Solid spherical particles (radius 300–700 Å) of methyl‐methacrylate marked with a fluorescent dye were administered to dogs by continuous intravenous injection in order to obtain a steady plasma concentration. Lymphatics were cannulated and lymph collected from four regions of the body: leg, liver, heart and bronchial lymphatics. The passage of particles across the blood‐lymph barrier was measured by means of simultaneous concentration measurements in blood and lymph, Particles up to 700 Å radius readily passed into liver lymph with a lymph‐plasma ratio of approximately 0.20 in the “steady state”. No measurable amounts of these particles were found in the lymph from leg, heart or bronchial lymphatics. In these regions protein molecules of “effective diffusion radii” up to 120 Å pass into lymph. If the large proteins pass by “bulk flow” through water filled pathways the size of these pathways or “capillary leaks” would lie between 120–300 Å radius.

SK-N-SH and SH-SY5Y human neuroblastoma cells treated by 12-)-tetradecanoyl-phorbol-13-acetate(TPA) express morphological and biochemical changes, which indicate that differentiation towards more mature cells has occurred. The most prominent morphological changes were the development in 40-60% of the cells of cell-surface projections longer than 50 micrometers and cytoplasmic neurosecretory granules demonstrated by electron microscopy. At the biochemical level, TPA induced a two-fold increase in the relative activity of neuron-specific enolase and 30- to 40-fold increase in noradrenaline and adrenaline concentrations. A decrease in proliferation rate of TPA-treated cells was observed. The biological effects of TPA were slightly potentiated by nerve growth factor.

1. The renal clearance of dextran of different molecular sizes has been measured in normal humans from 6 days to 61 years of age. Gel chromatography of dextran has been used for determination of molecular weight distribution.2. Information about the functional ultrastructure of the glomerular membrane has been deduced from the experimental clearance data in the light of theoretical models. The glomerular membrane was here visualized as a gel filter, localized in the basement membrane. The physical analogue of this membrane was interpreted as a somewhat heteroporous structure of quite well defined pore sizes: one system of smaller pores in the range of 20-28 A radius and an additional system of larger pores of radii up to 80 A. These larger pores are quite few in number with an approximate ratio of one large pore per 10 OOO small pores.3. The values obtained for the transglomerular pressure difference were low, about 1 cm of water or less. This supports the concept that tubular reabsorption may be the rate limiting factor in the process of urine formation and may also control the glomerular filtration rate.4. The changes of the dextran clearance with ageing found in this investigation may be explained by an increase of the pore radii of the glomerular membrane and a concomitant decrease of the transglomerular pressure difference.The sieving effect of the glomerular membrane has in electron microscopic studies been attributed to three different sites : fenestrae between endothelial cells, the basement membrane, and/or slits between epithelial cells in the urine space (Fig. 1). The functional ultrastructure of the glomerular membrane has also been evaluated by studying the transport of molecules of different sizes into urine.In the present study dextran was used as a test substance in order to investigate glomerular permeability, i.e. glomerular membrane porosity and fltration pressure. The high precision of

No abstract