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Biomedical subjects

S A Little

Publications and source records attributed to S A Little.

At least 19 recordsLinked to original sources
PubMed1992

Effects of 4-hydroperoxycyclophosphamide (4-OOH-CP) and 4-hydroperoxydechlorocyclophosphamide (4-OOH-deCICP) on the cell cycle of post implantation rat embryos.

In this study, we used preactivated forms of cyclophosphamide (CP) and dechlorocyclophosphamide (deClCP) to examine the effects of phosphoramide mustard (PM) and acrolein, respectively, on the cell cycle of postimplantation rat embryos. The percentage distribution of cells in the G1/G0, S, and G2/M phases of the cell cycle was determined by flow-cytometric analysis. At embryotoxic concentrations, 4-OOH-CP (PM) induced major cell cycle perturbations whereas 4-OOH-deClCP (acrolein) caused no major perturbation of the cell cycle. These data support the hypothesis that the mechanism of the embryotoxic action of PM involves alkylation of DNA, whereas the mechanism of action of acrolein does not. The primary effect of PM on the cell cycle was an initial delay in the S phase followed by a G2/M arrest. At low embryotoxic concentrations of 4-OOH-CP, there was apparent reversal of the G2/M arrest; at higher embryotoxic concentrations there was little recovery from the G2/M arrest. The high level of cell death found at higher drug concentrations suggests that prolonged G2/M arrest leads to cell death. Using radiolabeled CP and cell sorting, it was determined that PM predominantly alkylated DNA in the S phase of the cell cycle. Overall, the data from this study support the hypothesis that DNA cross-links, induced by the alkylation of DNA by PM, induce cell cycle perturbations. Furthermore, these cell cycle alterations may be one of the early steps in the mechanism leading to the embryotoxicity of PM.

Abnormalities, Drug-Induced↗
PubMed1992

Organization of cells and extracellular matrix in mesenteric arteries of spontaneously hypertensive rats.

Biochemical studies have been used to assess the quantitative changes in elastin and collagen in hypertensive vs. normotensive arteries. However, the relative distribution and organization of these fibrous proteins is likely to be equal in importance to their absolute amounts. In this study we have used scanning electron microscopy in association with selective digestion techniques to assess the organization of cellular and extracellular components of the tunica media of mesenteric arteries of spontaneously hypertensive rats. Superior and small mesenteric arteries were digested with acid, alkali, or bleach to exposure cells, collagen, or collagen and elastin, respectively. We observed that hypertension does not cause a qualitative change in the 3-dimensional arrangement of cells, collagen, or elastin in spontaneously hypertensive arteries when compared to normotensive arteries. However, cells in the superior artery are significantly different in overall shape and surface features when compared to cells of small arteries. These differences in surface morphology of cells are present in hypertensive and normotensive vessels and suggest that superior and small mesenteric artery cells transmit load to the isotropic matrix in different ways. In the elasto-muscular superior artery, force is transmitted across digitations throughout the cell surface. In the muscular small artery, force is transmitted across the tapered, smooth cell surface.

Animals↗
PubMed1992

An investigation of the relationship between microbial and particulate indoor air pollution and the sick building syndrome.

The sick building syndrome has been the subject of research for approximately 10 years. Although it is often suggested that symptoms in office workers are due to circulating micro-organisms or particles, epidemiological studies investigating the relationship between them have been lacking. This cross-sectional study has combined medical and aerobiological assessments of offices in Great Britain and has found that, although airborne particulates and micro-organisms are unlikely to be the sole cause of the sick building syndrome, positive associations between symptom prevalence rates and levels of airborne viable bacteria and fungi within groups of buildings with similar ventilation systems, suggest a possible causal link that should be explored.

Air Microbiology↗
PubMed1992

Three-dimensional characterization of dense bodies in contracted and relaxed mesenteric artery smooth muscle cells.

We have previously shown that dense bodies are not the static planar simple ovoidal structures they appear to be in thin sections. In this report, we present three-dimensional reconstructions from consecutive serial thin sections through shortened and non-shortened large mesenteric artery cells. Profiles of the cell surface, membrane dense bodies, and cytoplasmic dense bodies were reconstructed from consecutive thin sections and the distribution, size, shape, and spatial relationships among these components was examined. Within the cell, membrane dense bodies are numerous and occupy approximately 10% of the cell volume. Membrane dense bodies can attach to the cell surface laterally, obliquely or normally. An individual membrane dense body can be continuous over more than 2 microns of cell depth and can change shape throughout its depth. On cell shortening, many membrane dense bodies assume a crenated shape. Compared to membrane dense bodies, cytoplasmic dense bodies are smaller in all dimensions and occupy about 2% of the cell volume. In shortened cells, cytoplasmic dense bodies appear to cluster into groups. This redistribution of cytoplasmic dense bodies may be related to the reorganization of contractile units when the cell shortens.

