Abstract
The mechanism and distribution of the KOH-periodic acid-Schiff (PAS) effect in rat large intestine, human sigmoid colon, rabbit rectum and rabbit Brunner's glands have been investigated following the abolition of normally occurring PAS-positive vicinal diols by means of a periodate oxidation-sodium borohydride reduction sequence. The KOH-PAS effect was shown to be independent of the initial oxidation time and could be abolished by pretreatment with either methanolic-HCl or alcoholic KOH. The evidence suggests that the KOH-PAS effect is due to the removal of an o-acyl-ester substituent on a potential vicinal diol. The alternative hypothesis, that the effect is due to an ester involving the carbonyl function of a macromolecule or a lactone, is less likely. The difficulty of interpretation of histochemical results following methylation is discussed.