Comparisons of Pyronin Dyes Obtained from Various Commercial Sources. 1. History

Methyl green-pyronin Y staining of nucleic acids: studies on the effects of staining time, dye composition and diffusion rates

Since the introduction of the methyl green-pyronin Y procedure as a differential histological stain more than 100 years ago, the method has become a histochemical procedure for differential demonstration of DNA and RNA. Numerous variants of the procedure have been suggested, and a number of hypotheses have been put forward concerning kinetics and binding mechanisms. Using both filter paper models containing DNA, RNA or heparin and histological sections, we have attempted to evaluate the kinetics of staining and the role of staining time for methyl green and pyronin Y by applying the dyes individually, simultaneously and sequentially. The results are presented as color charts approximating the observed staining patterns using a computerized palette. Our results indicate unequivocally that the differential staining is not time-dependent, but that it is dictated by the relative concentrations of methyl green and pyronin Y and by the pH of the staining solution.

Purity of commercial non-certified European samples of Pyronin Y

The purity of six European non-certified samples of Pyronin Y was compared with that of two American samples certified by the Biological Stain Commission. The methods used were spectrophotometry and a Methyl Green-Pyronin staining test (both as applied by the Biological Stain Commission), thin layer chromatography, mass spectrometry, determination of pH, and content of some electrolytes. It was found that none of the European batches of Pyronin Y passed the complete test as prescribed by the Biological Stain Commission. Their dye content was uniformly low (between 5 and 19%). Furthermore, thin layer chromatography and mass spectrometry revealed that two of the dye samples contained no Pyronin Y or only traces. It is concluded that assessment of an unknown sample of a dye labelled Pyronin Y should be initiated with thin layer chromatography. The pH and content of electrolytes in an aqueous solution of the dye should also be determined in order to obtain reproducible staining results. Finally, the value of the work performed by the Biological Stain Commission is underlined, although more sophisticated methods are necessary for testing the purity of dyestuffs.

Methyl green-pyronin with hematoxylin and orange G for the identification of inflammatory cells in tissue sections

Methyl green-pyronin is a notoriously difficult stain to reproduce. Although very useful in detecting cells containing substantial amounts of RNA, it is of limited use in broader problems of cell identification. By careful standardization of the proportions of methyl green to pyronin and combination of these stains with hematoxylin to enhance nuclear contrast and with orange G to improve connective tissue staining, it was possible to produce a consistently reliable staining preparation in which it is possible to identify all the component cells of a mixed inflammatory infiltrate in routine paraffin sections.