamine (5-HT; 10.86 +/- 2.52 ng/i.u. amylase), all of which can be accounted for by the 5-HT recovered from the zymogen granule fraction of these cells (10.70 +/- 3.06 ng/i.u. amylase). When incubated with [14C]5-HT dispersed acinar cells take up the amine and concentrate it in zymogen granules. These cells will also take up [14C]5-HTP (5-hydroxytryptophan), decarboxylate it and store the [14C]5-HT so produced in zymogen granules. 5-HTP itself is not taken up by the granules. 5-HT is incorporated into zymogen granules early in their formation; no amine is accumulated by mature zymogen granules and the amine within the mature granule is not exchangeable with extragranular amine. When dispersed acinar cells pre-labelled with [14C]5-HT and [3H]leucine are stimulated with caerulein, there is a synchronous increase in amylase activity and secretion of [14C]5-HT and [3H]protein; the ratios of [3H]protein/[14C]5-HT in zymogen granules and in the secretory products are identical. Pancreas acinar cells take up L-DOPA, decarboxylate it and store the dopamine produced in zymogen granules but the dopamine is not retained by the granules (t1/2 approximately equal to 90 min) and dopamine secretion from cells exposed to caerulein could not be demonstrated. It is concluded that 5-HT is a normal component of rat pancreas acinar cell zymogen granule. The granular amine has a turnover rate similar to that of granular protein and is released when the cells are stimulated to secrete protein. All the 5-HT released from the cell originates in zymogen granules.

5-Hydroxytryptophan↗
PubMed1983

Drug-induced displacement of bilirubin from albumin in the newborn.

Kernicterus is probably caused by precipitation of insoluble bilirubin acid in brain cells. The pigment is transferred from blood plasma to cells. The tendency for precipitation depends upon the ratio of unconjugated plasma bilirubin concentration to the concentration of reserve albumin for binding of bilirubin and is increased when part of the albumin is occupied by competitive binding of a drug. Laboratory methods are available whereby it is possible, on certain well-defined presumptions, to measure this drug effect in quantitative terms. Measurements can be made in systems with pure albumin as well as in plasma samples from treated patients. It would thus appear feasible at the present stage to establish a basis for official testing of the bilirubin-displacing effects of drugs.

Bilirubin↗
PubMed1983

Performance characteristics of total hip femoral components as a function of prosthesis modulus.

A study of total hip femoral components was performed to demonstrate the effects of changes in prosthesis modulus upon strain levels and subsidence data measured in vitro. Femoral components of identical geometry but fabricated from dissimilar alloys were implanted sequentially in the same femoral specimens so that their relative performance could be compared. It was found that the components fabricated from titanium alloy produced higher levels of calcar strain than the cobalt-chromium components when collar/calcar contact was preserved. However, when collar/calcar contact was removed, cobalt-chromium stems showed a greater propensity for subsidence into the medullary cavity. The increased rate of subsidence of the stiffer stems produced concomitantly greater circumferential strain levels in the proximal cortical shell. It is concluded that the increased tensile hoop strain caused by subsidence of the cobalt-chromium stems will be particularly deleterious to the integrity of the cement mantle.

Biomechanical Phenomena↗
PubMed1982

The development of a child assessment interview for research and clinical use.

The Child Assessment Schedule (CAS) was developed to address the need for a standardized child interview that could be used for research and clinical purposes. The CAS has several distinguishing characteristics: (1) Questions and responses are standardized, (2) the format was designed to enhance rapport with the child, and (3) information necessary for DSM III childhood diagnoses is explicitly solicited. The CAS was administered to 32 child outpatients, 18 inpatients, and 37 normal controls. Derived scores were obtained for total psychopathology, 11 content areas, and 9 symptom complexes. Interrater reliability for the total CAS score was quite high. The CAS was able to discriminate among the three groups in total score indicating degree of psychopathology, on 9 of the 11 content areas, and on 8 of the 9 symptom complexes. Significant correlations were found between the CAS and maternal report of child behavior and between the CAS and child self-report of internal affects. It was concluded that the CAS has adequate reliability and validity, although further research is indicated.

Adolescent↗
PubMed1982

Early postnatal growth of low birthweight infants: what is optimal?

The question as to what is optimal depends on an examination of a number of questions which may be stated as follows: 1) Does physical growth as expressed by height and weight bear any relationship to functional or intellectual development? 2) Should postnatal growth of low birthweight (preterm) infants proceed at their presumed in utero growth rate? 3) Does caloric intake beyond a minimum level influence the growth rate and intellectual development of SGA infants? 4) What is optimal--or do we all need to be the same? These questions imply a projected benefit to nutritional techniques, amounts, and procedures. Against these must be balanced potential hazards which relate to a number of specific factors. These include the effort and expenditure of energies involved in feeding practices. The hazards inherent in gavage, intraluminal, and other forms of forced nutrition. Solute loading and the relationship of solute to free water content. The ommission of specific nutrients from any dietary regimen and the toxicity of other specific contents. A balanced approach combining all of these may best decide what is "optimal".

Body Height↗