No abstract

An Evaporimeter and a ventilated chamber technique have been compared in their ability to measure transepidermal water loss (TEWL) through rat skin. These techniques measure TEWL under very different conditions; the Evaporimeter measures the net TEWL under ambient relative humidity (RH) whereas the ventilated chamber employs a constant atmosphere, usually of low RH and thus measured the uni-directional diffusion of water. Paired Evaporimeter and ventilated chamber measurements were made of TEWL through normal skin and through skin whose barrier properties had been altered by tape-stripping (15 applications) or single applications of n-hexadecane (28.4 mumol cm-2). Both measuring techniques indicated the same level of TEWL through normal skin (mean 0.3 mg cm-2 h-1) and during increases in TEWL induced by n-hexadecane (max TEWL c 3.5 mg cm-2 h-1). However, the Evaporimeter was found to underestimate the higher rates of TEWL induced by tape-stripping, ie above TEWL raters of 7.5 mg cm-2 h-1. The Evaporimeter is portable, easy to use and suitable for measurements of net water loss up to 7.5 mg cm-2 h-1; it can only be used for comparative assessment of epidermal barrier function if used at a particular ambient RH. The more cumbersome ventilated chamber is to be preferred for accurate assessments of barrier function where high rates of TEWL occur.

A workshop was held to critically discuss the need for a non-rodent species and the role of the dog in regulatory toxicity testing of pharmaceuticals; to discuss opportunities to reduce and refine the use of dogs in preclinical toxicology; and to identify a number of specific recommendations which could be feasibly achieved to move the process forward. To facilitate a preliminary evaluation of the contribution of dog studies to the risk assessment process, anonymised, unpublished data were provided from fully evaluated, repeat dose toxicity studies in the rat and dog. Results ofthe International Life Sciences Institute (ILSI) Human Toxicity Project were also presented and discussed. Analysis of the data demonstrated that the dog can provide additional toxicity information, which, in some cases, was shown to be predictive for humans. Discussions indicated that there is potential for achieving a reduction in dog use and several possible approaches were identified. To further the progress of this initiative, there is a need to collate the results of pharmacology, toxicology, and clinical studies to address some of the proposed approaches. One of the outcomes of the workshop will be the establishment of a steering group to co-ordinate data collation for further analysis.

In the chain-lengthening of the oligosaccharide chains of endogenous dolichol-diphosphate oligosaccharides (Dol-P-P-oligosaccharides) by a pig liver microsomal preparation dolicholmonophosphate mannose (Dol-P-Man) was a more efficient donor of mannose (a maximum of 35 SC transferred by 5 min) than was GDP-Man (reaching 16 7; by 45 min). The effects of an excess of GDP, an excess of GDP-Man, a lack of Mn" and an excess of EDTA showed that the transfer from GDP-Man was via Dol-P-Man. The evidence also indicated the presence of two pools of Dol-P-Man one of which was difficult to extract and which was possibly closely associated with the Dol-P-P-oligosaccharides and the appropriate transferase.After 1 h of incubation transfer of '"C to 'insoluble polymer' from GDP-[14C]Man, Dol-P-[I4C]Man and Dol-P-P-['4C]~ligo~accharide~ reached approximately 3 x, 3 % and 13 % respectively, of that available. The result of adding excess unlabelled GDP-Man to an incubation with GDP-['"CIMan in progress confirmed the sequence GDP-Man + Dol-P-Man + Dol-P-P-oligosaccharide + insoluble polymer. Solubilisation with sodium dodecyl sulphate of the radioactive 'insoluble polymer' followed by gel chromatography showed the presence of radioactive glycoprotein and oligosaccharide when either GDP-['"CIMan or Dol-P-P-['4C]oligosaccharide was used as donor. The proportion of oligosaccharide formed rose sharply when excess EDTA was present and GDP-['"C]Man was the donor. Under these conditions the oligosaccharide contained 5-6 units and all of the radioactivity could be released by a-mannosidase. The glycoprotein was susceptible to proteolysis.When GDP-['"CIMan is incubated with microsoma1 preparations of various tissues [14C]mannose is transferred to dolichol monophosphate (Dol-P) and to dolichol-diphosphate (Dol-P-P) oligosaccharides [l -41. In the case of the pig liver system it has been shown that the oligosaccharide portion of the Dol-P-P-['"C]oligosaccharides so formed ranges in chain length from approximately seven to 13 sugar residues and that these are formed generally by addition of one mannose residue to the oligosaccharide chain of each endogenous Dol-P-P-oligosaccharide with a minority being formed by addition of two mannose residues [4]. It was of interest to determine if the dolichol-phosphate-['"C]mannose (Do~-P-['~C]-Ahhreviationu. Dol-P-Man, dolichol-monophosphate-mannose ; Dol-P-P-oligosaccharides, dolichnl-diphosphatc-oligosaccharides; GDP-Man, guanosinr-diphosphate-mannose. Man) formed in this system could act as a direct donor of mannose residues in the chain-lengthening of endogenous Dol-P-P-oligosaccharides and the results of experiments to this end are described in this paper. . We also report here on the relationships between the lipid-linked compounds and the formation of glycoprotein and oligosaccharide in the pig liver system.

No abstract

The transfer, catalysed by pig liver microsomal preparations, of mannose, from GDP-mannose, to lipid-linked oligosaccharides and the properties of the products are described. Solubility, hydrolytic and chromatographic data suggest that they are dolichol diphosphate derivatives. The presence of two N-acetyl groups in at least part of the heterogenous oligosaccharide portion was tentatively deduced. Reduction with borohydride of the oligosaccharide showed that the newly added mannose residues were not at its reducing end. Periodate oxidation suggested that 60% of these were at the non-reducing terminus and that 40% were positioned internally. T.l.c. showed the presence of seven oligosaccharide fractions with chromatographic mobilities corresponding to glucose oligomers with 7-13 residues. The molar proportions of the oligosaccharide fractions in the mixture were determined by borotritiide reduction and the number of mannose residues added to each oligosaccharide fraction during the incubation was calculated. Two of the oligosaccharide fractions had received on average one, or slightly more than one, mannose residue per chain during the incubation; four of the other fractions were each shown to be a mixture, 20-25% of which had received one mannose residue during the incubation and 75-80% of which had not been mannosylated during the incubation. This supported other evidence for the presence of endogenous lipid-linked oligosaccharides in the microsomal preparation which had been formed before the incubation in vitro. Evidence for the possibility of two pools of dolichol monophosphate mannose, one being more closely associated with mannosyl transfer to dolichol diphosphate oligosaccharides than the other, is also discussed.

No abstract

No abstract