Animals↗
PubMed1991

Three-dimensional structure of dense bodies in rabbit renal artery smooth muscle.

In this report, we present a three-dimensional computer assisted reconstruction study from serial thin sections through a rabbit renal artery smooth muscle cell. In a series of 32 consecutive thin (100-nm) sections, one longitudinally oriented cell was followed and photographed in alternating sections. The profiles of the cell surface and dense bodies were reconstructed from these 16 planes and the distribution, size, shape, and spatial relationships among these components was examined. The reconstructed images showed that the cell decreases in diameter from its widest region in the center to the two ends in a step-wise taper. Within the cell, dense bodies are numerous. Relative to the cell axes, a membrane associated dense body (MDB) can be less than or equal to 3.5 microns long, 0.25 micron wide, and may extend up to 2 microns in depth. While the MDB profile in one section may be aligned with the long axis of the cell, in an adjacent section the same dense body may appear almost circular or wedge shaped. The same is true of cytoplasmic dense bodies (CDBs). Compared with MDBs, CDBs are smaller in all dimensions. Some, but not all, CDBs line up in strings oriented with the long axis of the cell. The continuity of dense bodies over considerable cell depth and their change in shape may have important implications for integration of contractile activity and for transmitting passive tension to the extracellular matrix.

Animals↗
PubMed1991

Quantitation and immunohistochemical localization of DNA adducts in rat embryos and associated yolk sac membranes exposed in vitro to N-acetoxy-2-acetylaminofluorene (N-Ac-AAF).

Specific antibodies and radioimmunoassay (RIA) were used to measure the levels of acetylated and deacetylated C-8 substituted deoxyguanosine adducts in day 11 rat embryos and their associated yolk sacs after exposure of whole rat conceptuses in vitro to the teratogen N-acetoxy-2-acetylaminofluorene (N-Ac-AAF). The deacetylated adduct predominates in both the embryo and the associated yolk sac, and a dose response for adduct formation was observed when adducts were quantitated by RIA. Immunohistochemical localization of the deacetylated adducts revealed that adducts were confined to the nuclei in all tissues examined and that the abundance of adducts varied within and between tissues. Our initial findings indicate that specific DNA adduct antibodies may be useful in the study of teratogenesis induced by a wide variety of agents that modify DNA.

Acetoxyacetylaminofluorene↗
PubMed1991

Developmental regulation of heat shock protein synthesis and HSP 70 RNA accumulation during postimplantation rat embryogenesis.

Exposure of postimplantation rat embryos on days 9, 10, 11, and 12 of gestation to an in vitro heat shock of 43 degrees C for 30 min results in the induction of heat shock proteins (HSPs) in day 9 and 10 embryos, a severely attenuated response in day 11 embryos, and no detectable response in day 12 embryos. The heat shock response in day 9 embryos (presomite stage) is characterized by the synthesis of HSPs with molecular weights of 28-78 kDa. In heat shocked day 10 embryos, two additional HSPs are induced (34 and 82 kDa). In addition, two HSPs present on day 9 are absent on day 10. In day 11 heat shocked embryos, only three HSPs (31, 39, and 69 kDa) are induced, while in day 12 embryos no detectable HSPs are induced. Northern blot analysis of HSP 70 RNA levels indicates that the accumulation of this RNA, but not actin RNA, varies depending on developmental stage at the time of exposure to heat as well as the duration of the heat shock. Day 9 embryos exhibit the most pronounced accumulation of HSP 70 RNA while embryos on days 10-12 exhibit an increasingly attenuated accumulation of HSP 70 RNA, particularly after the more acute exposures (43 degrees C for 30 or 60 min). Thus, the ability to synthesize HSP 70 and to accumulate HSP 70 RNA changes dramatically as rat embryos develop from day 9 to day 12 (presomite to 31-35 somite stages).

Animals↗
PubMed1991

Organization of rat mesenteric artery after removal of cells of extracellular matrix components.

