Our results demonstrated clearly that membranous vesicles are normal constituents of the cauda epididymal fluid and that, although a small number of vesicles originate from the other accessory glands, this fluid is the main source of the vesicles retrieved in the ram seminal plasma. This is demonstrated by the very similar one-dimensional and two-dimensional SDS-Page protein profiles and the protein compositions found for the epididymal and seminal plasma vesicles of normal rams and the absence of these vesicles in the seminal plasma of vasectomized rams.
Several groups have suggested that small membranous vesicles could be formed by apocrine or bleb secretions from the testis, efferent ducts, and the epididymal epithelium. It has also previously been shown that the seminal plasma of different mammals, including the humans, contains neurosecretory-like vesicles, and some findings have indicated that these vesicles originated from the prostate and seminal vesicles. The epididymal membrane vesicles described here are quite homogeneous in size and delimited by a single bilayer membrane. Although their mean diameter is smaller than the average diameter reported for seminal plasma vesicles, it can be concluded that the seminal-fluid vesicles are composed of a mixture of vesicles originating from the different accessory glands, to which the epididymis largely contributes (see also).