Effects of 4% paraformaldehyde and modified Davidson's fluid on the morphology and immunohistochemistry of Xiang pig testes.

Modified Davidson's fluid (mDF) is a good fixative for morphological and antigen preservation. However, recent studies have shown that 4% paraformaldehyde (PFA) can better preserve the actin structure in rodent testes. It remains controversial which of these fixatives is best for testicular tissue. This study investigated the effects of both mDF and 4% PFA on the morphology and antigen preservation of Xiang pig testes using hematoxylin-eosin (HE) staining and immunohistochemistry (IHC). The stronger testis penetration of mDF compared with that of 4% PFA was primarily manifested as testicular color change and decrease in tissue weight loss. Testes fixed with 4% PFA displayed a severe shrinkage of both the tubular and interstitial compartments and the seminiferous tubule area decreased by 12.02% compared with that in mDF-fixed tissues. In contrast, IHC results showed that 4% PFA fixation achieved better IHC-positive performance than mDF fixation for antigens specifically expressed in germ cells, Leydig cells and Sertoli cells. Due to this improved antigen preservation by 4% PFA fixation, the relative immunoreactions intensity significantly increased by 39.8%, 27.8%, and 76.4%, respectively, compared with that in mDF fixation. In summary, fixation of Xiang pig testes with mDF was suitable for HE staining, while fixation with 4% PFA was more suitable for IHC.