Meldola blue: a new electron carrier for the histochemical demonstration of dehydrogenases (SDH, LDH, G-6-PDH).

A new electron carrier, Meldolar Blue (8-dimethylamino-2,3-benzophenoxazine; Boehringer Mannheim GmbH, Deutsche Patentschrift P 1959410) was tested for its usefulness in the histochemical demonstration of dehydrogenase activity in adrenal cortex, liver, heart muscle of guinea pig and human oviduct and compared with PMS. For demonstrating SDH activity Meldola Blue (MB) is as efficient as PMS. A decisive advantage of MB as compared with PMS is its low sensitivity to light exposure, facilitating direct visualisation of histochemical reaction processes. Generally, a high diffusion rate of reduced electron carriers (PMS and MB) from the section into the incubation medium (PVA) leads to a loss of reduction equivalents, particularly in the demonstration of NAD- or NADP-dependent dehydrogenases (LDH, G-6-PDH) with lower TNBT concentrations. However, no inhibition of SDH-, LDH- and G-6-PDH activities was observed with incubation media containing the tested concentrations of PMS and MB.