The histochemical localization of lactic dehydrogenase isoenzymes in the rat nephron by means of an improved polyvinyl alcohol method

Summary The histochemical localization of lactic dehydrogenase (LDH) activity and the prevailing type of isoenzyme in different segments of the nephron in male and female rats are described. Polyvinyl alcohol was added to the incubation medium in order to reduce enzyme diffusion. Localization of the reaction product was further improved by the use of a high concentration of Nitro BT (and of PMS and NAD).The three segments of the proximal tubules exhibited clearly different staining patterns. In glomeruli, terminal parts of the third proximal segments, thin limbs of Henle, and collecting ducts M subunits of LDH predominated, whereas in the remaining tubular segments H subunits prevailed. Sex differences were observed in respect to the LDH reaction in the proximal tubules, but not in the rest of the nephron. The localization of -hydroxy acid oxidase was also investigated, as this enzyme oxidizes lactate and therefore contributes to the reaction. Under certain conditions, i.e. high substrate concentration, the activity of -hydroxy acid oxidase was negligible in comparison with that of LDH.The Abbreviations used are PVA polyvinyl alcohol - PMS phenazine methosulfate - NAD nicotinamide adenine dinucleotide - Nitro BT nitroblue tetrazolium - Tris Tris (hydroxymethyl) aminomethane - PCMB p-chloromercuribenzoateSupported by grants from Fonden til Lægevidenskabens Fremme, and the Danish Medical Research Council.The terms H isoenzyme and M isoenzyme denote isoenzymes of LDH containing predominantly H subunits and M subunits, respectively.