Lysosomal Concept of Menstrual Bleeding in Humans

Abstract

Electron microscopic subcellular changes of acid hydrolases were studied in the human endometrium during the individual phases of the menstrual cycle. Acid phosphatase (Ac Pase) was identified at the electron microscopic level as the “marker enzyme” of acid hydrolase activity. The proliferative phase is characterized by development of the Golgi systems and lysosomes. The Golgi system becomes progressively more complex; it contains increasing amounts of Ac Pase reaction product, and with the release of more vesicles, the number of lysosomes continuously increases. After ovulation these changes become even more expressed, and during the mid secretory phase the Golgi complexes are developed to their greatest degree. The most dynamic enzymorphologic changes occur during the late secretory phase and early menstrual bleeding. They are characterized by increase of Ac Pase staining within the intercellular spaces of the stromal and epithelial layer; gradual penetration of Ac Pase into junctional complexes of the surface and glandular epithelium (desmosomes); swelling of arteriolar endothelia; and the finding of the Ac Pase reaction product on the arteriolar basement membranes and between adjacent endothelial cells. With the cycle day approaching menstruation, more autophagic bodies with sequestered organelles appear. The findings suggest that changes in lysosomal activity and acid hydrolases may represent a decisive step in the sequence of processes culminating in endometrial regression and bleeding.