Modulation by phenobarbital of the differentiation of 3T3 preadipocytes

The effect of phenobarbital upon the differentiation of two preadipocyte cell lines, 3T3 F442A and 3T3 L-1, was examined by measuring the synthesis and secretion of lipoprotein lipase. Extracellular enzyme was measured by treating intact cells with heparin, and the intracellular enzyme was subsequently assayed in cell homogenates. When confluent cultures of 3T3 F442A cells were treated with insulin, the cells underwent differentiation as indicated by increased activity of lipoprotein lipase within 6 days, followed in turn by increased levels of protein and triglyceride. Addition of phenobarbital with insulin enhanced total lipoprotein lipase, protein, and triglyceride content. The activity of lipoprotein lipase accumulated in the heparin-releasable fraction during differentiation was increased 2- to 3-fold and the intracellular enzyme was enhanced 15- to 20-fold by the addition of phenobarbital. The ability of phenobarbital to modulate differentiation was dependent upon the time of addition. When added early in the postconfluent period, there was a greater increase in lipoprotein lipase activity than when the drug was added at later times. Phenobarbital also stimulated lipoprotein lipase in differentiating 3T3 L-1 cells in the presence of insulin, although lipoprotein lipase activity was moderately enhanced by phenobarbital alone in these cells. These results suggest that phenobarbital may affect the conversion of adipoblasts into preadipocytes and thereby increase the proportion of cells susceptible to the differentiating stimulus.     

On the role of lysophosphatides in virus-induced cell fusion and lysis.

Three strains of Newcastle disease virus (NDV-HP-16, NDV-L-Kansas, and NDV-N) were propagated in chick embryo fibroblasts, equilibrium labeled with 32Pi, and the composition of phospholipid in the membranous envelope of the virions determined. A phospholipid identifed as monoacylphosphatidylserine was consistently observed in the viral strains which are listed as follows in their order of decreasing abundance of lysophosphatidylserine: NDV-HP 16greater than NDV-L-Kansas greater than NDV-N. The phosphatidylserine concentration in the virion envelopes of these strains decreased in proportion to the increase in the monoacylphosphatidylserine concentration. No other lysophosphatide was observed in significant quantity in virions of these strains. The degree of cell fusion in mouse fibroblast monolayers by each of the viral strains was independent of the lysophosphatidylserine content of the virions. The ability of the viral strains to induce fusion from within, i.e., that occurring in cells that are actively propagating virus was: NDV-L-Kansas greater than NDV-HP-16 greater than NDV-N. The ability of the viral strains to induce fusion from without, i.e., that occurring in response to incubation of cells with large quantities of irradiated virus was: NDV-HP-16 greater than NDV-N greater than NDV-L-Kansas. On the basis of these findings we conclude that there is no direct correlation between the level of lysophosphatide in the virion and its ability to induce cell membrane fusion. A direct correlation was observed, however, between the presence of high monoacylphosphatidylserine content and the ability of a strain to produce lytic infection.     

The ecological dynamics of pest-resource-people systems

Abstract

Pest problems involve people who value a resource affected by a pest that is managed by people, ideally the same as those who value the resource. Management that is not inclusive of pests, resources, people, and their interactions usually fails. Mammalian pests in New Zealand are of two sorts: those that are pests in their native land (usually r-strategists), and those that are not (usually K-strategists). The impact on New Zealand resources of r-strategists tends to be periodic and acute when their densities are high. Control works best against them when it is applied once densities become intolerable, or once such densities can be predicted. The impact of K-strategists is more stable but is chronic. Control operations against them need to be sustained and regular to retain the stability of the pest-resource interaction, but to drive it in favour of the resource. The basic strategies to deal with the impact of pests are: those for which a one-off management action has a permanent benefit (e.g., eradication); those that require ongoing action to gain a permanent benefit (e.g., sustained control); and those for which no management action is possible or justified. Idealist and cynical approaches to pest policies are discussed and rejected in favour of a pragmatic policy.     

Livedo Reticularis during Amantadine Treatment

Livedo reticularis is a common side effect of treatment with amantadine for Parkinson''s disease. Investigation of 40 such patients suggests that the livedo is a physiological response provoked by depletion of catecholamine stores in peripheral nerve terminals.