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Cytochemical and ultrastructural characteristics of the stallion epididymis (Equus caballus)
1Department of Cell Biology and Genetics, Faculty of Medicine, University of Chile, Santiago.
Insights
Stallion epididymis structure and function remain consistent across breeding seasons. Ultrastructural and cytochemical analysis reveals regional specialization for secretion, absorption, and sperm storage.
Area of Science:
- Reproductive Biology
- Veterinary Anatomy
- Cell Biology
Background:
- The stallion epididymis is an androgen-dependent organ crucial for sperm maturation.
- Understanding its structure-function relationship is key, despite stallions being considered seasonal breeders.
Purpose of the Study:
- To investigate the ultrastructural and cytochemical characteristics of the stallion epididymis across different seasons.
- To elucidate the structure-function relationship of this vital reproductive organ.
Main Methods:
- Subdivision of the stallion epididymis into six regions.
- Ultrastructural and cytochemical analysis (PAS, CFH, AB staining).
- Evaluation of cellular morphology for secretory and absorptive activity.
Main Results:
- No significant ultrastructural or cytochemical differences were observed between breeding and non-breeding seasons.
- Principal cells in the caput epididymidis exhibit protein/glycoprotein secretion, with maximal reactivity for acidic glycoproteins.
- Distal caput and corpus regions show absorptive and anabolic activity, with strong enzyme reactions for active transport and acid phosphatase.
- The cauda epididymidis displays metabolic activity and evidence of sperm resorption.
Conclusions:
- Stallion epididymis function is not significantly impacted by seasonal breeding status.
- Regional specialization exists for secretion (caput), absorption/transport (corpus), and sperm storage/resorption (cauda).
- Cellular activities of principal cells contribute to epididymal fluid composition and sperm maturation.
Abstract:
The epididymis of stallion castrated during the breeding and non breeding seasons were subdivided into six regions and their ultrastructural and cytochemical characteristics were studied in order to provide a better understanding of the structure-function relationship of this androgen target organ. Even when the stallion has been postulated to be a seasonal breeder, our results do not show significant ultrastructural or cytochemical differences in both seasons. The pseudostratified epithelium is composed mainly of principal and basal cells and intraepithelial lymphocytes. The principal cells show morphological features of protein or glycoprotein secretion, especially in the caput epididymidis. Although PAS, CFH and AB positive substances were found throughout the epididymis, the reactivity was maximal in the caput region. This positive reaction can be ascribed to acidic glycoproteins. In stallion tissues, 4.0 acetylated sialic acid occurs in relatively high amount and is possible that the acid glycoprotein observed in our material have also this characteristic. The principal cells of the distal caput and corpus epididymides also display morphological hallmarks of absorptive and anabolic activity. These results are consistent with the histological reactions that demonstrate that the enzymes involved in active transport showed the strongest reaction in the corpus region. The acid phosphatase reaction was also strongest in these segments. In the cauda region, where the spermatozoa are stored ready for ejaculation, morphological signs of metabolic activity were also observed, but less notorious than in the more proximal segments. Resorption of non ejaculated spermatozoa was also observed in this region. It is difficult to evaluate the functional meaning of the spermatophagy in the epididymis because the images of sperm phagocytosed by epithelial cells were seen only in one or two cases. The chemical composition of the epididymal fluids changes along the length of this organ, concomitantly with the sperm maturation process, and it is possible to assume that some of these changes are a result of the secretory and absorptive activities of the principal cells.