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Secretory granules and vesicles were demonstrated within human prostatic cells and in the acinar lumen. In size and ultrastructure the granules and vesicles were the same as those previously isolated from human prostatic fluid and seminal plasma. "Prostasomes" is suggested as the designation for these secretory granules and vesicles. As a rule they were found in storage vesicles within the secretory cells. Two mechanisms for translocation of the prostasomes from the cell interior to the acinar lumen are described. One mechanism involves exocytosis with binding of storage vesicles to, and fusion with the plasma membrane, resulting in release of prostasomes directly into the acinar lumen. The other mechanism implies displacement of storage vesicles in toto from the cell interior to the acinar lumen. This process differs from exocytosis and is here designated "diacytosis". Both phenomena appear to be of roughly equal frequency.

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DiscussionWe have found a specific Mg2+ and Ca'+-dependent ATPase of human prostatic fluid. This activity was recovered after differential centrifugation in a scanty pellet (pellet 11), containing secretory granules and vesicles as revealed by electron microscopy. A further evidence for the structural linkage of the ATPase activity to these membraneous structures was the density gradient centrifugation of pellet I1 (see Fig. 1). This prostatic fluid ATPase hydrolyzes off the terminal phosphate in ATP, thus giving rise to ADP and orthophosphate. Such a reaction is exergonic with a A G' of about -7 kcal/mole. Because of the exergonic character of the reaction and the structural linkage of the enzyme we postulate that a coupling may exist between the ATP hydrolysis and energy requiring reactions in the prostatic gland. Such a coupling may be chemo-mechanical or chemo-osmotic. In the first case a transduction of chemical energy into mechanical work is possible. In the second case a transduction may occur into osmotic work, i.e. transfer across a cell membrane of ions usually against an electrochemical gradient or sometimes against at least an apparent gradienti.e. a chemical gradient.Since the prostate gland is exocrine, the complex mechanisms underlying the exocytosis might be mediated through ATP, thus providing the link between cellular metabolism of the prostate gland and the energy requiring reactionseither contractile processes involving the microfilaments or microtubular system, or active ion movements such as Ca-ions of the secretory cells of the prostate gland.The secretory granules of pellet I1 as shown here may be derived from the Golgi complex (Helminen and Ericsson -1970;Brody et al. -1977). The exocytotic events underlying the exocrine function have particularly been studied in the pancreas (Jamieson and Palade -1971 ;Satir -1974;Singh and Webster -1976). The entire Golgi apparatus of cells from this gland has been claimed (Singh and Webster -1976) to be involved in the processing of secretory proteins, which are then transported through the Golgi vesicles nearest the endoplasmic reticulum. Such transport requires energy, which most probably is supplied by ATP (Jamieson and Palade -1968). The Golgi vesicles are considered to be transformed into secretory granules (Singh and Webster -1976). Such granules of the pancreatic cells can further on, after cholinergic stimulation, move towards and fuse with the plasma membrane. This process, generally called "exocytosis" 'is energy-dependent and Ca'+-dependent in the pancreatic exocrine cells (Jamieson and Palade -1971). *Part I see andrologia 10, 261-272 (1978).