Electron microscopic study of the secretion process in bovine reproductive organs

The origin and mechanism of the secretion of membrane-bound particles in bovine seminal plasma were studied with transmission (TEM) and scanning (SEM) electron microscopy of the epididymis, vas deferens, ampulla, and seminal vesicle of adult bulls. In the SEM study, all these organs were found to contain apical protrusions in the lining of the epithelial cells. Eventually the protrusions became detached and formed secretory bodies within the lumina of these organs. In the epididymis, the TEM study disclosed a granular and rather homogeneous content in the protrusions and bodies, whereas in the vas deferens they contained dilated cisternae of smooth endoplasmic reticulum. In the ampulla and seminal vesicle, the formation of the apical protrusions was associated with an accumulation of membrane-bound vesicles. These vesicles were found to be released from the storage bodies into the secretory fluid of the lumen. Both could be harvested from isolated seminal vesicle secretions by Percoll gradient centrifugation. It was concluded that various parts of the bovine reproductive organs discharge their secretory products at least partly by an apocrine mechanism. The membrane-bound particles in the seminal plasma, however, appear to be mainly derived from the ampulla and seminal vesicle.