Rat mesenteric arteries, perfusion fixed in relaxed or contracted conditions, were digested with acid and elastase, bleach (sodium hypochlorite), or alkali to selectively remove collagen, elastin, or cells. Scanning electron microscopy was used to study the three-dimensional organization of the remaining cells or extracellular components. Smooth muscle cells of the tunica media were elongated and circumferentially oriented. Superior mesenteric artery cells had an irregular surface with numerous projections and some ends were forked. Small mesenteric artery cells were spindle shaped with longitudinal surface ridges, and showed extensive corrugations upon contraction. Elastin was present both as laminae and as an interconnected fibrous meshwork. Collagen was arranged in an irregular network of individual fibrils and small bundles of fibrils that formed nests around the cells in both arteries. This irregular arrangement persisted, with no apparent reordering or loss of order, upon contraction. The lack of an ordered arrangement or specialized organization at the cell ends suggests mechanical coupling of the cells to elastin or collagen throughout the length of the cell, allowing for force transmission in a number of directions. The tunica media is thus a "composite" material consisting of cells, elastin, and collagen. The isotropic network of fibers is well suited for transmitting the shearing forces placed on it by contraction of smooth muscle cells and by pressure-induced loading.

Animals↗
PubMed1990

Measurement of airborne mite antigen in homes of asthmatic children.

The airborne concentration of major house dust mite antigen Der p1 was measured by low volume sampling (2 litres/min) in the homes of 68 allergic, asthmatic children. The presence of detectable airborne antigen was strongly associated with sensitivity to the mite, whereas there was no significant relation between sensitivity and the previously recommended threshold level of 2 micrograms Der p1 per g carpet dust. There was a significant association with lower threshold levels in carpet dust (0.5 microgram/g) but at no level was the association as strong as that with air measurements. Concentrations of airborne antigen were higher in rooms with wool carpets than in those with synthetic carpets or hard floors, but there was no significant difference between the dust levels of Der p1 in the two carpet types. Air sampling is a more appropriate method of assessing antigen exposure than dust sampling for asthmatic patients.

Adolescent↗
PubMed1990

Effects of temperature and buffer composition on calcium sequestration by sarcoplasmic reticulum and plasma membrane of rabbit renal artery.

45Ca electron microscopic autoradiography was used to examine the effects of buffer composition and temperature on the distribution of calcium in rabbit renal artery smooth muscle cells. The results show that the relative distribution of calcium is dependent on both the buffer used (Tris or Krebs) and the temperature of the bathing solution (25 degrees C or 34 degrees C). Krebs buffer at 34 degrees C gave the highest relative activity in the plasma membrane, sarcoplasmic reticulum, and mitochondria. Buffer and temperature had little effect on the relative activity of the nucleus or cytoplasm. Next, we identified the cellular sites of calcium accumulation after 5, 15, 30, or 60 min exposure to 45Ca in Krebs buffer at 34 degrees C. The results show that sarcoplasmic reticulum and plasma membrane are the primary sites of calcium accumulation during influx into these cells. Although the amount of 45Ca in the cell continues to increase with longer exposure, the relative distribution of calcium is essentially the same after 5 or 60 min. The data also indicate that the relative activity of plasma membrane + sarcoplasmic reticulum (a combination site that includes sarcoplasmic reticulum within a mean distance of 275 nm of the plasma membrane) is similar to the membrane alone and is lower than the sarcoplasmic reticulum alone.

Animals↗
PubMed1990

Binding of (chloroethyl 3H) cyclophosphamide to rat embryo proteins: two-dimensional gel analysis.

Cells of the heart of the day 10 rat embryo are resistant to the cytotoxic effects of cyclophosphamide (CP) while cells of neuroepithelium (head) are sensitive. Using radiolabeled CP we have investigated the hypothesis that this difference in sensitivity is related to the binding (alkylation) of drug to specific proteins in heart and head cells. Two-dimensional gel analysis reveals that CP alkylates a variety of proteins in both heart and head cells. Although minor differences in the profiles of alkylated proteins exist between heart and head cells, the major proteins alkylated by CP in the two populations are identical. These data, therefore, do not support the hypothesis that sensitivity to the cytotoxic effects of CP is related to drug binding to specific proteins.

Alkylating Agents↗
PubMed1990

Relationship of DNA damage and embryotoxicity induced by 4-hydroperoxydechlorocyclophosphamide in postimplantation rat embryos.

