Effect of dietary lipids on plasma lipoproteins and fluidity of lymphoid cell membranes in normal and leukemic mice

Mice of the GR/A strain were fed four different isocaloric semipurified diets, enriched in either (1) saturated fatty acids (palm oil), or (2) polyunsaturated fatty acids (corn oil), or (3) palm oil plus cholesterol, or (4) a fat-poor diet containing only a minimal amount of essential fatty acids. We have studied the effects of these dietary lipids on the density profile and composition of the plasma lipoproteins and on the lipid composition and fluidity of (purified) lymphoid cell membranes in healthy mice and in mice bearing a transplanted lymphoid leukemia (GRSL). Tumor development in these mice occurred in the spleen and in ascites. While the fatty acid composition of the VLDL-triacylglycerols still strongly resembled the dietary lipids, the effects of the diets decreased in the order VLDL-triacylglycerols greater than HDL-phospholipids greater than plasma membrane phospholipids. Diet-induced differences in the latter fraction were virtually confined to the content of oleic acid and linoleic acid, and they were too small to affect the membrane fluidity, as measured by fluorescence polarization using the probe 1,6-diphenyl-1,3,5-hexatriene. Healthy mice were almost irresponsive to dietary cholesterol, but in the tumor bearers, where lipoprotein metabolism has been shown to be disturbed, the cholesterol diet caused a substantial increase in the low- and very-low density regions of both blood and ascites plasma lipoproteins. The cholesterol-rich diet also increased the cholesterol/phospholipid molar ratio and lipid structural order (decreased fluidity) in GRSL ascites cell membranes, but not in the splenic GRSL cell membranes. We conclude that the composition of plasma lipoproteins and cell membrane lipids in GR/A mice is subject to exquisite homeostatic control. However, in these low-responders to dietary lipids the development of an ascites tumor may lead to increased responsiveness to dietary cholesterol. The elevated level of membrane cholesterol thus obtained in GRSL ascites cells did not affect the expression of various cell surface antigens or tumor cell growth.     

Stabilization of methionine-enkephalin in human and rat blood

Methods of preventing the degradation of 3H-methionine-enkephalin (3H-ME) in human blood both at 37 degrees C and under conditions of immediate cooling were examined. We found that, contrary to previous suggestions, use of aprotinin (with or without immediate cooling) was ineffective in preventing the degradation of 3H-ME in blood. Thus, previous reports on the circulating levels of ME which relied on such procedures to stabilize the ME may have reported artifactually low values. However, we found that citric acid effectively prevents 3H-ME breakdown in both human and rat blood. Thus, we propose the use of citric acid, mixed with blood immediately upon collection, as an effective method for the stabilization of ME in blood.     

Double immunocytochemical staining in the study of antibody-producing cells in vivo. Combined detection of antigen specificity (anti-TNP) and (sub)class of intracellular antibodies

Mice and rabbits were immunized with trinitrophenyl (TNP)-conjugated keyhole limpet hemocyanin (KLH). Cells producing specific antibodies against the hapten TNP were detected in vivo in spleen and lymph nodes using a TNP--alkaline phosphatase (AP) conjugate. Using horseradish peroxidase (HRP)-conjugated anti-mouse (sub)class (IgG2A, IgG2B, IgM) antibodies and anti-rabbit class (IgG, IgM) antibodies and a double immunocytochemical staining technique for simultaneous demonstration of the enzymes AP and HRP, we were able to determine both the antigen specificity (anti-TNP) and the (sub)class of intracellular antibodies produced by individual antibody-forming cells in vivo.     

Antagonistic effects of thyrotropin and epidermal growth factor on thyroglobulin mRNA level in cultured thyroid cells

