Involvement of a pertussis toxin-sensitive G-protein-coupled phospholipase A2 in lipopolysaccharide-stimulated prostaglandin E2 synthesis in cultured rat mesangial cells

E. coli lipopolysaccharide (LPS) stimulated a dose- and time-dependent release of prostaglandin E2 (PGE2) in cultured rat glomerular mesangial cells. Pertussis toxin, an inhibitor of several GTP-binding proteins (G proteins), blocked nearly 80% of the LPS-stimulated PGE2 formation, while having virtually no effect on calcium ionophore-stimulated PGE2 production. We tested the possibility that a G protein-coupled activation of phospholipase A2 mediated the LPS-stimulated PGE2 production. Evidence for LPS activation of phospholipase A2 included a time-dependent LPS-induced generation of [32P]lysophosphatidylcholine and the inhibitory effects of a phospholipase A2 inhibitor, mepacrine, on LPS-induced PGE2 formation. Possible roles for phospholipase C-dependent activation of PGE2 synthesis by LPS seemed unlikely, as LPS did not elevate the cytosolic free calcium concentration or augment the appearance of water-soluble inositol phosphates. We conclude that LPS-induced PGE2 synthesis in rat glomerular mesangial cells is mediated through a G-protein-coupled phospholipase A2 activation. The activation of phospholipase A2 releases arachidonic acid and stimulates PGE2 synthesis preferentially, thereby improving glomerular hemodynamic events in endotoxemia.

Effect of desynchronized inputs on compound sensory and muscle action potentials

Stimulation of the second (S1) or third (S2) digit elicits a median sensory potential at the wrist. Similarly, a shock applied to the median (Sm) or ulnar (Su) nerve at the wrist evokes a sensory potential of the fourth digit and a muscle potential over the thenar eminence. Hence, a concomitant application of S1 and S2 or Sm and Su with varying interstimulus intervals simulates the effect of desynchronized inputs. In 10 hands, a shift in latency on the order of 1 msec between S1 and S2 or Sm and Su caused a major reduction in sensory potential by as much as 30-40% but little change in muscle action potential. A latency difference slightly less than one-half the total duration of unit discharge maximized the phase cancellation between the two components and consequently the loss of area under the waveform.

Purification of a nuclear trans-acting factor involved in the regulated transcription of a human immunoglobulin heavy chain gene

The expression of the rearranged human immunoglobulin gamma 1 heavy chain gene (HIG1) was shown to be induced through its enhancer by the positive regulatory trans-acting factor(s) that was contained only in cells of B lineage. The trans-acting factors were purified from mouse myeloma NS1 cells, and HIG1-inducing activity was found mainly in fractions of molecular weight 53-127 kd and in a fraction eluted from a heparin-Sepharose column with 0.5 M KCI. This semipurified fraction contained proteins binding to the conserved octamer sequence, ATGCAAAT, in the promoter region, as well as to sequences in the enhancer region. The 0.5 M KCI eluates from a heparin-Sepharose column were applied to a DNA affinity column of synthetic oligonucleotides of the octamer sequence and the sequence TATTTTAGGAAGCAAA in the HpaII-BgIII region of the HIG1 gene enhancer. The protein eluted from the enhancer sequence-specific DNA affinity column showed a strong inducing activity for the HIG1 gene, and the molecular weight of a predominant protein was 96 kd.

Ground level refractivity and scintillation in space-earth links

Slant-path scintillations are investigated by means of measurements at microwaves made in Rome and Beijing using the SIRIO satellite. Comparison with ground level temperature, humidity, and radio refractivity is performed, and close similarity is found with daily and seasonal behavior of the scintillations. An explanation of this similarity is proposed that leads to simple empirical relationships between the scintillation intensity and the ground level quantities. The intensity of scintillations has been also estimated using meteorological radiosonde measurements, and satisfactory agreement is found with simultaneous direct scintillation measurements.

The effects of endotoxin on platelet-activating factor synthesis in cultured rat glomerular mesangial cells

Platelet-activating factor (PAF), a potent vasoactive phospholipid, may contribute to acute renal failure and septic shock accompanying endotoxemia. Rat glomerular mesangial cells in culture synthesize PAF and contract after the addition of PAF. We thus investigated the potential of mesangial cells to respond to Escherichia coli lipopolysaccharide endotoxin with enhanced PAF synthesis in vitro. The mesangial cells were incubated with [3H]acetate, substrate for lyso-PAF: acetyl-CoA acetyltransferase, and endotoxin at different concentrations for various periods of time at 37 degrees C. Lipids were extracted and PAF was isolated by thin-layer chromatography. Endotoxin stimulated PAF generation in a time- and dose-related manner. Whereas most of the PAF was associated with the cells, endotoxin more than doubled the amount of PAF released into the extracellular medium as compared to control. Furthermore, the PAF-like material obtained from endotoxin-stimulated mesangial cells irreversibly aggregated washed rabbit platelets. This effect was lost after alkaline methanolysis and was totally blocked by L-652,731, a specific PAF-receptor antagonist. Finally, the PAF-like material exerted a hypotensive effect, which was abolished by L-652,731, when infused intravenously into healthy rats. These data indicate that rat glomerular mesangial cells have the ability to synthesize PAF in response to endotoxin. This suggests that PAF, so generated within the glomerulus, may contribute to acute decrements of glomerular filtration rate in endotoxemia.

