[Cytochemical studies on the formation of multivesicular bodies in Leydig cells]

Multivesicular bodies were observed frequently in electron microscope photographs of Leydig cells from normal adult rat testes. Their formation, evolution and fate were analyzed morphologically in preparations treated to show cytidine monophosphatase (CMPase) activity and in animals sacrificed at various time intervals ranging from 5 min to 2 hrs after a single intratesticular injection of cationic ferritin (CF). Analysis of morphological and cytochemical data led to the following interpretation for the origin and fate of the multivesicular bodies in Leydig cells. The formation of multivesicular bodies in Leydig cells can be divided into three steps. Step 1, some endocytic vacuoles in Golgi region fuse with small vesicles to form pre-multivesicular bodies. Step 2, the pre-multivesicular bodies fuse together to form pale multivesicular bodies which are characterized by their large size, pale matrix and paucity of internal vesicles. Step 3, the pale multivesicular bodies remove their surplus enveloping membrane to become dense multivesicular bodies which are characterized by their smaller size, dense matrix and filling with internal vesicles. The pre-multivesicular bodies and pale multivesicular bodies do not contain hydrolytic enzymes, the dense multivesicular bodies acquire their hydrolytic enzymes by fusion with lysosomes and show CMPase activity. The dense multivesicular bodies often show a very close association with autophagosomes, and they might be involved in the autophagic activity of Leydig cells.