4-Hydroperoxydechlorocyclophosphamide (4-OOHdeCl-CP) is a preactivated analogue of cyclophosphamide (CP) that undergoes an elimination reaction to yield acrolein and the nonalkylating derivative of phosphoramide mustard (PM), i.e., dechlorophosphoramide mustard. We used this analogue to assess the role of acrolein in CP-induced embryotoxicity. Embryotoxicity was assessed using day 10 rat embryos cultured in vitro. 4-OOHdeC1-CP was embryotoxic over a concentration range of approximately 75-150 microM and produced complete embryolethality at concentrations of 175 microM and above. This analogue induced abnormal development characterized by tail defects at low drug concentrations and microencephaly or prosencephalic hypoplasia at high concentrations. Using the technique of alkaline elution, we also assessed DNA damage induced by embryotoxic concentrations of drug. When embryos were cultured in serum-containing medium during drug exposure, no DNA damage was detected, even at embryolethal drug concentrations. However, if cellular glutathione (GSH) was depleted with buthionine sulfoximine (BSO) before drug exposure and embryos were cultured in serum-free medium during drug exposure, DNA damage, primarily DNA single-strand breaks, was detected, but only at embryolethal concentrations. Using radiolabeled CP, we showed that acrolein does reach the embryo; however, more acrolein is incorporated into the yolk sac. Binding studies revealed that acrolein binds preferentially to cellular protein, whereas PM binds preferentially to DNA. These results suggest that, unlike the case with PM, the embryotoxic target for acrolein is protein and not DNA. Furthermore, our results indicate that acrolein may mediate its effects on the embryo via the yolk sac.

Acrolein↗
PubMed1988

Effect of calcium channel antagonists on calcium uptake and release by isolated rat cardiac mitochondria.

The effects of calcium channel antagonists on Ca2+ uptake and Na+-induced Ca2+ release were studied in isolated rat cardiac mitochondria. Diltiazem, nitrendipine and nimodipine were more effective inhibitors of Na+-induced Ca2+ release (IC50 = 19-100 microM) than of Ca2+ uptake (IC50 = 0.2-1 mM). Nitrendipine and nimodipine had virtually identical IC50 values for inhibiting Ca2+ uptake, but nitrendipine was 3-4 times more potent than nimodipine at inhibiting Na+-induced Ca2+ release. If these calcium channel antagonists achieve intracellular concentrations in the range of 10(-5)-10(-4) M, our results suggest that calcium channel antagonists would preferentially inhibit mitochondrial calcium release more than mitochondrial calcium uptake.

Animals↗
PubMed1987

DNA cross-linking and single-strand breaks induced by teratogenic concentrations of 4-hydroperoxycyclophosphamide and phosphoramide mustard in postimplantation rat embryos.

Postimplantation rat embryos (Day 10) were exposed in vitro to teratogenic concentrations of 4-hydroperoxycyclophosphamide, an activated form of cyclophosphamide, and phosphoramide mustard, the major teratogenic metabolite of cyclophosphamide. Following a 5-h exposure to these agents, drug-induced DNA damage was assessed by alkaline elution. Both drugs induced detectable DNA cross-linking at teratogenic concentrations. Alkaline elution combined with proteinase K digestion indicated that approximately half of the DNA cross-linking was DNA-DNA cross-linking and the other half was DNA-protein cross-linking. In addition to DNA cross-linking, phosphoramide mustard produced DNA strand breaks and/or alkaline labile sites. However, 4-hydroperoxycyclophosphamide did not produce detectable DNA strand breaks or alkaline labile sites. Our data also indicate that the induction of abnormal morphogenesis by 4-hydroperoxycyclophosphamide and phosphoramide mustard is correlated with drug-induced DNA cross-linking.

Animals↗
PubMed1987

Localization of calcium in vas deferens using 45Ca EM autoradiography: relationship to species and the effect of 45Ca removal.

The distribution of calcium was determined in the vas deferens of the guinea pig using 45Ca electron microscopic autoradiography of rapidly frozen, freeze-dried, and embedded tissue. A selective accumulation of calcium at the plasma membrane and SR was observed in vas deferens that had been incubated in 45Ca for 65-85 min prior to rapid freezing. Rinsing the tissue in nonradioactive calcium for 6 min prior to rapid freezing significantly altered the distribution of calcium among the plasma membrane, mitochondria, and cytoplasmic matrix. The influence of species on the observed distribution of calcium was also examined. The distribution of calcium in the guinea pig vas deferens was not significantly different from that in the rabbit vas deferens when the tissues were prepared under identical conditions.

Animals↗