Resting energy expenditure, body composition, and excess weight in the obese

This study investigated differences between measured and predicted resting energy expenditure (REE) in 80 women who averaged 104.6 kg in weight and were 49 kg and 88% overweight. Body composition analysis showed that 68% of the excess weight was fat and 32% was fat-free mass (FFM). Normalized for height, total body potassium (TBK) was 113 +/- 15% and total body water (TBW) was 133 +/- 21% of values in nonobese controls. The health of the FFM, defined as the potassium content per kg of FFM, was 84 +/- 13% of normal. Measured and predicted REE were only modestly related (r = +.59), and only 59% of measured REEs were within 10% of predicted values. A stepwise multiple regression indicated that weight was the single best predictor of measured REE and that the size of the FFM made a significantly greater contribution to REE than did the size of the fat mass. Commonly used equations for the prediction of REE are not appropriate for moderately or severely obese patients. Caloric prescription for weight reduction must be tailored to individuals rather than recommending the same caloric intake to persons with varying metabolic rates.

Seroprevalence of Legionella in Shanxi Province, China

Using an ELISA with bacterial sonicate antigens, the prevalence of antibodies to the antigens of 15 legionellae was determined in 319 healthy individuals residing in Taiyuan, China (Shanxi Province). Significant antibody levels were detected to 11 antigens. Confirming earlier studies, an association was noted between cigarette smoking and seroreactivity, however, none was observed between occupation, or sex and seroreactivity. When the response to specific antigens or antigenic "groups" was studied, an association with work site was apparent. These data suggested a higher rate of exposure to Philadelphia 1 type antigens at the Bureau of Mining dormitory and a nearby electric power plant, and to E-327F/NY-23 type antigens at the Shanxi Mining College and Shanxi Daily newspaper. Further studies will define the reservoirs and mechanisms of exposure.

Effects of lipid peroxides on prostacyclin and thromboxane generation in hypercholesterolemic rabbits

Rabbits fed an atherogenic diet for 60 days resulted in high levels of plasma lipid peroxides as well as extreme hypercholesterolemia. Both levels stayed high until 35 days after the atherogenic diet stopped. At the same time, plasma PGI2 level was remarkably decreased while TXA2 and platelet aggregability were increased. Atherosclerotic aortas contain high levels of lipid peroxides associated with decreased PGI2 and increased TXA2 generation. Atherosclerotic plaques had the highest level of lipid peroxides and TXA2 while PGI2 production was the least, as compared with nonplaque tissue of the same artery and the normal arteries. The condition of normal arteries was just the reverse. There was a negative correlation between lipid peroxides and prostacyclin production, and a positive correlation between lipid peroxides and TXA2, in both plasma and aorta of rabbits. These results suggest that there is a close correlation between atherosclerosis, elevated lipid peroxides, and disturbances in PGI2/TXA2 balances.

Role of arachidonic acid in luteinizing hormone-releasing hormone action: stimulation of progesterone production in rat granulosa cells

This study investigates the hypothesis that stimulation of ovarian progesterone (P) production by LHRH is mediated in part by arachidonic acid (AA). In rat granulosa cells prelabeled with [3H]AA or [3H]inositol, treatment with LHRH stimulates the accumulation of radiolabeled inositol phosphosphates, diacyglycerol, and unesterified AA. Treatment with AA (3 X 10(-7)-10(-5) M) enhances P production in a dose-dependent manner. Concurrent treatment with AA and LHRH (or a LHRH agonist) further stimulates P production. The stimulatory effect of AA on P production, either alone or in combination with LHRH, could be seen as early as 3 h after AA addition. Addition of a phorbol ester, 12-O-tetracecanoylphorbol-13-acetate (TPA), to granulosa cells stimulates P production. Interestingly, the concomitant presence of AA and TPA further enhances production compared with either TPA or AA treatment alone. The stimulatory effect of AA on P production is completely abolished by nordihydroguaiaretic acid, but not by indomethacin. On the other hand, addition of nordihydroguaiaretic acid (but not indomethacin) reduces LHRH-stimulated P levels by about 50%. Nordihydroguaiaretic acid, as well, markedly attenuates the P response due to combined treatment with LHRH and AA. Taken together, these results strongly support the notion that AA (or its lipoxygenated metabolites) partially mediates the action of LHRH. Along with the calcium and protein kinase-C pathways, AA metabolism may be involved in the biological actions of LHRH in the ovary.