Histochemistry of Plasmalogen

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Abstract
Unfixed frozen sections of kidney, heart and brain from Wistar rats were used for the following tests 1. relative reactivity of plasmalogen in different tissues to fuchsin-sulfurous acid (FSA); 2. effect of various mercury compounds in producing the plasmal reaction, and use of dithizone to verify the attachment of mercury to tissue plasmalogen; 3. effect of pH as shown by graded concentrations of HC1 and by phosphate and acetate buffers; 4. effect of various cations; 5. solubility of plasmaiogen in methanol, ethanol, isopropanol, n-butanol, t-butanol, n-pentanol and ethylene glycol; 6. effect of blocking reactions: acetal formation, bromination and iodination. The results showed that the amount of plasmalogen in brain is very much greater than that in heart muscle or in kidney and that the brain plasmalogen appears to be more reactive. All the highly ionized mercury compounds, HgCl2, Hg(NO3)2, Hg(CH3COO)2, and HgNO3 gave identical, immediate reactions. The moderately ionized K^HgIj gave a less rapid reaction. Hg compounds which are unable to deliver any appreciable amount of mercuric ion into solution (nonionized or insoluble) did not react. Dithizone, which forms a deep red color in combination with Hg-containing compounds, gave a positive reaction at the same sites that gave the plasmal reaction. This indicates that the Hg combines with tissue plasmalogen. The hydrolysis of plasmalogen as a function of pH and time showed that 6 N HC1 gave as rapid a reaction as HgCl2. As the pH was increased the rate of plasmal formation decreased. At pH 4.0 no plasmal was evident in 2 hr. AUCl3 and PdCl2 gave reactions identical with that of HgCl2. No other cation tested gave a plasmal reaction. Plasmalogen was rapidly dissolved by the short chain monohydric alcohols but not by ethylene glycol. Plasmalogen did not dissolve appreciably in 60% or lower grades of ethanol. Bromination or iodination abolished the plasmal reaction, but iodination required a longer time to do so. A 1.2 N HC1 solution in ethylene glycol inhibited the HgCl2-FSA reaction by the formation of an acetal which is relatively insensitive to HgCl2, but it did not inhibit the FSA reaction when hydrolysis was by 6 N HC1 instead of HgCl2,. The vinyl ether structure proposed by Rapport and associates (1957) for plasmalogen is supported by the specific reaction with HgCl2, the hydrolysis with acid, the addition of iodine, of bromine, and the formation of an acetal.

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