Experimental studies of apocrine secretion in the dorsal prostate epithelium of the rat

Abstract

Rat dorsal prostate epithelium was studied in intact adult animals, in animals castrated for three days and in rats after inhibition of prolactin secretion. Thin sections, electron-microscopic autoradiographs and freeze-fracture replicas were used to analyze the process of apocrine secretion in this gland. The rough endoplasmic reticulum and the Golgi apparatus of the secretory cells are well developed, but secretory granules are absent. The only sign indicating release of secretory material is the appearance of blebs originating from the apical plasma membrane. Freeze-fracture replicas of the apical plasma membrane reveal that the blebs develop randomly from the bases of microvilli-like protrusions. In vitro pulse labeling of the proteins using 3H-leucine resulted in a labeling of the apical blebs. A post-castration period of three days was sufficient to reduce drastically the number and size of the apical blebs conhree weeks by application of lisuride, a synthetic ergot alkaloid, also induced regressive changes in the secretory cells. The apical blebs were still present, but they were shrunken and their content appeared condensed. These experimental conditions proved that the apical blebs are closely related to the functional activity of the cells and are interpreted as true apocrine secretion in the rat dorsal epithelium.

Comparative study of glycoconjugates of the rat prostatic lobes by lectin histochemistry

“…It remains to be determined whether these two kinds of blebs differed in their lectin reactivities and whether the lectin-bound cytoplasmic granules represent different pathways of secretion in the rat dorsal prostate. As there are no specific electron-dense secretory granules in the secretory epithelial cells of the rat dorsal prostate as observed by electron microscopy [46] (also our unpublished observations), these lectin-stained cytoplasmic granules probably represent the secretory glycoconjugates present in the dilated cisternae of the rough endoplasmic reticulum where the glycoproteins are synthesized. Ultrastructural studies have shown that the contents of the apical blebs are finely dispersed and exhibit an electron density comparable to that of the < Fig.…”

“…Two pathways of protein secretion have been suggested by Bartlett et al [18] in the rat dorsal prostate, based on the in vitro translation and rates of secretion of DP I and II: DP II follows a slower pathway through the Golgi, whereas DP I is secreted rapidly and not through the Golgi. However, the evidence of ultrastructure and immunostaining of transglutaminase only supports the apocrine secretion in the rat dorsal prostate [19,46]. Both apocrine and merocrine secretions have been described in the hamster dorsal prostate as cytoplasmic blebs, and typical secretory granules or vacuoles are found in epithelial cells [47].…”

“…Although the lateral lobe is always described together with the dorsal lobe as the ''dorsolateral'' prostate, their epithelial cells are different in their ultrastructure: there are dense secretory granules, microvilli, and rough endoplasmic reticulum with flattened cisternae, but the absence of apical cytoplasmic blebs (structural features of which are not found in the dorsal lobe) indicate that its secretions are different from those of its counterpart [5,7,46]. Two types of lateral prostate differing in their ductal patterns have also been described in the rat [8].…”

“…parable to that of the contents of the dilated cisternae of the rough endoplasmic reticulum in the dorsal prostatic epithelial cells [46]. Therefore, the glycoconjugate contents of the some apical blebs may be synthesized and may originate from the rough endoplasmic reticulum.…”

“…The secretory epithelial cells of the rat dorsal prostate (also coagulating gland) are known to secrete their products in an apocrine manner, as characterized by the presence of cytoplasmic blebs at the apical surface of the epithelial cells and absence of typical secretory granules with electron-dense materials [46]. Two pathways of protein secretion have been suggested by Bartlett et al [18] in the rat dorsal prostate, based on the in vitro translation and rates of secretion of DP I and II: DP II follows a slower pathway through the Golgi, whereas DP I is secreted rapidly and not through the Golgi.…”