Urea formation in nephrectomized mice.

The rate of increase of blood urea levels in nephrectomized mice has been studied under a variety of conditions which might influence protein catabolism. Oral administration of substantial amounts of carbohydrates or intravenous administration of 5% glucose led to an increased rate of urea accumulation. The intravenous administration of 20% glucose slowed the rate of urea increase. However, this apparent protein-sparing action could be simulated by the administration of a hypertonic solution of sorbitol. </jats:p

Thrombin and NaF, but not epinephrine, raise cytosolic free Na⁺ in human platelets

We have investigated changes in [Na+]i in SBFI-loaded platelets stimulated at 37 degrees C with thrombin, epinephrine, and NaF. Basal [Na+]i was 4.9 ± 1.3 mM (n = 70). Stimulation of platelets with thrombin (0.1 U/ml) in the presence of 1 mM extracellular Ca2+ rapidly raised [Na+]i by 27.3 ± 6 mM (n = 16). Part of this increase (approx. 20-30%) is caused by Na+/H+ exchange, the rest is predominantly due to Na+ influx. Epinephrine (20 microM) failed to change [Na+]i both in the absence and presence of fibrinogen. This is in agreement with earlier reports showing that epinephrine also fails to activate Na+/H+ exchange in human platelets. NaF which activates platelets via a direct effect on GTP-binding proteins induced a slow rise in [Na+]i to 9.5 ± 2.5 mM (n = 4) and 33.0 ± 3.6 mM (n = 12) at 10 and 20 mM NaF, respectively. This effect was completely blocked by SK&F 96365, a blocker of receptor-mediated Ca2+ entry. Hence, the NaF-induced increase in [Na+]i is exclusively due to the opening of non-selective cation channels. This latter finding agrees with earlier observations which showed that NaF does not induce activation of Na+/H+ exchange in platelets

Study of Digoxin as inhibitor of the in vivo effects of acetyl glyceryl ether phosphorycholine (AGEPC) in mice

Acetyl glyceryl ether phosphorylcholine (AGEPC) and the cardiac glycoside digoxin were administered intravenously through the tail vein into ether-anesthetized SWR mice (two months old). The administered doses were 0.18 nmol AGEPC/ g.b.w. (a lethal one) and 75 or 125 ng digoxin/b.w. Digoxin ameliorates the effects of the lethal dose of AGEPC showing maximum activity when given 5 or 10 min after AGEPC administration to female and male animals respectively. Digoxin shows also a protective action towards the effects of AGEPC and maximum activity appears when it is given 10 min before AGEPC administration. In agreement with the picture of increased survival in digoxin pretreated animals, are our findings on life prolongation of mice which finally die from AGEPC, the amelioration of the expected fall in blood platelet counts after AGEPC administration as well as the improved performance of the animals in a series of physical tests. © 1988

Triacylglycerol storage in lipid droplets in procyclic Trypanosoma brucei

Carbon storage is likely to enable adaptation of trypanosomes to nutritional challenges or bottlenecks during their stage development and migration in the tsetse. Lipid droplets are candidates for this function. This report shows that feeding of T. brucei with oleate results in a 4-5 fold increase in the number of lipid droplets, as quantified by confocal fluorescence microscopy and by flow cytometry of BODIPY 493/503-stained cells. The triacylglycerol (TAG) content also increased 4-5 fold, and labeled oleate is incorporated into TAG. Fatty acid carbon can thus be stored as TAG in lipid droplets under physiological growth conditions in procyclic T. brucei. beta-oxidation has been suggested as a possible catabolic pathway for lipids in T. brucei. A single candidate gene, TFE alpha 1 with coding capacity for a subunit of the trifunctional enzyme complex was identified. TFE alpha 1 is expressed in procyclic T. brucei and present in glycosomal proteomes, Unexpectedly, a TFE alpha 1 gene knock-out mutant still expressed wild-type levels of previously reported NADP-dependent 3-hydroxyacyl-CoA dehydrogenase activity, and therefore, another gene encodes this enzymatic activity. Homozygous Delta tfe alpha 1/Delta tfe alpha 1 null mutant cells show a normal growth rate and an unchanged glycosomal proteome in procyclic T. brucei. The decay kinetics of accumulated lipid droplets upon oleate withdrawal can be fully accounted for by the dilution effect of cell division in wild-type and Delta tfe alpha 1/Delta tfe alpha 1 cells. The absence of net catabolism of stored TAG in procyclic T. brucei, even under strictly glucose-free conditions, does not formally exclude a flux through TAG, in which biosynthesis equals catabolism. Also, the possibility remains that TAG catabolism is completely repressed by other carbon sources in culture media or developmentally activated in post-procyclic stages in the tsetse