Further studies of the epithelium covering preovulatory rabbit follicles with special reference to lysosomal alterations.

The fine structure of the surface epithelium over preovulatory rabbit follicles was examined parallel with visualization of acid phosphatase at the electron microscopical level. Small enzyme positive vesicles were pinched off from the Golgi cisternae and similar vesicles fused and got incorporated into larger lysosomes of dense body type. Some lysosomes appeared in direct continuity with tubular enzyme positive structures. Other possible ways of increase of the lysosomal pool are indicated and discussed. As in previous studies a maximal accumulation of lysosomes was found in the apical epithelium at 8 h after an ovulatory dose of human chorionic gonadotrophin (HCG); thereafter a gradual loss of lysosomes ensued. Before the lysosomes disappeared from the surface epithelium they changed in character. They became more electron-lucent and revealed a fine-fibrillar matrix. Dense bodies deep in the cell interior appeared to communicate with each other and with the extracellular space below the surface epithelium. Openings were never seen towards the peritoneal cavity. tthe loss of lysosomal content from the apical surface epithelium before follicle rupture appeared in many respects similar to the histamine release process in mast cells. tthe findings support our working hypothesis that the surface epithelium over tgraafian follicles is an essential source of proteolytic enzymes and that these may be released extracellularly and actively contribute to the dissolution of the follicular apex before rupture.