Both thyrotropin (TSH) and epidermal growth factor (EGF) are potent mitogenic agents when added to dog thyroid cells in primary culture [Roger, P. P. and Dumont, J. E. (1984) Mol. Cell. Endocrinol. 36, 79-93]. The concomitant effect of these agents on the differentiation state of the cells was appreciated using cell morphology, iodide trapping, thyroglobulin synthesis and cytoplasmic thyroglobulin mRNA content as markers. Together with previous results [Mol. Cell. Endocrinol. 36, 79-93 (1984)] it is shown that cells cultured in the continuous presence of TSH maintain all the parameters at a near normal level. In the absence of TSH, thyroglobulin mRNA decreased to very low, though still detectable levels. Addition of TSH restored subnormal mRNA levels. Culture of cells in the presence of EGF for 4-6 days affected profoundly their morphology, abolished iodide trapping and decreased thyroglobulin synthesis and cytoplasmic mRNA content to undetectable levels. Addition of TSH to cells previously exposed to EGF reversed the growth factor effect on all four indexes. The redifferentiating effect of TSH was well observed within 3-4 days and was mimicked by the adenylate cyclase activators, forskolin and cholera toxin. When administered simultaneously, TSH and EGF achieved an intermediate situation, EGF antagonizing partially the effect of TSH on the expression of thyroglobulin gene. Another growth factor, fibroblast growth factor, while promoting thyroid cell proliferation also, did not interfere at all with TSH effects on cytoplasmic thyroglobulin mRNA content. Our results make the dog thyroid cell in primary culture an appropriate model to study the mechanisms involved in gene regulation by cyclic AMP and growth factors.     

Resonance Raman evidence for the activation of dioxygen in horseradish oxyperoxidase

Resonance Raman spectroscopy has been employed to investigate the molecular bases for the markedly different properties of horseradish oxyperoxidase and oxymyoglobin. The porphyrin core of oxyperoxidase is slightly more expanded with the iron atom closer to the porphyrin plane, and there is greater iron d pi-to-oxygen pi backbonding compared to oxymyoglobin. The iron-oxygen (stretching or bending) bands are observed at 570 and 562 cm-1, respectively, for oxymyoglobin and oxyperoxidase, and the iron-His stretching bands have been tentatively identified at 276 and 289 cm-1, respectively. It is suggested that the stronger iron-His bond in oxyperoxidase facilitates greater iron d pi-to-oxygen pi backdonation by raising the energy of the iron d pi orbitals closer to the energy of the oxygen pi orbitals. This weakens the O-O bond and activates dioxygen for use as an electron acceptor in the peroxidase-oxidase reaction.     

An immunocytochemical study of the optic ganglia of the crayfish Astacus leptodactylus (Nordmann 1842) with antisera against biologically active peptides of vertebrates and invertebrates

Summary The peptidergic system in the optic ganglia of Astacus leptodactylus is characterized by the immunocytochemical application of 15 antisera raised against biologically active peptides of vertebrates and invertebrates. Positive reactions were found with anti-FMRFamide, antiMSH, anti-vasotocin, anti-gastrin, anti-CCK, anti-oxytocin, anti-secretin, anti-glucagon and anti-GIP. Based on immunochemical reaction and localization it is possible to distinguish 30 cell groups. Only part of these cell groups is found in the known classical neurosecretory cell regions. This observation demonstrates a more extensive peptidergic system than formerly recognized. The morphology of this peptidergic system suggests that one part is neurohormonal and the other part neurotransmitter-like or neuromodulatory.     

Development of an assay to assess the functional integrity of the human sperm membrane and its relationship to other semen characteristics

The objective of this study was to develop a relatively simple test to evaluate the functional integrity of the membranes of human spermatozoa. As in some other species, human spermatozoa 'swell' under hypo-osmotic conditions due to the influx of water and the expansion of the membranes. A mixture of equal parts of fructose and sodium citrate (150 mosmol) with calculated ionic strength of 0.15 resulted in a maximal number of clearly identifiable swollen spermatozoa. Only small variations were seen when different aliquants of the same semen samples were separately evaluated. A high correlation (r = 0.94) was obtained between expected and observed values of swollen spermatozoa when known amounts of heat-treated spermatozoa, unable to undergo swelling, were added to untreated spermatozoa. A good correlation (r = 0.90) was also observed between the % spermatozoa in a semen sample that were capable of undergoing swelling and the % of denuded hamster oocytes that were penetrated by capacitated spermatozoa from the same semen sample. By contrast, the correlations between % sperm swelling in ejaculates and % normal sperm forms, % motile spermatozoa and % spermatozoa that do not stain with eosin-Y (supravital stain) in the same ejaculates were 0.30, 0.61 and 0.52, respectively. Therefore, the hypoosmotic swelling technique to evaluate the functional integrity of the sperm membrane appears to give high repeatability and accuracy and is closely correlated to the in-vitro fertilizing ability of spermatozoa. It may be a useful addition to the standard semen analysis.