SPECTROPHOTOMETRIC IN-VIVO DETERMINATION OF LOCAL MITOCHONDRIAL METABOLISM BY USE OF A TETRAZOLIUM SALT

The Erlangen micro-lightguide spectrophotometer (EMPHO) was used to de termine local mitochondrial activity. The measurement was based on a c ommercially available test (WST1, Boehringer Mannheim, Germany). A tet razolium salt is cleaved to formazan by the 'succinate-tetrazolium red uctase' system which belongs to the respiratory chain of the mitochond ria and is active only in viable cells. 50 mu l of the reagent is plac ed in a recess at the tip of the lightguide. The tip of the lightguide is then placed at the tissue surface. The reagent diffuses into the c ells and is cleaved to formazan. The absorption change is measured and analysed. This method was used in early chick embryos to determine th e metabolic activity of the area vasculosa during the first 6 d of nor moxic incubation. During this period of time the absorption change mea sured after 30 min increased from 0.001 units on day 2 to 0.262 units on day 6. This indicates an increase in local metabolic activity which may be due to an increase in metabolic activity of individual cells a nd/or an increase in the number of cells in the area under investigati on. The results show that it is possible to determine local metabolic activity under in vivo conditions.